Acta Metall Sin  2019, Vol. 55 Issue (11): 1359-1366    DOI: 10.11900/0412.1961.2019.00108
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Intrinsic Increment of Plasticity Induced by TRIP and Its Dependence on the Annealing Temperature in a Lean Duplex Stainless Steel
CHEN Lei1,2,HAO Shuo 1,2,MEI Ruixue 2,JIA Wei 2,LI Wenquan 2,GUO Baofeng2()
1. National Engineering Research Center for Equipment and Technology of Cold Strip Rolling, Yanshan University, Qinhuangdao 066004, China
2. College of Mechanical Engineering, Yanshan University, Qinhuangdao 066004, China
Abstract

Recently, advanced lean duplex stainless steels (LDXs) with exceptionally good tensile properties by transformation-induced plasticity (TRIP) have been developed to respond to the skyrocketing raw material cost. In these new alloys, TRIP in the metastable austenite phase is expected to dominate overall deformation of the steels. Solution annealing, as a critical step of production processing, affects the austenite characteristics in LDXs, such as volume fraction and mechanical stability of austenite, which in turn influences its TRIP behavior. In order to further develop advanced LDXs, an assessment in the plastic increment of TRIP and its dependence on solution treatment are necessary. In this work, the tensile deformation test of a LDX which was annealed in the range of 1000~1200 ℃ was carried out on a Gleeble-3800 machine. The microstructural mechanism of work hardening characteristics was characterized by TEM, and the saturation of strain-induced martensite (SIM) under different conditions was calculated by XRD. Some quantitative indicators which can characterize the plastic increment of TRIP were proposed, including apparent plastic increment ($Δe$), average plastic increment ($Δeˉ$) induced by unit volume SIM and intrinsic plastic increment ($Δe*$) related only to mechanical stability of austenite. Meanwhile, their dependences on annealing temperature were discussed. The results show that SIM can develop in two ways of γεα′ and γα′ whereby the work hardening of the LDX exhibit a "three-stage" characteristic. There is a critical deformation temperature (Md) where the TRIP is absent at every annealing temperatures. The higher the annealing temperature is, the smaller the Md and the $Δe$are. As annealing temperature increases, $Δeˉ$ increases, while $Δe*$ decreases, indicating a fact that the more stable the austenite is, the smaller the intrinsic plastic increment of TRIP is. In addition, both $Δeˉ$ and $Δe*$ show a linear relationship with the austenite stability coefficient (k).

 ZTFLH: TG142.1
Fund: National Natural Science Foundation of China(51675467);National Natural Science Foundation of China(51675465);Project Funded by China Post Doctoral Science Foundation Nos(2016M600194);Project Funded by China Post Doctoral Science Foundation Nos(2017T100712);and Natural Science Foundation of Hebei Province(E2016203284)
Corresponding Authors:  Baofeng GUO     E-mail:  baofengysu@163.com