Mo-V-Ni high temperature steels, articles made therefrom and method of making

Abstract

Low carbon carburizing (surface hardening) and higher carbon through hardening steels primarily containing molybdenum, vanadium and nickel and, to a lesser amount, chromium used for rolling contact bearings, gears and other similar applications where high hardness at elevated temperatures is required. The alloy steel includes, in % by weight: 0.05% to 1.25% C; up to 1.25% Cr; 0.40% to 4% Mn; up to 4.0% Mo; up to 2.0% V; 1.0% to 3.0% Ni; 4% to 8% (Mo+V+Ni+Cr); less than 0.20% Si; and balance Fe plus incidental additions and impurities. The method for providing a steel having improved hardness at elevated temperatures includes the steps of: (a) providing an alloy including, in % by weight: less than 1.25% Cr, 0.4% to 4% Mn, up to 4% Mo, up to 2% V, 1 to 3% Ni, 4% to 8% (Mo+V+Ni+Cr), less than 0.2% Si, a C content selected from one of 0.05% to 0.40% C defining a carburizing steel or greater than 0.40% to 1.25% C defining a through hardening steel, and the balance Fe plus incidental additions and impurities; (b) performing a step selected from the group consisting of (i) subjecting the carburizing steel to carburizing and quenching to provide a quenched carburized steel, or (ii) subjecting the high carbon steel to hot working to provide a wrought high carbon steel; (c) preheating the quenched carburized steel or wrought high carbon steel and then austenitizing said steel to provide an austenitized steel; (d)quenching the austenitized steel to provide quenched austenitized steel; and (e) tempering the quenched austenitized steel followed by air cooling.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to both low carbon carburizing (surface hardening) and higher carbon through hardening steels primarily containing molybdenum, vanadium and nickel and, to a lesser amount, chromium used for rolling contact bearings, gears and other similar applications where high hardness at elevated temperatures is required.[0003]2. Description of Related Art[0004]Piston driven aircraft engines and early jet engines used through hardening 52100 alloy steel or carburizing grades of alloy steels for most bearing applications, see Table 1. However, over the years, as power requirements rose, operating temperatures increased. Thus, alloys with more heat resistance were necessary. Minor improvements in the performance of 52100 alloy steel were achieved by adding small amounts of extra alloying elements. One of the most commonly added elements to enhance high temperature performance was silicon. TSB-600 is a typ...

AI Technical Summary

Benefits of technology

[0029]Providing an alloy consisting essentially of in % by weight less than 1.25% Cr, preferably 0.75% to 1.25% Cr, about: 0.40% Mn≦4%, 0≦Mo≦4.00, preferably 1.0% to 3.00% Mo, 0%≦V≦2.0%, preferably 0.75% to 1.25% V, 1.0%≦Ni≦3.0%, less than 0.20% Si, a carbon content selected from one of about 0.05%≦C≦0.40% defining a carburizing steel or 0.40%<C≦1.25% defining a high carbon steel, and the balance iron plus incidental impurities. Tungsten (W) is not purposely added to these alloys. The amount of tungsten is ideally zero, or as low as commercially feasible and practical, preferably no more than 0.20% W. In general, the total amount of (Mo+V) will be less than 4% and the amount of (Mo+V+Ni+Cr) will preferably be 4% to 8%. The uniqueness of these alloys is that they achieve excellent hot hardness with a minimum of the recited alloy additions, and contain manganese (Mn) to enhance carbon diffusion and increase hardenability. This is unlike normal high speed steels that achieve good hot hardness with large amounts of alloying elements. Elements such as nitrogen (N), niobium (Nb) or even titanium (Ti) and other similar elements may be added in small amounts up to about 0.05% each for grain refinement and enhanced toughness purposes.

Problems solved by technology

First, low melting point alloy carbides do not form in the steels, particularly the steels containing 1% carbon.

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