An approach to define the effective lath size controlling yield strength of bainite

A fully bainitic microstructure with negligible carbide precipitation is obtained in two ultra-low carbon steels. The size and misorientation of bainite laths are analysed by Electron Back Scattering Diffraction (EBSD). It is found that the yield stress of bainite is proportional to the inverse lath size defined with low boundary misorientation (2–7°). This can be explained by a theory predicting the flow stress of deformed metals, assuming that both lath boundary and dislocation cell boundary have similar capability of being dislocation obstacles.

Research highlightsIn this study, we developed a series of fully bainitic microstructures with negligible carbide precipitation in ultra-low carbon steels. Then, we investigated the microstructure by EBSD as well as their mechanical properties. It is found that the yield stress of such bainite is proportional to the inverse lath size defined with low boundary misorientation (2–7°). We explained this by employing a theory which predicts the flow stress of deformed metals, assuming that both lath boundary and dislocation cell boundary have similar capability of being dislocation obstacles.