彭以超
,
楼玉民
,
许好好
材料热处理学报
采用乙炔真空渗碳方式对未服役和服役5年的乙烯裂解炉管耐热钢HP40Nb进行了加速渗碳处理,并利用SEM和定量电子探针对渗碳前后炉管内壁的渗碳行为进行了系统分析.结果表明,未服役HP40Nb炉管内壁在渗碳前分布在晶界上的主要是以M7C3和NbC为主的链状一次碳化物.真空渗碳之后,强烈渗碳区域的碳化物形貌随着深度增加发生较大的变化,碳化物种类随深度增加也逐渐发生由M3C2、M7C3到M23C6的转变.渗碳造成表面硬度升高,脆性增加.服役态HP40Nb炉管的内壁横截面分为表面的氧化层、亚表层的贫碳化物区和内部的渗碳区3个区域,表面氧化层区又可以分为Cr2O3和SiO2两个区域.表面氧化层对于抗渗碳性能具有较大的影响.Cr2O3具有一定的抗渗碳能力,但在高碳活度下较长时间后Cr2O3会逐渐不稳定发生碳化.晶间氧化区主要以SiO2为主,SiO2在高碳活度下比较稳定,难以碳化,因而造成渗碳速率下降.
关键词:
HP40Nb
,
乙烯裂解管
,
真空渗碳
,
抗渗碳性
钱庆生
,
李海
,
王芝秀
,
王秀丽
,
史志欣
材料工程
doi:10.3969/j.issn.1001-4381.2011.08.013
为提高高温抗氧化性能,对HP40Nb钢进行了热浸镀Al-10%(质量分数)Si,并进行不同温度扩散处理,研究了不同扩散处理试样在1000℃条件下的高温氧化行为,通过SEM,EDS和XRD分析了经不同扩散处理后的渗层在高温氧化过程中的组织结构变化.结果表明:经800℃/4h扩散处理,渗层由内层(NiAl+ Cr3 Si)、中间层(Fe2 Al5+少量Ni2 Al3)和外层( FeAl3)组成；经900℃/4h扩散处理,渗层由内层(NiAl+ Cr3 Si)和外层(Fe2 Al5+少量Ni2 Al3)组成；经1000℃/4h扩散处理渗层由内层(α+Ni3Al,NiAl+ Cr3 Si)和外层(Fe2 Al5+ Ni2 Al3)组成.不同扩散工艺处理试样经高温氧化360h后渗层均由外层(NiAl+ Cr3 Si)和内层(σ,α+Ni3Al)组成；经1000℃/4h扩散处理试样高温氧化性能最好,其氧化增重速率仅为未浸镀试样的13%.氧化过程中,渗层表面经扩散处理生成的α-Al2O3能显著提高钢的高温抗氧化性能.扩散温度越高,α-Al2O3越完整,致密抗高温氧化性能越好；渗层中σ相能阻碍铝原子的内扩散,从而保证了氧化过程中渗层表面生成α-Al2 O3所需铝含量,除表面的α-Al2 O3外,渗层中的NiAl,Cr3 Si相也起到了抗氧化作用.
关键词:
HP40Nb
,
热浸镀铝
,
高温抗氧化性
,
α-Al2O3
Limin SHEN
,
Jianming GONG
,
Yong JIANG
,
Luyang GENG
金属学报(英文版)
HP40Nb steel, used as a candidate material for ethylene cracking furnace tube, suffers creep and carburization damage from the complex environment of high temperature, high carbon potential and low oxygen partial pressure, and they lead to failure of the furnace tubes ahead of designed life. In order to investigate damage evolution under the complex condition, coupled creep damage and carburization damage constitutive equations were developed according to continuum damage mechanics theory. Based on the finite element ABAQUS code, user subroutines were developed for analyzing damage evolution of ethylene furnace tube under the action of coupled creep-carburization. The results show that carburization accelerates the damage process dramatically, damage value reaches the critical value along the inner surface after serving for 75,000 h under the action of creep-carburization, meanwhile the damage value is only 0.53 along the outer surface after operating the same time under the action of creep alone, which means that microcracks are generated along the inner surface under the action of coupled creep-carburization, fracture begins along the outer surface of tube under the action of creep alone.
关键词:
Damage prediction
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