新型22Cr-15Ni奥氏体耐热钢高温低周疲劳行为

Study on high temperature low cycle fatigue behavior of a novel austenitic heat-resistant steel

22Cr15Ni3.5CuNbN新型奥氏体耐热钢是为620~650℃的超(超)临界电站锅炉管道制造而研发的新型奥氏体耐热钢,其高温性能的优劣对机组的安全可靠运行具有重要意义.文中通过22Cr15Ni3.5CuNbN钢在650℃下的低周疲劳试验,研究了其在不同应变幅条件下的应力-应变关系及疲劳寿命.通过对断口形貌的分析研究了其断裂机理.结果表明,22Cr15Ni3.5CuNbN钢在高温下表现出明显的循环硬化行为,且没有明显的应力饱和现象出现.其硬化行为与材料内部位错密度的增加有关.采用基于塑性应变能密度对其疲劳寿命进行了预测,取得了良好的预测效果.疲劳断口可以分为3个区域:裂纹源区、裂纹扩展区以及瞬断区.在较高的应变幅条件下,在断口处可观察到多个裂纹源.多个裂纹源的形成和二次裂纹的产生是导致其疲劳寿命下降的重要原因.

22Cr15Ni3.5 CuNbN austenitic heatresistant steel is a new type of austenitic heat-resistant steel developed for the manufacture of super(super)critical power station boiler pipes at 620-650℃.The high temperature performance of the material is of great significance to the safe and reliable operation of the unit.In this paper,the stress-strain relationship and fatigue life of 22 Cr15 Ni3.5 CuNbN steel under different strain amplitudes were studied by low-cycle fatigue tests at 650℃.The fracture morphology is analyzed to study the fracture mechanism.The results show that 22 Cr15 Ni3.5 CuNbN steel exhibits obvious cyclic hardening behavior at high temperature without obvious stress saturation phenomenon.The cyclic hardening behavior is related to the increase of dislocation density.The fatigue life was predicted based on the plastic strain energy density,and a good prediction effect was obtained.The fatigue fracture can be divided into three regions:crack source region,crack propagation region,and transient rupture region.Multiple crack sources can be observed at the fracture under high strain amplitudes.The formation of multiple crack sources and secondary cracks are important reasons for the decline in fatigue life.