Deformation-induced martensitic transformation that rapidly occurs generally leads to a significant reduction in elongation of metastable austenitic steels, particularly at low temperatures. However, we proved that the ultrafine-grained 304 stainless steel is an exception. Using a hybrid method of neutron diffraction and digital image correlation, we found that this material exhibits Lüders deformation after yielding, in which the deformation behavior changes from a cooperation mechanism involving dislocation slip and martensitic transformation to one primarily governed by martensitic transformation, as the temperature decreases from 295 K to 77 K. Such martensitic transformation-governed Lüders deformation delays the activation of plastic deformation in both the austenite parent and martensite product, resulting in delayed strain hardening. This preserves the strain-hardening capability for the later stage of deformation, thereby maintaining a remarkable elongation of 29 % while achieving a high tensile strength of 1.87 GPa at 77 K. Insights from this study point to a feasible pathway to achieve both high strength and high ductility by rearranging the deformation modes of ultrafine-grained materials.

中文翻译：

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马氏体相变控制的吕德斯变形使超细晶奥氏体不锈钢在低温下具有较大的延展性和后期应变硬化


快速发生的变形引起的马氏体转变通常会导致亚稳奥氏体钢的伸长率显着降低，特别是在低温下。然而，我们证明超细晶粒304不锈钢是一个例外。利用中子衍射和数字图像相关的混合方法，我们发现该材料在屈服后表现出吕德斯变形，其中随着温度的升高，变形行为从涉及位错滑移和马氏体相变的协作机制转变为主要由马氏体相变控制的机制。温度从 295 K 降低到 77 K。这种马氏体相变控制的 Lüders 变形延迟了奥氏体母体和马氏体产物中塑性变形的激活，导致延迟应变硬化。这保留了变形后期的应变硬化能力，从而保持了 29% 的显着伸长率，同时在 77 K 下实现了 1.87 GPa 的高拉伸强度。这项研究的见解指出了实现高强度和高强度的可行途径。通过重新排列超细晶材料的变形模式来获得高延展性。