Working and machining

of austenitic special stainless

steelsand nickel alloys
 3

Authors:

Hardy Decking
George Karl Grossmann

Krupp VDM GmbH

VDM Metals GmbH
Technical Marketing
Plettenberger Str. 2
58791 Werdohl

Index

4 Introduction

6 Forming
Hot working
Cold working

9 Thermal Treatment

10 Abrasive Treatment

10 Pickling

11 Machining
Turning
Milling
Drilling
Countersinking and counterboring
Tapping

15 Acknowledgements
4

Introduction Materials which by virtue of their chemical

This brochure discusses, with the exception of composition and the manufacturing process are
joining methods, the most important fabrication resistant to corrosion and/or high temperatures
processes employed in the manufacture of are naturally required to exhibit these properties
process equipment and piping and their special also in the finished component. That means,
characteristics for working of high-alloyed they should correspond to the as-delivered
austenitic stainless steels and nickelalloys. condition of the respective mill product such as
An overview of the materials discussed in these sheet and plate, rod and bar as well as tube and
guidelines is given in Tables 1, 2 and 3. pipe.

Material Designation Typical Analysis in wt.-%

CRONIFER® Alloy UNS W.-Nr. Ni Cr Mo Fe Others

1925 hMo 926 N 08926 1.4529 25 21 6.5 Balance Cu 0.9; N 0.19

NICROFER® Alloy UNS W.-Nr. Ni Cr Mo Fe Others

3033 33 R 20033 1.4591 31 33 1.6 Balance Cu 0.6; N 0.4

3127 LC 28 N 08028 1.4563 31 27 3.5 Balance Cu 1.3
3127 hMo 31 N 08031 1.4562 31 27 6.5 Balance Cu 1.3; N 0.2
3620 Cb 20 N 08020 2.4660 38 20 2.4 Balance Cu 3.4; Cb 0.2
4221 825 N 08825 2.4858 39 23 3.2 Balance Cu 2.2; Ti 0.8
4823 hMo G-3 N 06985 2.4619 48 23 7 19 Cu 2; Cb 0.3
6020 hMo 625 N 06625 2.4856 63 22 9 2 Cb 3.4
6616 hMo C-4 N 06455 2.4610 66 16 16 Ti 0.3
5716 hMoW C-276 N 10276 2.4819 57 16 16 6 W 3.5; V 0.2
5923 hMo 59 N 06059 2.4605 59 23 16

Table 1 – Corrosion-resistant Cr-Ni stainless steels and Ni-Cr-Mo-(Fe) alloys

Table 1 – Designation
Material Corrosion-resistant Cr-Ni stainless steels and Ni-Cr-Mo-FeTypical
alloys Analysis in wt.-%

VDM Designation Alloy UNS W.-Nr. Ni Cr Fe Cu Mo Others

VDM Ni 99.2 200 N 02200 2.4066 99.2
VDM LC-Nickel 99.2 201 N 02201 2.4068 99.2
Nicorros® 400 N 04400 2.4360 64 1.8 32 Mn 1
Nicorros® Al K-500 N 05500 2.4375 64 1.0 30 Al 2.8; Mn 0.6; Ti 0.5
Cunifer 30
®
CuNi 70/30 C 71500 2.0882 31 0.6 67 Mn 0.7
Cunifer 10
®
CuNi 90/10 C 70600 2.0872 10 1.6 87 Mn 0.8
Nimofer® 6928 B-2 N 10665 2.4617 69 0.8 1.7 28

Table 2 – Nickel, Ni-Cu, Cu-Ni, and Ni-Mo alloys

 5

The alloying constituents of the materials listed High-alloyed austenitic stainless steels and
in these tables exhibit mechanical properties nickelalloys can readily be worked and
which are generally markedly higher than that of machined by all conventional processes. How-
standard Cr-Ni stainless steels, e.g., AISI 316 ever, extremely exacting demands are made on
(UNS S31600 – German material no. 1.4571). tools and fixtures. The working processes are
This is true both at room temperature and at nowadays easily controllable, but they are often
elevated temperatures at which hot working is more cost-intensive than in the case with
carried out. conventional structural steels, and this should
appropriately be taken into account in cost
calculations.

Material Designation Typical Analysis in wt.-%

NICROFER® Alloy UNS W.-Nr. Ni Cr Mo Fe Others

1.4876 Si 0.4; Al 0.3;

3220 H 800 H N 08810
31 20 Balance
1.4958 Ti 0.3
Si 0.4; Al 0.4;
3220 HP 800 HP N 08811 1.4959 31 20 Balance
Ti 0.4
3718 (330) (N 08330) 1.4864 36 16 Balance Si 1.5
Si 2.7;
45 TM 45 TM N 06045 2.4889 45 28 24
R.E. 0.08
W 3; Co 3;
4626 MoW 333 N 06333 2.4608 46 25 3 Balance
Mn 1.6
4722 Co X N 06002 2.4665 Balance 22 9 18 Co 1.5; W 0.6
Co 12; Al 1;
5520 Co 617 N 06617 2.4663 54 22 9 1
Ti 0.4
6023 H 601 H N 06601 2.4851 60 23 14 Al 1.4
6025 HT 602 CA N 06025 2.4633 60 25 9 Al 2.1; Y 0.1
7216 H 600 H N 06600 2.4816 73 16 9
Table 3 – High-temperature and heat-resistant nickelalloys
6

Forming Table 4 shows, by way of example, the hot-

In the manufacture of vessels and process working and thermal-treatment temperatures for
equipment, hot and cold working is an indispens- a number of special stainless steels and nickel-
able part of fabrication. Hot working is generally alloys.
carried out at temperatures above or near the
recrystallization temperature, while cold working During hot working, care should be taken that
is used when the forming process is carried out deformation proceeds as uniformly as possible
at room temperature or at well below the so as to prevent the formation of an inhomoge-
recrystallization temperature. During hot working neous grain structure. In addition, for low
the resistance to deformation is much lower than amounts of deformation (≤ 30 % approx.), the
during cold working when materials work harden forming temperature should be as close as
which increases the resistance to deformation. possible to the lower limit in order to prevent a
duplex microstructure of coarse and fine-grained
Hot working areas. For higher amounts of deformation (> 30 %
Hot working is carried out in a temperature range approx.), the higher temperatures might
between the recrystallization temperature and the appropriately be applied.
solution-annealing temperature. As a result, the
resistance to deformation is greatly reduced and After every hot-working operation, a thermal
the forces required to work the material are treatment should be carried out in accordance
correspondingly lower. with the mill product manufacturer's recommen-
dation. Details with regard to heat control are
If, as the temperature falls, the forces required described under Thermal Treatment. Applicable
for forming are no longer adequate due to the thermal-treatment temperatures are listed in the
increasing resistance to deformation, hot respective material data sheets available from
working should be terminated and the workpiece Krupp VDM GmbH.
reheated or rapidly cooled to below approxi-
mately 100 °C (212 °F).

VDM designation Alloy UNS W.-Nr. Hot-working Solution Soft-annealing

temperature, heat-treatment temperature,
temperature,
°C °C °C

Cronifer® 1925 hMo 926 N 08926 1.4529 1200 - 900 1150 - 1180 -
Nicrofer 3033
®
33 R 20033 1.4591 1200 - 1000 1100 - 1150 -
Nicrofer 3127 hMo
®
31 N 08031 1.4562 1200 - 1050 1150 - 1180 -
Nicrofer® 5716 hMoW C-276 N 10276 2.4819 1200 - 950 1100 - 1160 -
Nicrofer 5923 hMo
®
59 N 06059 2.4605 1180 - 950 1100 - 1180 -
Nircrofer 6020 hMo
®
625 N 06625 2.4856 1150 - 900 - 950 - 1050
Nicrofer 3220 H
®
800 H N 08810 1.4876 1200 - 900 1150 -
Nicrofer® 45 TM 45 TM N 06045 2.4889 1180 - 900 1160 - 1200 -
Nicrofer 4626 MoW
®
333 N 06333 2.4608 1180 - 950 1150 - 1180 -
Nicrofer 6023 (H)
®
601 (H) N 06601 2.4851 1200 - 900 (1100 - 1180) 920 - 980
Nicrofer® 6025 HT 602 CA N 06025 2.4633 1200 - 900 1180 - 1220 -
Nicrofer® 7216 (H) 600 (H) N 06600 2.4816 1200 - 900 (1080 - 1150) 920 - 1000

Table 4 – Hot-working and thermal-treatment temperature ranges for selected special stainless steels and nickelalloys
 7

Cold working bending a sheet, which approximates uniaxial

Among the processes of cold working, only the stress conditions, can be determined. According
ones that are most important in manufacturing of to the given formula, a bending radius (r = inner
process equipment are considered here, i.e., radius) of 3x the sheet thickness results in a cold
bending - folding - rounding. deformation of approximately 14 %.

Austenitic stainless steels and nickel alloys Thus a bending radius of 3x the sheet thickness
in the thermally treated condition can be readily generally allows the component to be put into
cold worked. The specific material properties, service without a subsequent thermal treatment,
such as the yield strength and the rate of work as described below.
hardening resulting in a decrease in elongation
should, however, be taken into account. Cold working alters the mechanical properties of
metallic materials, as exemplified in Figure 2 with
Figure 1 shows how the degree of cold deforma- reference to stainless steel AISI 316 and nickel-
tion during the relatively simple operation of alloy Nicrofer 6020 hMo - alloy 625. As
typically seen in this figure, stainless steels and
nickelalloys are prone to appreciable
work hardening accompanied by a noticeable
decrease in the elongation which quickly results
in necking with subsequent fracture in tensile
testing.

German rules for pressure vessel constructions

therefore stipulate that in the case of austenitic
stainless steels cold working with 15 % deforma-
tion or more must as a rule be followed by a
thermal treatment (see AD-Merkblatt HP 7/3).

Conditions under which a thermal treatment is

not required after such cold working, e.g., after
forming of dished heads, are also specified in
this AD-Merkblatt.

Some materials, especially those containing Mo,

Fig. 1 – Calculation of the degree of cold deformation in bending
are prone to precipitation of intermetallic phases,
if, following extensive cold working, welding is
carried out in the area of deformation. As a
result, these areas may become sensitized, i.e.,
1600 their corrosion resistance may be impaired.
Typical tensile and yield strength, N/mm2

Nicrofer 6020 hMo - alloy 625

1400 Rp0.2
Rm Rm For most Krupp VDM materials cold working, up
Typical elongation, %

1200 60 to 15 % deformation, is permitted without

subsequent thermal treatment. In individual
1000 50
cases, though, depending on the material and
800 Rp0.2 AISI 316 40 the proposed application, a thermal treatment
may be necessary, even if the amount of cold
600 30 deformation is less than 15 %. This may be
400 20 the case when solution heat-treated high-
A5 temperature alloys are used. In other cases,
200 10 higher amounts of deformation may be permitted
0 0 without a thermal treatment, especially if no
0 10 20 30 40 50 60 70 welding is carried out in the area of deformation.
Cold deformation, %
As thermal treatment with the necessary follow-
Fig. 2 – Effect of cold deformation on mechanical properties up operations such as pickling and straightening
8

is very cost-intensive, it is advisable initially, at Forming of austenitic chrome-nickel stainless

the design stage, to provide, for example, for the steels and nickelalloys is often carried out
largest possible bending radii to be employed with tools, fixtures and machines that are used to
and to enter into discussions with the fabricator, also form mild steel. Extraneous ferrite particles
the enduser and material supplier regarding the on the surface of these tools resulting from
proposed design and fabrication details at an processing mild steel may in the presence of
early stage. This is especially true for critical moisture cause corrosive attack during later
applications. service. Under such conditions ferrite particles
can destroy the component's passive layer,
Cold working with 15 % deformation typically which in turn leads locally to a decrease in the
results in an increase of the 0.2 % yield strength corrosion resistance and eventually to corrosion.
to double the original value. Some high-alloyed Care should therefore be taken that all tools and
special stainless steels and nickelalloys equipment used during mild steel fabrication are
exhibit relatively high strength values even in always thoroughly cleaned so that no loose
the as-delivered condition; this significantly particles of mild steel are carried onto the
increases the force required to form these surface of high-alloyed workpieces.
materials, as schematically indicated in Figure 3.
Surfaces of finished components, which will be
Therefore, bending rollers and folding presses exposed to moisture or corrosive media during
may not be able to apply sufficient pressing or actual service should therefore be checked to
plunging force to obtain the desired final shape insure that no ferrite particles remain on the
of the component. In order to overcome this, the surface. This can be done, for example, by the
workpiece may be preheated to within a tempe- 'Ferroxyl Test for Free Iron' as described in ASTM
rature range at which the strength of the material specification A380. If ferrite particles are found
falls below the value at room temperature there- to be still present the finished component may
by greatly reducing the resistance to forming. have to be submitted to a further cleaning
operation, such as pickling followed by passi-
vation, before it can be delivered and put into
service.

Factor 1.0 1.5 2.0

Material UNS Alloy Strength

min Rm, N/mm2

Boiler plate H II 420

NIROSTA 4571 S 31600 316 520

Cronifer® 1925 LC N 08904 904 L 520

Nicrofer® 45 TM N 06045 45 TM 620

Cronifer® 1925 hMo N 08926 926 650

Nicrofer 3127 hMo
®
N 08031 31 650
Nicrofer 6025 HT
®
N 06025 602 CA 675

Nicrofer® 5923 hMo N 06059 59 690

Nicrofer® 5520 Co N 06617 617 750

Nimofer 6928
®
N 10665 B-2 760
Nicrofer 6020 hMo
®
N 06625 625 830

Fig. 3 – Comparison of forces required for cold working of various alloys

 9

Thermal Treatment from contamination, gas-fired furnaces are

Hot and/or cold working carried out in the acceptable if contaminants are kept at low levels.
fabricator's workshop alters the mechanical
properties and the corrosion behaviour associa- The furnace atmosphere should be neutral to
ted with the material in the as-delivered conditi- slightly oxidizing and must not fluctuate between
on. These properties can only be re-established oxidizing and reducing. Direct flame impinge-
by means of specific, controlled thermal treat- ment on the metal must be avoided.
ments. The thermal treatment causes the micro-
structure to form anew, generally through Generally recommended thermal treatment
recrystallization, and thereby eliminates the temperatures are stated in the relevant material
changes in the material's properties, which were data sheets. For selected special stainless steels
brought about by the forming operation. Thermal and nickel alloys they are summarized in Table 4.
treatments, though, are expensive and often
cannot easily be performed on a component. Workpieces made from materials with a high
alloying content of molybdenum should be
After hot working, the component should under- heated up rapidly. Such materials include the
go a thermal treatment. After cold working, 6%-Mo stainless steels Cronifer 1925 hMo -
a thermal treatment may not be necessary. alloy 926 and Nicrofer 3127 hMo – alloy 31, and
The question of whether a finished component the nickelalloys Nicrofer 6020 hMo – alloy
should be thermally-treated or not depends, for 625, Nicrofer 6616 hMo – alloy C-4, Nicrofer
example, on the amount of cold deformation 5716 hMoW – alloy C-276 and Nicrofer 5923 hMo
performed as discussed under Cold working and – alloy 59. For heating, they should therefore
should be agreed upon with the client in each be placed in a furnace, which has already been
specific case, unless applicable codes and speci- heated up to the desired temperature. After the
fications make a thermal treatment mandatory. workpiece has reached the desired temperature,
holding times according to Table 5 are generally
Prior to any thermal treatment, contaminants recommended and given as a guide.
such as grease, oil, marking paints and similar
substances must be removed from the surface of Cooling of high-molybdenum austenitic stainless
the workpiece usually with chlorine-free solvents steels and nickelalloys should be carried
such as acetone or isopropanol. Trichlorethylene out rapidly so as to prevent precipitation of unde-
(TRI), perchlorethylene (PER) and carbon tetra- sirable phases. Delayed cooling, e.g. in the fur-
chloride (TETRA) must, however, not be used. nace, should thus be avoided at all costs, as this
Among other things, these contaminants may leads to formation of precipitates, chiefly along
also contain sulfur, phosphorus and low-melting and close to grain boundaries. Such precipitates
point metals, which with nickel may form low- usually have an adverse effect both on the corro-
melting phases, which in turn may have a delete- sion resistance and the toughness properties of
rious effect on the material during service. the material.
Fuels must therefore be as low in sulfur as possi-
ble. Natural gas should contain less than 0.1 Satisfactory results are obtained with a cooling
wt.-% sulfur. Fuel oil with a sulfur content not rate of ≥ 150 °C/min. (300 °F/min.) from the
exceeding 0.5 wt.-% is considered suitable. material-specific thermal treatment temperature
down to below approx. 500 °C (932 °F).
Though electric furnaces are preferred due to
their close control of temperature and freedom

Workpiece thickness Holding time

≤ 10 mm 3 min./mm thickness
> 10 mm to ≤ 20 mm 30 min. + 2 min./mm thickness > 10 mm
> 20 mm 50 min. + 1 min./mm thickness > 20 mm

Table 5 – Holding times at temperature during heating for various workpiece thicknesses
10

Abrasive Treatment If the technical requirements, e.g., fume extrac-

It is usually necessary to remove the oxides, tion, are met, it is recommended to increase the
formed during a thermal treatment in air, from temperature of the bath to approx. 40 °C. This
components for wet corrosive service made of shortens the pickling time considerably.
stainless steels and nickelalloys. For com-
ponents intended for high-temperature service, However, high-temperature materials with fairly
there is in many cases no need for abrasive bla- high C-content as well as Ni-Mo and Ni-Cu alloys
sting as descaled material will again form an with low Cr-content are particularly sensitive to
oxide layer as soon as it enters service. In many over-pickling!
cases, the material is in fact deliberately preoxi-
dized to obtain better high temperature service After pickling, the component must be carefully
performance as a result of a protective oxide rinsed with plenty of water and brushed down.
scale. Agreement regarding the surface condition
of as-delivered material for high temperature Any oxide still adhering after pickling should be
service should therefore specifically be reached removed with a stainless steel wire brush. The
with the client before the order is processed. pickling operation should be repeated, if neces-
sary.
As oxides adhere very strongly in the case of
high-nickel containing materials, it is advisable to When using pickling agents, such as sprays and
blast clean the components with a suitable grit or pastes, a separate passivating treatment is not
with glass beads or to grind them with, for required, as this takes place simultaneously
instance, 80 grit mop wheels prior to pickling. If during the pickling operation.
the material is pickled after abrasive blasting the
use of carbon steel shot is cost-effective and will In all cases, applicable environmental-friendly
suffice. effluent management regulations are to be follo-
wed to insure that effluents, such as rinse water,
Pickling are properly neutralised prior to disposal.
Pickling to remove surface oxides is best carried Pickling by specialist firms, who also take care of
out by immersion in a pickling bath consisting of the effluent disposal, is often a cost-effective
approx. 15 to 22 % nitric acid and approx. 2 to 3 % alternative.
hydrofluoric acid. Alternatively, commercially
available pickling sprays or pastes can be used. Depending on the shape and size of the compo-
This method is particularly applicable for large nent, mechanical descaling by grinding or with
fabricated components or sections, which cannot buffing or mop wheels may also be appropriate,
be treated in conventional pickling tanks. finishing with a fine grit (80 or finer). If necessary
the required surface condition of the finished
Typical immersion times at room temperature for component should be established in consultation
various alloy groups can be seen in Table 6. with the enduser before commencing with the
finishing operation.
Actual immersion time depends on the material,
the oxide thickness and the temperature of the To impart optimum corrosion resistance to
pickling bath. If in doubt, tests should be carried components, it is generally advantageous, after
out at the start on the component to establish grinding, to pickle and passivate surfaces, which
optimum pickling parameters. come in contact with chemical process fluids.

Alloy group Typical pickling time

Cr-Ni stainless steels 2 - 8 hrs

Ni-Cr-Mo-(Fe) alloys 8 - 24 hrs
Nickel and Ni-Cu alloys 10 - 15 min.
Ni-Mo alloys 8 - 10 min.
Table 6 – Typical pickling times for various alloy groups
 11

Machining Turning
A high work-hardening rate and toughness Nowadays, metallic materials are predominantly
together with poor thermal conductivity are machined using tools with indexable carbide
characteristic for austenitic stainless steels and inserts. These tools produce the highest cutting
nickelalloys. In machining, allowance must rates and are recommended for most turning
therefore be made to these aspects by the follo- operations involving uninterrupted cuts.
wing measures:
To determine the cutting speed and the rate of
• Only use well-ground, sharp tools with smooth feed, it is necessary to consider the stress and
surfaces; wear on the tool.

• Ensure maximum stability of machine tools Tool wear is influenced by the following factors:
and secure work clamping in order to produce
a clean cut; • Removal of metal due to excessive mechanical
stress, e.g., chipping in the event of vibration;
• Apply plenty of coolant and lubricant;
• Abrasion;
• The tool should be constantly engaged, and
with a relatively low cutting speed, a higher • Shearing-off of pressure-welded points;
rather than lower rate of feed should be used
in order to limit work hardening of the material • Formation of deposits;
to a minimum;
• Oxidation.
• If vibrations occur, the cause should immedia-
tely be established and remedied, because Removal of metal due to excessive thermal
vibrations always lead to destruction of the stress should be seen in relation to the respec-
cutting edge. tive properties of the material being machined
and the tool. With toughened tools, the cutting
Of the various machining processes, essentially edge undergoes plastic deformation. This also
only turning, milling and drilling are dealt with happens if high temperature at the cutting edge
here. Most of the other working processes, such leads to softening of the tool. This may especially
as planing, sawing and the like, follow rules occur with those materials, which have rather
similar to those applicable to turning. poor thermal conductivity. Whereas thermal con-
ductivity for Cr-Ni stainless steels and nickel-
alloys is approx. 8 to 15 W/m·K, the value
for carbon steel lies in comparison with approx.
58 W/m·K by a factor of 4 to 7 times higher.

Workpiece The heat and temperature distribution in the

650 K contact zone ‘workpiece-tool-chip’ is illustrated in
Figure 4 for machining of steel. The severe ther-
870 K
mal stress on the cutting edge is clearly shown in
770 K
the diagram. Therefore, it is particularly impor-
970 K
tant when machining austenitic stainless steels
920 K Chip and nickelalloys to ensure adequate heat
g Rake removal by cooling.
870 K Tool

Coolants, either the chemical type or the oil

Workpiece material: steel Rm = 850 N/mm2
Cutting tool material: HM P 20
emulsion type, should be used for all roughing
Cutting speed: v = 60 m/min. operations and finish cuts with carbide tools.
Depth of stress: h = 0.32 mm Water-base coolants are preferred for use in
Rake angle: g = 10°
(according to Vieregge) high-speed operations such as turning and mil-
ling, because of their greater cooling effect.
Fig. 4 – Heat distribution in the workpiece, chip and tool during machining of steel These may be soluble oils or proprietary chemi-
according to Kronenberg cal mixtures.
12

Any work done with high-speed steel tools can however, no ISO standard available for these as
be improved by the use of sulfurized, chlorinated yet. The coating counteracts the tendency
cutting oil. For slower operations such as drilling towards metal pick-up. If coated inserts are
and boring, for example, heavy lubricants and used, the cutting speed can be increased by up
very rich mixtures of chemical coolants are to 20 %.
desirable.
Milling
Spray mist coolant is adequate for simple turning Conventional milling is recommended. Cutting
operations on all stainless steels and nickelalloys. guide values suggested for use in milling
operations are given in Table 8.

Tools should chiefly be manufactured from For end and cylindrical milling cutters, HSS-E
carbides of the ISO application groups P 10 to steels are used, which can be reground. Milling
P 50 and K 10 to K 40. heads with indexable inserts of the ISO groups
P 10 - P 30, e.g., SPUN 120308 P 30, are also
Tests in a neutral atmosphere have proven that used.
oxidation of carbide cutting edges accelerates
wear. Drilling
Drilling is one of the most difficult machining
Table 7 shows guide values for machining with operations, especially in the case of austenitic
uncoated indexable carbide inserts, resulting in stainless steels and nickelalloys. Problems
acceptable and economic service life; there is, which may be encountered generally stem from

Cutting data
Chip cross-section: Chip cross-section
Material categories rigid and/or continuous Non-rigid and/or discontinuous
Depth of cut Rate of feed Cutting ISO Depth of cut Rate of feed Cutting ISO
speed application speed application
aa f vc group aa f vc group
mm mm/rev. m/min. mm mm/rev. m/min.
Stainless steels 1 - 10 0.1 - 1.5 100 - 60 P10 - P30 1-6 0.1 - 1.0 80 - 40 P20 - P50

Special
stainless steels
Ni-Cu alloys, 1 - 10 0.1 - 1.5 80 - 40 P20 - P30 1-6 0.1 - 1.0 60 - 30 P20 - P50
soft annealed K10 - K20 K10 - K40

Nickel
Ni-Cu alloys, 1 - 10 0.1 - 1.5 60 - 20 K10 - K20 1-6 0.1 - 1.0 50 - 20 K20 - K40
age-hardened

Nickelalloys
Ni-Cr-Mo-(Fe)
with Mo ≤ 10 %
Nickelalloys 1 - 10 0.1 - 1.5 30 - 10 K10 - K20 1-6 0.1 - 1.0 20 - 8 K20 - K40
Ni-Cr-Mo-(Fe)
with Mo > 10 %
and/or Ti > 2 %
Cb > 5 %
Co > 10 %

Table 7 – Guide values for turning with uncoated, indexable carbide inserts
 13

the properties of the materials, which were high- of the drill by undercutting, e.g., in accordance
lighted under Turning, and from the complex with DIN 1414 shape A, is recommended.
drilling operation, involving extrusion of metal
by the chisel edge in the center of the drill and To optimize chip removal, a tool side rake angle
shear cutting by the lips of the tool. Because of of 25 to 30° (30 to 35° for pure nickel) should be
high strength and work-hardening tendencies, used.
drilling of high nickelalloys can be a
difficult operation if good drilling practice is On examining the metal-cutting operation during
not adhered to. drilling, one notes the variation in the cutting
speed, which steadily decreases to v = 0 m/min.
The use of short drills (according to DIN 1897) from the outside diameter of the drill towards its
with a large web thickness made of high-speed tip. This alone may cause considerable work
steel (HSS) alloyed with molybdenum and cobalt hardening.
is suggested. It has been found that drills made
of this material are, on account of its higher Work hardening may even occur during center-
elasticity, superior to carbide tools. ing. Pyramidal centering punches and light
centering facilitate the first cut.
Surface treatment of the drills by nitriding or
coating with TiN is advisable. When applying the drill, it is vital to ensure that
the cutting edge begins to cut immediately with-
To obtain favourable cutting conditions at the out rubbing for a while over the surface to be
drill tip, a tip angle of 120° to 130° and thinning cut. In this way work hardening can be avoided.

Cutting data
Material categories Depth of cut Rate of feed Cutting speed ISO application group
aa f vc
mm mm/min. m/min.

Stainless steels 3-6 30 - 50 20 - 30 P10 - P30

Special
stainless steels
Ni-Cu alloys, 3-6 30 - 50 25 - 15 P10 - P30
soft annealed
Nickel
Ni-Cu alloys, 3-6 30 - 50 18 - 10 P10 - P30
age-hardened
Nickelalloys
Ni-Cr-Mo-(Fe)
with Mo ≤ 10 %
Nickelalloys 3-6 30 - 50 12 - 8 P10 - P30
Ni-Cr-Mo-(Fe)
with Mo > 10 %
and/or Ti > 2 %
Cb > 5 %
Co > 10 %
Ni-Fe alloys 3-6 30 - 50 120 - 80 P20 - P30
with 36 % Ni

Table 8 – Guide values for milling with HSS-E steel end and cylindrical milling cutters
14

Manual feeding should be avoided as far as coolants. The use of special cutting fluids suita-
possible. If automatic feeding at a steady feed ble for Cr-Ni stainless steels is recommended.
rate cannot be used, even pressure should be
applied during manual feeding, so that the drill The cutting speeds recommended for drilling are
cuts steadily and continuously. If the drill slips, given in Table 9.
work-hardening occurs, and it is difficult to
resume cutting. In fact, the drill may break when Cutting speeds and feed rates in relation to
it does take hold again after restarting cutting. diameter suggested for drilling of various alloy
groups are shown in Figure 5.
For holes over 20 mm in diameter, pilot drilling
is recommended. Countersinking and counterboring
Countersinking and counterboring should be
With deeper hole depths, it is essential to raise carried out with single- or three-edged tools. In
and if necessary clean the drill on reaching a all other respects the instructions apply as given
hole depth of approx. 4 times the drill diameter under Drilling.
and again after every 0.7 times the drill diameter
by which the hole is further deepened. Tapping
Taps made of bright, nitrided or TiN-coated HSS
Special care should be taken to apply sufficient steel may be used for tapping. It is advantage-
coolant and lubricant. 10:1 emulsions as well as ous to use stable taps with discontinuous cutting
heavy and extra-heavy cutting fluids are used as edges. Core holes should be drilled as large as

0.5
Cutting speed Rate of feed
Materials vc
m/min. mm/rev.
0.2
Rate of feed, mm/rev.

Ni-Cr-Mo-(Fe) alloys,
0.1 Ni-Cu alloys approx. 6
(age-hardened)
0.05
Cr-Ni stainless steels approx. 8
0.03
0.02 Nickel, approx. 25
Ni-Cu alloys

2 5 10 20 50
Diameter, mm

Fig. 5 – Guide values for cutting speeds and rates of feed in relation to tool diameter for drilling with HSS tools

Alloy group Approx. cutting speed

Cr-Ni stainless steels 6 - 10 m/min.

Ni-Cr-Mo-(Fe) alloys 4 - 8 m/min.
Ni-Cu alloys (age-hardened) 4 - 8 m/min.
Ni-Mo alloys 3 - 7 m/min.
Nickel and Ni-Cu alloys 25 m/min.

Table 9 – Recommended cutting speeds for drilling

 15

possible. Maximum applicable diameters are

according to DIN 13.

The same cutting speeds as recommended

under Drilling should be used. The cutting fluids
used for drilling are often unsuitable here, as
they evaporate. Drilling pastes should be used
instead.

Acknowledgements The information contained in these guidelines

VDM Metals GmbH is grateful to the following are based on results of research and develop-
firms for supplying guide values for various ment work as well as on information from litera-
machining operations: ture available at the time of printing and does not
provide any guarantee of particular characteri-
Turning: Widia GmbH stics. Krupp VDM reserves the right to make
Münchener Strasse 90 changes without notice.
D-45145 Essen
Tel.: +49 (2 01) 72 50 The guidelines have been compiled to the best
Fax: +49 (2 01) 7 25 35 29 knowledge of Krupp VDM and are given without
any liability on the part of Krupp VDM. Krupp
Drilling: Günther & Co. VDM is only liable according to the terms of the
Eschborner Landstrasse 112 sales contract and, in particular, to the General
D-60489 Frankfurt Conditions of Sales in case of any delivery from
Tel.: +49 (69) 78 90 20 Krupp VDM.
Fax: +49 (69 ) 78 90 25 74
78 90 21 09 Cronifer, Cunifer, Nicorros, Nicrofer, and Nimofer
are registered trade names of Krupp VDM GmbH.

Any suggestions or recommendations for chan-

ges to be incorporated into future editions are
always gratefully received.

As updates of data sheets and brochures are not

automatically send out when issued, Krupp VDM
recommends to request the latest edition of
required documentation either
by phone +49 (23 92) 55-0
by fax +49 (23 92) 55-2
2217 or
by E-Mail under vdm @tthyssenkrupp.com.

October 2001 Edition.

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