P92钢奥氏体化后的冷却方式对650℃时效组织及硬度稳定性的影响

Effect of cooling modes after austenitization on stabilities of microstructure and hardness of P92 steel aged at 650℃

采用扫描电镜二次电子/背散射成像模式(SEM-SE/BSE)、能谱分析(EDS)和复相分离技术(MPST)研究P92钢试样于1060℃/1h奥氏体化后以不同方式冷却(空冷/置炉门口冷:缓冷)经760℃/2h回火(空冷)后再经650℃时效后的组织及硬度的稳定性。结果表明:P92钢时效后的显微组织均为基体相与析出相(M_(23)C_6相和Laves相);奥氏体化后冷却方式对650℃时效后组织及试样硬度有明显影响:缓冷时效试样的析出总量大而硬度低,且Laves相的体积分数/颗粒粗化倾向明显较大,M_(23)C_6相体积分数较小;在650℃时效1000h和3000h期间,空/缓冷时效试样的硬度基本不变/下降;此外,650℃时效试样组织及硬度的稳定性与过冷奥氏体及马氏体的稳定性有关。因此,工业现场管道奥氏体化后应尽快散热。

The stabilities of microstructures and hardness of P92 steel samples austenitized at 1060℃ for 1h followed by air cooling (AC)/slow cooling (SC) and tempered at 760℃ for 2h and then aged at 650℃ for 1000h/3000h were studied by SEM-SE/BSE,EDS and multiphase separation technology (MPST).The results show that the microstructures of P92 steel aged samples consist of martensite and precipitations (M23C6 and Laves phase).The cooling modes after austenitization have an obvious effect on microstructures and hardness of the samples aged at 650℃.Compared with the AC samples,the total volume fraction of the precipitations/Vickers hardness of the SC sample is higher/lower and the volume fraction of the Laves/M23C6 phase is remarkably higher/lower.Moreover,the Laves phase particles of SC sample is much more coarsened.The hardness of the SC sample decreases after ageing treatment at 650℃ for 1000h/3000h,while that of the AC sample is not obviously varied.In addition,the stabilities of microstructure and hardness of P92 steel aged at 650℃ are related to the stability of the austenite which in return affects the stability of the martensite transformed during cooling.Therefore,the P92 pipes cooled from austenitization should dissipate heat as soon as possible in the manufacturing scene.