Low-Temperature Micro-Fracture Toughness Testing of Grain Boundaries in Steel

Abstract

Temper embrittlement in high-strength steel occurs due to the segregation of impurity elements along prior austenite (£) grain boundaries, resulting in a decrease in intergranular strength. However, the grain boundary properties have not yet been experimentally investigated. In this study, we developed a micro testing method to selectively process micro-cantilever specimens based on a specific prior £-grain boundary to measure the grain boundary fracture toughness. Fracture toughness tests using micro-cantilever specimens with side grooves and notch were carried out at 183 K and brittle fracture behavior was successfully obtained. The fracture surface showed almost flat and brittle crack propagation along the prior £-grain boundary. The derived fracture toughness value, K Q , is lower than that from previous values. By employing this method for the evaluation of intergranular fractures in steel, we believe that we can evaluate more intrinsic prior £-grain boundary properties compared with conventional methods.