Medium manganese steels are promising alloys for highly demanding sheet steel applications. However, cold-rolled intercritically annealed ultrafine-grained dual-phase medium manganese steels exhibit Lüders banding, which is detrimental for the mechanical properties and for the surface finish after forming. Therefore, it is essential to prevent the formation of Lüders bands. To achieve this, it is crucial to understand the underlying micromechanisms of their formation and propagation. While the nucleation of Lüders bands was studied before in these alloys, understanding of their propagation is lacking. Here, we use electron channelling contrast imaging, with a resolution of ~8 nm to examine the defect populations within and across the Lüders front. While macroscopic digital image correlation shows a uniform strain gradient across the Lüders front, quasi in-situ tensile tests in combination with microscopic electron channelling contrast imaging investigations reveal strain localized regions (termed plastic zones) within the Lüders front. These plastic zones are aligned with the macroscopic Lüders front and parallel in nature, with less deformed regions sandwiched between them. Additionally, it is observed that the size and distribution of the plastic zones are affected by the mechanical stability of austenite. We further demonstrate the role of strain partitioning between the austenite and ferrite (austenite being the softer phase) in the formation of the plastic zones.

中锰钢是用于高要求钢板应用的有前途的合金。然而，冷轧临界间退火超细晶双相中锰钢表现出吕德斯带，这对机械性能和成型后的表面光洁度是不利的。因此，必须防止形成吕德斯带。为了实现这一点，了解它们形成和传播的潜在微观机制至关重要。虽然之前在这些合金中研究了 Lüders 带的成核，但对它们的传播缺乏了解。在这里，我们使用分辨率约为 8 nm 的电子通道对比成像来检查 Lüders 前沿内和跨过的缺陷群。虽然宏观数字图像相关性显示了跨越 Lüders 前沿的均匀应变梯度，准原位拉伸试验与显微电子通道对比成像研究相结合，揭示了 Lüders 前沿内的应变局部区域（称为塑性区）。这些塑性区与宏观 Lüders 前沿对齐并在本质上平行，中间夹有变形较小的区域。此外，据观察，塑性区的大小和分布受奥氏体机械稳定性的影响。我们进一步证明了奥氏体和铁素体（奥氏体是较软的相）之间的应变分配在塑性区形成中的作用。这些塑性区与宏观 Lüders 前沿对齐并在本质上平行，中间夹有变形较小的区域。此外，据观察，塑性区的大小和分布受奥氏体机械稳定性的影响。我们进一步证明了奥氏体和铁素体（奥氏体是较软的相）之间的应变分配在塑性区形成中的作用。这些塑性区与宏观 Lüders 前沿对齐并在本质上平行，中间夹有变形较小的区域。此外，据观察，塑性区的大小和分布受奥氏体机械稳定性的影响。我们进一步证明了奥氏体和铁素体（奥氏体是较软的相）之间的应变分配在塑性区形成中的作用。