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結晶器旋轉數值模擬及對高速鋼電渣錠碳化物的影響

Numerical simulation of mold rotation and its effect on carbides in HSS ESR ingot

  • 摘要: 為了改善M2高速鋼中的碳化物分布,通過數值模擬詳細分析了結晶器旋轉對M2高速鋼電渣重熔過程溫度場、金屬熔池形狀的影響,并進一步通過實驗室雙極串聯結晶器旋轉電渣爐研究了旋轉速率對M2高速鋼電渣重熔過程的影響。采用掃描電鏡觀察并分析了結晶器旋轉對電渣錠中碳化物形貌、分布的影響;采用小樣電解萃取實驗,分析了結晶器旋轉速率對碳化物組成的影響。結果發現,隨著結晶器旋轉速率的增加,渣池的高溫區從芯部向邊部遷移,溫度分布更加均勻;金屬熔池的深度變淺,兩相區的寬度收窄,從而導致局部凝固時間降低、二次枝晶間距減小。與此相對應,隨著結晶器旋轉速率的增加,M2電渣錠的渣皮更薄、更加均勻,結晶器對電渣錠的冷卻強度更大,碳化物網格開始破碎、變薄,碳化物由片狀改變為細小的棒狀。X射線衍射分析表明,不論結晶器是否旋轉,碳化物的類型始終不變,由M2C、MC和M6C組成,但是隨旋轉速率增加M2C含量增加,MC和M6C含量降低。碳化物組織得以改善的主要原因在于,結晶器旋轉導致金屬熔池深度降低、兩相區寬度收窄,改善了凝固條件,減輕了元素偏析。

     

    Abstract: High-speed steel contains a large amount of carbides, the shape and distribution of which have an important influence on its quality. To improve the distribution of carbides in M2 high-speed steel, the temperature field and the shape of the metal pool during the mold-rotation process were investigated in detail using a numerical simulation. Moreover, the effect of the mold-rotation speed on the electroslag remelting process was investigated using a rotating bifilar electroslag remelting furnace under laboratory conditions. The morphology and distribution of carbides in an ESR ingot were observed using an SEM, and the composition of carbides was analyzed through an electrolytic extraction experiment. Results show that with increase in mold rotation speed, the high-temperature zone of the slag pool moves from the core to the edge. Moreover, the temperature distribution becomes uniform. The depth of the metal pool becomes shallow, and the thickness of the two-phase region decreases, which results in a short local solidification time and small secondary dendrite spacing. Correspondingly, with the increase in the mold rotation speed, the slag skin of ESR ingot becomes thin and more uniform than earlier. The cooling intensity of the mold on the ESR ingot is high, and the carbide network begins to break and become thin. The morphology of carbides changes from flake to fine rod. XRD analysis determines whether the mold rotates or not, carbides always comprise M2C, MC, and M6C. However, the content of M2C increases and the contents of MC and M6C decrease with the increase in mold-rotation speed. The main reason for the improvement in the carbide structure is that the mold rotation decreases the metal pool depth and two-phase zone thickness, which improves the solidification conditions and reduces the element segregation.

     

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