Morphology of Solidification Structure and MnS Inclusion in High Carbon Steel Continuously Cast Bloom

Abstract

Present study was undertaken to investigate the characteristics of solidification structure and sulfide inclusions in the rail steel U75V continuously cast bloom using various methods, including the metallographic examination, traditional 2D optical microscopy, 3D electrolytic extraction, SEM detection with EDS analysis, and thermodynamic calculation for MnS inclusion precipitation. Metallographic examination shows that the area ratio of chill zone, columnar zone, mixed zone and equiaxed zone in the cast bloom are 5.3%, 43.1%, 21.5% and 30.1%, respectively. 2D/3D investigations on the morphology and distribution of sulfide inclusions reveal that the sulfide inclusions in the subsurface region with smaller equivalent diameter and lower aspect ratio are more fine and rounded compared with those in the bulk, and more complex sulfide inclusions consisting of MnS and TiS with the nuclei of Al₂O₃ particle are observed in the bloom centre. Moreover, the size and distribution of MnS inclusion precipitation in the rail steel U75V continuously cast bloom was numerical predicted, using the heat transfer model for continuous casting coupled with thermodynamic model for MnS inclusion precipitation, and the parametric study show that sulfide inclusions are much larger in size for the continuously cast bloom with high sulfur content and coarse cast structure.