Effect of Si on the Aging Behavior of Cold-Drawn Pearlitic Steel Wires
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UCTION
HIGH-STRENGTH pearlitic steel wires have been used for suspension bridges, automobiles, and springs. Zn hot-dip galvanization is necessary for pearlitic steel wires to improve its anti-corrosion properties.[1,2] Depending on post-deformation annealing conditions, age hardening or softening would alter steel wire strength remarkably.[3–12] Age hardening is the decomposition of lamellar cementite annealed at low temperatures and the diffusion of dissolved carbon atoms in lamellar ferrite and dislocation pinning by carbon atoms.[11,13,14] Thus, increasing annealing temperature and time would accelerate lamellar cementite decomposition. Age softening occurs at high annealing temperatures through the break-up and spheroidization of lamellar cementite and re-precipitation of cementite particles and recovery or recrystallization of lamellar ferrite.[8,10,12] Addition of Si reduces softening after hot-dip Zn galvanization.[1,15] Based on this, high tensile strength Zn-galvanized pearlitic steel wires with high Si content have been developed and used in long suspension bridges and similar structures. Previous studies have greatly improved the understanding for the effect of Si
YIYOU TU and XUEFENG ZHOU, Associate Professors, are with the School of Materials Science and Engineering, Southeast University, Nanjing 211189, and also with the Jiangsu Key Laboratory for Advanced Metallic Materials, Southeast University, Nanjing 211189, China. Contact e-mail: [email protected] XIAOHUI WANG and HUILING HUANG, Ph.D. Candidates, are with the School of Materials Science and Engineering, Southeast University. JIANQING JIANG, Professor, is with the School of Materials Science and Engineering, Southeast University, and with the Jiangsu Key Laboratory for Advanced Metallic Materials, Southeast University, and also with Nanjing University of Information Science & Technology, Nanjing 210044, China. Manuscript submitted July 5, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
on pearlitic steel wire properties; however, it remains a subject of debate and great interest. In the present work, we investigate the effects of Si on the aging behavior of pearlitic steel wires.
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EXPERIMENTAL PROCEDURE
Two hot-rolled pearlitic steel rods: (1) 0.22 pct-Si steel (Fe-0.93C-1.15Mn-0.22Si wt pct), (2) 0.22 pct-Si steel (Fe-0.93C-1.16Mn-0.95Si wt pct) were used in this work. Other impurities, such as P and S, were less than 50 ppm in these alloys. Both steel rods were quenched in salt bath [temperature range: 793 to 893 K (520 °C to 600 °C)] after being fully austenized at 1073 K (800 °C), and completed isothermal pearlitic transformation. Quenched rods (5 mm in a diameter) were pickled and drawn to wires to a final diameter of 2.05 mm (total reduction of 83.2 pct, e = 1.78). Average reduction per pass was approximately 10 pct. Post-deformation annealing treatment was performed on cold-drawn steel wires at different heating times of 15 seconds to 15 minutes at 698 K (425 °C), which is also the temperature of hot galvanization. Ultimate tensile str
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