Effect of trace magnesium on carbide improvement in H13 steel

In the present work, the carbides and inclusions in H13 steel with different magnesium contents were investigated with the scanning electron microscope ( SEM), energy dispersive spectroscopy ( EDS), and were calculated by the ThermoCalc and FactSage softwares, respectively. The growth of the MgAl2O4 spinel and Al2O3 at 1500 degrees C in molten H13 was analysed by the confocal laser scanning microscopy ( CLSM). The disregistries between the carbides and other phases were computed. The results are as follows. The primary carbides formed in H13 ingots were M(CN) and M6C, which existed in the segregation areas only. The MgAl2O4 particles, acting as more effective heterogeneous nuclei and providing more nucleation sites than Al2O3 particles, induced the formation of more developed austenite dendrites, and a greater number, smaller size and more uniform distribution of primary carbides, which finally relieved carbide segregation.