Evolution of Nonmetallic Inclusions in Ti‐Bearing Al‐Killed Steel during Heat Treatment at 1200 °C

Abstract

To understand the evolution behaviors of the inclusions in Ti‐bearing Al‐killed steel, steel samples taken from a 20CrMnTi casting billet are heated at 1200 °C for different times, and the changes in composition, size, and numbers of the inclusions are investigated. Some modeling experiments are also designed to reveal the interaction between solid steel and inclusions using premelted slags. It is found that oxysulfide, sulfide, and nitride inclusions are detected in the casting billet before heating. During heating, small changes are observed in the types of inclusions, while the size of these inclusions increases with time. The Mn and S in steel transfer to the sulfide phase of these inclusions and further generate a (Ca, Mn)S solution. The Ti in steel replaces some of the Al element in the oxide part of the inclusions, resulting in the increase of TiOx content and the drop of Al2O3 content in the inclusions. When the TiOx content is sufficient, a thin layer of TiN is predicated at the edges of the oxide part. The reaction between the TiOx in inclusions and the N in steel plays a role in this evolution.