氮元素对25-6Mo3型双相不锈钢耐孔蚀及缝隙腐蚀性能影响的研究

THE INFLUENCE OF NITROGEN ON PITTING AND CREVICE CORROSION RESISTANCE OF TYPE 25-6Mo3 DUPLEX STAINLESS STEEL

从孔蚀与缝隙腐蚀两方面考察氮对25-6Mo3型双相不锈钢耐蚀性能的影响。结果表明:随含氮量增加,材料的孔蚀阻力增大,缝隙腐蚀速率下降,且存在关系式:CCT(℃)=17.3+78.4N％(wt)。含氮量越高,氮在钝化膜中的富集程度越大,对于含0.28％N的钢,其最高富集系数可达14;随含氮量增高,孔蚀位置从Y相转移到α相,含0.096％N是孔蚀位置发生转移的分界点。模拟闭塞区试验表明,含氮量越高,闭塞溶液的最终pH值越大,用Nessler特性试剂检验,发现0.28％N钢的闭塞液中存在着NH,从而证实了双相钢中同样存在着氮元素的缓蚀效应。可见氮元素的作用是通过膜内富集,改善γ相耐蚀性能以及与H^+结合形成NH_4^+从而抑制闭塞液酸度变化达到缓蚀效应而得以实现的。

The influence of nitrogen on pitting and crevice corrosion resistance of the type 256Mo3 duplex stainless steel was evaluated. It was found that the resistance to both pitting and crevice corrosion increased with increasing nitrogen content, and that the critical crevice corrosion temperature was related to the nitrogen content of steel as follows: CCT(℃)=17.3+78.4N％wt. The more the nitrogen content of steel, the higher the enrichment of nitrogen in the surface layers. The maximum nitrogen concentration was about 14 times its bulk level for the steel containing 0.28％N; pitting sites were transferred from γ phase into α phase with the nitrogen content increasing to more than 0.096％. The simulated occluded cell(OC) testing indicated that the more the nitrogen content, the larger the pH value of solution in OC by the end of the test. The ammonium ions in solution were detected with Nessler reagent for material containing 0.28％ nitrogen, proving the inhibiting-effect of nitrogen on the duplex stainless steel. So it is concluded that the role of nitrogen is due to the enrichment of austenitic phase and inhibiting-effect by proton consuming reaction leading to a reduction of local acidification in OC.