Macro and micro behaviors of low alloyed TRIP780 steel with different biaxial proportional loading

To investigate the macro and micro behaviors of TRIP (transformation induced plasticity) steel under biaxial loading, experiment and finite element simulation were carried out for TRIP780 steel under proportional biaxial tension with displacement ratio of 1 : 1, 2 : 1, 3 : 1 and 4 : 1, respectively. The results show that cruciform specimens of TRIP780 steel fractured under proportional biaxial stretching when effective strain was about 1.5%, and fracture was always generated on the cross arm or cross links. During biaxial tension, stress and strain components in x and y directions of the center of the samples have the same nonlinear developing tendency, decreasing in one direction and increasing in another direction. Equal biaxial stretching stress state was helpful for retained austenite-martensite transformation than the other biaxial stress state. With increasing displacement ratio (DR) from 1 : 1 to 4 : 1, corresponding stress distributed unevenly on the yield ellipse from 30° to 60° in the first quadrant of stress space and corresponding retained austenite volume fraction distributed symmetrically in bow tie format.