超纯奥氏体不锈钢00Cr25Ni22Mo_2N非敏化态晶间腐蚀与磷(硅)的晶界偏聚

INTERGRANULAR CORROSION AND PHOSPHOR SEGREGATION AT GRAIN BOUNDARY OF NON-SENSITIZED 00Cr25Ni22Mo2N SUPERPURE AUSTENITIC STAINLESS STEEL

运用金相、电子显微镜观察及表面分析技术,研究了超纯奥氏体不锈钢00Cr25Ni22Mo2N制造的汽提管在尿素生产环境下的腐蚀形态和机理。结果表明,该钢种在生产条件下产生非敏化态晶间腐蚀,其特征是腐蚀介质不仅沿晶界向钢的内部渗入,而且同时向晶界的两侧扩展;晶界区磷的含量(约25%)比晶内高约三个数量级,由此造成的晶界与晶内在腐蚀电解质溶液中的电位差,是导致该钢种非敏化态晶间腐蚀的原因。

The corrosion behaviour and mechanism of superpure austenitic stain-less steel 00Cr25Ni22Mo2N in urea processing environment was studied. The resultsshow that the gas extraction tube made of non-sensitized 00Cr25Ni22Mo2N steelsuffered intergranular corrosion. Corrosive media penetrated not only into the tubewall through grain boundaries but also expanded from the boundary towards theinterior of the grain. Therefore, funnel shape penetration paths were formed, whichwere wider but less deep than common intergranular corrosion of sensitized stain-less steel. Neither depletion of Cr nor precipitates were found at the grain bound-ary. However, P (and Si) was segregated at grain boundaries to a great extent.Semiquantitative calculation indicates that P content at the grain boundary isabout 25 wt-%, three oders of magnitude higher than the content within the grain.Suggestion is made that the potential difference between the grain and its bound-ary due to the segregation resulted in the observed intergranular corrosion.