Heat transfer behavior and homogenous solidification control for high-speed continuous casting slab mold
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摘要: 從分析高拉速包晶鋼板坯連鑄結晶器內凝固傳熱行為特征入手，首先闡明拉速對結晶器內的界面熱阻、凝固坯殼的溫度與應力分布的影響規律，研究發現拉速超過1.6 m·min?1時，界面熱阻明顯增加，拉速由1.4 m·min?1提升至1.6 m·min?1和1.8m·min?1時，出結晶器坯殼厚度相應減少約10%，其發生漏鋼的危險不斷增加；在此基礎上，闡述了結晶器的內腔結構、保護渣、振動與液面控制等控制結晶器內坯殼凝固均勻性的相關技術。要實現高速連鑄，首要應考慮結晶器內腔結構的優化設計，使其能更好地迎合凝固坯殼的生長，研制適合包晶鋼等凝固特點的專用連鑄保護渣至關重要，鑄坯鼓肚控制也是保障高拉速液面穩定的關鍵。Abstract: High-speed continuous casting is the theme for developing a new generation of high-efficiency continuous casting technology as well as a high-efficiency and green steelmaking production line. Presently, the actual casting speed for slabs in China is no more than 1.8 m·min?1, and it is in the range of 1.2–1.4 m·min?1 for continuous casting of peritectic steel. With the increase in the casting speed, the negative factors affecting the solidification in continuous casting mold become more evident, and the lubrication between mold copper plate and solidifying shell deteriorates. The friction force increases due to the increase of heat flux and decrease of mold flux consumption. Hence, the thickness of solidifying shell reduces and becomes nonuniform, decreasing its ability to resist all types of stress and strain during casting. Thus, the occurrence of breakout and cracks with high frequency greatly influences production. The technical issue of high-speed casting and the key to making it a reality should be resolved to ensure homogeneous growth. In this paper, the behavior of heat transfer and solidification in slab mold with high-speed casting for peritectic steel was analyzed. The effect of casting speed on the interfacial heat transfer resistance and the distribution of temperature and stress for solidifying shells in mold were investigated. It was found that the interfacial heat resistance increased evidently as the casting speed was greater than 1.6 m·min?1. The thickness of solidified shell at the exit of the mold was reduced by approximately 10%, as the casting speed increased from 1.4 m·min?1 to 1.6 m·min?1 and 1.8 m·min?1, making it more dangerous for breakout. The relative technologies such as the shape, flux, oscillation, and surface fluctuation for mold with homogenous solidification were presented and discussed. The optimization of mold inner cavity fitting for the growth of solidifying shell should be considered first for the uniformity control of peritectic steel solidification in a high-speed continuous casting mold. It is critical to design mold flux that adjusts to the solidification characteristics of peritectic steel. Moreover, the control of strand bulging is the key to stabilizing the mold surface.
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圖 1 不同拉速包晶鋼板坯結晶器窄面中心線上的熱流密度分布
Figure 1. Heat flux distribution at narrow face centerline of slab mold for peritectic steel under different casting speeds
圖 2 拉速對出結晶器坯殼厚度的影響
Figure 2. Effect of casting speed on the thickness of solidified shell at the mold exit
圖 3 不同拉速下包晶鋼板坯結晶器內坯殼角部區域氣隙沿結晶器高度方向的分布
Figure 3. Distribution of air gap at corner region along the slab mold length for peritectic steel under different casting speed
圖 4 不同拉速下結晶器內坯殼角部區域保護渣沿高度方向的分布。（a）寬面；（b）窄面
Figure 4. Distribution of mold flux at shell corner along mold length under different casting speeds: (a) wide face; (b) narrow face
圖 5 不同拉速下結晶器內坯殼的表面溫度沿高度方向的分布。（a）寬面；（b）窄面
Figure 5. Distribution of shell surface temperature along the mold length under different casting speeds: (a) wide face; (b) narrow face
圖 6 拉速為1.4 m·min?1的結晶器寬面的氣隙分布
Figure 6. Distribution of air gap at the wide face of mold with casting speed of 1.4 m·min?1
圖 7 拉速對在結晶器出口處凝固坯殼應力分布的影響。（a）1.4 m·min?1；（b）1.6 m·min?1；（c）1.8 m·min?1
Figure 7. Effect of casting speed on the shell stress distribution at mold exit: (a) 1.4 m·min?1; (b) 1.6 m·min?1; (c) 1.8 m·min?1
圖 8 窄面坯殼凝固熱收縮沿結晶器高度方向的分布
Figure 8. Distribution of shrinkage for solidifying shell of the narrow face along the mold length
圖 9 曲面型結晶器窄面結構示意圖
Figure 9. Schematic of a convex-shaped structure of the mold narrow face
圖 10 新型曲面結晶器與傳統線性錐度結晶器角部區域氣隙沿其高度方向的分布。（a）寬面；（b）窄面
Figure 10. Distribution of air gap at the corner region for new convex surface mold and conventional mold along the mold length: (a) wide face; (b) narrow face
圖 11 新型曲面結晶器與傳統結晶器出口凝固坯殼生長情況
Figure 11. Comparison of solidified shell thickness at the exit between the new and conventional mold
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