Alloys with high corrosion resistance for engine valve applications

Abstract

Low cost alloys resistant to mechanical requirements related to high temperatures, resistant to corrosion, with high workability and which meet different requirements in the conditions for application in either exhaust or intake valves for internal combustion engines. The main features of the alloys is the precipitation of Ni3Nb in its microstructure. In percentage, its mass consists of: 0.01 to 0.15% C, up to 3.0% Mn, up to 1.0% Si, 18.0 to 25.0% Cr, 25.0 to 49.0% Ni, up to 0.50% Mo, up to 0.50% W, up to 0.50% V, up to 5.0% Cu, 1.0 to 3.0% Al, 0.5 to 2.5% Ti, 1.0 to 6.0% Nb, 0.001 to 0.02% B, 0.001 to 0.10% Zr, up to 2.0% Co, where (Ni+Co) is not higher than 50.0% in mass, nor lower than 25% in mass. As for the ration Al / Ti, it is lower than 2.0. The rest is made of iron and impurities inevitable to the Alloy manufacture procedure.

Description

[0001]This application claims benefit of provisional application 60 / 924,974, filed Jun. 7, 2007.FIELD OF THE INVENTION[0002]This invention deals with an Ni—Fe—Cr precipitation hardened superalloy for application in internal combustion engine valves, having as chief characteristics a high hot resistance through the precipitation of Ni3(Al,Ti,Nb) and a higher oxidation resistance as compared to the state-of-the-art alloys. The alloy project, based on its microstructure aspects, also allows for the alloy hereof to be provided with properties equal to or higher than those of the high nickel alloys used in internal combustion engine valves, associated with the alloy's significant cost reduction because of the lower nickel content.[0003]The alloy hereof is intended for valves' manufacture, where the alloy is required to have several properties, among them the following: high temperature oxidation resistance and heat resistance, because of the high temperatures used in the application.BACK...

AI Technical Summary

Benefits of technology

[0011]Other elements used by this invention in higher quantities than the state-of-the-art alloys are aluminum and chromium, which have prevailing functions in the alloys' corrosion resistance. Chromium is responsible for the formation of a passivating film of chromium oxide on the material's surface, which prevents the corrosive process progression. Aluminum is also a builder of a coherent intermetallic containing niobium, Ni3(Al,Nb), thus improving the material's heat resistance. Additionally, aluminum improves the alloy hot resistance oxidation.

[0036]Carbon is added with the intent of combining titanium and niobium in order to form carbides, which precipitate in the grain contours and improve the alloy's creep resistance, since they hinder the deformation mechanism by “grain contour sliding”. For that function, the carbide content shall be at least 0.03%, preferably above 0.03% and below 0.06%, preferably 0.05%.

Problems solved by technology

Such extreme stresses in terms of mechanical resistance and corrosion resistance at high temperatures require the use of costly nickel-based superalloys.

One example of an excellent performance alloy in these applications is the NCF 751 alloy, which is very costly because of its high nickel content, above 70%.

Images