QUALITY OF WHEEL STEEL WHEN USING SECONDARY METAL RAW MATERIAL: CONTROL AND REDUCTION OF NON-METALLIC INCLUSIONS

Abstract

Abstract. The article addresses a comprehensive scientific and technological solution to the pressing problem of improving wheel steel quality under conditions of an increasing share of secondary metal raw materials in steelmaking. In the context of stricter requirements of GOST 10791–2011 for strength and metal cleanliness, the content of non-metallic inclusions (NMIs) becomes a key limiting factor for the relia-bility and fatigue resistance of railway wheels. The paper systematizes modern concepts regarding the na-ture, formation mechanisms, and evolution of NMIs throughout all stages of metallurgical processing, from melt deoxidation to solidification of continuously cast billets. The authors propose an integrated methodology for controlling steel contamination based on a com-bination of automated particle analysis (APA) using SEM-EDS, multivariate cluster analysis of inclusion chemistry, extreme value statistics, and thermodynamic modeling of phase equilibria. This approach ena-bles not only classification of inclusion types (corundum, spinels, calcium aluminates, sulfides, and oxysul-fides) but also prediction of the probability of occurrence of critically dangerous particles in the bulk mate-rial. Special attention is given to the physicochemical mechanisms of oxide inclusion formation during aluminum deoxidation, their growth and coalescence, and their interaction with the solidification front in different structural zones of continuously cast billets. It is shown that the most unfavorable accumulation of NMIs occurs in the transition and central equiaxed zones, justifying targeted incoming inspection of bil-lets. A key technological tool for mitigating the harmful effects of NMIs is calcium modification of steel. Based on thermodynamic analysis and industrial experiments, the optimal [Ca]/[Al] ratio of 0.23–0.31 was established, ensuring transformation of angular corundum into globular calcium aluminates coated with CaS. An optimized ladle-furnace treatment combined with vacuum degassing and electromagnetic stirring during continuous casting was developed. This technology reduces sulfur, oxygen, and hydrogen levels, decreases hazardous inclusions by 60–70 %, and increases the yield of acceptable metal to 99 % and above. The results have direct industrial relevance for manufacturing high-reliability railway wheels from recycled metal and can be applied in developing advanced steel quality control standards.