CONTROL OF MICROSTRUCTURES OF FERRITE/ BAINITE (F/B) DUAL-PHASE STEELS AND ANALYSIS OF THEIR RESISTANCE TO DEFORMATION BEHAVIOR

Five ferrite/bainite(F/B) dual-phase steels with the chemistry of low carbon,high manganese and high niobium,and different volume fractions of bainite(15%—98%) were produced by control rolling+relaxing+ACC processing.With the help of the modified Crussard-Jaoul(C-J) analysis,the effects of soft phase(ferrite) content and its grain size on the work-hardening behavior of the steels and the cooperative deformation relationship between softer phase and harder phase were studied,which was validated by EBSD analysis.The results illustrate that a reasonable proportion of F/B can be helpful to improve initial work-hardening(a high R_(t1.5)/R_(t0.5)),reduce the yield ratio, and maintain a high uniform elongation.It is known that the cooperative deformation of ferrite and bainite is the main mechanism for improving the stress ratio and the uniform elongation of the F/B dual-phase steels.