Prediction of SCC Initiation in Weld Components by Multi-Scale Analysis Incorporating Crystal Plasticity

Abstract

A multi-scale analysis method of microscopic stress is proposed to predict the occurrence of stress corrosion cracking (SCC) in the welded components in power plants. The method includes a macroscopic model and microscopic models. Calculation of the stress was first performed in the macroscopic model. Subsequent to this calculation, simulation of the microscopic model was conducted to evaluate the microscopic stress on the scale of the grains and microstructure. Then, the nodal temperatures and nodal displacements were transferred from the macroscopic model to the microscopic model as boundary conditions. The proposed multi-scale analysis was used to evaluate the weld residual stress of a bead-on-plate weld model to demonstrate the validity of the method. Good agreement was obtained between the macroscopic and microscopic models in nodal temperature, nodal displacement, and in the residual stress distribution. Following the bead-on-plate model, the multi-scale analysis method was applied to the model of an SCC test specimen of type 600 Nickel-based alloy. Crystal plasticity and inhomogeneous grain shapes were introduced into the microscopic model to consider the effect of crystal orientation. The crystal orientation was measured by electron backscattering pattern (EBSP) technique and applied to the microscopic model. The stress concentration at the grain boundaries was shown by the multi-scale analysis. In the simulated SCC tests, cracks were observed in the grain boundaries. The locations where microscopic stress concentrations occurred in the multi-scale analysis were in good agreement with the locations of cracks observed in the SCC test. The proposed multi-scale analysis method of microscopic stress distribution is thus applicable to the prediction of the locations of stress corrosion cracks.