Hot tears (HT) and hot tear segregations (HTS) are common defects obtained in continuously cast steel. Their formation is closely related to microsegregation phenomena in combination with mechanical stresses exerted on the solidifying strand shell. In the vast majority of cases, the formation of HT/HTS in the casting process plays a minor role for an adequate product quality. However, it is well known that segregated hot tears most likely transform into undesirable hardening structures during subsequent rolling and heat treatment. The inhomogeneity on microscopic scale may seriously affect the performance of high-quality steel grades. In another scenario, internally located hot tears may propagate to the surface in the steel sheet forming process. Possible consequences are an increased scrap rate or the total failure of the component in the final application.
For a selected steel grade, case studies are presented by numerically investigate HT/HTS formation in a continuous slab caster. Therefore, a strain-based hot tearing criterion developed at the Chair of Ferrous Metallurgy (Montanuniversitaet Leoben) was implemented in an in-house solidification model; the software tool was programmed in a joint project together with voestalpine Stahl Linz GmbH. Within the simulation trials the influence of (i) increased content of strongly segregating elements (P, S), (ii) changes in the secondary cooling strategy, (iii) different casting machine configuration and (iv) the maintenance conditions (roll misalignment) on the hot tear formation tendency was systematically analyzed. The calculations were compared with macro etching samples and critical conditions in the casting machine were identified. Finally, hot tear formation in the casting process could be prevented by adjusting the secondary cooling practice according to numerical findings.