Forged austenitic stainless steel alloy components and method therefor

Abstract

A forgeable austenitic stainless steel alloy and forging process capable of producing forged components that exhibit mechanical and environmental properties and metallurgical stability suitable for use in thermally and chemically hostile environments, such as the environment of a component of a gas turbine engine shroud assembly. The alloy contains, by weight, 18.0 to 22.0% chromium, 8.0 to 14.0% nickel, 4.0 to 7.0% manganese, 0.4 to 0.6% silicon, at least 0.2 up to 1.0% nitrogen, at least 0.05 up to 0.075% carbon; up to 0.3% molybdenum, up to 1.0% niobium, up to 0.2% cobalt, up to 4.5% aluminum, up to 0.1% boron, up to 0.1% vanadium, up to 1.0% tungsten, and up to 5.0% copper, with the balance iron and incidental impurities.

Description

BACKGROUND OF THE INVENTION[0001]The present invention generally relates to stainless steel alloys and their processing. More particularly, this invention relates to a forgeable austenitic stainless steel alloy and forgings formed therefrom that have desirable mechanical and environmental properties and very stable microstructures over long periods of time at operating temperatures seen by internal components of gas turbine engines.[0002]Various alloys have been considered and used for high-temperature components of turbomachinery, with individual alloys being chosen on the basis of the particular demands of the application. Shrouds, which surround the outer blade tips within the turbine section of a turbomachine, such as a gas turbine engine, require high temperature strength and ductility, as well as good low cycle fatigue and oxidation properties. Furthermore, to maintain their performance at temperatures exceeding 700° C. for extended periods of time, e.g., in excess of 50,000 o...

AI Technical Summary

Benefits of technology

[0006]The present invention provides a forgeable austenitic stainless steel alloy and forging process capable of producing forged components that exhibit mechanical and environmental properties and metallurgical stability suitable for use in thermally and chemically hostile environments, such as those in gas turbine engines.

[0008]A significant advantage of this invention is the ability of the austenitic stainless steel alloy to be forged to produce components that have desirable mechanical properties and very stable, fully austenitic microstructures that avoid deleterious second phase formation during long exposures at high temperatures. Such mechanical and metallurgical properties are preferably comparable to and possibly better than wrought stainless steel type 310, while significantly reducing the level of nickel required in comparison to type 310 (19.0-22.0%). According to a preferred aspect of the invention, the forgeable austenitic stainless steel alloy can exhibit fatigue and oxidation resistance capable of withstanding the internal conditions of a gas turbine engine, such as components of a shroud assembly surrounding the turbine blades of the engine.

Problems solved by technology

Austenitic stainless steel alloys such as type 304, 347, 316, 321, etc., have stable austenitic microstructures at room temperature, but can suffer from loss of properties during extended exposures to high temperatures as a result of being prone to detrimental secondary phases formation, such as sigma phase.

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