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 degrees 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 degrees 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 degrees C).