Effects of strain and strain aging on fracture toughness of C–Mn weld metal

Abstract

Specimens of both as-deposited and fine-grained, reheated, manual metal arc C–Mn weld metal have been subjected to various strain and static strain-aging treatments in an attempt to simulate the thermomechanical cycles imposed upon the root region of a multipass weld as subsequent passes are made. The toughness was then measured, as a function of severity of treatment, using a crack opening displacement test. The strain aging treatments are found to lower markedly the cleavage resistance of the as-deposited and reheated microstructures. Non-metallic inclusions within the crack-tip plastic zone are found to be active as cleavage initiation sites in both types of microstructure. While the general shift in toughness can be explained by considering the changes in flow properties brought about by the various treatments, the observed variations in size and distance from the crack tip of the initiating inclusions are thought to be responsible for the associated experimental scatter. MST/157