Effect of Nb Content on Dendrite Segregation and Carbide Composition and Morphology of H13 Steel

H13 steel with different mass fractions (0,0.17%,0.38%) of Nb was prepared with vacuum induction furnace. The effect of Nb content on dendrite segregation, and eutectic carbide composition and morphology of H13 steel was studied. The results show that adding Nb could significantly refined the structure of H13 steel and reduce the segregation of the forming elements of interdendritic carbides. With the increase of Nb content, the number and size of eutectic carbides increased significantly, and their morphology changed from blocky or long strip to lamellar or fishbone. The carbides were M₇C₃, M₂₃C₆, M₆C and MC. With the increase of Nb content, the number of M₇C₃ and M₂₃C₆ type carbides decreased while the number of M₆C and MC type carbides increased; MC type carbides changed from VC to NbC and VC, and the precipitation temperature of MC type carbides increased significantly.