Effects of cold rolling on microstructure and mechanical properties of Fe–30Mn–3Si–4Al–0.093C TWIP steel Y.F. Shen a,c , C.H. Qiu a , L. Wang b , X. Sun c,n , X.M. Zhao d , L. Zuo a a Key Laboratory for Anisotropy and Texture of Materials (MOE), Shenyang 110004, PR China b R&D Center Automobile Steel Department, Baoshan Iron & Steel Co., LTD, Shanghai 201900, China c Pacific Northwest National Laboratory, Computational Science and Mathematics Division, PO Box 999, Mail stop K6-08, Richland, WA 99352, USA d The State Key Lab of Rolling & Automation, Northeastern University, Shenyang 110004, PR China article info Article history: Received 2 August 2012 Received in revised form 4 October 2012 Accepted 6 October 2012 Available online 24 October 2012 Keywords: Fe–30Mn–3Si–4Al steel Cold rolling Mechanical properties Deformation twinning abstract The effects of cold rolling on microstructure evolution and the associated mechanical properties of Fe–30Mn–3Si–4Al–0.093C twinning-induced plasticity (TWIP) steel are examined in this work with reduction levels of 10%, 20%, 30%, 40%, 50%, 60%, and 70%. Through texture analysis and transmission electron microscopy (TEM) observations, it is suggested that slip, mechanical twinning, the interaction between dislocation/twin boundaries (TB), and shear band formation have influenced the observed mechanical behavior and development of texture. Special components of weak initial textures are preferential for mechanical twinning, resulting in an increase in strain hardening rate. By mechanical twinning, the {1 1 1}/112S orientation is rotated into a position at the vicinity of the {1 1 0}/001S Goss orientation, and the {5 5 2}/115S (Cu-twin) texture is transformed to the {1 1 0}/001S orientation. The evolution of texture is closely related to the onset of shear banding resulting from deformation twinning. The sample with 10% cold reduction exhibits a favorable combination of yield strength and ductility, indicating a considerable capacity for energy absorption. With increasing rolling reductions, the deformation of the samples becomes inhomogeneous due to the high anisotropy of the microstructure. The localized shear bands resulting from the excessive cold rolling are detrimental to the ductility of the present TWIP steel. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Facing the challenges of high oil prices and increasingly stringent regulations on vehicle safety and fuel efficiency, global steel and automotive manufacturers are developing and employ- ing more advanced high-strength steels to reduce vehicle body weight. Recently, twinning-induced plasticity (TWIP) steels have received considerable attention due to the excellent mechanical properties exhibited by this class of materials [1,2]. Compared with conventional mild steels used in vehicle bodies, TWIP steels exhibit much higher strength [3,4] and superior ductility, making them attractive candidates for vehicle components with complex geometry. During plastic deformation, deformation twinning plays a key role for this class of materials [5], and the deformation mechan- isms are closely related to the stacking fault energy (SFE) of the austenitic phase. In general, the SFE depends on alloy composi- tions and deformation temperatures. It is well accepted that metals and alloys with a relatively low SFE aptly deform by mechanical twinning [6]. As the SFE decreases, the stacking faults (SFs) become wider, making cross-slip more difficult. Hence, mechanical twinning is favored. Meanwhile, phase transforma- tion also is closely related to the SFE of the austenitic matrix. A low SFE ( r20 mJ/m 2 ) can favor the g-a phase transformation, whereas a high SFE ( 420 mJ/m 2 ) suppresses this phase transfor- mation [7]. Consequently, fully austenitic, high-manganese steels are designed with specific compositions, resulting in an appro- priate level of SFE (20–40 mJ/m 2 ) to promote mechanical twin- ning instead of phase transformation [7,8]. The deformation mode of the steels changes from twinning to dislocation gliding for steels with higher SFE levels. In general, additions of aluminum increase SFE and, therefore, strongly suppress the g-a transformation so that the formation of deformation twins is favored. Al additions also have proven effective in suppressing delayed fracture in press-formed parts [9]. However, Al additions lead to a lower strain hardening rate, resulting in a decrease in tensile strength [10]. In contrast, silicon decreases the SFE and sustains the g-a transformation during cooling and deformation [11]. Mn is not only an effective austenite stabilizer but also an element decreasing the SFE of Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/msea Materials Science & Engineering A 0921-5093/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msea.2012.10.020 n Corresponding author. Tel.: þ1 509 372 6489; fax: þ1 509 372 6099. E-mail address: xin.sun@pnnl.gov (X. Sun). Materials Science & Engineering A 561 (2013) 329–337