For metallic materials, an increase in strength generally results in a decrease in plasticity, and the simultaneous improvement of strength and plasticity (SISP) has been a hot but difficult topic. In this study, through high-nitrogen (N) alloying, a novel high-N twinning-induced plasticity (HN-TWIP) steel was designed. It was surprisingly found that, with higher N content, the SISP was achieved successfully. Compared to 0.3 N, the ultimate tensile strength and uniform elongation of 0.6 N increased by 95 MPa and 5.6 %, respectively. Systematic microstructural analyses indicated that more and thinner twins formed at higher N content during the deformation. Especially, different with conventional TWIP (CV-TWIP) steels, numerous ultrafine nano-twins (<15 nm) were detected in HN-TWIP steels. Combined with the flow stress analyses, their strengthening behavior was found to be attributed to both the N solid solution strengthening and nano-twin strengthening. More importantly, by promoting planar slip, the ultrafine nano-twins provided an additional work-hardening and delayed the necking appearance, which resulted in plasticity enhancement. In other words, the origin of the strength-ductility trade-off avoidance was the nano-twins/ultrafine nano-twins microstructure. Further studies revealed that, by breaking the conflict of low stacking fault energy (SFE) and excellent austenite stability, HN-TWIP steels obtained a breakthrough reduction in SFE. HN-TWIP steels with the extremely low SFE could acquire the special nano-twin microstructure and the SISP mechanical behavior. Accordingly, only by continuously reducing the SFE in the alloying design, the difficult SISP could be realized in TWIP steels. This is a novel and simple strategy for the modification of the metal mechanical properties, and it is meaningful for materials in engineering applications.

中文翻译：

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同时提高强度和可塑性：用于新型高氮 TWIP 钢的纳米孪生结构


对于金属材料，强度的增加通常会导致塑性降低，同时提高强度和塑性 （SISP） 一直是一个热门但困难的话题。在本研究中，通过高氮 （N） 合金化，设计了一种新型高 N 孪晶诱导塑性 （HN-TWIP） 钢。令人惊讶的是，在更高的 N 含量下，SISP 得以成功实现。与 0.3 N 相比，极限拉伸强度和 0.6 N 的均匀伸长率分别提高了 95 MPa 和 5.6 %。系统的微观结构分析表明，在变形过程中，在较高的 N 含量下会形成更多和更薄的孪晶。特别是，与传统的 TWIP （CV-TWIP） 钢不同，在 HN-TWIP 钢中检测到许多超细纳米孪晶 （<15 nm）。结合流动应力分析，发现它们的强化行为归因于 N 固溶体强化和纳米孪晶强化。更重要的是，通过促进平面滑移，超细纳米孪晶提供了额外的加工硬化并延迟了颈缩外观，从而增强了塑性。换句话说，避免强度-延展性权衡的根源是纳米孪生/超细纳米孪生微观结构。进一步的研究表明，通过打破低堆叠断层能 （SFE） 和优异奥氏体稳定性的冲突，HN-TWIP 钢实现了 SFE 的突破性降低。具有极低SFE的HN-TWIP钢可以获得特殊的纳米孪晶微观结构和SISP力学行为。因此，只有在合金化设计中不断降低SFE，才能在TWIP钢中实现困难的SISP。 这是一种新颖而简单的金属力学性能改性策略，对工程应用中的材料具有重要意义。