Metallurgical uses - Cobalt Development Institute

Cobalt Facts
4
Metallurgical Uses
Cobalt in Metallurgical Uses
The use of cobalt as a constituent of metal alloys systems (not including magnets) is based on its ability to
impart high temperature strength, though this is a simple phrase which describes what can be a complex
effect and in the Co/Fe/V systems to provide controlled expansion. This section will cover the main uses of
cobalt in a simplified manner.
4.1
Superalloys
Superalloys are simply defined as “alloys developed for elevated temperature service, usually based on
group VIIA elements, where relatively severe mechanical stressing is encountered and high surface stability
is frequently required” (Sims – The Superalloys). Three classes of alloys have appeared - cobalt-base,
nickel-base, iron-base – to meet this definition.
The driving force behind their development has been the jet engine which has required ever higher operating
temperatures. The use of the alloys has, however, extended into many other fields – all types of turbines,
space vehicles, rocket motors, nuclear reactors, power plants, chemical equipment and possibly 20% of
alloys have arisen for corrosion resistant applications.
Leaving aside the cobalt-based alloys, the greater majority of alloys are what might loosely be termed super
stainless steels.
The strength in these alloys arises from strengthening the “close packed face centred cubic” (fcc) austenitic
lattice which is at the heart of the alloy. Until the 1930’s, this matrix, either in iron- or nickel-base, was
strengthened by carbide precipitation. However, cubic gamma prime γ’-Ni3Al was created in the matrix at
this time and the Nimonic 80 of the period (Ni76/Cr19/Al1-4%/Ti2-4%) contained this phase. This phase itself
is similar to the matrix and can also be hardened. It has a yield strength which perversely increases with
temperature.
So, nickel-based alloys which form the bulk of alloys produced, are basically nickel-chrome alloys with a fcc
solid solution matrix containing carbides and the coherent intermetallic precipitate γ(Ni3(Al1Ti). This latter
precipitate provides most of the alloy strengthening and results in useful operating temperatures up to 90%
of the start of melting. Further additions of aluminium, titanium, niobium and tantalum are made to combine
with nickel in the γ’ phase and of molybdenum, tungsten and chromium which strengthen the solid solution
matrix.
At last cobalt – the role of cobalt is not completely understood but it certainly increases the useful
temperature range of nickel-based alloys. γ’ also occurs as γ’’ which has a body centred tetragonal structure
(i.e. two cubes stacked). Cobalt is thought to raise the melting point of this phase thus enhancing high
temperature strength.
Figure 1 shows the plethora of elements which have become part of the superalloys stew, some to provide
hardening, some to prevent other unwanted phases from forming and some to stop required phases
disappearing. As small additions can make large differences, it is not surprising that impurities are of equal
importance, hence the superalloy user’s insistence on quality.
As well as structure, processing has been responsible for enhancement of these alloys.
From the 1930’s to the 50’s, these alloys were packed with increasing “structure” to strengthen them.
However, in the 1950’s, problems occurred with embrittling phases such as σ and Laves. The 1950’s saw
the generation of complex grain boundaries with carbides engloved in γ’, creating a dispersion strengthened
layer bonding the grains together. By 1970, hafnium was being added and the engloved structure was less
essential as Hf contorts the grain boundary to create strength and ductility in a more mechanical fashion as
well as generating additional γ’.
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Metallurgical Uses
Figure 1 – A qualitatively comparative view of trends in superalloy chemical compostion
Figure 2 depicts (at 10,000x) the 50-year development of nickel superalloy appearance. The upper 2/3 of
the picture show structures that have enhanced performance and the bottom part those which cause
brittleness, lower strength or have other problems.
Figure 2 – The microstructure. Panorama of development of nickel superalloy
microstructure showing both useful and deleterious phases
Cobalt-Based Alloys
The cobalt-base superalloys have their origins in the Stellite® alloys patented in the early 1990’s by Elwood
Haynes. These names live on with the Stellite® name now belonging to the Deloro Stellite company and the
later (Haynes-Stellite alloys) Hastelloys® being a registered name for the large range of corrosion resistant
superalloys made by the Haynes International company.
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Metallurgical Uses
The Co-Cr-Mo alloys started with the 1930’s Vitallium which was castable and used for dental prosthetics. It
was followed by HS21 which became the lead material for gas turbine applications in the 1940’s. Lastly, X40 which was synonymous with HS-31 and is still used today was invented in 1943 and this alloy has served
as a based for new generations of cobalt-based superalloys (X-40 – Co-based 25% Cr, 10%Ni, 8%W).
Although in terms of properties the (γ’) hardened nickel-based alloys have taken the lion’s share of the
superalloy market, cast and wrought cobalt alloys continue to be used.
WHY? Because:
1. Cobalt alloys have higher melting points than nickel (or iron) alloys. This gives them the ability to absorb
stress to a higher absolute temperature.
2. Cobalt alloys give superior hot corrosion resistance to gas turbine atmospheres, this is due to their high
chromium content.
3. Cobalt alloys show superior thermal fatigue resistance and weldability over nickel alloys.
Composition and Structure
Cobalt alloys are termed austenitic in that the high temperature “Face Centred Cubic” phase is stabilised at
room temperature. As such, they are comparable to stainless steels.
They are hardened by carbide precipitation, thus carbon content is critical. Chromium provides hot corrosion
resistance and other refractory metals are added to give solid solution strengthening – tungsten and
molybdenum – and carbide formation – tantalum, niobium, zirconium, hafnium.
Processing is of course vital and whilst the above metals are helpful, others such as dissolved oxygen are
not. Vacuum melting is therefore becoming the norm to give close alloy control. It is also critical that the
specified compositions are adhered to, as excess of the soluble metals, W, Mo, Cr, will tend to form
unwanted and deleterious phases similar to the nickel alloys σ and Laves (Co3Ti – tetragonal close packed
TCP phases).
Table 1 shows the effect of some additions and typical alloy compositions.
Table 1 – Function of Alloying Element Groups in Cobalt Superalloys
Nickel
Chromium
Tungsten
Ti, Zr, Cb, Ta
C
Surface Stability
+ Carbide Former
Solid-Solution
Strength
MC Formers
Carbide
Formation
Principal
Function
Austenite
Stabiliser
Problemsa
Lowers
Corrosion
Resistance
Forms TCP
Phases
Forms TCP
Phases
Harms Surface
Stability
Decreases
Ductility
Examples
X-40
MM-509
10
10
25
24
7.5
7.0
0.45
0.60
L-605
HS-188
10
22
20
22
15.0
14.0
–
3.5 Ta, 0.5Zr,
0.2 Ti
–
–
a
0.10
0.08
when added in excess
Casting is important for cobalt-based alloys and directionally solidified alloys (DS) have led to increased
rupture strength and thermal fatigue resistance.
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Cobalt Facts
Metallurgical Uses
The newest class of alloys as the (pm)
materials and the finer dispersion of
carbides and the small grain size have
increased properties above that of
cast
alloys
(pm
=
powder
metallurgical).
Further process development by hot
isostatic pressing (HIP) has even
further improved the properties by
removal of possible failure sites.
Figure 3 finally illustrates why cobaltbased alloys continue to be used in
gas turbines.
Figure 3 – Stress Rupture Properties
Compared to the nickel alloys, the
curve for the cobalt alloy (TD-CoCr) is
flatter and shows much lower strength
up to around 1800°F (980°C). The
greater stability of the carbides, which
provide the cobalt alloy strengthening
compared to γ’ which strengthens the
nickel alloys then asserts itself. This
factor is the primary reason cobalt
alloys are used in the lower stress,
higher temperature stationary vanes
of gas turbines.
Discussion
Superalloys in general are a complex subject and there is probably no other group of alloys in history into
which more effort had been channelled. The jet turbine is a hostile environment and superalloy metallurgists
have developed alloys more structured and used at higher fractions of their melting point than any other alloy
grouping.
It is difficult to give a list of all superalloys available, both cast and wrought, corrosion resistant, nickel-, ironand cobalt-based. The tables in Annex 1 give a summary of typical alloys.
Over the last 30 years, the use of directly solidified (DS) alloys has become well established. The purpose of
directional solidification is to produce alloys with a columnar-grained structure, so eliminating the transverse
grain boundaries in alloys cast by conventional means. DS superalloys have vastly superior fatigue life,
rupture life and rupture ductility than conventional alloys.
Even further improvements in strength and temperature resistance have been achieved by the development
of single crystal alloys. By definition, these alloys do not contain grain boundaries, so do not need elements
which are traditionally added to strengthen the boundaries, but which at the same time depress the alloys
melting point. Both these trends have allowed the development of higher thrust jet engines which operate at
even higher temperatures.
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Metallurgical Uses
4.2 Wear Resistant Alloys & Coatings
Cobalt is used in two ways to give hard, corrosion/erosion resistant, high temperature coatings. Firstly,
carbide coatings containing up to 17% cobalt (see section 7) can be deposited by flame and plasma guns on
to softer substrates to give the finish and hardness of carbide – work rolls, mixers, grinders, etc. The main
interest in this section is the metallurgical alloys based on cobalt, whose primary aim is wear resistance and
which may be applied by surface coating or used as castings and forgings.
Alloys
Once again in the history of cobalt, we have to go back to Elwood Haynes. The alloys used in this field are
again based on the Stellite® alloys developed in the early 1900’s, although coatings have moved on into
cobalt-containing nickel based alloys as well, strictly for corrosion resistance.
The Stellites® were originally used as cutting tools and whilst this use has mainly been replaced by carbide,
it does remain. More often now however, the CoCrW alloys are used to coat other metals or are used as
castings wherever their unique erosion resistance and high temperature properties are needed. They also
form the basis of the prosthetic alloys used to produce hip and knee replacement joints. Figure 1 shows a
few typical castings and Table 1 compositions of the alloys used.
Figure 1 – Cobalt-based alloy castings
The spray alloys used for plasma or flame spray are in powder form and contain silicon and boron to form a
low melting point eutectic which allows fusion with the substrate with minimum distortion.
In general, the cobalt-based alloys can be deposited by:
a) Welding – both rods and strip are available – MIG, TIG, submerged arc, oxy-acetylene, etc.
b) Plasma/flame spray – powders are available for both these processes or rod feed can be used
c) They can be cast and used as complete parts or as inserts – i.e. titanium hip joint with Co/Cr ball
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Metallurgical Uses
Table 1 – Standard Cobalt-Base Alloys – Nominal Compositions
Co
Cr
C
W
Mo
Ni
Si
B
Fe
Mn
Others
STELLITE 1
STELLITE 2
STELLITE 4
STELLITE 6
STELLITE 12
STELLITE 20
STELLITE 21
STELLITE 31
STELLITE 190
STELLITE 238
STELLITE 306
STELLITE 694
BASE
BASE
BASE
BASE
BASE
BASE
BASE
BASE
BASE
BASE
BASE
BASE
32
31
32
27
30
32
27
26
26
26
25
28
2.5
2.5
1
1
1.8
2.5
0.2
0.5
3.3
0.1
0.4
1
13
13
14
5
9
17
–
7
14
–
2
19
–
–
–
–
–
–
5
–
–
3
–
–
2.5
2.5
–
2.5
2.5
2.5
2.5
10
1
–
6
5
1
1
1
1
1
1
1
1
1
1
1
1
–
–
–
–
–
–
–
–
–
–
–
–
2.5
2.5
1.5
2.5
2.5
2.5
1.5
1.5
8
20
4
2.5
1
1
1
1
1
0.5
1
1
0.5
1
1
1
–
–
–
–
–
–
–
–
–
–
Nb = 5
V=1
SF1
SF6
SF12
SF20
BASE
BASE
BASE
BASE
19
19
19
19
1.3
0.7
1
1.5
13
7
9
15
–
–
–
–
13
13
13
13
3
2.5
3
3
2.5
1.7
2
3
3
3
3
2
0.5
0.5
0.5
0.5
Cu = 5
Cu = 5
Cu = 5
Cu = 5
STELLITE 250
STELLITE 251
STELLITE 100
STELLITE 314
STELLITE 703®
BASE
BASE
BASE
BASE
BASE
28
28
33
32
32
.08
0.3
2
1.9
2.4
–
–
19
6
–
–
–
2
–
12
–
–
1
6
3
1
1
0.4
1
1.5
–
–
1
–
–
20
18
1
5
3
1
1
0.3
1
1.5
–
Nb = 2
–
Nb = 6 Cu = 2
–
Surgical (ASTM
BASE
F75/82BSS:3351)
29
0.3
–
6
2
1
–
0.75
1
–
TRIBALOY T400 BASE
TRIBALOY T800 BASE
TRIBALOY® T900 BASE
8
17
18
0.1
0.1
<0.08
–
–
–
28
28
23
1
1
16
2.4
3.2
2.7
–
–
–
1
1
–
–
–
–
–
–
–
DENTAL
A range of alloys to meet national/international compositions
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Metallurgical Uses
4.3 High Speed Steel
What is a high-speed steel?
One should say before we get carried away, that unfortunately not all high-speed steels contain cobalt, but
as we shall see, possibly the newest and the best ones do.
The evolution of high-speed cutting tools commenced with Musket’s self-hardening tungsten-manganese
steel in 1860. The usefulness of these steels for cutting was only appreciated in 1900 when Taylor and
White developed the forerunner to modern high speed steels.
Table 1 – typical High-Speed Steel Compositions
M2
K945
M35
M42
ASP23
ASP30
ASP60
C
Cr
Mo
W
Co
V
0.87
0.91
0.90
1.08
1.28
1.28
2.30
4.2
3.7
4.1
3.9
4.2
4.2
4.2
5.0
5.0
5.0
9.4
5.0
5.0
7.0
6.4
1.8
6.4
1.5
6.4
6.4
6.5
–
2.5
4.8
8.0
–
8.5
10.5
1.9
1.2
1.9
3.1
3.1
3.1
6.5
M = Molybdenum type
ASP = Asea Stora Process
Steel is of course an iron-carbon alloy. Highspeed steels are also steel but with large
additions of refractory metals – tungsten,
chromium, molybdenum, vanadium and, of
course, in specialised cases, cobalt. The other
element in steel, namely “carbon”, forms
“carbides” in carbon steels with just iron and in
high-speed steels, with all the alloying additions
except cobalt which has other functions. So, in
essence, a high speed steels is a steel
containing large amounts of refractory carbides
which proved hardness, high temperature
strength, wear resistance to tempering, with
cobalt enhancing high temperature strength
(Table 1).
How are modern high-speed steels made?
As with many other modern alloys, high-speed steels have not changed greatly in basic composition since
their conception. What changed are the manufacturing techniques. Structure is of paramount importance in
tools steels and the aim is to get a very fine distribution of carbides. To this end, complex heat treatment
schedules have been devised, often with two or even three tempering stages.
Three current methods of manufacture seem to have evolved: I) air melt cast and work, ii) vacuum melt cast
and work, iii) atomise – cold isostatic press – sinter – hot isostatic press (see Cobalt News July 1991) – and
work.
As far as cobalt is concerned, one
would suppose that the route did
not matter – this, to some extent, is
true. However, the newer ASP
alloys made by method (iii) are
superior to other grades and the
best of these contain high levels of
cobalt (8-10%).
Figure 1 – Structures at x100 magnification
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The benefit of the powder route is
in the structure. Casting produces
segregation by its very nature and
further work and heat do little to
change
it.
Atomising
a
homogeneous molten metal gives
such rapid cooling that each “miniingot”
(powder
particle)
is
homogeneous unlike its large cast
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Cobalt Facts
Metallurgical Uses
brethren. The rest of the process is to stick these little ingots back together into a pore-free, homogeneous
form.
The final structures shown in Figure 1, illustrate the difference and in practice this can mean: a) better
stability in heat treatment, b) easier to grind, and c) FASTER CUTTING with higher cutting edge strength.
Why is cobalt in high-speed steels?
A good question as it doesn’t form carbides.
The reasons that have brought cobalt to prominence in these latest alloys are the same as they always were.
Cobalt dissolved in iron (ferrite and austenite) and strengthens it at the same time imparting high
temperature strength (temperature on cutting surfaces can be 850°C. During solution heat treatment (to
dissolve the carbides), cobalt helps to resist grain growth so that higher solution temperatures can be used
which ensures a higher percentage of carbides being dissolved. Steels are quenched after solution
annealing and the structure is then very hard martensite, plus the retained high temperature phase austenite
plus carbides peppered throughout the structure.
Tempering will precipitate the ultrafine
carbides still in solution and maximum
hardness will be attained. Here, cobalt
plays another important role, in that it delays
their coalescence. This is important as it
means that during cutting, the structure is
stable up to higher temperatures. Thus,
cobalt-containing tool steels are capable of
retaining strength to higher temperatures –
They cut faster for longer.
Figure 2 is the classic diagram showing the
effectiveness of cobalt in retaining
strength/hardness at high temperature by
resisting tempering and strengthening the
matrix.
Figure 2 – Effect of temperature hardness
of various types of tool steel
Use, New and Future
The types of steels we are talking about are aimed at the tope end of the cutting tool market. The workhorse
cutting alloys is M2 and this may well continue. The newer alloys are undoubtedly more expensive initially
(NB: ASP30 is four times the cost of M20. It is, however, easy to demonstrate that in many operations, the
initial tool cost is of little significance and the benefits of less tool wear, more holes/cuts, etc., soon far
outweigh it, so things may chance. Figure 3 shows typical tools – gear hobs, mills, taps and drills reamers,
broaches, single point tools for parting and final finishing could also be included.
Tools, however, are no longer as simple as they were. The surface can be modified by coating – with TiN or
TiC for example, put on by plasma or vapour deposition. These coatings increase cutting life by large
factors (4 and 5 times) and do so even after regrinding. This latter phenomenon looks inexplicable but
consider for example a gear hob. One would normally cut its way down a tapering gear tooth and failure
(much later on) is by crater wear. Cobalt reduces this wear by increasing hot strength. Even after
regrinding, the TiN coating remains on the flanks and life is still increased.
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Metallurgical Uses
The Market
In spite of these developments, the
trend to achieve high cutting
speeds for improved productivity
has meant there has been a
steady move from high-speed
steels to carbide tipped tools in
recent years.
Figure 3 – Typical tools
In 2001, the CDI estimated that
refined
cobalt
demand
in
hardfacing and high speed steels
totalled about 2,800 tonnes or 7%
of the world market. However, it is
unlikely that much refined cobalt
finds its way into high speed steels
as most is expected to be in the
form of cobalt-containing scrap.
4.4 Cobalt Prosthetic Alloys
The use of metals to repair and replace parts in the human body, may go back a long way. In 1775, iron
wire is reported as having been used to fix a fractured bone. It became known however that not all materials
were what we would now term biocompatible.
Several metals were used – platinum, gold, etc. – but in 1924, it was concluded by Zierold that a cobaltchrome alloy had the best combination of properties. In 1937, Vitallium arrived on the scene, this being a
CoCrMo alloy which had good strength, corrosion resistance and above all, was tolerated by the body.
Cobalt-chrome alloys of the Vitallium type are still used in the production of knees and hips, though they are
only used when wear resistance is paramount as they are relatively heavy.
Figures 1a & 1b – Typical knee and hip components
Typical alloys are 62%Co, 30%Cr, 5%Mo and 52%Co, 26%Cr, 14%Ni, 4%Mo. They are therefore basically
Stellites® being close to HS21 and 31.
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Metallurgical Uses
In recent years, Ti.318 (6Al4V) has moved into the prosthetic field
but the Co/Cr alloys have maintained their place and one now sees
composite hip joints with CoCr balls and titanium stems. This is
also an expanding market with replacement joints being fitted more
and more routinely to younger and younger people.
Figures 1 and 1b show typical knee and hip components made by
casting and powder metallurgy respectively.
Figure 2 shows an X-ray of a typical hip insert.
Figure 2 – X-ray showing cast hip
replacement in position
4.5 Controlled Expansion Alloys
These alloys are based on nickel/iron
alloys with the 36% nickel version
demonstrating the lowest expansion
coefficient 1 x 10-6 per °C. The coefficient
is however very temperature dependent
(see Figure 1) and even small changes
affect it. Other binary alloys such as 48%
nickel are more stable but one sacrifices
the very low values that can be obtained.
Figure 2 shows a general curve, relating
∆L/L the expansion coefficient to
temperature and this type of curve applies
to all the low expansion materials.
Figure 1 – Expansion coefficients of nickel-iron-cobalt alloys (0-1°C)
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Figure 2 – Typical expansivity curve of lowexpansion alloys
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Naturally, we would like a material where the flat part of the curve C-D is at a low level and T2 the
temperature, where the curve inflexes and climbs again is at high level.
In practice, substituting cobalt for nickel goes some way towards this. The lowest expansion occurs with 6%
Co substitution into the original 36% Ni alloy – Invar and we have Super-Invar.
In fact, various levels of cobalt can be used to vary ∆L/L and create a series of alloys with specific expansion
coefficients (Table 1).
Table 1 – Low-Expansion Cobalt Alloys
Trade or
Common
Name
Composition %
Co
Super-Invar
3.5
Ditto
4.0
“
4.0
“
4.0
“
5.0
“
5.0
“
6.0
“
6.0
“
5.0
“
6.0
Super-Nilvar
4-6
Stainless Invar
54
Japanese Invar 54.2
Fernico
15
Fernichrome
25
Kovar
18
Fe
Ni
Cr
Mn
62.5
63.5
63.0
62.5
63.5
62.5
63.5
62.5
64.0
63.0
Bal
36.5
36.0
54
37
54
34.0
34.0
33.0
33.5
31.5
32.5
30.5
31.5
31.0
31.0
31
–
–
31
30
28
–
–
–
–
–
–
–
–
–
–
–
9.5
9.4
–
8
–
–
–
–
–
–
–
–
–
0.35
0.38
–
–
0.37
–
–
min.
C
Coefficient
of expansion
10-6 per °C
0.007
0.007
0.007
0.007
0.007
0.007
0.007
0.007
0.007
0.007
–
–
0.05
–
–
min.
0.3
0.0
0.4
0.5
0.0
0.5
0.0
0.1
0.1
0.0
–
0.0
–
4.95
9.0
4.0
The original alloys – Invar,
etc. – may have had their
applications
linked
to
mechanical devices where
expansion was a problem –
like
clocks,
watches,
measuring devices, etc. – but
the Super-Invar and Kovar
now find their uses in the
electronic age.
They use
their controlled expansion to
match that of glass for glass
to metal seals, and also in the
electronic packaging industry
where they can match various
substrates
to
provide
hermetic seals which can
stand the rigours of the
+55°C −55°C expansion test
and also provide corrosion
resistance.
4.6 Cobalt in Steels
Cobalt is not an element commonly added
to alloy steels. It does have some effects
but these are also obtainable by other
additives at lower cost and mostly with
better results – Molybdenum, nickel, etc.
We have seen in other areas that cobalt
does not form carbides and that in fact, it
decreases hardenability (a measure of the
depth to which a steel hardens on
quenching). It hardens ferrite but only
marginally and has only a small influence
on the transformation temperature of iron.
Figure 1 – Effect of cobalt on tempering resistance of martensitic
stainless steel (0.1C, 12Cr, 4Mo)
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The factors above ensure that cobalt is
unlikely to ever find a use in high tonnage
low alloy steel production. It does however
have some niche markets in steel. In
martensitic steels, cobalt has the effect of
delaying tempering and this can be shown
by
plotting
hardness
against
a
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Cobalt Facts
Metallurgical Uses
time/temperature parameter as in Figure 1 (T = temperature, t = hours). Increasing cobalt levels produces
increased hardness and steels of this type 1%C, 12%Cr, 4%Mo and 7%Co have attractive properties.
Some steels such as Jethete M120 have been developed for use at high temperature using the effect of
cobalt to give high temperature strength in the range below which superalloys are more usual.
The steels where cobalt has found its home (apart from the high speed variety) are termed maraging. This
name is derived from the fact that they are aged in the martensitic form.
The original steels used were 20/25% nickel steels with small additions of Al, Ti and Nb. The secret of these
steels was and is, that simple air-cooling is sufficient to transform the Austenite high temperature phase to
Martensite, the hard unstable lower temperature form. On reheating, the temperature to return to Austenite
is found to be much higher than the Martensite forming temperature of 250°C and is in fact over 500°C.
Reheating (aging) at an intermediate temperature retains the Martensite but allows precipitation of various
hardening phases such as Ni3Mo, Ni3Ti, FeMo and these raise the hardness to up to 900 Vickers. The early
steels were found to be brittle and cobalt additions solved this problem. As usual, the role of cobalt is
obscure but it enhances the properties and accelerates the process. Table 1 shows a range of typical steels.
Table 1 – Composition and Properties of Maraging Steels
Grade
18Ni(200)
18Ni(250)
18Ni(300
18Ni(350)
13Ni(400)
Composition, wt.%
Ni
Co
Mo
Ti
18
8.3
18
7.5
18
9.0
17.5 12.5
13 15.5
3.25
4.8
4.8
3.8
10.8
0.2
0.4
0.6
1.7
0.2
Al
0.10
0.10
0.10
0.15
–
UTS
103 psi MN/m2
210
255
285
355
390
1450
1750
1960
2450
2690
Elong.
%
13
13
11
9
5
Hardness
Rc
43
50
54
58
59
Their properties are not the highest possible but they score in that they can be air-cooled without distortion,
machined without difficulty and finally, develop their properties with a relatively simple low temperature aging
process.
Maraging steels have found many uses in the aerospace and military industries where their strength coupled
with workability has got them the job over possibly stronger materials.
Typical applications are landing gears, arrestor hooks, torque shafts, rocket motor casings, gun barrels,
bolts, fasteners, extrusion arms, etc., etc. There are the areas where cobalt steels are best.
4.7 Other Alloys
Cobalt is used in other alloys, Co/Pt magnets, 36%Ni12%Cr spring alloys which can be varied to provide
given temperature expansion coefficients against elastic moduli. The main uses however are covered in the
preceding sections.
60
One use left until last is the role of cobalt in cancer treatment and flaw detection with the Co isotope.
Cobalt-59 is irradiated in a reactor for a long period and some of the metal is converted to 60Co. This isotope
has a half-life of 5.3 years and emits γ-rays as it decays. These rays can be used in portable machines in
lieu of X-rays for flaw detection. They have the advantage of portability and greater penetration over X-rays
tough they do not provide quite the same definition in photographic terms.
The rays can also be targeted at cancer cells and used to destroy them. This is the basis of radiation
therapy in cancer treatment. Food also has its life prolonged by irradiation after packing.
Cobalt Facts, © 2006 CDI
19
Cobalt Facts
Metallurgical Uses
4.8 Further Reading
1.
2.
3.
4.
5.
Cobalt in Superalloys – CDI 1985
Cobalt and its Alloys – w. Betteridge (Horwood ltd) 1982
Superalloys II – Sims & Hagel (Wiley)
The role of cobalt in wear/corrosion resistant materials – THE Cobalt Conference 1998, CDI
Powder metallurgical processing improves high carbon Co-Cr-Mo alloy – orthopaedic implants – THE
Cobalt Conference 2001, CDI
6. Cobalt in superalloys – THE Cobalt Conference 2004, CDI
Note: Stellite® is a registered trade name of the Deloro Stellite company, Hastelloy is registered by Haynes
International and Nimonic by Inco Alloys.
Cobalt Facts, © 2006 CDI
20
Cobalt Facts
Metallurgical Uses
Summary Tables
Nominal Chemistry and Density of Cast Nickel- and Cobalt-Base Alloys
Alloy
Ni
Cr
Co
Alloy 713C
IN-100
IN-731
MM-002
MM-004
MM-005
MM-006
MM-009
René 77
René 80
Udimet 500
74
60
67
61
74
59
63
59
58
60
52
12.5
10.5
9.5
9.0
12.0
8.5
9.0
9.0
14.6
14.0
18.0
0.0
15.0
10.0
10.0
0.0
10.0
10.0
10.0
15.0
9.5
19.0
Mo
W
Ta
Cb
0.0
0.0
0.0
2.5
0.0
3.8
1.5
0.0
0.0
0.0
0.0
2.0
0.0
0.0
0.0
2.0
0.0
0.0
1.0
0.0
0.0
0.0
Al
Ti
Fe
Mn
Si
C
B
Zr
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.12
0.18
0.18
0.14
0.05
0.11
0.14
0.14
0.07
0.17
0.07
0.012
0.014
0.015
0.015
0.015
0.015
0.015
0.015
0.016
0.015
0.007
0.10
0.06
0.06
0.05
0.05
0.05
0.05
0.05
0.04
0.03
0.05
0.0
0.0
0.0
0.7
0.25
0.85
0.60
0.50
0.010
0.005
0.000
0.000
0.00
0.20
0.50
0.00
Others
Density
3
3
lb/ in. g/ cm
Nickel-Base Alloys
4.2 0.0
3.0 0.0
2.5 0.0
0.0 10.0
4.5 0.0
2.0 8.0
2.5 10.0
0.0 12.5
4.2 0.0
4.0 4.0
4.2 0.0
6.1
5.5
5.5
5.5
5.9
4.8
5.5
5.0
4.3
3.0
3.0
0.8
4.7
4.6
1.5
0.6
2.5
1.5
2.0
3.3
5.0
3.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.0V
1.0V
1.5Hf
1.3Hf
1.4Hf
1.8Hf
1.8Hf
0.286
0.280
0.280
7.9
7.7
7.7
0.308
0.311
0.311
0.286
0.295
0.290
8.5
8.6
8.6
7.9
8.2
8.0
0.300
0.333
0.320
0.311
8.3
9.2
8.9
8.6
Cobalt-Base Alloys
FSX-414
MAR-M 302
Mar-M 509
X-40/X-45
10
0
10
10
29.0
21.5
23.5
25.5
52.0
58.0
55.0
54.0
Cobalt Facts, © 2006 CDI
0.0 7.5
0.0 10.0
0.0 7.0
0.0 7.5
0.0
9.0
3.5
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.2
0.0
1.0
0.0
0.0
0.0
0.0
0.0
0.0
0.7
21
Cobalt Facts
Metallurgical Uses
Nominal Chemistry and Density of Wrought Nickel-, Cobalt- and Iron-Base Alloys
Alloy
Ni
Cr
Co
Mo
W
Ta
Cb
Al
Ti
Fe
Mn
Others
3
3
Si
C
B
Zr
lb/ in. g/ cm
0.0
0.0
0.0
0.10
0.05
0.00
0.000
0.000
0.000
0.00
0.10
0.00
0.4
0.0
0.5
0.10
0.00
0.15
0.000
0.000
0.000
0.00 0.2N 0.02La 0.297 8.3
0.00
0.294 8.1
0.00 0.15N
0.296 8.2
Cobalt-Base Alloys
Haynes 188
MAR-M918
MP35N
22.0 22.0 39.2 0.0 14.0
20.0 20.0 52.5 0.0 0.0
35.0 20.0 35.0 10.0 0.0
0.0
7.5
0.0
0.0 0.0
0.0 0.0
0.0 0.0
0.0
0.0
0.0
3.0
0.0
0.0
0.0
0.0
0.0
0.330
0.320
0.304
9.1
8.9
8.4
Iron-Base Alloys
Haynes 556 20.0 22.0 20.0
Incoloy 903 38.0 0.0 15.0
N-155
20.0 21.0 20.0
3.0
0.0
3.0
2.5
0.0
2.5
0.9
0.0
0.0
0.0 0.3
0.0 0.7
0.0 0.0
0.0 29.0
1.4 41.0
0.0 30.0
1.5
0.0
1.5
Nominal Chemistry and Density of Wrought Nickel-, Cobalt- and Iron-Base Alloys
Alloy
Ni
Cr
Co
Mo
W
Ta
Cb
Al
Ti
Fe
Mn
Si
C
B
Zr
3
Others
lb/ in. g/ cm
3
Nickel-Base Alloys
Hastelloy
C-22
Hastelloy
C-276
Hastelloy
G-30
Hastelloy S
Hastelloy X
IN-100
Inconel 600
Inconel 718
Nimonic 90
Nimonic 105
Nimonic 115
Nimonic 263
René 95
Udimet 520
Udimet 710
Udimet 720
Waspaloy
51.6 21.5
2.5 13.5
4.0
0.0
0.0
0.0
0.0
5.5
1.0
0.1 0.01 0.000
0.00
0.3V
0.314
8.7
55.7 15.5
2.5 16.0
3.7
0.0
0.0
0.0
0.0
5.5
1.0
0.1 0.01 0.000
0.00
0.3V
0.321
8.9
42.7 29.5
2.0
2.5
0.0
0.8
0.0
0.0 15.0
1.0
1.0 0.03 0.000
0.00
2.0Cu
0.297
8.2
0.0
0.6
0.0
0.0
0.0
0.0
0.0
0.0
0.0
3.5
1.0
1.5
1.3
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
5.1
0.0
0.0
0.0
0.0
3.5
0.0
0.0
0.0
0.0
0.3
0.0
5.0
0.0
0.5
1.5
4.7
4.9
0.5
3.5
2.0
2.5
2.5
1.3
0.0 1.0
0.0 18.5
4.3 0.0
0.0 8.0
0.9 18.5
2.5 0.0
1.2 0.0
3.7 0.0
2.1 0.0
2.5 0.0
3.0 0.0
5.0 0.0
5.0 0.0
3.0 0.0
0.5
0.5
0.0
0.5
0.2
0.3
0.3
0.0
0.4
0.0
0.0
0.0
0.0
0.0
0.4
0.5
0.0
0.2
0.2
0.3
0.3
0.0
0.3
0.0
0.0
0.0
0.0
0.0
0.00
0.00
0.06
0.00
0.00
0.06
0.10
0.04
0.02
0.05
0.00
0.00
0.03
0.00
0.05La
0.316 8.8
0.297 8.2
0.284 8.1
0.304 8.4
0.297 8.2
0.296 8.2
0.289 8.0
0.284 7.9
0.302 8.4
0.297 8.2
0.292 8.1
0.292 8.1
0.292 8.1
0.296 8.2
67.0
47.0
55.8
76.0
52.5
59.0
53.0
60.0
51.0
61.0
57.0
55.0
55.0
58.0
15.5
22.0
12.4
15.5
19.0
19.5
15.0
14.3
20.0
14.0
19.0
18.0
17.9
19.5
5.5
0.0 14.5
1.5 9.0
18.5 3.2
0.0 0.0
0.0 3.0
16.5 0.0
20.0 3.0
13.2 0.0
20.0 5.9
8.0 3.5
12.0 6.0
15.0 3.0
14.7 3.0
13.5 4.3
Cobalt Facts, © 2006 CDI
0.00
0.10
0.07
0.08
0.04
0.07
0.13
0.15
0.06
0.15
0.05
0.07
0.03
0.08
0.000
0.000
0.020
0.000
0.000
0.003
0.005
0.160
0.001
0.010
0.005
0.020
0.033
0.006
0.8V
22