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金属学报  2016, Vol. 52 Issue (9): 1096-1104    DOI: 10.11900/0412.1961.2015.00627
  论文 本期目录 | 过刊浏览 |
基于热溶质对流及晶粒运动的柱状晶-非球状等轴晶混合三相模型*
李军1,葛鸿浩1,GE Honghao1,WU Menghuai2,3(),李建国1
1 上海交通大学材料科学与工程学院, 上海 200240
2 Simulation and Modeling of Metallurgical Processes, University of Leoben, A-8700, Austria
3 Christian-Doppler Lab for Advanced Process Simulation of Solidification and Melting, University of Leoben, A-8700, Austria
A COLUMNAR & NON-GLOBULAR EQUIAXED MIXED THREE-PHASE MODEL BASED ON THERMOSOLUTAL CONVECTION AND GRAIN MOVEMENT
Jun LI1,Honghao GE1,Menghuai WU2,3(),Andreas LUDWIG2,Jianguo LI1
1 School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
2 Simulation and Modeling of Metallurgical Processes, University of Leoben, A-8700, Austria
3 Christian-Doppler Lab for Advanced Process Simulation of Solidification and Melting, University of Leoben, A-8700, Austria
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摘要: 

基于Eulerian-Eulerian方法, 阐述了简化枝晶状等轴晶、柱状晶以及金属液三相完全混合的凝固模型. 模型考虑了等轴晶的移动及柱状晶对等轴晶的捕获, 跟踪了柱状晶尖端的位置并考虑了等轴晶和柱状晶的相互竞争生长, 因此该模型具备了预测柱状晶向等轴晶转变(CET)的能力; 为了在不过量增加计算量的前提下提高模型的精度, 模型对等轴晶采取了简单的枝晶化处理, 即采用简化方法描述等轴晶包络线内固相分数. 分别模拟了3.25和25 t钢锭的凝固过程, 成功预测了大型钢锭凝固过程所形成的底部锥形负偏析、“类-A型”偏析以及CET等现象. 分析认为长细形状铸锭中出现的顶部负偏析区, 是由于凝固后期所形成的局部小钢锭及等轴晶在其内部的沉积聚集而成.

关键词 数值模拟宏观偏析钢锭晶粒运动CET    
Abstract

The prediction of the macrosegregation in large ingot is a challenging issue due to the size of the ingots and the variety of the phenomena to be accounted for, such as thermal-solutal convection of the liquid, equiaxed grain motion, evolution of grain morphology by suitably considering a coupled grain growth model in the macroscopic solidification model, the columnar-to-equiaxed transition (CET), and shrinkage, etc.. Each of these phenomena is very important to the solidification pattern, while it is impossible for one model to consider all the phenomena together until now due to the computation power limited. Thus, the model capability and computational cost should be counterpoised for the simulation of large ingot. In this work, a mixed three-phase (simplified dendritic-equiaxed, columnar and liquid) solidification model is described based on Eulerian-Eulerian approach and volume average method. The model considers the thermosolutal buoyancy flow, the movement of equiaxed crystal, and the capture of the equiaxed crystals by growing columnar tree trunks. The mechanical interaction and impingement between columnar and equiaxed crystals are considered which give the capability to predict CET. In order to enhance the model capability without increasing the computational cost significantly, a simplified method is proposed to consider the dendritic of equiaxed crystal. This model is employed to simulate the formation process of macrosegregation for two different steel ingots (3.25 and 25 t). The general macrosegregation pattern predicted by this model includes the cone of negative segregation in the bottom of ingot, quasi-A-segregation in the columnar zone, and positive segregation in the top region, which are quite similar to the classic knowledge. The CET zones are also predicted. Although there is still some quantitative discrepancy, the macrosegregation distribution predicted by this model is quite similar to the experimental measurements. The non-globular equiaxed three-phase mixed model results are compared with the globular-equiaxed mixed three-phase model ones, which indicated that for large ingots the equiaxed dendritic structure plays an important role in liquid flow and it affects final characteristic of macrosegregation. It is predicted successfully that a negative segregation zone would be formed in the upper region due to the formation of a local mini-ingot and the subsequent sedimentation and piling up of equiaxed grains within the mini-ingot.

Key wordsnumerical simulation    macrosegregation    steel ingot    grain movement    CET
收稿日期: 2015-12-07      出版日期: 2016-06-22
基金资助:* 克里斯汀-多普勒(先进凝固和融化模拟实验室)项目, 国家自然科学基金项目51404152, 国家重点基础研究发展计划项目2011CB012900, 上海市浦江人才支持计划项目14PJ1404800和上海市国际合作项目14140711000资助

引用本文:

李军,葛鸿浩,GE Honghao,WU Menghuai,李建国. 基于热溶质对流及晶粒运动的柱状晶-非球状等轴晶混合三相模型*[J]. 金属学报, 2016, 52(9): 1096-1104.
Jun LI,Honghao GE,Menghuai WU,Andreas LUDWIG,Jianguo LI. A COLUMNAR & NON-GLOBULAR EQUIAXED MIXED THREE-PHASE MODEL BASED ON THERMOSOLUTAL CONVECTION AND GRAIN MOVEMENT. Acta Metall, 2016, 52(9): 1096-1104.

链接本文:

http://www.ams.org.cn/CN/10.11900/0412.1961.2015.00627      或      http://www.ams.org.cn/CN/Y2016/V52/I9/1096

图1  枝晶状等轴晶示意图[28]
图2  3.25 t钢锭示意图及相关初始条件和边界条件
图3  3.25 t钢锭凝固进程
图4  3.25 t钢锭偏析结果
Property Symbol Unit Value
Melting point of pure iron Tf K 1805.15
Liquidus slope m K%-1 -80.45
Equilibrium partition coefficient k - 0.36
Reference density ρl, ρe, ρc kgm-3 6990
Solid-liquid density difference Δρ kgm-3 150
Specific heat cpl, cpc, cpe Jkg-1K-1 500
Thermal conductivity kl, ke, kc Wm-1K-1 34.0
Latent heat L Jkg-1 2.71×105
Viscosity μ kgm-1s-1 4.2×10-3
Thermal expansion coefficient βT K-1 1.07×10-4
Solutal expansion coefficient βc %-1 1.4×10-2
Dendritic arm spacing λ1 m 5×10-4
Diffusion coefficient (liquid) Dl m2s-1 2.0×10-8
Diffusion coefficient (solid) De, Dc m2s-1 1.0×10-9
表1  3.25 t钢锭凝固过程模型的热物性参数
图5  25 t钢锭示意图及相关初始条件和边界条件、模拟与实验偏析结果
图6  铸锭上部负偏析区形成示意图
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