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采用扫描电镜、电子探针和X射线衍射等手段对不同服役时间(原始态、1.5a和6a)Cr35Ni45乙烯裂解炉管内壁的氧化与渗碳机理进行了系统分析.结果表明:高温长时服役后炉管内壁出现了氧化层、碳化物贫化区和碳化物富集区三个区域,其氧化行为包括Cr2O3外氧化和SiO2内氧化,且服役过程中外氧化膜发生反复破坏和重建;炉管服役过程的渗碳行为主要由内表面结焦引起,外氧化膜的反复破坏可以加重渗碳,但外氧化膜在破坏后能自动修复,所以服役态两个炉管的渗碳程度较轻;外氧化膜的反复破坏和重建使亚表层贫铬,导致形成碳化物的临界碳浓度增加,在内壁亚表层形成贫碳化物区,多余的碳原子在其内侧析出,形成碳化物富集区.
The oxidation and carburization mechanism of Cr35Ni45 ethylene pyrolysis furnace tubes at different service times (original state, 1.5a and 6a) were systematically analyzed by means of scanning electron microscopy, electron probe and X-ray diffraction. The results showed that: In the inner wall of the rear tube, three areas of oxide layer, carbide-depleted area and carbide-enriched area appear. The oxidation behavior includes Cr2O3 outer oxidation and SiO2 inner oxidation and repeated destruction and reconstruction of the outer oxide film during service. The carburizing behavior during service is mainly caused by the coke on the inner surface. Repeated destruction of the outer oxide film can increase the carburization, but the outer oxide film can be automatically repaired after it is destroyed. Therefore, the carburization of the two furnace tubes in service is light. Repeated destruction and reconstruction of the oxide film causes the sub-surface to be depleted of chromium, resulting in an increase of the critical carbon concentration of the carbide formed, forming a carbide-lean zone in the sub-surface of the inner wall, and excess carbon atoms precipitating on the inner side to form a carbide-enriched zone.