低炭素A1キルド鋼の凝固および熱延状態における硫化物系介在物形態におよぼすSi, Mn量の影響

抄録

The morphology and distribution of sulfides in steel ingots having different silicon contents from 0 to 2.0% at 0.3 to 1.5% manganese contents were investigated with a directional-solidification technique. The steels had carbon content of 0.05%, sulfur content of 0.05% and low oxygen content and they were solidified at cooling rate of 5°C/min. The deformation behavior of their sulfides during hot-rolling after heating at 800°1200°C was also investigated.
In the specimen containing 0% Si and 0.3% Mn, the manganese sulfides in the as-cast state were globular in shape and contained about 40% FeS (GlObular sulfide is called type It.). Silicon addition above 1.1% changed the morphology of sulfides from type It to type III according to Sims' classification and decreased the FeS content of manganese sulfide. Type II sulfide was observed in the specimens containing manganese in the range of 0.61.5% at 0% Si.
The relative plasticity of sulfides increased as the heating (_??_ rolling) temperature decreased from 1200°C. While with type II in 1.0% Mn steels the trend continued to 800°C, with type It and III in 0.3% Mn steels maximum plasticity was encountered at 1000°C. The decrease in relative plasticity had a close relationship with the increase in the FeS content of manganese sulfides and the decrease in manganese sulfide size. The difference in plasticity between type It and III MnS and type II MnS was thought to be due to presence of FeS.