Patent ID: 7691213
Filing Date: 2010-04-06
Classification: C21D,C23C,Y02P,Y10S

Abstract:
1. A case-hardened gear which is made from a steel material comprising 0.45 to 1.5 wt % C and 0.3 to 1.5 wt % Cr, and optionally including 0.1 to 0.5 wt % V, said steel material containing cementite ((Fe, Cr)3C) dispersed therein, wherein an average Cr concentration in said cementite is 2.5 to 10 wt %, and said gear having a rolling contact surface layer having a case-hardened layer being formed by induction heating from a temperature equal to or lower than the A1 temperature to a quenching temperature of 900 to 1100° C. and subsequent cooling of said rolling contact surface layer, said case-hardened layer having a structure tempered at a low temperature of 100 to 300° C. in which 2 to 18% by volume of the cementite containing solid-dissolved Cr therein is dispersed in a martensite parent phase, said martensite parent phase containing 0.25 to 0.8 wt % solid-dissolved carbon, wherein the cementite dispersed in the rolling contact surface layer is substantially granulated and the cementite has an average particle diameter of 0.1 to 1.5 μm.