441铁素体不锈钢在模拟汽车废气环境中的氧化行为

采用增重法研究了441铁素体不锈钢在模拟汽车废气环境中于900~1050 ℃范围内的氧化行为。运用XRD、SEM以及EDS技术分析了试样表面氧化膜的形貌和结构特征。结果表明，441铁素体不锈钢在汽车废气环境中的上限服役温度在900 ℃左右，该温度下形成的氧化膜为双层结构，外层的Mn-Cr尖晶石层和内部的Cr₂O₃层。当氧化温度升到950 ℃及以上时，氧化膜上出现瘤状氧化物，氧化物瘤沿初期Mn-Cr尖晶石层两侧分布，外部主要是铁的氧化物，内部为铁铬氧化物。氧化温度达到1050 ℃时，氧化物瘤内部会形成较多空隙。氧化物瘤的生长导致发生失稳氧化，并使氧化动力学从抛物线规律转变为直线规律。

Oxidation Behavior of Type 441 Ferritic Stainless Steel in Synthetic Exhaust Gas

The oxidation behavior of type 441 ferritic stainless steel in a synthetic automotive exhaust gas at 900~1050 ℃ was studied by means of mass change measurement, XRD, SEM and EDS. The results indicate that the oxide scale formed at 900 ℃ has a bi-layered structure, i.e., an outer Mn-Cr spinel layer and an inner Cr₂O₃ layer, while the temperature 900 ℃ is known as the upper service limit for the type 441 ferritic stainless steel in automotive. When the oxidation temperature increases to 950 ℃ and above, oxide nodules appears on the oxide scale. A nodule usually can be differentiated into two parts by the initial formed Mn-Cr spinel layer, Fe-oxides and Fe-Cr oxides mainly form on top of and beneath the spinel thin layer respectively. When the oxidation temperature reaches 1050 ℃, many voids form in the oxide nodules. The growth of oxide nodules leads to breakaway oxidation, therewith, changes the oxidation kinetics from parabolic to linear.