Com pany Expects Improved Earnings in Postwar Era
AISI STAINLESS STEEL TYPES
Fig. 2— Hardness ranges of the Group I hardenable grades of stainless Steel
Fig. 3— Effect of carbon and chromium on the “as quenched” hardness of stainless Types 410, 403, and 416 Fig. 4— Effect of initial hardening temperature on tire properties of Type 410 stainless which is stress relieved
after hardening
HARDENED
ROCKWELL “C” HARDNESS
BRIN ELL HARDNESS
ÜITIMATE T EN S IL E STR
1% YIELD STRENGTH
■SAMPLES S T R E S S RELIEVED A FTER HARDENING
■500” F - 2 H R S .-A IR COOL—
% ELONGATION IN 2
IZOD IMPACT STR
1600 1700 1800 1300 2000
I N I T I A L HARDENING T E M P E R A T U R E 'P.
31 MINUTES-OIL QUENCH H A R D E N I N G T E M P E R A T U R E * F .
Fig. 5— Effect of hardening temperature on hardness of Types 410, 403 and 416
IN ■ heat treating stainless steels, the general methods do not differ from those used with other steels. No special equip
ment is needed. Anyone with heat treat
ing experience can handle stainless steel successfully. However, to attain full ad
vantage of the excellent corrosion re
sisting and mechanical properties of stainless steels, proper attention should be paid to certain heat treating vari
ables. These should be followed faith
fully if the valuable properties of stain
less steel are to be developed to their full extent.
Stainless steels are available in a wide variety of chemical compositions. Each is designed to meet certain industrial requirem ents of corrosion and oxidation resistance as well as to provide an
ex-A ll m aterial in the accompanying article is from a copyrighted booklet published by the Rustless Iron & Steel Corp., Baltimore, and full reprint rights are retained.
200 175
Fig. 1— (A ) Straight chromium stainless steals may be flame-hardened readily as indicated by this typical setup; (B ) these stainless steel parts have been bright hardened in a controlled atmosphere furnace; (C ) typical high tem perature electric furnace setup, w ith gas generator, for hardening and an
nealing stainless; ( D ) salt bath furnaces provide excellent results in harden
ing stainless. Induction heating, not illustrated, also works well tensive range of mechanical properties.
From extreme softness to high hardness obtained by heat treatm ent or cold work
ing, stainless steels are remarkably ver
satile.
H eat Treating Equipment: H eat treat
ment of stainless steels may be carried out with any conventional type of electric, gas-fired, oil-fired, salt bath, or induction furnace, typ
ical installations being shown in Figs.
1 A, B, C and D. Because of the rela
tively high temperatures employed in hardening and annealing certain grades, care in furnace operation is required, especially with equipm ent not specifical
ly designed for high tem perature work.
W here electric, gas, and oil-fired equip
ment is employed, the usual precautions should be employed in loading the fur
nace to insure uniform heating. In gas and oil-fired furnaces the design should be such that the material is not exposed to the direct flame from the burners, to avoid decarburization. Although some latitude in temperature control is possi
ble in hardening or annealing these al
loys, the best results are always secured when proper precautions are taken to control temperatures accurately. This is particularly true in tempering the hard- enable stainless steels to narrow ranges of hardness and tensile properties w here the use of properly located
thermo-April 16, 1945 113
"Analysis for Rustless Iron & Steel Corp.— G rade 13-C-35; U sual Range 0 .3 5 /0 .4 5 .
Recommended Ranges for Stress-Relieving Group I Stainless Steels
1 lardncss
-AISI Type Tem perature Time in Hours Brinell Rockwell
4 1 0 ,4 0 3 , 4 1 6 ... 4 5 0 °-7 0 0 ° F. 1 - 3 360-380 C37-40
Average Results of Stress-Relieving Group I Stainless Steels
HARDNESS RANGE
Tens. Str. Yld. Str. Elong. Area Range P.S.I. P.S.I. in 2" % F t. Lbs. of Group I hardened stainless steels (A ) T ype 410, (B ) T ype 431, (C ) Type 420 and (D ) Type
440C. Magnification X500 couples and other standard pyrometric equipment is highly desirable to deter
mine temperatures accurately. both internally and externally heated, which are well suited for this work.
Salts should be chosen which do not contain materials which will introduce carbon or nitrogen into the surface of the work. Chemically neutral salts should be selected and new salts should be checked before they are used in pro
duction. Common salts employed in high temperature salt baths include chlo
rides of barium, sodium, calcium, and potassium. Sodium and potassium ni
trates are used for lower temperatures.
In no case is the use of any type of cyanide recommended, since carburiza- tion or nitriding of the surface of stain been successfully accomplished. Sec
tions can be hardened throughout the entire cross-section, or, by adjustment of conditions, a hard surface and mod annealing and hardening the stainless steels. Techniques are similar to those
Furnace Atmospheres: Although all stainless steels are highly resistant to oxidation, they may be expected to scale slightly at high heat treating tempera
tures. They will show no evidence of
TABLE VI
Average Results of Tem pering Fully H ardened Stainless Steel --- Average Mechanical
Properties-Izod
Ult. 2% % Red. of Im pact
AISI ---Hardness Range--- Tens. Str. Yld. Str. Elong. Area Range
Type Brinell Rockwell P.S.I. P.S.I. in 2" % F t. Lbs.
1000° F. (4 hours)
403-410 260-330 C 25-34 145,000 115,000 20 65 35-70
416 260-330 C 25-34 145,000 115,000 16 53 10-30
431 270-340 C 26-35 150,000 115,000 19 58 35-70
1100° F. (4 hours)
403-410 210-250 B 95-100 115,000 90,000 22 65 65-90
416 210-250 11 95-100 115,000 90,000 ' 18 53 20-35
414 250-290 B 100-29 135,000 110,000 20 60 25-40
431 245-285 B 99-C 29 130,000 100,000 20 58 45-80
1200° F. (4 hours)
403-410 200-230 • B 93-97 105,000 85,000 23 67 85-110
416 2 00-230 B 93-97 105,000 85,000 19 55 30-45
414 245-265 B 99-C 26 125,000 100,000 21 60 30-60
431 230-260 B 99-C 24 120,000 95,000 21 60 55-80
1300° F. (4 hours)
403-410 195-220 B 92-96 100,000 80,000 25 69 90-110
416 195-220 B 92-96 100,000 80,000 21 57 35-60
414 240-255 B 99-C 24 120,000 95,000 21 65 55-80
1400° F. (4 hours)
403-410 170-195 B 86-92 90,000 60,000 30 72 95-115
416 170-195 B 86-92 90,000 60,000 26 60 50-70
Type
440
TABLE VII
Annealing the H ardenable Stainless Steel Grades Process Annealing Procedure
---
Hardness---T em perature Time in Hours Cooling Brinell Rockwell
1 350-1450° F. 1 - 3 Any 170-195 B86-92
403 135-160 B 75-83 78,000 40,000 35
410 B 75-83
416 135-160 B 81-89 78,000 40,000 31
420 155-180 B 91-95 98,000 60,000 28
440A 190-215 B 95-99 105,000 65,000 23
440C 215-240 B 86-92 110,000 60,000 15
73
403 170-195 B 86-92 90,000 60,000 30 72 95-115
410
416 170-195 B 86-92 90,000 60,000 26 60 50-70
414 240-255 B 99-C 23 120,000 95,000 21 65 55-80
431 230-260 B 97-C 24 120,000 95,000 21 60 55-80
420 205-225 B 94-B 97 105,000 80,000 23 55 45-75
440A 230-245 B 97-C 22 115,000 85,000 21 50 15-30
'4 0 C 240-255 C 22-C 27 125,000 100,000 12 25 5-20
b m nos isao m o isss
IIITHI HUDEXIKG TINrCIHOtt *f.
U MIHUirX-Olt QUIHCH increases in thickness as the temperature is raised. M anufactured atmospheres, prepared from partially burned or other
wise treated fuels which are used to pre
vent or minimize the scaling of plain car
bon and low alloy steels generally will not give satisfactory results with stainless steels. They may produce a scale which is difficult to remove. W hen completely scale-free heat treatm ent is essential, spe
cially prepared atmospheres of dry cracked ammonia or dry hydrogen are used. Suitable gas-tight furnaces and equipm ent for generation of such at
mospheres are available commercially and have been demonstrated to give ex least affected. Experience shows good results are secured if definitely oxidiz
ing atmospheres are employed. Scale produced in such an atmosphere is most readily removed by pickling. Reducing atmospheres cause the formation of a thinner but much more impervious scale, which is often highly resistant to pick
ling.
It is a good practice to avoid car- burizing conditions, which often char
acterize reducing atmospheres. Nor should parts be packed in material which will introduce carbon into the surface.
Charcoal, coal and coke dust, boneblack, cast iron turnings and similar material will carburize stainless at heat treating temperatures and will result in serious the chromium-nickel steels with zinc or April 16, 1945
115
co 60
zinc-containing alloys should be care
fully avoided. Zinc rapidly penetrates along the grain boundaries of these steels at annealing temperatures and results in embrittlement.
Decarburization of the straight chro
mium steels may occur, usually, how tenitic chromium-nickel steels are unaf
fected.
Three Basic Groups: The stainless steels, based on their chemical composi
tions and response to heat treatment, fall naturally into three groups: (1) Straight chromium, hardenable grades; (2) straight chromium, nonhardenable grades; and (3) chromium-nickel, nonhardenable grades.
Group I, the straight chromium, hard
enable grades (martensitic), includes those grades which have chromium as their
They are magnetic. Because, when hard
ened, their crystalline structure is com
posed primarily of the microconstituent, martensite, they are commonly referred to as the “martensitic” stainless steels.
The chemical analysis of this group is given in Table I.
Chart shown in Fig. 2 illustrates the extent to which each of the hardenable grades listed in Table I responds to vari
ous recommended heat treatments. To meet a specific hardness requirem ent of a given application, a grade may be chosen in which the hardened and stress- relieved condition will provide the re
quired range of hardness. Tempering ot
Hardening: The term “hardenability,”
in the sense that it refers to the depth and distribution of hardening, has rela
tively little significance with the stain
less steels. This is because all harden
able stainless steels harden uniformly throughout, even in large sections, when rapidly cooled from above the critical tem perature. Degree to which straight chromium Group I stainless steels hard
en is referred to as the “as quenched,”
“full” or “maximum” hardness.
Hardening of these alloys is accom
plished by heating above the critical or transformation tem perature and then rapidly cooling in oil or air. By proper selection of grades and analysis of wide range of “as quenched” hardness is avail
able depending primarily on carbon and chromium contents. As an illustration cf this, Fig. 3 shows the effect of these
maximum quenched hardness desired.
Preheating: Preheating of Types 410, 403, 416 and 431 is generally unneces may cause thermal stresses sufficient to crack the material. Preheating the high carbon grades is recommended as a general rule because of their high carbon contents. Large sections should be started off at 1000 degrees Fahr.
and then raised slowly to 1450 degrees Fahr. Small sections may be brought immediately to 1450 degrees Fahr. The time at preheating temperatures should always be long enough to insure that the parts are soaked through, and in the case of high carbon grades may be extended up to 1 to 2 hours with advan
tage. After preheating, parts may be raised quickly to hardening temperature.
Hardening Tem perature: W hile hard
ening of these grades results whenever they are rapidly cooled from above the lower critical tem perature, maximum hardness is not secured until the hard
ening tem perature is raised several hun
dred degrees above this point. As might be expected, parts quenched from in
termediate tem peratures (1475 to 1700 degrees Fahr.) will develop hardnesses ranging from that of annealed «material up to that of fully hardened material depending on the quenching tem pera
ture, as illustrated i n , the chart in Fig.
5. Hardening from this range results in a heterogeneous microstructure which is generally less tough than w hen fully hardened.
W hen stress-relieving cr tempering Fig. 8— Effect nf stress-relieving temperature on hardness
and toughness of T ype 420
Fig. 9— Effect of stress-relieving temperature on hardness and toughness of T ype 440A
6 0 0 80 0 T E M P E R A T U R E ° F ( 2 H R . )
U 6 I
T E E L
1s t D R A W