Cr25Ni35Nb和Cr35Ni45Nb裂解炉管的抗高温渗碳能力

以Cr25Ni35Nb和Cr35Ni45Nb合金为炉管材料对象,通过渗碳试验研究了高温(1 000和1 100 °C)下2种合金的渗碳动力学规律,采用金相和扫描电子显微镜观察分析其中Fe、Cr、Ni与Nb元素含量和渗碳层变化、组织结构及微区成分转变的情况,并对其抗渗碳能力进行分析.结果表明：Cr35Ni45Nb的抗渗碳能力比Cr25Ni35Nb更强;经2次渗碳后,2种合金试样出现了表面渗碳层剥落的现象,且Cr25Ni35Nb较为严重,并使得裂解炉管结焦而管壁变薄,从而降低了炉管的承载能力和服役寿命;合金的非渗碳层区域析出了大量弥散的碳化物,碳化物的密度随渗碳层与试样表面距离的增加而降低;在1 100 °C下,2种合金的骨架状组织形态消失,且晶界处碳化物出现了剥离.

Study on the Carburization Resistance of Cr25Ni35Nb and Cr35Ni45Nb Alloys for Ethylene Cracking Furnace Tube at High Temperature

Carburization kinetic curve of the two alloys (Cr25Ni35Nb and Cr35Ni45Nb) for ethylene cracking tubes was investigated and analyzed by the carburization experiments at elevated temperature (1 000 and 1 100 °C). Contents of Fe, Cr, Ni and Nb, growth of carburization layer, microstructure and composition of different zones of the two carburized materials were also studied by means of optical microscopy and scanning electron microscopy (SEM). The experimental results show that the carburization resistance of Cr35Ni45Nb alloy is better than that of Cr25Ni35Nb alloy; some locations on the surface of the specimens carburized during two cycling of time spall off and the spallation of Cr25Ni35Nb alloy is much more serious, this indicates that the thickness reduction of the ethylene cracking furnace tube will occur due to high temperature carburization and its strength and service life will be reduced. A mass of dispersive distributed secondary carbides generates in the zone of non carburization to center zone of coupons, the density of which decreases with the distance increased from surface of coupon; at 1 100°C, the initial bone framework structural morphology of the two materials disappears after carburization and the secondary carbide along the grain boundaries spalls off after carburization.