本文關鍵詞：大鍛件12%Cr超超臨界轉子鋼鑄態(tài)熱變形行為的研究　出處：《上海交通大學》2015年碩士論文　論文類型：學位論文

  更多相關文章： 超超臨界轉子鋼 熱變形行為 微觀組織 熱加工圖

【摘要】：為了提高火力發(fā)電的效率,減少二氧化碳排放以及履行保護環(huán)境和節(jié)約能源的義務,許多發(fā)達國家都大力發(fā)展具有高容量和高效率的超臨界、超超臨界發(fā)電機設備。近年來,由于優(yōu)良的綜合性能,12%Cr馬氏體不銹鋼被廣泛用于超超臨界的發(fā)電機組上。然而,由于該鋼種合金含量高,工藝過程復雜,工藝參數(shù)變量多,使材料的熱加工性大大降低,通常會產(chǎn)生晶粒粗化、混晶(晶粒尺寸相差3個晶粒等級以上)甚至開裂等問題,嚴重地影響發(fā)電設備相關部件的可靠性和服役壽命。本文采用真空感應熔煉方法,設計不同的預熱溫度、過熱溫度和澆注溫度等鑄造參數(shù),在獲得具有代表性鑄態(tài)微觀組織試樣的基礎上,利用Gleeble單向壓縮實驗,研究了變形溫度和應變速率對12%Cr鋼熱變形行為的影響。通過光學顯微鏡(OM)、掃描電鏡(SEM)、和電子衍射(EBSD)等微觀組織分析,結合動態(tài)材料模型(DMM)建立了12%Cr鋼熱加工圖和動態(tài)再結晶(DRX)晶粒模型,詳細地研究了鑄態(tài)組織及工藝條件對12%Cr鋼熱變形行為和微觀組織變化規(guī)律的影響,得到以下主要結論:(1)根據(jù)流變應力、形變溫度和形變速率的相關性,計算得出鑄態(tài)12%Cr鋼熱變形激活能為477.73k J/mol,利用線性回歸方法構建了熱變形本構數(shù)學方程;(2)建立了DRX晶粒模型,揭示DRX晶粒尺寸與變形條件(形變溫度、速率)之間的關系。熱變形后的晶粒尺寸和DRX的體積分數(shù)伴隨著形變溫度的升高和形變速率的降低而呈增大的趨勢;(3)借助動態(tài)材料模型,繪制了熱加工圖。鑄態(tài)12%Cr馬氏體不銹鋼的安全加工參數(shù)為:溫度1050~1200°C,形變速率0.001~1s-1。在高應變速率區(qū)域時(10s-1),材料易出現(xiàn)流變失穩(wěn),微觀組織表現(xiàn)為局部變形帶、“項鏈組織”和相界處的微孔。由此說明在該區(qū)域內的變形為不均勻塑性變形,在熱變形階段應予以避免;(4)12%Cr鋼的鑄態(tài)組織晶粒形態(tài)和尺寸以及第二相(高溫鐵素體)含量與形態(tài)對熱變形微觀組織演變有重要影響。鑄態(tài)晶粒尺寸越小,DRX體積分數(shù)越大,變形后組織也越細小;第二相的含量越多,再結晶潛在形核位置點越多,越利于動態(tài)再結晶,得到的微觀組織越細小均勻。
[Abstract]:In order to improve the efficiency of thermal power generation, reduce carbon dioxide emissions and fulfill the obligations to protect the environment and save energy, many developed countries have vigorously developed a high-capacity and high-efficiency supercritical. Ultra-supercritical generator equipment. In recent years, due to its excellent comprehensive properties, 12Cr martensitic stainless steel has been widely used in ultra-supercritical generator sets. However, because of the high alloy content of the steel. The process is complex and the process parameters are many. The hot working property of the material is greatly reduced. The problems such as coarsening of grains, mixed grains (grain size difference of more than 3 grain grades) and even cracking are usually produced. The reliability and service life of related components of power generation equipment are seriously affected. In this paper, different casting parameters such as preheating temperature, superheating temperature and pouring temperature are designed by using vacuum induction melting method. On the basis of obtaining the typical as-cast microstructural specimens, unidirectional compression experiments were carried out by Gleeble. The effect of deformation temperature and strain rate on the hot deformation behavior of 12Cr steel was studied. The microstructure of 12Cr steel was analyzed by optical microscope, scanning electron microscope (SEM) and electron diffraction (EBSD). Based on the dynamic material model (DMMM), the hot working diagram of 12Cr steel and the grain model of dynamic recrystallization (DRX) were established. The effects of as-cast structure and technological conditions on the hot deformation behavior and microstructure of 12Cr steel were studied in detail. The following main conclusions were obtained: 1) according to the flow stress. According to the correlation between deformation temperature and deformation rate, the activation energy of hot deformation of as-cast 12Cr steel is 477.73kJ / mol, and the constitutive equation of thermal deformation is established by linear regression method. (2) the DRX grain model was established to reveal the grain size and deformation conditions (deformation temperature) of DRX. The grain size and the volume fraction of DRX increase with the increase of deformation temperature and the decrease of deformation rate. (3) with the help of the dynamic material model, the hot working diagram was drawn. The safety processing parameters of the as-cast 12Cr martensitic stainless steel are as follows: the temperature is 1050,1200 擄C. The deformation rate is 0.001 ~ (-1) ~ (-1). In the high strain rate region, the material is prone to rheological instability, and the microstructure is characterized by a local deformation zone. The "necklaces" and the micropores at the phase boundary show that the deformation in the region is inhomogeneous plastic deformation, which should be avoided in the thermal deformation stage. The grain morphology and size of as-cast microstructure and the content and morphology of the second phase (high temperature ferrite) have an important influence on the microstructure evolution of hot deformation. The smaller the grain size is, the smaller the grain size is. The larger the volume fraction of DRX is, the smaller the microstructure is after deformation. The more the content of the second phase is, the more the potential nucleation sites of recrystallization are, the more favorable the dynamic recrystallization is, the smaller the microstructure is.
【學位授予單位】：上海交通大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TG142.71

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