一种低合金高强度钢浪溅区的点蚀机理和氢渗透行为研究

The project will focus on the elucidation of the mechanism of pitting corrosion, the origin of hydrogen and hydrogen permeation behaviour by the study of pitting corrosion development, hydrogen permeation characteristics during the corrosion of bare surfaces，under integrated and damaged anti-corrosion wrapping layers of a low alloy high strength steel in the splashed zone. The use and development of high strength steels have become a trend for the consideration of saving resources, reducing the weight of structures and the environment burden. The corrosion of iron and steel materials in splashed zone is the most serious among all the marine corrosion zones. So, the researchers have never given up the endeavor to get a better understanding of the splashed zone corrosion behaviour and the development of its protection techniques. Low alloy high strength steels has the potential danger of pitting, stress corrosion and hydrogen induced cracking in the splashed zone. But the corrosion of steels in marine environment is often idealized as homogeneous, although in fact it is not such. Relatively less research on the pitting corrosion in the splashed zone was done. Experiments showed that the corrosion phenomena in splashed zone and full immersion zone exhibit obvious differences and can not be explained by the accepted full immersion zone pitting corrosion theory. The theoretical problems for the splashed zone pitting corrosion need to be solved. The safe use of high strength steels in splashed zone requires the mastering of corrosion regularity and mechanisms. The research on hydrogen permeation behaviour during splashed zone corrosion process was not covered in the past works, while the hydrogen entry for high strength steel can not be ignored due to its possible sensitivity to hydrogen embrittlement. Wrapping technique was proved to be an effective method for the splashed zone corrosion protection. It requires for verification if the hydrogen penetration to high strength steel still exists under anti-corrosion wrapping layers. With the increase of service life, any kinds of corrosion protection will inevitably loss function or suffer partial destruction, especially for long-term exposure to harsh conditions and the maintenance is not ideal. In this respect, it is still necessary to do an in depth study on the splashed zone pitting regularity and mechanisms as well as hydrogen permeation under rust layer. The combination of pitting corrosion and hydrogen permeation behavior research in one project has the benefit of obtaining two kinds of results in one batch of experiment. This research will enrich the splashed zone pitting corrosion theory and open a new research area for hydrogen permeation. The outcomes of this research have vital significance not only for the development of corrosion science theory itself, but also for the prediction of the splashed zone corrosion and safety assessment of high strength steels, having broad application prospects.

本项目将着重研究低合金高强度钢在海洋浪花飞溅区的点蚀机理，通过对高强钢腐蚀发展过程中、包覆防腐保护条件下和包覆层局部破损后的氢渗透行为的研究，阐明氢的来源及氢渗透机制。资源节约、结构轻量化的要求使得高强钢的应用成为发展方向。浪花飞溅区是最苛刻的海洋腐蚀环境。低合金高强度钢在浪花飞溅区具有发生点蚀、应力腐蚀及氢致开裂的潜在危险。为了高强钢在海洋环境中的安全使用，需要我们掌握它在浪花飞溅区的腐蚀破坏规律和机制。海洋腐蚀研究很少涉及材料在浪花飞溅区的氢渗透行为，而氢渗透对于高强钢而言又是不可忽视的。包覆防腐技术是有效的浪花飞溅区腐蚀防护方法。但是，高强钢在包覆防腐保护条件下和包覆层局部破损后是否仍有氢向高强钢内渗透需进行实验验证。该研究将丰富和完善点蚀理论、拓展氢渗透研究的范围，不仅对腐蚀科学理论的发展有重要意义、对高强钢浪花飞溅区腐蚀发展预测和腐蚀安全评估也有重要价值，具有广阔的应用前景。

资源节约、结构轻量化的要求使得高强钢的应用成为发展方向。低合金高强度钢在苛刻的浪花飞溅区具有发生点蚀、应力腐蚀及氢致开裂的潜在危险。为了高强钢在海洋环境中的安全使用，需要掌握它在浪花飞溅区的点蚀和腐蚀过程中氢渗透的规律和机制。包覆防腐技术是有效的浪花飞溅区腐蚀防护方法，但高强钢在包覆防腐保护条件下和包覆层局部破损后是否仍有氢向高强钢内渗透需进行实验验证。.对低合金高强度钢AISI 4135钢表面锈层发生、发展过程进行了观察，研究了润湿特征，分析了不同阶段锈层的组成，用电化学方法研究了锈层底部的点蚀发展规律和机制。研究表明，浪溅区试样表面润湿程度大体上随潮位升高润湿程度加大，潮位降低润湿程度降低的整体趋势，但在同一时刻试样的润湿状态与潮位和试样的位置关系具有不确定性。试样的润湿程度随暴露天数的增加有增加的趋势。热处理工艺对试样的腐蚀行为没有显著影响。实海暴露实验初期温度越高，腐蚀速率越大，实海暴露两年后出现点蚀穿孔现象。循环阳极极化曲线测试表明点蚀在低温下更容易发生。温度和湿度的日际和年际变化以及环境的湿-干-湿循环对海洋飞溅区锈层的结构和性质都有影响。当AISI 4135钢暴露于飞溅区一年后，产生了能够从飞溅和冷凝水中吸收海水的裂缝和空洞，为电解质和氧提供了侵入内锈层、接触锈底层的通道。含有裂缝的外锈层中有电化学活性物质γ-FeOOH存在，使裂缝内腐蚀加速。暴露一年后，其内锈层中含有高浓度的氯化物，所产生的低pH环境可促进β-FeOOH的生成。β-FeOOH易被还原，能够促进飞溅区环境下的腐蚀过程。锈层覆盖下的钢表面环境在干湿循环的干燥过程中pH有最小值。在狭窄的阳极通道内，与钢表面接触的强酸性条件会导致腐蚀速率增大，加速裂缝和空洞处的局部腐蚀，同时也是导致阴极过程有氢产生并向内部渗透的原因。氢渗透的研究表明试样的热处理工艺对试样的氢渗透行为和氢渗透量会产生一定的影响，等温淬火试样和分级淬火试样的氢渗透量相对较小；低合金高强度钢在包覆防护条件下即使局部破损氢渗透量也显著减少，在试样未腐蚀前进行包覆防护，能起到更好的抑制作用；证实包覆防腐技术可同时对高强度钢的腐蚀和氢向其内部渗透有显著的抑制作用。.该研究丰富和完善了点蚀理论、拓展了氢渗透研究的范围，不仅对腐蚀科学理论的发展有重要意义、对高强钢浪花飞溅区腐蚀发展预测和腐蚀安全评估也有重要参考价值，具有广阔的应用前景。