Influence of Allotriomorphic Ferrite under Different Growth Modes on the Variant Selection of Bainite in a Low Carbon Steel

A Fe-0.05C-2.94Mn-1.87Si steel is heat treated using a two-stage isothermal holding process to obtain allotriomorphic ferrite and bainite. Two kinds of allotriomorphic ferrite are obtained, one with only carbon partitioning and the other, alloying element partitioning. It is observed that the allotriomorphic ferrite stimulates the adjacent bainite to select the similar variant on the side where near K-S relationship is maintained between ferrite and prior austenite. The longer the border length of the allotriomorphic ferrite, the larger the stimulated bainite area. The statistical measurement shows that the alltriomorhpic ferrite with alloying element partitioning stimulates such bainite variant selection as well as that with only carbon partitioning.