【摘要】 以经过83 500 h长期在线服役的P91钢蒸汽管道接头作为研究对象，分析了其显微组织演化对疲劳裂纹扩展行为的影响.结果表明：长期服役后接头组织的主要变化为碳化物长大、小角度晶界比例降低和位错密度降低，并以接头热影响区（heat affected zone, HAZ）的碳化物长大和位错密度降低最为明显；长期服役后接头在熔合区（fusion zone, FZ）显著硬化、HAZ未见硬度异常的情况下，近门槛区疲劳裂纹扩展抗力已明显降低，以HAZ的疲劳裂纹扩展抗力退化最为显著；在P91钢接头高温服役过程中，HAZ缺陷和亚结构的演化促进了C,Cr, Mo等合金元素的扩散，引起HAZ碳化物的明显长大及位错密度降低，这是导致HAZ疲劳裂纹扩展速率显著升高(尤其是疲劳裂纹扩展门槛值ΔK_th显著降低)的重要原因.更多还原

【Abstract】 Adopting the P91 steel steam pipe joint that has been in long-term online service for 83 500 hours as the research object, the influence of microstructure evolution on the fatigue crack propagation behavior was analyzed. The results show that after long-term service, the microstructure changes of the joint mainly include the growth of carbide, the decrease of small angle grain boundary ratio, and the decrease of dislocation density, especially the growth of carbide and the decrease of dislocation density of HAZ. The fatigue crack propagation resistance near the threshold zone of the welded joint in long-term service is obviously reduced under the condition that the FZ is significantly hardened and the microhardness of HAZ is not abnormal. The degradation of fatigue crack growth resistance of HAZ is the most significant after long-term service. During the high-temperature service of P91 steel joints, the defects and substructure evolution of HAZ promote the diffusion of alloying elements such as C, Cr, and Mo, causing the significant growth of HAZ carbides and the reduction of dislocation density, which is an important reason for the significant increase of fatigue crack growth rate of HAZ(especially the decrease of ΔK_th).更多还原