国产核电主管道用316LN钢的低周疲劳性能评估

Evaluation of Low Cycle Fatigue Properties of 316LN Steel for Domestic Nuclear Power Primary Pipe

对CAP1400核电机组国产主管道用316LN钢开展室温(25℃)、服役温度(350℃)、500℃和600℃下的低周疲劳试验,得到该钢的循环应力响应特性和迟滞回线,基于RambergOsgood模型和Manson-Coffin模型拟合稳定循环应力幅-应变幅曲线和应变幅-失效反向数曲线,采用ASME锅炉及压力容器规范最佳拟合疲劳曲线和设计疲劳曲线对该钢的低周疲劳性能进行评估。结果表明:316LN钢的循环应力响应过程包含循环硬化、循环软化、稳定循环和最终失效4个阶段;500,600℃下316LN钢发生显著的动态应变时效,350℃下动态应变时效特征不明显,室温下不存在动态应变时效现象;Ramberg-Osgood模型和Manson-Coffin模型可以较好地描述316LN钢的稳定循环应力幅-应变幅和应变幅-失效反向数关系;在室温和350℃条件下316LN钢的疲劳试验数据均高于修订后的最佳拟合疲劳曲线,应变调整系数取2或疲劳寿命调整系数取12的试验数据均高于设计疲劳曲线,低周疲劳性能满足ASME规范要求。

Low cycle fatigue tests were carried out on 316LN steel for the main pipeline of CAP1400 nuclear power unit at room temperature(25℃),service temperature(350℃),500℃and 600℃,and the cyclic stress response characteristics and hysteresis loops of the steel were obtained.The stable cyclic stress amplitude-strain amplitude curve and strain amplitude-failure reverse number curve were fitted by Ramberg-Osgood model and Manson-Coffin model.The low-cycle fatigue properties of the steel were evaluated by the ASME boilers and pressure vessels code best fitting fatigue curve and design fatigue curve.The results show that the cyclic stress response of 316LN steel consisted of four stages of cyclic hardening,cyclic softening,cyclic stabilization and final failure.The dynamic strain aging phenomenon of 316LN steel was obvious at 500,600℃,but was not obvious at 350℃,and no dynamic strain aging occurred at room temperature.Ramberg-Osgood model and Manson-Coffin model could well describe the stable cyclic stress amplitude-strain amplitude and strain amplitude-failure reverse number relationships of 316LN steel,respectively.The fatigue test data of 316LN steel at room temperature and 350℃were higher than the revised best fitting fatigue curve,and the test data with strain adjustment coefficient of 2 or fatigue life adjustment coefficient of 12 were higher than the design fatigue curve,indicating that the low cyclic fatigue properties of the steel met ASME code requirements.