Mechanism of crack initiation and propagation in high-alloy steel slabs during the cooling and scarfing processes after the continuous casting process

Abstract

The continuous casting process, which is the initial process of manufacturing alloys, has drawn significant attention from researchers. In the continuous casting process, the molten alloy is solidified to form a slab, and most researchers have focused on the formation of cracks and microstructural changes during this process. Currently, various alloying elements, such as titanium, chromium, niobium, boron, and manganese, are added to high-carbon steel to obtain a light-weight and high-strength alloy. In some of these steel alloys, cracks are generated and fracture occurs during the cooling process preceding the next process after the continuous casting process. To investigate the phase transformation in the cooling process and the subsequent scarfing process following the continuous casting process, thermal analysis and thermal stress analysis were performed through finite element analysis. The probability of fracture according to the steel components was comparatively evaluated based on the 2000 MPa hot press forming steel, which fractured during the cooling process after the continuous casting process. In addition, the fracture toughness and impact toughness were measured for six types of steel alloys. The analysis confirmed that cracks are mainly formed at the corner of the slab during spontaneous cooling. Thus, the probability of fracture occurrence could be predicted. It was confirmed that fracture occurred due to the transverse cracks formed on the surface of the steel slabs during the scarfing process. In natural cooling conditions, it was found that the probability of cracking was highest after the scarfing process when the steel has carbon content of 0.3 wt% and without additive such as titanium, chromium, niobium, boron, or manganese. We also found that the cracking mechanisms were different during the cooling process and scarfing process. Based on this study, we proposed a method to suppress cracks formed by these mechanisms in steel.