This document discusses non-metallic inclusions in steel, including their types, sources, and effects. There are two main types of inclusions: indigenous, which form during steelmaking processes like deoxidation; and exogenous, which arise from refractory erosion or slag entrapment. Common inclusion types include oxides, sulfides, nitrides, and carbides. The presence of inclusions reduces steel properties like ductility, surface quality, and corrosion resistance. Proper argon stirring and controlling slag carryover can help remove inclusions to improve steel cleanliness. Inclusion size, shape (like dendritic alumina), and distribution also impact steel properties.