Critical characteristic ligament for cleavage fracture in spheroidized steels

Abstract

A method is proposed to estimate the critical characteristic ligament corresponding to the onset of cleavage fracture in spheroidized steels. This parameter depends on the size of microstructural elements and orientation of the cleavage plane with reference to the local stresses as governed by the magnitude and direction of the applied load. Assuming that the probability of cleavage fracture initiation is the largest in region ahead of a pre-existing crack, the critical ligament size is determined by invoking a cleavage strength and position of the cleavage plane. Results are obtained for a mild steel microalloyed with niobium. Appropriate heat treatment were applied to produce a microstructure with very low ferrite content and predominantly spherically-shaped carbides. The size of the critical ligament is found to increase with decreasing temperature.