摘要
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.
基金
financial support from the National Natural Science Foundation of China(Grant U1860109,51922054,U1808208 and U1764252)
financial support from the National Natural Science Foundation of China(Grant 51771100)
financial support from the National Natural Science Foundation of China(Grant 51771097)
Beijing Natural Science Foundation(2182024)
the Science Challenge Project(Grant TZ2018004)
financial support from China postdoctoral science foundation(2018M631459)。
