Co-based alloy

Abstract

A Co-based alloy containing not less than 0.001 mass % and less than 0.100 mass % of C, not less than 9.0 mass % and less than 20.0 mass % of Cr, not less than 2.0 mass % and less than 5.0 mass % of Al, not less than 13.0 mass % and less than 20.0 mass % of W, and not less than 39.0 mass % and less than 55.0 mass % of Ni, with the remainder being made up by Co and unavoidable impurities, wherein the contents of Mo, Nb, Ti and Ta which are included in the unavoidable impurities are as follows: Mo<0.010 mass %, Nb<0.010 mass %, Ti<0.010 mass %, and Ta<0.010 mass %.

Description

TECHNICAL FIELD[0001]The present invention relates to a Co-based alloy suitable for various components required to have a high strength in a high-temperature environment, such as for a gas turbine, an aircraft engine, a chemical plant, a vehicle engine and a high-temperature furnace. In particular, it relates to a Co-based suitable for casting.BACKGROUND ART[0002]A Ni-based alloy, a Co-based alloy, an Fe-based alloy or the like have been known as a superalloy used at a high-temperature. The Ni-based alloy is precipitation-strengthened by a γ′ phase having an L12 structure (Ni3(Al, Ti)), and exhibits a reverse temperature dependency where strength increases as a temperature increases. In addition, the Ni-based alloy has excellent high-temperature properties such as heat resistance, corrosion resistance, oxidation resistance and creep resistance. Thus, the Ni-based alloy is used for various purposes which require a high strength in a high-temperature environment. However, there is a p...

AI Technical Summary

Benefits of technology

[0023]A Co-based alloy including Al and W easily generates a phase harmful to hot workability. In particular, when excessive W is contained, a harmful phase is generated within grains and in grain boundaries, and thus hot workability is significantly decreased.

[0024]However, when a Co-based alloy has a composition adjusted in a predetermined range (in particular Al and W contents) and is subjected to homogenizing heat treatment, the Co-based alloy can include less harmful phase. In addition, when the alloy is subjected to solution heat treatment and aging treatment under predetermined conditions after hot working, a Co3(Al, W) strengthening phase (γ′ phase) is precipitated. Furthermore, when a predetermined amount of carbon is added to the Co-based alloy containing predetermined amounts of Al, W and Cr, carbide containing W and / or Cr is precipitated in addition to the γ′ phase after the aging treatment. At this time, granular carbide can be precipitated in grain boundaries of a γ phase matrix by optimizing the carbon content. The granular carbide precipitated in the grain boundaries has a large effect of suppressing grain boundary sliding at a high temperature.

[0025]That is, a predetermined amount of carbide is precipitated in the grain boundaries in addition to the precipitation of the γ′ phase, thereby a creep rupture property or high-temperature ductility, which is specifically required for a high-temperature material, is remarkably improved in comparison to a conventional Co-based alloy. Accordingly, a Co-based alloy having endurance strength equal to or greater than that of an existing Ni-based alloy can be obtained.

Problems solved by technology

However, there is a problem that the Ni-based alloy is inferior in machinability and hot workability.

However, there was a problem that a conventional Co-based alloy has a lower high-temperature strength than the Ni-based alloy and is inferior in hot workability to the Ni-based alloy, since a γ′-type intermetallic compound effective for improving the high-temperature strength properties of the Co-based alloy was not known.

However, the Co-based alloy including Al and W may have a second phase precipitate depending on heat treatment conditions, that is harmful to processing.

Thus, hot workability may be significantly decreased.

However, high-temperature strength properties of a conventional alloy are not always sufficient.

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