Effect of Mg addition on carbides in H13 steel during electroslag remelting process

Abstract

The effect of Mg on carbides precipitation in H13 steel was studied based on the Thermo-Calc thermodynamic calculation. The results showed that the precipitation temperature of MC phase was significantly improved by adding Mg. The Mg addition had no effect on the type of precipitated carbides. The as-cast microstructure and the characteristic of carbides in Mg-containing H13 steel were analyzed by OM and SEM-EDS. The results showed that the segregation of as-cast microstructure was released and the size of carbides was reduced by increasing Mg. The distribution of carbides was more homogeneous. The formed MgO · Al2O3 arising from Mg treatment provided preferred nucleation site for TiN, which was the core of heterogeneous nucleation of carbides, resulted in decreasing the size of carbides. Furthermore, partial Mg would melt into the carbides, which would change the morphology of carbide and induce the formation of leaf-like carbides. The electron probe micro-analysis (EPMA) results showed that the segregation of V and Mo in H13 steel was inhibited by Mg, and the dissolved Mg in carbide promoted the heterogeneous nucleation of carbides.