Simulation of the macrosegregation in the gear steel billet continuous casting process
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摘要: 基于國內某廠齒輪鋼小方坯連鑄生產過程，利用ProCAST軟件建立移動切片模型，能夠高效模擬連鑄過程中的宏觀偏析，模型分別模擬研究了不同過熱度、二冷水量和拉坯速度等對宏觀偏析的影響。模擬結果與碳偏析檢測結果吻合良好，驗證了移動切片模型模擬連鑄坯宏觀偏析的準確性。由于溶質浮力的影響，內弧側的宏觀偏析強于外弧側。隨著過熱度的增加，鑄坯中心碳偏析度從1.06增加至1.15。過熱度控制在25 ℃范圍內，可以保證鑄坯的宏觀碳偏析度控制在1.10范圍內。隨著連鑄二冷水量的增加，鑄坯中心偏析改善程度較小，鑄坯中心碳偏析度從1.16降低至1.13。隨著拉坯速度的增加，鑄坯中心偏析呈現加重的趨勢，鑄坯中心碳偏析度由1.14增加至1.21，拉坯速度控制在1.4 m·min–1范圍內，可保證鑄坯中心碳偏析度低于1.15。Abstract: Macrosegregation forms due to relative motion between liquid and solid phases on the macro scale during solidification. As macrosegregation is formed during a solidification process, it is difficult to remove it in the subsequent rolling and heat treatment processes, thereby deteriorating the mechanical properties and stability of products. Studies of macrosegregation of billets for industrial trials have become a challenge due to the high temperature of the casting process. To improve macrosegregation of billet, a moving slice model was developed using the ProCAST software based on a continuous casting process of gear steel billet in a domestic steel mill. During the continuous casting process, macrosegregation can be calculated using the above model. The effects of superheat, secondary cooling water flows, and casting speed on macrosegregation were simulated. These results were consistent with the measured outcomes of carbon macrosegregation, validating the moving slice model to calculate the macrosegregation of billet. The solute concentration on the loose side is higher than that on the fixed side due to solute buoyancy. The degree of carbon segregation in the billet center increases from 1.06 to 1.15, with an increase in superheat, which should be controlled below 25 ℃ to ensure the degree of carbon segregation within 1.10. However, the degree of carbon segregation in the billet center decreases from 1.16 to 1.13, with an increase of secondary cooling water flow and a little improvement in central segregation. With an increase in casting speed, the central segregation becomes serious, and the degree of carbon segregation in the billet center increases from 1.14 to 1.21. However, when the casting speed is lower than 1.4 m·min?1, the degree of carbon segregation in the billet center comes lower than 1.15.
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Key words:
- macrosegregation /
- superheat /
- secondary cooling water flow /
- casting speed /
- gear steel
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圖 2 鋼的熱物性參數。（a）熱導率；（b）密度；（c）熱焓；（d）黏度；（e）固相率
Figure 2. Thermophysical parameters of the steel: (a) conductivity; (b) density; (c) enthalpy; (d) viscosity; (e) solid fraction
圖 3 計算得到的鑄坯表面溫度和測量結果的對比
Figure 3. Comparison between the calculated and measured results of the billet surface temperature
圖 4 檢測得到的碳含量與模擬結果對比
Figure 4. Comparison between the calculated and measured results of the carbon content
圖 6 過熱度對鑄坯宏觀偏析的定量影響
Figure 6. Effect of superheat on the quantized results of the macrosegregation
圖 7 二冷水量對鑄坯宏觀偏析的影響
Figure 7. Effect of secondary cooling water flow on macrosegregation of the billet
圖 8 二冷水量對鑄坯宏觀偏析的定量影響
Figure 8. Effect of secondary cooling water flow on the quantized results of macrosegregation
圖 9 拉坯速度對鑄坯宏觀偏析的影響
Figure 9. Effect of casting speed on macrosegregation of the billet
圖 10 拉坯速度對鑄坯宏觀偏析的定量影響
Figure 10. Effect of casting speed on the quantized results of macrosegregation
圖 11 拉坯速度對凝固坯殼厚度的影響
Figure 11. Effect of casting speed on the shell thickness of the billet
表 1 齒輪鋼成分（質量分數）
Table 1. Element content of the gear steel
% C Si Mn P S Al Cr Ti 0.215 0.240 0.890 0.020 0.020 0.020 1.090 0.006 
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表 2 各區長度和冷卻水量
Table 2. Length and cooling water flow in each zone
Cooling zone Water flow/(m3·h?1) Length/m Mold 108 0.9 Zone1 3.32 0.35 Zone2 2.20 1.78 Zone3 1.03 1.85
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