Explaining the dilatometric behavior during bainite transformation under the effect of variant selection

Abstract

The selection of crystallographic variants in bainitic microstructures is a deeply studied topic which can be attributed to several reasons. In the cases where the prior austenite is textured, stressed or plastically deformed, the final ferrite texture and the dilatometry signal may change, being anisotropic. Although the causality between variant selection and the variation of the dilatometric signal has been previously assumed, it has not been thoroughly proved. In this work, the phenomenological theory of martensite was combined with a continuum mechanics analysis to calculate the relative length changes associated to the bainitic transformation during different bainitic transformations in order to prove the connection between the selection of crystallographic variants and the distortion of the dilatometry signal. To do so, four different bainitic microstructures were analyzed: one of them obtained by a pure isothermal treatment and the rest of them obtained by ausforming treatments. Some of the mentioned microstructures had shown to lead to negative longitudinal dilatometry signals and to present a strong variant selection. Results showed that the experimental trends could be explained by theoretical means, which enables to further understand the bainitic transformation.