青海盐湖大气环境下钢的腐蚀行为及锈蚀演化机制

IMR OpenIR

	青海盐湖大气环境下钢的腐蚀行为及锈蚀演化机制
	王军
学位类型	博士
导师	柯伟 ; 王振尧
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料学
关键词	碳钢低合金钢大气腐蚀锈层 Mg2++ Carbon Steel Low Alloy Steel Atmospheric Corrosion Rust Layer Mg2++
摘要	"大气腐蚀是一个材料与环境相互作用的非常复杂的过程，不同材料对相同大气环境的响应也可能会有所差异，因而仅仅依靠环境的气象参数和污染物数据来评价其大气腐蚀性并不是完全合理的。青海盐湖地区的大气环境与一般的海洋大气环境有所不同，其大气腐蚀性和相关的金属腐蚀数据相对缺乏，随着国家西部大开发战略的顺利实施，迫切需要对该地区的大气腐蚀性以及金属的腐蚀状况进行了解和调查。钢作为最重要的基础材料广泛应用于交通、资源、能源、农业以及建筑等各个领域。为了给盐湖地区的工程建设提供基础数据和技术支持，弄清该大气环境下影响钢铁材料腐蚀的主要因素，进一步为开发经济实用的耐大气腐蚀钢种提供理论依据，我们对Q235碳钢和CortenA耐候钢以及两种低合金钢分别进行了为期36个月和42个月的实地暴晒实验，研究了碳钢和低合金钢在青海盐湖大气环境下的腐蚀行为，探讨了其腐蚀动力学与表面锈层的成分与结构之间的关系。利用XRD、IRS、SEM、EDX、EPMA和电化学测试等技术手段，对锈层特征进行了系统的表征，同时阐述了Mg元素对其腐蚀进程的影响，提出了钢在盐湖地区的大气腐蚀模型，得到的主要结论如下：实地暴晒的失重结果表明，投放季节对钢的初期腐蚀阶段影响较大，大气相对湿度是决定性的影响因子。在整个暴晒周期内，CortenA耐候钢和Q235碳钢表现出了相似的阶梯状的腐蚀动力学行为，说明两种钢的表面锈层均未体现出保护性。平均腐蚀速率随季节呈现波动的趋势，表明在暴晒周期内大气相对湿度仍然是最重要的影响因子。低合金钢A暴晒42个月后的腐蚀失重比Q235碳钢和CortenA耐候钢暴晒36个月后的腐蚀失重还小，说明青海盐湖大气环境下低合金钢A具有最佳的耐候性。 SEM和EPMA分析的结果显示，Si、Al、Ca等外来元素仅仅以尘土及夹杂物的形式存在于锈层之中，破坏了锈层的均匀性及致密度，而Mg不仅以沉积盐的形成存在于锈层之中，极大的降低了腐蚀发生的临界相对湿度，延长了锈层的润湿时间，促进了金属基体的腐蚀，同时还参与了锈蚀演化进程而逐渐富集于锈层之中，改变了锈层的结构和属性，进而影响金属基体的后续腐蚀进程。 CortenA耐候钢户外暴露实验和实验室加速实验的电化学结果显示，锈层电阻Rr和电荷转移电阻Rt的值都很小，暗示了锈层的结构粗糙多孔，导电性好，有利于侵蚀性离子在锈层中的传输，加速了耐候钢基体的腐蚀。锈层电容Cr随暴露时间波动的变化趋势表明锈层的结构也一直处于不稳定的状态，难以形成致密结构，保护性很弱。极化测试结果显示，不同腐蚀周期的带锈电极阴极电流密度均很大，表明锈层内始终存在着大量的还原性组分，促进了电化学反应的进行。在整个暴晒周期内，四种钢的锈层成分演化过程相似，在暴晒的初期主要腐蚀产物均为β-FeOOH和γ-FeOOH，随着腐蚀时间的延长，锈层中开始出现Fe3O4相，接下来Mg通过取代中间产物中的亚铁离子生成了Mg4Fe(OH)8OCl•xH2O和MgFe2O4而逐渐富集于锈层之中，它们不仅增强了锈层的导电性，同时还使得锈层具有了阴离子选择性，促进了Cl离子在锈层中的扩散和传输，破坏了腐蚀产物膜的结构，加速了金属基体的腐蚀。青海盐湖大气环境下CortenA耐候钢表现出了和Q235碳钢相似的腐蚀行为，没有体现出优异的耐蚀性，Cr、Cu、P等合金元素没有发挥出相应的作用，而低合金钢A由于含有微量合金元素Ti和Nb体现出了相对最优的耐候性，说明不同合金元素在不同的暴晒环境和条件下对钢的抗大气腐蚀性影响也有所不同，合金元素有益效应的发挥需要一定合适的条件。"
其他摘要	"Atmospheric corrosion is a rather complex interaction between the materials and the surrounding environments. As the responds of various materials to the same atmospheric environment may be also different, it is not very reasonable to assess the atmospheric corrosiveness just by the meteorological parameters and pollution data of environment. The atmospheric environment in Qinghai salt lake region is different from common marine atmospheric environment, and there is a lack of research about the atmospheric corrosiveness and metal corrosion data. With the implement of the national western development project, it is exigent to investigate the atmospheric corrosiveness and metal corrosion situation of the salt lake region. Steels as the most fundamental materials are widely employed in traffic, resources, energy, agriculture and buildings. In order to supply the fundamental data and technical support to the construction in the salt lake region, and make clear the main impact factors of steel corrosion, further supply the theoretical basis for developing economical and practical weathering steel, we have performed an exposure test with duration of 36 months for Q235 carbon steel and CortenA weathering steel, and duration of 42 months for two kinds of low alloy steels. We investigated the corrosion behavior of carbon and low alloy steels, discussed the relations between the corrosion dynamics and the rust composition and structure. The rusts were characterized by XRD, IRS, SEM, EDX, EPMA and electrochemical techniques. The influence of Mg to the corrosion process is clarified and the atmospheric corrosion model of steels in Qinghai salt lake region is proposed. The following main conclusions were drawn: The weight loss results of exposure tests showed that the embarking season had a great influence on the initial corrosion stage of steels, and the relative humility was the key impact factor. In the whole exposure duration, CortenA weathering steel showed stepladder corrosion dynamics behavior as similar to Q235 carbon steel, indicating that the rust layers on both steels were not protective. The average corrosion rate showed a fluctuation tendency with time, indicating that the relative humility was still the main impact factor. The weight loss of low alloy steel A after 42 months’ exposure was less than that of Q235 and CortenA after 36 months’ exposure, displayed the best weatherability of low alloy steel A. SEM and EPMA analysis showed that the foreign elements such as Si, Al, Ca were existed in the rust just as the form of dust and impurities, destroyed the evenness and density of the rust layer, while Mg not only stayed in the rust as salt deposits, lowing the critical relative humility greatly, increasing the time of wetness, promoting the corrosion of metal matrix, but also took part in the rusting evolution process and accumulated in the rust, which changed the rust structure and properties, and further influenced the following corrosion process. The electrochemical results of both exposure test and laboratory accelerating test for CortenA weathering steel showed that both rust resistance Rr and charge transfer resistance Rt were small, indicating that the rust layer were rough, porous and conductive, facilitated the transportation of corrosive ions in the rust layer and accelerated the corrosion of the matrix. The rust capacitance Cr displayed a fluctuation tendency with exposure time, indicating that the rust was not stable and hard to form a density structure, which had poor protectiveness. The results of polarization test showed that all the cathodic current density of rusted samples for various corrosion times were very big, indicating that there were abundant reductive substances in the rust, which promoted the electrochemical reactions. In the whole exposure duration, the rust composition of all kinds of steels showed a similar evolution process. In the early stage of exposure, the main corrosion products were β-FeOOH and γ-FeOOH. As the corrosion time prolonged, Fe3O4 began to exist in the rust layer, then Mg was gradually accumulated in the rust by replacing some ferric ions in the intermediates and forming corrosion products MgFe2O4 and Mg4Fe(OH)8OCl•xH2O. They inhanced the conductivity of the rust, meantime made the rust layer anion-selective, promoted the diffusion of Cl ions, damaged the rust structure and accelerated the corrosion of metal matrix. In the Qinghai salt lake atmospheric environment, CortenA weathering steel showed a similar corrosion behavior with Q235 carbon steel and did not display a better corrosion resistance, the alloy elements Cr, Cu and P played no remarkable functions, while low alloy steel A which contains trace Ti and Nb showed the best weatherability, indicating that various alloy elements showed different influence on atmospheric corrosion resistance of steel in various exposure environment and conditions, the beneficial functions of alloy elements relies on some suitable conditions."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64468
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	王军. 青海盐湖大气环境下钢的腐蚀行为及锈蚀演化机制[D]. 北京. 中国科学院金属研究所,2012.