オーステナイト系ステンレス鋼の粒界型応力腐食割れ発生挙動

抄録

Stress corrosion cracking (SCC) is a degradation phenomenon induced by a combination of tensile stress and environment, and involves multiple processes ranging from micro (grain-sized) crack initiation to macro (millimeter-sized) crack coalescence and propagation. To evaluate the SCC life, it is necessary to consider the SCC process of crack initiation. In this study, to make clear nucleation behavior of stress corrosion cracks in a type 304 austenitic stainless steel (SUS304), oxalic acid etching test and constant load tests in tetrathionate solution were carried out using sensitized SUS304. As the results of etching test, nucleation of intergranular corrosion (IGC) was affected by grain boundary (GB) characters; low-angle GBs (less than 10 deg.) and some specific CSL GBs (∑3,∑5,∑11,∑13a, ∑15and ∑17a) exhibited the high resistance to IGC, although random GBs and the other CSL GBs were susceptible to IGC. As the results of constant load tests, stress corrosion cracks initiated at the random GBs and some specific CLS GBs. Based on the comparison of susceptibility of GBs to IGS with that to SCC, stress corrosion cracks selectively occurred at some GBs which exhibited susceptibility to IGC. Other factors, such as microscopic stress acting at GBs, may affect the susceptibility of GBs to SCC.