摘要
采用光学显微镜、扫描电镜、X射线衍射仪和振动样品磁强计分析了Cr25Ni35Nb和Cr35Ni45Nb两类合金长期服役后的氧化行为以及其对磁性的影响。结果表明:长期服役后形成的氧化层主要由Cr2O3、SiO_2、Fe2O3组成,并且氧化膜发生了破裂,外壁和内壁氧化膜的破裂分别是Cr2O3在高温下的不稳定性和周期性的结焦/清焦所造成的;裂解炉管内壁和外壁均出现了氧化层、贫碳化物区、碳化物区,外表层为连续的Cr2O3氧化层,SiO_2则在贫碳化物区沿晶界分布;氧化前两种奥氏体耐热合金均为顺磁性结构,经氧化后形成的贫碳化物区中,基体的Cr含量较低,因而转变为铁磁性结构,其饱和磁化强度均超过20 emu/g。因此,氧化也是乙烯炉管长期服役后转变为铁磁性结构的重要因素。
In this work,the oxidation behavior and the magnetic properties of Cr25Ni35Nb and Cr35Ni45Nb alloys after a long-term service were investigated by employing OM,SEM,XRD and VSM analysis.The results show that the oxidation layer formed consists of Cr 2O 3,SiO 2 and Fe 2O 3,and exhibits cracks and rupture.The high-temperature instability of Cr 2O 3 and the cyclic coking/decoking operation during long-term service are found to contribute to the rupture of the outer and inner surface oxidation layers,respectively.There could be observed three zones,i.e.oxidation layer,carbide-depleted zone and carbides zone,at both inner and outer walls of the pyrolysis furnace tubes.The oxidation film is a conti-nuous Cr 2O 3 oxide layer,and SiO 2 disperses along the grain boundaries at the carbide-depleted zone.The original two kinds of austenitic heat-resistant alloys are paramagnetic.And due to the lower Cr content of matrix at the carbide-depleted zones,the paramagnetic structures are transformed into ferromagnetic structures,with saturation magnetizations larger than 20 emu/g.Therefore,it could be concluded that oxidation is also one of the critical factors that impel ethylene pyrolysis furnace tube to the transformation into ferromagnetic structure.
作者
郭景锋
曹铁山
程从前
王富岗
孟宪明
赵杰
GUO Jingfeng;CAO Tieshan;CHENG Congqian;WANG Fugang;MENG Xianming;ZHAO Jie(School of Materials Science and Engineering,Dalian University of Technology,Dalian 116085;China Automotive Technology & Research Center,Tianjin 300300)
出处
《材料导报》
EI
CAS
CSCD
北大核心
2019年第4期650-653,共4页
Materials Reports
基金
国家"863"计划项目(2015AA034402)
国家自然科学基金资助项目(U1610256)~~
关键词
氧化
贫碳化物区
饱和磁化强度
裂解炉管
铁磁性结构
oxidization
carbide-depleted zone
saturation magnetization
pyrolysis furnace tube
ferromagnetic structure
