Influence of Prior Austenite Grain Size on the Dispersion of Fatigue Crack Propagation Thresholds in Weld Metal

Abstract

Fatigue crack propagation threshold is an important property for the structures with long life, such as nuclear turbine welded rotor. The fatigue crack propagation thresholds of multi-layer, multi-pass SAW weld metal of nuclear turbine rotor simulate are tested. But a big dispersion is found among test values, even at the same stress ratio . The dispersion of critical points between stable propagation zone and near-threshold zone is confirmed as an important reason. After the observation of microstructures around the critical points by backward inference method in different specimens, a good correspondence between the sizes of prior austenite grains and the maximum sizes of monotonic plastic zone at the crack tip is established. The inhomogeneous microstructures in SAW weld metal are the basic cause to dispersion of fatigue crack propagation thresholds at the same stress ratio.