Inhibiting the shrinkage porosity in 30Cr15Mo1N ingots by vanadium-nitrogen synergy during pressurized solidification

Shrinkage porosity in high -nitrogen stainless steel ingots can be eliminated through pressurized solidification. However, in practical industrial settings, achieving the necessary solidification pressure to inhibit shrinkage porosity is often time-consuming, labor-intensive, and challenging. In this study, the area ratio, formation height, type, and morphology of shrinkage porosity were investigated in the ingots with the different vanadium and nitrogen contents by experimental observations and statistical analysis. Then, the inhibition mechanism of the vanadium -nitrogen synergy on shrinkage porosity is revealed via an analysis that amalgamates the feeding resistance and critical feeding driving force. This indicated that the difficulty in generating shrinkage porosity intensified in the 0.2 V ingot compared with that in the 0 V ingot, and the primary type of shrinkage porosity changed from net shrinkage porosity to island shrinkage porosity and gas -shrinkage porosity. Gas -shrinkage porosity were more readily formed and relied on the presence of nitrogen pores. In the 0.4 V ingot, the shrinkage porosity virtually disappeared completely. This could be attributed to the suppression of the nucleation and growth of nitrogen pores with increasing vanadium content. Meanwhile, the dendritic growth restriction factor increased through the vanadium -nitrogen synergistic effect, inhibiting dendrite growth and resulting in a decrease in feeding resistance. This reduced the critical feeding driving force and promoted the feeding flow between the dendrites, ultimately inhibiting the formation of shrinkage porosity. This study revealed the mechanism by which the synergistic effect of vanadium and nitrogen inhibits the formation of shrinkage porosity during the solidification of 30Cr15Mo1N ingots, providing an efficient method for improving the solidification quality of high -nitrogen stainless steel, which is extremely helpful for its manufacture.