NaClO_(2)溶液中S2205不锈钢在点蚀初期的行为

Pitting Behavior of S2205Stainless Steel in NaClO_(2) Solution at Initial Stage

对NaClO_(2)溶液中失效S2205不锈钢管件进行组织分析,成分分析、腐蚀形貌观察等,明确了严重点蚀是管件失效的主要原因。采用电化学慢速动电位扫描法,对亚稳态点蚀电位Em、稳态点蚀电位Eb、亚稳态点蚀的形核数和小孔生长速率等参数进行分析,研究了S2205不锈钢在点蚀初期的行为。结果表明:在S2205不锈钢发生亚稳态点蚀的初期,Em受NaClO_(2)浓度影响较小,Eb随NaClO_(2)浓度增大而减小,点蚀敏感性随之增大;亚稳态点蚀形核以金属表面夹杂物诱发为主导,与NaClO_(2)浓度的变化关系不大,在较高电位区间,金属夹杂物溶解至小于临界尺寸,无法影响亚稳态点蚀形核,高电位抑制了亚稳态点蚀的形核;NaClO_(2)浓度升高,Cl-增多,其向孔内的扩散加速,促进了亚稳态点蚀的生长,较高电位提升了Cl-的活跃度,促进亚稳态点蚀的生长,并且浓度越高促进作用越明显。

Through microstructure analysis,composition analysis,and corrosion morphology observation of the failed S2205stainless steel pipe in NaClO_(2)solution,it was clear that severe pitting corrosion was the main reason for the failure of the pipe.The electrochemical slow dynamic potential scanning method was used to analyze the metastable pitting potential Em,the steady-state pitting potential Eb,the number of nucleation of the metastable pitting and the pore growth rate and other parameters.The initial behavior of pitting of S2205stainless steel was studied.The results showed that at the initial stage of metastable pitting of S2205stainless steel,Emwas less affected by the concentration of NaClO_(2),Ebdecreased with the increase of NaClO_(2)concentration,and the pitting sensitivity increased.Metastable pitting nucleation was dominated by the induction of metal surface inclusions,and had little relationship with the change of NaClO_(2)concentration.In the higher potential range,the metal inclusions dissolved to less than the critical size and could not affect the nucleation of metastable pitting.The high potential inhibitted the nucleation of metastable pitting corrosion.As the concentration of NaClO_(2)increased,Cl-increased and accelerated its diffusion into the pores and promoted the growth of metastable pitting.The higher potential increased the activity of Cl-and promoted the growth of metastable pitting,and the higher the concentration,the more obvious the promotion effect.