Effect of Pressure on Dendrite Structure and Characteristics of Carbides during Solidification Process of H13 Die Steel Ingot

In this paper, the effect of solidification pressure on the dendrite structure and characteristics of carbides in H13 die steel ingot was investigated by experimental and calculational methods. Based on the effect of pressure on the cooling rate, a formula is proposed to calculate the secondary dendrite arm spacing: λ2 = 71.45 × R−0.37. It is applicable when the maximum value of pressure is around 2 MPa and the cooling rate is between 0.5 and 3 K/s. With increasing pressure from 0.1 to 2 MPa, the effects of pressure on the segregation ratio of V, Mo, Cr and C are little and can be neglected, which caused by the combined effect of equilibrium partition coefficient, diffusion coefficient and cooling rate. Therefore, the characteristics of carbides are determined by the decreasing the secondary dendrite arm spacing and increasing cooling rate with the increment of pressure. With increasing pressure from 0.1 to 2 MPa, the types of carbides are not change, which are MC and M2C in H13 die steel ingot. Meanwhile, the mean area of carbides decreases obviously with increasing pressure, and the decrement in mean area at the edge is larger than that at the center of ingot.