Surface modification method and surface modification material for alloy steel for machine structure

摘要

PROBLEM TO BE SOLVED: To provide a method for modifying the surface of alloy steel for machine structures excellent in fatigue strength under the load condition in which stress ratio is positive, and to provide a surface modified material. SOLUTION: In this method for modifying the surface of alloy steel for machine structures, the surface of alloy steel for machine structures is subjected to vacuum carburizing treatment and is thereafter subjected to two step shot peening treatment in which the grain size of shots in the first shot peening treatment is smaller than that in the second shot peening treatment to introduce high compressive residual stress into the region directly below the surface of the alloy steel for machine structures and further to reduce the surface roughness. Moreover, as the prestage of the two step shot peening treatment superrapid-short time heating and rapid cooling treatment may be performed.