Mechanism and Control of Sulfide Inclusion Accumulation in CET Zone of 37Mn5 Round Billet

In the current study, the R/2 accumulation was found from the results of sulfide inclusion distribution across the diameter of 37Mn5 round billet using ASPEX. In order to reveal the mechanism and furthermore control this phenomenon, the distribution of sulfur content and the macrostructure of billet after etching were analyzed. The results showed that there was obvious segregation in the same position as sulfide inclusion accumulation, where the columnar-to-equiaxed transition (CET) took place. Therefore, the mechanism of sulfide inclusion accumulation in the CET zone was discussed on the basis of the mechanism of R/2 sulfur segregation. The interlaced and coarse dendrites in the CET zone blocked solute concentrated from select crystallization, thus caused sulfur segregation near R/2. Higher sulfur content and larger secondary dendrite arm spacing (SDAS) in the CET zone benefited the precipitation and growth of sulfide inclusions. The effect factors of CET position were discussed on the purpose that by proper cooling conditions, the morphology of solidification structure can be controlled, by which the element segregation can be modified; thereafter, the control of sulfide inclusion distribution in the billet can be realized.