Effect of Si and Mn Interactions on the Spheroidization and Coarsening Behavior of Cementite During Annealing in Severe
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UCTION
HEAVILY cold-drawn pearlitic steel wires have attracted extensive interest from manufacturers and researchers aiming to understand their strengthening mechanism better and enhance their mechanical properties further. High strength primarily results from cold deformation through refinement of the lamellar structure of pearlite.[1] Heavy cold drawing causes partial chemical decomposition and structural transition of cementite, and a large amount of carbon atoms move across the interface into ferrite lamellae in pearlite.[2–9] During bluing at 573 K to 673 K (300 °C to 400 °C) or hot-dip galvanizing at 823 K (550 °C) in the manufacturing process of pearlitic steel wire, the re-precipitation of decomposed cementite and spheroidization of lamellar cementite remarkably degrade the mechanical
YIYOU TU, Associate Professor, XUEFENG ZHOU, Associate Professor, and FENG FANG, Professor, are with the School of Materials Science and Engineering, Southeast University, Nanjing 211189, China, and also with the Jiangsu Key Laboratory for Advanced Metallic Materials, Southeast University, Nanjing 211189, China. Contact e-mail: [email protected] LINGHUI HUANG and XIAOHUI WANG, Doctoral 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 also with the Jiangsu Key Laboratory for Advanced Metallic Materials, Southeast University, and with the Nanjing University of Information Science & Technology, Nanjing 210044, China. Manuscript submitted June 28, 2015. Article published online November 3, 2015 254—VOLUME 47A, JANUARY 2016
property of pearlitic steel wire, especially torsional properties.[8,10,11] The coarsening behavior of cementite particles in Fe-M-C (M: alloying element) ternary systems has been extensively studied. Volume diffusion of M in the a-Fe matrix for partitioning serves as the process controlling the coarsening of cementite in the a-Fe matrix of Fe-M-C ternary systems.[12] The growth rate of cementite during annealing decreases substantially with increasing addition of Cr, Mn, and Si because of the redistribution of alloying elements between cementite and the ferrite matrix; Mn and Cr are more effective than Si in retarding the coarsening effect of cementite particles.[9,12–17] Suppression of coarsening of cementite particles by P or Sb is caused by segregation of these elements at the ferrite/cementite interface.[18] Although previous studies have achieved tremendous progress in improving the understanding of these phenomena, the interactive effects between alloying elements remain a subject of debate and great interest. In the present work, we investigate the effect of Si and Mn interactions on the spheroidization and coarsening behavior of cementite during annealing in severe cold-drawn pearlitic steel.
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EXPERIMENTAL PROCEDURE
Two hot-rolled pearlitic steel rods provided by Jiangyin Xingcheng Special Steel Co., Ltd. were used; the hypereutectoid compositions of
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