Precipitation Hardening of Inconel X-750

The Inconel X-750 is precipitation hardenable alloy comprised of nickel and chromium and employed in the significant industrial operations for its superior resistance to oxidation and corrosion as well as high potential feature at elevated temperatures of 1300oF. The alloy’s precipitation effect of hardening disappears with an increase in temperature up to 1300oF, heat processed material with an excellent strength of 1800oF. The alloy offers superior features to cryogenic temperatures.

In the below table the chemical composition of inconel X-750 is described:

Ni + Co 70 %
Cr 14.0-17.0 %
Fe 5.0-9.0 %
Ti 2.25-2.75 %
Al 0.40-1.00 %
Nb + Ta 0.70-1.20 %
Mn 1.00 %
Si 0.50 %
S 0.01 %
Cu 0.50 %
C 0.08
Co 1.00

The economics of inconel alloy X-750 combined with its presence in the standard mill forms have provided applications in the different kinds. The gas turbines use rotor blades that are made of inconel X-750 wheels, bolts and other structural properties. The inconel X-750 is also used in the rocket engine thrust chambers, hot air ducting systems, large pressure tubes and dies and more. The spring fasteners use inconel X-750 at temperatures from sub zero to 1200oF.

On the base of operations and properties of alloy required for certain purpose, the different heat processing methods are followed. For service temperature more than 1100oF, in which the loads are kept for prolonged period, the adequate features are received by solution processing at temperature of 2100oF and stabilization processing at 1550oF as well as the precipitation processing at 1300oF. The service lower than 1100oF temperature limits, the alloy can be provided high strength by the precipitation treatment subsequent to hot and cold processing or by precipitation treatment after equalizing or solution processing. The furnace quenching treatment is employed to increase the appropriate features for few applications.

The different heat processing and properties obtained are mentioned under the mechanical characteristics. The property information is the result of various analysis made for the typical inconel X-750 wire. The physical properties of alloy are shown in the below table:

Density 8.28 g/cm3
Melting Range 1393-1427oC or 2540-2600oF
Curie Temperature of hot-rolled -225oF
Magnetic Permeability at 70oF 200H
Emissivity, oxidized surface at 600oF 0.895
Linear Contraction during Precipitation Treatment (1300°F/20 hr), in/in, Hot-Rolled 0.00044

The thermal properties of inconel X-750 are shown in the below table:

Temperature,

oF

Mean Linear

Expansion

Thermal

Conductivity, Btu/in./hr/sq ft/°F

Specific Heat,

Btu/lb/°F

Diffusivity, ,

sq ft/hr

Electrical

Resistivity, ohm/circ

mil/ft

-250 6.5 67 0.073 0.150
-200 6.6 70 0.080 0.143
-100 6.7 74 0.090 0.135
70 83 0.103 0.132 731
200 7.0 89 0.109 0.133 739

The values of thermal expansion, thermal conductivity, specific heat and diffusion are received from the Lucks and Deem and the value of electrical resistivity is obtained from the analysis in an academic institute.

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Isha Changotra has wide experience in metals industry and is working for a renowned super alloys manufacturer located in China and United States. With extensive insight in metals and high performance super alloys, she aims to provide most useful information for folks engaged under this niche.

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