Inclusion Engineering in Medium Mn Steels: Effect of Hot-Rolling Process on the Deformation Behaviors of Oxide and Sulfide Inclusions

Abstract

Medium Mn steel (MMS) is a new category of the third-generation advanced high strength steel (3rd AHSS) which is developed in the recent 1-2 decades due to a unique trade-off of strength and ductility. Thus, this steel grade has a wide application potential in different fields of industry. The current work provides a fundamental study of the effect of hot-rolling on the inclusion deformation in MMS including a varied 7 to 9 mass pct Mn. Specifically, the deformation behavior of different types of inclusions (i.e., Mn(S,Se), liquid oxide (MnSiO3), MnAl2O4, and complex oxy-sulfide) was investigated. The results show that both MnSiO3 and Mn(S,Se) are soft inclusions which are able to be deformed during the hot-rolling process but MnAl2O4 does not. The aspect ratio of soft inclusions increases significantly from as-cast to hot-rolling conditions. When the maximum size of different inclusions is similar, Mn(S,Se) deforms more than MnSiO3 does. This is due to a joint influence of physical parameters including Young's modulus, coefficient of thermal expansion (alpha), etc. However, when the maximum size of one type of inclusion (e.g., MnSiO3) is much larger than another one (e.g., Mn(S,Se)), this maximum size of soft inclusions plays a dominant role than other factors. In addition, the deformation behavior of dual-phase inclusion depends on the major phase, i.e., either oxide or sulfide. Last but not least, empirical correlations between the reduction ratio of the thickness of plate, grain size, and aspect ratio of oxide and sulfide inclusions after hot-rolling are provided quantitatively. This work aims to contribute to the 'inclusion engineering' concept in the manufacturing of new generation AHSS.