大锻件12%Cr超超临界转子钢铸态热变形行为的研究

发布时间：2018-01-13 22:12

本文关键词：大锻件12%Cr超超临界转子钢铸态热变形行为的研究　出处：《上海交通大学》2015年硕士论文　论文类型：学位论文

【摘要】：为了提高火力发电的效率,减少二氧化碳排放以及履行保护环境和节约能源的义务,许多发达国家都大力发展具有高容量和高效率的超临界、超超临界发电机设备。近年来,由于优良的综合性能,12%Cr马氏体不锈钢被广泛用于超超临界的发电机组上。然而,由于该钢种合金含量高,工艺过程复杂,工艺参数变量多,使材料的热加工性大大降低,通常会产生晶粒粗化、混晶(晶粒尺寸相差3个晶粒等级以上)甚至开裂等问题,严重地影响发电设备相关部件的可靠性和服役寿命。本文采用真空感应熔炼方法,设计不同的预热温度、过热温度和浇注温度等铸造参数,在获得具有代表性铸态微观组织试样的基础上,利用Gleeble单向压缩实验,研究了变形温度和应变速率对12%Cr钢热变形行为的影响。通过光学显微镜(OM)、扫描电镜(SEM)、和电子衍射(EBSD)等微观组织分析,结合动态材料模型(DMM)建立了12%Cr钢热加工图和动态再结晶(DRX)晶粒模型,详细地研究了铸态组织及工艺条件对12%Cr钢热变形行为和微观组织变化规律的影响,得到以下主要结论:(1)根据流变应力、形变温度和形变速率的相关性,计算得出铸态12%Cr钢热变形激活能为477.73k J/mol,利用线性回归方法构建了热变形本构数学方程;(2)建立了DRX晶粒模型,揭示DRX晶粒尺寸与变形条件(形变温度、速率)之间的关系。热变形后的晶粒尺寸和DRX的体积分数伴随着形变温度的升高和形变速率的降低而呈增大的趋势;(3)借助动态材料模型,绘制了热加工图。铸态12%Cr马氏体不锈钢的安全加工参数为:温度1050~1200°C,形变速率0.001~1s-1。在高应变速率区域时(10s-1),材料易出现流变失稳,微观组织表现为局部变形带、“项链组织”和相界处的微孔。由此说明在该区域内的变形为不均匀塑性变形,在热变形阶段应予以避免;(4)12%Cr钢的铸态组织晶粒形态和尺寸以及第二相(高温铁素体)含量与形态对热变形微观组织演变有重要影响。铸态晶粒尺寸越小,DRX体积分数越大,变形后组织也越细小;第二相的含量越多,再结晶潜在形核位置点越多,越利于动态再结晶,得到的微观组织越细小均匀。
[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 掳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.
【学位授予单位】：上海交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG142.71

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