저탄소주강의 유화물 조직관찰에 대한 연구

Abstract

Fe-S alloys were produced in the condition of laboratory scale, and its microstructural characteristics were investigated. Sulfur powder and pure iron of Fe-31.6 wt% S composition were charged into a quartz tube. The quartz tube was vacuum-sealed, then held at 1,000℃ for 96 hours, after that quenched in water. The rod type Fe-31.6 wt. % S samples showed hyper-eutectic structure such as primary FeS and eutectic Fe-FeS, with a single phase FeS intermetallic compound. Nine specimens, classified in three types, which has Mn/S ratio of 1, 5, and 70 respectively by vacuum arc melting, suction casting and single roll type melt spinning were produced. Effects of Mn/S ratios and cooling rates on morphology and microstructure of sulfide were investigated. The influence of nital and sulfuric acid etchants on the microstructural characteristics were observed by using OM, SEM and EPMA. It was found that the matrix was etched by nital etchant and sulfides were etched by sulfuric acid preferentially, so that it was possible to distinguish the shape and microstructure of sulfides clearly. The sulfides, MnS and FeS, and the solidification structure were clearly identified by the etching of sulfuric acid. The various morphologies of sulfides such as eutectic phase, globular, granular, dendrites, clusters, chain, elongated rod, films and angular were observed in low carbon steel castings.