heat treatment of martensitic stainless steels

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Heat Treating of Martensitic
Stainless Steels*
THE HARDENING OF MARTENSITIC
STAINLESS STEEL is essentially the same as
for plain-carbon or low-alloy steels, in that maxi-
mum strength and hardness depend chiefly on car-
bon content. There are, however, important
differences stemming from the high alloy content
of the stainless grades. The high alloying causes
the thermal decomposition of austenite (into pearl-
ite) to be so sluggish that austenite undergoes
athermal decomposition (into martensite). This
being the case, the hardenability of martensitic
stainless steel is very high. Maximum hardness is
produced by air cooling in the center of sections
up to approximately 300 mm (12 in.) thick, and
quenching rate is not a significant issue given the
high hardenability of the martensitic stainless
steels. The martensitic stainless steels thus can be
more sensitive to heat-treating variables than are
carbon and low-alloy steels; some, especially
thosewith higher carbon levels,may have retained
austenite, which can lower hardness and cause
problems with dimensional stability. The quench-
ing rate also must be sufficient, however, to avoid
precipitation of carbides in the austenite during
quenching since the sensitization would persist in
the final microstructure. If this occurs, a subzero
treatment at below –75 �C (–100 �F) should be
undertaken immediately after quenching.
Tables 1 and 2 list the most significant of the
wrought martensitic stainless steel alloys. (See
the section “Casting Alloys” in this article for
heat treatment of cast martensitic stainless
steels.) Martensitic stainless steels are the least
corrosion resistant of all the stainless alloys.
The requirement that they be fully austenitized
limits the amount of corrosion-resisting chro-
mium and molybdenum they can contain.
Much of the carbon in them reduces the effec-
tive chromium content by forming chromium
carbides. In addition they are always suscepti-
ble to stress corrosion cracking (SCC) when
their hardness exceeds about 22 HRC. These
limitations combine to make their excellent
properties usable in only mild environments
compared to other stainless steels.
Alloying
The traditional martensitic stainless steels are
iron/chromium/carbon alloys, sometimes with a
ASM Handbook, Volume 4D, Heat Treating of Irons and Steels 
J. Dossett and G.E. Totten, editors
DOI: 10.31399/asm.hb.v04d.a0005985
Copyright # 2014 ASM InternationalW
All rights reserved
asminternational.org
Table 2 Compositions of nonstandard wrought martensitic stainless steels
Designation(a) UNS designation
Composition(b), %
C Mn Si Cr Ni P S Other
Type 410S S41008 0.08 1.00 1.00 11.5–13.5 0.60 0.040 0.030 � � �
Type 410 Cb (XM-30) S41040 0.15 1.00 1.00 11.5–13.5 � � � 0.040 0.030 0.05–0.20 Nb
E4 S41050 0.04 1.00 1.00 10.5–12.5 0.60–1.1 0.045 0.030 0.10 N
CA6NM S41500 0.05 0.5–1.0 0.60 11.5–14.0 3.5–5.5 0.030 0.030 0.5–1.0 Mo
416 Plus X (XM-6) S41610 0.15 1.5–2.5 1.00 12.0–14.0 � � � 0.060 0.15 min 0.6 Mo
Type 418 (Greek Ascolloy) S41800 0.15–0.20 0.50 0.50 12.0–14.0 1.8–2.2 0.040 0.030 2.5–3.5 W
TrimRite S42010 0.15–0.30 1.00 1.00 13.5–15.0 0.25–1.00 0.040 0.030 0.40–1.00 Mo
Type 420 F Se S42023 0.3–0.4 1.25 1.00 12.0–14.0 � � � 0.060 0.060 0.15 min Se; 0.6 Zr; 0.6 Cu
Lapelloy S42300 0.27–0.32 0.95–1.35 0.50 11.0–12.0 0.50 0.025 0.025 2.5–3.0 Mo; 0.2–0.3 V
Type 440 F S44020 0.95–1.20 1.25 1.00 16.0–18.0 0.75 0.040 0.10–0.35 0.08 N
Type 440 F Se S44023 0.95–1.20 1.25 1.00 16.0–18.0 0.75 0.040 0.030 0.15 min Se; 0.60 Mo
(a) XM designations in this column are ASTM designations for the listed alloy. (b) Single values are maximum values unless otherwise indicated. (c) Nominal compositions. (d) Source: Ref 1
Table 1 Compositions of standard wrought martensitic stainless steels
Type UNS designation
Composition(a), %
C Mn Si Cr Ni P S Other
403 S40300 0.15 1.00 0.50 11.5–13.0 � � � 0.04 0.03 � � �
410 S41000 0.15 1.00 1.00 11.5–13.5 � � � 0.04 0.03 � � �
414 S41400 0.15 1.00 1.00 11.5–13.5 1.25–2.50 0.04 0.03 � � �
416 S41600 0.15 1.25 1.00 12.0–14.0 � � � 0.06 0.15 min 0.6 Mo(b)
416Se S41623 0.15 1.25 1.00 12.0–14.0 � � � 0.06 0.06 0.15 min Se
420 S42000 0.15 min 1.00 1.00 12.0–14.0 � � � 0.04 0.03 � � �
420F S42020 0.15 min 1.25 1.00 12.0–14.0 � � � 0.06 0.15 min 0.6 Mo(b)
422 S42200 0.20–0.25 1.00 0.75 11.5–13.5 0.5–1.0 0.04 0.03 0.75–1.25 Mo;
0.75–1.25 W;
0.15–0.3 V
431 S43100 0.20 1.00 1.00 15.0–17.0 1.25–2.50 0.04 0.03 � � �
440A S44002 0.60–0.75 1.00 1.00 16.0–18.0 � � � 0.04 0.03 0.75 Mo
440B S44003 0.75–0.95 1.00 1.00 16.0–18.0 � � � 0.04 0.03 0.75 Mo
440C S44004 0.95–1.20 1.00 1.00 16.0–18.0 � � � 0.04 0.03 0.75 Mo
(a) Single values are maximum values unless otherwise indicated. (b) Optional
* Revised from: J. Douthett, Heat Treating of Stainless Steels, Heat Treating, Vol 4, ASM Handbook, ASM International, 1991, p 769–792 with adapted material from M.F. McGuire, Stainless
Steels for Design Engineers, ASM International, 2008.
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small amount of nickel and/or molybdenum
(Ref 1). The martensitic alloys themselves can
be made to be partially ferritic by forcing their
carbon contents to low levels, as is customarily
done with 410S (UNS S41003). More recently,
alloys have been developed for petroleum
applications that contain high copper, nickel,
and/or molybdenum and low carbon. The prin-
ciples of heat treatment are the same, but the
more highly alloyed newer alloys can be sim-
pler to heat treat because their low carbon and
nitrogen levels alleviate the need to temper.
A stainless martensitic alloy should have the
following characteristics:
� It must have at least 10.5% chromium to
qualify as stainless, and even more for better
corrosion resistance.
� It should be fully austenitic at some temperature.
� The temperature at which austenite forms on
heating should be sufficiently high to permit
tempering above the temper embrittlement
range.
These criteria are somewhat challenging to
meet. Figure 1(a) shows that at low-carbon
(0.05%) levels austenite is stable up to about
12% chromium, above which some d�ferrite
tends to be stable at all temperatures below
the melting point. Increasing carbon slightly
expands the chromium level at which full auste-
nitization can occur (Fig. 1b) (Ref 2).
The interplay between chromium and carbon
is further explained in Fig. 2(a) and Fig. 2(b),
which show that for higher chromium alloys
the range over which full austenitization can
occur is further restricted. The variety of mar-
tensitic stainless steels would be very limited
if only chromium and carbon were available
as alloying elements, but fortunately nickel
can again make an important contribution.
Nickel greatly expands the chromium levels
and temperatures at which austenite is stable,
as shown in Fig. 3 (Ref 2).
Table 3 quantifies the influences of the vari-
ous possible alloying elements on the key prop-
erties of martensitic stainless steels. It can be
seen that the elements that promote austenite,
with the exception of cobalt, all depress the
Ms temperature. This puts a limit on the amount
of total alloy that can be used and in the end
puts an upper limit on the ability of martensitic
stainless steels to achieve high corrosion resis-
tance. This is because as the main corrosion
fighters, chromium and molybdenum, which
are ferritizers, are increased, so must austeniti-
zers such as nickel be increased. The coordi-
nated increase in these elements lowers the
martensite start temperature (Ms) to such a
degree that the alloys become stably austenitic
before much higher corrosion resistance is
obtained.
The ability to temper without austenite rever-
sion is an important trait. Obviously, if trans-
forming martensite to austenite during tempering
caused subsequent untempered martensite or
other undesirable phases, this would limit one’s
ability to temper at a sufficiently high temperature
to achieve desired toughness. Thisfactor limits
the use of nickel while encouraging the use of
elements like molybdenum.
1600
C = 0.05 C = 0.1L
2910
2550
2190
1830
1470
1110
L
L + α L + α
α + M23C6
α + M23C6
α 
− 
K
2
α 
+ 
K
2
γ + α γ + α
1400
1200
T
e
m
p
e
ra
tu
re
, 
ºC
T
e
m
p
e
ra
tu
re
, 
ºF
1000
800
600
0 10 20 30
Cr, wt. %
0 10 20 30
Cr, wt. %
α
γ
γ
Fig. 1 Iron-chromium phase diagrams at two low-carbon levels
Fig. 2 Iron-chromium phase diagram at (a) 12% chromium and (b) 17% chromium
Fig. 3 The expansion of the range of austenite stability
with nickel content
Table 3 Influence of alloying elements on ferrite, MS, and austenite start
Element N C Ni Co Cu Mn Si Mo Cr V Al
Lowering of % ferrite per % element �220 �210 �20 �7 �7 �6 6 5 14 18 54
Lowering of MS per % element �475 �475 �17 0 to 10 �17 �30 �11 �21 �17 �46 � � �
Change of AC per % element 0 to 280 0 to 250 �30 to �115 0 0 �25 to �66 25 to 73 25 to 70 0 to 35 50 to 290 30 to 750
Heat Treating of Martensitic Stainless Steels / 383
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Copper has become an important alloying
element in martensitic stainless steels because
it greatly improves corrosion resistance in
certain environments without diminishing an
alloy’s ability to be tempered.
Thermal Process Metallurgy
The main concerns in processing martensitic
stainless steels are austenitizing, quenching, tem-
pering/stress relieving, and annealing (Ref 1).
Austenitizing is complicated in martensitic stain-
less steels because many grades contain carbon
at levels intended to produce carbides for wear-
resistance purposes. Since carbon solubility var-
ies strongly with temperature at austenitizing
temperatures (Fig. 1a, b), control of temperature
is vital in order to have the correct balance of
carbon in solution versus carbon as carbide since
carbon in solution has such a strong influence on
ferrite content, Ms, and mechanical properties.
Austenitizing temperature also determines
austenite grain size. This affects Ms, but more
importantly it influences subsequent toughness.
Phosphorus precipitates at prior austenite grain
boundaries during tempering with a maximum
effect at 475 �C (890 �F). This is the infamous
temper embrittlement. Figure 4 (Ref 2) shows
the significant toughness change that occurs as
increasing austenitizing temperature increases
austenite grain size and permits greater phos-
phorus concentrations at grain boundaries.
Refining phosphorus from any chromium-
containing steel is quite challenging thermody-
namically, so achieving low phosphorus levels
depends mainly on restrictions on raw materials
for melting. Because this is difficult or costly,
grain size control is the main tool for controlling
temper embrittlement.
The higher-carbon grades, those above
0.20% carbon, should be heated gradually
through stage heating to avoid cracking due
to thermal stresses. Soaking at 800 �C until
uniform temperature is achieved minimizes
this risk. Decarburization is another concern
during austenitizing. Heating in air to 1050 �C
(1920 �F) can cause surface carbon to decrease
by approximately 0.10% per hour. This loss
increases with base carbon level and austenitiz-
ing temperature.
Carbon or nitrogen pickup can also occur if
the atmosphere is rich in these elements. The
carbon potential of the furnace atmosphere
must be controlled to avoid potentially serious
problems. If hydrogen atmospheres are used
the danger of embrittlement after quenching
must be recognized. Stress relief without delay
would be mandatory.
The high chromium content of these alloys
renders them very deep hardening. Air harden-
ing is generally sufficient. Oil quenching which
is faster may be slowed by heating the oil.
Avoiding quench cracking and excessive warp-
age is almost always a greater concern than
depth of hardening so air quenching is standard.
Because the quenching and the transforma-
tion it causes are inevitably accompanied by
residual stresses in a brittle material, stress
relieving should be immediate to avoid crack-
ing. Higher-carbon grades should not even be
allowed below room temperature before stress
relief. Pickling should never be done on as-
quenched material because this could easily
result in hydrogen uptake and delayed cracking
by hydrogen embrittlement.
Heating as-quenched material to between
150 and 400 �C (300 and 750 �F) provides
stress relief. Besides the normal flow on a
microscopic scale, which we understand as
stress relieving, there is a slight growth in
the number of fine cementite particles and a
corresponding decrease in the amount of carbon
in solid solution. This results in a slight
decrease in hardness. At 400 �C, a further pre-
cipitation of M2X and M7C3 as well as the
transformation of M3C into M7C3 can result in
a secondary hardening, a true precipitation-
hardening effect. In the presence of strong
carbide-forming alloying elements such as
molybdenum, vanadium, and tungsten, the
M2X carbide can become the more stable spe-
cies and be responsible for the secondary hard-
ening. At 500 �C (930 �F), coarser M23C6 and
M7C3 begin to grow at grain boundaries. This
growth is accompanied by a pronounced soften-
ing. The hardening reduction with stress relief
and tempering for a 12% Cr alloy is shown in
Fig. 5 (Ref 3).
Separately, at the 475 �C (890 �F) range,
phosphorus segregation to prior austenitic grain
boundaries occurs. This effect begins to disap-
pear above 550 �C (1020 �F). Thus true temper-
ing is performed above this temperature. The
microstructural changes at these temperatures
are the above-mentioned loss of carbon from
solid solution, carbide precipitation and coars-
ening, and, of course, stress relief. The result
is a pronounced softening and toughening. If
the material contains retained austenite, it may
decompose to ferrite and carbide, with a nega-
tive effect on toughness.
The molybdenum-, vanadium-, and tung-
sten-alloyed grades will resist softening during
tempering because of the strength of the sec-
ondary hardening they undergo through pre-
cipitation hardening of carbides and nitrides.
Nickel seems to amplify this action by its
influence on reducing the solubility of carbon
in the matrix. Thus, the tempering of the
higher-alloy martensitic stainless steels can
truly be considered a precipitation-hardening
reaction.
The higher-carbon, higher-chromium grades
are typically stress-relieved only because the
removal of chromium from solution by carbide
formation at higher temperatures causes an
unacceptable loss of corrosion resistance.
Heat Treatment Preparations
Heat treatment processes for martensitic
stainless steels include annealing, hardening,
tempering, and stress relief. The ranges of sur-
face hardness for the various heat-treated condi-
tions are given in Fig. 6, and further details on
these processes are given separate sections of
this article. Preparations prior to heat treatment
include atmosphere selection, cleaning, and
preheating.Fig. 4 Influence of austenite grain size and phosphorus level on toughness
384 / Heat Treated High-Alloy Steels
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Prior Cleaning. To avoid contamination, all
parts and heat-treating fixtures must be cleaned
thoroughly before they are placed in the furnace.
Proper cleaning is particularly important when
the heat treatment is to be performed in a protec-
tive atmosphere. Grease, oil, and even location
lines made by an ordinary lead pencil can cause
carburization. Perspiration stains from finger-
prints are a source of chloride contamination
and may cause severe scaling in oxidizing atmo-
spheres. Furthermore, a protective atmosphere
cannot be effective unless it is permitted to make
unobstructed contact with metal surfaces.
Preheating. The thermal conductivity of
stainless steels is characteristically lower than
that of carbon andalloy steels. Accordingly,
high thermal gradients and high stresses during
rapid heating may cause warpage and cracking
in some parts. To avoid these problems, preheat-
ing is usually recommended in the treatment of
martensitic stainless steels. In annealing or hard-
ening, the following parts should be preheated:
� Heavy section parts
� Parts with both thin and thick sections
� Parts with sharp corners and reentrant angles
� Heavily ground parts
� Parts machined with heavy deep cuts
� Parts that have been cold formed or straightened
� Previously hardened parts that are being reheat
treated
Preheating is normally accomplished at
760 to 790 �C (1400 to 1450 �F), and heating
need be continued only long enough to ensure
that all portions of each part have reached the
preheating temperature. Large heavy parts are
sometimes preheated at approximately 540 �C
(1000 �F) prior to the 790 �C (1450 �F) preheat.
Types 403, 410, and 416 require less preheating
than the higher-carbon types 431, 420, and
440 grades.
Protective Atmospheres. Argon or helium, if
used as a protective atmosphere, should be excep-
tionally dry (with a dew point below �50 �C, or
�60 �F). Because they are expensive and cannot
be generated, they are rarely used. Exothermi-
cally- and endothermically-generated gas can
be used with excellent results (see the article
“Furnace Atmospheres” in this Volume). These
require dew-point or infrared control so as not to
carburize or decarburize the stainless grade being
heat treated. Endothermic gas containing approx-
imately 40%hydrogen can embrittle oil-quenched
martensitic stainless steels.
An exothermic gas ratio of 6.5 or 7 to 1 is
satisfactory for grades of stainless containing
not more than 0.15% C. For endothermic atmo-
spheres, dew points for specific steels and aus-
tenitizing temperatures are listed in Table 4.
Salt Baths. Many stainless steel parts are
heat treated in molten salt, with excellent
results. The baths usually employed consist of
barium chloride with 5 to 35% sodium or potas-
sium chloride. Alkaline-earth and other metallic
oxides build up in these baths through use, but
these oxides are not harmful to low-carbon
stainless steels. However, if these salt baths
are also to be used for hardening other alloy
steels, then to avoid surface decarburization it
is necessary to rectify the baths with graphite
to remove the metallic oxides and with methyl
chloride gas to convert the alkaline-earth oxides
back to chlorides. A bath treated with methyl
chloride will carburize a low-carbon stainless
steel unless the bath is aged for at least 24 h
before the steel is treated in it. To avoid this
problem, stainless steel parts should be heat
treated in a salt bath reserved exclusively for
stainless steels.
Hydrogen embrittlement can be an impor-
tant concern in the martensitic grades, generally
increasing with hardness and carbon content.
(It is variable and less acute in ferritic steels,
and is virtually unknown in the austenitic grades.)
The embrittling hydrogen may be acquired as a
result of the melting process, a heat-treating
atmosphere, or chemical and electrochemical pro-
cesses such as pickling and electroplating.
Most heat-treating atmospheres contain
hydrogen in the form of moisture, hydrocar-
bons, or elemental hydrogen as an atmosphere
or a dissociation product. The use of pure
hydrogen or dissociated ammonia for bright
annealing in one plant was associated with
cracking of wire coils of types 431 and 440C,
although other plants have reported no similar
difficulty. Nevertheless, it is possible that some
loss in ductility may result from the bright
annealing of any of the martensitic stainless
steels.
Less severely, the use of H2 annealing gas
with a titanium- or aluminum-bearing ferritic
or martensitic grade, such as type 409, can lead
to H2 pickup and a resultant loss of bend ductil-
ity as-annealed. Low-temperature soaks of
175 to 230 �C (350 to 450 �F) in air will outgas
embrittled ferritic alloys. There are mill specifi-
cations outlining such baking procedures.
Embrittlement has been found in oil-
quenched types 403, 410, 414, and 431. Air
quenching or the subsequent tempering of
oil-quenched material releases the entrapped
hydrogen, and ductility is restored. If a green
oxide appears on the oil-quenched alloy,
this must be removed prior to tempering or it
will interfere with the release of entrapped
hydrogen.
Fig. 5 Influence of tempering on hardness
Fig. 6 Effect of heat treatments on the hardness of
wrought martensitic stainless steels
Table 4 Dew points of selected wrought
martensitic stainless steels at various
austenitizing temperatures
Alloy
Austenitizing
temperature Dew point
�C �F �C �F
420 1010 1850 10–12 50–54
403,410, 414, 416, 431 980 1795 16–18 61–64
440C 1040 1905 2–4 36–39
Heat Treating of Martensitic Stainless Steels / 385
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Annealing
Annealing heat treatments include the following:
� Full annealing is an expensive and time-
consuming treatment; it should be used only
when required for subsequent severe form-
ing. Types 414 and 431 do not respond to
full or isothermal annealing procedures
within a reasonable soaking period.
� Isothermal annealing is recommended
where maximum softening is required and
adequate facilities for controlled slow cool-
ing are not available.
� Subcritical annealing is recommended for
all applications that do not require maximum
softness.
Full annealing, isothermal annealing, and espe-
cially repeated process annealing promote the
formation of coarse carbides that take longer
to dissolve at austenitizing temperatures. Tem-
peratures and resulting hardnesses for process
(subcritical) annealing, full annealing, and iso-
thermal annealing are given in Table 5.
Full annealing of martensitic stainless steels
depends on alloy level. If martensite cannot be
avoided by furnace cooling from austenitic
temperatures, then only subcritical annealing
is feasible. But even for nickel-free alloys the
hardenability is so great that annealing by slow
cooling is quite difficult. Martensitic alloys are
put into the annealed condition for processing
before they are quenched and tempered. Thus,
the more economic subcritical anneal is the pre-
dominant annealing heat treatment.
The nickel-bearing alloys have such high
hardenability that annealing in the critical range
cannot produce softening by any practical
cooling rate, so subcritical annealing is always
recommended for these alloys. Other additions
like vanadium, molybdenum, and tungsten pro-
mote secondary hardening and tempering resis-
tance, and subcritical annealing of these alloys
becomes a slow, difficult process. This is a char-
acteristic of the super 12Cr alloys.
Martensitic alloys have lower corrosion resis-
tance in the annealed condition than in the hard-
ened condition because in this state they have
the maximum amount of chromium tied up as
chromium carbide.
Hardening
Martensitic stainless steels are normally
hardened by being heated to the austenitizing
range of 925 to 1065 �C (1700 to 1950 �F)
and then cooled in air or oil. Martempering is
particularly easy with these steels because of
their high hardenability.
Austenitizing temperatures, soaking times,
and quenching media are summarized in
Table 6. When maximum corrosion resistance
and strength are desired, the steel should be
austenitized at the high end of the temperature
range. For alloys that are to be tempered above
565 �C (1050 �F), the low side of the austenitiz-
ing range is recommended because it enhances
Table 5 Annealing temperatures and procedures for wrought martensitic stainless steels
Type
Process (subcritical) annealing Full annealing
Isothermal annealing(c)Temperature(a)
Hardness
Temperature(b)(c)
Hardness�C �F �C �F Procedure(d) �C (�F) Hardness
403, 410 650–760 1200–1400 86–92 HRB 830–885 1525–1625 75–85 HRB Heat to 830–885 (1525–1625); hold 6h at 705 (1300) 85 HRB
414 650–730 1200–1345 99 HRB-24 HRC Not recommended Not recommended
416, 416Se 650–760 1200–1345 86–92 HRB 830–885 1525–1625 75–85 HRB Heat to 830–885 (1525–1625); hold 2 h at 720 (1330) 85 HRB
420 675–760 1245–1400 94–97 HRB 830–885 1525–1625 86–95 HRB Heat to 830–885 (1525–1625); hold 2 h at 705 (1300) 95 HRB
431 620–705 1150–1300 99 HRB-30 HRC Not recommended Not recommended
440A 675–760 1245–1400 90 HRC-22 HRC 845–900 1555–1650 94–98 HRB Heat to 845–900 (1555–1650); hold 4 h at 690 98 HRB
440B 675–760 1245–1400 98 HRB-23 HRC 845–900 1555–1650 95 HRB-20 HRC Same as 440A 20 HRC
440C, 440F 675–760 1245–1400 98 HRB-23 HRC 845–900 1555–1650 98 HRB-25 HRC Same as 440A 25 HRC
(a) Air cool from temperature; maximum softness is obtained by heating to temperature at high end of range. (b) Soak thoroughly at temperature within range indicated; furnace cool to 790 �C (1455 �F); continue cooling at
15 to 25 �C/h (27 to 45 �F/h) to 595 �C (1100 �F); air cool to room temperature. (c) Recommended for applications in which full advantage may be taken of the rapid cooling to the transformation temperature and from it to
room temperature. (d) Preheating to a temperature within the process annealing range is recommended for thin-gage parts, heavy sections, previously hardened parts, parts with extreme variations in section or with sharp reen-
trant angles, and parts that have been straightened or heavily ground or machined to avoid cracking and minimize distortion, particularly for types 420 and 431, and 440A, B, C, and F.
Table 6 Procedures for hardening and tempering wrought martensitic stainless steels to specific strength and hardness levels
Type
Austenitizing(a) Tempering temperature(d)
Tensile strength
Hardness, HRC
Temperature(b)
Quenching medium(c)
�C �F
�C �F min max min max MPa ksi
403, 410 925–1010 1700–1850 Air or oil 565 605 1050 1125 760–965 110–140 25–31
205 370 400 700 1105–1515 160–220 38–47
414 925–1050 1700–1925 Air or oil 595 650 1100 1200 760–965 110–140 25–31
230 370 450 700 1105–1515 160–220 38–49
416, 416Se 925–1010 1700–1850 Oil 565 605 1050 1125 760–965 110–140 25–31
230 370 450 700 1105–1515 160–220 35–45
420 980–1065 1800–1950 Air or oil(e) 205 370 400 700 1550–1930 225–280 48–56
431 980–1065 1800–1950 Air or oil(e) 565 605 1050 1125 860–1035 125–150 26–34
230 370 450 700 1210–1515 175–220 40–47
440A 1010–1065 1850–1950 Air or oil(e) 150 370 300 700 . . . . . . 49–57
440B 1010–1065 1850–1950 Air or oil(e) 150 370 300 700 . . . . . . 53–59
440C, 440F 1010–1065 1850–1950 Air or oil(c) . . . 160 . . . 325 . . . . . . 60 min
. . . 190 . . . 375 . . . . . . 58 min
. . . 230 . . . 450 . . . . . . 57 min
. . . 355 . . . 675 . . . . . . 52–56
(a) Preheating to a temperature within the process annealing range (see Table 5) is recommended for thin-gage parts, heavy sections, previously hardened parts, parts with extreme variations in section or with sharp reentrant
angles, and parts that have been straightened or heavily ground or machined, to avoid cracking and minimize distortion, particularly for types 420, 431, and 440A, B, C, and F. (b) Usual time at temperature ranges from 30 to
90 min. The low side of the austenitizing range is recommended for all types subsequently tempered to 25 to 31 HRC; generally, however, corrosion resistance is enhanced by quenching from the upper limit of the austenitizing
range. (c) Where air or oil is indicated, oil quenching should be used for parts more than 6.4 mm (0.25 in.) thick; martempering baths at 150 to 400 �C (300 to 750 �F) may be substituted for an oil quench. (d) Generally, the low
end of the tempering range of 150 to 370 �C (300 to 700 �F) is recommended for maximum hardness, the middle for maximum toughness, and the high end for maximum yield strength. Tempering in the range of 370 to 565 �C
(700 to 1050 �F) is not recommended because it results in low and erratic impact properties and poor resistance to corrosion and stress corrosion. (e) For minimum retained austenite and maximum dimensional stability, a
subzero treatment �75 � 10 �C (�100 � 20 �F) is recommended; this should incorporate continuous cooling from the austenitizing temperature to the cold transformation temperature.
386 / Heat Treated High-Alloy Steels
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ductility and impact properties. Austenitizing
temperature and holding time become most sig-
nificant when carbon exceeds 0.20%, the level
beyond which its solubility becomes a steep
function of temperature.
Excessive austenitizing temperatures can
cause the formation of undesirable d-ferrite, as
can low levels of carbon, which may be origi-
nally present in the alloy or arise from decarbu-
rization. It will cause lower hardness and
toughness if present. Heating rates should be
such that a uniform temperature is attained
before the bcc/fcc allotropic transformation,
which involves a more than 1% linear dimension
change and can cause distortion or cracking.
Oxidation during austenitizing can cause serious
carbon loss on the surface, which will result in
serious loss of surface hardness. Heating 410 in
air for 10 min at 1100 �C (2010 �F) can cause
surface carbon to decrease by one-half, lowering
hardness from HRC 45 to under 20.
The effect of austenitizing temperature on
the as-quenched hardness of three martensitic
grades is shown in Fig. 7. The hardness
increases with increasing austenitizing tempera-
ture to about 980 �C (1800 �F), then decreases
because of austenite retention and (occasion-
ally) the formation of d-ferrite.
Certain anomalies in these steels that should
be considered before specifying a heat-treating
procedure are exemplified in the opposing inju-
rious effects of the high and low extremes of
austenitizing temperature, depending on the
subsequent tempering temperature. Table 7
shows that the Izod impact properties of type
431 are caused by retained austenite.
Soaking times employed in the hardening of
martensitic stainless steels represent a compro-
mise between achieving maximum solution of
chromium-iron carbides for maximum strength
and corrosion resistance, and avoiding decarbu-
rization, excessive grain growth, retained aus-
tenite, brittleness, and quench cracking. For
sections 13 mm (0.5 in.) thick and under,
a soaking time of 30 to 60 min is sometimes
recommended. For most parts, adding 30 min
for each additional inch of thickness or frac-
tion thereof has proved adequate. However,
soaking times should be doubled if parts to be
hardened have been fully annealed or isother-
mally annealed.
The effect of soaking time at austenitizing
temperature and other variables, on the impact
strength and room-temperature hardness of
types 403, 420, and 431 is plotted in Fig. 8, 9,
and 10.
Fig. 7 Effect of austenitizing temperature onasquenched
hardness. Specimens were wrought martensitic
stainless steels containing 0.15% max C
Table 7 Izod impact energy of wrought
martensitic stainless steels using selected
heat treatments
Temperature
Izod impact energyAustenitizing Tempering
�C �F �C �F J ft � lbf
980 1795 315 600 20.3–33.9 15.0–25.0
1065 1950 315 600 40.7–81.3 30.0–60.0
980 1795 595 1100 74.6–108.5 55.0–80.0
1065 1950 595 1100 61.0–74.6 45.0–55.0
Fig. 8 Effect of variations in austenitizing temperature on hardness and impact strength of wrought martensitic stain-
less steels. Specimens were tempered at 480 �C (900 �F) for 4 h.
Fig. 9 Effect of variations in austenitizing time on hardness and impact strengths of wrought martensitic stainless
steels. Specimens were tempered at 480 �C (900 �F) for 4 h.
Heat Treating of Martensitic Stainless Steels / 387
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Quenching. Because of their high hardenabil-
ity, martensitic stainless steels can be quenched
in either oil or air. Some decrease in corrosion
resistanceand ductility, resulting fromair quench-
ing, may occur in these grades. These steels may
precipitate carbides in grain-boundary areas if
heavy sections are cooled slowly through the tem-
perature range of about 870 to 540 �C (1600 to
1000 �F). Too slow a cooling rate may impair
their corrosion resistance. Although oil quenching
is preferred, air cooling may be required for large
or complex sections to prevent distortion or
quench cracking.
Retained Austenite. The higher-carbon
martensitic grades, such as 440C, and the higher-
nickel type 431, are likely to retain large amounts
of untransformed austenite in the as-quenched
structure, frequently as much as 30% by volume.
Stress relieving at about 150 �C (300 �F) has little
effect. Delayed transformation, particularly in
type 440C, may occur as a result of temperature
fluctuations in service, thus resulting in embrittle-
ment and unacceptable dimensional changes.
Subzero Cooling. A portion of the austenite
retained in quenching may be transformed by
subzero cooling to about �75 �C (�100 �F)
immediately after quenching. To obtain maxi-
mum transformation of retained austenite, dou-
ble tempering may be necessary. Parts should
be air cooled to room temperature between the
tempering cycles.
Subzero cooling is frequently included in the
hardening treatment of parts such as the slides
and sleeves of slide valves, and bearings requir-
ing maximum dimensional stability.
Stress Relieving
For fully hardened steels, increasing degrees
of recovery are achieved by:
� Stress relieving at 150 to 370 �C (300
to 700 �F) after hardening to reduce trans-
formation stresses without significantly
affecting microconstituents or mechanical
properties;
� Tempering at intermediate temperatures to
modify properties;
� Subcritical annealing (variously called pro-
cess, mill, or low annealing) in the upper por-
tion of the ferritic range, just below the lower
critical Ac1 temperature, to achieve maximum
softening without the complications of reen-
tering the g or austenitic field; and
� Full annealing for maximum softening by
a return to the austenitic range, followed
by slow cooling.
If quenched martensitic steels are not im-
mediately tempered, then they should be
promptly stress relieved. Otherwise, the resid-
ual stress from quenching could result in stress
corrosion cracking even in seemingly benign
environments. Stress relieving is simply a
low-temperature tempering operation, but
some elimination of residual stress does occur.
Higher temperatures and longer times produce
greater stress relief and maximize elastic pro-
perties, but optimal toughness is obtained at
intermediate times and temperatures.
Tempering
During tempering, carbon in the supersatu-
rated state martensitic structure precipitates into
carbides. Even at low temperatures, carbon has
enough mobility to diffuse and precipitate as
carbide. Because carbon diffuses 106 times as
fast as iron, chromium, or other carbide for-
mers, it tends to precipitate with the abundant
iron atoms first. At higher temperatures and
longer times, more thermodynamically stable
carbides, such as Cr23C6, form.
Carbide formation is a complex function
of temperature, time, and composition. The
growth of carbides reduces strain and hardness.
There are exceptions, such as the precipitation
of Mo2C, whose morphology produces a pre-
cipitation hardening, or secondary hardening.
Niobium and vanadium also form carbides that
result in higher hardness at all tempering tem-
peratures. Had this fact been understood in the
early development of stainless steels, these
steels could have been correctly classified as
precipitation-hardenable (PH) stainless steels.
For example, AM-350 and AM-355 are marten-
sitic PH stainless steels that derive strength
from the precipitation of Mo2C and Mo2N. In
all other cases, higher tempering temperatures
lead to lower hardness.
The nickel-bearing alloys have a restricted
upper tempering temperature because of the
danger of re-forming austenite, which would
then transform to untempered martensite during
cooling, requiring a second tempering opera-
tion. Intermediate temperatures can lead to tem-
per embrittlement, which is caused by the
precipitation of phosphorus and other species,
including but not limited to carbides, at prior
austenitic grain boundaries. Temper embrittle-
ment is distinct from the precipitation of a’,
which causes the well-known 475 �C (890 �F)
embrittlement, which occurs more severely in
alloys with higher chromium levels (see the
article “Heat treating of Austenitic and Duplex
Stainless Steels” in this Volume).
The tempering temperatures most frequently
employed to achieve desired hardness and other
mechanical properties are given in Table 6. The
effect of tempering temperature on hardness
and tensile properties (Fig. 11-16) appears to
have the same general form as those of low-
alloy steel. A serious decrease in notch tough-
ness occurs when tempering between about
400 and 510 �C (750 and 950 �F), as illustrated
in Fig. 17 for Type 410 and Fig. 18 for other
alloys. Higher tempering temperatures result
in a drop in hardness and strength with a recov-
ery and improvement in toughness (Fig. 19-23).
Tempering on the high side of the tempera-
ture range also generally coincides with a
decrease in corrosion resistance (Figure 24).
Lower tempering temperatures and higher aus-
tenitizing temperatures are best for corrosion
resistance because both minimize the amount
of chromium tied up as carbide. Tempering of
410 and 416 stainless steels to a hardness under
40 HRC helps prevent stress corrosion cracking,
Fig. 10 Effect of variation in tempering temperature on hardness and impact strengths of wrought martensitic stain-
less steels
388 / Heat Treated High-Alloy Steels
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Fig. 14 Effect of austenitizing and tempering temperatures on typical mechanical
properties of type 420 martensitic stainless steel. Austenitized 30 min; oil
quenched to 65 to 95 �C (150 to 200 �F); double stress relieved at 175 �C (350 �F) for
15 min and water quenched; tempered 2 h. (a) Quenched from 925 �C (1700 �F).
(b) Quenched from 1025 �C (1875 �F)
Fig. 11 Effect of austenitizing and tempering temperatures on mechanical properties
of type 410 martensitic stainless steel. Austenitized 30 min; oil quenched to
65 to 95 �C (150 to 200 �F); double stress relieved at 175 �C (350 �F) for 15 rain and
water quenched; tempered 2 h. (a) Quenched from 925 �C (1700 �F). (b) Quenched
from 1010 �C (1050 �F)
Fig. 12 Effect of austenitizing and tempering temperatures on typical mechanical
properties of type 414 martensitic stainless steel. Austenitized 30 min; oil
quenched to 65 to 95 �C (150 to 200 �F); double stress relieved at 175 �C (350 �F) for
15 min and water quenched; tempered 2 h. (a) Quenched from 925 �C (1700 �F).
(b) Quenched from 1040 �C (1900 �F)
Fig. 13 Effect of austenitizing and tempering temperatures on typical mechanical
properties of type 416 martensitic stainless steel. Austenitized 30 min; oil
quenched to 65 to 95 �C (150 to 200 �F); double stress relieved at 175 �C (350 �F) for
15 min and water quenched; tempered 2 h. (a) Quenched from 925 �C (1700 �F).
(b) Quenched from 980 �C (1800 �F)
Heat Treating of Martensitic Stainless Steels / 389
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but it also results in a severe loss of corrosion pro-
tection. When a high tempering temperature is
used to get a hardness of 35–40 HRC in 410, cor-
rosion resistance could decrease by a factor of
50-fold due to this treatment. A much better
option for restricting the maximum hardness to
40 HRC was to either:
1. Restrict the maximum carbon to a lower
value (0.10 max) with the normal hardening
treatment and a 200 �C (400 �F) temper or;
2. Under-harden the steel in the range of
845–900 �C (1550–1650�F) with a final
temper at 200 �C (400 �F).
The latter treatment does not change the corro-
sion loss numbers.
The existence of temper embrittlement is the
reason to avoid certain temperature ranges for
tempering, as indicated in Table 6. Temper
embrittlement occurs as a consequence of the
tendency of impurities to congregate in grain
boundaries during austenitizing. Austenite has
low solubility for impurities such as phospho-
rous, so phosphorous is more highly concen-
trated in the grain boundary regions, and after
quenching, the austenite boundaries still main-
tain the micro-compositions that they had at
high temperatures. The resulting compositional
inhomogeneity leads to temper embrittlement.
It can be eliminated by higher tempering tem-
peratures or by the addition of molybdenum,
which combines with the phosphorus and pre-
vents the embrittlement.
Tempering within the range of 370 to
650 �C (700 to 1200 �F) also can result in
decreased resistance to stress-corrosion crack-
ing (Fig. 25). Double tempering (cooling parts
to room temperature after the first tempering
treatment) also is beneficial for resistance to
stress corrosion.
Fig. 15 Effect of austenitizing and tempering temperatures on typical mechanical
properties of type 431 martensitic stainless steel. Austenitized 30 min; oil
quenched to 65 to 95 �C (150 to 200 �F); double stress relieved at 175 �C (350 �F) for
15 min and water quenched; tempered 2 h. (a) Quenched from 925 �C (1700 �F).
(b) Quenched from 1040 �C (1900 �F)
Fig. 16 Effect of austenitizing and tempering temperatures on typical mechanical
properties of type 440C martensitic stainless steel. Austenitized 1 h at
925 �C (1700 �F) and 2 h at 1040 �C (1900 �F); oil quenched to 65 to 95 �C (150 to
200 �F); double stress relieved at 175 �C (350 �F) for 15 min and water quenched; tem-
pered 2 h. (a) Quenched from 925 �C (1700 �F). (b) Quenched from 1040 �C (1900 �F)
Fig. 17 AISI Type 410: Effect of tempering temperature on impact properties. Impact energy tests used Izod, Charpy
V-notch, or Charpy keyhole as indicated. Heat treatment of test specimens: heated to and held at 955 �C
(1750 �F) for 1 h; oil quenched, tempered for 4 h at temperature given; air cooled
390 / Heat Treated High-Alloy Steels
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Fig. 18 Effect of austenitizing and tempering temperatures on impact toughness of martensitic stainless steels (a) type 410 (b) type 414 (c) of type 416 (d) type 420 (e) type 420
(f) type 431 (g) type 440C. After austenitizing as indicated, steels were oil quenched to 65 to 95 �C (150 to 200 �F); double stress relieved at 175 �C (350 �F) for 15 min and
water quenched; tempered for two hours at indicated temperatures
Fig. 19 AISI Type 403: Effect of tempering temperature on tensile properties. Heat treated at 980 �C (1800 �F); oil quenched; tempered for 3 h at temperature given. Test speci-
mens were heat treated in 25 mm (1 in.) round; tensile specimens were 13 mm (0.51 in.) diam; Izod notched specimens were 10 mm (0.394 in.) square. Tests were con-
ducted using specimens machined to English units. Impact energy test used Izod specimens. Elongation was measured in 50 mm (2 in.); yield strength at 0.2% offset
Heat Treating of Martensitic Stainless Steels / 391
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Casting Alloys
Compositions of ACI designated martensitic
casting alloys are listed in Table 8. Casting
stresses in the martensitic castings noted above
should be relieved by subcritical annealing
prior to further heat treatment. When these
hardened martensitic castings are stress
relieved, the stress-relieving temperature must
be kept below the final tempering or aging
temperature. It is also frequently necessary
to homogenize some alloys at temperatures
above 1095 �C (2000 �F) in order to pro-
mote uniformity of chemical composition and
microstructure. Full annealing ofmartensitic cast-
ings results in recrystallization and maximum
softness, but it is less effective than homogeniza-
tion in eliminating segregation. Homogenization
is a common procedure in the heat treatment of
precipitation-hardening castings.
The heat treatment of stainless steel castings
follows closely in purpose and procedure the
thermal processing of comparable wrought
materials, though with some variations. The
standard heat-treating procedures for CA-15,
CA-40, and CA-6NM are given in Table 9. In
the hardened and tempered condition, CA-40
provides higher tensile strength and lower duc-
tility than CA-15 tempered at the same temper-
ature. Both alloys can be annealed by cooling
slowly from the range 845 to 900 �C (1550 to
1650 �F). Alloy CA-6NM (UNS J91540) is an
improved, cast martensitic alloy with better
casting behavior, improved weldability, and
mechanical, corrosion, and cavitation resistance
properties that equal or exceed properties of
CA-15. As a result, it has largely replaced the
older alloy.
Both CA-6NM and CA-15 castings are usu-
ally supplied in the normalized condition at
Fig. 20 AISI Type 410: Effect of tempering temperature on tensile properties. Heated to and held at 980 �C (1800 �F)
for 30 min; oil quenched; tempered 1 to 4 h. Impact energy test used Izod specimens. Elongation was
measured in 50 mm (2 in.); yield at 0.2% offset
Fig. 21 AISI Type 414: Effect of tempering temperature on tensile properties. Impact energy test used Izod specimens. Elongation was measured in 50 mm (2 in.); yield at 0.2%
offset
392 / Heat Treated High-Alloy Steels
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955 �C (1750 �F) minimum and tempered at
595 �C (1100 �F) minimum. However, when it
is necessary or desirable to anneal CA-6NM
castings, a temperature of 790 to 815 �C
(1450 to 1500 �F) should be used. The alloy
should be furnace-cooled or otherwise slow-
cooled to 595 �C (1100 �F), after which it
may be cooled in air. When stress relieving is
required, CA-6NM may be heated to 620 �C
(1150 �F) maximum and followed by slow
cooling to prevent the formation of martensite.
Castings of the CA-6NM composition should
be hardened by air cooling or oil quenching
from a temperature of 1010 to 1065 �C (1850
to 1950 �F). Even though the carbon content
of this alloy is lower than that of CA-15, this
fact in itself and the addition of molybdenum
and nickel enable the alloy to harden completely
without significant austenite retention when cooled
as suggested.
The choice of cooling medium is determined
primarily by the maximum section size. Section
sizes in excess of 125 mm (5 in.) will harden
completely when cooled in air. CA-6NM is
not prone to cracking during cooling from ele-
vated temperatures. For this reason, no problem
should arise in the air cooling or oil quenching
of configurations that include thick as well as
thin sections.
A wide choice of mechanical properties is
available through the choice of tempering tem-
perature. Castings of CA-6NM are normally sup-
plied normalized and tempered at 595 to 620 �C
(1100 to 1150 �F). Reaustenitizing occurs upon
tempering above 620 �C (1150 �F), the amount
of reaustenitization increasing with increasing
temperature. Depending on the amount of this
transformation, cooling from such tempering
temperatures may adversely affect both ductility
Fig. 22 AISI Type 420: Effect of tempering temperature on tensile properties. Heated
to 1010 �C (1850 �F); oil quenched; tempered at temperature indicated for 5
h. Heat treated as 25 mm (1 in.) diam. rod; tensile test specimens were 12.8 mm (0.505
in.) diam; Izod impact test specimens were 10 mm (0.394 in.) square. Tests were con-
ducted using specimens machined to English units. Elongation was measured in
50 mm (2 in.); yield strength at 0.2% offset
Fig. 23 AISI Type 431: Effect of tempering temperature ontensile properties. Heated to
1040 �C (1900 �F); oil quenched; tempered for 3 h at temperature given. Speci-
mens were heat treated as 25 mm (1 in.) round; tensile test specimens were 12.8 mm
(0.505 in.) diam; Izod notched impact test specimens were 10 mm (0.394 in.) square. Tests
were conducted using specimens machined to English units. Impact energy test used Izod
specimens. Elongation was measured in 50 mm (2 in.); yield strength at 0.2% offset
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and toughness through the transformation to
untempered martensite.
Even though the alloy is characterized by a
decrease in impact strength when tempered in
the range of 370 to 595 �C (700 to 1100 �F),
the minimum reached is significantly higher
than that of CA-15. This improvement in
impact toughness results from the presence of
molybdenum and nickel in the composition
1400
1200
1000
800
600
400
200
0
As
Quenched
Hardness, HRC
C41.5 C41 C40 C40 C40 C40 C41 C40 C36 C30 C23 C20 C17
400 500 600 700 800
Tempering temperature, ºF
Corrosion weight loss, g
W
e
ig
h
t 
lo
s
s
, 
g
T
e
m
p
e
ri
n
g
te
m
p
e
ra
tu
re
, 
ºF
900 950 1000 1050 1100 1200 1300
5
3
1
0.4
0
0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.3 3.7 6.1 5.2 0.5 0.3
/1962 
Fig. 24 Effect of tempering temperature on the corrosion resistance of a martensitic stainless steel (0.10 C and 12.50 %
Cr). Heat treatment conditions: austenitized at 955 �C (1750 �F), oil quenched, and tempered 1 h in air.
Corrosion test: Specimens with dimensions of 20 x 50 mm (0.75 x 2 in.) were submerged in 10 % acetic acid for 15 hours
Fig. 25 Effect of tempering temperature on the stress-
corrosion characteristics of two wrought mar-
tensitic stainless steels at high stress. Data apply to a stress
level of 350 MPa (80 ksi) for tests in a salt fog cabinet
Table 8 Compositions and typical microstructures of Alloy Casting Institute (ACI) corrosion-resistant cast steels
ACI type
UNS
No.
Wrought
alloy
type(a) ASTM specifications
Most common end-use
microstructure
Composition(b), %
C Mn Si Cr Ni Others(c)
Chromium steels
CA-15 J91150 410 A 743, A 217, A 487 Martensite 0.15 1.00 1.50 11.5–14.0 1.0 0.50 Mo(d)
CA-15M J91151 � � � A 743 Martensite 0.15 1.00 0.65 11.5–14.0 1.0 0.15–1.00 Mo
CA-40 J91153 420 A 743 Martensite 0.40 1.00 1.50 11.5–14.0 1.0 0.5 Mo(d)
CA-40F � � � � � � A 743 Martensite 0.2–0.4 1.00 1.50 11.5–14.0 1.0 � � �
Chromium-nickel steels
CA-6N J91650 � � � A 743 Martensite 0.06 0.50 1.00 10.5–12.5 6.0–8.0 � � �
CA-6NM J91540 � � � A 743, A 487 Martensite 0.06 1.00 1.00 11.5–14.0 3.5–4.5 0.4–1.0 Mo
CA-28MWV � � � � � � A 743 Martensite 0.20–0.28 0.50–1.00 1.00 11.0–12.5 0.50–1.00 0.9–1.25 Mo; 0.9–1.25 W; 0.2–0.3 V
CB-7Cu-1 J92180 � � � A 747 Martensite, age hardenable 0.07 0.70 1.00 15.5–17.7 3.6–4.6 2.5–3.2 Cu; 0.20–0.35 Nb; 0.05 N max
CB-7Cu-2 J92110 � � � A 747 Martensite, age hardenable 0.07 0.70 1.00 14.0–15.5 4.5–5.5 2.5–3.2 Cu; 0.20–0.35 Nb; 0.05 N max
(a) Type numbers of wrought alloys are listed only for nominal identification of corresponding wrought and cast grades. Composition ranges of cast alloys are not the same as for corresponding wrought alloys; cast alloy
designations should be used for castings only. (b) Maximum unless a range is given. The balance of all compositions is iron. (c) Sulfur content is 0.04% in all grades except: CG-6MMN, 0.030% S (max); CF-10SMnN,
0.03% S (max); CT-15C, 0.03% S (max); CK-3MCuN, 0.010% S (max); CN-3M, 0.030% S (max); CA-6N, 0.020% S (max); CA-28MWV, 0.030% S (max); CA-40F, 0.20–0.40% S; CB-7Cu-1 and -2, 0.03% S (max). Phos-
phorus content is 0.04% (max) in all grades except: CF-16F, 0.17% P (max); CF-10SMnN, 0.060% P (max); CT-15C, 0.030% P (max); CK-3MCuN, 0.045% P (max); CN-3M, 0.030% P (max); CA-6N, 0.020% P (max); CA-
28MWV, 0.030% P (max); CB-7Cu-1 and -2, 0.035% P (max). (d) Molybdenum not intentionally added. (e) CF-3A, CF-3MA, and CF-8A have the same composition ranges as CF-3, CF-3M, and CF-8, respectively, but have
balanced compositions so that ferrite contents are at levels that permit higher mechanical property specifications than those for related grades. They are covered by ASTM A 351. (f) Nb, 8 � %C min (1.0% max); or Nb + Ta �
%C (1.1% max). (g) For CN-7MS, silicon ranges from 2.50 to 3.50%.
Table 9 Heat treatment of martensitic stainless steel castings
Alloy
Annealing temperature(a)
Hardening treatment
Typical ultimate tensilestrength(c)Austenitizing temperature(b) Tempering temperature
�C �F �C �F �C �F MPa ksi
CA-15 845–900 1550–1650 � � � � � � � � � � � � 550 80
� � � � � � 925–1010(d) 1700–1850(d) 370 max(e) 700 max(e) 1380 200
� � � � � � 925–1010(d) 1700–1850(d) 595–760 1100–1400 690–930 100–135
CA-40 845–900 1550–1650 � � � � � � � � � � � � 620 90
� � � � � � 980–1010 1800–1850 315 max(e) 600 max(e) 1515 220
� � � � � � 980–1010 1800–1850 595 1100 1035 150
� � � � � � 980–1010 1800–1850 650 1200 965 140
� � � � � � 980–1010 1800–1850 760 1400 760 110
CA-6NM 790–815 1450–1500 � � � � � � � � � � � � 550 80
� � � � � � 950–980 1750–1800 595–620 1100–1150 830 120
(a) Annealing for maximum softness; slow furnace cool from temperature. (b) Quench in oil or air. (c) Approximate. (d) Hold at temperature for a minimum of 30 min. (e) Tempering at 370 to 595 �C (700 to 1100 �F) is not
recommended because low-impact ductility results.
394 / Heat Treated High-Alloy Steels
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and from the lower carbon content. The best
combination of strength with toughness is
obtained when the alloy is tempered above
510 �C (950 �F).
Figure 26 describes the effect of tempering
temperature on the hardness, strength, ductility,
and toughness properties of CA-6NM and illus-
trates that strengths even higher than those con-
sidered typical can be obtained by tempering at
lower temperatures without a disturbing loss of
ductility or toughness.
The minor loss of toughness and ductility
that does occur is associated with the lesser
degree of tempering that takes place at the
lower temperature and not with embrittlement,
as might be the case with other 12% Cr steels
that contain no molybdenum. The addition of
molybdenum to 12% Cr steels makes them
unusually stable thermally and normally not
susceptible to embrittlement in the annealed
or annealed-and-cold-worked conditions, even
when exposed for long periods to temperatures
of 370 to 480 �C (700 to 900 �F). There are no
data currently available on such steels in the
quenched-and-tempered or normalized-and-
tempered conditions.
Another significant practical advantage of
CA-6NM is its relative freedom from the rapid
drop in hardness when tempered above about
510 �C (950 �F). Figure 27 shows clearly that
a given increase in tempering temperature
produces a much more gradual decrease in
hardness than with CA-15. This makes heat
treating much easier and cheaper and decreases
the frequency of rejections and/or the necessity
for reheat treatment.
The hardening procedures for CA-15 castings
are similar to those used for the comparable
wrought alloy (type 410). Austenitizing consists
of heating to 955 to 1010 �C (1750 to 1850 �F)
and soaking for a minimum of 30 min; the high
side of this temperature range is normally
Fig. 26 Effect of tempering temperature on the mechanical properties of a CA-6NM standard keel block. Courtesy of
ESCO Corporation
Fig. 27 Effect of tempering temperature on the hardness
of CA-6NM and CA-15. Courtesy of ESCO
Corporation
Table 10 Effects of four methods of heat treatment on typical mechanical properties of
cast CA-15. Specimens were taken from shell mold cast keel blocks; data indicate results
obtained on four specimens treated by each method
Heat treatment(a)
Ultimate tensile
strength Yield strength
Elongation in
50 mm (2 in.), %
Reductionin area, %MPa ksi MPa ksi
Treatment 1 1230 178 1005 146 9.0 13.0
Homogenize: 1 h at 1040 �C (1900 �F), AC 1250 181 970 141 12.5 28.0
Solution anneal: 30 min. at 955 �C (1750 �F), OQ 1275 185 985 143 7.0 14.0
Temper: 3 h at 300 �C (575 �F), AC 1315 191 1020 148 8.0 12.5
Treatment 2 1260 183 1115 162 6.5 9.5
Anneal: 1 h at 900 �C (1650 �F), FC 1296 188 1130 164 5.5 16.0
Solution anneal: 75 min at 1010 �C (1850 �F), OQ 1340 194 1070 155 9.0 23.0
Temper: 3 h at 370 �C (700 �F), OQ 1380 200 1050 152 12.0 42.0
Treatment 3(b) 795 115 485 70 15.5 60.0
Anneal: 1 h at 900 �C (1650 �F), FC 810 117 630 91 16.5 37.0
Solution anneal: 75 min at 1010 �C (1850 �F), OQ 830 120 680 98 9.5 23.0
Temper: 2 h at 620 �C (1150 �F), AC 860 125 585 85 12.5 32.0
Treatment 4(c) 685 99 525 76 21.0 65.0
Anneal: 1 h at 900 �C (1650 �F), FC 710 103 545 79 20.5 56.0
Solution anneal: 90 min at 995 �C (1825 �F), FAC 710 103 545 79 18.5 61.5
Temper: 2 h at 705 �C (1300 �F), AC 720 104 550 80 20.5 60.0
(a) Each treatment comprised three processes as listed. AC, air cool; OQ, oil quench; FC, furnace cool; FAC, forced-air cool. (b) AMS 5351-B.
(c) MIL-S-16993
Fig. 28 Effect of tempering temperature on typical
room-temperature mechanical properties of
CA-15 castings
Heat Treating of Martensitic Stainless Steels / 395
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employed. Parts are then cooled in air or
quenched in oil. To reduce the probability of
cracking in the brittle, untempered martensitic
condition, tempering should take place immedi-
ately after quenching.
Tempering is performed in two temperature
ranges: up to 370 �C (700 �F) for maximum
strength and corrosion resistance, and from
595 to 760 �C (1100 to 1400 �F) for improved
ductility at lower strength levels. Tempering
in the range of 370 to 595 �C (700 to 1100 �F)
is normally avoided because of the resultant
low impact strength. Figure 28 shows the nominal
mechanical properties obtained in CA-15 cast-
ings as a function of tempering temperature.
Additional data on mechanical properties are
given in Table 10. These data are based on sev-
eral heats of shellcast CA-15 alloy.
ACKNOWLEDGMENT
The information in this article is revised from
J. Douthett, Heat Treating of Stainless Steels,
Heat Treating, Vol 4, ASM Handbook, ASM
International, 1991, p 769–792, with adapted
material from M.F. McGuire, Stainless Steels for
Design Engineers, ASM International, 2008.
REFERENCES
1. M.F. McGuire, Stainless Steels for Design
Engineers, ASM International, 2008
2. Bletton, Aciers Inoxidables, Les Editions de
Physique les Ulis, Paris, 1993, p 481
3. K.J. Irvine et al, JISI, Vol. 195, ISIJ Interna-
tional, 1960, p 386–405
396 / Heat Treated High-Alloy Steels
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