Influence of carbon content on solidifying shell growth of carbon steels at the initial stage of solidification

Abstract

A dipping test that a water cooled copper plate was continuously dipped at 14 mm/s was performed in order to investigate solidifying shell growth in initial solidification. Anomalous rough surfaces and uneven shell growth were exhibited for an ultra-low carbon steel (0.005 mass% C) and a hypo-peritectic carbon steel (0.116mass% C), while for a low carbon steel (0.044 mass% C) and a hyper-peritectic carbon steel (0.304 mass% C), flat surfaces were formed. The carbon content dependence of the anomalous uneven shell growth can be explained by stress caused by solidification shrinkage and δ/γ transformation occurring from a fraction solid 0.7, where shell begins to have strength, to 1.0, complete solidification state. Besides the analysis shows that decrease of the cooling rate can reduce the stress in the shell generated during the initial solidification.