CrMoV-9%Cr转子钢窄间隙埋弧焊焊接接头的蠕变行为研究
发布时间：2019-01-17 07:45
【摘要】：高温下焊接接头的蠕变损伤与失效是汽轮机高中压焊接转子研制需要重点考虑的瓶颈之一。本文以汽轮机中压焊接转子为对象,研究了焊接接头各部位的微观组织及力学性能变化规律,采用小试样进行了接头局部微区的高温蠕变性能试验,重点研究了多道焊缝金属的不均匀蠕变行为及损伤机制,系统探讨了冶金不均匀对焊接接头微细观损伤的影响。主要研究工作和结论如下:(1)窄间隙多道焊CrMoV-9%Cr接头的微观组织对机械性能的影响。采用金相、SEM以及显微拉伸试验,研究了多道焊接头局部微区的组织与力学性能分布规律,结果显示:尽管CrMoV侧的细晶区(CrMoV-FGHAZ)组织强度最弱,但在常温及高温下跨接头拉伸试样均断裂于CrMoV母材(CrMoV-BM)中,主要源于多道焊局部搭接区削弱效应。(2)焊接接头微区的原位蠕变试验研究。采用数字散斑与原位加载装置相结合的方案,分别进行了焊缝、热影响区等部位微试样的蠕变试验,得到了局部蠕变性能数据。结果发现:焊缝环向(WM-C)的蠕变强度最大,CrMoV热影响区(CrMoV-HAZ)的蠕变强度最小,碳化物粗化和组织回复是导致其蠕变性能削弱的原因。相比于焊缝环向(WM-C)和焊缝径向(WM-R),CrMoV-HAZ没有明显的蠕变第一、二阶段,大部分寿命消耗在蠕变第三阶段。(3)焊缝微区不均匀对蠕变性能的影响。研究表明多道焊缝金属由柱状晶区(CGZ)、等轴晶区(EGZ)、重结晶区(RGZ)和粗晶区(CGHAZ)组成,各局部微区的显微硬度和拉伸性能差别不大,但蠕变性能有明显差异,多道焊缝金属具有不均匀的蠕变行为,尤其表现为蠕变第三阶段的损伤各向异性。(4)多道焊微区蠕变损伤各向异性的微观表征。微观分析了原位蠕变断裂试样的微观组织演化,比较了断口形貌、蠕变孔洞分布、析出物及位错亚结构的差异,探讨不均匀组织对蠕变孔洞萌生、生长的影响。结果发现,改变取样方向导致垂直受力方向晶界排布不同,改变取样位置导致微区材料的蠕变抗力不同,二者的耦合作用是不均匀蠕变损伤的主要原因。(5)多道焊接头损伤各向异性耦合的有限元分析。损伤有限元分析了多道焊缝的焊道排布形式、焊接热输入、焊接速度等对接头蠕变寿命的影响。结果表明:高应力水平下焊缝不均匀组织对蠕变损伤影响不大,低应力下不均匀组织对蠕变损伤的作用明显;多个焊道的交错排布可以提升接头的蠕变寿命;降低焊接速度、选用较高的焊接热输入可以改善接头蠕变性能。
[Abstract]:Creep damage and failure of welded joints at high temperature is one of the bottlenecks to be considered in the development of high pressure welded rotor of steam turbine. In this paper, the variation of microstructure and mechanical properties of welded joints in various parts of steam turbine was studied, and the creep properties of local micro-regions of joints were tested with small samples. The inhomogeneous creep behavior and damage mechanism of multi-pass weld metal were studied, and the effect of metallurgical inhomogeneity on micro-damage of welded joint was systematically discussed. The main work and conclusions are as follows: (1) the effect of microstructure on mechanical properties of narrow gap multipass welded CrMoV-9%Cr joints. The distribution of microstructure and mechanical properties in the local microzone of multi-pass welded joints was studied by metallography, SEM and microtensile tests. The results showed that the microstructure strength of the fine crystal region (CrMoV-FGHAZ) on the CrMoV side was the weakest, However, the tensile specimens of straddle joints at room temperature and high temperature all fracture in CrMoV base metal (CrMoV-BM), mainly due to the weakening effect of local lap zone in multi-pass welding. (2) the in-situ creep test of the microzone of welded joints. The creep tests of weld and heat affected zone microspecimen were carried out by the combination of digital speckle and in-situ loading device, and the local creep performance data were obtained. The results show that the creep strength of weld circumferential (WM-C) is the largest, the creep strength of CrMoV heat affected zone (CrMoV-HAZ) is the least, and the carbide coarsening and microstructure recovery are the causes of its creep property weakening. Compared with the circumferential (WM-C) and radial (WM-R) of the weld, the CrMoV-HAZ has no obvious creep in the first and second stages, and most of the life is consumed in the third stage of creep. (3) the effect of weld micro-region inhomogeneity on the creep performance. The results show that the multi-pass weld metal is composed of columnar (CGZ), equiaxed region (EGZ), recrystallization region (RGZ) and coarse crystal region (CGHAZ). The microhardness and tensile properties of each local microregion are not different, but the creep properties are obviously different. The multipass weld metal has inhomogeneous creep behavior, especially the damage anisotropy of the third stage of creep. (4) the microcosmic characterization of the creep damage anisotropy of the multi-pass welding microzone. The microstructure evolution of in-situ creep fracture specimens was analyzed, and the differences of fracture morphology, creep pore distribution, precipitate and dislocation substructure were compared, and the effect of non-uniform microstructure on creep pore initiation and growth was discussed. The results show that changing the sampling direction leads to different grain boundary arrangement in the vertical force direction, and changing the sampling position leads to different creep resistance of the microzone materials. The coupling between them is the main cause of the inhomogeneous creep damage. (5) finite element analysis of anisotropic coupling of damage in multi-pass welded joints. The damage finite element method is used to analyze the influence of welding pipe layout, welding heat input and welding speed on the creep life of multi-pass welds. The results show that the effect of non-uniform microstructure on creep damage is not significant at high stress level, but the effect of non-uniform microstructure on creep damage is obvious at low stress level, and the creep life of joints can be improved by staggered arrangement of multiple welds. The creep property of joints can be improved by reducing welding speed and selecting higher welding heat input.
【学位授予单位】：华东理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TK263.61
[Abstract]:Creep damage and failure of welded joints at high temperature is one of the bottlenecks to be considered in the development of high pressure welded rotor of steam turbine. In this paper, the variation of microstructure and mechanical properties of welded joints in various parts of steam turbine was studied, and the creep properties of local micro-regions of joints were tested with small samples. The inhomogeneous creep behavior and damage mechanism of multi-pass weld metal were studied, and the effect of metallurgical inhomogeneity on micro-damage of welded joint was systematically discussed. The main work and conclusions are as follows: (1) the effect of microstructure on mechanical properties of narrow gap multipass welded CrMoV-9%Cr joints. The distribution of microstructure and mechanical properties in the local microzone of multi-pass welded joints was studied by metallography, SEM and microtensile tests. The results showed that the microstructure strength of the fine crystal region (CrMoV-FGHAZ) on the CrMoV side was the weakest, However, the tensile specimens of straddle joints at room temperature and high temperature all fracture in CrMoV base metal (CrMoV-BM), mainly due to the weakening effect of local lap zone in multi-pass welding. (2) the in-situ creep test of the microzone of welded joints. The creep tests of weld and heat affected zone microspecimen were carried out by the combination of digital speckle and in-situ loading device, and the local creep performance data were obtained. The results show that the creep strength of weld circumferential (WM-C) is the largest, the creep strength of CrMoV heat affected zone (CrMoV-HAZ) is the least, and the carbide coarsening and microstructure recovery are the causes of its creep property weakening. Compared with the circumferential (WM-C) and radial (WM-R) of the weld, the CrMoV-HAZ has no obvious creep in the first and second stages, and most of the life is consumed in the third stage of creep. (3) the effect of weld micro-region inhomogeneity on the creep performance. The results show that the multi-pass weld metal is composed of columnar (CGZ), equiaxed region (EGZ), recrystallization region (RGZ) and coarse crystal region (CGHAZ). The microhardness and tensile properties of each local microregion are not different, but the creep properties are obviously different. The multipass weld metal has inhomogeneous creep behavior, especially the damage anisotropy of the third stage of creep. (4) the microcosmic characterization of the creep damage anisotropy of the multi-pass welding microzone. The microstructure evolution of in-situ creep fracture specimens was analyzed, and the differences of fracture morphology, creep pore distribution, precipitate and dislocation substructure were compared, and the effect of non-uniform microstructure on creep pore initiation and growth was discussed. The results show that changing the sampling direction leads to different grain boundary arrangement in the vertical force direction, and changing the sampling position leads to different creep resistance of the microzone materials. The coupling between them is the main cause of the inhomogeneous creep damage. (5) finite element analysis of anisotropic coupling of damage in multi-pass welded joints. The damage finite element method is used to analyze the influence of welding pipe layout, welding heat input and welding speed on the creep life of multi-pass welds. The results show that the effect of non-uniform microstructure on creep damage is not significant at high stress level, but the effect of non-uniform microstructure on creep damage is obvious at low stress level, and the creep life of joints can be improved by staggered arrangement of multiple welds. The creep property of joints can be improved by reducing welding speed and selecting higher welding heat input.
【学位授予单位】：华东理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TK263.61
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