本研究主要探討含矽電磁鋼在模擬熱軋過程中之高溫氧化現象，並分析表面生成之銹皮結構與性質。研究所用之鋼材矽含量在0.01~1.91 wt.%之間，利用熱機軋延模擬機(Thermo-mechanical simulator)於850~1200 ℃之間，在乾燥或含水蒸氣的空氣中氧化2分鐘，部分鋼片在氧化過程施以8%應變。經模擬熱軋氧化後的含矽鋼，利用X-ray繞射分析儀鑑定其銹皮結晶結構，並藉由掃描式電子顯微鏡與穿透式電子顯微鏡觀察氧化銹皮的形貌，配合能量散射光譜儀及電子微探針分析儀鑑定銹皮組成。

研究結果顯示，在850 ℃下氧化後，三種不同矽含量的鋼材表面均生成Fe2O3。在1000 ℃氧化後，矽含量0.01 wt.%的低碳鋼表面生成三種氧化鐵，α-Fe2O3、Fe3O4及FeO；而矽含量1.91 wt.%的電磁鋼氧化後，銹皮內側形成良好抑制氧化的含矽氧化層，外側則僅生成Fe2O3。隨著鋼材矽含量的增加，含矽氧化物存在於內側銹皮變得顯著；阻礙鐵離子的向外擴散並降低鋼材的氧化速率，使氧化銹皮總厚度減少且低價數氧化鐵有消失的趨勢。若提升至1200 ℃氧化，三種不同矽含量的鋼材銹皮厚度均大幅度增加。對於矽含量0.51 wt.%以上的鋼材，銹皮之氧化矽與FeO共晶反應生成熔融態矽酸鐵，反而有利於鐵離子的擴散，造成氧化速率的上升，故FeO、Fe3O4與Fe2O3於外側銹皮生成。

當氧化過程中施以8 %的拉伸應變。在850 ℃下氧化後，矽含量0.01 wt.%之鋼材表面銹皮為Fe2O3、Fe3O4和FeO，其銹皮厚度高於未施應變氧化的結果。在1000 ℃氧化後，矽含量較高的鋼材仍可發現矽氧化物聚集在基材與銹皮介面處並提供保護性，其外側生成之氧化鐵種類與未施應變相同。於1200 ℃氧化後，矽含量高於0.51 wt.%的鋼材於基材與銹皮界面處生成之熔融矽酸鐵皆有變薄的趨勢。可能是施加拉伸應變促使連續且具保護性的矽氧化物或矽酸鐵無法生成，因此鐵離子更容易沿著應力造成的缺陷擴散至外部形成氧化鐵，進而加速氧化。

當含矽鋼於含水蒸氣的空氣下氧化時。在850 ℃氧化後，矽含量0.01 wt.%的鋼材銹皮厚度遠大於空氣下氧化的結果，顯示水蒸氣具加速氧化的效果。對於矽含量高於0.51 wt.%的鋼材，雖然在1000 ℃氧化後仍可觀察到矽氧化物存在於內側銹皮，但與空氣下氧化相較，氧化鐵種類改變與銹皮厚度增加，顯示其保護性有下降的趨勢。在1200 ℃氧化後，仍可於鋼材內側銹皮發現熔融態矽酸鐵的生成，但其厚度明顯較薄，使其阻礙擴散與抑制氧化能力下降。故在含水蒸氣的環境下氧化時生成之銹皮總厚度大於空氣下氧化的結果。

The main goal of this study is to investigate the high-temperature oxidation of the three hot-rolling steels containing 0.01, 0.51, and 1.91 wt.% Si over the temperature range of 850~1200oC at various O2-containing environments. The thermo-mechanical simulator (Gleeble machine) was employed for oxidation tests in various conditions. The effect of 8% applied tensile strain on the scale constitution and phases of these steels was also investigated through XRD, SEM, EPMA, and TEM analyses.

The results showed that an exclusive layer of Fe2O3 formed on the three steels after oxidation at 850oC for 2 min, however, the scales formed at 1000oC for 2 min were strongly dependent on Si content, being composed of FeO, Fe3O4, and Fe2O3 for the 0.01%Si steel. However, the scales formed on the 1.91%Si steel consisted of SiO2 or Fe2SiO4 in the inner-portion and of Fe2O3 formed in the outer-portion. The amounts of Si-rich oxides gradually increased with increasing Si-content, which cause a reduction of outward iron-diffusion and inward oxygen-diffusion, thereby reducing the amounts of FeO and oxidation rates. The scale thickness of the alloys significantly increased when exposed at 1200oC for 2 min. The formation of partial melting fayalite for the steels containing 0.51% Si or higher enhanced outward diffusion of iron, which increased the oxidation rates and in turn resulted in the formation of iron oxides (FeO, Fe3O4, and Fe2O3).

When 8% tensile strain was applied during oxidation at 850oC, FeO, Fe3O4, and Fe2O3 formed on the 0.01%Si steel, and the scale thickness was much thicker than that of the strain-free oxidation. The Si-rich oxide grown in the inner-portion of the scales can provide its passivity when oxidized at 1000oC although iron oxides formed in the outer-portion of the scales were nearly identical to those of the strain-free condition. At 1200oC, however, the fayalite layer became much thinner under the applied-strain condition, indicating that the protective fayalite layer was difficult to form, which in turn enhanced outward iron diffusion along the defects created under tensile strain, thereby causing faster oxidation rates.

In addition, the effect of water vapor on the oxidation behavior of the steels was also investigated. It was concluded that the scale thickness of the three steels was much thicker when they were exposed in wet air.

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