亜共晶，過共晶鋳鉄の凝固過程に及ぼすMn, Sの影響

Abstract

The solidification process of hypo-and hyper-eutectic Fe-C alloy was investigated by thermal analysis and quenching method. The flake graphite separated from the eutectic austenite in hypo-eutectic iron, while in hyper-eutectic alloy the primary graphite separated directly from the melt and was surrounded by small austenite dendrites followed by the eutectic solidification around them. Addition of manganese to these alloy made plate-like cementite in the melt at eutectic or at primary solidification which neucleates the ledeburite colonies, and the ledeburite structure was normal and the solidification temperature was not so much supercooled. On the contrary, addition of sulphur changed the flake graphite to undercooled structure containing small amount of nodular graphite or cluster-type mesh-like graphite and then produced the inverse-chilled or massive ledeburite structure. The temperature of austenite-graphite eutectic solidification was lowered by increasing the sulphur content and that of the formation of plate-like cementite in eutectic or hyper-eutectic melt was lowered considerably. By these investigations it was considered that manganese stabilized the cementite and made its formation more easy than that of the eutectic austenite or the primary graphite, but sulphur interrupted the formation of eutectic austenite or primary graphite and supercooled the melt resulting in the formation of some abnormal graphites or massive ledeburite.