双相不锈钢的相腐蚀及应力腐蚀裂纹萌生发展机制研究

The corrosion resistance of duplex stainless steel is directly affected by the differences of composition and organization structure in two-phase. However, due to the limits of device resolution and sensitivity, single-phase corrosion and two-phase corrosion resistance coupling mechanism are rarely studied in micro-nano scale. In this project, we intend to use the Electronic Speckle Pattern Interferometry, micro-electrochemistry and atomic absorption spectroscopy technology to carry out the "real-time in situ large horizons" research on duplex stainless steel 2205. For stainless steels in H2SO4/HCl solution with different concentrations, by research of selective corrosion rule and mechanisms, stability of passive film and correlation mechanism of phase structure, mechanism of alloying elements influence on phase corrosion as well as the initiation and development of pitting corrosion and stress corrosion cracking, the scientific issues "electrochemical corrosion law and two-phase coupling evolution mechanism of austenite phase and ferrite phase in duplex stainless steel, as well as the initiation and development of pitting corrosion and stress corrosion cracking in these two phases " are expected to be solved. Meanwhile, the research work in micro-nano scale on duplex stainless steel will be promoted.

双相不锈钢中两相成分及组织结构的差异性直接影响其耐蚀性，而现有研究受设备分辨率及敏感性限制，极少从微纳米尺度研究单相腐蚀及两相耐蚀性偶合作用机制。本项目拟采用激光电子散斑、微区电化学和原子吸收光谱等先进技术开展2205双相不锈钢的"实时原位大视野"研究，通过研究不锈钢在不同浓度的H2SO4/HCl溶液中的选择性腐蚀规律和机制、表面钝化膜稳定性和相结构的关联机制、合金元素对相腐蚀的影响机制以及点蚀和应力腐蚀裂纹萌生发展规律，以期解决"双相不锈钢中奥氏体相和铁素体相的腐蚀电化学规律和两相偶合演化机制，以及点蚀和应力腐蚀裂纹在两相的萌生发展机制"的科学问题，并推进双相不锈钢相腐蚀的微纳米尺度研究工作。

双相不锈钢区别于普通单相不锈钢的是其微双相结构，也因此双相不锈钢表面形成的是异质钝化膜。所以，考虑到双相中弱相的钝化性质对整体的钝化性质有着决定性的影响，准确地了解双相不锈钢中单相的钝化行为和机理非常重要。本项目利用选择性溶液制备出可以准确模拟双相钢中单相行为性质的试样；利用了一系列宏观和微观电化学方法表征两单相的钝化行为，并且得到了钝化膜成分的区别，并发现：利用选择性溶解可以制备品相良好的单相试样，并且制备的单相可以较好地表现实际2205双相不锈钢中单相的行为；铁素体相钝化膜的生长比奥氏体相的更快，但是奥氏体相钝化膜的稳定性要高于铁素体；铁素体相钝化膜的Fe粒子的稳定性比奥氏体相的更强（可能因为铁素体相中较高的Mo含量）；奥氏体相钝化膜的Cr (Ⅲ)粒子相比于铁素体相的有着更好的稳定性（可能因为奥氏体相中较高的Ni含量和N含量）。.2205 DSS试样在服役过程中两相的行为有着独立性，也存在耦合作用。耦合作用至少能够增强铁素体相钝化膜中外层的Cr (Ⅲ)粒子稳定性；整体钝化膜的钝性在耦合作用的影响下增强；两单相试样耦合之后奥氏体和铁素体相有着800 μm的耦合作用区，并且提高了耦合区铁素体相钝化膜的稳定性。最终确定两相之间电偶作用的主要对象就是铁素体相上的钝化膜；电偶作用降低了铁素体钝化膜外层的中的氧空位浓度，降低了铁素体钝化膜中氧空位的转移速率，从而大大提高了钝化膜的稳定性，其中稳定性提高最多的就是铁素体钝化膜的外层。