高温高圧純水におけるＳＵＳ３０４鋼の応力腐食割れ 溶体化処理温度および鋭敏化処理の影響

Abstract

Effects of solution temperature and sensitization time on the stress corrosion cracking (SCC) cf type 304 stainless steel were studied in high temperature water at 562 K containing dissolved oxygen of 8 ppm, using the slow strain rate testing (SSRT) technique at the strain rate of 4.17×10-6 s-1.For the specimen solution-treated at 1373 K, the SCC drastically occured by the sensitization treatment at 923 K for 7.2 ks. but the SCC hardly occurs even at 100 ks of sensitization time for the specimens solution-treated at 1473 K and 1573 K.For the specimen solution-treated at 1373 K, the size of grain boundary carbides and the width of attacked grain boundaries after sensitization treatment of 7.2 ks, are larger than the size and width solutiontreated at 1473 K and 1573 K according to transmission electron microscopy and Strauss test. The corrosion rates of grain boundary attack on Huey test increased with the holding time in solution treatment at 1373 K for both the solution-treated specimen and the sensitized specimen after solution-treated.The results suggest that impurity elements segregate to the grain boundaries during solution treatment at 1373 K, and accelerate the precipitation of grain boundary carbides during sensitization.The SCC occurs under the presence of both the Cr depleted zone by the sensitization and impurity elements at grain boundary.