Thermodynamic Analysis of MnS Inclusion Precipitation in Non-Quenched and Tempered 46MnVS5 Steel

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Based on the theories of thermodynamic equilibrium and non-equilibrium solidification, this paper systematically investigated the precipitation behavior of MnS inclusions during the solidification of non-quenched and tempered 46MnVS5 steel. By calculating the standard Gibbs free energy change, equilibrium constant, activity coefficient, and liquidus and solidus temperatures for the MnS formation reaction, and combining these with the Scheil-Gulliver model and FactSage 8.1 software, this study analyzed the changes in the concentration product, the conditions for the onset of precipitation, the patterns of element segregation, and the influence of alloying element content during the solidification process. The results indicate that MnS precipitation is jointly controlled by temperature reduction and the enrichment of Mn and S elements, with substantial precipitation occurring primarily during the late stage of solidification (solid fraction > 0.95); the Scheil model predicts a precipitation onset temperature of 1290 ℃ and a final MnS mass fraction (relative to the total system mass) of approximately 0.09%; the contents of C, Mn, and S significantly influence MnS precipitation behavior, while those of Al, Si, and P have a negligible effect. These findings provide a theoretical basis for controlling the morphology of MnS inclusions in non-quenched and tempered steels.

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