预氧化处理对G115钢高温蒸汽氧化行为的影响Effect of Pre-oxidation Treatment on the Behavior of High Temperature Oxidation in Steam of G115 Steel

　　以Ar气为保护环境，对G115马氏体耐热钢进行了预氧化处理。通过循环蒸气氧化实验，研究了未预氧化处理和预氧化处理2种试样在650°C水蒸气中的高温氧化行为。采用分析天平测量氧化增重数据，得到了氧化增重动力学曲线。通过扫描电镜（SEM）及附带的能谱分析仪（EDS）分析了氧化皮的形貌和结构，采用X射线衍射仪（XRD）结合EDS对氧化产物进行了相鉴定。实验结果表明，预氧化处理明显降低G115钢1800h以内的氧化增重。通项公司了解，预氧化处理后，G115钢的蒸气氧化动力学由立方型转变为直线型，氧化皮结构由典型的双层结构转变为多层结构。预氧化处理试样的氧化皮最外层为由Fe向外扩散形成的富Fe层，中层为含Cr量达46%（质量分数）的富Cr层，最内层是由金属基体转变而成的。其中氧化皮中层由于Cr含量高而具有良好的保护性，是整体氧化过程的控制步骤。另外该层厚度接近常数，使得预氧化处理试样的氧化动力学呈直线型。以氧化皮结构和氧化过程机制为根据，对预氧化处理的长期效果进行了评估，结果表明预氧化处理能整体上降低氧化增重约30%。

　　In order to improve the steam oxidation resistance of G115 steel (9Cr3W3CoVNbCuBN) at 650 °C, pre-oxidation treatment was carried out in argon environment with low oxygen partial pressure. The oxidation behavior of the pre-oxidized and untreated samples were simultaneously investigated by a cyclic oxidation experiment. Weight gains of samples were measured by analytical balance, phases of oxide products were identified by X-ray diffraction (XRD) and energy dispersive spectrometer (EDS), morphology and structure of scales were characterized by scanning electron microscope (SEM) and EDS. The result showed that pre-oxidation treatment significantly decrease oxidation weight gains in 1800 h. After pre-oxidation treatment, the oxidation kinetics transformed from cubic into linear form, and the scale structures transformed from duplex layers into triple layers. In the scale of pre-oxidized samples, the outermost layer was enriched in Fe, the middle layer was enriched in Cr, and the innermost layer was transformed from the matrix metal. The middle layer had a chromium content as high as 46% (mass fraction) and was considered to be conformed of chromite (FeCr2O4). This layer was the most protective layer due to its highest Cr content, and the diffusion of O and Fe though it was the main controlling process of the whole oxidation. It suggested that the stable structure of the middle layer improved the oxidation resistance of pre-oxidation samples. The thickness of the middle layer nearly kept constant during the whole oxidation process, which was the main reason why the pre-oxidized sample had a linear oxidation kinetics. The long term effect of the pre-oxidation treatment was evaluated based on the scale structure and oxidation mechanism. It suggested that the pre-oxidation treatment could decrease oxidation weight gains by 30 percent.