Texture and Microstructural Evolution in Pearlitic Steel During Triaxial Compression
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MATERIALS with ultra-fine grains produced by severe plastic deformation (SPD) exhibit improved mechanical and physical properties.[1,2] The characteristic feature of SPD includes retention of the dimension of the work piece even after imparting large strain. Various SPD processes such as equal channel angular extrusion, high-pressure torsion, and mechanical milling are well reported for producing ultra-fine-grained materials. However, complicated dies involved in many of these processes limit their applicability on industrial scale. Two processes have potential for scaling up, namely, accumulative roll bonding (ARB) and multiaxial forging (MAF). ARB can be used to produce flat products, whereas MAF can impart a large amount of strain in large billets, which can be used to obtain any desired shape. This process involves a combination of uniaxial and plane strain compression along the three directions normal to the faces of a cuboidal work piece. A similar but much simpler manifestation of the process is triaxial compression in which the work piece is uniaxially compressed successively on three mutually perpendicular faces. This process is based on normal up-set forging and, therefore, does not involve any die. MAF or triaxial compression has been carried out on a variety of materials[3–6]; however, most studies are limited to PANKAJ KUMAR, Master Student, NILESH P. GURAO, Post Doctoral Fellow, and SATYAM SUWAS, Associate Professor, are with the Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India. Contact e-mail: satyamsuwas@ materials.iisc.ernet.in ARUNANSU HALDAR, Senior Researcher, is with Tata Steel, Research and Development Section, Jamshedpur 831001, India. Manuscript submitted November 24, 2010. Article published online January 24, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
single-phase ductile metals and alloys. Investigations of ferrous materials have been rare.[7,8] One such material with tremendous industrial applications is pearlitic steel. The microstructure of pearlitic steel consists of alternate lamellae of ferrite (a-Fe) and cementite (Fe3C) phases arranged in colonies with random orientations. It has excellent mechanical properties such as high strength, good wear resistance, high fatigue strength, etc. Cementite is the harder phase that imparts strength to pearlitic steel. It has been reported that coarse lamellar cementite reduces the ductility of steels and hence significantly limit its application. Breaking these cementite lamella causes refinement and, hence, improvement in properties such as increase in toughness, formability, and machinability. Several studies have been focused on the change in morphology of the cementite lamella[8–10] and also on the evaluation of mechanical properties associated with the resulting microstructure. These investigations suggest that a composite microstructure with tiny cementite particles distributed in ultra-fine ferrite matrix yields a good balance between strength and ductility. The present study is primarily aimed at e
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