为了探究Mn元素偏析对中锰钢力学性能、微观结构及变形机制的影响，本工作以一种奥氏体基双相中锰钢(0.3C-11Mn-2.7Al-1.8Si-Fe，质量分数，%)为研究对象，对比分析了Mn偏析对显微组织的影响，着重探究了Mn偏析对冷轧退火后中锰钢力学行为的微观作用机制。结果表明，Mn偏析使得中锰钢中奥氏体表现出带状分布特征，富Mn偏析带内奥氏体晶粒粗大且稳定性高，铁素体晶粒细小且分布稀疏。塑性变形过程中，无偏析区内奥氏体的主控变形机制为孪晶和马氏体相变，即相变诱导塑性(TRIP) + 孪晶诱导塑性(TWIP)效应共存，但相变速率较快。富Mn区奥氏体稳定性增加，变形机制虽为马氏体相变，但TRIP效应受限。与均质非偏析中锰钢相比，尽管含富Mn区中锰钢细晶区域可提供较高的加工硬化能力，但塑性与断裂韧性明显降低。

Improvements in passenger safety and fuel efficiency are crucial issues in the automotive industry. The use of advanced high-strength steel (AHSS) in automotive parts has been suggested as a solution to these issues because it enables large weight reduction and good crash worthiness. Strength and ductility are the key mechanical properties of automotive AHSS. However, high strength is often accompanied by low ductility, resulting in the so-called strength-ductility trade-off dilemma. Currently, there is an increasing demand for automotive AHSS that exhibits a balance between strength and ductility. Lightweight and high-strength medium Mn steel (MMnS with a Mn mass fraction of 3%-12%), as a representative example of the third-generation automotive AHSS, has an excellent combination of strength and plasticity due to the effective usage of the coupled transformation-induced plasticity (TRIP) effect and twinning-induced plasticity (TWIP) effect of the metastable austenite constituent upon deformation. To further improve comprehensive mechanical properties, MMnS with a high Mn content were developed to increase the austenite fraction. Thus, a duplex structure with an ultrafine ferrite and austenite matrix was formed. However, Mn segregation is likely to occur in MMnS with increasing Mn content, especially in the cases of Mn > 10% (mass fraction), which considerably influences MMnS's performance. Therefore, the effects of Mn segregation on the overall mechanical properties, microstructure, and deformation mechanism of MMnS need to be elucidated in more details. In this paper, the influence of Mn segregation on the microstructure and mechanical properties of MMnS with an austenite-ferrite duplex structure and a nominal composition of 0.3C-11Mn-2.7Al-1.8Si-Fe was systemically investigated. Specifically, the underlying mechanism of Mn segregation that affects the mechanical and microstructural behavior of cold-rolled and annealed MMnS was analyzed. The results show that Mn segregation causes the formation of a Mn-rich banded structure, where the grain size of austenite is larger, austenite stability is higher, and fine ferrite is distributed more sparsely on the austenite matrix compared with the case without Mn segregation. The dominant plastic deformation mechanism of austenite in the non-Mn segregation zone involves martensitic transformation and twinning, leading to the coupled TRIP + TWIP effect, while the rate of martensitic transformation is higher than those without Mn segregation. However, the martensitic transformation is inhibited in the austenite of the Mn-rich structure because of its higher stability, limiting the TRIP effect. Consequently, the test MMnS with Mn segregation shows lower ductility and fracture resistance than those without Mn segregation; moreover, its finer austenite enhances the work-hardening capacity.