A phase diagram was drawn through thermodynamic calculation to understand the equilibrium conditions of 2MgO · SiO2 , MgO · Al2O3 , 3Al2O3 · 2SIO2, and 2MgO·2Al2O3 · 5SiO2 formation in Mg-AI-Si-O system of 430 stainless steel melts at 1873 K. Further, the thermodynamic formation and transformation conditions of MgO · Al2O3 inclusion were discussed. The following results are obtained when ws, =0.26% and wo = 1.0 × 10^-5 in molten steel. The uniphase cordierite inclusion is difficult to exist stably; MgO· At203 inclusion cannot he formed in case of wAl being less than 1× 10^- 6 ; 3Al2O3 · 2SiO2 would change to MgO· Al2O3 and 2MgO · SiO2 in turn with increasing the Mg content when wAl is above 1.7× 10^- 6 ; with the formation of MgO · Al2O3 inclusion, A1 content increases with increasing Mg content when wMg is over 1. 7 × 10^- 9. For equilibrium condition and calculated steel composition, 2MgO·SiO2 inclusion would be formed ultimately and MgO · Al2O3 is almost inexistent.
Refining process of 430 stainless steel in AOD （argon oxygen decarburization） was simulated under the experimental condition. Al was chosen as deoxidizer, Mg-Al alloy was added in process of refining, and slag used in oxidation period of AOD was chosen in the experiments. The variation of total oxygen content, the size, morphology and composition of inclusions in refining process and the mechanical properties, pitting corrosion resistance of final samples were studied. The results show that no obvious differences in total oxygen content were observed among all the experiments. Neither chain nor cluster Al_2O_3 inclusions were found in refining process of experiments treated by Mg-Al alloys, the average size of inclusions in the steel treated by Mg-Al alloys was less than that of inclusions in steel not treated by Mg-Al alloy. 430 stainless steel treated by Mg-Al alloy shows better tensile strength, yield strength, and pitting resistance than that in the contrast experiment.
