Micro-tension behaviour of lath martensite structures of carbon steel

A micro-tension testing technique was used to investigate the deformation behaviour of lath martensite structures with several types of boundaries in carbon steel. The martensite structures exhibited sufficient necking strains and ductile fractures, whereas the uniform strain was limited owing to a lack of strain-hardening ability despite the increased flow stress. The yield stress of the lath martensite structures strongly depended on the in-lath-plane orientation. The critical resolved shear stress of the in-lath-plane slip systems was considerably lower than that of the out-of-lath-plane slip systems. This finding suggests that the block boundaries are an effective grain boundary for impeding dislocation gliding. Plastic deformation transfer was restricted by the packet boundaries, which greatly rotated the crystallographic orientation of the in-lath-plane slip systems between neighbouring martensite variants.