Abstract: In order to analysis the formation of inclusions in 18Ni350 steel, based on the theory of minimum Gibbs free energy, the equilibrium solidification process and the precipitation behavior of the inclusion particles were investigated by using thermodynamics software FactSage under the specific composition. The effect of composition on precipitation process was studied. Meanwhile, ASPEX and SEM-EDS were used to detect the composition and size distribution of inclusions in the samples before and after magnesium treatment. The inclusions in the samples were mainly Al₂O₃-Ti₂O₃ series. The inclusions size was refined after magnesium treatment and the inclusions were with MgAl₂O₄ as core normally. It played a heteronucleation role in the formation of complex inclusions. The results provided important theoretical significance for the formation and control of inclusions in the molten pool of 18Ni350 steel.

Key words: inclusion, Mg-treatment, 18Ni350 steel, thermodynamic analysis