Effects of Mn/S Ratios and Cooling Conditions on High-temperature Embrittlement in Continuous Casting

Abstract The demand for high-quality steel products has been increasing in recent years. During continuous casting of those steels, the prevention of defect formation is crucial to ensure the highest surface quality. This contribution focuses on the effects of different Mn/S ratios and cooling conditions on the high-temperature embrittlement under continuous casting conditions using the In-Situ Material Characterization by Bending (IMC-B) test. At low Mn/S ratio and rapid cooling conditions, large surface cracks were observed. A FE-SEM investigation of the fracture surface revealed that fine (Mn, Fe) S precipitated along prior austenite grain boundaries may be considered to be the primary factor of embrittlement. Mild cooling promoted sulfide growth and reduced the number density, thereby decreasing crack susceptibility. Contrary to hot tensile tests, embrittlement was observed even at low strain rates. This discrepancy is attributed to differences in the amount of applied strain associated with the evaluation methods. Results from the present study indicate the importance of understanding the characteristics of evaluation methods and their differences from actual processes.