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采用光学显微镜、XRD、扫描电镜和电子探针等手段对不同服役时间(原始态、服役1.5年及6年)Cr35Ni45型裂解炉管的组织形态及析出相演化规律进行系统分析。结果表明,原始铸态炉管的组织为奥氏体基体、长条状M7C3碳化物及鱼骨状NbC与基体的共晶体;高温长期服役过程中,M7C3发生向M23C6碳化物的转变,共晶碳化物NbC发生向铌镍硅化物或η相转变,同时,晶内析出大量弥散分布的颗粒状二次M23C6碳化物;随着高温服役时间的进一步延长,碳化物形态从原始的条状、鱼骨状向块状转变并逐渐连接成网,晶内析出的二次碳化物随服役时间的延长逐渐溶解合并,数量减少。造成Cr35Ni45钢高温长时服役过程中析出相结构及形貌变化的主要原因在于该钢1000℃左右的服役条件及高温下析出相的稳定性。
Microstructure, morphology and evolution of Cr35Ni45 pyrolysis tubes were systematically analyzed by optical microscopy, XRD, SEM and electron probe. The results show that the microstructure of the original as-cast tube is the eutectic of austenite, elongated M7C3 carbides and fishbone NbC. When M7C3 is transformed into M23C6 carbides, Carbide NbC to niobium nickel silicide or η phase transition, while the precipitation of a large number of particles dispersed secondary granular M23C6 carbide; with extended service time at high temperatures, carbide morphology from the original strip, fish Bone to the massive transformation and gradually connected into a network, the crystallization of secondary carbides gradually dissolve with the extension of service time combined, the number decreased. The main reason for the phase structure and morphological changes of Cr35Ni45 steel during service at high temperature is the service life of the steel at about 1000 ℃ and the stability of precipitated phase at high temperature.