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266 Rulesof Thumb for Mechanical Engineers
Stainlesssteels
A specialclass of iron-based alloys have been developed
for resistance to tarnishing and are known as stainless
steels. These alloys may be martensitic (body centeredtetragonal), austenitic(FCC), rfemitic (BCC) depending
on the alloying additions that have been made to the iron.
Useof stainless steels shouldbe considered carefully. The
use of some classes should be limited to oxidizing envi-
ronments in which the alloy has the chance to form a pro-
tective oxide scale. Use of alloys requiring the oxide scale
for protection in reducing environments, such as carbon
monoxide which can electrochemically or thermodynam-
ically convert oxides to metals, can be disastrous. Tables
7 and 8contain a partial list of common stainless steel com-
positions and acceptable use environments.
A thin oxide scale forms on the stainless steel and pro-tects it from further oxidation and corrosion. Chromium is
typically the element responsible for stainless steel's "stain-
less" appearance.
Ferritic stainless steels have typically up to 30%Cr and
0.12% C andare moderately strong, solid solution and strain
hardened,and low cost. The strengths can be increased by
increasing the Cr and C; unfortunately, these actions resultin carbide precipitation and subsequent embrittlement.Ex-
cessive Cr additions can alsopromote the precipitation of a
brittle second phase known as sigma phase.
Martensitic stainless steels contain up to 17%Cr andfrom
0.1-1.0% C. These alloys are strengthened by the forma-
tion of martensite on cooling from a single-phase austen-
ite field. With the range of carbon contents available,
martensite of varying hardness can be produced. Marten-
sitic stainlesssteelshave good hardness, strength, and cor-
rosion resistance. Typical uses are in knives, ball bear-
ings, and valves. They soften at temperatures above 500°C.
Austenitic stainless steels have high chromium and high
nickel content. The generic term is 18-8 stainless, whichrefers to 18%Cr and 8%Ni. The nickel is required to sta-
bilize the gamma or face centered cubic (FCC) phase of the
iron, and the Cr imparts the corrosion resistance. Theseal-
loys can be used to 1,OOO"C. Above this temperature, the
chromium oxide that forms can vaporize and will not pro-
tect the substrate, so rapid oxidation can occur.
Table 7
Composition of Standard StainlessSteels
Composition (%)
UNSType Number C Mn Si Cr Ni P S Other
Austenitic
types201 s20100 0.1 5 5.5-7.5 1oo 16.0-18.0 3.5-5.5 0.06 0.03 0.25 N304 S30400 0.08 2.00 1oo 18.0-20.0 8.0-10.5 0.045 0.03 -304L S30403 0.03 2.00 1oo 18.0-20.0 8.0-1 2.0 0.045 0.03 -31 0 531000 0.25 2.00 1.50 24.0-26.0 19.0-22.0 0.045 0.03 -31 6 S31600 0.08 2.00 1.OO 16.0-18.0 10.0-1 4.0 0.045 0.03 2.0-3.0 Mo
347 S34700 0.08 2.00 1 oo 17.0-1 9.0 9.0-1 3.0 0.045 0.03 1OX%c
min Nb+Ta
450 S40500 0.045 1oo 1 oo 11 s1 4. 5 - 0.04 0.03 0.1-0.3 AI430 S43000 0.1 2 1.25 1oo 16.0-18.0 - 0.04 0.03 -erritic types
Martensitic
0.15 1.oo 1.00 113-1 3.0 - 0.04 0.03 -- 0.04 0.03 -10 s41000
420 S42000 0.15 1 oo 1 oo 12.0-1 4.0431 S43100 0.20 1 oo 1 oo 15.0-1 7.0 1.25-2.50 0.04 0.03 -
Precipitation-
hardening
types
17-4PH S17400 0.07 1.00 1.00 15.5-1 7.5 3.0-5.0 0.04 0.03 3.0-5.0Cu;
17-7PH S17700 0.09 1oo 1 oo 16.0-18.0 6.5-7.75 0.04 0.03 0.75-1.!XI0.15445 (Nb+Ta)
Adapted from ASMMetals Handbook,Vol. 49th Ed.[a].
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Materials 267
Table 8
Resistanceof Standard Types of Stainless Steelto VariousClasses of Environments
X X
mpe Mild Atmospheric Atmospheric Sat Chemical
Austenitic
andFreshWater Industrial Marine water Mild Oxidizing Reducing
stainless steels201 X X X X X
304 X X X X X
310 X X X X X
316 X X X X X
347 X X X X X
stainless steels
405 X X
430 x X X
stainless steels
410 X X
420 X
431 x X X X
Ferritic
Martensitic
Precipitation hardening
stainless steels
17-4PH X X X X X
17-7PH X X X X X
X
An 4r" notation indicates tha t the specific type is m is tan t to the Mlrrosiye environment.Adapted h m SM Metals Handbook, VoL 3,Hh Ed. I40J
Since austenitic stainless steels areFCC, they tend not to
be magnetic.Thusan easy test to separate austenitic stainless
steel from ferritic or martensitic alloys is to use a magnet.
Austenitic stainless steels are not as strongasmartensitic
stainless steels, but can be cold worked to higher strengths
than ferritic stainless steels since they are strengthened viasolid solution hardening in addition to the cold work. They
are more formable and weldablethan he other two types
of stainless steel. They are also more expensive due to the
high nickel content.
The amount of carbon in an austenitic stainless steelis im-
portant;if it exceeds0.03%C, the Cr can form chromium car-
bides which locally decrease the Cr content of the stainless
steel and can sensitize it. A sensitized alloy forms when
slowly cooled from below about 870°C to about 500°C.It is
prone to corrosion along thegrainboundaries where the local
Cr content drops below 12%.Figure 4 shows a schematic of
a sensitized alloy.A rapid quench through this temperature
range should prevent the formation of the chrome carbides.
Elements suchasTiorNb , which are strong carbide formers,
canbe added to the alloy to form carbides and stabilize the
alloy, for example, types347 and321 .
Austenitic stainless steels also have good low tempera-
ture properties. Since they are FCC, they do not undergo a
ductile to brittle transition like body centered cubic metals
(BCC). Austenitic stainless steels can be used at cryogenic
temperatures.
The precipitation hardening alloys are strengthened by
the formation of martensite and precipitates of copper-
niobium-tantalum.
Low Chromium Austenite
Chromium Carbide
High Chromium Austenite
A-A
Figure4. Sensitized stainlesssteel.Cr contentnear grain
boundary is too low for corrosion protection.
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268 Rulesof Thumb for Mechanical Engineers
Superalloys
Iron-based superalloys have high nickel contents to sta-
bilize the austenite, chromium for corrosion protection,
and niobium, titanium, and aluminum for precipitationhardening. Refractory elements are introduced for solid SD-
lution hardening. They also confer some creep resistance.
Creep resistance is further enhanced by the presence of small
coherent precipitates. Unfortunately, the fine precipitates
that improve the creep strength the most are also the most
likely to dissolve or coalesce and grow.
Nickel- and cobalt-based superalloys have higher tem-
pemturecapabditiesthan ron-basedsupedoys.The strength-
ening mechanisms for nickel-based alloys are similar to
those for iron-based alloys. The nickel matrix is precipita-
tion hardened with coherent preciptitates of niobium, alu-
minum, and titanium. Carbides andboridesare used asgrainboundary strengtheners, and refractory elements are added
as solid solution strengtheners. The gamma prime (Ni3AI,13)
is a very potent strengthener that is a coherent precipitate.
These precipitates are present up to 70% in modern, ad-
vanced nickel-based alloys. They permit the use of nickel-
based alloys to approximately0.75 times the meltingpoint.
Nickel-based alloysarealsocastas single crystals whichp
vide significant strength and creep improvements over poly-
crystallinealloys of the same composition.Sometypical com-
positions and applications are listed in Tables9 and 10.
Table9
Nominal CompositionsofVpically Used Iron-, Nickel-, and
Cobalt-based Superalloys
MlOY Co Ni Fe Cr Al TI Mo W hb Cu Other
wiought Alloys
HASTELLOPC-4'
HASTEUOY@-22m'
HASTELLOPC-276.
HASTELLOPD-205w
HASTELLOPS
HASTELLOPWHASTEUOY@C 1.5
HAYNES188' Bal
HAYNES214TM*
HAYNES2301"Alby 625.Alloy 716'
W - P W 14
INCONELQ MA 54t
lNCONELQMA956f
Bal
Bal
BalBal
Bal
BalBal22
Bal
BalBal
Bal
BalBal
3
5
6
6
18
3
19
1Bal
16
22
16
20
16
5
22
22
16
2221
18
19
2020
16
13
16
2.5
15
24
9
4.5
290.5 11.5 3 4
0.3 0.5
4.5 0.5
3
4
20 5 s
La
0.6
14 La
Y14 La3.5
5
yflsy2os
Cast alloys"
Alloy 713 Bal 12.5 6.1 0.8 4.2
IN-100 15 Bal 10 5.5 4.7 3
IN-738 8.5 Bal 18 3.4 34 1.7 2.6 0.9 Ta
MarM 247 10 Bal 8.3 5.5 1 0.7 10 Ta
Mar4 509 Bal 10 23.5 7 Ta
X-40 BaI 10 25.5 7.5 0.7 Mn
~ ~ I n t e m a t l o n a l . p m d u c t s u l l e h i r H - l o B Q D l 1 8 9 9 .trrom r n Adbyshtemat4mal, f+oduct Hanalbook, 19BB' * F mShs, t al.B6lbypennlssbnof JohnWTW& Sons, rc.
Cobalt alloysarenot strengthened by a coherent phaselike
Ni3Al, rather, they are solid solution hardened and carbide
strengthened. Cobalt alloys have higher melting points andflatter stress rupture curves which often allow these alloys
to beused at higher absolute tempratms thannickel-or iron-
based alloys. Their use includes vanes, combustorliners,and
other applications which require high temperature strength
and corrosion resistance. Most cobalt-based superalloys
have better hot corrosion resistance than nickel-based su-
peralloys. They also have better fabricability, weldabiity,and
thermal fatigue resistance than nickel-based alloys.
Table 10
Common Application of Iron-, Nickel-, and
Cobalt-based Superalloys
Wrought A l l o y
HASTELLOF C-4*
HASTELLOP C-22m'
HASTELLOP C-276"
HASTELLOP D-2W'*
HASTELLOPS'
HASTELLOPWHASTELLOPC
HAYNES" lee*
HAYNES@214m
HAYNESa230m'
IN%=*
IN-71FWm d O y tINCONEL@MA754t
INCONEL@ MA gs6t
cast Alloys
Alloy 713
IN-100
IN-738
M a r 4 247
Mar-M 509
X-40
High temperature stability to 1,900"F.Excellent
corrosion resistance.
Universal iller metalformsion-resistant
welds. Resistance o localized cormdon,
stress corrosion cracking, and oxidizing and
reducing chemicals.
Excellent resistanceto oxidizingand reducing
corrosives, mixed acids, and chlorine beating
hydrocarbons.
Superior performance n sulfuric acidof various
concentrations.
Lowstressgas turbine parts. Excellent
dissimilar iller metal.
Aircraftenglne repairandmaintenance.Aircraft, marine, and industrial gas turbine
engine combustors and fabricated parts.
Suhidation resistant. Mil ii ty and civilian aircraft
engine combustors.
Honeycomb seals demanding industrial heating
applications.
Gas turbine combustors and other stationary
members, industrial heating, and chemical
procesdng.
processing.
Aerospace, industhlheating, and chemical
Extensiveuse in gas turbines.
Gas turbine components.
Mechanicallyalloyedfor mproved alloystability.
Gas turbine vanes.Mechanicallyalloyed for imp we d alloystability.
Gas turbine cornbustors.
Turbine blades.
Turbine blades.
Turbine blades.
Turbine bladesand vanes.
Turbine vanes.
Turbine vanes.
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Materials 269
Aluminum Alloys
Aluminum alloys do not possess the high strength and
temperature capability of iron-, nickel- or cobalt-based al-
loys. They are very useful where low density and moder-ate strength capability are required. Becauseof their rela-
tively low melting point (less than 660°C), they can be
readily worked by a number of different processesthatmet-
als withhigher melting points cannot. Aluminum alloys are
designated by their major alloying consituent. The common
classes of alloying additions are listed in Table 11. Since
alloy additions affect the melting range and strengthening
mechanisms, a number of classes of alloys are generated
that can have varying responses to heat treatment.Someal-
loys are solution heat treated and naturally aged (at room
temperature),while someare solutiontreatedand df i c i a l ly
aged (at elevated temperature). Table 12 lists several pos-
sible treatments for wrought aluminum alloys, and Table
13 lists typical applications.
Table 12
CommonAlAlloy Temper Designations
0
F
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
Annealed.
As fabricated.
Cooled rom an elevated temperature shaping process and
Cooled rom anelevated temperature shaping process, cold
naturallyaged to a substantially stable condition.
worked, and naturally aged to a substantially stable
condition.
substantially stable condition.
stable condition.
artifically aged.
Solution heat treated, cold wotked, and naturally aged to a
Solution heat treated and naturally aged to a substantially
Cooled rom an elevated temperature shaping process and
Solution reated and artificially aged.
Solution reated and stabilized.Solution reated, cold worked, and arti ficially aged.
Solutiontreated, cold worked, and artif icia lly aged.
Cooled from an elevated temperature shaping process, coldworked, and artificially ased.-
From ASM Metals Handbook,Vo/.2,m Ed.p2J
Table 13
Typical Applications and Mechanical Properties of
Aluminum Alloys
Table 11
Major Alloying Elements for Aluminum Alloys andCompositions for Some Commonly UsedAlloys10501100
201 4
2024
4032
4043
5052
6063
7075
Chemical equipment, railroad ank carsSheetmetalwork, spun hollowware, fin stockHeavyduty forgings, platesand extrusions for aircraft fittings,
Truck wheels, screw machineproducts,aircrafts t t ~ c t ~ r e ~
Pistons
Welding electrodeSheet metalwork, hydraulic ube, appliances
Pipe railing, furniture, architectural extrusionsAircraft and other structures
wheels, truck frames
Alloying elementeries
l X X X
2xxx
3xxx
4xxx
5xxx
6xxx7xxx
8xxx
9XXX
~
None99.00% or greater AI
Copper
Manganese
Silicon
Magnesium
Magnesium and silicon
Zinc
Other element
Unused series
Tensile Yield Elongation HardnessStrength Srength in50mm HB
Alloy Temper mi) &Si) ( O h ) (500@/lo mm ball)
1050
1100
2014
0 11
0 13
0 27
T6 700 27
T3 70
T6 550 21
0 28
0 13
T1 22
T6 35
0 38T6 83
-23
45
13547
120
120
36
25
42
73
60
150
-znu-0.12
4.4
4.4
0.9
Mg--0.5
1.5
1 o
AI
99.50
99.00
93.5
93.5
85.0
94.8
97.2
98.9
90.0
Si--0.8
12.2
5.2
0.4
---
Mn--0.8
0.6
AA
1050
1100
2014
2024
4032
4043
5052
6063
7075
2024
40324043
5052
6063
-0.9Ni-
0.25
0.23
-.5
0.7
2.5
--1.6
70755.6
Adapted from ASM Metals Handbook, vd. 2,W Ed.p]. Adapted fromASM MetalsHandbook,VOL 2,9th Ed.p2].