On Ductile Fracture of Steels Containing the Coarse Second Phase

Abstract

Effects of the strength and microstructure of the coarse second phase on tensile ductile fracture processes were studied. The materials used were 0.16% carbon steel composed of ferrite (matrix) and martensite or pearlite colony (coarse second phase). With an increase in martensite strength which was adjusted by tempering temperature, void formation mode was changed from a fracture of the colony to a decohesion at the interface, and fracture strain (ε_f) was decreased. This decrease of ε_f was due to a decrease of void initiation strain (ε_f). In comparison with martensite colony's case, number of voids produced during deformation and ε_f vs ε_i relation in ferrite-pearlite material were quite different. The reason seemed to be in the anistropic fracture strength of pearlite colony.