Analysis of phase equilibria in liquid chromomanganese steel in the presence of calcium. Report 3. Phase equilibria in the system Fe–Ca–Cr–Mn–C–O (high-alloy steel)

Abstract

The quantity and morphology of non-metallic inclusions (NI) in structural steels have a significant impact on the performance properties of metal products. The chemical and phase composition of the resulting NIs depend on the composition of the steel and the content of impurity elements in it, which in turn is determined by the characteristics of the technological process at a particular enterprise. In this work, phase equilibria are studied in systems for which deoxidation processes of high-alloy steel are realized, i.e. in melts with a high (10–13%) content of chromium and manganese. Based on a thermodynamic analysis of the interaction processes of oxygen, chromium, manganese, calcium and carbon in iron, the solubility surfaces of components in liquid metal (SSCM) were constructed. Analysis of the data obtained suggests that the main NIs in this case should be solid oxides CaO and MnO with a small amount of FeO, as well as solid solutions of spinels. For steels with a chromium content of 13% and higher, there is a possibility of calcium chromite and Cr3O4 formation. At a carbon concentration of 1% and a high chromium concentration (10 and 13%), the formation of a CO-based gas phase is possible. In the absence of stronger deoxidizers, the oxygen content in the melt remains high (100–200 ppm or more), which is unacceptable in the industrial production of products from this type of steel. To obtain high-quality metal products from high-alloy steels, it is necessary to use stronger deoxidizing agents (for example, aluminum) or special technological methods, such as vacuum melting