As the temperature decreased during the solidification of the molten steel and the variation of the temperature during the heating of the solid steel, the equilibrium between the steel and inclusions shifted, leading to the variation of inclusion composition. The heating modified the structure and properties of the steel and induced reactions between alloy elements in the solid steel and oxide inclusions as well. The transformation of inclusions in the SiMn-killed stainless steel and the Al-killed calcium-treated steel during heating was investigated experimentally and theoretically.