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金属学报  2018, Vol. 54 Issue (5): 801-808    DOI: 10.11900/0412.1961.2017.00557
  金属材料的凝固专刊 本期目录 | 过刊浏览 |
侯渊, 任忠鸣(), 王江, 张振强, 李霞
上海大学省部共建高品质特殊钢冶金与制备国家重点实验室 上海 200072
Effect of Longitudinal Static Magnetic Field on the Columnar to Equiaxed Transition in Directionally Solidified GCr15 Bearing Steel
Yuan HOU, Zhongming REN(), Jiang WANG, Zhenqiang ZHANG, Xia LI
State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai 200072, China
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进行了外加纵向静磁场下GCr15轴承钢的定向凝固实验,考察了纵向静磁场对试样凝固过程中柱状枝晶向等轴枝晶转变(columnar to equiaxed transition,CET)的影响。结果表明,在温度梯度(104 K/cm)和抽拉速率(20 μm/s)一定时,随着磁场强度的增加(0~5 T),试样棒边缘柱状枝晶的生长逐渐地遭到破坏,从而发生不同程度的CET;当磁场强度和温度梯度分别为4 T和104 K/cm时,在较低抽拉速率(5 μm/s)下,试样的凝固组织发生了完全CET;在试样发生完全CET后,其合金元素分布趋于均匀。结合数值模拟,可将这些现象归结为纵向静磁场与热电流相互作用产生的热电磁力对枝晶和熔体的作用所致。

关键词 GCr15轴承钢纵向静磁场定向凝固偏析柱状晶向等轴晶转变    

Columnar to equiaxed transition (CET) generating a fine-grain structure of GCr15 bearing steel with the homogeneity of the solute contents and the rather small amount of internal defects is often desired in solidification processes. In recent years much attention has been paid to the effect of static magnetic fields on the CET of Al base alloys, Pb-Sn alloys and Ni base superalloys. However, there are few papers to investigate the effect of static magnetic fields on the CET of GCr15 bearing steel. The present work investigates how longitudinal static magnetic fields affect the CET in directionally solidified GCr15 bearing steel. Experimental results show that columnar dendrites degenerate and transform into equiaxed dendrites at the edge of the sample as the longitudinal static magnetic field increases at pulling rate of 20 μm/s and temperature gradient of 104 K/cm. The dendritic morphology without the longitudinal static magnetic field is regular and columnar at pulling rate of 5 and 50 μm/s and temperature gradient of 104 K/cm. When the 4 T longitudinal static magnetic field is applied, the dendritic morphology is still regular and columnar at pulling rate of 50 μm/s and temperature gradient of 104 K/cm. However, the CET occurs at low pulling rate of 5 μm/s and temperature gradient of 104 K/cm. This phenomenon is simultaneously accompanied by more uniformly distributed alloying elements. The corresponding numerical simulations verify that the thermoelectric (TE) magnetic force is induced by the interaction between the longitudinal static magnetic field and TE current. Owing to TE magnetic force localized into the root of the dendrite, the dendritic fragments detach from the primary dendrites. Then the TE magnetic convection induced by TE magnetic force acting on the melt transports the fragments from the interdendritic spacing to the region ahead of columnar dendrites. It can be deduced from above phenomena that the TE magnetic force leads to the CET under the longitudinal static magnetic field.

Key wordsGCr15 bearing steel    longitudinal static magnetic field    directional solidification    microsegregation    columnar to equiaxed transition
收稿日期: 2017-12-25     
ZTFLH:  TG146  
基金资助:资助项目 国家自然科学基金项目Nos.U1560202、51604171、51690162,上海市科委项目No.17JC1400602及上海商用航空发动机联合创新项目Nos.AR910 和AR911

作者简介 侯 渊,男,1985年生,博士生


侯渊, 任忠鸣, 王江, 张振强, 李霞. 纵向静磁场对定向凝固GCr15轴承钢柱状晶向等轴晶转变的影响[J]. 金属学报, 2018, 54(5): 801-808.
Yuan HOU, Zhongming REN, Jiang WANG, Zhenqiang ZHANG, Xia LI. Effect of Longitudinal Static Magnetic Field on the Columnar to Equiaxed Transition in Directionally Solidified GCr15 Bearing Steel. Acta Metall Sin, 2018, 54(5): 801-808.

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图1  纵向静磁场下Bridgman 定向凝固装置示意图
图2  温度梯度和抽拉速率分别为104 K/cm和20 μm/s时GCr15轴承钢在不同纵向静磁场强度下固/液界面处纵截面的组织
图3  温度梯度为104 K/cm和有无4 T磁场作用时GCr15轴承钢在不同抽拉速率下固/液界面处纵截面的组织
图4  在温度梯度和抽拉速率分别为104 K/cm和5 μm/s时,有无4 T磁场时GCr15轴承钢在固/液界面下15 mm处Cr元素的径向分布
Parameter Unit Value in solid Value in liquid
Absolute thermoelectric power S VK-1 -1×10-6 -4×10-6
Dynamic viscosity μ Pas - 5.5×10-3
Electrical conductivity σ Ω-1m-1 8.5×105 7.2×105
Density ρ kgm-3 7.4×103 7.02×103
Thermal conductivity λ Wm-1K-1 32.5 31.2
表1  GCr15轴承钢数值模拟的相关参数[32,33,34]
图5  在温度梯度和抽拉速率分别为104 K/cm和20 μm/s时,5 T纵向静磁场下GCr15轴承钢单个柱状枝晶的几何模型、热电流分布和作用于枝晶上的应力的分布
图6  在温度梯度和抽拉速率分别为104 K/cm和50 μm/s时,5 T纵向静磁场下GCr15轴承钢柱状枝晶阵列的几何模型、热电流分布、热电磁对流的分布和糊状区内不同z轴位置x-y平面上热电磁对流的分布
图7  有无纵向静磁场下定向凝固GCr15轴承钢柱状枝晶向等轴枝晶转变(CET)示意图
Parameter Unit Value
Heterogeneous nuclei density N0 m-3 9×108
Supercooling necessary for
nucleation ΔTN
K 1.5
Diffusion coefficient D m2s-1 4.79×10-9
Partition coefficient k - 0.34
Liquidus slope m K%-1 -78
Gibbs-Thomson parameter Γ Km 1.9×10-7
表2  计算GCr15轴承钢CET图的相关参数[31,32,42]
图3  有无纵向静磁场下定向凝固GCr15轴承钢CET图
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