局所ひずみに基づく粒界型応力腐食割れ発生条件の検討

抄録

This study evaluated the nucleation of stress corrosion cracking (SCC) on a smooth surface of sensitized austenitic stainless steel SUS304 from viewpoints of microscopic strain and GB structure. Before SCC testing, microscopic strains were measured on a surface of a specimen subjected to an initial tensile strain of 1% by digital image correlation (DIC) technique. SCC testing was conducted under a constant load corresponding to the initial strain in a tetrathionate solution. After testing, crystal orientations on the cracked surface were measured by electron backscattered diffraction (EBSD) technique. The site and structure of each GB were identified by EBSD, and the distributions of normal and shear strains at the GBs were calculated by DIC. From the microstructural viewpoint, stress corrosion cracks tended to be mainly initiated at large-angle random GBs, and no cracks were initiated at low-angle GBs and Σ3 boundaries. From the viewpoint of microscopic strain at GBs, the cracks occurred at a part of GB where the normal strain was high, and then grew along the whole GB. On the other hand, the relationship between shear strain at the GBs and SCC nucleation was not found. As a result, crack initiation was characterized using the maximum normal strain along GBs.