服役8.8万小时后超临界机组P91钢马氏体结构的退化行为

Martensitic degeneration behavior of P91 steel served for eighty-eight thousand hours in a supercritical unit

采用SEM、EBSD和TEM从不同尺度对比服役超8万小时P91钢与未服役P91钢的马氏体结构差异,并对马氏体结构作定量统计对比,分析长期服役P91钢马氏体结构的退化行为,讨论马氏体退化对力学性能的影响机制。结果表明,服役后马氏体板条块(Block)结构粗化,平均尺寸增大61.6%,尺寸正态分布顶点数值增大70%;板条束集(Packet)结构粗化,平均尺寸增大21%,正态分布顶点数值增大25.4%。板条束集结构粗化通过板条块的粗化来实现,板条块结构粗化程度大于板条束集。长期服役P91钢马氏体结构位错密度降低,导致取向差小于15°的结构占比减小8.6%。板条块(Block)结构粗化和马氏体结构内位错密度降低是导致长期服役后P91钢强度降低的重要因素。

Martensite structure differences between P91 steel not in service and in service over 80 000 hours were compared by means of SEM, EBSD and TEM at different scales. The statistical and quantitative comparison of martensitic structure was made, the degradation behavior of martensitic structure in long-term service was analyzed, and the influence mechanism of martensitic structure degradation on mechanical properties was discussed. The results show that the structure of martensite block is coarsened, the average size of block increases by 61.6%, and the vertex value of size normal distribution increases by 70%. The martensite packet structure is also coarsened, the average size increases by 21%, and the normal distribution vertex value increases by 25.4%. The structure coarsening of packet is realized by the coarsening of block, and the degree of coarsening of block is greater than that of packet. The dislocation density decreases, resulting in a decrease of 8.6% in the proportion of structure with misorientation less than 15°. The coarsening of block structure and the decrease of dislocation density in martensitic structure are the important factors leading to the decrease of strength of the P91 steel after long-term service.