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金属学报  2017, Vol. 53 Issue (6): 760-768    DOI: 10.11900/0412.1961.2016.00468
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Fe-C-Mn三元合金中奥氏体-铁素体相变的相场模拟
张军1,2,陈文雄2,郑成武2(),李殿中2
1 中国科学技术大学化学与材料科学学院 合肥 2300262 中国科学院金属研究所沈阳材料科学国家(联合)实验室 沈阳 110016
Phase-Field Modeling of Austenite-to-Ferrite Transformation in Fe-C-Mn Ternary Alloys
Jun ZHANG1,2,Wenxiong CHEN2,Chengwu ZHENG2(),Dianzhong LI2
1 School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, China
2 Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
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摘要: 

采用相场法研究了Fe-C-Mn三元合金在临界区等温过程中发生的奥氏体-铁素体相变。基于Gibbs自由能守恒理论,在相场模型中考虑了替换型元素Mn在奥氏体/铁素体相界面内扩散所导致的自由能耗散,描述了Fe-C-Mn三元合金中因Mn在相界面偏聚所导致的相变停滞和相变不完全现象。利用相场模型研究了Mn含量对奥氏体-铁素体相变微观组织转变和相变动力学的影响。结果表明,随着Mn含量的增加,铁素体相的转变速率和体积分数降低,Mn在奥氏体/铁素体相界面内扩散所导致的溶质拖曳现象越明显,相变不完全程度加剧。

关键词 相场法奥氏体铁素体Gibbs自由能耗散相变不完全    
Abstract

The effect of Mn on the austenite-to-ferrite transformation has been widely studied by both physical models and experiments due to its technological importance for alloy design in steel industries. In recent years, an increasing interest of this issue is moved onto the effect of alloying element on the migrating interface during the austenite-to-ferrite transformation. For ternary Fe-C-Mn alloys, the interfacial condition is more complicated than that of binary Fe-C alloys in view of the large difference in the diffusivity between the interstitial and substitutional alloying elements. Generally speaking, there are two main concepts, i.e. the paraequilibrium model and the local-equilibrium model, which have been proposed to describe the phase transformation kinetics in ternary Fe-C-Mn alloys based on different assumptions about the diffusion of the substitutional elements. And many modeling attempts have been made to study the effect of Mn on the migration kinetics by using these theories. In this work, a multi-phase-field (MPF) model coupling with a Gibbs-energy dissipation model was developed to simulate the isothermal austenite-to-ferrite transformation in ternary Fe-C-Mn alloys. This model has considered the Mn diffusion inside the migrating interface in a physical manner and takes its effect on the transformation kinetics into account. Comparison simulations were made to analyze the difference in the transformation kinetics and ferrite morphologies with and without considering the energy dissipation at the moving interface. It shows that the incomplete transformation phenomenon does occur due to the Mn diffusion inside interface. The modified MPF model was then used to study the effect of Mn contents on the microstructures and kinetics of the phase transformations. It is found that the ferrite growth along the austenite/austenite boundaries is faster than that in the perpendicular direction. This difference is intensified with increasing the Mn concentration, which hence leads to the ferrite morphology changed from elliptical to flat alike. It also produces a slower transformation kinetics and a larger degree of the incomplete transformation when increasing the Mn concentration.

Key wordsphase-field method    austenite    ferrite    Gibbs-energy dissipation    incomplete transformation
收稿日期: 2016-10-21      出版日期: 2017-03-31
基金资助:国家自然科学基金项目Nos.51371169和51401214

引用本文:

张军,陈文雄,郑成武,李殿中. Fe-C-Mn三元合金中奥氏体-铁素体相变的相场模拟[J]. 金属学报, 2017, 53(6): 760-768.
Jun ZHANG,Wenxiong CHEN,Chengwu ZHENG,Dianzhong LI. Phase-Field Modeling of Austenite-to-Ferrite Transformation in Fe-C-Mn Ternary Alloys. Acta Metall, 2017, 53(6): 760-768.

链接本文:

http://www.ams.org.cn/CN/10.11900/0412.1961.2016.00468      或      http://www.ams.org.cn/CN/Y2017/V53/I6/760

图1  相界面处Mn化学势的分布示意图
图2  γ→α相变过程中耗散自由能(ΔGdis)的变化
Parameter (unit) Value Ref.
σα,γ(Jm-2) 0.4 [20,31]
σγ,γ(Jm-2) 0.79 [31]
DintMn(cm2s-1) 0.5exp-247650/RT [20]
MCγ( m2molJ-1s-1) 1RT1.5×10-5exp-142000/RT [32]
MCα( m2molJ-1s-1) 1RT2.2×10-4exp-125000/RT [32]
Mp( mmolJ-1s-1) 0.5exp-140000/RT [32]
表1  模拟所采用的物理参数
图3  973 K等温时单个铁素体晶粒的生长过程
图4  973 K等温时铁素体晶粒的生长动力学
图5  相界面迁移过程中ΔGchem与ΔGdis的变化情况
图6  不同合金的奥氏体-铁素体化学驱动力(ΔGchem)与相变温度(T)的关系
图7  1043 K等温时不同合金相变过程中微观组织演化的模拟结果
图8  1043 K等温时不同合金相变过程中C浓度场演化的模拟结果
图9  不同合金在1043 K等温时的转变动力学
图10  不同Mn含量下相变不完全的转变程度
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