Surface Hardening of Stainless Steels

Materials and Applications Series, Volume 20

S u r f a c e H a r d enin g o f S tain l ess S tee l s

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 S u r f a c e H a r d enin g o f S tain l ess S tee l s

Contents

Surface Hardening of Stainless Steels 1 Introduction 2

First Edition 2013 2 Principle 3
(Materials and Applications Series, Volume 20) 3 Thermochemical diffusion methods 5
© Euro Inox 2013 3.1 Carburising 6
3.2 Gas nitriding 7
Publisher 3.3 Plasma (ion) nitriding and liquid nitriding 10
Euro Inox 3.4 Nitrocarburising 11
Diamant Building, Bd. A. Reyers 80 3.5 Boriding or boronising 13
1030 Brussels, Belgium 4 Applied energy methods 14
Phone: +32 2 706 82 67 4.1 Induction hardening 14
Fax: +32 2 706 82 69 5 Costs 15
E-mail: info@euro-inox.org 6 Summary 16
Internet: www.euro-inox.org 7 References 17

Author
Alenka Kosmač, Brussels (B)

Cover photos
Expanite, Hillerød (DK) (left)
Heat & Surface Treatment, Eindhoven (NL) (bottom right)
iStockphoto (top right)

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S u r f a c e H a r d enin g o f S tain l ess S tee l s

1 Introduction

Scratch resistance of Surface hardening provides surfaces for

the surface is often
different consumer products and ensures
requested for high-
visibility applications.
that stainless home appliances, household
objects, cutlery and highly exposed objects
maintain their pleasing appearance and du-
rability. It is also necessary in applications
where exceptional wear resistance com-
bined with corrosion resistance are needed.
A wide range of such applications can be
Stainless steel is widely used in applica- found in [1, 2, 3, 4, 5]:
tions in which corrosion resistance is of high • consumer goods
importance. In many end-uses, the material • home appliances
is also expected to have a hard, non-scratch • food and beverage industry
surface. When improved wear resistance is • mobile devices
required, surface engineering provides so- • industrial fluid handling
lutions. Commonly available processes are • industrial and consumer fasteners
available that improve surface hardness, • valve and pump parts
scratch and wear resistance. • medical applications
• marine applications
Properties most often expected from sur- • automotive components
face hardening [1, 2]: • axis and rotating parts
• scratch resistance
• surface hardness above 900 HV0.05
• unchanged corrosion resistance
Surface hardening can
• reduced friction coefficient be used in many differ-
• no dimensional change ent areas, from building
• minimal or no change in visual appearance and architecture to
the food and beverage
• no cracking or flaking of the hardened layer
industry. Photo: Heat
• minimal or no change in surface roughness & Surface Treatment,
• no pre-treatment Eindhoven (NL)
• no post-treatment
• enhanced lifetime and reduced downtime
and costs
• weldability

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 S u r f a c e H a r d enin g o f S tain l ess S tee l s

2 Principle

Surface hardening includes a wide variety of There are three distinctly different ap-
techniques. Most often it is used to improve proaches to the various surface-hardening
the wear resistance of parts without affect- methods [7]:
ing the softer, tough interior necessary to 1. Thermochemical diffusion methods,
resist impact occurring during operation. which modify the chemical composition
of the surface with hardening species
Wear involves the physical removal of such as carbon, nitrogen and boron. Dif-
material from a solid object. It can be fusion methods allow effective hardening
divided into three categories: abrasive, of the entire surface of a part and are gen-
adhesive and fatigue wear. erally used when a large number of parts
Abrasive wear is when two surfaces rub are to be surface hardened.
together and the harder surface grinds 2. Applied energy or thermal methods,
away the softer. It can be characterized which do not modify the chemical com-
by a rough appearance. Often, work position of the surface but rather improve
hardening of the surface can occur. properties by altering the surface struc-
Adhesive wear, like abrasive wear, is ture – that is they produce a quench-hard-
caused by loaded surfaces rubbing to- ened surface, without additional alloying
gether. With adhesive wear, high local- species. They can be used to harden the
ized temperatures are created by friction entire surface or only part of it (selective
at the tips of opposing asperities on rub- surface-hardening).
bing surfaces. These tips can deform and 3. Surface coating or surface-modification
“weld” together, due to localized tem- methods, which involve the intentional
peratures. They usually break and fall build-up of a new layer on the steel sub-
away as debris. strate.
Fatigue wear occurs whenever a surface
is subjected to repeated high-stress Various process methods for the surface
load. Wear rates are less affected by tem- hardening of steels are shown in Table 1.
perature than is corrosion [6]. These long-established techniques are
continually improved and remain among
the most widely applied ones. This publica-
tion discusses the most important surface-
hardening methods used on stainless steels
(marked in italics in the table overleaf).

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S u r f a c e H a r d enin g o f S tain l ess S tee l s

Table 1. Process methods for the surface hardening of steels [7]

Diffusion methods Coating and surface modification

Carburising Hard chromium plating
Nitriding Electroless nickel plating
Nitrocarburising Thermal spraying
Carbonitriding Weld hardfacing
Boriding or boronising Chemical vapour deposition
Thermal diffusion process Physical vapour deposition1
Applied energy methods Ion implantation
Flame hardening Laser surface processing
Induction hardening
Laser-beam hardening
Electron-beam hardening

Vickers test scheme The pyramidal diamond An indentation left in case-

indenter of a Vickers hardness hardened steel after a Vickers
tester. hardness test. The difference
in length of both diagonals and
the illumination gradient, are
both classic indications of an
out-of-level sample. This is not
Source: Wikipedia; Vickers hardness test a good indentation.
Photos: R. Tanaka (middle); Dennis M. Clarke, (right)

1
Physical vapour deposition is discussed in the Euro Inox publication Colouring Stainless Steel, Materials and Applications
Series, Volume 16, http://www.euro-inox.org/pdf/map/ColouringStainlessSteel_EN.pdf

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 S u r f a c e H a r d enin g o f S tain l ess S tee l s

3 Thermochemical diffusion methods

Traditional thermochemical treatment on ties and tribological properties [8]. Some

stainless steel is associated with a loss of recently developed processes, in contrast,
corrosion resistance as nitrogen and car- do not diminish the corrosion resistance of
bon react with chromium to form carbides/ stainless steels.
nitrides, thus withdrawing chromium from
solid solution. In the case of stainless
steels, hardening by thermochemical treat-
ment has been considered bad practice or
a compromise between corrosion proper-

Table 2. Typical characteristics of thermochemical diffusion treatments for stainless steels [7, 8]

Process Typical case Case

Process Name of case temperature depth hardness Process characteristics
°C µm HV

Nitriding/Carburising/Nitrocarburising
Hardest cases from nitriding
Diffused nitrogen and/
Gas 420−600 10−200 750−1600 steels, low distortion, bulk
or carbon compounds
batches possible
High equipment cost, close
Diffused nitrogen and/
Ion 380−600 10−200 750−1600 case control, good controlla-
or carbon compounds
bility of layer formation
Other
Produces a hard diffusion
Boriding or Diffused boron, boron 1500 to over
700−1000 10−50 layer, high process tempera-
boronising compounds 2800
ture can cause distortion

Photo: Heat & Surface

Treatment, Eindhoven (NL)

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S u r f a c e H a r d enin g o f S tain l ess S tee l s

3.1 Carburising Chromium content [%]

30
Grain boundary M23C6
Stainless steels can be carburised to im-
25
prove surface hardness and resistance to
galling. During the carburising process, the
20
carbon atoms diffuse through the surface
and have the affinity to react with the chro-
mium present in stainless steels. They can 15

form chromium carbide (Cr23C6). This pro-

cess is known as sensitisation. Some chro- 10 Boundary of passivity
mium could therefore be lost and eventually
corrosion resistance reduced. Conventional 5
carburising has mostly been replaced by ni-
tridation, which does not incur problems of 0
sensitisation [10].
about 1000–1200 HV0.05. High compressive
Sensitisation occurs when the material is stresses are formed on the surface, due to in-
heated to the 600−800 °C temperature terstitial solution of carbon atoms. No loss of
range. At these temperatures, chromium corrosion resistance is reported in austenitic
and carbon diffuse to the grain bounda- stainless steel 1.4401/1.4404 (316/316L). The
ries to form type Cr23C6 chromium car- process has also been successfully applied to
bides. As the carbides form, chromium duplex stainless steel grades. Sharp edges,
is depleted from the base material but the inside of bores and gaps present no limi-
is considerably increased at the grain tation to the process [4, 11, 12, 13].
boundaries. In areas with a low chromi-
um level, the chromium content is below
that of the bulk alloy, making these areas
susceptible to corrosion.

Some recently developed techniques have a

hardening effect without affecting the origi-
nal corrosion resistance. No coating is ap-
plied to the surface, but a carbon-rich (up
to 2–3 % weight rate) diffusion zone is pro-
duced from the surface inwards, with excel-
lent toughness and no risk of delamination
or peeling. It is low-temperature carburising,
at a diffusion temperature below 450 °C. The
process increases the surface hardness of
most austenitic stainless steels to a level of

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 S u r f a c e H a r d enin g o f S tain l ess S tee l s

since they form nitrides that are stable at ni-

triding temperatures. Because of their chro-
mium content, all stainless steels can be
nitrided to some degree [9]. However, the
high chromium content of some stainless
steels makes them more difficult to nitride.
This is because chromium forms a passive
layer on the stainless steel surface, which
has to be removed before nitriding. Once
Uniform hardening of sharp edges can be achieved
the passive film is broken down (by dry hon-
with a carburised layer. Photo: Bodycote Hardiff,
Apeldoorn (NL) ing, wet blasting, pickling, chemical reduc-
tion in a reducing atmosphere, submersion
in molten salts or one of several proprietary
3.2 Gas nitriding processes), nitriding is effective. The posi-
tive side of this is usually a high surface-
Gas nitriding is a case-hardening process hardness value. Other alloying elements,
whereby nitrogen is introduced into the such as nickel, copper and manganese,
surface by holding the steel at a suitable have little if any effect on nitriding charac-
temperature in contact with a nitrogenous teristics [7]. Nitridable stainless steels are:
gas, usually ammonia. Quenching is not re-
quired for the production of hard case. The • Martensitic stainless steels. The hard-
nitriding temperature for most steels is be- enable martensitic stainless steels are
tween 500 °C and 550 °C. Although nitrid- capable of providing high core strength
ing adversely affects corrosion resistance, to support the nitrided case. Hardening,
it increases surface hardness and provides followed by tempering at a temperature
a lower coefficient of friction, thus improv- at least 15 °C higher than the nitriding
ing abrasion resistance. Before being gas temperature, should precede the nitrid-
nitrided, austenitic stainless steels and fer- ing operation.
ritic steels should be annealed and relieved
of machining stresses. Normal annealing • Austenitic stainless steels. Austenitic
treatments generally employed to obtain stainless steels are the most difficult to
maximum corrosion resistance are usually nitride. Nevertheless most can be suc-
adequate. Martensitic steels should be in cessfully nitrided [9]. If nitrided, parts
the quenched-and-tempered condition2 [9]. must be in the annealed condition, to
prevent flaking or blistering of the nitrid-
Alloying elements such as chromium and ed case. Stabilised or low-carbon grades
molybdenum are beneficial in nitriding, are recommended for nitriding, for the

2
More information on specific heat treatment conditions of different stainless steels can be found in the Euro Inox publica-
tion Stainless Steels: Tables of Fabrication Parameters, Materials and Applications Series, Volume 17,
http://www.euro-inox.org/pdf/map/Tables_Fabrication_Parameters_EN.pdf

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S u r f a c e H a r d enin g o f S tain l ess S tee l s

obvious reason that the nitriding tem- • Ferritic stainless steels. Ferritic stainless
perature of approximately 540 °C is in steel grades are non-hardenable by con-
the sensitising range. The nitrided case ventional heat treatment methods. How-
that can be achieved on austenitic ever, the grades on which surface hard-
grades is very thin and seldom above ening can be successfully applied include
0.125 mm. In addition, it seriously im- 1.4016 (430) and 1.4749 (446).
pairs resistance to corrosion in most me-
dia. Nitriding austenitic stainless steels • Precipitation-hardening stainless steels.
is therefore only carried out for highly Steel grades such as 1.4542, 1.4548 (17-4
specialised applications – for example, PH), 1.4564, 1.4568 (17-7 PH), 1.4545 (15-
when the material must be non-magnetic 5 PH), 1.4980 (A-286) can be successfully
and still have an abrasion-resistant sur- nitrided.
face [14].

Distance below surface, 0.0001 in. Distance below surface, 0.0001 in.
0 2 4 6 8 0 2 4 6 8
1600 1600

(302) 1.4541 (321)

1200 5 suppliers 1200 5 suppliers
Hardness, HK

Hardness, HK

800 800

400 400

0 0

1600 1600

1.4016 (430) 1.4749 (446)

1200 5 suppliers 1200 5 heats
Hardness, HK

Hardness, HK

800 800

400 400

0 0
0 50 100 150 200 250 0 50 100 150 200 250
Distance below surface, µm Distance below surface, µm

Figure 1. Hardness related to case depth for four stainless steels that were annealed prior to nitriding. The anneal-
ing temperature was 1065 °C for steel grades 302 and 1.4541 (321), 980 °C for steel grade 1.4016 (430) and 900 °C
for steel grade 1.4749 (446). Hardness is measured in Knoop values [9].

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 S u r f a c e H a r d enin g o f S tain l ess S tee l s

Table 3. Surface hardness ranges and case depth for some corrosion-resistant and acid-resistant steels [7]

Steel designation Nitride hardness

Hardness
Approximate depth
EN Number EN Name HV
AISI/ASTM mm

1.4028 X30Cr13 420 950−1200 0.2 max.

1.4104 X14CrMoS17 - 950−1200 0.2 max.

1.4112 X90CrMoV18 440 B 950−1200 0.2 max.

1.4117 X38CrMoV15 - 950−1200 0.2 max.

1.4301 X5CrNi18-10 304 950−1600 0.2 max.

1.4305 X10CrNiS18-9 303 950−1600 0.2 max.

1.4401 X5CrNiMo17-12-2 316 950−1600 0.2 max.

1.4535 X90CrCoMoV17 - 950−1600 0.2 max.

300
Austenitic (300 series)

525 °C
Depth of case, 0.001 in.

200 8
Depth of case, µm

550 °C

Martensitic (400 series)

100 4
525 °C

Stainless steel 550 °C

20–35% dissociation
0 0
0 10 20 30 40 50

Duration of nitriding, h

Figure 2. Comparison of the nitriding characteristics of austenitic (300 series) and martensitic (400 series) stain-
less steels, single-stage nitride at 525 °C and 550 °C [9]

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S u r f a c e H a r d enin g o f S tain l ess S tee l s

3.3 Plasma (ion) nitriding and liquid in etched cross-sections [9]. This process is
nitriding particularly suitable for stainless steels.

Plasma (or ion) nitriding is a method of sur- Liquid nitriding is performed in a molten,
face hardening that uses glow-discharge nitrogen-bearing, fused-salt bath contain-
technology to introduce elemental nitro- ing either cyanides or cyanates. Cyanide-
gen to the surface of a metal part, for sub- free liquid nitriding salt compositions have
sequent diffusion into the material. In a also been introduced. However, in the active
vacuum, high-voltage electrical energy is bath, a small amount of cyanide, generally
used to form plasma, through which nitro- up to 5 %, is produced as part of the reac-
gen ions are accelerated to impinge on the tion. This is a relatively low concentration
workpiece. This ion bombardment heats and these compositions have gained wide-
the workpiece, cleans the surface and pro- spread acceptance within the heat-treating
vides active nitrogen. It actually avoids the industry because they contribute substan-
need to remove the passive layer, as this is tially to the alleviation of a potential source
removed by sputtering prior to the nitriding of pollution. Liquid nitriding treatments re-
phase. Ion nitriding provides better con- sult in some loss of corrosion resistance be-
trol of case chemistry and uniformity and cause the formation of nitrides and carbides
has other advantages, such as lower part depletes adjacent matrix areas. Corrosion
distortion than conventional gas nitriding. data based on weight loss indicates that in
For most ferrous alloys, the diffusion zone some cases liquid-nitrided stainless steels
formed by nitriding cannot be seen in a met- face some loss of corrosion resistance. How-
In stainless steel cutlery, allographic image, because the coherent ever, these materials remain largely superior
surface hardening is precipitates are generally not large enough to untreated carbon and low-alloy steels [9].
available as an option to to resolve. In stainless steels, however, the
improve wear resistance.
chromium level is high enough for exten-
Photo: WMF, Geislingen
(D) sive nitride formation, which can be seen

10
 S u r f a c e H a r d enin g o f S tain l ess S tee l s

3.4 Nitrocarburising Cross-section of low-

temperature nitrocarbur-
ised precipitation-hard-
Some gas-based and plasma-based pro- ening stainless steel.
cesses dissolve carbon and/or nitrogen at- Photo: Bodycote Hardiff,
oms in the surface region of the material. Apeldoorn (NL)

Dissolution of carbon and nitrogen atoms is

possible due to their smaller size compared
to the alloy metal atoms. The surface hard-
ening results not in a coating but in a sur-
face zone with a high concentration of car- The outer zone is richer in nitrogen and the
bon and/or nitrogen [1, 2, 3]. Large amounts inner one in carbon. The thickness of each
of atomic nitrogen and/or carbon dissolve zone can be influenced by gas composition
in stainless steel at temperatures below – i.e. by modifying the nitrogen and carbon
approximately 450−550 °C, expanding the content in the gas. The combinations of
original microstructure. The maximum lattice thickness of each zone allow different ma-
expansion can reach nearly 40 % (by terial properties to be achieved. Gas-based
volume) for nitrogen. The thickness of the and plasma-based processes enable nitrid-
zone is approximately 20−40 μm. Expanded ing, carburising or nitrocarburising to be
austenite surfaces are four to eight times employed, depending on requirements.
harder than those of the base material.
Along with the increase in hardness and
wear resistance, corrosion resistance is fully
maintained [15, 16].
Cross section of nitro-
carburised stainless
steel (left), depth profile
(right). Photo: Expanite,
Hillerød (DK)

11
S u r f a c e H a r d enin g o f S tain l ess S tee l s

Surface hardening can

be used also on the ob-
jects like watch cases.
Photo: Askania, Berlin (D)

It is also possible to nitrocarburise marten- phase and tends to decompose upon pro-
sitic stainless steels. Grade 1.4057 (431), longed thermal exposure [16]. Nitrocarburis-
treated for 75 minutes, yielded a case ap- ing should not be confused with carbonitrid-
proximately 20 μm thick with a surface hard- ing, which is a higher temperature process
ness higher than 1800 HV. Depending on used for low-carbon steels.
other process parameters, the hardened
zone can be tailored – i.e. it is possible to
obtain expanded austenite, however, the
principle can also be applied to martensi-
tic and precipitation hardening grades. As a
consequence of the very high surface hard-
ness, the surface is virtually scratchproof
[15]. Expanded austenite is a metastable

Nitrocarburising can
also be successfully
applied in small bores
and even in very small
cavities. Photos: Body-
cote Hardiff, Apeldoorn
(NL) left and Expanite,
Hillerød (DK) right

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 S u r f a c e H a r d enin g o f S tain l ess S tee l s

3.5 Boriding or boronising cient, boronised steel parts can be vacuum

hardened afterwards to achieve the desired
Boriding or boronising is a thermochemical mechanical properties of the base mate-
process in which boron atoms are diffused rial. The process temperature for boronis-
into the surface of a workpiece to form com- ing depends on the material grade and lies
plex borides with the base metal. It is a diffu- between 700 °C and 1000 °C. To minimize
sion-controlled process. In addition to nickel, distortion, a stress-relieving treatment can
titanium, cobalt alloys and cemented car- be carried out after machining and prior to
bides, nearly any ferrous material can be bo- boronising. Other heat treatments before
ronised. It should be noted that the diffusion boronising, such as quench-hardening,
rate slows down with higher-alloyed steels. should not be performed, since the boron-
ising process removes the results of a pre-
Because of their high hardness, boronised heat treatment [5, 17]. Where dimensional
steels are extremely resistant to abrasion accuracy (exactness of fit) is paramount,
and their service life can be significantly the workpiece must be undersized during
increased. The process uses boronising manufacturing, since the boride layer will
agents such as powders, granulates of add 20−30 % of its thickness to the size of
various grain sizes and pastes, which are the part [5].
commercially available. The diffusion lay-
er thickness is in a range of 20−200 µm
depth, depending on the requirements of
the parts. In the case of austenitic stain-
less steels, layers are much thinner. Due
to the similar thermal expansion coeffi-

Table 4. Proven applications for boronised steels [7]

Steel designation
Approximate Applications
EN Number EN Name
AISI/ASTM

- - 302 Screw cases, bushes

Perforated or slotted-hole screens,

1.4401 X5CrNiMo17-12-2 316 parts for the textile and rubber
industries

1.4006 X12Cr13 410 Valve components, fittings

Valve components, plunger rods, fit-

1.4031 X39Cr13 420
tings, guides, parts for chemical plants

13
S u r f a c e H a r d enin g o f S tain l ess S tee l s

4 Applied energy methods

Surface hardening by applied energy in- to a temperature within or above the trans-
cludes conventional thermal treatments formation range. The process is followed by
such as induction hardening and flame immediate quenching. It is an electromag-
hardening and high-energy treatments, netic process, using a copper inductor coil
such as laser or electron beams. All these fed a current at a specific frequency and
methods can be classified as thermal treat- power level.
ments without chemistry changes. The
modification of the surface is done by aus- Induction hardening is favoured for compo-
tenitising the steel followed by fast cooling. nents subjected to heavy loading, especial-
The entire surface of the application can be ly parts that experience torsional loading
treated, or only a part of it. When the heat- and surfaces that experience impact forces.
ing is only done locally, the treatment is Typical applications of induction-hardening
called selective surface hardening [7]. include gears, shafts, spindles – mostly
symmetrical parts [18].
4.1 Induction hardening

The induction hardening process is used

to increase wear resistance, surface hard-
ness and fatigue life through the creation
of a hardened surface layer, while main-
taining an unaffected core microstructure.
The parts to be heat-treated are placed in-
side a copper coil then heated above their
transformation temperature by applying an
alternating current to the coil. The alternat-
ing current in the coil induces an alternating
magnetic field within the workpiece, which
causes the outer surface of the part to heat

Table 5. Induction-hardenable stainless steels and their approximate induction austenitising temperatures

Steel designation Carbon, Austenitising

Approximate in mass temperature
EN Number EN Name % °C
AISI/ASTM

1.4005 X12CrS13 416 < 0.15 1065

1.4021 X20Cr13
1.4028 X30Cr13
420 > 0.15 1065
1.4031 X39Cr13
1.4034 X46Cr13

1.4125 X105CrMo17 440C 0.95−1.20 1065

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 S u r f a c e H a r d enin g o f S tain l ess S tee l s

5 Costs

Cost must be weighed against the perfor- • the time required for a given surface
mance required from the surface-treatment treatment
system. A low-cost surface treatment that • fixturing, masking and inspection costs
fails to perform its function is a wasted ex- • final finishing costs
pense. Unfortunately, it is nearly impossible • material costs
to give absolute comparative costs for dif- • energy costs
ferent surface-engineering options. Prob- • labour costs
ably the most important factor concerning • environment-related costs (for example,
the cost of producing a wear-resistant sur- disposal of spent solutions)
face on a part is part quantity. Treating many • expected service life
parts usually allows economies in treat-
ment and finishing. Another consideration Because of these various factors, it is diffi-
when assessing surface-treatment costs is cult to compare costs with a high degree of
part size. There are critical sizes for each accuracy [7].
surface-treatment process above which the
cost of obtaining the treatment may be high.
Other factors to be considered are:

Surface hardening can

also be applied to com-
plex parts with recess
areas. Photo: Heat &
Surface Treatment,
Eindhoven (NL)

15
S u r f a c e H a r d enin g o f S tain l ess S tee l s

6 Summary

There are several processes by which the It is common belief that surface-hardening
surface of stainless steels can be success- techniques diminish the original corrosion
fully hardened. These processes not only resistance of stainless steels. The latest
improve the hardness of the surface but also techniques developed show that this is no
increase the material’s scratch and wear longer the case and that corrosion resist-
resistance. Such surfaces are also used in ance can be retained. Services are available
applications where galling is an issue or from specialised companies, some of them
cutting edges are required (for example, in offer also plug-and-play technologies.
medical equipment). All processes showed
in this publication are based on altering the
original surface without an additional layer
being applied, which might peel or wear off.

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 S u r f a c e H a r d enin g o f S tain l ess S tee l s

7 References

[1] Expanite – Surface Hardening of Stainless Steel, available from http://www.expanite.com/

[2] Specialty Stainless Steel Processes (S3P) Benefits available from http://www.body-
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[4] Formosa, D., Hunger R., Spiteri, A., Dong, H., Sinagra, E., & Buhagiar, J. (2012) Corro-
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[5] Hunger H.-J., Wear Protection by Boronizing, available from http://www.bortec.de/
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national 2002
[8] Christiansen, T.L., Somers, M.A.J., Characterisation of Low Temperature Surface Hard-
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[10] Kumar, T., Jambulingam, P., Gopal, M., Rajadurai, A. Surface Hardening of AISI 304,
316, 304L and 316L SS Using Cyanide Free Salt Bath Nitriding Process, ISRS, 2004
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brochures/147-302_body_kolst_rd_gb_finr.pdf
[12] Faccoli, M., Cornacchia, G., Roberti, R., Bordiga, V., Effect of Kolsterising Treatment on
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Science and Market, 2011
[13] Van Der Jagt, R. H., Kolsterising – surface hardening of austenitic and duplex stainless
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[14] Heat Treater’s Guide, Practices and Procedures for Irons and Steels, edited by H.
Chandler, ASM International, 1995
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papers/DMS2010_Towards.pdf
[16] Christiansen, T.L., Hummelshøj, T.S., Somers, M.A.J, Low Temperature Thermochemical
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less Steel Conference Science and Market, 2011
[17 Hunger, H. J.; Trute, G.; Löbig, G., Rathjen, D.: Plasmaaktiviertes Gasborieren mit
Bortrifluorid. HTM 52 (1997) 1, pp. 39-45
[18] Induction Hardening, Bodycote, available from http://www.bodycote.com/services/
heat-treatment/harden-and-temper/induction-hardening.aspx

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 ISBN 978-2-87997-387-6

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