Characterization of the formation of slag rims of mold powder during hypo-peritectic steel continuous casting based on full-sectional microstructures

• A full-sectional microstructure characterization method was developed to investigate coarse slag rim formation during hypo-peritectic steel continuous casting. • Slag rim formation is driven by liquid slag solidification during mold oscillation, with average heating rates of ~100 K·s−1 and cooling rates of ~400 K·s−1 producing lamellar microstructures. • Two distinct formation pathways for highly crystalline mold powders were identified: powder A (higher breaking temperature/viscosity, narrower solidification range) forms coarse, thick rims; powder B (lower values, wider range) forms thin rims. • The findings provide critical insights into controlling longitudinal surface cracks in hypo-peritectic steel by understanding and managing slag rim formation.