Precipitation Behavior of Primary Carbide in H13 Bloom Die Steel

To analyze the solidification and precipitation behaviors of primary carbides in H13 bloom die steel, the size, morphology, distribution, and type of carbides from the chilling edge to the center of bloom H13 steel are studied by using a scanning electron microscope (SEM), an X-ray diffractometer and a Thermo-Calc thermodynamic software, and both formation time of carbides under equilibrium and non-equilibrium solidification are discussed. Results show that the primary carbides are distributed in the final solidification of steel, mainly including MC type V–Ti PC, V PC and M₇C₃ type Mo–Cr PC. From the edge to the center, the average area of primary carbide increases by 620.22 μm², with an increase of 3.53%. From the edge to 1/4 position, V-rich and Mo–Cr-rich carbides mainly exist; at the 1/4 position, V-rich and Mo–Cr-rich carbides are interconnected; from 1/4 position to center, three kinds of interconnected V–Ti PC, V‑rich PC and Mo–Cr PC carbides exist. Oxides promote the precipitation of MC type while sulfides promote the precipitation of M7C3 type. Thermodynamics show that the primary carbide MC will not be formed in the equilibrium solidification, but will precipitate in non-equilibrium, with the precipitation temperature of 1108°C at the solidification fraction of 0.9987.