Inclusion characteristics of stainless steel castings

The characteristics of non-metallic inclusions in 347 stainless steel samples taken during a net-shape casting process after different holding times and melting temperatures were investigated using electrolytic extraction and polished cross-sections. The inclusions can be classified into three groups: oxides, composite inclusions and sulphides. Within the first two groups the inclusions were subdivided based on their morphology into the following categories: spherical, irregular and clusters. As the temperature decreased, sulphide and NbC precipitated within the steel melt as well as on the surface of existing oxides. The number density and area fraction of inclusions as well as the total oxygen contents increased with higher melt temperatures and longer holding times. The results obtained from thermodynamic calculations carried out using the FactSage™ commercial software agreed well with the experimental observations. In addition, it has been concluded that turbulent collisions are the dominant mode for the growth of inclusion clusters.