347不锈钢在硝酸熔盐中的腐蚀行为研究

通过2000 h浸泡实验，研究了347不锈钢在565 ℃下硝酸熔盐 (60%NaNO₃+40%KNO₃) 中的静态腐蚀行为。采用增重法测量347不锈钢在不同时段的重量变化，得到材料的腐蚀动力学曲线，利用XRD、SEM/EDS对347不锈钢表面及横截面腐蚀产物形貌、成分和结构进行分析，并讨论相关腐蚀机理。结果表明，347不锈钢在565 ℃下硝酸熔盐中的腐蚀表现为增重，前300 h腐蚀速率很快，300 h后腐蚀速率逐渐减缓。随着腐蚀时间延长，其表面氧化层中的尖晶石形状逐渐由针状和片状转变为块状，2000 h时基本全部趋于块状。腐蚀达到2000 h时，347不锈钢的外层腐蚀产物厚度均匀且较疏松，并且出现一定程度的开裂，由Fe₂O₃和NaFeO₂组成；内层腐蚀产物厚度不均匀且较致密，主要为 (Fe，Cr)₃O₄。

Corrosion Behavior of 347 Stainless Steel in Molten Nitrate Salts

The static corrosion behavior of 347 stainless steel (347SS) at 565 ℃ in molten nitrate salts (60%NaNO₃+40%KNO₃) was investigated via 2000 h immersion test. Corrosion kinetic curve of 347SS in molten salts at 565 ℃ were obtained through measuring the weight changes of the specimens at each time intervals. Moreover, XRD, SEM/EDS were used to characterize the morphology, composition and microstructure of the corrosion products on the surface and the cross section of corroded specimens, the corrosion mechanisms were also briefly described. Results showed that the corrosion behavior of 347 SS in molten nitrate salts at 565 ℃ was characterized by mass gain, its corrosion rate was very fast in the first period of 300 h, and then gradually slowed down after 300 h. As the corrosion time prolonged, the oxide scale of spinel gradually changed from needle-like and sheet-like to block-like, and it basically all tended to be block-like for corrosion up to 2000 h. After 2000 h corrosion, the outer portion of corrosion product, composed of Fe₂O₃ and NaFeO₂, was uniform and loose with certain amount of cracks, while the inner portion of corrosion product, composed merely of (Fe,Cr)₃O₄, was non-uniform and dense.