Medium Mn steel is one of the promising high strength steels with excellent ductility. There is, however, an issue that extended intercritical annealing is necessary to enrich Mn into austenite (γ). To obtain sufficient stable γ by short intercritical annealing, the effects of the pre-existed γ morphology on the kinetics of reverted γ formation and the elemental partitioning behavior during annealing were investigated using a medium Mn steel (Fe-0.16Cwt%-0.5wt%Si-3.5wt%Mn). Three different initial microstructures, comprising only martensite, martensite with a thin-film of γ, and martensite with a thick-film of γ, were prepared by controlling the interrupted quenching temperature after austenization. The fractions of reverted γ of these samples were evaluated during intercritical annealing. Although the fraction of γ during annealing increased as the amount of pre-existed γ increased, the largest amount of retained γ after cooling was obtained in the sample containing thin-film pre-existed γ with a volume fraction of 6 %, and not in the sample having thick-film pre-existed γ with a volume fraction of 35 %. A three-dimensional atom probe (3DAP) analysis and a simulation using diffusion-controlled transformations (DICTRA) software revealed that stable retained γ was obtained by homogeneous enrichment of Mn into γ due to the short diffusion distance of Mn in γ in the sample with thin-film pre-existed γ. Thus, it was found that a large amount of retained γ enriched with C and Mn could be obtained in medium Mn steels via short intercritical annealing by forming thin-film γ before intercritical annealing.

中文翻译：

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通过控制中等锰钢中预先存在的奥氏体形态来加速残余奥氏体的形成和元素分配

中锰钢是具有优异延展性的有前途的高强度钢之一。然而，存在一个问题，即需要扩展临界间退火才能将 Mn 富集到奥氏体 （γ） 中。为了通过短临界间退火获得足够的稳定γ，使用中等锰钢 （Fe-0.16Cwt%-0.5wt%Si-3.5wt%Mn） 研究了预先存在的γ形貌对退火过程中恢复γ形成动力学和元素分配行为的影响。通过控制奥氏体化后的间断淬火温度，制备了三种不同的初始微观组织，仅包括马氏体、具有γ薄膜的马氏体和具有γ厚膜的马氏体。在临界间退火期间评估这些样品的还原γ分数。尽管退火过程中γ的分数随着预先存在γ量的增加而增加，但冷却后保留γ量最大的是在含有体积分数为 6 % 的薄膜预先存在γ的样品中获得的，而不是在体积分数为 35 % 的厚膜预先存在γ样品中获得的。三维原子探针 （3DAP） 分析和使用扩散控制变换 （DICTRA） 软件的模拟表明，由于在薄膜预先存在的 Mn 样品中γ扩散距离短，因此通过将 Mn 均匀富集成γ获得了稳定的保留γ γ。因此，发现在临界间退火之前形成薄膜γ，通过短的临界间退火，可以在中锰钢中获得大量富含 C 和 Mn 的保留γ。