Delving Deep into the Influence of Pressure on Columnar-to-Equiaxed Transition in High-Nitrogen Steel Ingot by Thermodynamics and Kinetics

Abstract

Based on the analysis of thermodynamic driving force and solidification kinetics under pressure, the influence mechanism of solidification pressure on columnar-to-equiaxed transition (CET) of high-nitrogen steel is clarified. It is observed that increasing the solidification pressure from 0.5 to 2 MPa results in a shift of the CET positions toward the center. This is attributed to the fact that higher solidification pressure can promote the growth of columnar dendrites by increasing the solidification rate, temperature gradient, and cooling rate. Meanwhile, increasing the solidification pressure shortens the length of the diffusion zone ahead of the advancing columnar front and reduces the supercooling. As a result, it becomes more difficult for equiaxed dendrites to nucleate ahead of the advancing columnar front, leading to CET positions closer to the center. This indicates that the main influencing factor for the change in CET caused by changing solidification pressure is solidification kinetics, that is, changes in the nucleation and growth environment of equiaxed dendrites, while thermodynamic driving forces are not the primary factor causing CET position changes.