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690合金作为压水堆核电站蒸汽发生器传热管的一种关键材料,其在碱性环境下还原态硫导致的钝化膜的腐蚀退化是引发应力腐蚀开裂的关键原因之一.本文采用动电位极化曲线,结合扫描电镜(SEM)、俄歇能谱(AES)、二次离子飞行时间质谱(To F-SIMS)研究了690合金在300°C模拟碱性水化学中的腐蚀行为,并分析了硫代硫酸根与硫酸根对钝化膜特性的影响.实验结果表明:300°C碱性溶液中690合金表面钝化膜为外层的多孔层与内层的紧密层组成的双层结构,所加入的硫酸盐种类对690合金的耐蚀性有较大影响;硫代硫酸根使690合金钝化电流密度增加,过钝化电位降低,即钝化膜的耐蚀性降低;此外,硫代硫酸根使钝化膜中的Cr含量降低而Ni含量提高,硫代硫酸根会在合金表面电化学还原成为更低价态的硫进入钝化膜,使钝化膜中的硫化物增多也是导致钝化膜防护性能变差的原因;而硫酸根与钝化膜的作用较弱,对钝化膜的影响较小.
690 alloy is one of the key materials for heat transfer tube of steam generator of PWR nuclear power station and corrosion degradation of passivation film caused by reduced sulfur in alkaline environment is one of the key reasons for stress corrosion cracking.In this paper, The corrosion behavior of 690 alloy in simulated alkaline water chemistry at 300 ° C was studied by potentiodynamic polarization curve, combined with scanning electron microscopy (SEM), Auger energy dispersive spectroscopy (AES) and time of flight mass spectrometry (To F-SIMS) The effects of thiosulfate and sulfate on the properties of passivation film were analyzed.The experimental results show that the passive film on the surface of 690 alloy in 300 ° C alkaline solution is the double Layer structure, the type of sulfate added has a significant effect on the corrosion resistance of 690 alloy; thiosulfate increases the passivation current density of the 690 alloy and decreases the passivation potential, ie, the corrosion resistance of the passivation film decreases; In addition, thiosulfate decreases the Cr content in the passivation film and increases the Ni content, and the thiosulfate electrochemically reduces to a lower valence state on the alloy surface and enters the passivation film to cure the passivation film Increases also lead to deterioration of the passivation film protective properties; and sulfuric acid The effect of root and passivation film is weak, the impact on passivation film is small.