Effect of TMCP on Microstructure and Mechanical Properties of 304 Stainless Steel Pratik Mallick, Nisith Kumar Tewary, Swarup Kumar Ghosh,* and Partha Protim Chattopadhyay The present study investigates the evolution of microstructure and mechani- cal properties of 304 stainless steel after thermo-mechanical controlled processing (TMCP). Three different FRTs (finish rolling temperatures) have been adopted and the micro-constituents are identified as austenite grains, stacking faults, annealing, and deformation twins. Fine austenite grains in the range of 1–30 μm are obtained at lower FRT (700  C) whereas at higher FRT, coarse grains are formed. TEM and X-ray analyses indicate the formation of M 23 C 6 ((Cr, Fe) 23 C 6 ) precipitates for higher FRT (900  C). Specimen processed with 700  C FRT results into 37% enhancement in UTS compared to the base metal which is attributed to fine partially recrystallized grain, extensive deformation twinning and high dislocation density. Maximum elongation (68%) is obtained due to the formation of strain-free equiaxed grains (40 μm) at 900  C FRT. 1. Introduction Grain refinement is one of the effective methods employed for enhancing the strength with a favorable ductility of steel. [1] There are several methods which produce fine grain structure like equal channel angular pressing (ECAP), [2] high-pressure torsion (HPT), [3] accumulative roll bonding (ARB) [4] reversion annealing of martensitic structure etc. However, the main problem in these methods is the formation of stain induced martensite, which lowers the ductility. [5] In this connection, it is important to note that reversion of strain induced martensite improves the ductility in the steels processed under aforesaid routes. [6,7] During reversion, the formation of fine grains and inhomoge- neous distribution of these fine grains lead to strain localization causing improvement in the ductility value. [8,9] Cold rolling, as well as hot rolling, has been employed for achieving grain size refinement. Cold working improves the strength of the material and lowers the ductility by higher forming forces, while hot rolling allows simultaneous recrystallization, which controls the grain refinement. To avoid high working temperatures and forces, warm rolling (0.35T m < T < 0.55T m ) is commonly used as the intermediate process, [10] which allows recovery but not recrystallization to get a favorable combination of strength and ductility. Among the available methods, grain refinement by thermo- mechanical treatment has drawn great attention in steel research, because it improves both corrosion and mechanical properties of the stainless steel. [11–13] During thermo-mechanical processes (TMCP), the steel undergoes various metallurgical phenomena such as work hardening, dynamic recovery and dynamic recrystallization. Among these processes, dynamic recrystallization [14,15] is the most important mechanism during thermo- mechanical controlled processing (TMCP) of low stacking fault energy FCC alloys, because it influences the final micro- structures and thereby the mechanical properties of the materials. [16] Thermo-mechanical controlled processing (TMCP) and its influence on the microstructure and mechanical properties are well established in low and ultralow carbon steels. [17,18] However, limited studies have been carried out on this aspect in austenitic stainless steels. In view of the above, in the present study, 304 austenitic stainless steel has been thermo-mechanically processed with three different finish rolling temperatures (FRT) of 700, 800, and 900  C to study the effect of FRT on microstructure and mechanical properties of the steel. Recrystallization and grain growth which strongly influence the mechanical properties of steel are known to occur during TMCP. The purpose of the present work is to vary the grain size with altering the finish rolling temperature during TMCP and the presence of different types of microstructural features generally form in austenitic stainless steel which strongly affects the strength-ductility combination of the steel. 2. Experimental Section The material used for this study is commercially available 304 stainless steel. Its chemical composition has been analyzed in an optical emission spectrometer (ARL 4460) and the values are listed in Table 1. The hot rolled steel with a thickness of 25 mm was cut down to a cross-section of 12  12 mm and 100 mm length. The Prof. S.K. Ghosh, P. Mallick, N. K. Tewary Department of Metallurgy & Materials Engineering Indian Institute of Engineering Science and Technology Shibpur, Howrah 711103, India E-mail: skghosh@metal.iiests.ac.in Prof. P.P. Chattopadhyay National Institute of Foundry & Forge Technology (NIFFT) Hatia 834003, Ranchi, India DOI: 10.1002/srin.201800103 XXXX www.steel-research.de FULL PAPER steel research int. 2018, 1800103 © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1800103 (1 of 7)