Characterization of the three-dimensional morphology of MnS precipitate in Ca-treated resulphurized free-cutting steel via fracture surface analysis

ABSTRACT MnS precipitates in resulfurized free-cutting steels are elongated in the rolling direction and then have a large size in length. It is difficult to accurately obtain the characteristics especially full length of MnS by two-dimensional observation. Three-dimensional morphology of MnS in a Ca-treated resulfurized free-cutting steel was investigated by using tensile method and scanning electron microscopy. Compared with the statistical results of MnS in two-dimension, the size in three-dimension was larger. In two-dimension image, the length of MnS was in the range of ~100 μm, and the percent of MnS with size in the rage of 50~100 μm was about 1.15%. In three-dimension image, however, the length of MnS observed was in the range of ~325 μm, and the percent of MnS with size larger than 100 μm was about 5.73%. The results provide an insight into the role of fracture surface analysis in MnS characterization in resulfurized free-cutting steels.