Type
Analysis
|
Element
|
Min
|
Max
|
|
Carbon
|
--
|
0.08
|
|
Manganese
|
--
|
0.35
|
|
Silicon
|
--
|
0.35
|
|
Phosphorus
|
--
|
0.015
|
|
Sulfur
|
--
|
0.015
|
|
Nickel + Cobalt
|
50.0
|
55.0
|
|
Chromium
|
17.0
|
21.0
|
|
Cobalt
|
--
|
1.00
|
|
Iron
|
Balance
|
|
Aluminum
|
0.35
|
0.80
|
|
Molybdenum
|
2.80
|
3.30
|
|
Titanium
|
0.65
|
1.15
|
|
Boron
|
0.001
|
0.006
|
|
Copper
|
--
|
0.15
|
|
Cb + Ta
|
4.75
|
5.50
|
Description
Alloy 718 is a precipitation
hardenable nickel-based alloy designed to display exceptionally high
yield, tensile and creep-rupture properties at temperatures up to
1300°F. The sluggish age-hardening response of alloy 718 permits
annealing and welding without spontaneous hardening during heating
and cooling. This alloy has excellent weldability when compared to
the nickel-base superalloys hardened by aluminum and titanium. This
alloy has been used for jet engine and high-speed airframe parts such
as wheels, buckets, spacers, and high temperature bolts and
fasteners.
Physical
Constants
Density Electrical resistivity
lb/cu in .............................. 0.293 ohms-cir mil/ft ................................ 728
kg/cu m .............................. 8220 microhm-mm ................................. 1210
Melting Range
°F ................................ 2200-2450
°C .................................1210/1344
Modulus of Elasticity (E)
|
Temperature
|
psi
x 10(6)
|
MPa
x 10(3)
|
|
°F
|
°C
|
|
70
200
400
600
800
1000
1200
1400
1600
1750
|
21
93
204
316
427
538
649
760
871
954
|
29.6
29.2
28.8
27.6
26.5
25.5
24.5
23.1
18.1
11.1
|
208
205
202
194
186
179
172
162
127
78
|
Coefficient of Thermal Expansion
|
Temperature
Range
|
10(-6)/°F
|
10(-6)/°C
|
|
77°F to
|
25°C to
|
|
200
400
600
800
1000
1200
1400
|
93
204
316
427
538
649
760
|
7.1
7.5
7.7
7.9
8.0
8.4
8.9
|
12.8
13.5
13.9
14.2
14.4
15.1
16.0
|
Heat
Treatment
The following heat treatment should
be used to obtain the best combination of tensile properties and
stress rupture properties:
1 hr 1750°F to 1800°F (954 to
982°C) air cool + 8hr 1325°F (718°C) cool 100°F /hr
to 1150°F (56 °C/hr to 621°C), hold 8 hrs and air
cool.
To obtain the best room temperature and cryogenic tensile
properties, the following heat treatment should be used:
1 to 2
hr 1950°F (1066°C), air cool + 8 hr 1325°F (718°C)
cool 100°F/hr to 1150°F (56°C/hr to 621°C), hold 8 hr
and air cool.
Workability
Hot Working
Hot-working is
carried out using a 2050°F (1121°C) maximum furnace
temperature. Hot-cold working in the range 1700/1850°F
(927/1010°C) will improve the strength of the forging if the
service temperature is below about 1100°F (593°C). Prolonged
soaking at the forging temperature is not desirable. The material
should be given uniform reductions to avoid the formation of duplex
grain structures.
Machining
The alloy can be
readily machined in either the annealed or the age-hardened
condition. The age-hardened condition gives better chip action on
chip breaker tools and produces a better finish. The annealed
condition will give a slightly longer tool life.
Welding
Alloy 718 can be
welded in either the annealed or the age condition. Welding in the
aged condition will cause the formation of a softened heat-affected
zone.
Typical
Mechanical Properties
Elevated Temperature Tensile
Tests
1/2" bar stock
|
Test
Temperature
|
0.2%
Yield
Strength
|
Tensile
Strength
|
%
Elongation
2"
|
|
°F
|
°C
|
ksi
|
MPa
|
ksi
|
MPa
|
|
200
400
600
800
1000
1200
1400
|
93
204
316
427
538
649
760
|
170
163
159
156
155
149
110
|
1172
1124
1096
1076
1069
1027
758
|
204
198
195
191
185
168
110
|
1407
1365
1344
1317
1276
1158
758
|
21.0
20.0
20.0
19.0
18.0
19.0
27.0
|
Heat
Treatment: 1 hr - 1800°F, air cool + 8 hr-1325°F, cool
100°F/hr to 1150°F, hold 8 hr, air cool.
Stress Rupture Data
|
Test
Temperature
|
Stress
for Rupture
|
|
°F
|
°C
|
100 Hours
|
1000 Hours
|
|
Smooth
|
Notch
|
Smooth
|
Notch
|
|
ksi
|
MPa
|
ksi
|
MPa
|
ksi
|
MPa
|
ksi
|
MPa
|
|
1100
1200
1300
1400
|
593
649
704
760
|
170
110
75
44
|
1172
758
517
303
|
220
195
130
63
|
1517
1344
896
434
|
130
85
55
25
|
896
586
379
172
|
205
170
80
35
|
1416
1172
552
241
|
Heat
Treatment: 1 hr - 1850°F, air cool + 8 hr - 1325°F,
furnace cool to 100°F/hr to 1150°F, hold 8 hr, air cool.
| 
