钛合金TC4真空自耗熔炼工艺参数对宏观偏析影响

Effect of Vacuum Arc Remelting Process Parameters on Macrosegregation in TC4 Titanium Alloy

摘要:

采用Fluent软件模拟了钛合金TC4真空自耗熔炼过程中温度场、流场和溶质场相互作用，研究了与铸锭直接相关的3个工艺参数（熔速、铸锭上表面温度和冷却强度）对铸锭宏观偏析的影响规律。结果表明：不同熔炼条件下，在铸锭1000 mm高度处的铁元素径向偏析均呈钟形分布，即铸锭芯部为正偏析，表面区域为负偏析，且负偏析程度均大于正偏析。熔炼速度对铸锭温度场和宏观偏析的影响最为明显：当熔炼速度由0.15 mm/s增加到0.18 mm/s时，铸锭达到稳定熔炼阶段时的高度由1200 mm增加到1600 mm，熔池深度由494 mm增加到738 mm。当距铸锭中心距离小于130 mm时，偏析随熔炼速度增加而减小，在熔炼速度为0.15 mm/s时达到最大值，为3.36%；当距铸锭中心距离大于295 mm时，偏析随熔炼速度增大而增大，在熔炼速度为0.21 mm/s时达到最大值6.23%。铸锭上表面温度和冷却强度对宏观偏析和熔池深度的影响不明显。通过正交分析得到3个主要工艺参数对宏观偏析影响程度为：熔炼速度＞冷却强度＞铸锭上表面温度，并得到最优工艺参数为熔炼速度0.15 mm/s、铸锭上表面温度2179 K、冷却强度500（底部）/1000（侧面） W·m^-2·K^-1。

Abstract:

Fluent software was used to simulate the interaction among the temperature field, flow field, and solute field in the vacuum arc remelting process of TC4 titanium alloy. The effects of three process parameters (smelting rate, upper surface temperature of the ingot, and cooling intensity), which are directly related to the ingot, on the ingot macrosegregation were studied. Results show that under different smelting conditions, the radial macrosegregation of Fe element shows a bell-shaped distribution at the ingot height of 1000 mm, i.e., the core of ingot presents the positive macrosegregation whereas the surface area presents the negative macrosegregation, and the degree of negative macrosegregation is greater than that of the positive macrosegregation. The effect of smelting rates on the temperature field and macrosegregation of the ingot is the most obvious: with increasing the smelting rate from 0.15 mm/s to 0.18 mm/s, the ingot height to reach the stable melting stage is increased from 1200 mm to 1600 mm, and the depth of the molten pool is increased from 494 mm to 738 mm. In the area within the distance of 130 mm from the ingot center, the macrosegregation is decreased with increasing the smelting rate, and the maximum value is 3.36% when the smelting rate is 0.15 mm/s. In the area beyond the distance of 295 mm from the ingot center, the macrosegregation is increased with increasing the smelting rate, and the maximum value is 6.23% when the smelting rate is 0.21 mm/s. The effect of upper surface temperature and cooling intensity on macrosegregation and molten pool depth is not obvious. Through the orthogonal analysis, the influence degree of three main process parameters on macrosegregation is as follows: smelting rate>cooling intensity>ingot upper surface temperature. The optimal conditions are smelting rate of 0.15 mm/s, ingot upper surface temperature of 2179 K, and cooling intensity of 500 (bottom)/1000 (side) W·m^-2·K^-1.