The effect of the Mo element on the intergranular corrosion behavior was investigated on super-austenitic stainless steels. The σ-phase structure and compositional changes of stainless steels with different Mo contents during aging at 800–900°C were investigated by TEM, combined with electrochemical tests, and two different intergranular corrosion mechanisms were revealed. The low-Mo 904 L stainless steel induces severe intergranular electrochemical corrosion due to selective anodic dissolution at grain boundaries caused by decreased passivation ability and σ-phase composition changes. The σ-phase precipitation of 254SMo and AL-6XN with high-Mo leads to Cr and Mo depletion reduces passivation film continuity, and causes intergranular corrosion.

中文翻译：

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Mo对超级奥氏体不锈钢晶间腐蚀行为的影响

研究了Mo元素对超级奥氏体不锈钢晶间腐蚀行为的影响。利用TEM研究了不同Mo含量的不锈钢在800~900℃时效过程中的σ相结构和成分变化，并结合电化学测试，揭示了两种不同的晶间腐蚀机制。低Mo 904L不锈钢由于钝化能力下降和σ相成分变化导致晶界选择性阳极溶解，导致严重的晶间电化学腐蚀。高Mo的254SMo和AL-6XN的σ相析出导致Cr和Mo的贫化，降低了钝化膜的连续性，并引起晶间腐蚀。