Transformation of Inclusions in 430 Stainless Steel During Heat Treatment at 1473 K (1200 °C)

To investigate the evolution mechanism of inclusions in solid 430 stainless steel during heat treatment, in this study, two kinds of experiments were performed: one was a heat treatment experiment conducted at 1473 K (1200 °C) for different times in the range of 0 to 8 hours under an argon atmosphere; the other was a diffusion couple experiment performed using a steel sample and an oxide sample to clarify the diffusion of elements at the interface between the steel matrix and inclusion during heating. The results showed that [Cr], [Mn] and [Ti] in the steel could react with SiO2 in the single-phase MgO–Al2O3–SiO2–CaO inclusion during the heat treatment at 1473 K (1200 °C), resulting in the formation of the Al2O3–TiOx–Cr2O3–MnO phase in the MgO–Al2O3–SiO2–CaO inclusion. This phenomenon was also observed and demonstrated in diffusion couple experiments. Thermodynamic calculation results indicated that when the interfacial reaction reached equilibrium, the content of the Al2O3–TiOx–Cr2O3–MnO spinel phase in the inclusion could reach more than 20 mass pct. In addition, dissolved [Ti] and [N] in the steel combined with each other and led to the precipitation of the TiN phase on the surface of the Al2O3–TiOx–Cr2O3–MnO phase during heat treatment at 1473 K (1200 °C).