低炭素鋼におけるMnS系介在物の形成過程

抄録

Steels containing 0.25% carbon, 0.03% sulfur and 0.3 to 1.2% manganese were melted and quenched at various temperatures between the final stage of solidification and 400°C. The number, volume fraction and distribution of sulfides were investigated in connection with the grain boundary and dendritic structure.
Sulfides were grouped into two categories; the first was crystallized by a eutectic reaction and the second was precipitated from solid steel. The increase in manganese content and cooling rate was favorable to the formation of eutectic sulfides. These were mainly distributed at grain boundaries and interdendritic regions. On the other hand, precipitated sulfides increased in number as the manganese content and cooling rate decreased. These sulfides were classified into the colony type and non-colony type. The former was observed mostly at grain boundaries, and the latter tended to be precipitated within grains and dendrite arms.