Effects of micro-alloying elements and continuous casting parameters on reducing segregation in continuously cast slab

Highlights: • Two mathematical models for simulating macrostructure and secondary dendritic arm spacing were established and coupled. • Effective solidification time directly determined the value of secondary dendritic arm spacing. • Micro-alloying elements had larger influence ratios on secondary dendritic arm spacing than superheat and casting speed. • The secondary dendritic arm spacing got refined and the segregation defect got improved after optimization. In this work, CAFE model and SDAS model were established to study the macrostructure and secondary dendrites of slab cross-section, respectively. The influences of micro-alloying elements (Nb, V, and Ti), superheat, and casting speed on secondary dendrite arm spacing (SDAS) were investigated. The results revealed that within the adjustable range of micro-alloying elements, the increase of Nb and V contents in steel can contribute to refining SDAS. The value of average SDAS with the increase of Ti content had a big fluctuation. The variation of SDAS attributed to the influence of micro-alloying elements on the thermal conductivity which further resulted in the change of effective solidification time (EST). EST played a leading role in determining SDAS. The decrease of superheat or casting speed can contribute to refining SDAS. The influence ratios of micro-alloying elements on SDAS were larger than that of superheat and casting speed. After adjusting the micro-alloying elements contents and CC process parameters, the SDAS in the experimental slab obtained effective refinement and the center equiaxed crystal ratio of slab cross-section increased by 8.5%. The segregation defect in the center of experimental slab got improved as well.