In order to uncover the mechanism of elastic modulus degradation during plastic deformation, uniaxial ten- sile test of transformation-induced plasticity （TRIP） steels under different prestrain levels was carried out. The real elastic modulus unloaded at each prestrain was calculated by linearly fitting. The microstructure evolution with plas-tic strain and the fracture morphology were monitored by using a scanning electron microscope （SEM）. Dislocation density and its distribution were detected under a transmission electron microscope （TEM）. Microscopic mechanism of the elastic modulus degradation of TRIP steels was discussed in detail. Experimental results indicated that the in- vestigated TRIP600 steel was of severe elastic modulus degradation during plastic deformation. The new-born mar tensite distributed among the retained austenite, resulting in the combination of good ductility and high strength for TRIP steels. It was the change of dislocation movement that induced the variation of atomic binding force and finally led to the variation of elastic modulus.
In order to investigate the springback performance of a cold-rolled transformation-induced plasticity （TRIP） steel sheet during cyclic bending, three-points bending experiments were performed. The specimen was firstly forward bended and then reversed bended according to three basic punch strokes, 10 mm, 20 mm and 30 mm, respectively. The outlines of the deformed specimens, punch load and crosshead displacement were obtained. The experimental procedures and the method of determining the springback displacement were reported in detail. The contributi^m of the strain hardening and decrease of elastic modulus to the overall springback was explained. The results demonstrated that springback increases both with the cycles and with the punch stroke during the cyclic bending process. Furthermore, springback in forward bending is larger than that in the corresponding reverse bending. This may be helpful to understand the complex springback behavior of the complicated sheet metal pancls.
