Contents lists available at ScienceDirect Materials Science & Engineering A journal homepage: www.elsevier.com/locate/msea EBSD study of microstructure evolution during axisymmetric hot compression of 304LN stainless steel Matruprasad Rout a , Ravi Ranjan b , Surjya K. Pal a, ⁎ , Shiv B. Singh b a Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India b Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India ARTICLE INFO Keywords: Dynamic recrystallization EBSD GOS Microstructure Compression test Stainless steel ABSTRACT In the present work, axisymmetric compression tests were carried out on 304LN stainless steel at temperatures of 900 ℃, 1000 ℃ and 1100 ℃ at strain rates of 0.01 s -1 , 0.1 s -1 and 1 s -1 . Electron back scatter diffraction (EBSD) technique was used to characterize the microstructure, qualitatively as well as quantitatively. The re- sultant microstructures were a mixture of both elongated deformed and equi-axed recrystallized grains for samples deformed at 900 ℃. For samples deformed at 1000 ℃ and 1100 ℃, the microstructures are almost fully recrystallized with a high fraction of Σ3 twin boundaries. Partitioning of these microstructures, based on grain orientation spread (GOS) approach, was done to separate the deformed grains and the recrystallized grains. The obtained recrystallization fraction was used to estimate the flow stress value between the peak stress and the steady state stress. A good agreement between the predicted and the experimental flow stress value was ob- served. 1. Introduction The properties, in particular the mechanical properties, offered by a material depend on many features, viz., grain size and their distribu- tions, alloying elements, types of phases and their distribution, etc. Improvement of the combination of material properties, e.g., strength and ductility, has always been a challenging job for materials engineers. In the case of a single phase material, for a given composition, such as used for the present study (304LN austenitic stainless steel), grain re- finement perhaps is the most suitable approach. The refinement of grains requires the application of an optimum combination of proces- sing parameters, such as, strain, strain rate, temperature etc. The evo- lution of a deformed microstructure during a processing occurs in three stages, viz., recovery (RCV), recrystallization (REX) and grain growth. The application of deformation results in the formation defects, like dislocations to accommodate the applied strain. In a recovery process, annihilation and rearrangement of dislocations takes place through rapid occurrence of cross slip and climb, whereas, the recrystallization process results in the formation of new equi-axed strain-free grains that effectively minimizes the deformation effects. The new strain-free re- crystallized grains are generally smaller in size than the parent auste- nite grain. The smaller grains, forms as a result of recrystallization, can be maintained if its further growth is restricted. This presents an im- mediate advantage of recrystallization over the recovery process. However, the extent to which these mechanisms operate in a material on the application of deformation is primarily dependent on the stacking fault energy (SFE) [1]. A material with high SFE is more likely to show a higher degree of recovery, while the recrystallization process is the dominant mechanism of softening in the material with low SFE. Hence, the advantage of recrystallization, i.e., grains refinement, can be successfully utilized in a material with the low value of SFE. Accord- ingly, controlling the recrystallization along with its subsequent growth arises as the most effective way to achieve simultaneous improvement of the various mechanical properties in typical austenitic stainless steels. The recrystallization process is generally classified as, static re- crystallization (SRX), meta-dynamic recrystallization (MDRX) and dy- namic recrystallization (DRX). Recrystallization process that occurs after the deformation is called SRX, while it is termed as DRX when the recrystallization process occurs during the deformation. The MDRX is the intermediate of the above two processes and reflects the growth of the nuclei formed during deformation, but could not undergo DRX [2]. The SRX requires a definite time, after the deformation, for refinement of grains. Hence, SRX losses its significance with respect to the process where the inter-pass time between the successive deformation passes is less. In this case, refinement can only be achieved through optimizing the processing parameters, e.g., strain, strain rate, deformation tem- perature, etc., that triggers the DRX. Austenitic stainless steel, a mate- rial having low SFE, exhibits DRX during hot working process [3–6]. It https://doi.org/10.1016/j.msea.2017.11.059 Received 12 July 2017; Received in revised form 23 September 2017; Accepted 15 November 2017 ⁎ Corresponding author. E-mail address: skpal@mech.iitkgp.ernet.in (S.K. Pal). Materials Science & Engineering A 711 (2018) 378–388 Available online 21 November 2017 0921-5093/ © 2017 Elsevier B.V. All rights reserved. T