MICROSTRUCTURAL CHARACTERIZATION OF L-GRADE STAINLESS STEELS RELATIVE TO THE IGSCC BEHAVIOR IN BWR ENVIRONMENTS

摘要

Analytical electron microscopy techniques were used to provide insight to the IGSCC behavior of L- grade stainless steels in boiling water nuclear reactor (BWR) environments. Grain boundary Cr- depletion and cold work are well known as important material parameters affecting IGSCC. Characterization of cracked L-grade BWR core components revealed significant surface cold work and W-shaped grain boundary Cr-depletion profiles. Grain boundary composition measurements of other actual and simulated BWR core components revealed differences in the Cr and Mo profiles as a function of the bulk composition and distance from the weld fusion line. An electron back scattered pattern technique (EBSP) identified significant strains in the weld HAZs of BWR components. Strain characterization of various BWR core shroud weld HAZs revealed significant strains nearest the weld fusion line. These residual strains are attributed to shrinkage that occurs during weld fabrication and are believed to act synergistically with high corrosion potentials to accelerate IGSCC in unsensitized stainless steels. The influence of grain boundary Cr depletion, produced by thermal non-equilibrium segregation (TNES), on the IGSCC behavior requires further study.