STEEL MATERIAL, PROCESS FOR PRODUCING STEEL MATERIAL, AND APPARATUS FOR PRODUCING STEEL MATERIAL

摘要

A process for producing a steel material is provided which includes subjecting a highly strengthened steel material (W) to a heat treatment to thereby cause part of the steel material to have a lower hardness than the remainder of the steel material (W).  The heat treatment comprises: a heating step in which that part of the steel material (W) which ranges from the surface to a certain depth is rapidly heated by induction heating or direct ohmic heating; and a cooling step in which the steel material (W) which has undergone the heating step is rapidly cooled at a given time period after the heating step.  In the heating step, the steel material (W) is heated to a temperature not lower than transformation point Ac1.