Austenite formation from a ferrite-cementite mixture is a crucial step during the processing of advanced high strength steels (AHSS). The ferrite-cementite mixture is usually inhomogeneous in both structure and composition, which makes the mechanism of austenite formation very complex. In this contribution, austenite formation upon continuous heating from a designed spheroidized cementite structure in a model Fe-C-Mn alloy was investigated with an emphasis on the role of heating rate in kinetic transitions and element partitioning during austenite formation. Based on partition/non-partition local equilibrium (PLE/NPLE) assumption, austenite growth was found alternately contribute by PLE, NPLE and PLE controlled interfaces migration during slow-heating, while NPLE mode predominately controlled the austenitization by a synchronous dissolution of ferrite and cementite upon fast-heating. It was both experimentally and theoretically found that there is a long-distance diffusion of Mn within austenite of the slow-heated sample, while a sharp Mn gradient was retained within austenite of the fast-heated sample. Such a strong heterogeneous distribution of Mn within austenite cause a large difference in driving force for ferrite or martensite formation during subsequent cooling process, which could lead to various final microstructures. The current study indicates that fast-heating could lead to unique microstructures which could hardly be obtained via the conventional annealing process.

在高级高强度钢（AHSS）的加工过程中，由铁素体-钙钛矿混合物形成奥氏体是至关重要的步骤。铁素体-钙钛矿混合物通常在结构和组成上均不均匀，这使得奥氏体形成的机理非常复杂。在此贡献中，研究了在模型Fe-C-Mn合金中从设计的球化渗碳体组织连续加热时形成的奥氏体，重点是加热速率在奥氏体形成过程中动力学转变和元素分配中的作用。根据分区/非分区局部平衡（PLE / NPLE）假设，发现PLE，NPLE和PLE控制的界面在缓慢加热过程中的迁移交替产生了奥氏体生长，NPLE模式主要通过快速加热时铁素体和渗碳体的同步溶解来控制奥氏体化。从实验和理论上都发现，在缓慢加热的样品的奥氏体中Mn的长距离扩散，而在快速加热的样品的奥氏体中Mn的尖峰保留。Mn在奥氏体中如此强的异质分布会在随后的冷却过程中导致铁素体或马氏体形成的驱动力差异很大，这可能会导致各种最终的显微组织。当前的研究表明，快速加热可能导致独特的微观结构，而传统的退火工艺很难获得这种独特的微观结构。从实验和理论上都发现，在缓慢加热的样品的奥氏体中Mn的长距离扩散，而在快速加热的样品的奥氏体中Mn的尖峰保留。Mn在奥氏体中如此强的异质分布会在随后的冷却过程中导致铁素体或马氏体形成的驱动力差异很大，这可能会导致各种最终的显微组织。当前的研究表明，快速加热可能会导致独特的微观结构，而传统的退火工艺很难获得这种独特的微观结构。从实验和理论上都发现，在缓慢加热的样品的奥氏体中Mn的长距离扩散，而在快速加热的样品的奥氏体中Mn的尖峰保留。Mn在奥氏体中如此强的异质分布会在随后的冷却过程中导致铁素体或马氏体形成的驱动力差异很大，这可能会导致各种最终的显微组织。当前的研究表明，快速加热可能会导致独特的微观结构，而传统的退火工艺很难获得这种独特的微观结构。Mn在奥氏体中如此强的异质分布会在随后的冷却过程中导致铁素体或马氏体形成的驱动力差异很大，这可能会导致各种最终的显微组织。当前的研究表明，快速加热可能会导致独特的微观结构，而传统的退火工艺很难获得这种独特的微观结构。Mn在奥氏体中如此强的异质分布会在随后的冷却过程中导致铁素体或马氏体形成的驱动力差异很大，这可能会导致各种最终的显微组织。当前的研究表明，快速加热可能导致独特的微观结构，而传统的退火工艺很难获得这种独特的微观结构。