Multiscale investigation of early-stage boundary sliding mechanisms in lath martensite of low-carbon-steel

Previous studies have identified two primary deformation mechanisms in lath martensite under tensile loading, particularly highlighting intra-lath crystallographic slip based on direct dislocation observations. In this study, a multiscale approach was employed to further advance the understanding of boundary sliding in low-carbon lath martensite. High-resolution digital image correlation (HR-DIC), molecular dynamics (MD) simulations, and electron channeling contrast imaging (ECCI) were integrated to investigate the boundary sliding process in the early stage of plastic deformation. Both macro-scale HR-DIC analysis and atomic MD simulation revealed that the sub-block and twin boundaries preferentially accommodate boundary sliding. Systematic shear simulations on twist boundaries representing various variant pairs clarified that the critical resolved shear stress (CRSS) for low-angle boundaries with dense hexagonal dislocation networks correlates with the ratio of <111> to <100> screw dislocation lengths within the network. Furthermore, simulations demonstrated that mobile “in-out” edge dislocations interact with these interfacial networks, facilitating misorientation changes that promote boundary sliding. Complementary submicron-scale ECCI observations provide experimental evidence for the presence of such dislocation networks near substructure boundaries.