Effect of thermomechanical cyclic quenching and tempering treatments on microstructure, mechanical and electrochemical p
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Effect of thermomechanical cyclic quenching and tempering treatments on microstructure, mechanical and electrochemical properties of AISI 1345 steel Muhammad Arslan Hafeez 1), Ameeq Farooq 2), Kaab Bin Tayyab 2), and Muhammad Adnan Arshad 2) 1) School of Civil and Environmental Engineering, National University of Sciences and Technology, Islamabad 44000, Pakistan 2) Department of Metallurgy & Materials Engineering, University of the Punjab, 54590 Lahore, Pakistan (Received: 2 June 2020; revised: 8 July 2020; accepted: 10 July 2020)
Abstract: Thermomechanical cyclic quenching and tempering (TMCT) can strengthen steels through a grain size reduction mechanism. The effect of TMCT on microstructure, mechanical, and electrochemical properties of AISI 1345 steel was investigated. Steel samples heated to 1050°C, rolled, quenched to room temperature, and subjected to various cyclic quenching and tempering heat treatments were named TMCT-1, TMCT-2, and TMCT-3 samples, respectively. Microstructure analysis revealed that microstructures of all the treated samples contained packets and blocks of well-refined lath-shaped martensite and retained austenite phases with varying grain sizes (2.8–7.9 µm). Among all the tested samples, TMCT-3 sample offered an optimum combination of properties by showing an improvement of 40% in tensile strength and reduced 34% elongation compared with the non-treated sample. Nanoindentation results were in good agreement with mechanical tests as the TMCT-3 sample exhibited a 51% improvement in indentation hardness with almost identical reduced elastic modulus compared with the non-treated sample. The electrochemical properties were analyzed in 0.1 M NaHCO3 solution by potentiodynamic polarization and electrochemical impedance spectroscopy. As a result of TMCT, the minimum corrosion rate was 0.272 mm/a, which was twenty times less than that of the nontreated sample. The impedance results showed the barrier film mechanism, which was confirmed by the polarization results as the current density decreased. Keywords: thermomechanical treatment; cyclic heat-treatment; nanoindentation; potentiodynamic polarization; electrochemical impedance spectroscopy
1. Introduction Several industrial applications, particularly automotive industries, are demanding economical steels with superior strength, ductility, and impact toughness to manufacture lightweight structural components [1–4]. These properties can be achieved by producing stable and ultrafine grained microstructures [5]. For this purpose, several techniques, i.e., microalloying (of cobalt, copper, and boron in steel composition) [6], oxide dispersion strengthening technique [7–8], high-pressure torsion, equal channel angular pressing, accumulative roll bonding [5,9], controlling initial microstructure, austenitizing temperature, and austenitizing time [10], thermomechanical treatment (TMT) [11], and cyclic heat treatments [12], have been reported. TMT is a well-recognized, economical, and effic
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