MORPHOLOGICAL DETAILS OF STRAIN-INDUCED MARTENSITE IN COLD-ROLLED Cr – Ni STEEL

"The investigation presents the evolution of strain-induced martensite during cold rolling of AISI 304 stainless steel at 10% and 50% degree of deformation. The morphologies and characteristics of ’ martensite have been studied using optical-image analysis, scanning and transmission electron microscope. The influence of strain-induced martensite on mechanical properties and hardness of AISI 304 steel have been reported. Plastic deformation during the cold rolling of AISI 304 steel induces a martensitic transformation (γ→α’) in the whole range of applied deformation degree. The equiaxial grains of austenite containing annealing twins were observed within the microstructure of steel at delivery state. During the deformation process the shape of austenite grains was changed into long slim bands parallel to the rolling direction. Many shear bands and micro-twins were observed in the microstructure at large deformations degrees. The martensite, which was formed as a result of the transformation (γ→α’) induced by deformation, has a distinct influence on properties of the investigated steel grade. It was found that the effect of steel hardening is a result of a significant increase of the volume fraction of the ’-martensite in the structure. "