结晶器旋转数值模拟及对高速钢电渣锭碳化物的影响

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。 

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

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.