機械構造用鋼の軽圧下‐粗大粒発生挙動におよぼすC量およびCr，Mo添加の影響

Abstract

The purpose of this research is to clarify the effects of carbon content and chromium-molybdenum addition on grain coarsening behavior in hot working by small strain of steels for machine structural use. The tendency of grain coarsening is as remarkable as high carbon steel. The influence of carbon content is slight to grain coarsening behavior of the austenite grain in hot working with small strain. In low carbon steels, ferrite structure occupies the great portion of microstructure. In these steels, two or more ferrite grains generate from one austenite grain, and those divide an austenite grain. Therefore, the coarse grain or mixed grain of austenite is not directly taken over to a transformed microstructure. It is based on the above reason that the tendency which a coarse grain pearlite structure generates is reduced in low carbon steels. In SCM435 steel, ferrite-bainite structure occupies the great portion of transformed microstructure and includes the coarse bainite structure. This is because coarse grain or mixed grain of austenite structure is directly taken over to a bainite structure.