通过系列循环加载实验，研究了TRIP型双相不锈钢Fe-19.6Cr-2Ni-2.9Mn-1.6Si在循环变形条件下的力学特性，同时结合TEM分析，讨论了微观机理。结果表明，Fe-19.6Cr-2Ni-2.9Mn-1.6Si钢在单调加载条件下力学性能优异，表现出TRIP型双相不锈钢典型的“三阶段”硬化特征；Fe-19.6Cr-2Ni-2.9Mn-1.6Si钢的循环硬化/软化特性对应变幅和循环周次敏感。在小应变幅下，Fe-19.6Cr-2Ni-2.9Mn-1.6Si钢先初始循环硬化(循环周次N<5 cyc)，随后大幅循环软化后逐渐稳定。而在大应变幅下，Fe-19.6Cr-2Ni-2.9Mn-1.6Si钢变形初期(N<5 cyc)迅速循环硬化后，持续循环软化，未达循环稳定而直至疲劳失效。循环变形过程中铁素体相中形成的位错墙是Fe-19.6Cr-2Ni-2.9Mn-1.6Si钢整体循环软化的主要原因；而较大应变幅下奥氏体会发生循环诱导ε马氏体相变，抑制软化，从而使得Fe-19.6Cr-2Ni-2.9Mn-1.6Si钢循环软化率随(塑性)应变幅的增大表现出先快速增大，后缓慢增大，最后降低的趋势。相比于单调加载状态，Fe-19.6Cr-2Ni-2.9Mn-1.6Si钢随应变幅的增加表现出“硬化→软化→再硬化”规律。另一方面，Fe-19.6Cr-2Ni-2.9Mn-1.6Si钢循环应力幅与塑性应变幅间(lgσ_a-lgε_a)表现出三阶段的线性关系，对应的循环硬化指数(n')分别为：0.16 (阶段Ⅰ)、0.09 (阶段Ⅱ)和0.17 (阶段Ⅲ)；各阶段n'的变化分别与两相间协调变形(Ⅰ→Ⅱ)及循环诱导ε马氏体相变(Ⅱ→Ⅲ)有关。

Duplex stainless steel (DSS) is a type of steel with ferritic-austenitic duplex structure. It has been widely used in the engineering field such as petrochemicals and oceans. Recently, a series of economical DSSs with TRIP effect have been developed by replacing Ni-Mo with Mn-N. Generally, most structural components are subjected to periodic alternating loads during service, and then cyclic deformation which causes different mechanical responses with monotonous loading condition occurs. In this work, the mechanical properties of a Mn-N bearing DSS Fe-19.6Cr-2Ni-2.9Mn-1.6Si during cyclic deformation condition were studied and the microstructural mechanism was characterized by TEM. The results show that the Fe-19.6Cr-2Ni-2.9Mn-1.6Si steel exhibits enhanced mechanical properties and a typical "three-stage" hardening characteristic due to TRIP effect under monotonic loading condition. Cyclic hardening/softening characteristics of the Fe-19.6Cr-2Ni-2.9Mn-1.6Si steel are sensitive to strain amplitude and the number of cycle (N). At a small strain amplitude, cyclic hardening occurs firstly when N<5 cyc, then cyclic softening starts and cyclic deformation gradually trends to a stabilization. At a large strain amplitude, after a rapidly cyclic hardening (N<5 cyc), the Fe-19.6Cr-2Ni-2.9Mn-1.6Si steel is continuously softened until failure and no stabilization occurs. The dislocation walls form in ferrite during cyclic deformation which responsible for the overall cyclic softening of the Fe-19.6Cr-2Ni-2.9Mn-1.6Si steel; While austenite undergoes cyclic induced ε martensite transformation at large strain amplitude whereby the softening is suppressed, so that the cyclic softening rate of the Fe-19.6Cr-2Ni-2.9Mn-1.6Si steel increases rapidly with the increase of the (plastic) strain amplitude, followed by a slow increase and a final decrease. Compared with the monotonous loading condition, the Fe-19.6Cr-2Ni-2.9Mn-1.6Si steel shows a law of "hardening→softening→ re-hardening" with the increase of strain amplitude. In particular, there is a three-stage linear relationship between logarithmic cyclic stress amplitude and logarithmic plastic strain amplitude (lgσ_a-lgε_a), and the corresponding cyclic hardening index (n') are: 0.16 (stage I), 0.09 (stage II) and 0.17 (stage III), respectively. The change of n' in each stage is related to the coordinated deformation between two phases (I→II) and the cyclic induced ε martensitic transformation (II→III).