Type Analysis | Description | Corrosion Resistance | Physical Properties
Heat Treatment | Workability | Typical Mechanical Properties

Type Analysis

Description

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.

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

Electrical Resistivity

Modulus of Elasticity

Coefficient of Thermal Expansion

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 - 1800°F (982°C), time commensurate with thickness, 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

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