Effect of Pressure on Second Dendrite Arm Spacing and Columnar to Equiaxed Transition of 30Cr15Mo1N Ingot

Abstract

In order to clarify the effects of pressure on the second dendrite arm spacing (SDAS) and columnar to equiaxed transition (CET) of 30Cr15Mo1N ingot, changes in solidification parameters, cooling rate and columnar dendrite tip growth rate with pressure have been investigated. A formula is proposed to obtain the quantitative correlation between pressure (≤ 2 MPa) and interfacial heat transfer coefficient: . And then, A formula is proposed to calculate SDAS with cooling rate: , which is applicable for low pressure (≤2 MPa) and low cooling rate (0.4–1.4 K · s−1). There are tiny changes in solidification mode and equilibrium partition coefficient with increasing pressure from 0.5 to 2 MPa. Therefore, increasing pressure refines SDAS mainly by enlarging cooling rate. Pressurization can increase columnar dendrite tip growth rate by enhancing undercooling, and inhibit nucleation and growth of equiaxed dendrite by decreasing constitutional undercooling. It results that the distance between the center of ingot and CET position decreased with increasing pressure from 0.5 to 2 MPa. And a formula is proposed to calculate columnar dendrite tip growth rate with undercooling: , which is suitable for low pressure (≤2 MPa).