Deformation behavior in cold-rolled medium-manganese TRIP steel and effect of pre-strain on the Lüders bands

Deformation behavior was studied in cold-rolled 0.2C-1.6Al-6.1Mn-Fe transformation-induced plasticity (TRIP) steel subjected to intercritical annealing. The steel intercritically hardened at 650 ℃ exhibited excellent mechanical properties, and the excellent ductility was primarily associated with the discontinuous TRIP effect. Moreover at 650 ℃, the formation of Lüders bands was associated with TRIP effect and cooperative dislocation glide. The length of Lüders strain was gradually reduced with increasing pre-strain, and was eventually eliminated when the pre-strain was increased to 10%. The increased average stability of retained austenite and increased dislocation density in ferrite induced by pre-strain was responsible for decrease and ultimate elimination of Lüders bands. While in steel intercritically annealed at 600 ℃, ferrite and austenite was predominantly deformed, which was responsible for poor work hardening rate and inferior tensile properties.