2009 Volume 49 Issue 6 Pages 851-858
This work studies the effect of chemical composition, C and Mn contents, and cooling rate on both the solidification mode and the evolution of phases during the solidification of three steels; two of hypo-peritectic and one of hyper-peritectic composition. Furthermore, the cracking susceptibility associated to both the differences in mechanical behavior of δ and γ phases, and contraction during solidification, was inferred.
Slight variation of C or Mn, in the order of 0.04%, promoted significant changes in the evolution of phases during solidification. It was observed that for the hypo-peritectic steel closer to the peritectic point, the Mn microsegregation observed for high cooling rates promoted at the end of solidification a hyper-peritectic solidification mode. On the other hand, independently of the solidification mode and chemical composition of the studied steels, the differences in the mechanical behavior of δ and γ phases led to a cracking susceptibility in two solid fraction zones.
Furthermore, for the steel exhibiting hypo-peritectic solidification mode the peritectic transformation occurred at higher solid fraction compared with the steels showing hyper-peritectic solidification mode. Therefore, the remaining liquid ability to feed the contraction in the solid–liquid shell associated to the peritectic transformation resulted adversely affected. Hence, the cracking susceptibility observed in the hypo-peritectic steel is not only generated by differences in the mechanical behavior of δ and γ phases, but also by the liquid inability to compensate the contraction associated to the peritectic transformation.