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摘要: 为了改善M2高速钢中的碳化物分布，通过数值模拟详细分析了结晶器旋转对M2高速钢电渣重熔过程温度场、金属熔池形状的影响，并进一步通过实验室双极串联结晶器旋转电渣炉研究了旋转速率对M2高速钢电渣重熔过程的影响。采用扫描电镜观察并分析了结晶器旋转对电渣锭中碳化物形貌、分布的影响；采用小样电解萃取实验，分析了结晶器旋转速率对碳化物组成的影响。结果发现，随着结晶器旋转速率的增加，渣池的高温区从芯部向边部迁移，温度分布更加均匀；金属熔池的深度变浅，两相区的宽度收窄，从而导致局部凝固时间降低、二次枝晶间距减小。与此相对应，随着结晶器旋转速率的增加，M2电渣锭的渣皮更薄、更加均匀，结晶器对电渣锭的冷却强度更大，碳化物网格开始破碎、变薄，碳化物由片状改变为细小的棒状。X射线衍射分析表明，不论结晶器是否旋转，碳化物的类型始终不变，由M2C、MC和M6C组成，但是随旋转速率增加M2C含量增加，MC和M6C含量降低。碳化物组织得以改善的主要原因在于，结晶器旋转导致金属熔池深度降低、两相区宽度收窄，改善了凝固条件，减轻了元素偏析。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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图 1 不同转速下渣池的焦耳热分布
Figure 1. Joule heat distribution of slag pool with different mold-rotation speeds
图 2 渣池表面的流场和温度场随结晶器旋转的变化
Figure 2. Variations of the flow and temperature fields on the slag pool surface with different mold-rotation speeds
图 3 渣−金界面处的流场和温度场随结晶器旋转的变化
Figure 3. Variations of the flow and temperature fields on the slag/metal−pool interface with different mold-rotation speeds
图 4 不同结晶器转速下电渣锭/渣池的纵向温度场分布
Figure 4. Longitudinal temperature distribution of the ESR ingot and slag pool with different mold-rotation speeds
图 5 不同转速下液相线与固相线的位置. (a) 液相线; (b) 固相线
Figure 5. Locations of liquidus and solidus phases with different mold-rotation speeds: (a) liquidus temperature; (b) solidus temperature
图 7 结晶器旋转速度与渣皮厚度关系
Figure 7. Relationship between mold-rotation speed and slag-skin thickness
图 9 不同结晶器转速对网状碳化物的影响
Figure 9. Effect of different mold-rotation speeds on the carbide network
图 10 不同结晶器转速下碳化物的三维形貌
Figure 10. Three-dimensional morphology of the carbides under different mold-rotation speeds
图 11 结晶器转速为0与9 r·min−1时高速钢萃取碳化物粉末的X射线衍射图
Figure 11. XRD pattern of carbide powder obtained from high-speed steel at the mold-rotation speed 0 and 9 r·min−1
图 14 碳化物生长示意图. （a）
$\omega $ =0；（b）$\omega $ >0Figure 14. Schematic of carbide growth: (a)
$\omega $ =0; (b)$\omega $ >0表 1 计算所需相关参数
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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