The Interaction Between Oxidation-Related Phenomena Along Grain Boundaries on Surface Crack Formation in Continuous Casting

Oxidation-related surface defect formation in continuous casting is an under-researched topic, as most of the experiments, which aim to define surface defect mechanisms, are performed under a protective atmosphere. However, intergranular oxidation or the formation of low-melting Cu-rich phases at the grain boundaries may lead to tremendous problems during straightening. This study exclusively addresses the impact of oxidation-related pre-defects on surface crack formation in continuous casting and how different parameters, such as cooling cycle and cooling atmosphere, affect the outcome. The investigations were performed using in-situ material characterization by bending tests (IMC-B) to evaluate crack susceptibility and simultaneous thermal analysis (STA) to analyze oxidation mechanisms in detail. Both the damage of grain boundaries by intergranular oxidation due to a low-melting fayalite-wustite eutectic and due to low-melting Cu-rich phases favor crack formation at lower temperatures significantly. A stronger external oxidation can have both positive and negative effects on surface crack formation, depending considerably on the specific steel composition. Regarding intergranular oxidation, increased external oxidation helps minimize internal and intergranular oxidation, thereby reducing potential nuclei for surface defect formation in subsequent processing steps. However, in the presence of Cu and Sn, which do not readily oxidize due to their low oxygen affinity, enhanced external oxidation promotes their enrichment, consequently increasing the risk of defect formation.