热老化作用下Z2CND18.12N管材棘轮效应及棘轮疲劳性能研究

发布时间：2018-12-12 05:23

【摘要】：核电站管道材料在使用和加工制造过程中会处于高温环境,此高温环境会导致材料发生热老化效应,使奥氏体在晶界处产生析出物,即“敏化”。这种热老化效应对材料的力学性能有明显影响。核电站压水堆一回路辅助管道在运行期间,会承受内压、振动等复杂载荷工况,导致材料发生棘轮效应,缩减材料或结构的疲劳寿命,影响管道的安全可靠性。为了保障核电站压力管道的安全运行,本文针对压水堆一回路辅助管道用材Z2CND18.12N奥氏体不锈钢,从材料热老化效应、棘轮效应、棘轮疲劳寿命、微观机理以及本构模型等方面进行了系统的研究。本研究对核电站压力管道的设计及运行具有重要的指导意义。利用电液伺服疲劳实验机对Z2CND18.12N奥氏体不锈钢管材进行了单轴拉伸试验及单轴棘轮试验,得到材料在室温条件下基本的力学性能。在单轴棘轮试验中,棘轮应变随加载率的增加而降低,随平均应力的增加而增加,随应力幅值的增加而增加。加载历史与应力比对棘轮应变也有明显的影响。对Z2CND18.12N奥氏体不锈钢进行高温老化,分别在500℃和700℃下将管材老化1小时、10小时、50小时、100小时和500小时。利用疲劳实验机对老化后的管材进行了室温下的单轴拉伸试验及单轴棘轮试验。在单轴拉伸试验中,老化后的材料与原始材料相比,杨氏模量与屈服应力有小幅度的降低。拉伸强度与延伸率没有明显变化。在单轴棘轮试验中,承受同一载荷条件下,棘轮应变随老化温度的升高而增加,随老化时间的增长而增加。棘轮疲劳寿命随老化温度的升高而减少,随老化时间的增长而减少。提出了老化损伤的概念,并对老化材料的棘轮疲劳寿命进行预测,取得了较好的预测结果。对老化后的试样进行了SEM与EDS微观观测与分析。通过SEM的观测结果得出材料热老化过程的析出行为随老化温度、老化时间的规律。利用EDS对析出物进行了成分分析,确定了析出物的类型随老化条件的改变而改变,包括M_(23)C_6,η,x等。利用OW II模型结合各向同性强化准则,对原始材料的棘轮行为进行预测,并将OW II模型中的强化律指数m修正为与老化时间相关的指数形式,并对老化后材料的棘轮应变进行预测,得到了较好的预测结果。
[Abstract]:Nuclear power plant pipeline materials will be in a high temperature environment in the process of using and processing. This high temperature environment will lead to the thermal aging effect of the materials, which makes austenite produce precipitates at grain boundaries, that is, "sensitization". This effect of thermal aging has a significant effect on the mechanical properties of the material. The auxiliary pipeline of primary circuit of PWR in nuclear power station will bear complex load conditions such as internal pressure and vibration during operation, which will lead to ratchet effect of material, reduce the fatigue life of material or structure, and affect the safety and reliability of pipeline. In order to ensure the safe operation of nuclear power plant pressure pipeline, the Z2CND18.12N austenitic stainless steel, which is used in the primary circuit auxiliary pipeline of PWR, is studied in this paper from the effect of material thermal aging and ratchet fatigue life. The microscopic mechanism and constitutive model are systematically studied. This study has important guiding significance for the design and operation of nuclear power plant pressure pipeline. Uniaxial tensile tests and uniaxial ratchet tests were carried out on Z2CND18.12N austenitic stainless steel pipes by electro-hydraulic servo fatigue test machine. The basic mechanical properties of the materials were obtained at room temperature. In uniaxial ratchet test, ratchet strain decreases with the increase of loading rate, increases with the increase of average stress and increases with the increase of stress amplitude. The loading history and stress ratio also have obvious influence on ratchet strain. The Z2CND18.12N austenitic stainless steel was aged at 500 鈩，

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