Patent ID: 7544255
Filing Date: 2009-06-09
Classification: C23C,Y10S

Abstract:
1. A rolling element having a rolling contact surface layer, which is made from a steel material which comprises at least 0.2 to 0.8 wt % C, 0.3 to 1.5 wt % Cr and 0.2 to 2.0 wt % in total of one or more alloy elements selected from the group consisting of V, Ti, Zr, Nb, Ta and Hf, and in which a total of 0.4 to 4.0% by volume of carbides of said alloy elements having an average particle diameter of 0.2 to 5 μm and 7.5 to 20% by volume of cementite are dispersed therein; wherein the rolling contact surface has been carbonitrided or nitrided so that one or more compounds selected from the group consisting of nitrides and carbonitrides of an element selected from the group consisting of V, Ti, Zr, Nb, Ta and Hf, and having an average particle diameter of 0.2 μm or less are additionally precipitately dispersed in the rolling contact surface layer; and the carbon content of the rolling contact surface layer is adjusted to 0.65 to 1.5 wt % and the nitrogen content of the rolling contact surface layer is adjusted to 0.1 to 0.7 wt %, while 7.5 to 20% by volume of the cementite is dispersed therein; wherein cementite has been spheroidized by thermal treatment and cooling after carbonitriding or nitriding, thereby allowing Cr to concentrate in the cementite and the rolling contact surface layer is further induction hardened by induction heating to form austenite grains and quench hardened to form martensite, followed by low- temperature tempering; wherein 2 to 15% by volume of the spheroidized cementite containing 2.5 to 10 wt % Cr as an average composition are dispersed in an undissolved condition in a martensite parent phase of the rolling contact surface layer by the spheroidizing and a soluble carbon concentration in the martensite parent phase of the rolling contact surface layer is adjusted to 0.35 to 0.8 wt % by induction heating.