2008 Volume 94 Issue 9 Pages 357-362
The solidification cracking susceptibility with the dependence of the selection of the primary phase was clarified with the Trans-Varestraint test, since the solidification mode of alloy tool steel (SKD61) was transited from FA mode (L → L+δ → L+δ+γ → L+γ→γ) to A mode (L → L+γ → γ) at high solidification velocity. It was obtained that the Brittle Temperature Range was enhanced to 587K for A mode while it was 105K for FA mode in the augmented strain of 2%.
In order to clarify the change of dendrite morphology during the solidification process, the liquid tin quenching was curried out. Though the interdendritic microsegregation can be reduced due to the dendrite arm development, the solidification cracking susceptibility was sensitized in A mode solidification. Therefore, the selection of the primary phase is extremely important.
The effect of primary phase selection on the interdendritic microsegregation was theoretically proven using the solidification velocity dependence of microsegregation model taking into the diffusion of the solute in the solid phase. It was found that the solidification cracking susceptibility obtained by the Trans-Varestraint test can be simply evaluated as the influence of the mode transition below the solidification velocity of 10 mm s−1 and the reduction of Si, P and S content can be effective on decreasing the risk of solidification crack.
