高强度螺栓用钢的氢扩散动力学及氢致延迟断裂控制技术研究

发布时间：2018-01-20 12:21

本文关键词： 高强度螺栓氢致延迟断裂氢扩散动力学控制技术慢应变速率拉伸试验　出处：《哈尔滨工程大学》2016年博士论文　论文类型：学位论文

【摘要】：高强度螺栓广泛应用于海洋工程装备,在恶劣的海洋环境中,易于发生氢致延迟断裂现象,给装备的正常运行带来极大的安全隐患。材料的组织、氢和应力状态是高强度螺栓氢致延迟断裂的三个重要因素,尤其是内氢在螺纹根部应力集中处的扩散、富集,是高强度螺栓断裂的主要因素。氢致延迟断裂的防控需从这三方面因素着手进行研究分析,因而,研究高强度螺栓连接结构的应力状态、氢在材料中的扩散动力学及氢致延迟断裂的控制手段具有重要的理论和工程意义。本文选取典型的海洋工程用高强度螺栓材料40CrNiMoA、0Cr16Ni5Mo和12CrNi9MoV钢,并利用有限元分析、力学测试、微观组织观察及电化学测试等手段,对三种试验钢的氢致断裂问题的内因和外因进行剖析、总结,并试图找出氢致延迟断裂的合理控制手段。为研究材料在使用中氢聚集后的力学和化学行为,需要研究试验钢的阴极充氢工艺以制备研究的试样。结果表明,充氢过程应采用“长时间,小电流”的原则,可以起到氢原子均匀分布于试样,且有效避免试样表面产生氢致损伤的作用。氢含量均随充氢时间的延长及充氢电流密度的增加而增加,达到一定时间后,处于稳态值。该工作能够为工程应用中研究内氢在螺栓中某一部位扩散、富集并最终达到稳态值提供试验验证,同时也为内氢聚集达到稳态值的计算奠定基础。氢扩散系数是表征氢在钢中扩散能力的重要参量。本文采用氢扩散理论中的穿透时间法和时间滞后法计算了试验钢的表观氢扩散系数。利用不同类型螺栓用钢的氢扩散系数,评估了氢在钢中富集部位达到平衡状态的时间及富集程度,从而为评价氢在不同材质螺栓应力集中处聚集的过程及趋势做铺垫。利用升温脱氢分析技术,研究了氢在试验钢中的陷阱行为,并以逸出激活能的形式评估了钢中不同类型氢原子的逸出能力。本工作对研究内氢在不同类型螺栓用钢中的扩氢难易程度及利用有益氢陷阱来降低氢致延迟断裂敏感性具有重要意义,同时也为不同类型螺栓用钢的选材提供参考。采用慢应变速率拉伸试验,本文研究了氢对缺口试样和光滑试样应力应变特性的影响。该研究能够很好地评价不同类型螺栓用钢在内氢作用下的承载能力,且其内氢含量与缺口强度及塑性指标的对应关系能够为工程应用中螺栓强度的选择和安全性评价提供参考。同时,拉伸试样的断口形貌表明,氢致断裂断口形貌随着钢中氢含量的升高,由韧窝型韧性断口逐渐向穿晶准解理甚至沿晶断裂特征过渡,从而为实际工况中螺栓失效分析提供复原模拟作用。采用有限元分析模拟手段,缺口试样的根部区域应力分布得到了直观的呈现。通过设计模型中不同的缺口半径和材料参数,获得了不同缺口半径、不同强度状态下缺口根部的应力集中系数。此分析为应力诱导氢扩散模拟提供了预定义场。利用应力诱导-氢扩散顺次耦合的有限元程序,获得了氢在应力诱导下缺口根部氢浓度的分布状态及富集趋势,为工程应用中螺栓发生氢致断裂的断口形貌分析提供借鉴,也可为螺栓的安全性评价提供参考。本文利用理论计算与有限元模拟相结合的手段,探讨了高强度螺栓氢致延迟断裂的控制技术。缺口根部的微区塑性变形对于应力集中的缓解具有重要作用,而氢原子的引入,对塑性变形具有复杂影响。内氢含量、缺口半径和螺栓用钢的氢致局部断裂临界应变三者之间的关系,成为防控高强度螺栓氢致延迟断裂的关键,也为高强度螺栓的合理选材、结构设计提供理论参考。高强度螺栓在实际应用时,通常根据使用环境来选择合适的电镀层来增加零件的使用年限。本文利用电化学手段对常用的几种螺栓镀层进行耐蚀性评价及镀层腐蚀阶段的电化学反应过程进行分析,探讨了其不同的耐蚀性机理。通过系统地对比分析,找出海洋工程应用中,适合高强度螺栓低氢脆、低后脆的防护镀层。其中,Zn-Ni和Cd-Ti镀层的耐蚀性相当,但从环保性、经济性考虑,在海洋大气环境中,Zn-Ni镀层有望替代Cd-Ti镀层;而在海水中,可以考虑将阴极性镀层Ni-W-P替代Cd-Ti镀层作为高强度螺栓阻氢及低后脆的防护措施。
[Abstract]:High strength bolts are widely used in marine engineering equipment, in the harsh marine environment, prone to hydrogen induced delayed fracture phenomenon, bring a great security risk to the normal operation of equipment. The microstructure, hydrogen and stress state are three important factors induced delayed fracture of high strength bolts of hydrogen, especially in diffusion. The hydrogen at the thread root stress concentration enrichment, is a major factor in fracture of high strength bolts. The prevention and control of hydrogen induced delayed fracture from these three factors were analyzed, thus, the research of high strength bolt connection structure stress state, has important theoretical and practical significance to control the means of diffusion induced delayed fracture kinetics and hydrogen in the material. The material selection for high strength bolts 40CrNiMoA typical ocean engineering, 0Cr16Ni5Mo and 12CrNi9MoV steel, and the use of finite element analysis, mechanical test, microstructure observation Method and electrochemical test, the internal and external problems caused by fracture of three steel test of hydrogen to analyze, summarize, and try to find out the reasonable control method of hydrogen induced delayed fracture. As the research materials in the use of hydrogen concentration of the mechanical and chemical behavior, need cathodic hydrogen charging process of steel production research to test for the samples. The results showed that the hydrogen charging process should use "long time, small current" principle, can play the role of hydrogen atoms are evenly distributed in the sample, and avoid the sample surface to produce hydrogen induced damage. The hydrogen content increased with the increase of hydrogen charging time delay and hydrogen charging current density increases. After a certain period of time, in a steady state value. The work can be a part of the hydrogen diffusion in the engineering application in the bolt, and eventually reached a steady value for enrichment experiments, but also for the hydrogen accumulation reaches the steady state value calculation Foundation The foundation. The hydrogen diffusion coefficient is an important parameter for characterization of diffusion of hydrogen in steel. This paper uses the hydrogen diffusion theory in the penetration time and time lag method to calculate the test steel apparent hydrogen diffusion coefficient. The use of different types of steel for bolts on the hydrogen diffusion coefficient, and evaluated the degree of enrichment of hydrogen in steel. Part time reaching equilibrium state, so as to pave the way for the evaluation process and the trend of hydrogen in different material bolt stress concentration accumulation. Using heating dehydrogenation analysis technology, studied the behavior of hydrogen in steel trap in the test, and to escape the activation energy of different forms of assessment of hydrogen atoms in steel. The ability to escape work on the study of hydrogen diffusion hydrogen in different types of bolts in steel and ease of use of beneficial hydrogen traps to reduce the significance of hydrogen induced delayed fracture susceptibility, but also for different types of bolt steel selection Provide reference material. Using slow strain rate tensile test, this paper studied the hydrogen effect of stress and strain characteristics of notched specimens and smooth specimens. The study can well evaluate the different types of bolt steel, hydrogen loading, and the corresponding relationship between the hydrogen content and the notch strength and plasticity index it can provide the reference for the bolt strength in engineering application and safety evaluation. At the same time, show that the fracture morphology of tensile specimens, hydrogen induced fracture morphology with increasing hydrogen content in steel, the dimple fracture and intergranular fracture characteristics of quasi cleavage transgranular to transition gradually, so as to provide recovery simulation function failure analysis for the actual bolt condition. By means of finite element simulation and analysis of the root zone of notched specimen stress distribution has been presented directly. Through the notch radius and different materials in the design model. The number of the different notch radii, notch stress intensity under the condition of different concentration coefficient. The analysis of stress induced by the hydrogen diffusion simulation provides predefined field. By using the finite element program of stress induced hydrogen diffusion coupling, the hydrogen distribution and enrichment trend in stress induced by Notch hydrogen the concentration, to provide reference for the engineering application of bolt fracture morphology of hydrogen induced fracture analysis, but also provide a reference for the safety evaluation of bolt. According to the theoretical calculation and finite element simulation using phase method, discusses the control technology of induced delayed fracture of high strength bolts hydrogen. Notch micro plastic deformation zone to alleviate the stress concentration plays an important role, and the hydrogen atoms are introduced, which has complex effect on plastic deformation. The hydrogen content, the notch radius and bolt steel hydrogen induced fracture of the three local critical strain The relationship between induced delayed fracture prevention and control become the key of high strength bolts for hydrogen, reasonable selection of high strength bolts, provide theoretical reference for structure design of high strength bolt. In practical application, usually based on the use of the environment to select suitable plating layer to increase the service life of parts. In this paper, the electrochemical method of several bolts coating the analysis of electrochemical reaction in corrosion resistance and corrosion evaluation stage, discusses the different resistance mechanism. Through the systematic comparison and analysis, find out the marine engineering application, suitable for high strength bolts of low hydrogen embrittlement, protective coating brittle and low. The corrosion resistance of Zn-Ni coating and Cd-Ti quite, but from the environmental and economic considerations, in marine atmospheric environment, is expected to replace the Zn-Ni coating Cd-Ti coating; and in the sea, can be considered to be Ni-W-P instead of Cd-Ti cathode coating coating as Protective measures for hydrogen resistance and low embrittlement of high strength bolts.

【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】：TG142.1

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