Alloy X-750 is a precipitation-hardenable alloy which has been used in applications such as high temperature structural members for gas turbines, jet engine parts, nuclear power plant applications, heat-treating fixtures, forming tools, and extrusion dies. The alloy is highly resistant to chemical corrosion and oxidation and has high stress-rupture strength and low creep rates under high stresses at temperatures up to 1500°F (816°C) after suitable heat treatment.

inconel-x750[1]

Type Analysis

ElementMinMax
Carbon--0.08
Manganese--0.30
Silicon--0.50
Sulfur--0.01
Nickel + Cobalt70.0 min
Chromium14.017.0
Iron5.009.00
Aluminum0.401.00
Titanium2.252.70
Copper--0.50
Cb + Ta0.701.20

Corrosion Resistance

Alloy X-750 has excellent resistance to chloride ion stress-corrosion cracking. It exhibits satisfactory resistance to numerous oxidizing environments. The alloy has similar corrosion resistance to alloy 600 in many media.

Physical Properties

Density
lb/cu in...................................... 0.300
kg/cu m...................................... 8303
Melting Range
°F........................................ 2540/2600
°C.........................................1393/1427

Thermal Conductivity

TemperatureBtu-in/ft²-hr-°FW/m-K
°F°C
300
600 
1000 
1200 
1400
1600
149 
316 
538 
649 
760 
871
117 
142 
184
199 
218 
245
16.9 
20.5
26.5
28.7
31.4 
35.3

Electrical Resistivity

Conditionohm-cir mil/ftmicrohm-mm
At Room Temperature
Hot Rolled
Solution Treated
Solution Treated
and Aged
764
716

746
1270
1190

1240

Modulus of Elasticity

Temperaturepsi x 10(6)MPa x 10(6)
°F°C
80
500
1000
1350
1500
26.7
260.0
538.0
732.0
816.0
31.0
28.7
25.0
21.0
18.5
213.7
197.9
172.4
144.8
127.6

Heat Treatment

Alloy X-750 is austenitic under all conditions. The alloy is heat treated by several different methods depending upon the application or requirement. Two common treatments are:
1. For maximum creep, relaxtion and rupture strength at temperatures above 1100°F (593°C):
Solution Treatment - 2100°F (1149°C), 2 to 4 hrs, air cool.
Intermediate Age - 1550°F (843°C), 24 hrs, air cool.
Final Age -1300°F (704°C), 20 hrs, air cool.
2. For highest room temperature yield strength and tensile ductility:
Stress Equaliztation - 1625°F (885°C), 24 hrs, air cool.
Precipitation Age - 1300°F (704°C), 20 hrs, air cool.

Workability

The furnace temperature should be 2100°F (1149°C)-for optimal starting temperatures of 1950/2000°F. For service below 1100°F (593°C), higher strength can be obtained by combining some cold work with heat treatment because the effects are additive.

Machinabiliy
Alloy X-750 work hardens quickly and is more difficult to machine than most standard ferritic and martensitic alloys. The alloy is most easily machined in the stress-equalized condition. Because specific cutting forces are high, the machine tools used must have ample power and the cutting speed should be slow. The tools must have smooth finishes, be sharp, and be very rigid. To avoid work hardening , a continuous, smooth cutting action should be maintained; thus, the machines must have a minimum of backlash and the tool and workpiece must be rigidly supported. If at all possible, avoid very small cuts and feeds.

Welding
Alloy X-750 should be welded in the stress-equalized condition, 1625°F (885°C) heat treatment, and solution treated and age hardened after welding has been completed. If this is not practical, the alloy should be welded in the solution-treated condition and age hardened after welding with or without the inclusion of a short-period stress-relieving treatment at 1625°F. Weld joints, because of softening of the alloy within the heat-affected zone, should be located where lower creep properties are required.

Typical Mechanical Properties

Room Temperature Mechanical Properties

Temper

Tensile Strength,
psi

Yield Strength
0.2% offset, psi

Elongation
in 2", %

Hardness,
Brinell

Hot-finished + 1300°F/20 hr,A.C

Hot-finished + Annealed
1800°F/1 hr, A.C + 1350°F/
8 hr, F.C. 100°F/hr to 
1150°F (total 18 hr), A.C.

Hot-finished + 1625°F/24 hr,
A.C + 1300°F/20 hr, A.C.

Cold-rolled, annealed +
1300°F/20 hr, A.C.

170,000-206,000


162,000-193,000



160,000-188,000



160,000-197,000

120,000-163,000


115,000-142,000



100,000-135,000



105,000-150,000

25-15


30-15



30-15



30-20

313-400


300-390



302-363



300-400

Bar Stock:
Treatment #1

Solution treatment 2100°F (1149°C), 2 to 4 hrs., air cool intermediate age 1550°F (843°C), 24 hrs., air cool
Final age 1300°F (704°C), 20 hrs., air cool

Test TemperatureShort-Time Tensile Properties Tests
°F°CYield Strength 0.2% offsetUltimate Tensile Strength% Elongation in 2" (50.8 mm)% Reduction of Area
ksiMPaksiMPa
70 
1000 
1200 
1400 
1500
21.1
538.0 
649.0 
760.0
816.0
92 
83
82
68 
45
634
572 
565
469
310
161 
140 
120 
80 
47
1110 
965 
827 
552
324
22 
20
10 
10 
20
30
30 
21 
22 
32