Dendrite Segregation Changes in High Temperature Homogenization Process of As-cast H13 Steel

The microstructural evolution and microhardness changes of the H13 ingot during homogenization process were investigated to characterize the dendrite segregation changes by optical microscopy (OM), scanning electron microscopy (SEM), electronic probe micro-analyzer (EPMA), X-Ray diffraction (XRD) and microhardness testing. The results showed that the severe dendrite segregation existed in H13 ingot, and there were a large amount of coarse non-equilibrium eutectic carbides (MC and M7C3) in dendrite region. After the soaking time of 15 h at 1 200 degrees C, the dendrites almost disappeared, the contents of eutectic carbides decreased sharply. The values of segregation ratio SR were 1.20 for Cr, 1.26 for Mo and 1.41 for V, which were the critical values of SR that marked the end of homogenization. After 20 h, a small amount of MC carbides still distributed at the grain boundaries. The SR values almost remained constant with the values of 1.10, 1.14 and 1.14 for Cr, Mo and V element respectively. The homogenization kinetics was established and it matched well with the experimental data. The microhardess in different soaking time reflected well the dendrite segregation changes, it decreased from 817.8 HV to 645.7 HV and then increases to 752.5 HV, finally it decreases gradually.