Microstructure Characterization of Fiber Laser Welds of S690QL High-Strength Steels
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S690QL steel is a high-strength steel that offers a higher performance in yield strength, weldability and corrosion resistance than that of mild steel.[1] The S690QL steel has been used widely in construction,[2] shipbuilding for applications such as the manufacturing of hoists and cranes, construction machines, transportation tanks, for parts and assemblies,[3] and welded structures.[4] BAOMING LI, HONGYING GONG, and CHUANGEN LIU are with the College of Materials Engineering, Shanghai University of Engineering Science, Shanghai 201620, People’s Republic of China. Contact e-mail: [email protected] PEIQUAN XU is with the College of Materials Engineering, Shanghai University of Engineering Science, and also with the Shanghai Key Laboratory of Materials Laser Processing and Modification, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China. FENGGUI LU and HAICHAO CUI are with the Shanghai Key Laboratory of Materials Laser Processing and Modification, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China. Manuscript submitted July 6, 2017.
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To achieve a better welded joint, it is important to control the welding parameters, which include the initial preheating, a controlled heat input during welding, and an additional post welding heat treatment. All of these conditions indicate that it is necessary to use a new welding method to satisfy the welding quality requirements. Paillard et al.[5] have successfully used different friction parameters during friction stir welding to weld S690QL high-yield-strength steel, reporting that the microstructural and mechanical properties were satisfied. However, the use of friction stir welding method can cause the resilience of the weld bead to decrease.[6,7] The microstructure of the heat-affected zone (HAZ) of S690QL electron-beam-welded joint was confirmed to be martensite (M),[8] and it was further found that the primary factors necessary to control the grain growth at the HAZ were the micro-alloy precipitate characteristics and the peak temperature.[9] Błacha et al.[8] have conducted electron beam welding of S690QL steel, where metallographic examination revealed that the concentrated electron beam significantly affected the changes of the microstructures. However, electron beam
welding requires rigorous welding conditions such as a vacuum.[10] The research proposed by Shin et al.[11] indicated that the weld metal of a flux-cored arc-welded joint had a slightly greater low-temperature impact toughness than that of a shielded-metal arc-welded joint. Compared with traditional arc welding, laser welding has become increasingly attractive and has excellent industrial prospects in many fields such as aerospace, automotive, off-road vehicles, shipbuilding, oil, and pressure vessel industries.[12–15] Research by Pinto et al.[16] revealed that laser welding caused dominant M formation, which led to prohibitive hardness values. Further, research on the fatigue behavior of laser welds in lap-shear samples of hig
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