Evolution of oxide and sulfide inclusions during the production of an Al-killed free-cutting steel

Abstract

The evolution of oxide and sulfide inclusions during the refining, continuous casting, and rolling of an aluminum-killed free-cutting steel was investigated. The composition, morphology, size, number density, and area fraction of inclusions in the steel were detected, and showed a remarkable variation during each production step of the steel. After the addition of ferroalloys into the molten steel during LF process, the content of CaO in oxide inclusions increased from 1.32 wt.% to 4.35 wt.% and that of CaS increased from 3.12 wt.% to 13.86 wt.%. During vacuum degassing process, the removal fraction of inclusions from the steel was approximately 40.9% and 52.9% for the number density and area fraction, respectively. With a proper amount of calcium addition, the elongation of MnS inclusions in the steel after rolling was efficiently decreased, which was predicted using thermodynamics calculation in the current paper.