Three-Dimensional Numerical Model Considering Phase Transformation in Friction Stir Welding of Steel
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TRODUCTION
FRICTION stir welding (FSW) of steel, as a solid-state joining process, prevents the generation of typical defects during fusion-based welding processes because no melting occurs during the process. Additionally, the process reduces manufacturing costs by eliminating shielding gas and costly weld preparation. In addition, FSW produces high-quality welds with superior mechanical properties compared with fusion-based welding processes.[1–3] Understanding of the heat transfer and material flow during FSW is crucial in optimizing the process and the resultant microstructure/properties of the welded joint. Therefore, many attempts to understand the complicated interactions among physical variables during FSW have been made for steels. Cho et al.[4,5] used a two-dimensional heat and material flow model to predict the material flow, thermal response, and strain hardening during FSW of 304L stainless steel. These authors used a simplified Hart’s model[6] to calculate the HOON-HWE CHO, Researcher, is with the Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, IL 60208. DONG-WAN KIM and KEUNHO LEE, Ph.D. Students, and HEUNG NAM HAN, Professor, are with the Department of Materials Science & Engineering and Center for Iron & Steel Research, RIAM, Seoul National University, Seoul 151-744, Republic of Korea. Contact e-mail: [email protected] SUNG-TAE HONG, Associate Professor, and YONG-HA JEONG, Ph.D. Student, are with the School of Mechanical Engineering, University of Ulsan, Ulsan 680-749, Republic of Korea. YI-GIL CHO, Researcher, is with the Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, PA 19104. SUK HOON KANG, Researcher, is with the Nuclear Materials Research Division, Korea Atomic Energy Research Institute, Daejon 305-353, Republic of Korea. Manuscript submitted on April 27, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
flow stress and non-Newtonian viscosity. Nandan et al. reported the results of three-dimensional (3D) heat transfer and material flow during FSW of 304 austenitic stainless steel[7] and 1018 low carbon steel.[8] These authors examined the temperature fields, cooling rates, and plastic flow fields by solving the equations for conservation of mass, momentum, and energy in three dimensions. These researchers also considered heat generation, non-Newtonian viscosity, and temperature-dependent physical properties in the calculation. More recently, Cho et al.[9] developed a 3D thermo-mechanical model considering the heat transfer and material flow during FSW of 409 ferritic stainless steel. Using the numerical model, these researchers confirmed that the microstructural characteristic changes during/after the FSW process are closely related to those of the temperature, strain rate, viscosity, material flow, and texture. These researchers also demonstrated that the rigorous numerical model can directly predict the microstructural characteristic changes during FSW. The various models mentioned above h
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