窄间隙埋弧焊焊接残余应力及其热处理消除的模拟和优化研究

发布时间：2018-06-16 04:48

本文选题：窄间隙埋弧焊 + 焊接残余应力　；参考：《华东理工大学》2017年硕士论文

【摘要】：转子作为核电汽轮机组核心部件之一,其可靠性和稳定性直接决定着汽轮机组的安全性和使用寿命。目前,焊接转子已经成为核电低压汽轮机转子的发展趋势,分析汽轮机焊接转子焊接瞬时应力的演化和焊接残余应力分布状态对转子设计具有重要的意义。现阶段通过实验测量与有限元相结合的研究方法是探讨窄间隙埋弧焊厚壁焊件焊接瞬时应力的演化和焊接残余应力分布状态的重要手段,但对壁厚大于150mm窄间隙埋弧焊厚壁焊件的焊接残余应力分析的文献比较少。另一方面,焊后热处理通常作为降低或消除厚壁焊件焊接残余应力的重要手段,而工程中焊后热处理参数的设定大多依靠施工经验,缺少一定的理论依据。基于此,本文以焊接转子模拟件为研究对象,采用ABAQUS有限元分析软件,编写FILM、DFLUX和UEXPAN子程序完成焊接转子模拟件的焊接分析;开展热处理过程中转子焊接残余应力释放行为的数值研究,并讨论了焊后热处理主要参数对热处理过程中应力释放行为的影响。主要完成内容及相关结论如下:(1)基于热-力顺序耦合方法,研究了焊接转子模拟件焊接瞬时应力的演化和焊接残余应力分布状态。研究结果表明:固态相变对焊缝及其附近高应力区焊接残余应力分布状态具有明显的影响,不仅影响该区域焊接残余应力数值的大小,甚至影响着焊接残余应力的分布方向;在平行于焊缝外表面路径上,焊缝及其附近区域焊接残余应力较大,而远离该区域残余应力逐渐减小到忽略不计;在焊缝中心线路径上,焊接残余应力整体分布均匀,且应力值较大,;无论是平行于外表面的路径还是焊缝中心线,在焊接过程中,其路径上的焊接应力在后续焊道添加到一定厚度后都基本不再变化。(2)基于瞬态热分析法,引入Norton-Bai1ey蠕变本构方程,探讨和研究了焊后热处理过程中应力释放机制和演化过程。研究结果表明:焊后热处理过程中,应力释放的主要机制是高温条件下材料发生的蠕变,而非高温导致的材料软化;焊接残余应力的释放主要发生在升温阶段,保温阶段应力释放量较小,而降温阶段应力有所升高;在焊缝中心线路径上,当材料温度由外及内逐渐高于蠕变温度时,焊接残余应力表现出明显的由外及内的迅速消除过程。(3)基于控制变量法,探讨了焊后热处理参数对热处理过程中焊接残余应力释放效果的影响。研究结果表明.:焊后热处理温度是决定残余应力释放量的关键因素,热处理过程中焊件中心达到热处理温度是保证热处理效果的重要环节;焊后热处理保温时间对应力释放量的影响不大,在仅考虑应力释放的情况下,可以适当地缩短保温时间;通过研究不同壁厚焊件在不同升温速率下的温度曲线,为最大升温速率和最短保温时间的选择提供了一定的理论参考。
[Abstract]:As one of the core components of nuclear turbine unit, the reliability and stability of rotor directly determine the safety and service life of steam turbine unit. At present, welding rotor has become the development trend of nuclear power low-pressure steam turbine rotor. It is very important to analyze the evolution of welding transient stress and the distribution of welding residual stress in steam turbine welding rotor. At present, the research method of combining experimental measurement with finite element method is an important means to discuss the evolution of instantaneous stress and the distribution of residual stress of thick wall welded parts in narrow gap submerged arc welding (SAW). However, there are few literatures on the residual stress analysis of thick wall welding parts with wall thickness greater than 150mm narrow gap submerged arc welding. On the other hand, post-welding heat treatment is usually used as an important means to reduce or eliminate the residual stress of thick wall welds, and the parameters of post-welding heat treatment in engineering are mostly based on construction experience and lack of certain theoretical basis. Based on this, this paper takes the welding rotor simulation as the research object, uses Abaqus finite element analysis software, compiles the FILMMU DFLUX and the UEXPAN subprogram to complete the welding analysis of the welding rotor simulation. Numerical study on residual stress release behavior of rotor during heat treatment was carried out, and the influence of main parameters of post welding heat treatment on stress release behavior during heat treatment was discussed. The main contents and related conclusions are as follows: (1) based on the thermo-mechanical sequential coupling method, the transient stress evolution and residual stress distribution of welded rotor simulators are studied. The results show that the solid phase transformation has an obvious influence on the welding residual stress distribution in the weld and its surrounding high stress zone, which not only affects the magnitude of the welding residual stress value, but also affects the distribution direction of the welding residual stress. On the path parallel to the outer surface of the weld, the welding residual stress in the weld and its adjacent area is larger, but the residual stress in the weld far away from this area is gradually reduced to neglect, and the welding residual stress distributes uniformly on the path of the weld centerline. And the stress value is large, whether the path parallel to the outer surface or the weld centerline, in the welding process, the welding stress on the path is basically no longer changed after the subsequent welding pipe is added to a certain thickness) based on transient thermal analysis, Norton-Bai1ey creep constitutive equation was introduced to study the stress release mechanism and evolution process during post-welding heat treatment. The results show that the main mechanism of stress release during post-welding heat treatment is the creep of the material at high temperature, not the softening of the material caused by high temperature, and the release of residual stress of welding occurs mainly at the stage of heating up. The stress release in the heat preservation stage is small, but the stress in the cooling phase is increased, and in the path of the center line of the weld, when the material temperature is gradually higher than the creep temperature from the outside and inside, Based on the control variable method, the influence of welding parameters on the release effect of welding residual stress during heat treatment was discussed. The results show that: the temperature of post-welding heat treatment is the key factor to determine the amount of residual stress release, and it is an important link to ensure the heat treatment effect that the center of the welding piece reaches the heat treatment temperature during the process of heat treatment. The heat preservation time of post-welding heat treatment has little effect on the stress release amount, and the heat preservation time can be shortened properly by considering only the stress release. The temperature curves of different wall thickness welds at different heating rates are studied. It provides a theoretical reference for the selection of the maximum heating rate and the shortest heat preservation time.
【学位授予单位】：华东理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG404;TG441.8

【参考文献】