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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。
The microstructure and mechanical properties of T91 steel tube for boiler reheater used in long-term over-temperature service were tested by metallographic microscope, scanning electron microscope, energy spectrum analyzer, microhardness tester and universal testing machine. The results show that under long-term over-temperature service conditions, the original martensite lamellae evolve into massive ferrite due to coarsening of subgrain, and the existence of creep voids is also found in the microstructure. The size of precipitated phase of M_ (23) C_6 in T91 steel obviously increases and presents granular morphology. Over-temperature T91 steel to the fire side of the micro-hardness decreased significantly, the hardness value from the inside of the pipe wall to the outside of the pipe gradually decreased. Backfire hardness distribution is more uniform, no significant decrease. Long-time over-temperature service T91 steel due to the deterioration of the microstructure so that its tensile strength was significantly reduced. T91 steel in the operation process must be strictly monitored service temperature, to prevent the occurrence of component materials over-temperature.