On the correlation among dislocation density, lath thickness and yield stress of bainite

The present work investigates quantitatively, for the first time, the correlation among dislocation density, lath thickness and yield stress of bainite. It is found that the dislocation density increases with the decrease of lath thickness in bainitic steels. Based on the correlation among dislocation density, lath thickness and yield stress, a physical model is proposed to predict the yield stress of bainitic steels, incorporating the contributions of dislocation strengthening as well as lath boundary strengthening. Furthermore, it is found that the dislocation strengthening gradually becomes more significant than lath boundary strengthening with the refinement of bainite lath, which explains the transition of strengthening mechanisms from lath boundary strengthening to dislocation strengthening when the lath thickness is below one micron.

(a) The relation between lath thickness and dislocation density in bainitic steels; (b) EBSD image of a bainitic steel.500