Mechanism of local solidification time variations with melt rate during vacuum arc remelting process of 8Cr4Mo4V high-strength steel

A 2D axisymmetric numerical model was established to investigate the variations of molten pool with different melt rates during the vacuum arc remelting of 8Cr4Mo4V high-strength steel, and the ingot growth was simulated by dynamic mesh techniques. The results show that as the ingot grows, the molten pool profile changes from shallow and flat to V-shaped, and both the molten pool depth and the mushy width increase. Meanwhile, the variation of both the molten pool shape and the mushy width melt rate is clarified by the thermal equilibrium analysis. As melt rate increases, both the molten pool depth and the mushy width increase. It is caused by the increment in sensible heat stored in the ingot due to the limitation of the cooling capacity of the mold. The nonlinear increment in sensible heat leads to a nonlinear increase in the mushy width. In addition, as melt rate increases, the local solidification time (LST) of ingot decreases obviously at first and then increases. When melt rate is controlled in a suitable range, LST is the lowest and the secondary dendrite arm spacing of the ingot is the smallest, which can effectively improve the compactness degree of 8Cr4Mo4V high-strength steel.