<p>This study investigates the effects of tramp element accumulation on surface hot shortness in electric arc furnace (EAF) steels with an emphasis on the underlying high-temperature interfacial phenomena and process-relevant compositional limits. As scrap utilization increases in EAF steelmaking, the enrichment of tramp elements such as copper becomes unavoidable, necessitating a mechanistic understanding of their role in high-temperature degradation. The chemical compositions of industrial EAF steels (specifically from South Korean practice) were analyzed to quantify the current levels and accumulation trends of tramp elements under high scrap usage. To elucidate the origin of surface hot shortness, high-temperature oxidation experiments were conducted in conjunction with thermodynamic calculations to examine the formation, evolution, and stability of Cu-enriched liquid phases at the steel/oxide scale interface. The results reveal that copper preferentially segregates and forms a low-melting liquid phase at the interface during oxidation, promoting intergranular penetration and surface cracking. The thermodynamic predictions are in good agreement with experimental observations, validating the proposed approach for describing phase stability and interfacial behavior. Based on this mechanistic framework, a copper-equivalent parameter is introduced to quantify the combined effects of tramp elements, and a critical compositional threshold for the onset of surface hot shortness is established. These findings provide a physically grounded criterion for assessing hot shortness susceptibility in scrap-based steels and offer practical guidance for controlling tramp element levels in EAF processes, thereby supporting the reliable operation of high-scrap steelmaking systems.</p>