Peritectic Transformation in Low Carbon Steels Containing High Phosphorus Concentration

Abstract

A boundary of austenite grain formed in the primary arm spacing of dendrites when the niobium concentration was over 1 mass% in Fe–0.1mass%C–Xmass%Nb ternary alloys. This means that the shape of the group of a delta primary dendritic array might be indicated that of the subsequently formed austenite grain, depending on the addition of a ferrite former such as niobium. In this study, phase transformation from the delta to austenite phases and the effect of phosphorus on the correlation between the morphologies of the group of the delta dendritic array and austenite grains were investigated in carbon steels with various phosphorus concentrations. The results showed the occurrences of the delta, austenite and their coexisting phases might agree with each phase in the pseudo-binary phase diagram of an F–1.0mass%C–Xmass%P alloy, in which X mass% shows the P concentration within 0.01 to 0.40 mass%. Moreover, the shape of the group of the primary delta dendritic array coincided with that of the subsequently formed austenite grains in alloys over 0.26 mass% P. However, the shape of the group of the delta dendrites did not coincide with that of the austenite grains in alloys under 0.18 mass% P, even though dendritic patterns could be seen.