深海环境对纯Ni及NiCrMoV钢焊接接头腐蚀行为机制的影响

发布时间：2019-02-16 20:27

【摘要】：本论文利用电化学测试、光学及电子显微镜研究了静水压力对纯镍在氯化钠溶液中的腐蚀行为的影响。随着静水压力的升高,纯镍的点蚀电位降低,维钝电流升高,恶化了纯镍的耐点蚀性能。研究结果同时表明静水压力对纯镍的腐蚀行为有着三个方面的影响:静水压力的升高对纯镍表面钝化膜的形成具有阻碍作用;静水压力的升高阻碍B1过程(点蚀生长和湮灭的随机模型)并加速A3过程(点蚀生长随机模型);静水压力提高了纯镍的点蚀生长概率。金属Ni作为一种重要的合金元素添加到新型低合金钢10Ni5CrMoV钢中提高其耐蚀能力。10Ni5CrMoV钢作为新一代深海工程用钢广泛应用于建造深海工程及深潜器。深海工程及深潜器的建造工作离不开焊接技术的支撑,l0Ni5CrMoV钢焊接接头的耐腐蚀性能直接影响到深海工程及深潜器的服役安全。因此,开展焊接工艺对焊接接头深海腐蚀的影响的研究工作变得十分迫切。本文基于1.85KJ/mm、2.34KJ/mm、3.17KJ/mm三种焊接线能量加工的10Ni5CrMoV钢焊接接头,利用MSC.Marc有限元方法数值模拟焊接加工过程。研究结果表明,当线能量由小变大,焊缝金属及热影响区的温度场呈现出焊缝金属区域高温持续时间变长,应力场和应变场的值逐渐变小。金相分析结果显示焊接线能量越大,形成的热影响区的区域宽度也就越大。焊接线能量越大,冷却速度相对降低,发生马氏体相变转变为贝氏体相变的可能性也就越高,焊接接头所处的焊接残余热应力水平值越高。腐蚀试验结果表明,线能量为1.85KJ.mm-1、线能量为3.17KJ.mm-1焊接接头在深海环境下的有严重的局部腐蚀,采用线能量为2.34KJ.mm-1焊接工艺的10Ni5CrMoV钢焊接接头在深海环境下的耐蚀性能最好,具有良好的耐深海腐蚀性能。10Ni5CrMoV钢焊接接头在深海环境下出现局部腐蚀甚至点蚀,这种现象产生的原因有两个方面:一方面,焊接热循环带来焊接接头残余热应力导致其表面的力学-化学不均匀性导致的焊接接头材料深海环境下的腐蚀敏感性提高:另一方面,焊接接头特征区域之间的金属材料在深海环境下较大的电位差出现电偶腐蚀,加速其在深海环境下焊缝金属和热影响区的腐蚀速度,使深海环境下材料腐蚀危害性加剧。利用有限元完成深海多因素耦合环境下焊接接头复杂耦合的腐蚀电化学模型模拟,研究结果表明深海环境中10Ni5CrMoV钢焊接接头的焊缝金属和热影响区具有较强的腐蚀敏感性,容易在深海环境下发生局部腐蚀,危害焊接接头的深海腐蚀服役安全。
[Abstract]:The effect of hydrostatic pressure on the corrosion behavior of pure nickel in sodium chloride solution was investigated by electrochemical measurement, optical and electron microscopy. With the increase of hydrostatic pressure, the pitting potential of pure nickel decreases and the UB current increases, which deteriorates the pitting corrosion resistance of pure nickel. The results also show that the hydrostatic pressure has three effects on the corrosion behavior of pure nickel: the increase of hydrostatic pressure hinders the formation of passivation film on the surface of pure nickel; The increase of hydrostatic pressure hinders B1 process (random model of pitting growth and annihilation) and accelerates A3 process (pitting growth stochastic model), and hydrostatic pressure increases pitting growth probability of pure nickel. As an important alloy element, metal Ni is added to the new low alloy steel 10Ni5CrMoV steel to improve its corrosion resistance. As a new generation of deep sea engineering steels, 10Ni5CrMoV steel is widely used in the construction of deep sea engineering and deep submersible vehicles. The construction of deep sea engineering and deep submersible can not be separated from the support of welding technology. The corrosion resistance of welded joints of l0Ni5CrMoV steel has a direct impact on the safety of deep sea engineering and deep submersible. Therefore, it is urgent to study the effect of welding process on deep-sea corrosion of welded joints. Based on 1.85KJ / mm 2.34KJ / mm 3.17KJ / mm 10Ni5CrMoV steel welded joints, the welding process is simulated numerically by MSC.Marc finite element method. The results show that when the linear energy increases from small to large, the temperature field of weld metal and heat-affected zone becomes longer, and the value of stress field and strain field becomes smaller. Metallographic analysis shows that the larger the welding line energy, the larger the width of the heat affected zone. The higher the welding line energy, the lower the cooling rate, the higher the possibility of martensitic transformation to bainite transformation, and the higher the level of welding residual thermal stress. The corrosion test results show that the line energy is 1.85KJ.mm-1, and the linear energy is 3.17KJ.mm-1 welding joint, which has serious local corrosion in deep-sea environment. The welded joints of 10Ni5CrMoV steel with linear energy as 2.34KJ.mm-1 welding process have the best corrosion resistance and good corrosion resistance in the deep sea environment. Local corrosion and even pitting corrosion occur in the deep sea environment of 10Ni5CrMoV steel welded joints. There are two reasons for this phenomenon: on the one hand, Welding thermal cycling results in residual thermal stress of welded joints resulting in increased corrosion sensitivity of welded joint materials in deep-sea environments due to mechanical-chemical inhomogeneity on their surfaces: on the other hand, The large potential difference between the characteristic regions of welded joints is galvanically corroded, which accelerates the corrosion rate of weld metal and heat-affected zone in deep-sea environment, and makes the corrosion harm of materials in deep-sea environment more serious. Using finite element method, the corrosion electrochemical model of complex coupling of welded joints in deep-sea multi-factor coupling environment is simulated. The results show that the weld metal and heat-affected zone of 10Ni5CrMoV steel welded joints in deep-sea environment has a strong corrosion sensitivity. Local corrosion is easy to occur in deep sea environment, which endangers the safety of deep sea corrosion service of welded joints.
【学位授予单位】：哈尔滨工程大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG407;TG172

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