| 摘要 |
PURPOSE:To provide superior wear resistance to a low alloy steel having a specified composition by carbonitriding the surface of the steel and austempering it to form a martensite structure in the surface layer. CONSTITUTION:A low alloy steel member contg. 0.55-0.65% C, <0.50% Si, 0.40-1.30% Mn, <4.00% Ni, 0.55-1.30% Cr and <0.70% Mo is carbonitrided at 850-880 deg.C to increase the C content of the surface layer to 0.75-1.00% and the N content to 0.15-0.40%. The member is austempered by putting in a cooling medium at a high temp. such as a salt bath at 230-260 deg.C, and it is held for such a time that transformation to bainite is caused in most of the member and is not caused in the surface layer. The held member is rapidly cooled or air- cooled. A martensite structure with high hardness is formed in the surface layer, and superior wear resistance is provided to the layer. |
