Sensitization and Electrochemical Reactivation Behavior of Alloy 600

• Main Authors: Tsung-Feng Wu, 吳宗峰
• Other Authors: Wen-Ta Tsai
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/28554480000317095753

博士 === 國立成功大學 === 材料科學及工程學系 === 90 === Recently, much attention has been paid for intergranular stress corrosion cracking (IGSCC) which is induced by sensitization in Alloy 600 while the materials widely used in many caustic environments. Therefore, it becomes the important topic that how to evaluate the degree of sensitization of Alloy 600 effectively and precisely. However, there still is no standard parameter in electrochemistry method, which is considered conveniently to determinate the differential in degree of sensitization of Alloy 600. In this investigation, we try to explore the differences in the reactivation behaviors of Alloy 600 under different experimental conditions conducted by the single loop electrochemical potentiokinetic reactivation (SL-EPR) test. The goal is further to determine the possible reactions tool place in the reactivation process and its occurrence potential range. Besides, the feasibility of that whether the SL-EPR test is suitable to determine the degree of Alloy 600 is also evaluated. The results showed that the reactivation of the sensitized Alloy 600 in H2SO4＋KSCN solutions was composed by three individual reactions. They were pitting corrosion induced by TiN precipitation, matrix corrosion and intergranular corrosion, respectively. The anterior two were also revealed in the non-sensitized Alloy 600. The magnitudes of maximum current density at +30 mV potential could be used as the criterion to determine the degree of sensitization of Alloy 600. Additionally, the key to affect the reactivation of Alloy 600 in such solutions is the component concentration. The reactivation behavior is decided by the magnitudes of H2SO4 / KSCN concentration ratio in solutions. In other words, the similar shape of the reactivation curve was formed in the solutions with the same H2SO4 / KSCN concentration ratio. The optimal sensitization sensitivity was occurred in the solutions with the H2SO4 / KSCN = 10. The reactivation curves in fixed H2SO4 concentration solutions with different KSCN additions showed that with KSCN concentration increasing, the value of maximum current density at +30 mV is first increased then decreased. The possible explanation to this phenomenon is described in following. The adsorbed sulfur decomposed from SCN- ion may enhance the corrosion in the Cr-depletion. On the contrary, the adsorption formed by SCN- ions adsorbed on the specimen surface could restrain the corrosion. With low KSCN concentration additions, the effect of enhancement corrosion was noticeable. However, with higher KSCN concentration, corrosion inhibition contributed by SCN- ions adsorption played the main role.