Process simulation and inclusion characterization in stainless steel ingot casting

For the ingot casting process, fluid flow of steel plays an important role in quality control and industrial operations. Using CFD software (FLUENT), this study overviews the fluid flow pattern in the bottom-teeming ingot filling process with three different swirl-modified upgate designs. Turbulent flow and mass transfer are considered main factors in controlling the process. The motion of the slag phase was also considered. In addition to the modeling studies, inclusions in stainless steel poured into ingots with a traditional and a swirl-modified upgate system were investigated using an optical microscope, SEM-EDS and ASPEX automated feature analysis technology. The main inclusions observed were Al₂O₃, MnS, and oxide-sulfide. This work provides a comprehensive description and understanding of the morphology and distribution of inclusions in bottom-poured ingot casting. Fewer inclusions were observed at the center and mid-radius of the swirl-modified ingot than that of the traditional ingot. More inclusions were found at the center of the ingot than nearer the walls. The re-designed upgate system did have positive effect on the flow pattern in the ingot and indirectly cause fewer inclusions in size range of 0~10µm, but made no major difference beyond the change in the smallest size range. --Abstract, page iii