Effect of Nitrogen on Solidification Structure and Microsegregation of Electroslag Remelted 7Cr13 Steel

The macrostructure, microstructure and alloying element microsegregation of electroslag remelted (ESR) 7Cr13 steel with different nitrogen contents (0.043, 0.084, 0.164 pct) were studied. The maximum solubility of nitrogen in7Cr13 steel was calculated to be 0.161pct. The peritectic reaction does notoccur once the N content of the steeexceeds 0.121 pct, which leads to the coarsening of the grains of the remelted ingot. The width of the mushy zone decreases but the depth of the metal bath increases with the increase of N content from 0.043 to 0.164 pct. The reduction in the width of the mushy zone is beneficial to the reduction of the local solidification time and the refinement of the secondary dendrites. The microstructure of the ingot is composed of austenite, martensite and eutectic carbides, and irrespective of the N content of as-cast ingot. Nitrogen increases the equilibrium distribution coefficient of N, C and V elements, which is beneficial to the suppression of microsegregation of these elements during liquid steel solidification. The refinement of secondary dendrites makes the distribution of Cr element more uniform although the addition of nitrogen reduces the equilibrium distribution coefficient of Cr.