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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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Key words:
- electroslag remelting /
- high speed steel /
- carbide /
- mold /
- numerical simulation
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圖 1 不同轉速下渣池的焦耳熱分布
Figure 1. Joule heat distribution of slag pool with different mold-rotation speeds
圖 2 渣池表面的流場和溫度場隨結晶器旋轉的變化
Figure 2. Variations of the flow and temperature fields on the slag pool surface with different mold-rotation speeds
圖 3 渣?金界面處的流場和溫度場隨結晶器旋轉的變化
Figure 3. Variations of the flow and temperature fields on the slag/metal?pool interface with different mold-rotation speeds
圖 4 不同結晶器轉速下電渣錠/渣池的縱向溫度場分布
Figure 4. Longitudinal temperature distribution of the ESR ingot and slag pool with different mold-rotation speeds
圖 5 不同轉速下液相線與固相線的位置. (a) 液相線; (b) 固相線
Figure 5. Locations of liquidus and solidus phases with different mold-rotation speeds: (a) liquidus temperature; (b) solidus temperature
圖 7 結晶器旋轉速度與渣皮厚度關系
Figure 7. Relationship between mold-rotation speed and slag-skin thickness
圖 9 不同結晶器轉速對網狀碳化物的影響
Figure 9. Effect of different mold-rotation speeds on the carbide network
圖 10 不同結晶器轉速下碳化物的三維形貌
Figure 10. Three-dimensional morphology of the carbides under different mold-rotation speeds
圖 11 結晶器轉速為0與9 r·min?1時高速鋼萃取碳化物粉末的X射線衍射圖
Figure 11. XRD pattern of carbide powder obtained from high-speed steel at the mold-rotation speed 0 and 9 r·min?1
圖 14 碳化物生長示意圖. （a）
$\omega $ =0；（b）$\omega $ >0Figure 14. Schematic of carbide growth: (a)
$\omega $ =0; (b)$\omega $ >0表 1 計算所需相關參數
Table 1. Relevant parameters required for calculation
Parameters Value Thickness of slag pool/mm 40 Electrode diameter/mm 28 Electrode gap/mm 20 Electrode insertion depth/mm 15 Mold diameter/mm 96 Voltage/V 34 Mold-rotation speed / (r·min?1) 0, 6, 13, 19 
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