超温服役T91钢的显微组织与力学性能

Microstructure and mechanical properties of T91 steel after exposure to abnormal high serving temperature

采用金相显微镜、扫描电镜、能谱分析仪、显微硬度计和万能材料试验机对长时超温服役的火力发电厂锅炉再热器用T91钢管进行了微观组织表征和力学性能测试。结果表明,长时超温服役条件下,T91钢由于亚晶粗化而导致原马氏体板条演变为块状铁素体,此外组织中还发现了蠕变空洞的存在。T91钢中M_(23)C_6析出相尺寸明显增加,呈现颗粒状形貌。超温的T91钢管向火侧显微硬度明显降低,硬度值从管壁内侧向管壁外侧逐渐减小。背火侧硬度分布较为均匀,未见明显降低。长时超温服役的T91钢由于显微组织的劣化而使得其抗拉强度明显降低。T91钢在运行过程中需严格监控服役温度,防止发生部件材料超温。

Microstructure and mechanical properties of T91 steel tube used as reheater in fossil power plant which served under abnormal high temperature for long term were characterized and tested by using optical microscopy,scanning electron microscopy,energy dispersive spectroscopy,microhardness tester and universal material testing machine. The results show that,under the serving condition of long-term and abnormal high serving temperature,the martensite lath is evolved into block ferrite due to the subgrain coarsening. Besides,creep cavities are observed in the microstructure. The size of M_（23）C_6 precipitates with granular morphology in T91 steel increases apparently.Microhardness of the side exposed to flame of the T91 tube which underwent abnormal high temperature drops obviously,and its value decreases gradually from the inside wall to the outside wall of the tube. In comparison,microhardness of the surface unexposed to the flame shows uniform distribution of hardness value without any apparent decrease. Due to the deterioration of microstructure,the tensile strength of T91 steel served under abnormal high temperature for long-term decreases obviously. The serving temperature of T91 steel should be monitored strictly during the service of the component in order to avoid the occurrence of overheating of the material.