MULTI-SCALE ANALYSIS OF MICROSCOPIC STRESS CONCENTRATION AT GRAIN BOUNDARY IN WELD METAL OF NI-BASED ALLOY JOINT FOR SCC EVALUATION

摘要

An analysis method to calculate the microscopic stress distribution in crystalline grain scale was proposed in order to predict the occurrence of SCC in weld metal of nuclear power plant components. Crystal plasticity theory was incorporated in order to calculate microscopic stress concentration at columnar grain boundary in Ni-based alloy weld metal. SCC tests of Alloy 600 weld metal were performed to identify the location of cracks. Cracks were occurred at grain boundaries. The crystal orientation was measured by electron backscatter pattern (EBSP) method and was introduced into the microscopic model of the multi-scale analysis. The multi-scale analysis was applied to the evaluation of the microscopic stress distribution in the SCC test specimen. Microscopic model that has the actual grain shapes and crystal orientations were generated based on EBSP analysis result. A tensile loading was applied to the model and the microscopic stress distribution was estimated. The stress concentration was occurred at grain boundaries. Stress concentration at grain boundaries was possible to be predicted by the proposed multi-scale analysis and was in good agreement with the experimentally observed cracks.