Texture Development and Plastic Deformation in a Pilgered Zircaloy-4 Tube
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THE pilgering process, originated by the Mannesmann brothers,[1–4] is an asymmetrical and non-monotonic incremental tube forming process, which can give high percentage reduction of both diameter and thickness of tubes with excellent control of dimensions.[5,6] The process involves repeated rolling of the tube over a mandrel using rolls (Figure 1(a)) with a tapered groove in their circumference.[1–4] Each pass is comprised of a forward stroke and a return stroke. The tube is pushed forward along its axis and turned about its axis before either the forward or return stroke. Each rolling stroke involves ‘biting’, followed by reducing/forging and then polishing and idling.[7–10] The dimensions of the partly pilgered Zircaloy-4 tube is expected to trace the grooved rolls. Only a part of the inner surface of the tube, termed the groove, contacts the mandrel during the stroke. The remainder, which does not contact the mandrel, is called the flange. The turn about the tube axis given before each stroke ensures that different parts of the inner tube surface form the groove and flange in different passes. The imposed triaxiality of stresses or strains, which is JAIVEER SINGH, Research Scholar, GULSHAN KUMAR, Research Scholar, PRITA PANT, Associate Professor, and I. SAMAJDAR, Professor, are with the Department of Metallurgical Engineering & Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India. SIVASAMBU MAHESH, Associate Professor, is with the Department of Aerospace Engineering, Indian Institute of Technology Madras, Chennai 600 036, India. Contact e-mail: [email protected] D. SRIVASTAVA, Head, Physical Metallurgy Section, and G.K. DEY, Associate Director, Materials Group, are with the Materials Science Division, Bhabha Atomic Research Centre, Trombay, Mumbai, 400 085 India. N. SAIBABA, Chairman & Chief Executive, Nuclear Fuel Complex, is with the Nuclear Fuel Complex, PO: ECIL, Moula-ali, Hyderabad 500 062, India. Manuscript submitted April 15, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
intrinsic to pilgering, is known to offer better formability than typical draw bench operations.[11–13] Because it offers strong dimensional control, superior surface finish, and controlled developments in deformed microstructure and crystallographic texture, pilgering is often used as the fabrication tool for a variety of critical components, e.g., zirconium-alloy tubes used in thermal nuclear reactors.[5,6,14,15] Typically, hot-extruded tubes are pilgered to achieve desired dimensions and microstructures/textures. The in-reactor performance of these components demands stringent quality control,[16] which, in turn, demands detailed understanding of microstructure and property evolution during this complex incremental manufacturing process. Efforts to quantify the microstructure and properties of zirconium-alloy tubes produced by cold pilgering are described in the literature. Tenckhoff and Rittenhouse[17] characterized the final basal and prism pole figures and described the dependence of the texture
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