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金属学报  2024, Vol. 60 Issue (11): 1531-1544    DOI: 10.11900/0412.1961.2022.00544
  研究论文 本期目录 | 过刊浏览 |
钛合金三次真空自耗电弧熔炼过程中的宏观偏析传递行为
郭杰1, 黄立清1,2, 吴京洋1, 李俊杰1, 王锦程1, 樊凯2()
1 西北工业大学 凝固技术国家重点实验室 西安 710072
2 湖南湘投金天钛业科技股份有限公司 常德 415001
Evolution of Macrosegregation During Three-Stage Vacuum Arc Remelting of Titanium Alloys
GUO Jie1, HUANG Liqing1,2, WU Jingyang1, LI Junjie1, WANG Jincheng1, FAN Kai2()
1 State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China
2 Hunan Xiangtou Goldsky Titanium Industry Technology Co. Ltd., Changde 415001, China
引用本文:

郭杰, 黄立清, 吴京洋, 李俊杰, 王锦程, 樊凯. 钛合金三次真空自耗电弧熔炼过程中的宏观偏析传递行为[J]. 金属学报, 2024, 60(11): 1531-1544.
Jie GUO, Liqing HUANG, Jingyang WU, Junjie LI, Jincheng WANG, Kai FAN. Evolution of Macrosegregation During Three-Stage Vacuum Arc Remelting of Titanium Alloys[J]. Acta Metall Sin, 2024, 60(11): 1531-1544.

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摘要: 

宏观偏析是钛合金真空自耗电弧熔炼铸锭中的一种典型凝固缺陷,且在后续加工过程中难以消除,对铸锭性能具有重要影响。实际钛合金铸锭生产中通常采用三次真空自耗熔炼工艺,以减少夹杂、提高成分均匀性,然而当前对于宏观偏析在多次熔炼中的传递规律仍缺乏清晰理解。本工作通过数值模拟方法对钛合金三次真空自耗熔炼过程中熔池内的液相流动及溶质偏析行为进行分析,发现前次铸锭的径向成分不均匀会在对流作用下消除,对下一次熔炼铸锭的宏观偏析无影响;而前次铸锭沿轴向的成分不均匀会传递给下一次熔炼的铸锭,这一传递效果在熔池深度增大时由于对流作用而被削弱。此外,模拟结果还表明,如果三次熔炼中始终保持铸锭正置作电极,铸锭宏观偏析最重;至少一次将铸锭反置作电极,可显著减轻宏观偏析。对TC4合金采用真实熔炼工艺参数进行模拟,获得的Al元素及V元素偏析规律与实验观测结果基本吻合。

关键词 宏观偏析凝固真空电弧熔炼钛合金数值模拟    
Abstract

Macrosegregation is a typical solidification defect formed during vacuum arc remelting (VAR) process. This defect adversely affects the property of ingots as the defect sustains even in the subsequent heat treatment process. In the industrial production of titanium alloys, VAR is repeated thrice to eliminate inclusions and improve the homogenization of composition. However, the evolution of macrosegregation during the different stages of the triple VAR process remains unclear. In this study, the melt flow behavior and macrosegregation of titanium ingots in the multistage VAR process are examined via solidification simulations, considering both buoyancy and electromagnetic force. The results show that the strong fluid flow in the upper part of melting pool eliminates nonuniform concentration along the radial direction of the electrode. In contrast, the nonuniform concentration along the axial direction can be inherited in the sequential ingot. However, with the increase in the depth of melt pool, the sustained melt flow from the bottom to upside can reduce the axial macrosegregation delivery. In addition, the use of the previous ingot directly as the electrode for the subsequent remelting process results in severe macrosegregation. However, turning the previous ingot upside-down at least once during the three-stage VAR process can substantially reduce the macrosegregation. Overall, the simulated macrosegregation of Al and V elements in TC4 ingot agree well with that observed in experiment.

Key wordsmacrosegregation    solidification    vacuum arc remelting    titanium alloy    numerical simulation
收稿日期: 2022-10-25     
ZTFLH:  TG244  
基金资助:凝固技术国家重点实验室自主课题项目(2020-TS-06)
通讯作者: 樊 凯,fk@xtjtty.com,主要从事凝固理论及数值模拟研究
Corresponding author: FAN Kai, senior engineer, Tel: (0736)7326915, E-mail: fk@xtjtty.com
作者简介: 郭 杰,男,1998年生,硕士生
Parameter descriptionSymbolValueUnit
Densityρ4170kg·m-3
Diffusion coefficient for V in liquidDlV4.0 × 10-9m2·s-1
Diffusion coefficient for Al in liquidDlAl4.0 × 10-9m2·s-1
Latent heat of fusionL3.77 × 105J·kg-1
Partition coefficient for VkpV0.95-
Partition coefficient for AlkpAl1.08-
Liquidus slope for VmV-2.0K·%-1 (mass fraction)
Liquidus slope for AlmAl-4.44K·%-1 (mass fraction)
Solutal expansion coefficient for VβSV-0.35%-1 (mass fraction)
Solutal expansion coefficient for AlβSAl0.4%-1 (mass fraction)
Heat capacitycp975J·kg-1·K-1
Thermal conductivitykT32.7W·m-1·K-1
Thermal expansion coefficientβT6.5 × 10-5K-1
Viscosity of liquidμl3.1 × 10-3kg·m-1·s-1
Electric conductivityσ1.0 × 106S·m-1
Magnetic permeabilityμ01.26 × 10-6H·m-1
表1  计算模型采用的物性参数
图1  三次真空自耗电弧熔炼(VAR)过程中电极放置方案示意图
图2  第一次熔炼过程中溶质场及流场演化
图3  第二次熔炼时的溶质场及流场演化
图4  第二次熔炼过程中不同时刻下径向浓度分布曲线
图5  第二次熔炼时电极及铸锭中径向平均浓度随高度变化曲线
图6  第三次熔炼时的溶质场及流场演化
图7  第三次熔炼过程中不同时刻下径向浓度分布曲线
图8  第三次熔炼时电极及铸锭中径向平均浓度随高度变化曲线
图9  全部三次熔炼铸锭最终成分分布对比
图10  各次熔炼铸锭的整体宏观偏析指数(GMI)对比
图11  TC4合金三次熔炼铸锭中V、Al成分分布的模拟结果
图12  TC4合金不同熔炼方案下铸锭中V元素和Al元素的GMI
图13  铸锭取样方式
图14  TC4合金三次熔炼最终铸锭中不同部位径向V浓度分布和Al浓度分布的模拟结果与实验结果对比
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