Evolution of dislocation density in bainitic steel: Modeling and experiments

Bainitic steels with intensive lath boundaries demonstrate an excellent combination of strength and toughness. The bainite lath has an inhomogeneous distribution of dislocations across its lath thickness. The present work investigates quantitatively the effect of bainite lath boundaries with inhomogeneous dislocation distribution on the evolution of dislocation density in bainitic steels by both modeling and experimental works. For the first time, the Kocks-Mecking (K-M) model is extended by including two new terms to probe the boundary induced dislocation multiplication and annihilation mechanisms in bainitic steels. The initial dislocation density and the lath thickness of bainite are obtained by synchrotron X-ray diffraction analysis and microscopy observation, respectively. Based on the modeling and experimental works, it is found that the enrichment of dislocations at the lath boundary exhibits significant influence on multiplication as well as annihilation of dislocations during tensile deformation. The dislocation density at the bainite lath boundary is estimated by the present model as twice as the value in the bath interior, which is consistent with experimental observations. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.