A New Cooling Strategy in Curved Continuous Casting Process of Vanadium Micro-alloyed YQ450NQR1 Steel Bloom Combining Experimental and Modeling Approach

Abstract

In the continuous casting process of steel, the bloom surfaces would experience intensive cooling from the water-cooled copper mold to secondary cooling water spray. If the cooling process is not controlled properly, hot ductility of the bloom surface microstructures would deteriorate, and bloom surface cracks would form easily under straightening deformation in a curved caster. Considering the above facts, the cooling scheme for the continuous casting of YQ450NQR1 steel bloom, a kind of vanadium-containing micro-alloyed steel, is studied with both experimental investigation and mathematical modeling in this work. The authors first investigate the hot ductility of bloom surface microstructures at various cooling rates using a Gleeble thermal simulator. Then, the precipitation of V(C, N) particles and its influence on ferrite formation during continuous cooling are studied and characterized using High-Temperature Laser Scanning Confocal Microscopy. Based on these, the preferred cooling rate for surface microstructures at the straightening position in the caster is obtained. To further reduce the solute macro-segregation through enlargement of the equiaxed crystal zone, a cellular automaton-finite element model is used to calculate heat transfer and solidification structure evolution during the continuous casting process. After calibration with industrial trials, the model is utilized to determine the critical position for columnar to equiaxed transition and to adjust the pouring temperature for the melt. Combining the above research, a new cooling strategy for YQ450NQR1 steel bloom is obtained, which can improve crack resistance of bloom surface microstructures and reduce solute macro-segregation at the same time.