改良型CrMoV钢焊缝金属各向异性蠕变行为研究

发布时间：2018-06-13 04:17

本文选题：焊缝金属 + 蠕变　；参考：《华东理工大学》2015年硕士论文

【摘要】：蠕变破坏是高温高压工作条件下焊接部件的主要安全隐患。高温服役的汽轮机转子是汽轮机的关键部件,其结构大型,锻造困难,常使用窄间隙焊接方法将多个锻件连在一起。受焊接过程中焊接冷热循环的影响,焊接接头的微观组织极不均匀,高温下表现出明显的各向异性蠕变特性,它像一个寿命削弱系数影响接头的结构完整性。但究其机理、影响和研究手段,国内外的系统研究还十分有限。本文以CrMoV钢焊接接头焊缝金属为研究对象,采用试验研究和数值模拟方法相结合的方法,系统研究了焊缝金属各向异性蠕变机理及其对接头蠕变损伤的影响。主要研究内容和结论如下：(1)对接头焊缝金属进行金相观察、透射电镜试验和硬度试验。金相试验结果显示,焊缝金属由柱状晶区、粗晶区、等轴晶区及焊缝中心等轴晶区组成；柱状晶和粗晶形状相似,柱状晶晶界模糊,而粗晶轮廓清晰,等轴晶颗粒清晰,而焊缝中心等轴晶并无明显晶界。透射电镜试验表明,焊缝内部的微观组织主要是条状和粒状贝氏体,且粗晶区、等轴晶区、柱状晶区及焊缝中心等轴晶区内的亚晶尺寸逐渐变小。显微维氏硬度测试结果表明,焊缝中心是焊缝最薄弱部位。(2)对焊缝金属环向、径向和轴向微平板试样进行拉伸试验。结果表明,环向、径向和轴向试样的抗拉强度依次降低。径向试样易在柱状晶区断裂,轴向试样易在焊缝中心等轴晶区断裂。(3)对焊缝金属焊道上的环向和径向、焊缝中心径向微圆棒试样进行蠕变试验。发现焊道上的环向、径向试样和焊缝中心径向试样的蠕变寿命及稳态蠕变速率依次降低,焊接接头具有明显的各向异性蠕变行为。结合蠕变断裂试样的断口分析、微观组织观察及有限元分析表明,粗晶区、等轴晶区、柱状晶区和焊缝中心等轴晶区的蠕变性能依次降低,焊接接头各向异性蠕变行为受柱状晶区、粗晶区、等轴晶区及焊缝中心等轴晶区应力重分布的影响。(4)基于改装后的材料蠕变行为原位测试系统,采用微平板试样,对焊缝金属焊道上的环向和径向试样进行蠕变试验。结果表明,微平板试样也可以表征焊缝金属的各向异性蠕变行为,它与微圆棒蠕变试样所测规律一致。
[Abstract]:Creep failure is the main safety hazard of welding parts under high temperature and high pressure. Steam turbine rotor in service at high temperature is a key component of steam turbine. Its structure is large and forging is difficult. Narrow gap welding is often used to connect multiple forgings together. The microstructure of the welded joints is extremely uneven due to the cold and thermal cycles during welding. The creep behavior of the welded joints shows obvious anisotropic creep characteristics at high temperature, and it affects the structural integrity of the joints like a weakening coefficient of life. But its mechanism, influence and research means, domestic and foreign systematic research is still very limited. Taking the weld metal of CrMoV steel welded joint as the research object, the anisotropic creep mechanism of weld metal and its effect on the creep damage of the joint are systematically studied by means of the combination of experimental study and numerical simulation. The main contents and conclusions are as follows: (1) metallographic observation, transmission electron microscope test and hardness test. The results of metallographic test show that the weld metal is composed of columnar, coarse, equiaxed, equiaxed and equiaxed regions, the shape of columnar and coarse grains is similar, the boundary of columnar grains is blurred, and the outline of coarse grains is clear, and the equiaxed grains are clear. The equiaxed grain in the center of the weld has no obvious grain boundary. Transmission electron microscopy (TEM) tests show that the microstructure of the weld is mainly stripe and granular bainite, and the subcrystal size of the coarse grain, equiaxed, columnar and equiaxed zone of the weld becomes smaller. The micro-Vickers hardness test results show that the center of the weld is the weakest part of the weld, and the tensile tests are carried out on the circumferential, radial and axial micro-plate specimens of the weld metal. The results show that the tensile strength of annular, radial and axial specimens decreases in turn. The radial specimen is easy to fracture in the columnar crystal region, and the axial specimen is easy to fracture in the equiaxed zone of the weld seam. It is found that the creep life and steady state creep rate of the radial specimen and the radial specimen on the welding pipe decrease in turn and the creep behavior of the welded joint is obvious anisotropic. In combination with fracture analysis, microstructure observation and finite element analysis of creep fracture specimens, the creep properties of coarse grained region, equiaxed zone, columnar zone and equiaxed zone of weld are decreased in turn. Anisotropic creep behavior of welded joints is affected by stress redistribution in columnar, coarse, equiaxed and equiaxed regions and in the center of welds. Based on the modified in-situ testing system for creep behavior of materials, microplate specimens are used. Creep tests were carried out on the circumferential and radial specimens of weld metal pipe. The results show that the anisotropic creep behavior of weld metal can also be characterized by the microplate specimen, which is consistent with the rule measured by the micro-circular rod creep specimen.
【学位授予单位】：华东理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG407

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