肌焼鋼の浸炭焼入れひずみに及ぼすCC鋳片断面形状の影響

抄録

Distortion in case hardened JIS-SCM420 specimens was investigated with relation to the shape of continuous casting molds. Hot rolled bars made from two cast blocks, where one of the blocks has round section (Steel A) and the other has rectangular section (Steel B), were prepared. Macro-etched pattern in a cross section of the bars has round shape for Steel A and rectangular shape for Steel B, respectively. After carburizing, ring specimens produced from Steel B were distorted to an oval shape, whose line on upside was correspondent to the longitudinal direction of the rectangular macro-etched pattern. On the other hand, the ring specimens of Steel A did not show conspicuous change in shape. It was also confirmed that the shape change in gears of Steel A was smaller than that of Steel B. Furthermore, it was found that the specimens cut from the inner part of the macro-etched pattern expanded less than ones cut from the outer. And a FEM analysis was carried out to check the distortion in mesh models that consisted of a round or rectangular area surrounded by an area with higher expansion coefficient. The calculated shape changes were consistent with the shape change observed in ring specimens and gears.