Instructions / Assembly

46
www.lincolnelectric.com
GMAW
Precipitation Hardening Stainless Steels
There are three categories of precipitation hardening stainless
steels – martensitic, semiaustenitic and austenitic.
The martensitic stainless steels can be hardened by quenching
from the austenitizing temperature [around 1900°F (1038°C)]
then aging between 900 - 1150°F (482 - 621°C). Since these
s
teels contain less than 0.07% carbon, the martensite is not very
hard and the main hardening is obtained from the aging
(precipitation) reaction. Examples of this group are 17-4PH,
15-5PH and PH13-8Mo. Nominal compositions of precipitation
h
ardening stainless steels are listed in Table 10.
The semiaustenitic stainless steels will not transform to
m
artensite when cooled from the austenitizing temperature
because the martensite transformation temperature is below
room temperature. These steels must be given a conditioning
treatment which consists of heating in the range of 1350 to
1750°F (732 to 954°C) to precipitate carbon and/or alloy ele-
ments as carbides or intermetallic compounds. This removes
alloy elements from solution, thereby destabilizing the austenite,
which raises the martensite transformation temperature so that a
martensite structure will be obtained on cooling to room
temperature. Aging the steel between 850 - 1100°F (454 - 593°C)
will stress relieve and temper the martensite to increase tough-
ness, ductility, hardness and corrosion resistance. Examples of
this group are 17-7PH, PH 15-7 Mo and AM 350.
The austenitic precipitation hardening stainless steels remain
a
ustenitic after quenching from the solutioning temperature even
after substantial amounts of cold work. They are hardened only
by the aging reaction. This would include solution treating
between 1800 and 2050°F (982 to 1121°C), oil or water
q
uenching and aging at 1300 to 1350°F (704 to 732°C) for up to
2
4 hours. Examples of these steels include A286 and 17-10P.
I
f maximum strength is required in martensitic and semi-
austenitic precipitation hardening stainless steels, matching or
nearly matching filler metal should be used and the component,
before welding, should be in the annealed or solution annealed
c
ondition. Often, Type 630 filler metal, which is nearly identical
w
ith 17-4PH base metal, is used for martensitic and semi-
austenitic PH stainlesses. After welding, a complete solution
heat treatment plus an aging treatment is preferred. If the post
weld solution treatment is not feasible, the components should
be solution treated before welding then aged after welding.
Thick sections of highly restrained parts are sometimes welded
in the overaged condition. These would require a full heat
treatment after welding to attain maximum strength.
The austenitic precipitation hardening stainless steels are the
most difficult to weld because of hot cracking. Welding should
preferably be done with the parts in the solution treated
condition, under minimum restraint and with minimum heat
input. Nickel base alloy filler metals of the NiCrFe type or
conventional austenitic stainless steel type are often preferred.
UNS Composition - Percent *
Type Number C Mn Si Cr Ni P S Other
Precipitation-Hardening Types
PH 13-8 Mo S13800 0.05 0.10 0.10 12.25-13.25 7.5-8.5 0.01 0.008 2.0-2.5 Mo;
0.90-1.35 Al; 0.01 N
15-5 PH S15500 0.07 1.00 1.00 14.0-15.5 3.5-5.5 0.04 0.03 2.5-4.5 Cu;
0.15-0.45
Nb(Cb)
+ Ta
17-4 PH S17400 0.07 1.00 1.00 15.5-17.5 3.0-5.0 0.04 0.03 630 3.0-5.0 Cu;
0.15-0.45
Nb(Cb)
+ Ta
17-7 PH S17700 0.09 1.00 1.00 16.0-18.0 6.5-7.75 0.04 0.03 631 0.75-1.15 Al
PH 15-7 Mo
S15700
0.09
1.00 1.00 14.0-16.0 6.5-7.75 0.04 0.03 2.0-3.0 Mo; 0.75-1.5 Al
17-10 P 0.07 0.75 0.50 17.0 10.5 0.28
A286 S66286 0.08 2.00 1.00 13.5-16.0 24.0-27.0 0.040 0.030 660 1.0-1.5 Mo; 2 Ti; 0.3 V
AM350
S35000
0.07-0.11
0.5-1.25 0.50 16.0-17.0 4.0-5.0 0.04 0.03 2.5-3.25 Mo; 0.07-0.13 N
AM355 S35500 0.10-0.15 0.5-1.25 0.50 15.0-16.0 4.0-5.0 0.04 0.03 2.5-3.25 Mo
AM363 0.04 0.15 0.05 11.0 4.0 0.25 Ti
Custom 450
S45000
0.05 1.00 1.00 14.0-16.0 5.0-7.0 0.03 0.03 1.25-1.75 Cu; 0.5-1.0 Mo
8 x %C -
Nb(Cb)
Custom 455 S45500 0.05 0.50 0.50 11.0-12.5 7.5-9.5 0.04 0.03 0.5 Mo; 1.5-2.5 Cu;
0.8-1.4 Ti; 0.1-0.5
Nb(Cb)
Stainless W S17600 0.08 1.00 1.00 16.0-17.5 6.0-7.5 0.04 0.03 0.4 Al; 0.4-1.2 Ti
Duplex Types
2205
S32205
0.03 2.0 1.0 22.0 5.5 0.03 0.02 3.0 Mo; 0.18 N
2304 S32304 0.03 2.5 1.0 23.0 4.0 0.1 N
255 0.04 1.5 1.0 25.5 5.5 3.0 Mo; 0.17 N; 2.0 Cu
NU744LN
0.067 1.7 0.44 21.6 4.9 2.4 Mo; 0.10 N; 0.2 Cu
2507 S32750 0.03 1.2 0.8 25 5.5 0.035 0.020 4 Mo; 0.28 N
*Single values are maximum values. (From ASM Metals Handbook, Ninth Edition, Volume 3) and ASTM A638
ASTM
A
GRADE
TABLE 10 — Nominal Compositions of Precipitation Hardening and Duplex Stainless Steels
NOMINAL COMPOSITIONS