Fracture evolution in ferrite/martensite dual-phase flange steel

Abstract

ABSTRACT Ferrite/martensite dual-phase steel is indispensable for manufacturing different automobile parts. In the present study, uniaxial tension tests and metallographic analyses are performed to reveal the fracture evolution in ferrite/martensite dual-phase flange steel with a high hole-expansion ratio. The results indicate that in the ferrite/martensite dual-phase steel, cracks originate at the interface between ferrite grains and martensite islands, and at the Al2O3 and sulfide inclusions. Further, dislocations obviously aggregate at the interface between the ferrite grains and martensite islands, providing many preferential crack nucleation sites. Stress concentrations tend to occur at the edge of Al2O3 and sulfide particles. In addition, the fraction of low-angle grain boundaries increases with prolonged deformation, and the size of ferrite grains gradually decreases with deformation, weakening their effect of inhibition of crack propagation. Moreover, the existence of the γ fiber texture and the {001} texture in the tensile deformation area facilitates crack propagation.