服役态Cr35Ni45Nb合金高温真空渗碳行为及相演化机理研究
发布时间：2018-12-26 10:00
【摘要】：采用乙炔真空渗碳方式对服役6 a的乙烯裂解炉管合金Cr35Ni45Nb进行了加速渗碳处理,并利用SEM,XRD及定量电子探针等手段对渗碳前后炉管内壁的渗碳行为及相演化机理进行系统研究.结果表明,炉管内表面形成了较厚的Cr2O3/Si O2复合氧化层.复合氧化层表现出良好的抗腐蚀能力,是阻止C渗入炉管内部的有效障碍.材料的抗渗碳能力主要取决于表层Cr2O3的连续性、致密性和亚表层Si O2的稳定性.在低氧分压且具有还原性的气氛中,表层的Cr2O3层逐渐碳化为Cr3C2,并且Cr3C2逐渐剥离和脱落,使得保护性Cr2O3膜的抗渗碳能力逐渐减弱甚至消失.亚表层的Si O2虽具有优良的热力学稳定性,但Si较低的活度使得Si O2层不够连续,仍有部分C从氧化层空隙间渗入.当移除该复合氧化层或者渗碳时间足够长使得复合氧化层抗渗碳能力急剧减弱时,炉管材料内部由于发生严重的内部渗碳使得组织结构发生了显著变化:枝晶间碳化物严重合并和粗化,并原位发生由M23C6到M7C3的转变,同时在碳化物内部析出类似于离异共析状的蠕虫状g相.距表面越近,C活度越高,导致在约0.5 mm深的范围内发生以大量石墨析出为特征的金属尘化现象.碳化物的严重合并粗化以及金属尘化现象会造成炉管组织的严重弱化、宏观裂纹的产生以及炉管服役寿命的降低.
[Abstract]:The accelerated Carburizing of ethylene cracking furnace tube alloy Cr35Ni45Nb with 6 years service was carried out by means of acetylene vacuum carburization, and SEM, was used. The Carburizing behavior and phase evolution mechanism of furnace tube before and after Carburizing were systematically studied by XRD and quantitative electron probe. The results show that a thick Cr2O3/Si O 2 composite oxide layer is formed on the inner surface of the furnace tube. The composite oxidation layer exhibits good corrosion resistance and is an effective barrier to prevent C from infiltrating into the furnace tube. The carburization resistance of the material mainly depends on the continuity, compactness and stability of Si O 2 in the surface layer. In the atmosphere of low oxygen partial pressure and reductive atmosphere, the surface layer of Cr2O3 was gradually carbonized into Cr3C2, and Cr3C2 was gradually stripped and shedded off, which made the Carburizing resistance of protective Cr2O3 film weakened or even disappeared. Although the Si O 2 in the subsurface layer has excellent thermodynamic stability, the low activity of Si makes the Si O 2 layer not continuous enough, and some C is still infiltrating between the oxidation layer voids. When the composite oxidation layer is removed or the carburizing time is long enough, the Carburizing resistance of the composite oxide layer decreases sharply. Due to the serious carburization inside the furnace tube, the microstructure of the furnace tube is changed significantly: the dendrite carbides are merged and coarsened, and the transformation from M23C6 to M7C3 occurs in situ. At the same time, a vermicular g phase similar to a divorced eutectoid is precipitated in the carbides. The closer it is to the surface, the higher the activity of C is, which leads to the dedusting of large amount of graphite in the depth range of 0. 5 mm. The serious coalescence and coarsening of carbides and metal dust will lead to the serious weakening of furnace tube structure, the occurrence of macroscopic cracks and the decrease of service life of furnace tubes.
【作者单位】： 北京科技大学材料科学与工程学院;中国特种设备检测研究院;
【基金】：国家高技术研究发展计划资助项目2012AA03A513~~
【分类号】：TG156.81
，
本文编号：2391934
[Abstract]:The accelerated Carburizing of ethylene cracking furnace tube alloy Cr35Ni45Nb with 6 years service was carried out by means of acetylene vacuum carburization, and SEM, was used. The Carburizing behavior and phase evolution mechanism of furnace tube before and after Carburizing were systematically studied by XRD and quantitative electron probe. The results show that a thick Cr2O3/Si O 2 composite oxide layer is formed on the inner surface of the furnace tube. The composite oxidation layer exhibits good corrosion resistance and is an effective barrier to prevent C from infiltrating into the furnace tube. The carburization resistance of the material mainly depends on the continuity, compactness and stability of Si O 2 in the surface layer. In the atmosphere of low oxygen partial pressure and reductive atmosphere, the surface layer of Cr2O3 was gradually carbonized into Cr3C2, and Cr3C2 was gradually stripped and shedded off, which made the Carburizing resistance of protective Cr2O3 film weakened or even disappeared. Although the Si O 2 in the subsurface layer has excellent thermodynamic stability, the low activity of Si makes the Si O 2 layer not continuous enough, and some C is still infiltrating between the oxidation layer voids. When the composite oxidation layer is removed or the carburizing time is long enough, the Carburizing resistance of the composite oxide layer decreases sharply. Due to the serious carburization inside the furnace tube, the microstructure of the furnace tube is changed significantly: the dendrite carbides are merged and coarsened, and the transformation from M23C6 to M7C3 occurs in situ. At the same time, a vermicular g phase similar to a divorced eutectoid is precipitated in the carbides. The closer it is to the surface, the higher the activity of C is, which leads to the dedusting of large amount of graphite in the depth range of 0. 5 mm. The serious coalescence and coarsening of carbides and metal dust will lead to the serious weakening of furnace tube structure, the occurrence of macroscopic cracks and the decrease of service life of furnace tubes.
【作者单位】： 北京科技大学材料科学与工程学院;中国特种设备检测研究院;
【基金】：国家高技术研究发展计划资助项目2012AA03A513~~
【分类号】：TG156.81
，
本文编号：2391934
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