Abstract: Meltflow-VAR software was employed to simulate the vacuum arc remelting process of Φ660 mm large-scale ingot of M54 ultra-high strength steel， six processing curves with steady-state melting rates of 3.6， 3.9， 4.2， 4.5， 4.8， and 5.1 kg/min were selected for the study. Calculation results showed that as the melting rate increased， the depth and volume of the molten pool increased. The molten pool was completely in contact with the crucible at the melting rate of 4.8 kg/min or above， resulting improved cooling effect. The primary dendrite spacing monotonically increased with the increase of melting rate， while the local solidification time and secondary dendrite spacing decreased with the increase of melting rate in the range of 3.6-4.8 kg/min， whereas no significant change in the range of 4.8-5.1 kg/min. To verify the simulation results， a melting rate of 4.2 kg/min was chosen for industrial trial production. The shape of the molten pool was in good agreement with the calculated results. The degree of macro-segregation in steel ingots was relatively low， while the degree of micro-segregation （dendrite segregation） could reach over 30%. Micro-segregation was positively correlated with the spacing between secondary dendrites in the presence of secondary dendrite structures， while positively correlated with the spacing between primary dendrites in the absence of secondary dendrite structures. Taking into account the influence of melting rate on the shape of the molten pool， dendrite spacing and element segregation， it is recommended to optimize the steady-state melting rate to 4.8 kg/min.

Key words: M54 Ultra-high Strength Steel, Simulation of Vacuum Arc Remelting Process, Molten Pool Geometry, Dendrite Arm Spacing, Micro-segregation

摘要： 采用Meltflow-VAR软件，选取稳态熔速为3.6、3.9、4.2、4.5、4.8、5.1 kg/min六种工艺曲线，对M54超高强度钢Φ660 mm大锭型真空自耗重熔工艺进行仿真。计算结果表明：随熔速增加，熔池深度和体积增加，熔速4.8 kg/min及以上熔池与结晶器完全接触，冷却效果得到改善。一次枝晶间距随熔速增大单调上升，局部凝固时间和二次枝晶间距在3.6～4.8 kg/min范围随熔速增加下降、在4.8～5.1 kg/min范围无明显变化。选取4.2 kg/min熔速开展工业化试制验证，熔池形状与计算结果吻合良好。钢锭宏观偏析程度较低，但微观偏析（枝晶偏析）的程度可达30%以上。微观偏析在有二次枝晶结构存在的位置与二次枝晶间距正相关，在无二次枝晶结构的位置与一次枝晶间距正相关。综合考虑熔速对熔池形状、枝晶间距、元素偏析的影响，建议稳态熔速优化为4.8 kg/min。

关键词: M54超高强度钢, 真空自耗重熔仿真, 熔池形状, 枝晶间距, 微观偏析