氮改善00Cr18Ni5Mo3Si2双相不锈钢应力腐蚀破裂性能的机制

THE MECHANISM OF NITROGEN EFFECT ON THE SCC BEHAVIOR OF 00Cr18Ni5Mo3Si2 DUPLEX STAINLESS STEEL

用 AES 分析了含氮双相不锈钢在30%MgCl_2(沸)溶液中浸泡后的表面膜。结果表明,氮在表面膜中富集.氮量越高,富集的量越多。钼和镍的富集均与钢中的氮含量有关.钼的富集要求氮含量在0.11%以上,镍的富集要求氮含量在0.073%以上,氮和钼的联合作用使钢表面膜的钝化能力得到加强。恒电位浸泡实验表明,阳极极化增厚了表面膜,降低了氮的作用。在0.5V NaCl(50℃,pH=7)溶液中,由模拟闭塞区实验得出:氮对裂缝尖端的化学状态无明显影响,闭塞区内未发现 NH_4^+。透射电镜(TEM)分析表明,氮量提高使位错由层状结构变为网状结构,增加了层错能。

After immersion in 30%MgCl_2 solution (boiling),the surface films of the 00CrlSNi5Mo3Si2 steels with different nitrogen contents were analyzed.Nitrogen was found to enrich in the surface film,and the higher the nitrogen content in the duplex stain- less steel was,the more amount of nitrogen was enriched in the surface film.Enrichment of Ni and Mo was influenced by nitrogen content with the content of nitrogen≥0.073% for Ni alone,and≥0.11% for both Ni and Mo.The combined effect of nitrogen and Mo increased the passivation ability of the surface film.The potentiostatic immersion test showed that anodic polarization thickened the surface film and weakened the effect of ni- trogen.A simulated occluded cell (OC) was used to study the chemical changes in the OC of the duplex stainless steel in 0.5N NaCl solution (50℃,pH=7).It was found that nitro- gen had little effect on either the pH fall or Cl^- enrichment in the OC,and that there was no NH_4^+ in the OC.TEM analysis showed that dislocation changed from layer structure in- to net structure and that stacking fault enrgy increased with the increase of nitrogen con- tent.