Mechanism of formation of internal and surface defects in casting and their transformation into surface defects of sheet

Abstract

This study aimed to elucidate the formation mechanisms of micro-macrostructural heterogeneities in the ingot's cortical zone and their transformation into surface defects during heating, plastic deformation, and rolling processes. The methodology and results of studying the macro- and microstructural and chemical heterogeneities of ingots and finished rolled sheets are presented. A comparative method of structuralconcentration analysis of metal at the end-to-end metallurgical processing stage of ingot - slab - rolled sheets was developed. The technique utilizes metallographic methods to study the structure and perform qualitative analysis of non-metallic inclusions. The research findings indicate that the quality of the rolled sheet surface is predominantly determined by the physical heterogeneity of the ingot's crust zone, while the internal defects in thin rolled sheets are largely influenced by the contamination of the metal with non-metallic inclusions. A novel mechanism is proposed for the transformation of defects in the casting cortical zone into surface and internal defects in rolled sheets. This study contributes to a deeper understanding of the formation and transformation of defects during metal processing, enabling the development of strategies for improving the quality of rolled sheets. Additionally, the study highlights the importance of controlling the physical heterogeneity of the ingot's crust zone and minimizing non-metallic inclusion contamination to achieve high-quality rolled sheets.