南海环境下稀土微合金化对高强钢腐蚀行为的影响机理

Rare earth is of resource advantage in our country. It is most important to develop rare earth microalloying high-strength steel (REHSS) used in maritime engineering for the development of marine engineering equipment industry. Wherein, corrosion failure is one of the key problems in affecting service life of materials. However, it is far from enough in the aspect of research on the corrosion mechanism of REHSS, might even not concern yet. The corrosion behavior of REHSS in sea water is originated from localized corrosion, followed by the diffusion and coalescence, and then becomes general corrosion. On account of the South China Sea environment, the purpose of this project is to solve such scientific problems: How does the rare earth element affect pitting corrosion and intergranular corrosion behavior of high-strength steel in the initial stage of corrosion. What are the effects of rare earth on electrode reaction process and the compactness and adherence of rust layer in general corrosion. Based on this, the effects of rare earth microalloying on the corrosion mechanism of high-strength steel can be elucidated comprehensively. The implement of this project can not only provide theoretical significance in material and corrosion science, but also provides the design reference and basic technical assistance for the development of new materials in marine engineering equipment industry. It is of high significance to promote the development of marine strategy in practice.

发展具有我国资源优势的海洋工程用稀土微合金高强钢对促进我国海洋工程装备产业的发展具有重要意义。其中，腐蚀失效是影响材料服役寿命的关键问题之一。然而，关于稀土微合金高强钢腐蚀机理的研究远远不够，甚至是尚未涉及。稀土微合金高强钢在海洋环境下的腐蚀行为是以局部腐蚀为先导、局部腐蚀扩散合并进而形成的全面腐蚀。针对南海环境，本项目力求解决这样的科学问题：稀土元素如何影响高强钢腐蚀初期点蚀和晶间腐蚀行为，稀土元素在全面腐蚀中对电极反应过程和锈层的致密性、粘附性有何作用，在此基础上全面阐述稀土微合金化对高强钢腐蚀行为的影响机理。本项目的开展不仅对材料和腐蚀科学具有重要的理论意义，还能为海洋工程装备产业新材料的开发提供设计依据和基础技术支持，对于推动我国海洋战略的发展具有重要的实践意义。

海洋环境下，腐蚀失效是影响材金属料服役寿命的关键问题之一。海洋工程用稀土微合金高强钢具有优良的综合力学性能，对促进我国海洋工程装备产业的发展具有重要意义，但其腐蚀机理的研究远远不够。因此，本项目首先评估了稀土微合金化高强钢在模拟海洋大气加速环境、浅海环境和深海环境下的腐蚀速率，结果表明，三种海洋环境下添加稀土元素能够减缓微合金钢的腐蚀速率。研究发现，稀土掺杂的变质夹杂效果显著，稀土微合金钢的中夹杂物主要以稀土硫化物、稀土（合金）氧化物、以及稀土（合金）氧硫化物为主。稀土硫化物及硫氧化物的功函数较低优先发生腐蚀溶解，而氧化物的功函数高于Fe基体不发生溶解但在夹杂物边缘产生微裂纹，最终夹杂物整体脱落诱发点蚀形核。微合金钢的腐蚀行为是以局部腐蚀为先导、局部腐蚀扩散合并进而形成的全面腐蚀，于是，对稀土在微合金钢全面腐蚀中的作用进行了分析研究。结果表明，添加稀土元素后，微合金钢中保护性腐蚀产物α-FeOOH的含量与未添加稀土元素的普通微合金钢中的含量差别不大，电化学阻抗谱亦无明显差异。因此，稀土元素掺杂对微合金耐腐蚀性能的提高主要体现在变质夹杂影响微合金钢腐蚀初期局部腐蚀行为，而对全面腐蚀过程影响不显著。