Materials Science & Engineering A 814 (2021) 141260 Available online 14 April 2021 0921-5093/© 2021 Elsevier B.V. All rights reserved. On the effect of Mn-content on the strength-ductility balance in Ni-free high N transformation induced plasticity steels Mahsa Khorrami a , Abbas Zarei Hanzaki a, * , Hamid Reza Abedi b, ** , Mohammad Moallemi a , Javad Mola c , Guanghui Chen c a Hot Deformation and Thermomechanical Processing Laboratory of High Performance Engineering Materials, School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran b School of Metallurgy & Materials Engineering, Iran University of Science and Technology (IUST), Tehran, Iran c Materials Design and Structural Integrity Laboratory, Faculty of Engineering and Computer Sciences, Osnabrück University of Applied Sciences, 49076, Osnabrück, Germany A R T I C L E INFO Keywords: Transformation induced plasticity Twinning induced plasticity Ductility Microstructure ABSTRACT The present work deals with the room temperature microstructure-mechanical properties relationship in Ni-free high N transformation induced plasticity steels. The tensile properties of the alloy with lower Mn content of 4%, and thus lower austenite fraction and austenite stability, was mainly controlled through sequential (extended) transformation route of γ→ε→α ′ . The extended route resulted in a higher strain hardening rate and lower ductility value. In addition, the formation of thermally-induced martensite before plastic deformation reduced the capacity of strain partitioning and load transition between the austenite and ferrite. In contrast, the tensile properties of the alloy holding higher Mn content of 8% with higher austenite fraction and stability was mainly governed by twin-aided transformation route of γ→γ twinned →α ′ . It was found that the higher strain compatibility between austenite and ferrite resulted in a substantially high uniform elongation and moderate strain hardening rate. 1. Introduction Duplex stainless steels (DSSs), holding lower Ni content than con- ventional stainless steels, have drawn much attention due to their su- perior mechanical properties and corrosion resistance [1–3]. The second-generation of DSSs are characterized by their high nitrogen (N) content, which greatly infuences on the solid solution hardening of the austenite phase and increases the yield strength values [4–9]. The corrosion resistance (particularly intergranular and pitting corrosion) of high N DSSs is higher than that of austenitic stainless steels [10,11]. However, the high production cost of highly alloyed DSSs and their tendency to form brittle intermetallic precipitates has led to develop- ment of lean DSSs [12,13]. The lean DSSs in which Ni and Mo are mostly or completely replaced by Mn and N, beneft from the advantages of low costs of production, high formability indices, together with low ratios of yield strength to ultimate tensile strength and good corrosion resistance [2,14,15]. In fact, Mn increases N solubility and if an appropriate alloying strategy is considered, an optimum austenite stability would be obtained [16–20]. This provides a proper condition for activation of several deformation mechanisms such as transformation-induced plas- ticity (TRIP), twinning-induced plasticity (TWIP) and dislocation slip, and results in high strain hardening capacity and enhanced plasticity [21,22]. Comparing with austenitic stainless steels, the mechanical behaviour of lean DSSs is more complicated due to the coexistence of two massive phases where the strain partitioning between ferrite and austenite should be considered as infuencing factor [23]. Due to its high stacking fault energy (SFE) and the ease of the cross slip, ferrite mainly deforms by dislocation slip [24,25]. Deformation mechanisms of austenite also change from dislocation slip to TWIP to TRIP, as SFE decreases [24,26, 27]. In a more detailed view, the previous studies emphasized on the signifcant dependence of TRIP/TWIP effects and subsequent mechani- cal properties of lean DSSs on the austenite stability. In this regard, local phase chemistry has been introduced as one of the main factors affecting the SFE and austenite stability [21,28,29], and several reports have indicated that the kinetics and activation of TRIP/TWIP effects are * Corresponding author. ** Corresponding author. E-mail addresses: zareih@ut.ac.ir (A.Z. Hanzaki), habedi@iust.ac.ir (H.R. Abedi). Contents lists available at ScienceDirect Materials Science & Engineering A journal homepage: http://www.elsevier.com/locate/msea https://doi.org/10.1016/j.msea.2021.141260 Received 4 November 2020; Received in revised form 3 April 2021; Accepted 7 April 2021