低合金高强度钢浪花飞溅区点蚀行为及机理研究

发布时间：2018-01-19 05:35

本文关键词： 高强度钢点蚀浪花飞溅区锈层干湿交替　出处：《中国科学院研究生院(海洋研究所)》2016年博士论文　论文类型：学位论文

【摘要】：低合金高强度钢通常是指含碳量为0.2%-0.45%质量分数、配以适当合金元素,并经淬火、回火等工艺处理的低合金钢。为了应对海洋环境的强耐蚀性,海洋用低合金高强度钢常会采用Cr、Ni、Mo、Cu、P、Si等元素进行合金化处理。随着海洋用新材料研究工作的不断深入,高强度钢的性能不断提高,其在整个海洋环境的使用将成为可能,海洋用低合金高强度钢代表着一种趋势,在我国海洋开发和利用中有广阔的应用前景。海洋环境中钢铁材料的局部腐蚀,尤其是点蚀(也称小孔腐蚀),是影响钢铁材料强度和寿命的重要原因。在浪溅区,钢结构表面几乎连续不断地被充分而又不断更新的海水所润湿,具有干燥时间短、水膜停留时间长、干湿交替频率高、海盐粒子量大等特点。由于波浪和海水飞溅,海水与空气充分接触,海水含氧量达到最大程度,浪溅区海水的冲击也加剧材料的破坏。材料表面被锈层覆盖后,其腐蚀过程不再是简单的金属阳极溶解和氧的阴极还原,而是一种十分复杂的多种物质参与的氧化还原过程。钢的腐蚀行为与钢材表面锈层的多孔性、导电性、离子选择性和还原性等性质关系很大。目前,对于浪溅区钢铁材料的局部腐蚀机理研究相对较少,而浪溅区的腐蚀是海洋环境各区带中最严重的,锈层结构也与其它区带不同,因此,针对高强度钢浪溅区锈层覆盖下的点蚀破坏规律及机制进行深入研究对于促进高强度钢在海洋环境中的应用推广及安全评估有重要意义。基于以上背景,本文以低合金高强度钢AISI 4135钢为研究对象,对浪花飞溅区低合金高强度钢表面锈层发生、发展过程进行了观察,包括实海挂片实验和实验室模拟实验两部分。在实海实验的不同阶段,通过分析锈层的组成分析了主要的腐蚀环境因子。根据这些结果对锈层和钢材界面的状态进行模拟,为用电化学方法研究锈层底部的点蚀机制创造了条件。实验室模拟实验主要通过调整浪花飞溅区温度和干湿交替变化研究其对点蚀发展规律及机制的影响。本论文的主要研究结果如下:1.AISI 4135钢经过合适的热处理能提高钢的强度并改善力学性能,但当海水液膜的温度升高,所有热处理试样的开路电位降低,腐蚀速率增加。热处理影响试验材料的力学性能,但在相同温度海水液膜下的腐蚀行为没有显著影响。2.浪花飞溅区实海暴露实验的结果表明,暴露初期的温度对AISI 4135钢的腐蚀影响很大,暴露初期温度越高,腐蚀速率越大。经过一年四季温度的更替后,暴露初期温度高的试样比暴露初期温度低的试样腐蚀要严重的多。另外,AISI4135钢在浪花飞溅区实海暴露两年后出现点蚀穿孔现象。3.在不同温度海水液膜下,循环阳极极化曲线的滞后环的面积在低温下大于其在高温下的面积,表明点蚀在低温下更容易发生。钝化膜或者是氧化物膜在低温下存在,但当温度升高时会变的不稳定或完全消失。4.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,这些裂缝为电解质和O2提供了侵入内锈层、接触锈底层的通道。5.暴露于飞溅区的AISI 4135钢含有裂缝的外锈层中有γ-FeOOH存在,γ-FeOOH是能加速裂缝腐蚀的电化学活性物质。其次,AISI 4135钢暴露于飞溅区一年后,其内锈层中含有高浓度的氯化物,所产生的低pH可促进β-FeOOH的生成。β-FeOOH易被还原,能够促进海洋飞溅区环境下的腐蚀过程。6.锈层覆盖下的AISI 4135钢在浪花飞溅区的干湿循环的干燥过程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。
[Abstract]:High strength low alloy steel usually refers to the carbon content of 0.2%-0.45% mass fraction, with appropriate alloying elements, and after quenching, tempering process of low-alloy steel. In order to cope with the strong corrosion resistance of the marine environment, marine high strength low alloy steel is often used by Cr, Ni, Mo, Cu, P. Si and other alloying elements such as the oceans. The use of new materials and the deepening of the research work, the properties of high strength steel continues to improve, it will become possible in the use of the marine environment, marine high strength low alloy steel represents a trend, and has broad application prospects in the marine development and utilization in China local corrosion of steel in marine environment, especially pitting (also known as pitting corrosion), is an important factor affecting the steel material strength and life. In the splash zone, the surface of the steel structure is almost continuously being fully and continuously updated with water wetting. Short drying time, water retention time long, alternate high frequency characteristics of large amount of sea salt particles. Due to wave and seawater splash, full contact with seawater and air, oxygen levels in the water to reach the maximum level, the impact area of seawater splash also increased the damage of materials. The surface of the material being covered in rust layer after the corrosion process is no longer the cathodic reduction of anodic dissolution of metal oxygen and simple, but a variety of complex substances involved in the redox process. The porosity and corrosion behavior of the steel surface rust layer steel electrical conductivity, large ion selectivity and reductive properties. At present, the study on the local corrosion mechanism of steel splash zone the material is relatively small, and the splash zone corrosion is the most serious marine environment in each zone in the rust layer structure and other areas with different, therefore, to cover the splash zone of high strength steel rust pitting failure rules The law and mechanism of in-depth study has important significance for promoting the application and safety evaluation of high strength steel in marine environment. Based on the above background, this paper with high strength low alloy steel AISI 4135 steel as the research object, the splash zone of high strength low alloy stainless steel surface layer, the development process were observed. Including the real sea test and laboratory simulation experiment. The two part in different stages of real sea experiment, corrosion of main environmental factors were analyzed by analysis of the composition of the rust layer. According to the results of the rust layer and steel interface state simulation, to create the conditions for the research on the mechanism of pitting corrosion by electrochemical method of rust layer at the bottom. Simulation study on its influence on the law of development of pitting and mechanism mainly by adjusting the temperature and humidity in the splash zone alternating laboratory experiment. The main results are as follows: 1.AISI 4135 steel After proper heat treatment can improve the strength of steel and improve the mechanical properties, but when the water film temperature increases, all heat treated specimens of open circuit potential decreased, the corrosion rate increased. The effect of heat treatment on mechanical properties of test materials, but the corrosion behavior in seawater film under the same temperature did not significantly affect the.2. real splash zone the sea exposure experiment results indicated that the effects of exposure to the initial temperature corrosion of AISI 4135 steel, early exposure to higher temperature, higher corrosion rate. After a year after the change of temperature, exposure to high temperature samples than the initial samples exposed the initial corrosion of low temperature to be more serious. In addition, the real sea two years of exposure of AISI4135 steel in splash zone after pitting perforation phenomenon of.3. in seawater film under different temperature, hysteresis cyclic anodic polarization curves in the area is greater than that in the high temperature surface at low temperature That product, pitting more easily occur at low temperature. The passivation film or existing oxide film at low temperature, but when the effect of diurnal and annual variation of temperature will become unstable or disappear completely.4. temperature and humidity of the environment and the wet dry wet cycle of marine splash zone of rust layer the structure and properties of AISI 4135 steel. When exposed to the splash zone after one year, produced from splash and condensed water absorption water cracks and holes, these cracks as the electrolyte and O2 provide invade the inner rust layer, gamma -FeOOH outer rust layer contact the bottom of the rust channel.5. exposed to splash zone AISI 4135 steel containing cracks, gamma -FeOOH is electrochemically active substances can accelerate crack corrosion. Secondly, AISI 4135 steel exposed to splash zone after a year, containing a high concentration of chloride in the inner rust layer, caused by low pH can promote the formation of beta -FeOOH beta -FeOOH. Easy to be reduced, pH can promote the drying process of wet and dry cycle environment marine splash zone under the AISI corrosion process under the cover of.6. rust layer of 4135 steel in splash zone has a minimum value. In the anode channel narrow, strong acidic condition in contact with the steel surface will cause the corrosion rate increases, accelerate local corrosion and crack empty place.

【学位授予单位】：中国科学院研究生院(海洋研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P755.3

【参考文献】