Abstract—Electron back-scattered diffraction was used to follow the evolution of microstructure from the base metal to the stir zone (SZ) in a duplex stainless steel subjected to friction stir welding. In the stir zone (SZ), a continuous dynamic recrystallization (CDRX) was evidenced for ferrite, while it was suggested that a static recrystallization together with CDRX may occur for austenite. It was found that ferrite and austenite grains in the SZ take a typical shear texture of bcc and fcc materials respectively. Keywords—Friction stir welding, Dynamic recrystallization, Electron backscattering diffraction (EBSD), Duplex stainless steel I. INTRODUCTION T has been shown that friction stir welding (FSW) can alleviate most of the problems caused by the fusion welding processes in duplex stainless steels (DSS) [1]. This motivation has influenced some researchers to deal with the microstructure and mechanical properties of friction stir welded DSS [2], [3]. Sato et al. [2] conducted a detailed examination of the microstructure and the mechanical properties in the friction stir welding of SAF 2507 super duplex stainless steel. They found that FSW significantly refined the ferrite (α) and austenite (γ) phases in the SZ. Based on the obtained results, they concluded that fine grains of both α and γ increased hardness and strength in the SZ. Recently, using a WC-based tool, Saeid et al. [3] investigated the effect of welding speed on the microstructure and mechanical properties of SZ in SAF 2205 DSS. They reported that increasing the welding speed decreased the size of the α and γ grains, and hence, improved the mean hardness value and the tensile strength in the SZ. The above-mentioned efforts have yielded some significant knowledge on microstructure, and mechanical properties in friction stir welded DSS, but relatively little attention have been paid to details of grain structure formation. Especially, recrystallization phenomena of two constituent phases have not been systematically investigated. For example, Sato et al. [2] and Saeid et al. [3] supposed, according to previous findings about conventional deformation, annealing, hot T. Saeid, A. Abdollah-zadeh and H. Assadi. are with the department of Materials Engineering, Tarbiat Modares University, P.O. Box 14115-143, Tehran, Iran (corresponding author: Prof. A. Abdollah-zadeh, Tel/fax: +98 21 88005040; e-mail: zadeh@ modares.ac.ir). T. Shibayanagi and K. Ikeuchi are with the Joining and Welding Research Institute, Osaka University, 11-1 Mihogaoka, Ibaraki, Osaka 567–0047, working, and superplastic processing of DSS, that discontinuous dynamic recrystallization of austenite and continuous dynamic recrystallization of ferrite simultaneously occur in the SZ. These findings were developed from experiments involving conditions of approximately uniform straining and isothermal deformation conditions. However, during FSW, material experiences large stresses and high temperatures under conditions that include rapid transients and steep gradients in strain, strain rate and temperature [4]. Therefore, the potential contributions of the steep gradients in strain, strain rate and temperature that are characteristic of FSW could not be reflected by conventional deformation methods, and it is imperative to gain better understanding and control of developed grain structure in these circumstances. The recent emphasis on production of fine and desirable microstructures, without the risk of grain growth in weld zone of duplex and microduplex stainless steels [5], has also accentuated the need for a systematic study to provide insight into mechanisms by which grain structure forms. The results of such a study in DSS, as a microstructurally less complicated material, could be used to predict the microstructural changes of hypo-eutectoid carbon steels during FSW. Since in these carbon steels γ-transus temperature is relatively low and under the condition of welding the peak temperature in the SZ generally exceeds A1 temperature. As a result, FSW is performed in α+γ two-phase region, and γ to α phase transformation during cooling cycle of weld hinders the microstructural evidences, which are affected directly from FSW. Thus, the history of microstructural changes occurred in two-phase region is difficult to trace by a postmortem microstructural analysis, such as that performed by Fujii et al. [6]. Accordingly, in this paper, we concentrate on EBSD results to investigate the microstructural and textural evolution of DSS. II. EXPERIMENTAL PROCEDURE The base material was a SAF 2205 duplex stainless steel, which was supplied in a form of rolled and annealed (at 1050 ◦C for 1 h) plate. This plate was cut into a specimen with dimensions of 300mm×100mm×2mm and then subjected to friction stir welding in a bead-on-plate configuration. Welding was conducted along the rolling direction of the plate at a welding speed of 100 mm/min and a rotational speed of 800 rpm. Details about welding parameters, used tool and machine have been given in a previous paper [3]. Microstructural EBSD Investigation of Friction Stir Welded Duplex Stainless Steel T. Saeid, A. Abdollah-zadeh, T. Shibayanagi, K. Ikeuchi, H. Assadi I World Academy of Science, Engineering and Technology International Journal of Materials and Metallurgical Engineering Vol:4, No:1, 2010 43 International Scholarly and Scientific Research & Innovation 4(1) 2010 scholar.waset.org/1307-6892/15905 International Science Index, Materials and Metallurgical Engineering Vol:4, No:1, 2010 waset.org/Publication/15905