Experimental investigation of the surface crack sensitivity of a scrap-based steel under conventional and thin slab casting conditions

The increasing use of electric steelmaking routes and the utilization of low-grade, obsolete scrap as input material pose the risk of contaminating the steel with unwanted and harmful tramp elements, such as Cu and Sn. Tramp elements deteriorate the steel quality during the production process and consequently the quality of the final product. The focus of this study is on the impact of Cu and Sn on continuous casting, particularly during the straightening of the slab. The present study aims to experimentally simulate and assess the surface crack formation tendency of a conventional and a Cu- and Sn-contaminated Medium Carbon (MC) steel during straightening, simulating conventional continuous casting (cc) and thin slab casting (tsc) by applying the in-situ material characterization by bending (IMC-B) test. For the MC steel, a moderate ductility trough can be observed in the temperature range of 850 °C to 950 °C for cc conditions; however, hardly any ductility trough can be observed for tsc. For the MC steel with Cu and Sn, a pronounced ductility trough can be observed between 850 °C and 1050 °C under cc conditions, whereas for tsc conditions, only 1000 °C shows critical behavior. A high-resolution SEM-EDX study of intergranular cracks reveals the contribution to surface cracking of Cu/Sn phases during the bending test and shows that at 900 °C, the faster tsc process can lead to a lower amount of harmful Cu/Sn phases present on the crack fracture surface.