低温渗铝涂层对P92钢650℃饱和蒸汽氧化行为的影响

Effects of Low-temperature Aluminized Coating on Oxidation Behavior of P92 Steel in Saturated Steam at 650℃

利用低温粉末包埋渗法在P92钢服役温度下制备了铝化物涂层,并结合氧化增重法、扫描电镜观察及X射线衍射分析,研究了P92钢及其铝化物涂层在650℃下的饱和蒸汽氧化行为。结果表明:P92钢抗蒸汽氧化性能不足,350 h前氧化动力学遵循抛物线规律,外层疏松层氧化物Fe3O4+Fe2O3与内层氧化物FeCr2O4呈双层结构,氧化700 h后外层氧化膜发生严重剥落;低温包埋渗铝后,试样表面形成保护性Al2O3氧化膜,可显著提升P92钢抗蒸汽氧化性能;Al2O3氧化膜具有较慢的生长速度,因此铝化物涂层的耗损并不是继续形成Al2O3带来的消耗,而是Al向内扩散形成AlN相以及Fe向铝化物涂层扩散形成Fe3Al相,从而降低Al浓度梯度。

An aluminized coating was prepared for P92 steel using low-temperature pack cementation process at service temperatures, while a study was carried out on the oxidation behavior of P92 steel and the aluminized coating in saturated steam at 650℃ by the way of oxidation weight gain, scanning electron microscope and X-ray diffraction analysis. Results show that P92 steel has poor steam oxidation resistance and its oxidation kinetics follow the parabolic law in the first 350 h;the double-layered oxide scales consist of Fe3O4+Fe2O3 outer loose layer and FeCr2O4 inner layer formed during exposure, and the outer loose layer peels off severely after oxidation for 700 h. As for aluminized P92, however, its steam oxidation resistance could be improved significantly due to the formation of a protective Al2O3 film on the surface. The major degradation of aluminized coating is not the consumption of aluminum to grow Al2O3 due to its slow growing-rate, but the inward diffusion of aluminum into the substrate to form AIN phase and the outward diffusion of Fe into the coating to form Fe3Al, thus decreasing the concentration gradient of aluminum from the top surface to the base metal.