CrMoV-9%Cr轉子鋼窄間隙埋弧焊焊接接頭的蠕變行為研究
發(fā)布時間：2019-01-17 07:45
【摘要】：高溫下焊接接頭的蠕變損傷與失效是汽輪機高中壓焊接轉子研制需要重點考慮的瓶頸之一。本文以汽輪機中壓焊接轉子為對象,研究了焊接接頭各部位的微觀組織及力學性能變化規(guī)律,采用小試樣進行了接頭局部微區(qū)的高溫蠕變性能試驗,重點研究了多道焊縫金屬的不均勻蠕變行為及損傷機制,系統(tǒng)探討了冶金不均勻對焊接接頭微細觀損傷的影響。主要研究工作和結論如下:(1)窄間隙多道焊CrMoV-9%Cr接頭的微觀組織對機械性能的影響。采用金相、SEM以及顯微拉伸試驗,研究了多道焊接頭局部微區(qū)的組織與力學性能分布規(guī)律,結果顯示:盡管CrMoV側的細晶區(qū)(CrMoV-FGHAZ)組織強度最弱,但在常溫及高溫下跨接頭拉伸試樣均斷裂于CrMoV母材(CrMoV-BM)中,主要源于多道焊局部搭接區(qū)削弱效應。(2)焊接接頭微區(qū)的原位蠕變試驗研究。采用數(shù)字散斑與原位加載裝置相結合的方案,分別進行了焊縫、熱影響區(qū)等部位微試樣的蠕變試驗,得到了局部蠕變性能數(shù)據(jù)。結果發(fā)現(xiàn):焊縫環(huán)向(WM-C)的蠕變強度最大,CrMoV熱影響區(qū)(CrMoV-HAZ)的蠕變強度最小,碳化物粗化和組織回復是導致其蠕變性能削弱的原因。相比于焊縫環(huán)向(WM-C)和焊縫徑向(WM-R),CrMoV-HAZ沒有明顯的蠕變第一、二階段,大部分壽命消耗在蠕變第三階段。(3)焊縫微區(qū)不均勻對蠕變性能的影響。研究表明多道焊縫金屬由柱狀晶區(qū)(CGZ)、等軸晶區(qū)(EGZ)、重結晶區(qū)(RGZ)和粗晶區(qū)(CGHAZ)組成,各局部微區(qū)的顯微硬度和拉伸性能差別不大,但蠕變性能有明顯差異,多道焊縫金屬具有不均勻的蠕變行為,尤其表現(xiàn)為蠕變第三階段的損傷各向異性。(4)多道焊微區(qū)蠕變損傷各向異性的微觀表征。微觀分析了原位蠕變斷裂試樣的微觀組織演化,比較了斷口形貌、蠕變孔洞分布、析出物及位錯亞結構的差異,探討不均勻組織對蠕變孔洞萌生、生長的影響。結果發(fā)現(xiàn),改變取樣方向導致垂直受力方向晶界排布不同,改變取樣位置導致微區(qū)材料的蠕變抗力不同,二者的耦合作用是不均勻蠕變損傷的主要原因。(5)多道焊接頭損傷各向異性耦合的有限元分析。損傷有限元分析了多道焊縫的焊道排布形式、焊接熱輸入、焊接速度等對接頭蠕變壽命的影響。結果表明:高應力水平下焊縫不均勻組織對蠕變損傷影響不大,低應力下不均勻組織對蠕變損傷的作用明顯;多個焊道的交錯排布可以提升接頭的蠕變壽命;降低焊接速度、選用較高的焊接熱輸入可以改善接頭蠕變性能。
[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.
【學位授予單位】：華東理工大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：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.
【學位授予單位】：華東理工大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TK263.61
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