預氧化處理對G115鋼高溫蒸汽氧化行為的影響

預氧化處理對G115鋼高溫蒸汽氧化行為的影響Effect of Pre-oxidation Treatment on the Behavior of High Temperature Oxidation in Steam of G115 Steel

以Ar氣為保護環境，對G115馬氏體耐熱鋼進行了預氧化處理。通過循環蒸氣氧化實驗，研究了未預氧化處理和預氧化處理2種試樣在650°C水蒸氣中的高溫氧化行為。采用分析天平測量氧化增重數據，得到了氧化增重動力學曲線。通過掃描電鏡（SEM）及附帶的能譜分析儀（EDS）分析了氧化皮的形貌和結構，采用X射線衍射儀（XRD）結合EDS對氧化產物進行了相鑒定。實驗結果表明，預氧化處理明顯降低G115鋼1800h以內的氧化增重。預氧化處理后，G115鋼的蒸氣氧化動力學由立方型轉變為直線型，氧化皮結構由典型的雙層結構轉變為多層結構。預氧化處理試樣的氧化皮最外層為由Fe向外擴散形成的富Fe層，中層為含Cr量達46%（質量分數）的富Cr層，最內層是由金屬基體轉變而成的。其中氧化皮中層由于Cr含量高而具有良好的保護性，是整體氧化過程的控制步驟。另外該層厚度接近常數，使得預氧化處理試樣的氧化動力學呈直線型。以氧化皮結構和氧化過程機制為根據，對預氧化處理的長期效果進行了評估，結果表明預氧化處理能整體上降低氧化增重約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.

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