Characterization and Analysis of Non-Metallic Inclusions in Low-Carbon Fe-Mn-Si-Al TWIP Steels

Abstract

A characterization of non-metallic inclusions in Fe–Mn–Si–Al twinning-induced plasticity (TWIP) steels during argon oxygen decarburization–electroslag remelting–forging (AOD–ESR–forging) process has been performed. The two main kinds of inclusions found in TWIP–AOD ingots are single Al(O)N and MnS(Se)–Al(O)N aggregates. After the ESR process, Al(O)N and MnS(Se) inclusions in all size ranges significantly decrease while other kinds of inclusions show only minor changes. In the present study, the precipitation, growth, and dissolution of AlN and MnS inclusions have been analyzed by thermodynamics and kinetics. It is found that AlN inclusions in TWIP steels can already precipitate in the liquid. Furthermore, AlN inclusions precipitated in the liquid TWIP steels can act as the heterogeneous nuclei of MnS inclusions, and thus forming Al(O)N and MnS(Se) · Al(O)N clusters. After ESR refining, the precipitation temperature of AlN and MnS inclusions will be significantly decreased, and AlN inclusions cannot be formed in the liquid TWIP steels in particular. The kinetic analysis show that the growth of AlN inclusions will be difficult during the ESR process, because their growth rate decreases significantly, while the dissolution rate increases.