预氧化处理对G115钢高温蒸气氧化行为的影响

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℃水蒸气中的高温氧化行为。采用分析天平测量氧化增重,得到了氧化增重动力学曲线。通过SEM及附带的EDS分析了氧化皮的形貌和结构,采用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1800 h以内的氧化增重。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Cr含量达46%(质量分数)的富Cr层,最内层由金属基体转变而成。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。

In order to improve the steam oxidation resistance of G115 steel（9 Cr3 W3 Co VNb Cu BN）at 650 ℃, pre-oxidation treatment was carried out in argon environment with low oxygen partial pressure.The oxidation behaviors 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 XRD and EDS, morphology and structure of scales were characterized by 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 preoxidized 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 chromium content as high as46%（mass fraction） and was considered to be conformed of chromite（Fe Cr2 O4）. 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 linear oxidation kinetics. The long term effect of the pre-oxidation treatment was evaluated based on the scale structure and oxidation mechanism.