Formation Mechanism of Band Delta-Ferrite in 416 Stainless Steel and Its Relationship with MnS and M23C6

AISI 416 steelSteel with a banded structureBanded structure (BS) that is formed by element segregationSegregation, and its MnS significantly affects its microstructureMicrostructure and properties during the hot working processProcess. In this study, we investigated the formation mechanism of the BS and its relationship with MnS in 416 steelSteel by carrying out thermodynamic calculations and microscopic characterizationCharacterization measurements. The BS was identified to be a delta-ferrite phase rich in Cr. In addition, when the volume fraction of delta-ferrite was the largest during the 1665 K, the BS was most likely to precipitate. The fine M23C6M23C6 particles around the BS enhanced the segregationSegregation of Cr and worked with the MnS inclusionsMnS inclusion to pin the surrounding grains. The metastable-banded structureBanded structure formed near the BS transformed into a martensite phase. The MnS inclusionsMnS inclusion pinned and refined the grains and showed four types of distributions.