高強度低合金鋼の3.5%食塩水中・繰返し荷重下における短い表面き裂の伝ぱ挙動 Short Surface Crack Growth of a High-Strength Low-Alloy Steel under Cyclic Loading in 3.5% NaCl Solution

The growth of short surface cracks in a high-strength low-alloy steel, JIS SNCM439, was examined under cyclic loading in deaerated aqueous 3.5 % NaCl. Under cyclic loading, the crack 'growth rates were controlled by the stress intensity factor independent of crack size, when the value maximum stress intensity factor, K_<max>, was larger than the stress corrosion cracking threshold, K_<ISCC>. In this region of stress intensity factor, both short and long cracks grew along prior austenite 'grain boundaries. For K_<max><K_ISCC>, short surface cracks grew up to 10 times faster than long cracks the same stress intensity factor. The size effect was attributed to the difference in the crack growth ode, i. e., short surface cracks grew in an intergranular mode along prior austenite grain boundaries, while long cracks propagated by a transgranular mode. The short crack size, therefore, accelerated crack growth when K_<max><K_ISCC>.