Effect of heat treatment on the impact toughness and brittle fracture initiation mechanism of a quenched and tempered nuclear Pressure Vessel Steel

Abstract

The effect of heat treatment conditions on the tensile properties, impact toughness properties and the brittle fracture initiation mechanisms of a low-alloy steel were investigated. Only one type of location for the cleavage initiation sites, common to all cooling rates, was identified. Cleavage crack initiation always occurred in the very vicinity of a high angle boundary. MnS inclusions and Ti(CN) precipitates may play a role, but they did not seem to be necessary for cleavage initiation. The critical stress for cleavage increased with the cooling rate and decreased with the tempering parameter. This is consistent with the observed differences in the ductile-to-brittle transition behavior with the heat treatment conditions.