ROLE OF 2ND PHASE PARTICLES IN THE DUCTILE FRACTURE OF HIGHER CARBON-STEELS

Fractographic studies indicate that ductile fracture of medium and high carbon steels occurs at all except the highest strength levels when voids formed at carbide particles coalesce and link the larger voids formed at weakly bonded non-metallic inclusions. The attainment of a critical strain, identified as that necessary to nucleate and coalesce voids at carbide particles, over a range equal to the inclusion spacing is proposed as a microstructural fracture criterion for these steels. Experimental evidence of the microstructural dependence of ductility and toughness is advanced to support this proposal. A simple model based on this fracture criterion is seen to predict the form of the microstructural dependence of the ductile toughness of quenched and tempered higher carbon steels. © 1979.