Contents lists available at ScienceDirect Materials Science & Engineering A journal homepage: www.elsevier.com/locate/msea Strain hardening mechanisms during cold rolling of a high-Mn steel: Interplay between submicron defects and microtexture I.R. Souza Filho a,b,* , M.J.R. Sandim a , D. Ponge b , H.R.Z. Sandim a , D. Raabe b a Lorena School of Engineering, University of Sao Paulo, 12602-810, Lorena, Brazil b Max-Planck-Institut für Eisenforschung, Max-Planck Str. 1, D-40237, Düsseldorf, Germany ARTICLE INFO Keywords: 17.6 wt.% Mn steel Strain hardening mechanisms Submicron defects Local strain partitioning Microtexture ABSTRACT The formation of submicron structural defects within austenite (γ), ε- and α′-martensite during cold rolling was followed in a 17.6 wt.% Mn steel. Several probes, including XRD, EBSD, and ECCI-imaging, were used to reveal the complex superposition of the strain hardening mechanisms of these phases. The maximum amount of ε- martensite is observed at a strain of ε = 0.11. At larger strains, the amount of ε decreases suggesting that it precedes the α′-formation (γ → ε → α′). Stacking faults and twins are the main planar defects noticed in ε- martensite. The remaining γ is finely subdivided by stacking faults and twins up to ε = 0.22. From ε = 0.51 on, twinning and multiplication of dislocations are the principal strain hardening mechanisms in austenite. Deformation is accommodated in α′ by the rearrangement of dislocation tangles into dislocation cells plus shear banding at ε = 1.56. During cold rolling, austenite develops a Brass-type texture component, which can be associated to mechanical twinning. ε-martensite presents its basal planes tilted ∼24° from the normal direction towards the rolling direction. The α′-martensite develops and strengthens both, the bcc α- and γ-texture fibers during cold rolling. 1. Introduction There is a raising interest in high-Mn steels containing 15–25 wt.% Mn as they enable the reduction of body-car weight without compro- mising crashworthiness properties [1–5]. The steels have very good mechanical properties and high ductility, enabled by the interplay of several complex strain hardening mechanisms. The stacking fault en- ergy (SFE) of these alloys ranges between 10 and 21 mJ/m 2 [6,7]. Therefore, the metastable austenite (γ) in these low-SFE materials can accommodate deformation by means of partial dislocation slip, me- chanical twinning, and/or transforming into ε- (hcp) or α′-martensite (bcc) [8–10]. Upon straining, the dissociation of perfect dislocations into Shockley partials promotes the formation of stacking faults (SFs) which can eventually lead to the formation of twins and ε-phase [11]. In this context, twinning and ε-formation take place through the motion of Shockley partial dislocations on successive and alternating (111) planes of γ, respectively [12]. With regard to α′-martensite, its forma- tion has been observed to occur at the intersection of crystallographic defects created during deformation, including ε-martensite [12]. When the ε-phase intermediates the α′-formation (γ → ε → α′), excellent strain hardening rates are observed upon deformation of high-Mn alloys [13–16]. Once α′-martensite is the major phase, further deformation is accommodated in this phase by slip and shear banding [11]. Prior to the ε → α′ reaction, the motion of Shockley partials on the basal (0001) planes of the ε-martensite leads to the creation of intrinsic and extrinsic SFs, and also twins [11]; i.e., ε-martensite accommodates its incommensurate deformation by faults and twins. Recently, some works focused on straining of the ε-phase in Fe-Mn [18], Fe-Mn-C [17], and Fe-Mn-Al-Si-C [11] systems. A few studies also reported about austenite in cold-rolled high-Mn steels, whose SFEs range within the interval of 12–29 mJ/m 2 [17,19,20]. However, the hierarchical for- mation of planar defects (e.g. SFs and twins) in metastable γ and ε- martensite in high-Mn steels with SFE < 10 mJ/m 2 remains barely ex- plored. Only a few studies have dealt with the interplay between the evolution of submicron defects and texture [6]. In fact, studies of crystallographic texture have mainly been conducted for high-Mn steels displaying SFEs higher than 10 mJ/m 2 [6,19,20]. Therefore, the aim of the present work is to throw light on the strain hardening mechanisms of high-Mn alloys with a lower SFE than those reported in Refs. [6,11,17–20]. Also, the aim of obtaining better understanding of the complex superposition and interaction of several displacive and in- commensurate transformation reactions, including γ → SFs, γ → twins, SFs as precursor for twins or ε, and γ → ε → α’, was also taken as motivation for the present work. https://doi.org/10.1016/j.msea.2019.03.116 Received 2 February 2019; Received in revised form 26 March 2019; Accepted 27 March 2019 * Corresponding author. Lorena School of Engineering, University of Sao Paulo, 12602-810, Lorena, Brazil. E-mail address: isnaldi.filho@usp.br (I.R. Souza Filho). Materials Science & Engineering A 754 (2019) 636–649 Available online 30 March 2019 0921-5093/ © 2019 Elsevier B.V. All rights reserved. T