Analysis of three-dimensional morphology of sulfides in continuous casting billet of 20MnCr5 gear steel
ZHANG Xiaoyu, ZHAO Menghao, ZHU Qiangbin, XU Xiangyu, FU Jianxun*
Center for Advanced Solidification Technology(CAST),State Key Laboratory of Advanced Special Steel, School of Materials Science and Engineering,Shanghai University,Shanghai 200444, China
Abstract：20MnCr5 gear steel has good matching performance between fatigue and easy-to-cut properties. The morphology and distribution of sulfides in the steel are important factors affecting the properties of materials. In order to explore the three-dimensional morphology and distribution law of sulfides in the continuous casting slab of 20MnCr5 gear steel, the continuous casting billet was analyzed by metallographic microscope, scanning electron microscope and three-dimensional etching technology. The results showed that the main type of sulfides in 20MnCr5 continuous casting billet was the composite inclusion of MnS and MnS+Al2O3. The size of sulfides in the billet increased at first and then decreased from the edge chilled layer to the central equiaxed crystal zone. The three-dimensional morphology of sulfides in the chilled layer was mainly ellipsoid and strip-like, which accounted for about half of each. At the end of the columnar crystal region, the proportion of ellipsoid sulfides was reduced to less than 10%, and the proportion of long strip and irregular sulfides was 55% and 35%, respectively. Meanwhile, a small amount of octahedron began to appear. The proportion of irregular sulfides in the central equiaxed crystal region increased to 60%, while the proportion of long strip sulfides decreased to about 30%. The proportion of octahedral sulfide accounted for about 10%, and the proportion of ellipsoid decreased to less than 5%. The three-dimensional morphology of the main sulfides was different in different regions of the continuous casting billet: it was ellipsoidal and long strip in the chilled layer, long strip in the columnar crystal zone, and irregular in the equiaxed crystal zone.
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