2022 Volume 108 Issue 8 Pages 552-559
The mechanism of monotectic sulfide formation in free-machining ferritic stainless steel (SUS430F) was investigated. Monotectic sulfides were observed in SUS430F ingots with Si-Mn deoxidation. Eutectic sulfide was found in Al deoxidized ingot. The selection of sulfide morphology can be predicted by the thermodynamic calculation using FactSage software. It was thought that the decrease in sulfide activity by dissolved oxygen as an oxy-sulfide was contributed to the monotectic sulfide formation. Microsegregation of sulfur and oxygen during solidification reduces the interfacial energy between liquid and sulfides and promotes the nucleation of sulfides. Thermodynamic stability was considered to determine the selection of sulfide morphology in SUS430F.
