Steel

selection guide
Guide to selection of engineering steels
The object of this guide is to provide assistance in selection of a suitable
engineering steel for your application. The grades included are those to be
found in our extensive stock programme. Of course, alternative grades and
executions exist but we have chosen to focus on materials available from
stock with short lead times.

If you consider that your application everything but should be used to In what follows, we have chosen
requires an engineering steel other provide a preliminary indication. to refer to engineering-steel grades
than those in our stock programme, With engineering steels, it is especially by their designation in EN-standards.
then do not hesitate to contact us important to try and achieve a correct Older Swedish Standard designations
even at the design stage. By so doing, balance between the demands of the (SS-) are presented in parentheses.
we will be able to help in steel selection application and available properties.
for just your project and also give advice Once again, you are welcome to Example
on analysis, properties, execution and contact Tibnor if your project has S355JR (SS 2172)
if nec­essary, heat treatment. special material requirements outside 34CrNiMo6 (SS 2541-03/05)
This guide does not pretend to be those which are considered here.
a reference work with answers for
CONTENTS

High standards allow an optimal steel selection. . . . . . . . 4

Choosing the right steel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Alloying elements in steel and their effects. . . . . . . . . . . . . 8
Steel selection based on stipulation of requirements. . . . 10
Dimensions and tolerances. . . . . . . . . . . . . . . . . . . . . . . . . . 18
Bar tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Tube tolerances. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Standard constructional steels;
micro-alloyed constructional steels. . . . . . . . . . . . . . . . . . 23
Case-hardening steels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Quenched-and-tempered steels . . . . . . . . . . . . . . . . . . . . 28
Yield and tensile strengths
for quenched-and-tempered steels. . . . . . . . . . . . . . . . . . 30
Spring steels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Bearing steels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Hard chrome bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Free-machining steels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
M-steels for machinability. . . . . . . . . . . . . . . . . . . . . . . . . . 40
Hardness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Welding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Cold forming. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Fatigue and how the risk for
fatigue failure can be lessened. . . . . . . . . . . . . . . . . . . . . . 47
Reducing weight of components and constructions. . . 50
Standards for steel grades. . . . . . . . . . . . . . . . . . . . . . . . . . 52
Colour coding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Certification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Translation of seventh edition

of Tibnor’s Stålvalsguide
published March 2012 (in Swedish).
Our suppliers improve their products continually
and we therefore cannot assume responsibility for
changes to data given in this document. For the most
recent up-dates and current product catalogues,
see www.tibnor.se.
4

HIGH STANDARDS ALLOW AN

OPTIMAL STEEL SELECTION
Our aim through collaboration with both customers and suppliers is to develop
the best solutions for material selection, logistics and manufacture.
Material that is to be processed by machining must have close tolerances and
consistent quality so that it behaves in exactly the same way from one delivery
to the next. It is for this reason that we have taken extra care in formulating
specifications for just engineering steels.
Since machining often represents a large portion of the cost to manu­facture
a part, another important facet of our offer from a customer perspective is
to increase efficiency; for example, via increased automation or by supplying
material with improved machinability.
A quality-control system certified according to SS-ISO 9001:2008 and
the environmental-control system certified in accord with SS-ISO 14001:2004
constitute the touchstone of our activities and behaviour. More information
can be found on www.tibnor.se.
5
6

CHOOSING THE RIGHT STEEL

A correct steel selection necessitates that you can stipulate the requirements of
the application for your part or construction. Some requirements are easy to
define while others may be less tangible. For example, it is sometimes difficult to
exactly specify the loading that a part is subjected to and thereby the mechanical
properties which are necessary as a basis for material selection.

In many instances, one relies on The concept of hardness and ways of alloy additions also elevate yield
experience and makes the same measuring it will be discussed in more stress in particular. For example, the
material choice as in similar com­ detail later on in this guide. yield strength of steel S355JR
ponents which previously have (SS 2172) with 0.15 % C and 1.5 % Mn
functioned satisfactorily. For the most Hardenability is more or less the same as that for
part, this philosophy works well but Hardenability defines the ease with C45E (SS 1672) with 0.45 % C.
does not give consideration to new which a given steel can be hardened So-called micro-alloy additions,
steel grades or executions which may by rapid cooling from high temperature. such as niobium and vanadium, are
be more suitable or cheaper or both. A steel with low hardenability, particularly effective in raising yield
In order to use this guide, you will must be cooled more quickly if it strength since even very small
need to spipulate the requirements is to be hard. On the other hand, if amounts (<0.1 %) give rise to a strong
for the part or construction of interest. hardenability is higher, cooling need contribution from precipitation
Once you have done this, a suggestion not be so rapid and larger dimensions hardening.
as to how to proceed can be found on can be hardened. Hardenability Heat treatment, in particular
pages 10-17. First however, we will by increases with increasing content of hardening and tempering, has a
way of background look briefly at the carbon and alloying additions. pronounced effect on both yield and
most important properties of steel Of course, a successful hardening tensile strength. Quenched-and-
from the standpoint of its behaviour operation depends not only on the tempered steels develop their highest
both in manufacturing and in service. hardenability of the steel but also strength when alloying with carbon is
on the method of cooling. Common combined with additions of chromium
Availability cooling media are water, polymer- (Cr), nickel (Ni) and molybdenum
When considering your steel selection, water mixtures, oil and even air. (Mo) in amounts between 0.2 - 2 %.
availability is a primary concern and Very rapid cooling, in water for example, For a given content of carbon
it is obviously advantageous if the engenders an effective hardening and alloying elements, the achievable
material of your choice is both but also results in greater dimensional strength is very dependent on
available and can be delivered quickly. changes and increased risk for cracking. dimension with larger dimensions
This is seldom an issue since Tibnor’s Hardened steel is normally having lower strength than smaller
stock programme encompasses the tempered which improves toughness ones. Hence, it is necessary to select
most extensive range of grades, and relieves stresses from hardening. a steel with greater alloy content if
properties and executions all of which The tempering temperature can lie a certain level of strength needs to
can be supplied with minimum lead anywhere between 200 and 700°C. be retained over a wide dimensional
times. Should the material of your Quenched-and-tempered steels in range.
choice not be available from stock, Tibnor’s stock programme have been Fatigue strength is an important
then please feel free to contact us tempered at higher temperatures property which defines how the steel
for more information on the product, (500-700°C), which admittedly can stand up to variable or pulsating
lead times, minimum quantities etc. reduces hardness but improves loads. This quantity, which is intim­
toughness dramatically. ately coupled to tensile strength, is
Hardness/wear resistance discussed in more detail in a separate
For the most common engineering Strength-yield stress/tensile stress section of this guide.
and constructional steels, increasing The yield strength or yield stress
hardness is synonymous with greater determines the load that a Toughness/ductility
resistance to wear. High-carbon steels component can be subjected to By toughness is meant the resistance
hardened to 60-62 HRC show best without plastic deformation resulting of a material to the initiation and
wear resistance. However, steels in a permanent change of dimension. propagation of cracks upon loading
through hardened to such high hardness The tensile strength or ultimate tensile which can cause failure of a component.
are rather brittle and surface hardening, stress on the other hand, relates to the A material is tough if such cracking
which combines a hard, wear-resistant maximum tensile load a component requires considerable energy whereas
surface with a softer tougher core, can withstand without breaking. a brittle material breaks very easily
may be a preferable alternative. Grossly oversimplified, one can with the expenditure of very little
Examples of such surface-hardening say that the yield and tensile strengths energy. Toughness can be measured
methods are induction hardening, of steel increase with carbon content. in a number of different ways and
case hardening and nitriding. For a given carbon content, some some are technically rather complicated.
 7

Impact testing constitutes a method Machinability You will find more detailed information
that is relatively simple and cheap, Generally speaking, higher hardness on welding later on.
and by far the most widely used is commensurate with poorer
testing method is Charpy-V (KV). machinability. However, softer low- Cold formability
KV-testing of most steels is char­acter­ carbon steels have a tendency to Parts made of steel are often shaped
ised by a transition from ductile to stick to the cutting tools with negative by cold-forming operations such as
brittle fracture, see the diagram below. consequences in relation to surface bending, upsetting, cold drawing,
The ductile-brittle transition finish and tool life. Steels with hard­ deep drawing etc. Cold formability
temperature can vary between ness in the range 180-220 HB and determines the extent to which the
50 and -100°C. Generally speaking, which give short chips machine best. steel can undergo such plastic
toughness decreases (i.e. the transition Machinability is often acceptable forming without cracking. Cold
temperature is raised) with increasing when the hardness is less than about formability is thus strongly correlated
hardness and strength, even if there 300 HB, even if steels with hardness to ductility. In consequence, cold
are exceptions to this rule. A fine up to 450 HB can be machined formability decreases with increasing
microstructure is positive for both satisfactorily if the cutting speed is strength but certain high strength
strength and toughness and quenching lowered. Working of even harder steels can be cold formed using
and tempering is an example of a steels necessitates grinding or simpler methods such as bending or
means to optimise the combination machining in stable machines with upsetting without problem. See later
tensile strength-toughness. special tooling. for more detailed information on cold
The concept ductility relates to Deliberate addition of certain forming of engineering steels.
the ability of a material to undergo elements such as sulphur or lead,
plastic deformation without the results in markedly enhanced machin­ Protection against corrosion
development of cracks or complete ability, although this improvement is One of the major disadvantages of
failure. The parameters defining most often achieved to the detriment steel is that the element iron corrodes
ductility that can be measured in a of other properties. Machinability is (rusts) rather easily. Steel will rust in
tensile test are elongation to fracture also improved by Si/Ca-treatment, the atmosphere outdoors (especially
(A5) or the reduction in area at fracture, sometimes termed M-treatment close to the sea or if humidity is high),
Z; these are normally expressed as a (M-steels are discussed later in this in oxygenated water or if buried. In all
percentage of the original sample guide). these cases, electrochemical cells are
length or cross-sectional area. created in which iron is dissolved to
Ductility and toughness are in many Weldability react with oxygen thereby forming a
respects similar and there exists a With the correct technique and corrosion product (rust).
clear correlation between KV-values consumables, all of the steels referred The principle of corrosion protection
at higher temperatures where the to in this guide can be welded, at least is to by some means limit this electro-
failure is ductile and, for example, the if the sole aim of welding is to join chemical reaction. For example, the
reduction in area in a tensile test. together. However, if welding procedures surface of the steel can be painted or
With some exceptions, ductility is shall not be too complicated and oiled in order to prevent physical
lowered as strength increases. Steel requirements are placed on weld contact with the external environment.
cleanliness is also an important factor mechanical properties, the carbon Galvanising involves covering the
and large amounts of inclusions in content should be limited to < 0.25 % steel surface with a layer of zinc,
the steel are negative in relation to and other alloy additions should not which is a metal that corrodes even
ductility. be too high either. This means that more easily than iron. So long as the
steels with high strength and wear zinc remains and corrodes prefer­
resistance are more difficult to weld. entially, the steel will stay protected.
In some cases, one can coat the
surface of the steel with another metal
having better corrosion resistance
Absorbed energy, (J) such as chrome, tin or nickel. Chrome
250 plating brings the added advantage
of increasing the wear resistance of
Ductile/fibrous the surface. Surface treatment by
200 nitriding, and especially by ion nitriding,
also gives increased protection from
corrosion as well as improved resistance
150
to wear.

100
Schematic impact transition curve
from Charpy-V testing of a
50
low-carbon steel. In this case,
the transition temperature, e.g. the
Brittle
27J temperature corresponding to an
0 absorbed energy of 27J, is -28°C.
-80 -40 0 40 80
Test temperature (°C)
8

ALLOYING ELEMENTS
IN STEEL AND THEIR EFFECTS
Steel is a unique constructional material. No other metal can achieve such a
broad array of mechanical properties ranging from soft and formable to hard,
strong and wear resistant. This outstanding versatility is coupled to the
transformation of iron between different states depending upon temperature
and the influence of alloying with carbon on this transformation.
Metallic elements other than iron exist which undergo similar transformations
but the positive effect of carbon is exclusive to iron.

Carbon (C) additions which have a higher affinity Manganese (Mn)

Alloying with carbon constitutes the for oxygen than iron. Manganese and Virtually all steels contain manganese
basis of all steel (with the exception silicon are almost always present but which fulfils a number of different
of some special alloys and for most if a more complete de-oxidation is functions. Apart from its effect as a
types of stainless steel where carbon required then aluminium is added as de-oxidant (see above), manganese
is considered an unwanted impurity). well. The reaction between these refines the microstructure of the steel
Carbon increases the strength of steel de-oxidants and oxygen results in the which is positive for both strength
but to the detriment of ductility and formation of slag particles, manganese and toughness. For example, the
toughness. Carbon is essential if steel silicate and/or aluminium oxide. higher strength of S355JR (SS 2172)
is to be hardened (pure iron cannot These are lighter than the steel and in comparison with S235JR (SS 1312)
be hardened) and the achievable are eliminated from the melt by derives completely from the
hardness and wear resistance increases flotation. However, a small fraction difference in manganese content
with carbon content (see diagram remains in the finished steel as non- (typically 1.5 % and 0.7 % respectively).
below). metallic inclusions. Control of the In combination with sulphur,
content of inclusions is important manganese gives rise to manganese
De-oxidants/manganese(Mn), since they affect the properties of the sulphide inclusions which improve
silicon (Si), aluminium (Al) steel, most often negatively. De- machinability (see section on free-
& sometimes calcium(Ca) oxidation with calcium in conjunction machining steels).
During manufacture, the steel melt with silicon gives rise to inclusions of a
becomes contaminated with oxygen specific type which have a positive
(from air) which is negative for effect on machinability (see separate
properties and must be removed. This present­ation on M-steels).
so-called de-oxidation is effected by

Hardness, HB
800
65.5 HRC

60 HRC

600

43 HRC
400
Hardened

200 Dependence of hardness on

carbon content for carbon steels in
Hot-rolled
the as-hot-rolled and as-hardened
0 condition.
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Wt. % Carbon
 9

Additions which increase cost-effective alternative to more cost-efficient in that they do not
hardenability/manganese (Mn), alloyed heat-treatable steels. Boron’s require heat treatment in order to
chromium (Cr), nickel (Ni), hardenability-raising effect is, however, achieve high strength.
molybdenum (Mo), silicon (Si) limited and disappears more or less
Carbon increases the hardenability completely when the carbon content Additions that enhance
of steel but its effect is insufficient if exceeds 0.4 %. Boron steels find machinability/sulphur (S),
anything other than small dimensions extensive application for wear parts lead (Pb), calcium (Ca)
is to be hardened. Larger dimensions which are hardened in water and used Deliberate addition of sulphur to a
require alloying additions to supplement un-tempered. Toughness is often not steel alloyed with manganese results
and enhance the hardening derived especially good but sufficient for this in small manganese sulphide
from carbon. As is clear from the type of application. inclusions which give improved
diagram, manganese, chromium and machinability especially when using
in particular molybdenum have a Micro-alloying additions/ high-speed steel tooling. Otherwise
strong positive effect on hardenability niobium (Nb), vanadium (V), sulphur is generally regarded as an
whereas the influence from nickel is titanium (Ti), aluminium (Al) undesirable impurity.
weaker. Nickel is, however, desirable For weldable low-carbon steels, grain Another addition for enhancing
for toughness in quenched-and- refinement is the sole means whereby machinability is lead. Free-machining
tempered steels. strength as well as toughness can be steels containing lead and/or sulphur
In the quenched-and-tempered increased simultaneously. Grain do not have particularly good
condition, steels alloyed with chromium, refiners are added in small quantities mechanical properties since the
molybdenum and nickel are character- between 0.01-0.1 % (micro-alloying) inclusions of lead and/or manganese
ised by an outstanding combination in order to counteract microstructural sulphide have a negative influence on
of strength and toughness even in coarsening in connection with hot both ductility and toughness.
larger dimensions. Furthermore, working, heat treatment or welding. Treatment of a steel melt with
NiCrMo-steels have sufficient harden- These micro-additions have the silicon plus calcium (often called Si/
ability that effective hardening of common characteristic that that they Ca-treatment) has a very favourable
larger dimensions is possible even have a strong affinity for carbon or influence on machinability without
when cooling is slow (in oil or even nitrogen or both (nitrogen from air is too negative repercussions for other
air) with reduced risk for dimensional absorbed by a steel melt). properties. More information is given
changes and/or cracking. Furthermore, niobium, vanadium in the section on M-steels later in this
The hardenability raising effect and titanium all give rise to sub- guide. The benefit of Si/Ca treatment
of silicon is limited. Even so, certain microscopic particles of nitrides and/ is most prevalent at high machining
grades of spring steel have high or carbides which make an additional speeds as can, for example, be
silicon content. contribution to strength via so-called achieved with coated carbide tooling.
precipitation hardening. Micro-alloying Processing with Si/Ca necessitates
Boron (B) with vanadium is particularly favourable careful control in steelmaking;
Very small amounts of boron, as little in this respect and its effect is more or otherwise the beneficial effect for
as 0.001 %, exert a marked positive less independent of carbon content. machinability can vary from heat to
influence on hardenability. To a certain Vanadium micro-alloyed steels attain heat or in the worst scenario be
degree, boron steels, which apart high strength even after hot rolling absent altogether.
from boron are often alloyed with since precipitation takes place during
manganese and chromium, offer a subsequent cooling. Such grades are

Hardenability factor
6.0

Mn
4.5
Mo Cr

3.0

Ni
Si
1.5

Illustrating the effect of various alloy

0 additions on hardenability.
0 0.5 1.0 1.5 2.0 2.5

Weight %
10

STEEL SELECTION
BASED ON STIPULATION
OF REQUIREMENTS
The requirements on an engineering steel to manufacture a specific component
or construction can conveniently be divided into three categories:

1. Economic requirements Please now attempt to specify When you have come to a decision
Examples are low cost for starting the requirements that are to be met as to the steel type which conforms
materials, no extra expenses in by the engineering steel in your most closely to your requirements
manufacturing arising from special application. You can categorise the profile, the next step is to refine the
precautions, good material yield and requirements as above if you wish or selection making use of the detailed
low scrap rates, minimal risk for claims use any other system which better property specifications for all
and payment of compensation. suits your needs. The requirements engineering steel grades in Tibnor’s
Of course, availability from stock should then be rated according to stock programme. You will find these
permitting supply of exact quantities the following: listed on pages 12-17. In this instance,
with short lead times is also a require- - absolute requirement (level 5), even more negative properties with
ment with an economic dimension. - very important requirement rating 1 or 2 are included so that you
(level 4), are made aware of any negative
2. Manufacturing requirements - rather important requirement repercussions coupled to your
These include all necessary steps (level 3). selection. Moreover, details of the
involved in production of the part or profiles, surface finishes and tolerances
construction – welding, machining, On the next page, you will find a list which are available are specified on
cold forming, heat treatment etc. with various types of engineering pages 18-21.
The steel selected should be amenable steel and their properties with emphasis For the reader needing more
to cost-efficient, trouble-free on the more positive characteristics. information on a specific steel type
processing using the machine park Tibnor’s stock programme comprises and its characteristic features and
which is available. a number of grades from all of these properties, a more detailed descrip-
steel groups, each of which is thereby tion for each group can be found later
3. Requirements on satisfactory available in exact quantities with short on in this guide.
service performance lead times. Every property has been If after following these guidelines,
These are requirements coupled to assigned a rating where 1 is worst and you still have difficulty in finding a
the application in which the part or 5 best. Try to find the steel type which grade which matches the require­
construction will serve. Examples are best fits the requirements profile for ments profile for your application or
stiffness, strength, fatigue resistance, your application bearing in mind that if there is a property of interest which
toughness and resistance against wear. some degree of compromise may be has not been covered, then you are
necessary. In some instances, attention most welcome to contact us at Tibnor.
It is not always the case that require-­ is drawn to the fact heat treatment We will see to it that you receive all
ments from all three categories are may be required in order that the the information and help you need.
compatible. For example, the highest given property rating is achieved.
level of service performance is seldom Heat treatment will always involve extra
achievable in parity with uncompli­ costs even if carried out “in-house”.
cated manufacturing and low material
costs.
 11

–Strength (2) –Strength (4) –Wear resistance (5)

–Weldability (5) –Weldability (4) –Fatigue strength
–Toughness (3) –Toughness (4) (bend/impact) (5)
–Cold formability (3) –Cold formability (3) –Surface hardness (5)
–Price (5) –Price (3-4) –Toughness (3)
–Price (3)

CONSTRUCTIONAL MICRO-ALLOYED CASE-HARDENING

STEELS STEELS STEELS (*)

–Strength (4–5) –Strength (5) –Strength (5)

–Fatigue strength (4–5) –Fatigue strength (4) –Fatigue strength (5)
–Toughness (4–5) –Wear resistance (4) –Wear resistance (5)
–Price (2–3) –Spring properties (5) –Surface hardness (5)
–Toughness (1–2) –Edge strength (4)
–Price (3) –Toughness (2)
–Price (2)

QUENCHED-AND- SPRING STEELS (*) BEARING STEELS (*)

TEMPERED STEELS

–Machinability (5)
–Strength (2)
–Toughness (1)
–Tolerance of product in stock (4)
–Price (3)

FREE-MACHINING
STEELS

Ratings for properties: Ratings for price:

(5) – very good (5) –  low
(4) –  good (4) –  medium-low
(3) –  quite good (3) –  medium
(2) –  less good (2) –  medium-high
(1)  –  rather poor (1)  –  high
* Does not apply to delivery condition – must be heat treated to attain these ratings.
12

CONSTRUCTIONAL
STEELS
with properties profile:

–Strength - less good (2) S235JRC+C Compressed axle (*)

–Weldability - very good (5) (SS 1312-06) Cold-drawn flats(*)
–Impact toughness
S235JR Hot-rolled or peeled/turned (*) rounds
- quite good (3)
(SS 1312) Hot-rolled squares and profiles
–Cold formability
- quite good (3) S355J2 Hot-rolled or peeled/turned (*) rounds
–Price - low (5) (SS 2172) Hot-rolled squares and profiles
E355+SR Cold-drawn tubes, skived/roller-burnished (**)

* Tolerances on product in stock - good (4)

** Tolerances on product in stock - very good (5)
 13

MICRO-ALLOYED
CONSTRUCTIONAL
STEELS with properties profile:

–Strength - good (520M (3)) S450J0/280 Hot-rolled or peeled (*) rounds

(4) (SS 2142) Centerless-ground bars (**)
–Weldability - good (4)
OVAKO 280 Hot-rolled seamless tubes
–Impact toughness - good (4)
–Machinability - good (520M) (4) E470 Hot-rolled seamless tubes
–Cold formability - quite good (3)
S355J2/520M Hot-rolled or peeled/turned (*) rounds
–Price - medium-low (4)

–Strength - quite good (3) 520MW+ Hot-rolled or peeled (*) rounds

–Machinability - very good (5)
Hydax 25 Hot-rolled flats and squares
–Weldability - rather poor (1)
–Impact toughness - quite good (3)
–Price - medium (3)

–Strength - good (4) 550M Cold-drawn rounds

–Impact toughness - less good (2)
S355JRC+C Cold-drawn rounds
–Weldability - good (4)
–Machinability - good (4)
–Tolerances on product
in stock - good (4)
–Price - medium-high (2)

–Strength - good (4) 550MW+ Cold-drawn rounds

–Impact toughness- less good (2)
–Machinability - very good (5)
–Weldability - rather poor (1)
–Tolerances on product
in stock - good (4)
–Price - medium-high (2)

–Strength - very good (5) 280D Cold-finished seamless tubes

–Impact toughness - less good (2)
–Weldability - good (4)
–Machinability - quite good (3)
–Tolerances on product
in stock - good (4)
–Price - medium-high (2)

* Tolerances on product in stock - good (4)

** Tolerances on product in stock - very good (5)
14

CASE-HARDENING
STEEL
with properties profile:

–Wear resistance - very good (5) 16NiCrS4 Hot-rolled or peeled/turned (*) rounds
–Fatigue resistance (bending, (SS 2511)
impact) - very good (5)
–Surface hardness - very good (5)
–Impact toughness
- quite good (3) (*)
–Weldability - quite good (3) (*)
–Machinability - good (4) (*)
–Price - medium (3)

* As supplied or core after * Tolerances on product in stock - good (4)

case-hardening
 15

QUENCHED-AND-
TEMPERED STEELS
with properties profile:

–Strength - less good/ SS-EN C45R Hot-rolled or peeled/turned (*) rounds

quite good (2-3) (*) (SS 1672) Centerless-ground bars (**)
–Impact toughness - less good (2)
SS-EN C45E Hot-rolled flats and squares
–Weldability - less good (2)
(SS 1672)
–Machinability - good (4)
–Potential for induction SS-EN C45E+N Forged and turned (*) rounds
hardening - good (4) (SS 1672)
–Price - medium-low (4)

–Strength - good (4) SS-EN 25CrMoS4 Hot-rolled or peeled (*) rounds

–Impact toughness - good (4) (SS 2225) (quenched-and-tempered)
–Weldability - quite good (3)
–Machinability - good (4)
(if M-steel)
–Price - medium (3)

–Strength - very good (5) SS-EN 42CrMoS4 Hot-rolled or peeled (*) rounds
–Fatigue strength - good (4) (SS 2244) (quenched-and-tempered)
–Impact toughness - good (4)
- Weldability - rather poor (1)
- Machinability - good
(if M-steel). (4)
- Wear resistance - quite good (3)
- Price - medium (3)

–Strength - very good (5) SS-EN 34CrNiMo6 Hot-rolled or peeled (*) rounds
–Fatigue strength - very good (5) (SS 2541) (quenched-and-tempered)
–Impact toughness - very good (5)
–Weldability - rather poor (1)
–Machinability - quite good (3)
(if M-steel)
–Wear resistance - good (4)
–Price - medium-high (4)

* As-rolled (2); quenched-and- * Tolerances on product in stock - good (4)

tempered (3) ** Tolerances on product in stock - very good (5)
16

SPRING
STEELS
with properties profile:

–Strength - very good (5) SS-EN 56Si7 Hot-rolled flats

–Fatigue strength - good (4) (SS 2090-00)
–Spring properties
SS-EN 51CrV4 Peeled (*) rounds
(resilience) - good (4)
(SS 2230-02M)
–Impact toughness - less good (2)
–Machinability - quite good (3) (*)
–Wear resistance - good (4)
–Price - medium (3)

* As supplied. Other properties * Tolerances on product in stock - good (4)

relate to hardened/tempered
execution

BEARING
STEELS
with properties profile:

–Strength - very good (5) 100Cr6 Peeled (*) rounds

–Fatigue strength - very good (5) (Ovako 803) Hot-rolled seamless tubes
–Wear resistance - very good (5)
100CrMo7 Hot-rolled seamless tubes
–Surface hardness - very good (5)
(Ovako 824)
–Edge strength - good (4)
–Impact toughness - less good (2) 100CrMo7-3 Peeled (*) rounds
–Machinability - quite good (3) (*) (Ovako 825)
–Price - medium-high (4)

* As supplied (full annealed) * Tolerances on product in stock - good (4)

 17

HARD-CHROME-
PLATED BARS
with properties profile

–Wear resistance - good S450J0/280X Hard-chrome-plated round bars

(low friction) (4) (SS 2142) Hard-chrome-plated tubes
–Corrosion resistance
Ovako 482 Induction hardened hard-chrome-plated
- quite good (3)
round bars (*)
–Strength - good (4)
–Weldability - good (4)
–Impact toughness - good (4)
–Machinability - quite good (3)
–Tolerances on product in stock
- very good (5)
–Price - medium-high (4)

* Resistance to external impact - very good (5)

FREE-MACHINING
STEELS
with properties profile:

–Machinability - very good (5) 11SMnPb30 + C Cold-drawn rounds, squares and hexagons
–Strength - less good (2) (SS 1914) (amenable to case-hardening)
–Impact toughness
MACH 50 Cold-drawn rounds and squares
- rather poor (1) (*)
(S + Pb leg.) (amenable to case-hardening and induction hardening)
–Tolerances on product

in stock - good (4)
520MW+ Peeled rounds
–Price - medium (3)
(amenable to case-hardening and nitriding)
550MW+ Cold-drawn rounds
(amenable to case-hardening and nitriding)

* 520MW+ has quite good impact

toughness (3)
18

DIMENSIONS AND TOLERANCES

For engineering components, the correct choice of execution is just as
important for manufacturing costs as an optimum steel selection.
Tibnor’s stock programme comprises a number of different executions
such as hot-rolled, peeled or turned, centre-less ground and cold drawn.
The dimensional tolerances for the various executions are for the most
part standardised. On occasion, products may have special tolerances
which have been tailored for a specific project or application.

All dimensions in mm. The density of steel is 7.85 kg/dm3.

Round bar Tube D = Nominal diameter

Dy = Nominal outside diameter
Wall Di = Nominal inside diameter
Wall = Nominal wall thickness
Round bar: weight/metre
D Di D2 X 0.006165 kg/m

Dy Tube: weight per metre

(Dy2 – Di2) X 0.006165 kg/m

Square bar Flat bar T = Nominal edge length or

thickness
T B = Nominal width
Square bar: weight/metre
T2 X 0.00785 kg/m
T B Flat bar: weight/metre
T X B X 0.00785 kg/m

Hexagonal bar Hexagonal bar: weight/metre

N2 x 0.006798 kg/m

A = 1.155 X N

N
A
 19

BAR TOLERANCES
Dimensional tolerances Ovality Surface defects
– Hot-rolled bar is usually The ovality of a round bar is defined Steel is a mass-produced commodity
characterised by a ± tolerance on D, as the difference between two and as such surface defects will always
T and B. Since the bar contracts mutually perpendicular diameter be present to some degree. Larger
during cooling after hot rolling, measurements. This difference is as a defects such as scale, cracks, flakes,
the tolerance achieved is very rule expressed as a percentage of the laps, decarburisation etc. must be
dependent on process control tolerance range for diameter. detected and remedied at the steel
during this operation. – Hot-rolled: The ovality shall be less mill. Even so, for the product supplied
– Peeled rounds have as a rule a minus than 75 % of the tolerance range for D. to the market, especially when in the
tolerance on D. The standards allow – Peeled or turned:The ovality shall be hot-rolled condition, smaller defects
a variation between h12 and h15 less than 50 % of the tolerance range inevitably remain and this should
depending on diameter, with larger for D. be taken into consideration when
diameters having the widest – Ground: The ovality shall be less assessing machining allowance.
tolerance range. than 33 % of the tolerance range for Of course, surface defects will be
– Rough-turned rounds can have D. fewer for executions such as peeled
either an h or a ± tolerance. Very – Cold-drawn: The ovality shall be less or ground, in which the hot-rolled
large diameters are generally turned than 100 % of the tolerance range surface has been removed. On the
to tolerances similar to hot-rolled for D. other hand, defects originating from
but tighter, +3/-0 mm is common. hot rolling can remain on drawn bars.
– Centre-less ground or cold-drawn As an example, consider a ground bar The extent, type and size of surface
rounds have as standard an with D = 40 mm. The tolerance h8 defects that are allowed on steel
h-tolerance, normally h8 for ground means that the actual diameter shall products are regulated in the
and h10 for cold drawn. be between 39.961 and 40.000 mm. standard, SS-EN 10221.
– Hard-chrome-plated bar (round) The tolerance range is hence 0.039 mm
has tolerance f7 as standard but this and the ovality shall be less than one Internal defects
tolerance range is also covered by third of this or 0.013 mm. Cavities, larger inclusions, excessive
h9. The tolerance range f is minus/ segregation, pipe etc. are controlled
minus while h is zero/minus. Straightness by the steel manufacturer either
Straightness, which is especially through testing of cast material or via
important for bars that have to be ultrasonic examination performed on
machined by turning, is measured as finished products. Some degree of
the greatest gap between the bar and segregation and smaller inclusions
a horizontal flat surface upon which it are inevitable features of all steel
is placed. For a regular hot-rolled bar products and in most instances are
with normal straightness, this gap of no consequence for service
should be less than 0.004 x length. performance.
In other words for a standard 6-metre It is important that in the event of
bar, the maximum allowed gap is special requirements as regards
6000 x 0.004 = 24 mm. For other freedom from internal defects, the
executions, the straightness is often requested levels should be clearly
better, for example 0.002 x L for specified in any enquiries preferably
peeled bar and 0.001 x L for cold- with reference to appropriate
drawn or ground bar. standards (for example SS-EN
10247:2007 for defining allowable
inclusion levels).
20

Hot-rolled rounds and squares Hot-rolled flats and universal bars

D or T, mm Tolerance B, mm Tolerance Thickness tolerance
up to and up to and
above above T ≤20 >20 – 40 >40
including including
5.5 10 ±0.4 – 40 ±0.7 ±0.5 ±1.0 –
10 15 ±0.4 40 80 ±1.0 ±0.5 ±1.0 ±1.3
15 25 ±0.5 80 100 ±1.5 ±0.5 ±1.0 ±1.3
25 35 ±0,6 100 120 ±2.5 ±0.5 ±1.0 ±1.3
35 50 ±0.8 120 150 ±2.5 ±0.5 ±1.0 ±1.3
50 80 ±1.0 150 200 ±2 % ±0.5 ±1.0 ±1.3
80 100 ±1.3 200 275 ±2 % ±0.5 ±1.0 ±1.3
100 120 ±1.5 275 400 ±2 % -0.4/+0.8 -0.7/+1.1 -1.0/+1.4
120 160 ±2.0
160 200 ±2.5 All tolerances are in mm unless stated otherwise.
200 270 ±3.0

Peeled rounds for further machining

D, mm D, mm
Tolerance limits, mm Tolerance limits, mm
Nominal Toler- Nominal Toler-
upper lower kg/m upper lower kg/m
dia. ance dia. ance
20.8 h12 20.8 20.59 2.67 102 h13 102 101.46 64.1
22.8 22.8 22.59 3.20 107 107 106.46 70.6
25.8 25.8 25.59 4.10 112 112 111.46 77.3
28.8 28.8 28.59 5.11 117 117 116.46 84.4
30.8 30.8 30.55 5.85 122 122 121.37 91.7
32.8 32.8 32.55 6.63 127 127 126.37 99.4
36.0 36.0 35.75 7.99 132 132 131.37 107
39.0 39.0 38.75 9.37 138 h14 138 137.00 117
41.0 41.0 40.75 10.4 143 143 142.00 126
43.0 43.0 42.75 11.4 148 148 147.00 135
46.0 46.0 45.75 13.0 153 153 152.00 144
49.0 49.0 48.75 14.8 163 163 162.00 164
51.2 51.2 50.90 16.2 173 173 172.00 184
53.2 53.2 52.90 17.4 184 184 182.85 209
56.2 56.2 55.90 19.5 194 194 192.85 232
59.2 59.2 58.90 21.6 204 204 202.85 256
61.2 61.2 60.90 23.1 214 214 212.85 282
63.2 63.2 62.90 24.6 224 224 222.85 309
66.2 66.2 65.90 27.0 235 h15 235 233.15 340
69.2 69.2 68.90 29.5 245 245 243.15 370
71.4 71.4 71.10 31.4 255 255 252.90 401
73.4 73.4 73.10 33.2 285 285 282.90 501
76.4 76.4 76.10 36.0 306 306 303.90 577
79.4 79.4 79.10 38.8 326 326 323.70 655
81.4 81.4 81.05 40.0 356 356 353.70 781
86.4 86.4 86.05 46.0 386 386 383.70 918
91.4 91.4 91.05 51.5 406 406 403.50 1016
96.4 96.4 96.05 57.3

Cold drawn and ground rounds

Tolerance h6 - h11
Nominal dia, mm h6 h7 h8 h9 h10 h11
up to and
above Upper limit always +/-0. Lower limit as below, mm
including
1 3 –0.007 –0.009 –0.014 –0.025 –0.040 –0.060
3 6 –0.008 –0.012 –0.018 –0.030 –0.048 –0.075
6 10 –0.009 –0.015 –0.022 –0.036 –0.058 –0.090
10 18 –0.011 –0.018 –0.027 –0.043 –0.070 –0.110
18 30 –0.013 –0.021 –0,033 –0.052 –0.084 –0.130
30 50 –0.016 –0.025 –0.039 –0.062 –0.100 –0.160
50 80 –0.019 –0.030 –0.046 –0.074 –0.120 –0.190
80 120 –0.022 –0.035 –0.054 –0.087 –0.140 –0.220
120 180 –0.025 –0.040 –0.063 –0.100 –0.160 –0.250
 21

TUBE TOLERANCES
– Straightness: The maximum – Maximum finished dimension – Surface defects: Tubes shall have
allowed gap depends on execution depends on whether the tube is smooth surfaces. Local high and
but is at most 1 mm over a length of centred internally or externally low points along with shallow
1 metre (1000 x 0.001). when machining. The finished longitudinal cracks are allowed so
– Ovality: The ovality is at most dimension which is guaranteed long as they lie within the limits for
65 % of the tolerance range for Dy is coupled to a machined length diameter tolerance.
(does not apply for ISO-tubes). which is dependent on Dy.
– Internally skived/roller-burnished – Cold drawn tubes have a Dy
cylinder tubes are characterised tolerance of +0.6/-0 mm and have
by an H-tolerance (a plus/zero straightness corresponding to a gap
tolerance) on Di with H8 as standard. which is less than 1mm over a length
The Dy-tolerance conforms to of 1 metre (1000 x 0.001).
EN 10305-1.
Wall thickness Maximum variation
< 6 mm 0.7 mm
6-8 mm 0.8 mm
> 8 mm 0.9 mm

Tolerances Ovako 280 hot-rolled

Machined length for
Grade Outside diameter
finish dimension
280 Hot-rolled Dy ≤80 mm ±0.4 mm 3 x Dy (applies for all Dy)
280 Hot-rolled Dy >80 mm ±0.5%
Wall
280 Hot-rolled <12 mm ±0.7 mm
280 Hot-rolled >12 mm ±(5% x wall + 0.1 mm)

Tolerances SS-EN 10294-1:2005 hot-rolled

Machined length for
Grade Outside diameter
finished dimension
E470 Hot-rolled Dy ≤75 mm ±0.5 mm 3 x Dy (applies for all Dy)
E470 Hot-rolled 75 <Dy ≤180 mm ±0.75%
E470 Hot-rolled Dy >180 mm ±1 %
Wall
Grade Dy ≤180 mm Dy >180 mm
E470 Hot-rolled ≤15 mm ±12.5% ≤30 mm ±12.5%
or 0.4 mm*
E470 Hot-rolled >15 mm ±10% >30 mm ±10%

Tolerances cold-finished tubes 280

Machined length for
Grade Outside diameter Wall
finished dimension
280D Cold finished ±0.2 mm ±0.2 mm 2.5 x Dy

Tolerances E355+SR skived/roller-burnished tubes

Tolerance H8
Nominal Di, mm
up to and
upper Upper limit as below, mm. Lower limit always +/-0.
including
30 50 +0.039
50 80 +0.046
80 120 +0.054
120 180 +0.063
180 250 +0.072

*The greater alternative is the one which applies.

22
 23

STANDARD
CONSTRUCTIONAL STEELS;
MICRO-ALLOYED
CONSTRUCTIONAL STEELS
Standard constructional steels can be used for components and constructions
with moderate strength requirements irrespective of whether or not their
manufacture involves welding. If higher strength is needed, micro-alloyed steels
are more suitable. The carbon and alloy content of both types is adapted so that
under normal circumstances, they can be welded without pre-heating.
Both yield and tensile strength are increased as a result of micro-alloying
which means that in many cases, smaller dimensions can be used without
having to compromise in relation to strength requirements thereby reducing the
weight of the construction (weight saving is discussed in more detail in a later
chapter of this guide). A micro-alloyed constructional steel has just as high or
even higher yield strength than a medium-carbon steel but is much easier to weld.

Machining of these steel types can Bars in standard constructional Cold working gives rise to residual
give difficulties in the shape of built- steels and micro-alloyed steels are stresses which are normally greatest
up edge formation leading to excessive usually as-hot-rolled with straightening closer to the surface and decrease
tool wear, poor surface finish and long as the only finishing operation. However, towards the centre of the section.
chips, which may prove troublesome larger dimensions can be heat-treated Hence, machining of such material
in unmanned operations. In order to by normalising so as to refine the can result in dimensional changes;
improve machinability, this type of microstructure and improve toughness. in particular, long components can
steel is available from Ovako Imatra Cold-finished material is normally become crooked. Welding of cold-
in “M-steel” execution. M-steel treat­ used in the condition in which it is worked steel requires some thought
ment confers improved machin­ability supplied. Cold drawing or cold rolling in that the strength can be reduced
without significant negative influence engenders increased strength as well in the heat-affected zone adjacent
on other properties. More information as improving the tolerance of both to the weld; it is therefore prudent
on M-steels is given in the section bars and tubes. Cold working is to some to locate welds in areas where the
devoted to machinability. degree also positive for machinability. service loading is low.
24

Grade Mechanical properties

Impact
Tensile test Hardness test
SS-EN 10002-1 SS-EN ISO 6506-1 SS-EN ISO 148‑1

Dim- Re* Rm A5 KV
Typical ension ** N/mm2 N/mm2 % min 27 J
analysis % Execution mm min min HB at °C
C 0.18 Hot rolled bar -16 355 470-630 22 140-200 -20
S355J2
(SS 2172)
Can be case-
hardened or
nitrided

Si 0.30 >16-40 345 470-630 22 140-200 -20

Mn 1.50 > 40-63 335 470-630 21 140-200 -20
S 0.050 > 63-80 325 470-630 20 140-200 -20
> 80-100 315 470-630 20 140-200 -20
> 100-150 295 470-630 18 140-200 -20
> 150-200 285 450-630 17 140-200 -20
> 200-250 275 450-630 17 140-200 -20
Normalised bar -250 300 470-620 21 140-200 -20
>250- 500 260 470-610 20 140-200 -20
Hot-rolled tube -5 340 470-610 21 140-200 -20
> 5-16 320 470-610 21 140-200 -20
> 16-40 300 470-610 21 140-200 -20
Cold-drawn bar 5-16 490 600-850 9 190-250
> 16-40 460 600-820 9 185-240
> 40-63 400 580-800 10 180-230
> 63-80 375 550-740 11 175-220
C 0.18 -00 Hot rolled bar -80 450 580-750 19 180-230
280
(S450J0)
Can be case-
hardened or
nitrided

Si 0.35 > 80-160 410 580-750 19 180-230

Mn 1.50 > 160-185 380 580-750 19 180-230
V 0.10 -01 Normalised bar -16 390 490-630 20 140-200 -20
S 0.015- > 16-35 380 490-630 20 140-200 -20
0.035 > 35-50 370 490-630 20 140-200 -20
> 50-70 360 490-630 20 140-200 -20
C 0.19 Hot-rolled tube ≤ 25 500 670 min 20 ≈ 225 +20
OVAKO 280
Can be case-
hardened,
nitrided or
quenched-and-
tempered

Si 0.38 > 25 470 640 min 20 ≈ 220 +20

Mn 1.53 Normalised tube ≤ 15 430 600 min 25 ≈ 190 -40
V 0.10 >15-25 400 580 min 25 ≈ 185 -40
S 0.020- > 25 380 560 min 25 ≈ 180 -40
0.035 Quenched-and-
tempered tube ≤ 30 600 700 min 20 ≈ 260 -40
C 0.20 Hot-rolled tube ≤ 16 470 650 min 17 ≈ 225
E470

Can be case-
hardened or
nitrided

Si 0.40 17-≤ 25 460 620 min 17 ≈ 220

Mn 1.60 26-≤ 40 430 600 min 17 ≈ 190
Cr 0.25 41-≤ 50 430 550 min 17 ≈ 180
V 0.12
S 0.035
Cold-finished tube 740 760 min 10 ≈ 250
280D

C < 0.20 Hot-rolled bar 20-70 380 490-630 22 ≈ 170 -20

520M
(S355J2)
Can be case-
hardened or nitrided

Si < 0.55 > 70-180 350 490-630 20 ≈ 165 -20

Mn < 1.60 > 180-200 285 450-630 17 ≈ 150 -20
V 0.09 > 200-210 275 450-630 17 ≈ 150 -20
S 0.02-
0.04
CEV 0.45
max
C < 0.20 Hot-rolled bar 25-70 380 490-630 22 140-200 -20
520MW+

Can be case-
hardened or
nitrided

Si < 0.55 > 70-90 350 490-630 20 140-200 -20

Mn < 1.60 > 90-180 350 490-630 20 140-200 0
V  0.09
S 0.13-
0.17

*Re: Upper yield stress (ReH) or if discontinuous yield is absent 0.2 % proof stress, Rp0,2
** D, T or B for respectively round, square or flat bars, wall thickness for tubes
Blue = Not stock standard
 25

Grade Continued from previous page Mechanical properties

Impact
Tensile test Hardness test
SS-EN 10002-1 SS-EN ISO 6506-1 SS-EN ISO 148‑1

Dim- Re* Rm A5 KV
Typical ension ** N/mm2 N/mm2 % min 27 J
analysis % Execution mm min min HB at °C
C < 0.20 Cold-drawn bar 20-55 500 550-750 12 ≈ 200 +20
550M
S355J2C+C
Can be case-
hardened or
nitrided

Si < 0.55
Mn < 1.60
V  0.09
S 0.02-
0.04
C < 0.20 Cold-drawn bar 20-55 500 550-750 ≈ 12 ≈ 200 +20
550MW+

Can be case-
hardened or
nitrided

Si < 0.55
Mn < 1.60
V 0.09
S 0.13-
0.17
C < 0.26 Hot-rolled bar > 80-180 320 490-630 20 ≈ 200 0
482 HYDAX 25

Can be case-
hardened

Mn < 1.60
S 0.09-
0.15

C < 0.40 Hot-rolled bar - 100 580 850-1 000 14 250-300

Suitable for
induction hardening

Si < 0.50 > 100 580 850-1 000 14 250-300

Mn < 1.40
Cr < 0.25
Ni < 0.25
V < 0.16
S 0.020-
0.035

*Re: Upper yield stress (ReH) or if discontinuous yield is absent 0.2 % proof stress, Rp0,2
** D, T or B for respectively round, square or flat bars, wall thickness for tubes
Blue = Not stock standard

Heat treatment of constructional steels

Constructional steels are usually supplied and used in the hot-rolled condition.
However, they sometimes require to be heat treated or processed as follows
in order to improve certain properties.

Forging
900 – 1 200°C Cooling freely in air.

Normalising
900 – 930°C Holding time 15-20 min. Cooling freely in air.

Quenching and tempering

Hardening 900 – 930°C. Holding time 15-30 min.
Quenching in water or polymer.
Tempering 550 – 600°C. Air cooling.

Stress relieving
550 – 600°C Holding time 1-2 h. Slow cooling.

Case hardening
Carburising 850 – 930°C.
Hardening 780 – 830°C. Quenching in water, oil or salt bath.
Tempering 150 – 200°C. Air cooling
26

CASE-HARDENING STEELS
Case-hardening steels have a low content of carbon and are supplied in a soft,
easy to machine condition. The component is first machined, then subjected to a
surface hardening treatment (case hardening) and finally finished via grinding.
Case-hardening steels are used in applications with requirements which may at
first sight appear incompatible: wear resistance, toughness, ability to withstand
impact and resistance to fatigue.

Case-hardening as a process involves as 16NiCrS4 (SS 2511), than for one the same time as the process permits
heating the steel in a carburising requiring hardening in water as a better control so that the toughness
medium, normally a gas mixture S355J2 (SS 2172). of the hardened layer and the corrosion
containing hydrocarbons. The carbon Carbonitriding is similar to case protection afforded by it can better
liberated from the gas mixture diffuses hardening but in addition to carbon be optimised.
into the steel to an extent which is even nitrogen is diffused into the steel. Nitriding is usually carried out as a
determined by temperature and time. In respect of hardening, the effects of final operation on finished components.
The carburised components are then carbon and nitrogen are additive so Especially after ion nitriding, the
quenched to effect hardening which that simpler, lesser-alloyed steels, surface finish is more or less the same
results in the combination of a hard which normally would need to be as that prior to treatment. Parts nitrided
wear-resistant surface (the case) hardened in water, can be quenched via gas or salt bath may require a light
and a tough core. The surface carbon in oil with benefits for dimensional polish if the application demands an
content is typically between 0.8 and and shape stability. extremely fine surface.
1.0 % giving a surface hardness >60 Nitriding is a surface hardening Generally speaking, the surface
HRC. The hardening depth can be process which is carried out at far hardness achievable with nitriding
anywhere between 0.2 and 1.5 mm lower temperatures than case hardening increases with the alloy content in the
depending on temperature, time and and involves diffusion of nitrogen into steel. Some examples of typical levels
carbon activity, i.e. the medium used the surface of a component. Unlike case attainable with ion nitriding are given
for carburising. It is possible to reduce hardening, no quenching operation below.
the process time for carburising by is necessary and the hardening effect Surface Core
selecting a steel with higher base from nitrogen is attained directly. Grade HV1 (*) HV10 (*)

carbon content, but there is then a Nitriding can be effected in a variety C45E (SS 1672) 490 180
risk that the core properties will be of ways, via ammonia-containing gas, S450J0/280 (SS2142) 650 200
jeopardised. by immersion in special salts or through 42CrMoS4 (SS 2244) 650 300
Case-hardened components are a plasma. With the gas method, it is 16NiCrS4 (SS 2511) 730 175
characterised by high strength and possible to use a mixture of ammonia 34CrNiMo6 (SS 2541) 650 290
excellent fatigue resistance. During and hydrocarbons so that carbon as * See the section on hardness later in the guide.

hardening the outer layer with high well as nitrogen is introduced into the
carbon content would occupy a steel. The process is then called It is noteworthy that nitriding of
greater volume but for the fact that nitrocarburising. S450J0/280 results in the same
it is constrained by the softer core, Nitrided layers are characterised hardness as considerably higher-
with the result that high compressive by high hardness and good resistance alloyed grades. This is coupled to the
residual stresses are developed in to wear but also by low friction and micro-alloying with vanadium which
the case. This type of residual stress some degree of corrosion protection. is a very potent nitride former and
distribution is favourable for counter- Furthermore, shape and dimensional gives high hardness even though the
acting the initiation and growth of changes are much smaller than with amount added is small. Manganese in
fatigue cracks which require tensile case hardening. Nitriding also improves this grade makes an additional contri­
stresses in order to develop. fatigue resistance but not to the same bution to the high hardness achieved.
Additional consequences of the degree as case hardening. The vanadium in S450J0 prevents
volume increase when the carburised Ion nitriding is a process in which microstructural coarsening at high
layer is hardened are dimensional and a plasma is created between the temperatures which means that this
shape changes, which depend on the components to be treated and the grade is also very amenable to case
form of the component but which can wall of a chamber filled with nitrogen hardening.
be quite large. For parts with high gas. The parts are bombarded with Hardenability is an important
requirements on dimensional tolerance, highly reactive nitrogen ions which property for case-hardening steels
a finishing adjustment will be necessary diffuse into the steel in the same way since it determines the core properties
usually by grinding. Dimensional as with other nitriding processes. after quenching and tempering. It is
changes will also depend on quench Ion nitriding does not require so high normally defined in terms of a Jominy
rate and are therefore less with a steel temperatures, which means that diagram which shows hardness as a
which can be hardened in oil, such dimensional changes are minimal at function of the distance for a sample
 27

that has been quenched by water at processes. This is most often defined Process Hardness level
its one end in accord with a standard­ as the distance in mm from the surface Case hardening: ≥550 HV1
ised procedure. over which the hardness exceeds a Carbonitriding: ≥550 HV1
Depth of hardening is an essential specified level. Nitriding: ≥400 HV1
parameter for all surface hardening Induction hardening: ≥400 HV1

Grade Mechanical properties

Impact
Tensile test Hardness test
SS-EN 10002-1 SS-EN ISO 6506-1 SS-EN ISO 148‑1

Dimension, Re Rm A5 KV
Typical D N/mm2 N/mm2 % min 27 J
analysis % Execution mm min min HB at °C
16NiCrS4 C 0.15 Hot-rolled or forged >20-430 max 217
(SS2511) Si <0.40 Cold drawn 10-20 500 625-750 10 200-240
Mn 0.90
Ni 1.00
Cr 0.80
S 0.02-
0.04

Other steel types that can be case-hardened are standard and micro-alloyed constructional steels and
free-machining steels.

Heat-treatment of case-hardening steels

Forging
900 – 1 200°C Rapid heating from 1000°C.
Hold only until heated through.
Free cooling in air.

Normalising
860 – 890°C Free cooling in air.
This heat treatment is carried out so as to refine grain size
prior to case-hardening.

Annealing
600 – 670°C Holding time 2h.
Cooling in furnace or freely in air.

Case-hardening
Carburising 850 – 930°C. Temperature and time determined by
carburising medium and required hardening depth.
Annealing 650 – 700°C. Will be necessary if the part is to be machined
after carburising.
Hardening 780 – 830°C. Oil quench. (Direct hardening with quenching
immediately after carburising is sometimes practised).
Tempering 150 – 200°C

Hardenability from Jominy test (see SS-EN 10084)

Distance* (mm) 1.5 3 5 7 9 11 13 15 20 25 30 35 40
16NiCrS4 HRC Max 47 46 44 42 40 38 36 34 32 30 29 28 28
(SS2511-08) HRC Min 39 36 33 29 27 25 23 22 20

*From the quenched end.

28

QUENCHED-AND-
TEMPERED STEELS
Quenched-and-tempered steels find application whenever a good combination
of strength and toughness is required. Low-alloy quenched-and-tempered steels
are supplied in a heat-treated execution. In this condition, these grades will,
generally-speaking, withstand both static and dynamic loading better than
carbon steels and weldable constructional steels. Hence, such materials offer
an interesting alternative to lesser-alloyed steels if it is advantageous to reduce
the weight of a component or construction that does not require welding.

The only low-alloy, quenched-and- and where the hardness and strength This is discussed in more detail later
tempered grade that is possible to is lowered. Welds should therefore be on in the guide. The quenched-and-
weld using relatively simple procedures placed where loading is least. If this is tempered grades in our stock at
is 25CrMoS4 (SS 2225). Other grades not feasible, it may be necessary to Tibnor are for the most part M-treated.
with higher carbon content are more consider hardening and tempering As already made clear, quenched-
difficult to weld. If welding is absolutely once again of the finish-welded part. and-tempered steels are supplied in a
necessary, attention should be given Machining this type of steel is heat-treated, ready-to-use execution
to the effects of changes of micro- usually troublesome and tools wear and further heat treatment is usually
structure in the weld heat-affected quickly even if the cutting speed is not required. The medium-carbon
zone. The material adjacent to the reduced. However, M-treatment has steel C45E/R (SS 1672) is an exception
weld will be re-hardened and thereby a strong positive effect in relation to and the stock standard is as-hot-rolled/
embrittled. Further away from the machining of quenched-and-tempered forged; any heat treatment that may
weld is a region where the temperature steels without significant negative be necessary will need to be carried
has exceeded that used for tempering effects as regards other properties. out after machining of the component.
 29

Grade Mechanical properties

Impact
Tensile test Hardness test
SS-EN 10002-1 SS-EN ISO 6506-1 SS-EN IS 148‑1

Dim- Re* Rm A5
Typical ension** N/mm2 N/mm2 % Min J
analysis % Execution mm min min HB at °C
C 0.47 Cold-drawn /C45E 8-16 320 590-740 9 165-220
C45E/C45R
(SS 1672)
Suitable for
induction
hardening

Si 0.25 Hot-rolled /C45R >16-40 310 590-740 14 165-220

Mn 0.60 >40-63 300 590-740 14 165-220
S <0.035/ >63-300 280 590-740 14 165-220
C45E Forged/C45E+N >300-550 280 590-740 16 165-220
0.02- -03 Quenched-and-tempered -100 370 630-780 17 180-230
0.04/ -04 Quenched-and-tempered -40 430 650-800 16 190-235
C45R -05 Quenched-and-tempered -16 490 700-850 14 205-250
C 0.26 -03 Quenched-and-tempered -100 500 700-850 17 205-250 27@-20
SS 2225 M
(25CrMoS4)
Suitable for
induction
hardening

Si 0.25 -05 Quenched-and-tempered -40 700 900-1050 13 270-325 27@-20

Mn 0.62 -06 Quenched-and-tempered >100-160 410 640-780 16 185-230 27@-20
Cr 1.05 Cold-drawn 15-20 700 900-1050 10 275-325
Mo 0.20
S 0.02-
0.04
C 0.26 Quenched-and-tempered -16 700 900-1100 12 45@+20
25CrMoS4

Suitable for
induction
hardening

Si <0.40 >16-40 600 800-950 14 50@+20

Mn 0.75 >40-100 450 700-850 15 50@+20
Cr 1.05 >100-160 400 650-800 16 45@+20
Mo 0.23
S 0.02-
0.04
C 0.42 -05 Quenched-and-tempered -105 690 900-1050 12 270-310 27@-20
SS 2244 M
(42CrMoS4)
Suitable for
induction
hardening

Si 0.25 -04 Quenched-and-tempered >105-160 600 800-950 14 235-285 27@-20

Mn 0.75 Cold-drawn 15-20 700 900-1050 10 275-320
Cr 1.05
Mo 0.20
S 0.02-
0.04
C 0.42 Quenched-and-tempered -16 900 1100-1300 10 30@+20
42CrMoS4

Suitable for
induction
hardening

Si <0.40 >16-40 750 1000-1200 11 35@+20

Mn 0.75 >40-100 650 900-1100 12 35@+20
Cr 1.05 >100-160 550 800-950 13 35@+20
Mo 0.23 >160-250 500 750-900 14 35@+20
S 0.02-
0.04
C 0.36 -03 Quenched-and-tempered -275 700 900-1050 12 270-325 27@-20
SS 2541 M
(34CrNiMo6)
Suitable for surface
treatment via
induction hardening
or nitriding

Si 0.25 Cold-drawn 10-20 700 900-1100 10 275-335

Mn 0.70
Cr 1.40
Ni 1.40
Mo 0.23
S 0.02-
0.035
C 0.34 Hot-rolled. quenched -16 1000 1200-1400 9 35@+20
34CrNiMo6

Suitable for surface

treatment via
induction hardening
or nitriding

Si <0.40 -and-tempered >16-40 900 1100-1300 10 45@+20

Mn 0.65 >40-100 800 1000-1200 11 45@+20
Cr 1.50 >100-160 700 900-1100 12 45@+20
Ni 1.50 >160-250 600 800-950 13 45@+20
Mo 0.23
S 0.02- Forged, quenched-and-tempered 285-610 600 800-950 13 240-290 27@-40
0.035
*Re: Upper yield stress (ReH) or if discontinuous yield is absent 0.2 % proof stress, Rp0,2
** D, T or B for respectively round, square or flat bars
Blue = Not stock standard

Quenching and tempering of C45E/R

Hardening 820 – 860°C. Quenching in water, polymer or fast-quenching oil.
Tempering 600 – 650°C. Free cooling in air.
30

YIELD AND TENSILE STRENGTH

FOR QUENCHED-
AND-TEMPERED STEELS
Below you find a comparison between the old SS-standard and the current
SS-EN-standard.

Yield strength minimum

RP0.2min, N/mm2
1 200

1 000

800
SS 2225-05
600 SS 2225-04
SS 2225-03
400 SS-EN 10083-25CrMoS4

200

0
20 40 60 80 100 120 140 160
Diameter in mm

RP0.2min, N/mm2
1 200

1 000

800
SS 2244-05
SS 2244-04
600
SS-EN 10083-42CrMoS4

400

200

0
20 40 60 80 100 120 140 160
Diameter in mm

RP0.2min, N/mm2
1 200

1 000
SS 2541-04

800 SS 2541-05
SS-EN 10083-34CrNiMo6
SS 2541-03
600 SS 2541-08

400

200

0
20 40 60 80 100 120 140 160
Diameter in mm
 31

The change to SS-EN means that yield or tensile strength applies within 900 N/mm2 respectively or as
requirements based upon the old SS- a certain range of dimensions while 2541-05 with respectively 800 N/mm2
standard may need re-assessing in the old SS standard allowed for and 1000 N/mm2. However, in SS-EN,
order to check conformance to the different strength levels for one and this dimension is available only
new standard. It could be necessary the same size. For example, diameter with the combination 800 and
to change grade or to see whether or 80 mm for grade SS 2541 could 1000 N/mm2, i.e. the same as 2541-05.
not the requirements can be modified. be specified as 2541-03 with yield/
SS-EN is such that a given level of tensile strength 700 N/mm2 and

Tensile strength minimum

Rmmin, N/mm2
1 200

1 000
SS 2225-05
800 SS 2225-04
SS 2225-03
SS-EN 10083-25CrMoS4
600

400

200

0
20 40 60 80 100 120 140 160
Diameter in mm

Rmmin, N/mm2
1 200

1 000
SS 2244-05
SS-EN 10083-42CrMoS4
800
SS 2244-04

600

400

200

0
20 40 60 80 100 120 140 160
Diameter in mm

Rmmin, N/mm2
1 200
SS 2541-04

1 000 SS 2541-05
SS-EN 10083-34CrNiMo6
SS 2541-03
800 SS 2541-08

600

400

200

0
20 40 60 80 100 120 140 160
Diameter in mm
32

SPRING STEELS
Spring steels contain about 0.5 % carbon which means that high levels of
yield and tensile strength plus excellent resistance to fatigue can be achieved
via quenching and tempering. As the name implies, the principal area of
application is springs but the high strength means that these steels also
function well in tools, wear parts and for some machine components.

For spring applications, spring steels Both silicon-chrome and chrome- For smaller dimensions, results
are tempered in the range 350-500°C vanadium spring-steel grades are similar to those achieved by hardening
to attain a hardness of 44-50 HRC, included in Tibnor’s stock programme. and tempering can be attained by
corresponding to tensile strengths At a given hardness level, these steels cold working followed by heat treat-
1 400-1 650 N/mm2. The associated are more or less equivalent but the ment at low-temperature.
high yield strength is concomitant Cr-V steel has better hardenability The service temperature of
with good spring properties since and can be used for heavier sections. components made from spring steels
large amounts of elastic energy can Remember that the product stocked should not exceed 200°C (Si-Cr)
be stored and released repeatedly. is either as-hot-rolled or annealed or 225°C (Cr-V); higher temperatures
However, the toughness is less good and that finished parts must be heat will result in loss of strength.
at these high strength levels. treated in order to realise high strength.
 33

Grade Mechanical properties

Impact
Tensile test Hardness test
SS-EN 10002-1 SS-EN ISO 6506-1 SS-EN ISO 148‑1

Re Rm A5 KV
Typical Dimension N/mm2 N/mm2 % min 27 J
analysis % Execution mm min min HB at °C
C 0.56 -00 As hot-rolled All <248
SS2090
(56Si7)

Si 1.7 flat bars

Mn 0.85
Cr 0.3
S 0.035
C 0.52 -02 Annealed All <240
SS2230
51CrVS4

Si 0.28 round bars

Mn 0.85
Cr 1.15
V 0.15
S 0.035

Heat treatment

Forging SS 2090 SS 2230

Cooling freely in air. 800 – 1 025°C 800 – 1 050°C

Hot forming
Cooling freely in air. 830 – 900°C 800 – 900°C

Annealing
Holding time 0.5 h after attaining 680 – 720°C 730 – 750°C
full temperature.
Furnace cool ca 20°C /h to 650°C,
followed by cooling free in air.

Stress relieving
Holding time ≈ 2 h after 550 – 650°C 550 – 650°C
attaining full temperature.
Furnace cool to 500°C,
followed by cooling free in air.

Hardening in oil
850 – 910°C 840 – 870°C

Tempering
Should be carried out immediately the material can be touched by hand.
Temperature 350-600°C. See tempering graph for SS2230 below.

SS2230 oil quenched from 860°, holding time 1 h.

600 Hardness (HV30)

400

200
100 300 500 700
Tempering temperature (C°)
34

BEARING STEELS
Bearing steels were developed specifically for service as ball and roller bearings.
This application requires good resistance to wear at the same time as the repeated
nature of the loading on bearings demands a high level of fatigue strength.
Hence, bearing steels can be and are used in other applications with the same
basic requirements, i.e. combined fatigue and wear resistance. In terms of their
chemical analysis, bearing steels are very similar to simpler tool-steel grades.

Since bearing steels contain about 1 % Let’s look at an example: dimension and shape along with a
carbon, they can be considered as an considerable risk for hardening cracks.
alternative for parts that usually are Component Requirements Hence, this choice of steel and heat-
case hardened. In such an instance, (See photo treatment method will necessitate an
the gain is that case hardening, which on left below) appreciable finish grinding allowance
is a time-consuming and therefore D40 X 300 mm Surface hardness in order that the requirements on
expensive heat treatment, can be re- ≥60 HRC; tolerance and straightness can be met.
placed by a straightforward hard­ening good
and tempering operation. The straightness; 100Cr6 (Ovako 803) induction
properties obtained thereby are more close tolerances. hardened. The base steel is admittedly
or less equivalent to what is attainable more expensive but the part will be
via case hardening. If a hard surface in One can envisage several alternatives straight after hardening and a minor
combination with a tough core is to manufacture this part; two are final adjustment by grinding is all that
required, then bearing steels can even described below. will be required in order to achieve the
be induction hardened. dimensional tolerances.
S355JR case hardened to a depth of
about 0.8 mm with the final tolerance This constitutes a good example of
being achieved by finish grinding after how choosing a more expensive
the surface treatment. In order to attain material can reduce the overall cost to
the required hardness, this grade would manufacture a part; induction hardening
for the relevant dimension need to be costs far less than case hardening
hardened by quenching in water which and a time-consuming and therefore
will result in significant changes in expensive finishing operation is avoided.
 35

Grade Mechanical properties

Impact
Tensile test Hardness test
SS-EN 10002-1 SS-EN ISO 6506-1 SS-EN ISO 148‑1

Re Rm A5 KV
Typical Dimension N/mm2 N/mm2 % min 27 J
analysis % Execution mm min min HB at °C
C 1.00 -02 Annealed bar All 340 ≈640 30 ≈190
100Cr6
(OVAKO 803)

Si 0.25 -06 Cold-finished bar 225-260

Mn 0.35 Cold-finished tube ≈8801) ≈9801) ≈101) ≈300
Cr 1.50

C 0.97 Annealed tube All 370 ≈670 27 ≈200

100CrMo7
(OVAKO 824)

Si 0.30
Mn 0.20
Cr 1.80
Mo 0.35

C 0.97 Annealed bar All 390 ≈690 25 ≈210

100CrMo7-3
(OVAKO 825)

Si 0.30
Mn 0.30
Cr 1.80
Mo 0.35

1)
Approximate values depending on degree of reduction.

Heat treatment of bearing steels

Full annealing
800 – 820°C Holding time 2-5 h after attaining full temperature. Furnace
cool 15–20°C/h to 650°C followed by free cooling in air.

Stress relieving
550 – 650°C Holding time 2 h after attaining full temperature.
Furnace cool to 500°C followed by free cooling in air.

Hardening in oil
830 – 875°C For large and/or complicated parts the quench should
be interrupted at 100-150°C with subsequent double
tempering.

Surface hardening treatment

This type of steel can be induction hardened and tempered
at 150-200°C to attain a surface hardness of 60-65 HRC.

Tempering
100 – 500°C Tempering in the interval 250-350°C causes embrittlement
and should be avoided. Tools for blanking are normally
tempered at 150-200°C. If better toughness is needed then
a tempering temperature >350°C should be chosen.
36

HARD-CHROME BARS
Hard-chrome-plated bars do not represent a steel type but rather a special
execution. The principal application is for piston rods in hydraulic and pneumatic
cylinders. Induction-hardened hard-chrome bars characterised by a hardened
zone beneath the chrome layer, which is resistant to both wear and impact,
have proved usable even for service as pivot pins.

As standard, Tibnor stocks hard chrome- Hard-chrome bar can also be moderate. This is because the
plated bar in grade 280X, which is a supplied in an induction-hardened chromium layer is hard and has
micro-alloyed, low-carbon construc- execution, in which case the steel considerable internal stress which
tional steel with an analysis corres­­- base is Ovako 482, a micro-alloyed results in a network of fine micro-
ponding to EN-SS S450J0 (SS 2142). steel with medium carbon level. cracks. However, by good control of
However, the steel is optimised such The surface hardness of the induction- the plating process and suitable
that the yield and tensile strengths are hardened layer is minimum 55 HRC finishing, it is possible to achieve
about 20 % higher than is normal for and the depth of hardening about sufficient corrosion resistance for
EN-SS S450J0, and this improvement 2 mm. This product is used for hydraulic normal applications involving
is achieved without compromise in applications where the piston rods run exposure to damp air or oxygenated
regard to weldability or machinability. the risk of being damaged by impact water. If your application requires
This higher strength provides an or similar external factors. long-term exposure to a salty/marine
opportunity to downsize piston rods Chromium metal has excellent or acidic environment, then it is a
thereby enabling savings in weight corrosion properties, but nevertheless good idea to seek the advice of
and cost to be achieved. the corrosion resistance afforded by Tibnor for alternative products with
hard-chrome plating of steel is only better corrosion resistance.

Grade Mechanical properties

Impact
Tensile test Hardness test
SS-EN 10002-1 SS-EN ISO 6506-1 SS-EN ISO 148‑1

Dim- Re* Rm A5 KV
Typical Execution and ension, D N/mm2 N/mm2 % min 27 J
analysis % tolerance mm min min. HB at °C
C 0.18 Hard-chrome plated 10–18 520 650–800 12 200-240
280X
(S450J0)

Si 0.35 f7 20-90 520 600–800 19 200-240 -20

Mn 1.55 > 90-140 440 600–750 19 180-230
V 0.10
S 0.025
C 0.39 Hard-chrome plated 12-125 580 850-1 000 14 250-300
482
(38MnVS5)

Si 0.40 induction-hardened f7
Mn 1.20
V 0.13
S 0.020

*Re: Upper yield stress (ReH) for 280X, Rp0.2 for 482
Additional characteristics - Surface finish: Ra≤0.2μm, Rt≤2μm. Straightness: ≤0.1 mm/0.5 m for D<30 mm,
≤0.1 mm/m for larger diameters. Chrome layer: thickness minimum 20μm with minimum hardness 850 HV0.1.
Blue = Not stock standard
37
38

FREE-MACHINING STEELS
Free-machining steels as the name suggests are designed to be easy to machine.
Very high cutting speeds are possible and the chips are short and easy to
transport, which is a considerable advantage when working unmanned with
CNC-equipment. The excellent machinability derives from additions of sulphur
either on its own or in combination with lead.

Most of the dimensions in Tibnor’s are not eliminated by cold drawing ”orange-peel surface”. If appearance
stock programme of free-machining even though the depth of such will be is important, the surface should
steels are in a cold-drawn execution decreased. The cold-finished surface first be improved by fine machining
with close tolerances (h9-h11) and should therefore not be left unworked or grinding prior to any surface-
smooth surfaces. Furthermore, the if the application involves load treatment operation.
cold working contributes further to variations and concomitant risk for Free-machining steels are
the excellent machinability. The good fatigue. The standardised maximum optimised for machinability and this
dimensional tolerances constitute an allowable crack depth on cold-drawn is achieved at the expense of other
additional advantage when processing rounds is 2 % of the diameter per side properties, especially ductility and
in automatic machines. (see SS-EN 10277-1, class 1). toughness. This type of material
It should be remembered that Another issue, which can arise if should therefore only be used for
surface defects from hot-rolling such un-machined as-drawn material is to components or constructions that in
as cracks, scratches and impressions be surface treated, is so-called service are subjected to low loads.
 39

Grade Mechanical properties

Impact
Tensile test Hardness test
SS-EN 10002-1 SS-EN ISO 6506-1 SS-EN ISO 148‑1

Re Rm A5 KV
Typical Dimension* N/mm2 N/mm2 % min 27 J
analysis % Execution mm min min HB at °C
C <0.14 -04 Cold-finished 5-10 440 510-810 6 150-250
11SMnPb30+C
(SS 1914)
Can be case-
hardened

Si 0.05 drawn >10-16 410 490-760 7 150-220

Mn 1.10 >16-40 370 460-710 8 140-240
S 0.30 >40-63 300 400-650 9 130-230
Pb 0.25 >63-100 245 360-630 9 120-220
Peeled 80-140 240 360-520 10 <170

C 0.43 Cold-finished - 16 510 710-860 6 >210

MACH 50
Can be
quenched-and-
tempered
or induction
hardened

Si 0.10 drawn >16-40 460 650-800 7 >185

Mn 1.40 >40-90 390 620-780 8 >180
S 0.26
Pb 0.25

C 0.36 Cold-finished 5-10 500 660-960 6 210-270

36SMnPb14+C
(SS1957+Pb-04)

Si 0.20 drawn >10-16 440 620-920 6 200-260

Mn 0.90
S 0.20
Pb 0.25

C <0.20 Cold-finished 20-55 500 550-750 12 ≈ 200 +20

550MW+

Si <0.55 drawn
Mn <1.60
V 0.09
S 0.13-
0.17
C <0.20 Hot-rolled 25-70 380 490-630 22 150-200 -20
520MW+

Si <0.55 >70-90 350 490-630 20 150-200 -20

Mn <1.60 >90-180 350 490-630 20 150-200 0
V 0.09
S 0.13-
0.17

* D, T, B or N for rounds, squares, flats and hexagons respectively.

40

M-STEELS FOR MACHINABILITY

Machining represents a large portion of the total cost of manufacturing a
component, often up to 50 %. As a complement to the programme of free-
achining steels, Tibnor has therefore made the decision to stock all grades of
quenched-and-tempered steels and case-hardening steels in M-execution.
The so-called M-treatment confers improved machinability without significant
negative effect for other properties. For a given degree of tool wear, M-treated
steels can be machined at 20-30 % greater cutting speed; conversely, machining
with the same data as for equivalent conventional steels results in up to four
times longer tool life.

The improved machinability derives tooling to the same degree while at temperature and will be lost from
from the special nature and shape of the same time a lubricating film the melt unless the addition is made in
non-metallic inclusions in the steel. containing calcium and sulphur is a proper way. If too little calcium ends
Instead of hard aluminium oxides, established between the tool and up in the steel, the inclusions that are
which cause excessive tool wear, the the chips. formed do not have the correct
characteristic inclusions in M-steels The manufacture of M-steels character and the positive effect for
consist of calcium aluminates necessitates careful control if the machinability is impaired or is maybe
surrounded by a skull of calcium improvement of machinability is to be even absent completely.
sulphide. This type of inclusion is achieved consistently from heat to
relatively soft and does not wear heat. Calcium boils at a relatively low
 41

The lubrication effect from M-steels:

M-treatment eliminates hard,
Standard steel M-steel
abrasive inclusions at the same time
as a lubricating film is created on
Chip Chip
the cutting edge at high machining
Flank Flank
wear wear speeds.
Normal Lubricating
crater wear film

Flank wear, mm
0.6
M-steel High-speed machining of steel
which has not undergone
M-treatment results in significant
0.4
Standard steel
flank wear after a short time.
For the same steel which has been
M-treated, the point at which rapid
Wear criterion VB=0.3 mm
0.2
wear occurs is shifted to longer
times. Crater wear is close to zero
thanks to the lubricating film which
develops at the cutting edge.
0
0 5 10 15 20 25 30
Contact time (min)

Crater wear, mm
0.4

Standard steel

0.2
Wear criterion KT=0.18 mm
M-steel

0
0 5 10 15 20 25 30
Contact time (min)

Turning parameters: depth of cut = 2.5 mm, feed = 0.4 mm/rev.,

cutting speed = 450 m/min
Insert: GC 415 P15

The positive effect of M-treatment is greatest when the cutting speed,

and thereby the cutting-edge temperature is high. The M-effect is therefore
very pronounced when machining with coated carbide tooling but far less
for cutting at the lower speeds with non-coated high-speed steel (HSS)
tools. The improvement in machinability is also significant for cutting with
cermets and certain types of ceramic inserts. The table summarises the
effect of M-treatment for machining with various types of cutting tool.

Compatibility between various types of cutting tools and M-steels

Tool material Conditions Effect of M-treatment
HSS uncoated High speeds Quite good
HSS uncoated Low speeds Less good
HSS TiN-coated High speeds Quite good
HSS TiN-coated Low speeds Good
Carbide P10 uncoated High stability Excellent
Carbide P20 uncoated Normal Good
Carbide P30 uncoated Normal Less good
Carbide-coated TiC-Al2O3-TiN Normal Excellent
Carbide-coated Al2O3 Normal Good
Cermets (all) Fine machining Excellent
Mixed ceramic Al2O3+TiC High stability Excellent
Ceramic Al2O3 High stability Less good
42

HARDNESS
The term hardness defines the resistance offered by the steel (or any other
material) to indentation by an external force. Hence, we measure hardness by
pressing a ball or tip with a predetermined load into the surface of the steel.
From the size of the resulting impression in terms of its area or depth,
the hardness can be assessed; a soft material gives a large/deep impression
and a hard material a small/shallow one.

In what follows, you find a description hardness in these instances is to the tensile strength in N/mm2.
of the three most common methods reported as kgf/mm2. This means that This relationship is useful if one
to measure the hardness of steel. for a given steel, the numerical values requires an estimate for tensile strength
for HB and HV are quite similar (the (after heat treatment, for example)
Brinell (HB) deviation is about 5 %). On the other but only has access to a hardness
The indenter is a ball of hardened hand, HRC is based on the depth of tester. The correlation between tensile
steel or cemented carbide (D= 10 mm) the impression and is very approx­ strength and hardness works
and the force used to make the imately a tenth of the values for HB somewhat better for HB than for HV.
impression is usually 3 000 kgf (3 tons). and HV. Furthermore, since Rockwell In the table below, a comparison is
This method is mostly used for soft/ impressions are rather deep, the test given between hardness values
medium-hard steels. is not really suitable for thin parts. obtained using the different methods
For unalloyed and low-alloy steels, and tensile strength. An exact
Rockwell C (HRC) there exists quite a close correlation conversion is not possible and the
This test, in which the indenter is a between hardness and tensile strength. values should be regarded as
conical-shaped diamond, is most If the HB-value for a certain steel is approximate only. The table is identical
often used for hard steels. Its main divided by 3 and the result multiplied to the one given in SS-EN ISO 18265.
advantage is speed since the hardness by 10, the answer is surprisingly close
is read off directly from a scale on
the hardness tester. Rockwell C
hardness measurement requires quite
Photo: Struers
careful sample preparation by grinding
or polishing.

Vickers (HV)
The Vickers indenter is a pyramid-
shaped diamond and the test can be
used over the entire hardness
spectrum. The load can be adjusted
between 0.1 and 30 kgf. Hence, when
reporting Vickers hardness, the load
should also be specified, for example
HV1 or HV10. When determining
hardness profiles on surface-hardened
parts treated by case hardening,
nitriding etc., it is best if the hardness
impressions are not too large and 1 kgf
is a suitable load for such measurements.

All three methods have their

specific advantages and limitations.
Since by alloying and heat treatment,
the hardness of steel can vary over
a very wide range (from soft and
formable to hard and wear resistant),
one test or the other is used depending
on steel grade, heat-treat condition
and test-piece geometry.
HB- or HV-values are calculated by
dividing the applied load by the area
of the resulting impression and the
 43

Correlation between various hardness values and tensile strength

HV10 HRC HB Rm, N/mm2 HV10 HRC HB Rm, N/mm2

150 143 480 290 28.5 276 920

160 152 510 300 29.8 285 950
170 162 540 310 31.0 295 990
180 171 570 320 32.2 304 1020
190 181 600 330 33.3 314 1050
200 190 635 340 34.4 323 1080
210 200 670 350 35.5 333 1115
220 209 695 370 37.7 352 1175
230 219 725 400 40.8 380 1275
240 228 755 420 42.7 399 1345
250 22.2 238 785 450 45.3 423 1440
260 24.0 247 825 470 46.9 442 1500
270 25.6 257 855 500 49.1 466 1610
280 27.1 266 880 550 52.3 509 1805
44

WELDING
The higher the carbon and/or alloy content of a steel, the less suitable it is to be
welded. In other words, steels with higher strength and hardness (wear resistance)
are more difficult to weld. It is preferable that the carbon level is below 0.25 %
and that the sulphur content is also low if a component requires welding as a step
in its manufacture.

A simple way of quantifying weld- > 0.55 % should always be pre-heated any hydrogen which has been
ability for constructional steels, carbon prior to welding. Furthermore and introduced is expelled. The latter is
steels and low-alloy steels is through irrespective of CEV, it is always a good important since higher-strength
the carbon equivalent value (CEV): idea to pre-heat whenever parts with steels are more sensitive for hydrogen
larger cross-sections are to be welded. embrittlement.
CEV = C+Mn+(Cr+Mo+V)+(Cu+Ni) Standard constructional steels and With the exception of free-
6 5 15 micro-alloyed steels with CEV <0.55 machining steels, grades which are
(symbols relate to content in weight %) % are most suitable for constructions stocked in a cold-drawn execution
or components where welding is can be welded without problem.
A steel with low CEV is easy to weld required. These grades can in most However, one should be aware that
and vice versa. cases be welded without pre-heating the strength level and hardness can
An element, which is very negative and do not normally require any post- decrease somewhat in the heat-
for weldability but which does not weld treatment so long as the section affected zone.
appear in the carbon-equivalent is not too large. If higher strength MAG welding with shielding gas
formula, is sulphur, for which does not is needed, then EN-SS 25CrMo4 and wire consumables gives better
appear in the weld metal can give rise (SS 2225), which has quite good control and less risk for contamination
to hot cracking. The negative weldability especially in smaller by hydrogen. For MMA/SMA-welding,
influence of sulphur is limited when dimensions, can be considered. basic electrodes are to be preferred
also manganese is present since Even higher-strength steels with and it is important that these are
sulphur is then bound as manganese more carbon and appreciable alloy properly dried so that ingress of
sulphide (MnS). For this reason, the content can be welded successfully hydrogen is mitigated to as great a
ratio Mn:S should be at least 10:1 in as long as correct procedures are degree as possible. If you are uncertain
steels that are to be welded. Free- followed and suitable consumables as to details concerning welding
machining steels containing sulphur selected. Pre-heating is an absolute procedure, it is advisable to seek the
are not at all suitable for welding, even requirement and the heat-input advice of either your Tibnor represen­
grades where the content of carbon should be limited by building up the tative or your supplier of welding
and other alloying elements is low. joint with a large number of smaller equipment and consumables. This
Weldability can be improved to beads, all to lessen the risk for applies particularly whenever higher-
some degree by prior pre-heating. occurrence of brittle regions in the strength steels with elevated contents
This has the effect of lowering the weld metal and heat-affected zone. of carbon and alloying elements are
cooling rate after welding which If quenched-and-tempered steels to be welded.
counteracts the formation of brittle with higher carbon content need The following table lists suitable
microstructures in the heat-affected to be welded, then a second full consumables (ESAB-designations)
zone of the weld. The slower cooling hardening and tempering heat and gives some general recommend­
also contributes to elimination of any treatment of the finish-welded part ations for welding of some of the eng-
eventual hydrogen in the weld, is to be recommended, at least for ineering steel grades in Tibnor’s stock
thereby reducing the risk for cold critical cases. A second heat treatment programme.
cracking as a result of hydrogen carries the additional benefit that
embrittlement. Steels with CEV residual stresses are reduced and that
 45

MAG welding MMA/SMA welding

Grade Wire/shielding gas* Electrode Pre-heat? Other remarks
S235 12.51/M21 OK48.00 Not normally Femax 33.XX
Femax 33.XX required are rutile electrodes
(hydrogen uptake
can give problems)
S355/280/520M/550M 12.51/M21 OK 48.00, OK 55.00 > 150°C for larger See above
12.64/M21 Femax 38.65 dimensions
C45E 12.64/M21 OK 74.78 > 200°C

25CrMoS4 (SS 2225) 13.12/M21 OK 74.78, OK 78.16 > 150°C In critical cases,
13.29/M21 unless parts are hardening and
very small tempering after
welding may be
necessary
16NiCrS4 (SS 2511) 13.12/M21 OK 74.78 > 150°C Compatible with
13.29/M21 unless parts are base steel only
very small
42CrMoS4 (SS 2244) 13.12/M21 OK 75.75, OK 76.18 > 300°C In critical cases,
13.29/M21 hardening and
tempering after
welding may be
necessary
*M21 = 80 % Ar, 20 % CO2

46

COLD FORMING
The cold formability of a material relates to the degree to which it can be worked
without cracking in a cold-forming operation, like bending for example. The cold
formability of steel is coupled to its ductility. Hence, high-strength steels are
generally more difficult to cold form since ductility is reduced as carbon content
and strength level are raised (see diagram below). The ductility of steels can
be increased by reducing the carbon content to very low levels (< 0.01 %) but
this kind of material, usually in the form of thin strip, is used for press forming
and deep drawing. For the grades and executions which are the focus of our
attention in this guide, relevant cold-forming operations are bending, cold
heading or cold forging.

Among the steel types that are longitudinal direction of a bar (or tube) improving machinability. Even so,
discussed in this guide, standard and give rise to so-called fibre. One cold formability both parallel to and
constructional and micro-alloyed steels consequence of this is that the ductility transverse the rolling direction is
show best cold formability. Generally is considerably less in a direction always best if the steel is clean and
speaking, the ductility of this type of transverse to the bar axis than parallel the number of inclusions is reduced
material is improved by normalising, to it. This difference is of significance to a minimum.
which might be worth considering if in bending where tensile stresses are Cold heading and cold forging are
the manufacture of a part necessitates generated on the outside of the bend. forming methods which for the most
extensive cold forming. Hence, for flat bars, the bendability is part involve loading in compression.
Non-metallic inclusions have a quite a lot better if the bend axis is at Under such circumstances, cold
strong negative influence on ductility right angles to the length direction of formability is normally much better
since they act as initiation points for the bar rather than parallel to it. than in processes where tensile stresses
cracks. Hence, a clean steel has better The typical inclusions in M-steels are generated, such as bending.
cold formability than one containing are not elongated during hot-rolling However, even in cold heading and
large amounts of inclusions. Basically to the same degree as other inclusion cold forging, tensile stresses can arise
all types of inclusions are deleterious types, such as manganese sulphides at free surfaces as a result of frictional
for ductility, even those that are and silicates. Hence, the difference forces between the work material
deliberately present as in free-machining in ductility between longitudinal and the tool. Such stresses are
steels and M-steels. and transverse directions is less generated at right angles to the axis
Non-metallic inclusions bear an pronounced for this type of steel of compression and can give rise to
influence on cold formability in a treated with silicon-calcium than for cracking if they act in a direction
second way. During hot-rolling, the other steels containing large amounts corresponding to the transverse
inclusions are elongated in the of inclusions for the purpose of direction of the original rolled bar.

Fracture elongation, %
60

Very low carbon steels

30
Normalised

Constructional and micro-alloyed steels

Hot-rolled
The dependence of ductility
(fracture elongation, A5 ,
Quenched-and-tempered steels Spring steels in longitudinal direction) on
tensile strength for a number
0 of different steel types.
0 500 1 000 1 500 2 000
Tensile strength, N/mm2
 47

FATIGUE AND HOW THE RISK

FOR FATIGUE FAILURE
CAN BE LESSENED
Fatigue is a damage process occurring under conditions of variable loading and
which is characterised by the initiation and growth of cracks at stress levels
considerably less than the tensile strength of a material. A rough estimate is that
80-90 % of all failures of machine parts and constructions can be put down to
fatigue. In many instances, it is possible to avoid fatigue failure by giving some
thought to suitable shape and/or surface finish of a component.

A part that has failed due to fatigue Steel is rather unique among -  Stress concentration effects
will have a fracture surface with a very common metallic materials in that associated with sharp corners,
characteristic appearance. It is it exhibits a fatigue limit, i.e. fatigue sudden changes in section, fillets etc.
normally quite easy to see where the failure does not occur if the stress are very negative in relation to
failure has started, most often but not amplitude remains below a certain fatigue resistance.
always at an external surface. The level. For the data shown in the – Residual stresses affect fatigue
crack-growth phase is characterised Wöhler diagram below, the fatigue resistance, negatively if such are
by convex so-called striations limit is about 380 N/mm2. Hence, tensile (in the vicinity of welds for
concentric with the starting point; this when one refers to the fatigue strength example) and in a positive sense
part of the fracture surface is rather of a certain steel, it is normally the if the stresses are compressive in
flat. When the fatigue crack has level of fatigue limit that is implied. nature. Favourable compressive
grown to a critical length, the final The fatigue strength of a steel residual stresses can be generated
failure of the part takes place and the component depends upon a number either by cold working (shot peening
fracture surface is then considerably of factors. The most important ones or roller burnishing) or through heat
more irregular. are listed below. treatment (case hardening, induction
The fatigue properties for steel are – Fatigue strength increases with hardening, nitriding etc.).
normally presented as a so-called increasing hardness and tensile
Wöhler diagram (see the example strength. In addition, fatigue strength is
below) in which the stress amplitude – Steel cleanliness. Non-metallic influenced by the character of the
(half the difference between the inclusions, and especially very hard loading that a part might be
greatest and least stress in a load inclusions, have a negative effect on subjected to, for example bending,
cycle) is plotted against the number fatigue resistance. pushing/pulling or twisting. The type
of cycles to failure. The number of – Surface finish. A polished surface of loading is defined by the mean
cycles that the material can resist shows much better fatigue strength stress which is the average of the
before it breaks decreases as the than, for example, one with a rough, highest and lowest values in a load
stress amplitude increases. hot-rolled finish. cycle. As an example, consider a
rotating axle subjected to a constant
Stress amplitude, N/mm2
900

500

Not broken

Wöhler diagram for steel Ovako 482

(38MnV5 – medium-carbon,
micro-alloyed steel) as determined
100 by rotating-bend testing
10 100 1 000 10 000 100 000
No. of cycles to failure, thousands (logarithmic scale)
48

load (rotating bending). A given point Welds are particularly dangerous Measures whereby the risk for
on the surface will experience from a fatigue standpoint. There are fatigue failure of a part can be reduced
alternating tensile and compressive two reasons for this; on the one hand, if not completely eliminated are:
stresses with the same magnitude but typical weld defects such as large
opposite signs; the mean stress is inclusions, cracks, pores, lack of 1. Select a material with better fatigue
therefore zero. The influence of mean penetration etc. can function as starting strength.
stress on fatigue resistance can be points for failure, and secondly, welds 2. Change the design of the
summarised as follows: are inevitably associated with component so that stress raisers
- Fatigue strength is lowered from the unfavourable tensile residual stresses. are avoided or at least their effects
level for mean stress zero if the load The negative effect on fatigue lessened.
cycle is dominated by tensile stresses strength derived from stress raisers, 3. Improve the surface finish.
(mean stress positive). surface finish and corrosive environ- 4. Treat so as to generate compressive
- The fatigue strength will be increased ment become progressively more residual stresses in the surface.
from the level for mean stress zero pronounced as the tensile strength 5. If welding is necessary, give
if the load cycle is predominantly increases. In other words, high-strength consideration to the location
compressive in nature (mean stress steels are more sensitive to the said of welds.
negative). In fact, fatigue does not effects. The diagram below shows the
occur at all if a component or degree to which the fatigue strength is Difficulties in defining the load
construction is subjected to only reduced as a function of tensile strength. variations in a given application
compressive stresses. The fatigue strength (fatigue limit) combined with lack of material data
Load cycles consisting only of tensile obtained in bending of polished for fatigue strength means that it can
stresses, so-called pulsating tension, samples of low-carbon constructional sometimes be problematic to design
are the most dangerous ones. steels and quenched-and-tempered and dimension a component so that
Corrosion and corrosive environ­ steels with Rm < 1200 N/mm2 can be the risk for fatigue failure is minimised.
ments are extremely deleterious in roughly approximated to half the For safety-critical parts, the only
relation to fatigue. Furthermore, the tensile strength. For loading in pulsating alternative is to measure service load
characteristic fatigue limit for steel no tension with positive mean stress and variations and to test finished
longer exists under corrosive conditions minimum stress zero, the fatigue limit components subjected to realistic
and failure can occur even at very low is lowered to 35-40 % of the tensile load spectra. Of course, this type of
levels of loading. Unfortunately, certain strength. testing is expensive. For less critical
surface treatment methods aimed to applications, the risk for failure can be
protect against corrosion, plating with lessened by adhering to some or all
chrome or nickel for example, also of the measures listed above and which
impair fatigue resistance. now will be discussed in more detail.

1. Select a material with

better fatigue strength
The fatigue resistance of steels
increases with increasing tensile
strength (hardness). The diagram on
% decrease of fatigue strength in
the next page shows the approximate
relation to polished
100% Polished relationship between tensile strength
and fatigue limit for bend loading.
For tensile strengths < 1200 N/mm2,
Ground
the fatigue limit is about 50 % of the
Fine machined tensile strength. However, this
percentage decreases successively
75
Rough machined as the tensile strength is increased.
As has already been pointed out,
non-metallic inclusions are negative in
relation to fatigue resistance and
steels used for components which are
50
subjected to high levels of fluctuating

Ring-shaped V-notch

Illustrating the reduction in fatigue

Hot rolled
25
strength derived from different
surface finishes, a stress raiser
Fresh-water environment (notch) and corrosive environment.

Salt-water environment (Source: K B Lundqvist ”Strength of

Materials”, Albert Bonniers Förlag
0 (1959), p.44 – in Swedish).
0 500 1 000 1 500 2 000
Tensile strength (Rm) N/mm2
 49

load should be clean, i.e. contain only a - The transition from one section to burnishing, or through suitable heat
small amount of non-metallic inclusions. another is gradual. treatment. All surface heat-treatment
The reason is that inclusions can - Corners have generous as opposed methods, case hardening, nitriding,
function as starting points for fatigue to very sharp radii. induction hardening etc, give rise to
and as the tensile strength increases, - Fillets are eliminated as far as an increase of volume in a surface
the critical inclusion size to initiate possible. layer which is counteracted by the
fatigue is reduced. Steel cleanliness is underlying material. In this way,
therefore of particular importance for Notch effects are sometimes unavoid­ compressive stresses are introduced
high-strength steels which are usually able, in components with threads for which are very positive from the point
manufactured using special refining example. There is then no choice other of view of fatigue.
procedures coupled with vacuum than to select a steel with suitable The improvement of fatigue
treatment. The oxygen content of strength, assess the notch effect of strength resulting from the generation
the material is by so doing reduced the thread (can be found in standard of surface compressive stresses is
along with the amounts of hard (and tables) and dimension accordingly greatest for loading modes in which
consequently dangerous) oxide depending on the loading to which the highest stress is attained at the
inclusions. the part is subjected. It is worth noting surface, e.g. bending or twisting.
In some steel types, such as free- that rolled threads exhibit far better In axial push-pull loading, when the
machining steels and M-steels, fatigue strength than ones which have stress is relatively constant over the
additions such as sulphur and calcium been machined. cross section of a component, surface
are made in order to deliberately compressive stresses have far less
promote certain types of inclusion 3. Improve surface finish effect or even no effect at all; this is
with the aim of improving machinability. Components where there is a risk for irrespective whether the stresses are
Such inclusions can affect fatigue fatigue failure must be manufactured derived from cold working or heat
resistance negatively and the use of with care. The finer the surface finish, treatment.
free-machining steels for parts which the better is the fatigue resistance,
are subject to appreciable load and the sensitivity for sub-standard 5. Avoid welds or at least consider
variations is not to be recommended. surface finish increases with the level where they are placed
As regards M-steels, the characteristic of tensile strength. It is not by chance As already pointed out, welds are
inclusions (calcium aluminates with a that balls, rings and rollers in bearings, very negative in respect of fatigue
skull of calcium sulphide) exert only a with a hardness of 60-62 HRC, are fine resistance and it is preferable that
minor negative influence on fatigue ground or polished. welding is avoided in machine
resistance so long as the hardness is applications where there is risk for
below 350HB and the inclusions 4. Introduce favourable residual fatigue failure. If this is not possible,
remain relatively small. At higher stresses then one should bear in mind the
hardness levels, M-treatment reduces Fatigue cracks start and grow only following:
fatigue strength. during the tensile part of a load cycle. - Welds should be located where
This means that compressive residual loads (stresses) are lowest.
2. Limit as far as possible stress stresses are favourable for fatigue - Fatigue strength can and should be
raisers and notch effects strength since they counteract tensile improved via careful weld finishing.
Stress concentrations due to changes stresses felt as a result of the service Suitable methods are grinding of the
in section, holes and sharp corners loading. Surface compressive stresses weld bead or TIG-remelting of the
give rise to a considerable decrease in can be created by cold working, for weld metal and the transition zone
fatigue strength. Hence, for best example shot peening or roller with the base material. In both
fatigue resistance, it is essential that: instances, the aim is to reduce the
number of welding defects which
potentially can initiate fatigue cracks.
However, these finishing procedures
Fatigue limit, N/mm2 can be time-consuming and therefore
900 costly. A cheaper finishing method,
which nevertheless gives some
improvement of fatigue life, is cold
Bearing steels hammering of the weld bead.
700
- Machine components with welding
Spring steels as a manufacturing step should be
stress relieved in order to reduce the
Quenched-and-tempered steels
500 level of tensile residual stress.

Carbon steels
300
Constructional steels
Variation of fatigue limit in rotating
bending as a function of tensile
100 strength for various types of steel.
0 500 1 000 1 500 2 000 2 500
Tensile strength, N/mm2
50

REDUCING WEIGHT
OF COMPONENTS AND
CONSTRUCTIONS
Engineers and designers have strived towards lighter constructions for many
years but the driving force for weight reduction has intensified in recent times,
especially in the motor-vehicle industry. It has to some degree proved possible
to replace steel with lighter materials like aluminium or plastics but for parts
which are heavily loaded, there is really no economical alternative to steel.
The strength range which is achievable with steel is so broad that it is in principle
always possible to swap ”ordinary” steels, such as S355JR, for a higher-strength
material allowing the dimensions of the part to be reduced, thereby saving
weight. Unfortunately, it is seldom so simple and what is feasible depends on
which properties have been used as the basis for dimensioning of the part at
the design stage.

In many instances, the principal exceed the yield strength of this steel is changed to the quenched-
requirement for a component or material. On the other hand, the yield and-tempered grade 42CrMoS4 (SS
construction is that it is elastically strength of the micro-alloyed grade 2244) giving a weight saving of more
stiff; in other words, bending, twisting, E470 (Ovako 280) is greater than the than 35 %. However, it is noteworthy
axial elongation or axial compression largest bending stress so this material for this particular example, that the
can only be tolerated to a limited constitutes a feasible alternative. angle of twist when plastic deformation
degree. The difference now is that the tube starts is only 10° for S355JR but it is
All steels have more or less the weighs only 4.2 kg compared with 26° for the steel with higher yield
same elastic modulus, so it is not 9.9 kg for the 50/30-tube, a weight strength. This greater elastic twisting
possible to reduce dimensions without saving of almost 60 %! must be tolerated in order that the full
a greater elastic shape change, i.e. If instead the service requirement weight saving can be enjoyed.
stiffness is reduced. But sometimes, it is that no permanent shape changes For components or constructions
is possible to decrease weight without can be allowed, i.e. plastic deformation subjected in service to variable
compromising stiffness. Consider for is not tolerated, then a weight saving loading and thereby risk for fatigue
example, a simply supported tube will always be possible by changing to failure, weight savings can almost
with dimensions 50/30 mm, length a steel with higher strength. As an always be achieved by switching to a
1 m which is subjected to a load of example, let us look at twisting (torsion) steel with higher strength/hardness.
1.5 tons at its middle. The maximum of a solid bar (see sketch). An axle in After all fatigue resistance increases
deflection is about 5 mm independent S355JR (SS2172) with diameter 50 mm with tensile strength. But, as we have
of steel grade so S355JR (SS 2172) and length 1 m can be subjected to already seen in the section dealing
is a sound economic choice. However, a twisting moment of up to approx­ with fatigue, such a change requires
if instead we change to a tube with imately 9kN.m before the outside of some prior consideration. The
dimensions 70/65 mm, with everything the axle starts to deform plastically influence of surface finish, stress
else unaltered, the deflection is still (9 kN.m corresponds to transmission raisers (e.g. changes in section etc.)
about 5 mm but it is no longer possible of a power of 100 kW at 100 rpm). and welds is far more prevalent when
to use S355JR since the stress at the However, the same power can be the strength level of the base steel is
outside of the tube would then transmitted by a 40 mm axle if the raised. Hence, if the aim is to save
 51

weight by reducing the dimensions of a more brittle than the base steel and then has sufficient toughness that the
component susceptible to fatigue, therefore cannot deform plastically part will bend rather than fracture
then one is perhaps forced to improve without cracking. It is less well when the buckling load is exceeded.
surface finish, optimise the design in documented that buckling resistance The examples given above are
relation to stress raisers and in some when long, thin parts are loaded certainly not the only ones, but serve
instances, eliminate or re-locate welds. axially is improved considerably by as an indication of what is possible by
In loading modes where the surface hardening and especially applying a little thought. Higher-
greatest stress occurs at the surface induction hardening. Since the buckling strength steels are admittedly more
of a part, for example bending or load is often well below that corres­ expensive but allow a weight reduction
twisting, surface treatments such as ponding to the yield strength of the which in certain applications may well
case hardening, induction hardening, material, an appreciable dimensional motivate the extra cost. Furthermore,
nitriding etc., which result in an reduction will be achievable if the the higher price per kilo is often
increase of strength/hardness of the buckling resistance can be increased. compensated by the fact that the
outer layer, will allow dimensions to be This possibility is of special interest for purchased weight per component is
reduced. One must, however, take into high-strength, micro-alloyed steels reduced.
account that the hardened surface is since the induction-hardened layer

Bending of tube
with free ends

Twisting (torsion)
of round bar A–>
–A’
A’
A
52

STANDARDS FOR STEEL GRADES

Below you find a table which compares Tibnor’s internal designations and other different standards so the comparisons
SS- (discontinued Swedish standards) international standards. There is given should rather be regarded as
and the new SS-EN standards with seldom exact correspondence between “the closest equivalent standard”.

CONSTRUCTIONAL STEELS
SS SS-EN 10025-2:2004 TIBNOR DIN W.Nr AISI/SAE AFNOR
1312 S235JR 1312/S235JR St 37-2 1.0116 A570 Gr.36 E 24-2
2172 S355JR S355J2 S355JR 1.0045 1518 A 50-2

MICRO-ALLOYED STEELS
SS SS-EN 10025-2:2004 TIBNOR DIN W.Nr AISI/SAE AFNOR
2142 S450J0 280/280X 20MnVS6 1.5217 20MV6
2144-01 S355J2 520M/520MW+ St 52-3 1.0045
2144 S355J2+C 550MW+ St 52-3 1.0045

CASE-HARDENING STEELS
SS SS-EN 10084 TIBNOR DIN W.Nr AISI/SAE AFNOR
2127 16MnCrS5 16MnCr5 1.7131
2506 21NiCrMo2 21NiCrMo2 1.6523 8620 15NCD2
2511 16NiCrS4 2511M/16NiCrS4 15CrNi6 1.5919 3115 16NC5
2523 17NiCrMoS6-4 17CrNiMo6 1.6587 18NCD6

QUENCHED-AND-TEMPERED STEELS
SS SS-EN 10083 TIBNOR DIN W.Nr AISI/SAE AFNOR
1672 C45E 1672/C45E 2C45 1.1191 1045 XC45
1672M C45R 1672M/C45R
2225 25CrMo4 2225/25CrMo4 25CrMo4 1.7218 4130 25CD4
2225M 25CrMoS4 2225M/25CrMoS4
2234 34CrMo4 34CrMo4 1.7220 4135 35CD4
2244 42CrMo4 2244/42CrMo4 42CrMo4 1.7225 4140 42CD4
2244M 42CrMoS4 2244M/42CrMoS4 42CrMoS4
2541 34CrNiMo6 2541M/34CrNiMo6 34CrNiMo6 1.6582 4340 35NCD6

SPRING STEELS
SS SS-EN 10083 TIBNOR DIN W.Nr AISI/SAE AFNOR
2090 56Si7 2090 55Si7 1.5026 9255 55S7
2230 51CrVS4 2230 51CrV4 1.8159 6150 50CV4

HOT-FINISHED SEAMLESS TUBES

SS SS-EN 10294 TIBNOR DIN W.Nr AISI/SAE AFNOR
2142 E470 E470 20MnVS6 1.8905 20MV6
2142 E470 280 20MnVS6 1.8905

BEARING STEELS
SS SS-EN ISO 683-17 TIBNOR DIN W.Nr AISI/SAE AFNOR
2258 100Cr6 803/2258 100Cr6 1.3505 52100 100C6
100CrMo7 824 100CrMo7 1.3537 A4853 100CD7
100CrMo7-3 825 100CrMo7-3 1.3536

FREE-MACHINING STEELS
SS SS-EN 10277-3 TIBNOR DIN W.Nr AISI/SAE AFNOR
2144-01 S355J2 520MW+
2144 S355J2+C 550MW+
1914 11SMnPb30 1914 95MnPb28 1.0718 12L14
1957+Pb-04 36SMnPb14 1957 1.0765
 53

COLOUR CODING

Constructional steels, case-hardening steels, quenched-and-tempered steels and bearing steels

OVAKO
16NiCrS4 S355J2
803,824,825
GREYISH BLUE BLACK
RED

520 M
SS 2541 C45
GREENISH
MAROON GREEN
YELLOW

OVAKO 280 E470 SS 2090

ORANGE DARK BLUE RED/GREEN

520MW+
550MW+ SS 2244 BLACK/
PINK BROWN GREENISH
YELLOW

SS 2230
COMP. AXLE SS 2225
BROWN/
WHITE OLIVE GREEN
YELLOW

Free-machining steels

SS 1914 MACH 50
BLUE SILVER

The colour coding for an SS-standard is the same as for the equivalent in SS-EN.
54

CERTIFICATION
SS-EN 10204 is the standard which specifies certification of metallic materials.
In this section, we give a short description of the contents and limitations of
the various types of inspection documents which are defined in this standard.

Declaration of compliance Inspection certificate 3.1 Inspection certificate 3.2

with order 2.1 This is a document issued by the This type of certificate is issued jointly
In this, the manufacturer certifies manufacturer which not only by the manufacturer’s inspection
that the goods supplied are in declares that the goods supplied are representative together with an
accordance with the requirements in accordance with the order but inspection representative authorised
of the order but no specific test also includes specific test results by the purchaser. These two instances
results are given. on the material actually delivered. make a mutual declaration that the
A 3.1 certificate must be validated goods supplied are in accordance
Test report 2.2 by a manufacturer’s inspection with the order and also validate
This is a declaration that the goods representative that is independent specific test results on the material
supplied are in accordance with the of any production department. actually delivered. Such so-called
order but which also includes non- third-party certification normally
specific test results from similar involves an inspector from a specified
material. company or authority either being
present during testing or actually
performing the testing stipulated by
the purchaser.

What information can be found in these different certificate types?

Test report 2.2 testing can indeed be carried out. Important to note!
This type of report will normally give The purchaser shall also specify From the above, it will be clear that
the typical analysis along with the company or authority that is to the sampling location is in many
minimum guaranteed mechanical constitute the third party. instances close to the bar surface.
properties. Unless agreed otherwise in For heavy-section bars, this means
advance, mechanical testing data that the mechanical properties at the
Inspection certificate 3.1 reported on 3.1 or 3.2 certificates relate centre can differ quite considerably
Quenched-and-tempered steels to samples taken at a standardised from the values certified. For the
Chemical analysis, yield stress, location in, for example, a bar. quenched and tempered grades
tensile stress, elongation to fracture, SS-EN 25CrMo4 and SS-EN 42CrMo4,
area reduction at fracture and impact Quenched-and-tempered steels the maximum dimension defined in
toughness. For dimensions D > 25 mm, the test the appropriate standard (SS-EN
sample is taken such that its centre is 10083) is 160 mm. This is because,
Case-hardening steels at least 12.5 mm from the bar surface. for these steels with relatively low
Chemical analysis, hardness and For D ≤ 25 mm, the centre of the test alloy content, the mechanical
Jominy-values. sample should coincide with the properties at the bar centre would for
centre of the bar. larger diameters deviate excessively
Constructional steels from those certified. The grade SS-EN
Chemical analysis, yield stress, tensile Constructional steels 34CrNiMo6, which is more highly
stress, elongation to fracture, area For dimensions D, B or T > 25 mm, alloyed, is standardised up to larger
reduction at fracture (optional) and the tensile-test sample is taken such dimensions, D=250 mm.
impact toughness. that its centre is at least one third of
the distance between the surface and
Inspection certificate 3.2 centre of the bar. If D, B or T ≤ 25 mm,
The test data to be reported in this the centre of the tensile-test sample
type of certificate are regulated by should coincide with the centre of the
the purchase order or agreement. bar. As regards the sampling location
In other words, the purchaser shall for testing of impact toughness, the
define the testing to be done and the one side of the sample should be at
manufacturer must confirm that such least 2 mm from the surface of the bar.
NOTES
56

CONTACT US

Sweden
Phone: +46 10 484 00 00
Fax: +46 10 484 00 75

Norway
Phone: +47 22 90 90 00
Fax: +47 22 90 90 70

Denmark
Phone: +45 43 23 77 00
Fax: +45 66 11 08 61

Finland
Phone: +358 20 593 09 30
Fax: +358 20 593 09 37

Estonia
Phone: +372 658 89 20
Fax: +372 658 89 30

Latvia
Phone: +371 676 774 18
Fax: +371 670 449 01

Lithuania
Phone: +370 5 232 23 14
Fax: +370 5 232 23 18
 Tibnor is the steel and metal supplier to the Nordic region.
We assure the flow of materials to industrial users in the Nordic and also the Baltic countries.
We work strategically and long-term together with both customers and suppliers
in order to develop the best material, logistic, production and
administrative solutions. We are therefore an essential link for
many interesting industrial products and projects.
www.tibnor.no/en

TIBNOR JUNE 2015