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

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: hi=(28.01P2+299.28P+1129.10)t-0.24. And then, A formula is proposed to calculate SDAS with cooling rate: lambda 2=21.48xR-0.77, which is applicable for low pressure (<= 2 MPa) and low cooling rate (0.4-1.4 K center dot 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: V=1.33x10-5 Delta T2+2.71x10-7 Delta T3, which is suitable for low pressure (<= 2 MPa).

Automated summary

The research indicates that increasing pressure mainly refines SDAS by enlarging cooling rate. Pressurization can enhance columnar dendrite tip growth rate by increasing undercooling and inhibit equiaxed dendrite nucleation and growth by decreasing constitutional undercooling. The formula for calculating columnar dendrite tip growth rate with undercooling is suitable for low pressure (<= 2 MPa).