核级不锈钢焊接接头钝化膜耐蚀性能和半导体特性研究

采用电化学阻抗谱(EIS)、场发射扫描电子显微镜(SEM)、Auger扫描能谱仪(AES)以及容抗测试技术(M-S曲线),研究了316LN/316L不锈钢焊接接头在模拟压水堆一回路高温高压水中形成的钝化膜的耐蚀性能和半导体特性。结果表明,焊缝区、热影响区和母材区形成的钝化膜的耐蚀性能不同,热影响区钝化膜开路电位及电化学阻抗等均低于其他区域,说明热影响区钝化膜的耐蚀性能最差,这主要与钝化膜的致密程度、厚度及Cr氧化物的含量有关。M-S曲线表明,母材区钝化膜平带电位为-0.7V,较其他区域(-0.4V)负移,表明有BO-3等阴离子在钝化膜表面吸附,加之具有较低的施主和受主浓度,可排斥侵蚀离子的腐蚀,使之较其他区域有更强的耐蚀性能。

Study on Corrosion Resistance and Semiconductor Property for Passive Film of Nuclear Grade Stainless Steel Welding Joint

The corrosion resistance and semiconductor property of passive film formed on the surface of welding joint of 316LN/316L stainless steel in simulated high temperature and high pressure primary water of PWR were investigated through EIS, SEM, AES and Mott-Schottky methods. The test results show that the passive films formed on weld metal (WM) zone, heat affect zone (HAZ) and base metal (BM) zone have different corrosion resistance properties. Both the open circuit potential (OCP) and electrochemical impedance values of passive film formed on HAZ are lower than that of the other zones. This shows that HAZ passive film has the worst corrosion resistance. It’s related to film’s density, thickness and content of chromium oxide. The Mott-Schottky curve reveals that the flat band potential of BM zone passive film is -0.7 V, which is shifted negative compared with the other zones (-0.4 V). The change of E_fb was discussed as a function of anions (BO^-₃) adsorption on surface of passive film. With lower donor and acceptor density, preventing the adsorption of Cl^- in passive film, the corrosion resistance of BM zone is better than that of the other zones.