Contents lists available at ScienceDirect Materials Science & Engineering A journal homepage: www.elsevier.com/locate/msea Influence of annealing temperature on deformation behavior of 329LA lean duplex stainless steel Nithi Saenarjhan a , Jee-Hyun Kang a , Soo Chan Lee b , Sung-Joon Kim a, ⁎ a Graduate Institute of Ferrous Technology (GIFT), Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea b Technical Research Laboratories, POSCO, Pohang 37859, Republic of Korea ARTICLE INFO Keywords: Duplex stainless steel Transformation induced plasticity Mechanical properties Electron microscopy ABSTRACT Tensile behavior of a 329LA lean duplex stainless steel at room temperature is investigated after annealing at different temperatures. The austenite composition and thereby, its stability depend on the annealing temperature. For recrystallized alloys, austenite stability increases with the annealing temperature. Therefore, martensitic transformation is effectively suppressed during cooling and deformation, which results in low tensile strength and strain hardening rate, when the steel is annealed at higher temperature. Accordingly, transformation-induced plasticity is more pronounced in alloys annealed at lower temperature. During deformation, α′-martensite forms with a blocky morphology with the absence of the deformation bands indexed as an hcp phase. Thus, it is suggested that austenite directly transforms to α′-martensite during deformation rather than via the deformation bands due to a relatively high driving force for α′-martensite transformation in the present alloy. 1. Introduction Duplex stainless steels (DSSs) exhibit excellent combination of corrosion resistance and mechanical properties, which has enabled their development as structural components in chemical and pulp industries as well as on/offshore applications. In order to achieve the requirements for the application, conventional DSSs contain consider- able amounts of expensive alloying elements such as Cr, Ni, and Mo [1]. Recently, efforts have been made to develop lean DSSs with lower amount of the expensive alloying elements. In this regard, Ni and Mo were replaced with Mn and N [1]. Mn plays an important role in both stabilizing austenite and increasing the solubility of interstitial ele- ments such as C and N. N also acts as a strong austenite stabilizer and has beneficial effects on the strength and pitting corrosion resistance [2–5]. DSSs contain two phases, ferrite and austenite, the equilibrium fractions of which depend on annealing temperature. Accordingly, there is a possibility to alter the partitioning of alloying elements into the phases by annealing at different temperatures. Changing the composition of austenite affects its stability, and therefore, determines if it transforms into martensite during quenching as well as deforma- tion. The austenite stability can be represented by the thermodynamic driving force, which is calculated as the difference in Gibbs free energies of fcc and bcc structures. The driving force can be further related with martensite start temperature [6] and stacking fault energy [7]. Especially, stacking fault energy is often connected to the deforma- tion mechanisms. It is often reported that austenite in lean DSSs experiences deformation-induced martensitic transformation (DIMT) [8–10]. DIMT plays an important role in mechanical properties by enhancing tensile strength and ductility, which is known as transfor- mation-induced plasticity (TRIP). TRIP results in an excellent combi- nation of strength and elongation over 1 GPa-60% in a DSS [11]. Further increase in stacking fault energy by adjusting the chemical composition [12] or deformation conditions [13–15] can lead to different deformation mechanisms such as twinning and pure disloca- tion glide rather than DIMT. Hence, the present work is conducted to study the influence of different annealing temperatures on the mechanical behavior and deformation mechanism of a 329LA lean DSS. Tensile tests were conducted along with microstructure analysis, and deformation me- chanism is discussed with the assistance of thermodynamic calcula- tions. 2. Experimental procedures The chemical composition of a 329LA lean DSS used in this study is Fe-0.17N-0.02C-20.5Cr-2.0Ni-1.8Mn-0.7Cu-0.6Mo-0.5Si (wt%). A 4.0 mm thick hot-rolled plate was cold- rolled to 1.0 mm in thickness. http://dx.doi.org/10.1016/j.msea.2016.10.062 Received 10 August 2016; Received in revised form 9 October 2016; Accepted 12 October 2016 ⁎ Corresponding author. E-mail address: sjkim1@postech.ac.kr (S.-J. Kim). Materials Science & Engineering A 679 (2017) 531–537 0921-5093/ © 2016 Elsevier B.V. All rights reserved. Available online 21 October 2016 crossmark