Measurement of strain distribution of lath martensite microstructure during tensile deformation

Abstract

Local deformation behavior of lath martensite was investigated in low-alloyed steel in the strain range of 0-10% under uniaxial tensile loading. Local strain measurement was in-situ conducted in SEM by digital image correlation method, and it was revealed that strain distribution was relatively uniform in the early stage of deformation less than 2% of strain and then strain localization arises along the lath as the strain increases. Schmid factor was evaluated for each block of martensite by EBSP analysis and was compared with the measured local stain distribution. It was clarified that the strain concentration occurs in blocks that have higher Schmid factor in in-lath-plane slip systems than in out-of-lath-plane slip systems. On the other hand deformation was less significant than average in blocks that have higher Schmid factor in out-of-lath-plane slip systems. It was suggested by an estimation of dislocation glide distance that the anisotropy of deformation of lath martensite was caused by the interaction between dislocations and lath boundaries and consequent selection of preferable slip systems. © 2009 The Japan Institute of Metals.