Analysis of Flow Behavior of an Nb-Ti Microalloyed Steel During Hot Deformation
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THE increasing demand for high-performance structural steels with good weldability and corrosion resistance has resulted in development of high-strength low-alloy (HSLA) steels.[1,2] Mechanical properties of these steels are improved by the cooperation of two factors: a carefully designed chemical composition and
MOHAMMAD SADEGH MOHEBBI is with the School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, P.O. Box 11155-4563, Tehran, Iran and also with the Department of Mechanical Engineering, Qom University of Technology, P.O. Box 37195-1519, Qom, Iran. MOHAMMAD HABIBI PARSA is with the School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, and also with the Center of Excellence for High Performance Materials, School of Metallurgy and Materials Engineering, University of Tehran, Tehran, Iran and also with the Advanced Metal Forming and Thermomechanical Processing Laboratory, School of Metallurgy and Materials Engineering, University of Tehran, Tehran, Iran. Contact email: [email protected] MOHAMMAD REZAYAT is with the Department of Materials Engineering, Sahand University of Technology, P.O. Box 51335-1996, Tabriz, Iran. L’UBOMI´R OROVCˇI´K is with the Institute of Materials & Machine Mechanics, Slovak Academy of Sciences, Du´bravska´ cesta 9, 841 04 Bratislava 4, Slovakia. Manuscript submitted October 11, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
an optimized thermomechanical processing. These factors can result in a refined microstructure of austenite with high density of nucleation sites for ferrite in the following phase transformation. Consequently, a microstructure of very fine ferrite with excellent mechanical properties is formed by cooling. In terms of chemical composition, the addition of microalloying elements such as Niobium, Titanium, and Vanadium is one of the most effective approaches. Precipitation of fine niobium carbonitrides during thermomechanical processing of microalloyed steels is a great example of cooperation of these two factors to prevent austenite grain growth.[1] The proper design of thermomechanical processing requires deep knowledge about the hot flow behavior of microalloyed steels which is, in fact, governed by several simultaneous microstructural phenomena. Hardening, dynamic recovery (DRV), and dynamic recrystallization (DRX) are known as major phenomena during hot deformation of austenite.[3–5] In order to incorporate such complicate phenomena into simulation tools, it is necessary to mathematically express them as proper constitutive equations or models. Constitutive models help to formulate the hot flow behavior at various deformation conditions. While several constitutive equations are developed for this purpose, most attention has been paid to the physically based models which try
to formulate the contributions of the microstructural phenomena to the flow stress. Therefore, the flow stress is defined as a function of deformation parameters, i.e., the strain, strain rate, and temperature.[4,6,7] Sever
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