本文選題：焊縫金屬 + 蠕變�。� 參考：《華東理工大學(xué)》2015年碩士論文

【摘要】：蠕變破壞是高溫高壓工作條件下焊接部件的主要安全隱患。高溫服役的汽輪機轉(zhuǎn)子是汽輪機的關(guān)鍵部件,其結(jié)構(gòu)大型,鍛造困難,常使用窄間隙焊接方法將多個鍛件連在一起。受焊接過程中焊接冷熱循環(huán)的影響,焊接接頭的微觀組織極不均勻,高溫下表現(xiàn)出明顯的各向異性蠕變特性,它像一個壽命削弱系數(shù)影響接頭的結(jié)構(gòu)完整性。但究其機理、影響和研究手段,國內(nèi)外的系統(tǒng)研究還十分有限。本文以CrMoV鋼焊接接頭焊縫金屬為研究對象,采用試驗研究和數(shù)值模擬方法相結(jié)合的方法,系統(tǒng)研究了焊縫金屬各向異性蠕變機理及其對接頭蠕變損傷的影響。主要研究內(nèi)容和結(jié)論如下：(1)對接頭焊縫金屬進(jìn)行金相觀察、透射電鏡試驗和硬度試驗。金相試驗結(jié)果顯示,焊縫金屬由柱狀晶區(qū)、粗晶區(qū)、等軸晶區(qū)及焊縫中心等軸晶區(qū)組成；柱狀晶和粗晶形狀相似,柱狀晶晶界模糊,而粗晶輪廓清晰,等軸晶顆粒清晰,而焊縫中心等軸晶并無明顯晶界。透射電鏡試驗表明,焊縫內(nèi)部的微觀組織主要是條狀和粒狀貝氏體,且粗晶區(qū)、等軸晶區(qū)、柱狀晶區(qū)及焊縫中心等軸晶區(qū)內(nèi)的亞晶尺寸逐漸變小。顯微維氏硬度測試結(jié)果表明,焊縫中心是焊縫最薄弱部位。(2)對焊縫金屬環(huán)向、徑向和軸向微平板試樣進(jìn)行拉伸試驗。結(jié)果表明,環(huán)向、徑向和軸向試樣的抗拉強度依次降低。徑向試樣易在柱狀晶區(qū)斷裂,軸向試樣易在焊縫中心等軸晶區(qū)斷裂。(3)對焊縫金屬焊道上的環(huán)向和徑向、焊縫中心徑向微圓棒試樣進(jìn)行蠕變試驗。發(fā)現(xiàn)焊道上的環(huán)向、徑向試樣和焊縫中心徑向試樣的蠕變壽命及穩(wěn)態(tài)蠕變速率依次降低,焊接接頭具有明顯的各向異性蠕變行為。結(jié)合蠕變斷裂試樣的斷口分析、微觀組織觀察及有限元分析表明,粗晶區(qū)、等軸晶區(qū)、柱狀晶區(qū)和焊縫中心等軸晶區(qū)的蠕變性能依次降低,焊接接頭各向異性蠕變行為受柱狀晶區(qū)、粗晶區(qū)、等軸晶區(qū)及焊縫中心等軸晶區(qū)應(yīng)力重分布的影響。(4)基于改裝后的材料蠕變行為原位測試系統(tǒng),采用微平板試樣,對焊縫金屬焊道上的環(huán)向和徑向試樣進(jìn)行蠕變試驗。結(jié)果表明,微平板試樣也可以表征焊縫金屬的各向異性蠕變行為,它與微圓棒蠕變試樣所測規(guī)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.
【學(xué)位授予單位】：華東理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TG407

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本文編號：2012683