Propagation form of internal cracks induced by continuous casting soft reduction and control strategy for internal quality

The propagation form of internal cracks induced by continuous casting soft reduction and the control strategy for enhancing the internal quality of 45 steel through industrial trials and a three-dimensional flow-heat transfer-solidification coupling model were investigated. The results showed that the internal cracks induced by soft reduction exhibited a characteristic of being "coarse in the middle and fine at both ends", and displayed an elliptical arc distribution on the loose side of the strand cross section. The cracks originated within the brittle temperature range and propagated inward to the liquid impenetrable temperature and outward to the zero ductility temperature or below. The control strategy for enhancing the internal quality of the 45 steel strand through soft reduction is to adjust the casting speed or the reduction zone appropriately, ensuring that the central solid fraction of the reduction zone falls within the range of 0.33-0.99. At this point, a reasonable reduction amount is allocated to eliminate the center shrinkage cavities and center segregation, even if it results in minor reduction-induced cracks.