In this paper, the precipitation of carbide and wear loss of high-carbon 8 mass% Cr tool steel at two tempering conditions (i.e., 773–803 K and 823–853 K) were studied by INCA Steel, EPMA-1720H, XRD, and ML-10 tester. The results show that the particles of test steels include the carbides (Cr₇C₃ and Cr₂₃C₆) and carbides nucleated on Al₂O₃. When carbides are of the same size, the number of carbides in test steel at a tempering temperature of 773–803 K is greater than that at a tempering temperature of 823–853 K, especially when the size of carbides is less than 5 μm. Compared with the test steel tempered at 823–853 K, the distance between adjacent actual particles reduced by 80.6 μm and the maximum amount of reduction was 9.4% for single wear loss at the tempering temperature of 773–803 K. It can be concluded from thermodynamics results that Al₂O₃ inclusions began to precipitate in liquid, and the precipitation of carbides was at the solid–liquid region. Al₂O₃ can be used as the nucleation interface of carbide, thus promoting the formation of carbides. During the cooling of molten steel, a lower temperature can increase the difference of actual solubility product bigger than equilibrium solubility product, thus promoting the carbide formation.

The composition of CaO-SiO₂-MgO-Al₂O₃-CaF₂ slag was designed by thermodynamic calculation of [Al]-[O] equilibrium of FeNi-based expansion alloy. On this basis, the deoxidation and inclusion evolution in the process of slagging and smelting FeNi-based expansion alloy in the medium frequency induction furnace were investigated. The results show that the oxygen content in the alloy melt is mainly controlled by the [Fe]-[O] equilibrium, and the change trend of the equilibrium oxygen content calculated by [Fe]-[O] equilibrium is consistent with the actual oxygen content. The total oxygen content of the final ingot is 45 ppm. After Al deoxidation in the melting process, the inclusions in the alloy are transformed into composite oxide inclusions rich in Al₂O₃ and MgO. After final deoxidation with Si-Ca alloy, the contents of Al₂O₃ and MgO in the inclusions decreased significantly, while the CaO content increased. And there are mainly CaO-SiO₂-MgO-Al₂O₃ composite oxide inclusions in the ingot.