In the course of the decarbonization of steel production, electric steel production will continue to gain importance. The processing of low-quality scrap will also play an important role, which may lead to an increase in the content of so-called tramp elements in steel production and further processing. This article examines the effect of the elements Cu, Sn, and Ni on the formation of surface cracks under the conditions of the continuous casting process. Results of an in situ bending test are compared with the results of the experimental simulation of high-temperature oxidation and thermodynamic analysis based on the CALculation of PHase Diagrams (CALPHAD) approach. For a temperature of 900 °C, an equivalent Cu content of 0.20 wt% must be considered as the critical upper limit. The presumable reason is the existence of Cu- and Sn-rich liquid phases at the austenite grain boundaries. The results clearly show the effect of the investigated elements but also point to the importance of the gas atmosphere and cooling conditions on the results. This can be a groundbreaking result for extending the process window for casting steels with increased tramp element contents.