S-03钢渗氮面点蚀机理与钝化工艺优化

针对S-03钢(022Cr12Ni10MoTi)渗氮后表面出现点腐蚀现象,进行深入机理分析,发现渗氮后表面生成CrN,造成渗氮表面贫Cr,不能形成致密完整的钝化膜,导致材料耐蚀性能降低,易发生点蚀。并对原有磷酸体系钝化工艺进行改进优化,提出了复合钝化工艺。利用循环极化、电化学阻抗谱(EIS)等技术手段,研究了复合钝化后S-03钢渗氮表面的腐蚀行为,并与未钝化和磷酸体系钝化进行对比。结果表明,经复合钝化处理的S-03钢渗氮表面点蚀电位E b最高,腐蚀速率最小,且钝化膜修复能力最强。说明复合钝化工艺能在S-03渗氮表面形成x Cr 2 O 3·y CrOOH稳定的非晶态氧化膜,增强了表面抗点蚀能力,其耐蚀性能要远高于磷酸体系钝化和未钝化表面。同时复合钝化工艺可有效提高S-03钢渗氮表面钝化膜厚度,增强钝化膜修复能力。

Pitting mechanism and passivation process optimization of nitriding surface of S-03 steel

The mechanism of pitting corrosion on nitriding surface of S-03 steel(022Cr12Ni10MoTi)was analyzed,CrN was found on the nitriding surface which caused poor Cr.So the dense and complete passivation film did’t formed,which caused the corrosion resistance of material to decrease and prone to corrosion.The passivation process of phosphoric acid system was optimized,and then the compound passivation process was proposed.By cyclic polarization curves and electrochemical impedance spectroscopy(EIS),the corrosion behavior of compound passivated S-03 steel nitriding surface was studied,and compared with non passivation and the passivation process of phosphoric acid system.The results show that the pitting potential of S-03 steel with compound passivation treatment is the largest,and the corrosion rate is lowest,and the passivation film has the strongest repairing ability.It indicates that the compound passivation process can form a stable amorphous oxide film x Cr 2 O 3·y CrOOH which improves the pitting corrosion resistance,and its corrosion resistance is much higher than that of the passivation process of phosphoric acid system and unpassivated surface.Meanwhile the compound passivation process can effectively improve the thickness of passivation film for nitriding surface of S-03 steel and enhance the repairing ability of passivation film.