Abstract: To study the vacuum arc remelting process and improve the homogenization and cleanliness level of large-sized superalloy ingot， numerical simulation and industrial experiment were carried out to investigate the evolution of molten pool， solidification characteristics and inclusion distribution in a ϕ690 mm GH4738 superalloy ingot during vacuum arc remelting. The results show that as the melting progresses， the simulated molten pool morphology changes from a "shallow flat" shape to a "shallow U " shape. After melting for 500 minutes， the depth of the molten pool and the width of the mushy zone tend to stabilize， with maximum molten pool depth and mushy zone width being 200.88 mm and 72.38 mm respectively. During stable melting， the cooling rate at the surface and center of the casting ingot is 0.126K / s and 0.009 K/s， respectively， and after the height of the ingot is exceeds 0.4 m， the cooling rate of the casting ingot is basically stable.The trajectories of six particle size inclusions in the molten pool were simulated. Large size inclusions （>20 μm） were subjected to the fluid flow and buoyancy to move helically in the molten pool and were eventually trapped at the ingot sidewalls， while small size inclusions （≤10 μm） entered the molten pool and then moved inward along the bottom of the pool， eventually remaining inside the ingot， which is basically consistent with the detection value of the industrial ingot.

Key words: Ni-based superalloy, Vacuum Arc Remelting, Numerical simulation, Molten Pool, Inclusion, GH4738 Alloy

摘要： 为探究大尺寸高温合金真空自耗重熔工艺，提高铸锭均质化、洁净化水平，采用数值模拟与工业试验相结合的方法，研究了ϕ690 mm锭型GH4738合金真空自耗重熔过程熔池演变、凝固特征以及夹杂物分布规律。结果表明，随着熔炼的进行，模拟的熔池由“浅平”形逐渐向“浅U”形转变，熔炼500 min后，熔池逐渐趋于稳定，冶炼过程最大熔池深度和糊状区宽度分别为200.88、72.38 mm。稳定熔炼期间，铸锭表面和中心的冷却速率分别为0.126、0.009 K/s，高度超过0.4 m后，铸锭冷却速率基本维持稳定。模拟了6种粒径的夹杂物在熔池中的运动轨迹，>20 μm的夹杂物在熔池内作螺旋运动，大部分在熔池表面与铸锭侧壁接触面被捕获，≤10 μm的夹杂物进入熔池后沿熔池底部向内运动，最终停留在铸锭内部，与工业铸锭检测值基本一致。

关键词: 镍基高温合金, 真空自耗重熔, 数值模拟, 熔池, 夹杂物, GH4738合金