On the characteristics of Portevin-Le Chatelier bands in cold-rolled 7Mn steel showing transformation induced plasticity

Strain localization during tensile deformation of cold-rolled and annealed 7Mn steel were investigated under various strain rates and deformation temperatures. The retained austenite grain size, strain rate and deformation temperature all have remarkable influences on the appearance of PLC bands. Higher strain rate clearly suppressed the formation of PLC bands whilst deformation temperature had a more complicated influence. During the room-temperature deformation at the quasistatic strain rate of 6.67 x 10(-4)/s, Luders bands appeared in all specimens whilst PLC bands only in the specimens that were annealed above 700 degrees C. Digital image correlation (DIC) analysis showed the specimen annealed at 700 degrees C exhibited the type A PLC bands during the entire period of deformation; whilst the one annealed at 720 degrees C showed the more complicated type A+B bands before 600s and the type A bands afterward. All of these phenomena have been discussed in relation to the interaction of C atoms/C-Mn pairs and dislocations for sound interpretation.