【作者】 黄毓晖；

【导师】 涂善东； 轩福贞；

【作者基本信息】 华东理工大学 ， 化工过程机械， 2011， 博士

【摘要】 随着石油、化工、能源等工业装置向着高温、高压和大型化方向发展,构件的服役环境日趋复杂,由腐蚀引发的事故大为增加,特别是承载构件的腐蚀所引发的一系列毫无征兆的灾难性事故引起了人们的广泛关注。长期以来,人们对于应力作用下的腐蚀问题进行了广泛的研究,但是由于应力与腐蚀过程之间交互作用的复杂性和多样性,迄今为止仍是一个富有挑战性的难题。本文以304不锈钢在氯离子溶液中的腐蚀为研究对象,围绕单轴塑性变形对材料表面活化溶解的影响、多轴应力状态对材料活化溶解的影响和多轴交变载荷对材料腐蚀性能的影响,进行了理论分析和实验研究,所取得的主要进展和结论如下：研究了304不锈钢在含有不同氢离子的氯化钠溶液中的应力腐蚀敏感性,分析304不锈钢在该腐蚀环境中的应力腐蚀开裂机理。研究表明,在0.63mol/L NaCl+0.5mol/L HCl溶液中,304不锈钢具有较强的应力腐蚀敏感性。采用恒载荷作用下的电化学实验研究了氢和应力对阳极活化溶解的影响。研究表明塑性变形显著加速阳极活化溶解而氢和应力的交互作用对阳极活化溶解的影响较小。基于热力学和电化学基础,从塑性变形引起的应变能密度和位错引起的表面电子活度变化出发,建立了氢和应力对阳极活化溶解影响的理论模型。恒载荷实验与理论计算取得了较好的一致。从而得出在酸性的氯离子溶液中,304奥氏体不锈钢的应力腐蚀开裂机理并不是氢加速阳极溶解型。通过点蚀坑内复杂应力状态对阳极活化溶解的影响,将点蚀坑内部的应力状态与局部腐蚀环境相耦合,开展了在外加载荷作用下点蚀坑内局部腐蚀环境的有限元分析,探讨了外加载荷、温度、点蚀坑尺寸对局部腐蚀环境中电化学性能及各离子浓度分布的影响。通过该模型可以判断温度、点蚀坑大小以及外加应力对点蚀坑内局部腐蚀环境的影响,为实际的生产实践提供趋势性的预测。在多轴交变载荷的作用下,采用比例与非比例加载方式研究了复杂交变载荷对304不锈钢腐蚀疲劳性能的影响。研究发现,与比例加载相比,非比例载荷加载过程中主应力面的持续旋转对点蚀坑的形成起了一定的阻碍作用。但是,非比例加载过程中主应力面的不断旋转使材料不能形成稳定的位错结构,提高了材料的附加强化,这种附加强化的形成对材料疲劳寿命降低起主导作用,从而使腐蚀环境的影响则相对较弱。因此,在相同的腐蚀环境和等效应力幅作用下,比例加载产生的疲劳寿命损失率大于非比例加载。更多还原

【Abstract】 As the installations in petrochemical, power generating and metallurgical industries are developing towards high temperature, high pressure and large-scale applications, corrosion-induced accidents have been a common occurrence, especially when the components are subjected to complex environments and applied loads. For a long time, extensive research efforts have been taken on the corrosion problem with applied stress. However, it remains as a significant challenge due to the complexity and diversity of the interaction between stress and corrosion. In the thesis, the corrosion behavior of 304 stainless steel in chloride solution was investigated. The effect of uniaxial plastic deformation on active dissolution, the effect of local deformation on active dissolution and the effect of multiaxial cycle loading on corrosion property were studied theoretically and experimentally. The main contents and conclusions of the thesis are as follows:The stress corrosion cracking sensitivity in the chloride solution with different acid concentration was firstly studied. The stress corrosion cracking mechanism was analyzed. Test results showed that, in the environment of 0.63mol/L NaCl+0.5 mol/L HCl solution,304 stainless steel had a relatively high sensitivity to stress corrosion cracking.Electrochemical tests under constant loading was conducted to study the effect of hydrogen and applied stress on anodic active dissolution. Test results revealed that the plastic deformation had a strong effect on active dissolution and the synergistic effect between stress and dissolved hydrogen only slightly promoted the process of active dissolution. On the basis of thermodynamics and electrochemistry, a theoretical model which reflects the effect of applied stress on active dissolution was proposed in terms of the stored strain energy and electron work function. A good agreement between the prediction and test results which revealed that the stress corrosion cracking mechanism of 304 stainless steel in acid chloride solution was not hydrogen-facilitated anodic dissolution.A mathematical model for simulating a stressed metal surface with a pit in which active dissolution occurs had been developed. An active dissolution mechanism was assumed and extended to the pit surface by including a multiaxial stress state dependent bare metal dissolution current density. The influence of applied tensile stress, pit radius and temperature was addressed. Through accounting for the thermal activation energy and the stress state in pit bottom, the distribution of solution potential and species concentration was predicted for different applied tensile stresses. The effect of multiaxial cyclic loading on corrosion property of 304 stainless steel was studied by use of proportional loading and non-proportional loading. It was found that, compared with proportional loading, the continuous rotation of the principle stress plane during multiaxial non-proportional loading blocked the formation of pits. Furthermore, the lack of stable dislocation structure during the non-proportional loading enhanced the additional hardening of material which strongly reduced the fatigue life of specimen while the corrosion environment only played a promotional role.更多还原