Asymmetric Rolling of Interstitial-Free Steel Using Differential Roll Diameters. Part II: Microstructure and Annealing E
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I.
INTRODUCTION
INTERSTITIAL-FREE (IF) steel in sheet form is often used for car body panels and a variety of consumer products. However, the shapes of these products are becoming increasingly complex, while requirements for weight reduction and strength increase are concurrently becoming more stringent. Therefore, the simultaneous improvement of deep drawability and strength of IF steel sheet is needed now more than ever before. The conventional—that is symmetric—cold rolling (SR) process is normally used for the production of IF steel sheets of appropriate thickness.[1] It is typically followed by an annealing heat treatment before the deep drawing operation, as the ductility of the cold-rolled sheet is exhausted due to severe work hardening. However, the optimization of this route of thermomechanical processing[2–4] has reached its limit in terms of obtained mechanical properties in SR. Therefore,
DMITRY ORLOV, Senior Researcher, is with the Department of Materials Engineering, Monash University, Clayton, VIC 3800, Australia, and now with the Research Organization of Science and Technology, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577, Japan. Contact e-mail: [email protected]; orlov@ fc.ritsumei.ac.jp RIMMA LAPOVOK, Research Associate Professor, is with the Department of Materials Engineering, Centre for Advanced Hybrid Materials, Monash University. LASZLO S. TOTH, Director, is with the Laboratoire d’Etude des Microstructures et de Me´canique des Mate´riaux, CNRS UMR 7239, Universite´ de Lorraine, Ile du Saulcy, 57045 Metz Cedex 01, France, and also with the Laboratory of Excellence, Design of Alloy Metals for low-mAss Structures (DAMAS), Universite´ de Lorraine, Metz, France. ILANA B. TIMOKHINA, Senior Research Academic, and PETER D. HODGSON, Director, are with the Institute for Frontier Materials, Geelong Technology Precinct (GTP) Research, Deakin University, Geelong Waurn Ponds Campus, Geelong, VIC 3217, Australia. ARUNANSU HALDAR, Manager (Research, Development and Technology), and DEBASHISH BHATTACHARJEE, Director (Research, Development and Technology), are with the R&D Division, Tata Steel Europe, 30 Millbank, London SW1P 4WY, U.K. Manuscript submitted October 10, 2012. Article published online August 28, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
different approaches are being investigated to further improve the properties. A further increase in the properties may be obtained by asymmetric rolling (ASR).[5–15] The main advantage of ASR is that in addition to the reduction in thickness, it can introduce homogeneous simple shear through the thickness of the sheet.[15] Such a shear increases the efficiency of grain refinement, rotates the rolling texture, and increases the yield and ultimate tensile strengths. Nevertheless, both the uniform and the total elongations decrease to such an extent that a subsequent deep drawing operation is not possible immediately after rolling. Hence, an annealing treatment is still required. However, it is expected that the annealing kinetics of the
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