定電位ＳＳＲＴ法によるフェライト系ステンレス鋼の腐食挙動に関する研究

Abstract

The stress corrosion cracking or hydrogen embrittlement is defined as the localized fracture phenomenon caused by the interaction between applied stress and electrochemical process. Recently, a number of studies incorporating the electrochemical method and the slow strain rate technique (SSRT) have been carried out in various corrosive environments as a way for understanding the corrosion behavior of metallic materials in a short period.In this study, in order to clarify the corrosion behavior of two types of ferritic stainless steels which were made by laboratory, the SSRT tests were carried out under those potentials corresponding to the hydrogen evolution region, stable passive state region, transpassive state region and pitting corrosion region of the anodic polarization curve which was obtained in 3% NaCl solution. Also the changes of current and mechanical properties in both test specimens were compared and examined.The main results obtained are summarized as follows.(1) The presence of the stable passive and unstable transpassive state regions was confirmed in both test specimens from the measurement of anodic polarization curves in 3% NaCl solution. The passive film formed on No.2 specimen which contains 2% nickel may be considered as stable, because the passive current in the passive state region was constant.(2) From the change in current through the loaded specimen under various characteristic potentials, particularly in the case of the fixed potential of -0.375V (vs. S.C.E.) corresponding to the passive state region, the metal dissolution hardly occurs because the repassivation of passive film takes place rapidly even if it is ruptured by tensile deformation.