某厂热处理燃气加热炉辐射管在服役不到2 a后发生了开裂。采用宏观观察、化学成分分析、金相检验、扫描电镜和能谱分析等方法,分析了辐射管开裂的原因。结果表明:辐射管外保护气体碳势控制不当,辐射管自外壁向内壁大量渗碳,晶界和晶内析出大量粗大的Cr₂₃C₆,使辐射管脆性升高,在热应力作用下,辐射管自外壁起裂,并向内壁扩展;由于碳化物的大量析出,固溶在辐射管基体中的铬元素含量降低,这使得辐射管抗氧化性能降低,在管内高温氧化气氛环境中,辐射管发生氧化、腐蚀,辐射管内部铸造缺陷加速裂纹扩展,最终导致辐射管开裂。

The radiant tube of heat treatment gas heating furnace in a factory cracked after serving for less than 2 years. By means of macroscopy observation, chemical composition analysis, metallographic examination, scanning electron microscope and energy spectrum analysis, the reasons for cracking of radiant tube were analyzed. The results showed that the carbon potential of the protective gas outside radiant tube was not properly controlled, radiant tube was carburized from the outer wall to the inner wall, and a large amount of coarse Cr₂₃C₆ was precipitated in the grain boundary and in the grain, which increased the brittleness of radiant tube. Under the action of thermal stress, the radiant tube cracked from the outer wall and expanded to the inner wall. Due to the large amount of carbide precipitation, the content of chromium element dissolved in the matrix of radiant tube decreased, which reduced the oxidation resistance of radiant tube. In the high temperature oxidizing atmosphere in the tube, the radiant tube was oxidized and corroded, and the internal casting defects of radiant tube accelerated the crack propagation, which eventually led to the cracking of radiant tube.