Study on microsegregation model and MnS precipitation behavior of continuous casting ultra-low sulfur steel slab

Abstract

The central segregation of elements in continuous casting slab is an important factor affecting the properties of steel materials. S segregation exists in the form of MnS. It is found in production practice that despite the ultra-low sulfur content of [ S ] ≤ 10 ppm in steel, MnS will still precipitate if the central segregation of slab is not well controlled, and MnS is an important factor causing the unqualified flaw detection of high-grade thick plate products. There are few studies on the microsegregation of ultra-low sulfur steel continuous casting slab. In this paper, the microsegregation model of continuous casting slab is established, and the effect of phase transformation on element segregation is fully considered. The precipitation behavior of MnS and the microsegregation of S, P, C, and Mn elements during slab solidification are discussed. Taking X pipeline steel as the research object, the simulation calculation shows that the segregation degree of P, S, and C is higher than that of Mn. When the solid fraction fs is greater than 0.9, the inflection point of S segregation decreases and MnS is formed. The segregation ratios of P, S, and C (CL / C0) after complete solidification were 4.5, 4.1, and 5.5, respectively. The carbon content affects the degree of element segregation by affecting the local solidification time. With the increase of carbon content, the degree of element segregation at the end of liquid steel solidification decreases.