Phase-field analysis of quenching and partitioning in a polycrystalline Fe-C system under constrained-carbon equilibrium condition
Phase-field analysis of quenching and partitioning in a polycrystalline Fe-C system under constrained-carbon equilibrium condition
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DOI：
10.1016/j.commatsci.2018.12.023
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发表时间：
2019-03-01
影响因子：
3.3
通讯作者：
Nestler, Britta
中科院分区：
文献类型：
--
作者：
Amos, P. G. Kubendran;Schoof, Ephraim;Nestler, Britta
残余奥氏体能显著提高钢的力学性能。特别是，它已被证明，最近开发的热处理技术称为淬火和分区（Q&P）稳定奥氏体有效。本文采用相场方法模拟了多晶Fe-C系淬火和分配过程中的相变和碳扩散。弹性相场模型结合了CALPHAD数据库中的化学驱动力，恢复了锐界面解，模拟了三种不同淬火温度下的马氏体（α '）相变。由此产生的马氏体体积分数与分析预测完全一致。首次，在这项研究中，约束碳平衡（CCE）的条件被引入到多晶设置产生预测的分配端点。在CCE条件下，采用以化学势为动力学变量的相场模型分析了碳在两种不同成分合金中的分配。残余奥氏体的体积分数和分布确定从碳分布和它的时间演变过程中的分配进行了研究。据确定，在分配的初始阶段，由于扩散率和CCE端点的显著差异，碳沿着γ α '-界面积累在奥氏体（γ）中。这种积累使界面附近的奥氏体稳定。然而，取决于马氏体体积分数和合金成分，稳定奥氏体的演变变化。此外，相分布对残余奥氏体时间演化动力学的影响也得到了阐明。
Mechanical properties of steels are significantly enhanced by retained austenite. Particularly, it has been shown that a recently developed heat-treatment technique called Quenching and Partitioning (Q&P) stabilises austenite effectively. In the present work, the phase-field approach is adopted to simulate the phase transformation and carbon diffusion, which respectively accompanies the quenching and partitioning process of the polycrystalline Fe-C system. By incorporating the chemical driving-force from the CALPHAD database, the elastic phase-field model, which recovers the sharp-interface solutions, simulates the martensite (alpha') transformation at three different quenching temperatures. The resulting martensite volume-fractions are in complete agreement with the analytical predictions. For the first time, in this study, the constrained carbon equilibrium (CCE) condition is introduced in the polycrystalline set-up to yield the predicted partitioning endpoints. Under the CCE condition, the carbon partitioning in two alloys of varying composition is analysed through the phase-field model which employs chemical potential as the dynamic variable. The volume fraction and distribution of retained austenite is determined from the carbon distribution and its temporal evolution during the partitioning is investigated. It is identified that in the initial stages of partitioning carbon gets accumulated in the austenite (gamma) along the gamma alpha'-interface, owing to the substantial difference in the diffusivities and CCE endpoints. This accumulation stabilises the austenite adjacent to the interface. However, depending on the martensite volume-fraction and the alloy composition, the evolution of the stabilised austenite varies. Furthermore, the influence of the phase distribution on the kinetics of the temporal evolution of retained austenite is elucidated.