通过实验方法和基于MICRESS的相场模型，对Fe-0.6%C-2%Mn (质量分数)合金在720和740℃等温时的珠光体-奥氏体相变进行研究。实验结果表明，由动力学曲线可粗略估测出奥氏体/珠光体界面迁移速率，并通过Mn在新生奥氏体中的分布，验证奥氏体相变模式在720和740℃等温时分别为间隙型合金元素C的扩散控制(PLE)模式和置换型合金元素的扩散控制(NPLE)模式。利用相场模拟研究γ、α和界面扩散通道的引入对PLE和NPLE模式下奥氏体/珠光体界面迁移速率的影响，其中NPLE模式下C元素的主要扩散通道可能为奥氏体和铁素体；在PLE模式下，Mn主要通过相界面进行扩散，但相较于奥氏体扩散通道，铁素体扩散通道对相界面迁移产生更大贡献，因此在热动力学分析中不可将其忽略，这与对PLE模式分析的传统认知有所差异。

In the development of advanced steel, accurate and detailed knowledge about the kinetics of phase transformations and microstructure formation is critical. The critical issue in pearlite-austenite transformation is the consideration of diffusional paths of the alloy element. Simulation has been an available method to study the diffusion of alloy elements and the migration rate of the phase boundary in the complex morphological evolution of austenite growth. The isothermal pearlite-austenite transformations at 720 and 740^oC in Fe-0.6%C-2%Mn (mass fraction) alloy were studied by phase-field methods based on MICRESS. At different temperatures, the effects of diffusional paths on the austenite transformation were discussed. To achieve a semiquantitative verification of the simulated results, the migration rates of the austenite/pearlite boundary at 720 and 740^oC were estimated from the experimental kinetics curves by fitting the JMA equation. By measuring the Mn profile in austenite, the modes of the austenization at 720 and 740^oC can be verified as partitioned local equilibrium (PLE) and non-partitioned local equilibrium (NPLE) modes. The heterogeneous distribution of Mn in austenite at 740^oC can be observed with STEM-EDS. However, the homogenous distribution of Mn can be found near the pearlite/austenite boundary in austenite at 720^oC. The cases considering the γ, α, and interface-diffusional paths were simulated by phase-field methods to compare with the migration rates of the austenite/pearlite boundary. Because carbon is an interstitial element in steel and has an interstitial diffusional mechanism, it can be speculated reasonably that the diffusion of C mainly proceeded in austenite and ferrite through the considerations of the atom-size of carbon and the experimental results. Phase-field methods were used to study Mn diffusion in the lamellar pearlite-austenite transformation. With the analysis of the experimental estimations, the interface-diffusional path was observed as the dominant path for the Mn diffusion. It is because the Mn atoms have greater diffusivity in interfaces than in γ or α-diffusional paths. Furthermore, the diffusional activation energy is closely related to the diffusivity of Mn at the interface. Moreover, compared with the γ-diffusional path, the diffusional flux of Mn in ferrite is much larger than that in austenite. Thus, it can be concluded that the contribution of the α-diffusional path to the migration rate of the pearlite/austenite boundary is larger than that of the γ-diffusional path. As a result, considering the α-diffusional path in the thermodynamics analysis under NPLE mode makes more sense. However, ignoring the interface- and α-diffusional path, which is different from the traditional cognition in PLE mode, will result in a magnitude error for the thermodynamics analysis.