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利用光学显微镜、扫描电镜及透射电镜对571℃、24.5 MPa条件下服役40 000 h的主蒸汽P91钢管道弯管段和直管段的组织进行了观察,并测试了其力学性能。结果表明,弯管段的硬度、拉伸强度较直管段严重偏低;组织对比发现,弯管段的马氏体组织较直管段发生严重的板条宽化,而且碳化物和亚晶粗化长大,位错密度降低,马氏体转变成铁素体。分析认为,热处理工艺不当导致弯管段出现块状铁素体是导致P91钢管弯管段长期服役后硬度和强度偏低的主要原因。
The microstructures of the elbow section and the straight pipe section of main steam P91 steel pipe which were used for 40,000 h at 571 ℃ and 24.5 MPa were observed by optical microscope, scanning electron microscope and transmission electron microscope. The mechanical properties were also tested. The results show that the hardness and tensile strength of the bend section are seriously lower than those of the straight section. The microstructure comparison shows that the martensite structure of the bend section undergoes severe slat width and the carbide and subgrain coarsening Growing, dislocation density decreases, martensite into ferrite. The analysis shows that the improper heat treatment process causes massive ferrite in the elbow section which is the main reason for the low hardness and strength of P91 pipe section after long service.