Predicting Grain Structure in Continuously-Cast Stainless Steel Slab

Abstract

Macrostructural features in continuously-cast stainless steel slabs such as the distribution of equiaxed and columnar grains, and microporosity, are crucial to the post-processes, and the mechanical properties of the final steel products. Among the methods for controlling grain structure during the continuous casting process, the application of electromagnetic stirring (EMS) during casting is known to alter the grain structure of the slab. In this study, we predicted macrostructural features in a continuous-cast stainless steel slab using computer simulation. We approximated the heat transfer system as a one-dimensional heat conduction model with solidification. The effect of EMS was investigated by introducing an effective thermal conductivity of the melt. We assumed that EMS caused turbulent flow, and enhanced the thermal conductivity. Columnar-to-equiaxed transition (CET) and microporosity were estimated with the models proposed by Hunt and Niyama, respectively. The effect of EMS on microporosity was negligible, and microporosity was inevitable in the centerline of the slab. EMS made a second equiaxed region between the outer wall and the center of the slab. Because the effective thermal conductivity was high due to EMS, the temperature field in the slab was distorted, and the Hunt criterion for CET was satisfied in the region. The CET results were compared and verified with cellular automata simulation. Various process parameters including casting speed, superheating, and the position of the EMS module, were examined to predict the macrostructure of the slab.