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通过原始T91管的高温时效试验和T91过热器爆管段的取样,分析T91钢在长期服役中的组织演变,包括亚结构、沉淀相等,研究组织退化对高温持久强度和硬度的影响。结果表明,T91钢在高温服役过程中的主要组织变化有:板条马氏体结构发生回复和再结晶,退化为等轴铁素体晶粒,位错密度降低,M23C6型碳化物粗化,Z相在老化末期析出;在等效600℃、0~10万h时效条件下,T91钢的显微组织和高温持久强度非常稳定。Z相析出以前就发生的M23C6粗化及板条亚结构退化为等轴晶是T91钢服役中持久强度降低和爆管的主要因素。T91显微组织退化导致持久强度和硬度的降低。
Through the high temperature aging test of the original T91 pipe and the sampling of the pipe burst section of the T91 superheater, the microstructure evolution, including the sub-structure and the precipitation of the T91 steel during long service life were analyzed. The effect of tissue degradation on the long-term strength and hardness at high temperature was studied. The results show that the main microstructural changes of T91 steel during service life are as follows: the martensite structure of the slab reverts and recrystallizes, it is degraded into equiaxed ferrite grains, the dislocation density decreases, the M23C6 carbides coarsen, The Z phase precipitated at the end of aging. Under equivalent aging conditions of 600 ℃ and 0 ~ 100,000 h, the microstructure and high temperature long-term strength of T91 steel were very stable. The coarsening of M23C6 and the degeneration of lath substructure into equiaxed grains occurred before the precipitation of Z phase is the main factor for the decrease of long-term strength and burst pipe in service of T91 steel. Degradation of T91 microstructure leads to a decrease in long-term strength and hardness.