二相ステンレス鋼溶接継手部の水素脆化型応力腐食割れの解析的評価とその機構（第１報） 二相ステンレス鋼の水素脆化型応力腐食割れ感受性に及ぼす電位と組織の影響

Abstract

In this paper the authors discussed the depedence of crack initiation properties on potential and the effect of microstructures on the crack initiation and propagation properties in duplex stainless steels. It was clear that at less noble potential crack initiation occured from ferritic phase near the tip of austenitic phase which was controled by HESCC in this region. On the other hand, at noble potential crack initiated from corrosion pets which was formed at the boundary of ferritic and austenitic phases. As the effect of potential on the time to failure with decreasing the potential the time to failure decreased greatly both in a single ferritic phase stainless steel and duplex stainless steels, but even at the potential of -1.5V vs SCE there were no failures to he observed in a single austentic phase stainless steel, which means that austenitic phase is unsusceptible to HESCC. Additionally, as the effecc of ferrite content on HESCC properties of duplex stainless steels, with decreasing ferrite content the threshold stress increased and crack growth rate decreased greatly, which means that austenitic phase has a keying effect on crack propagating through ferritic phase. At the region of ferrite content less than 45%, threshold stress was nearly as same as the tensile strength of the materials and crack could not propagate through austenitic phase because of the continuousness of the austenitic phase which will prevent crack propagating through ferritic phase. Therefore, ferrite content of 45% should be considered as a critical value for crack initiating and propagating in duplex stainless steels.