Effect of heat input on microstructure and properties of hybrid fiber laser-arc weld joints of the 800 MPa hot-rolled Nb-Ti-Mo microalloyed steels |
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| Institution: | 1. Shagang School of Iron and Steel, Soochow University, Suzhou 215021, Jiangsu, China;2. Laser Processing Research Center, Soochow University, Suzhou 215021, Jiangsu, China;3. Laboratory for Excellence in Advanced Steel Research, Department of Metallurgical, Materials and Biomedical Engineering, University of Texas at El Paso, TX 79968, USA;1. Physics Department, Faculty of Science, Mansoura University, Mansoura, Egypt;2. Physics Department, Faculty of Science, Aswan University, Aswan, Egypt;3. BIAS-Bremer Institut für angewandte Strahltechnik, Klagenfurter, Bremen, Germany;1. National Aeronautics and Space Administration, Langley Research Center, Hampton, VA, USA;2. National Institute of Aerospace, Hampton, VA, USA;3. 1900 Engineering, LLC, Clemson, SC, USA;4. Department of Chemical and Biomolecular Engineering, Clemson University, Clemson, SC, USA;1. State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, No. 92 West Dazhi Street, Harbin 150001, China;2. Shandong Provincial Key Laboratory of Special Welding Technology, Harbin Institute of Technology at Weihai, No. 2 West Wenhua Road, Weihai 264209, China;1. MOE Key Lab for Liquid-Solid Structure Evolution and Materials Processing, Institute of Materials Joining, Shandong University, Jinan 250061, China;2. Technische Hochschule Brandenburg, Brandenburg an der Havel, D-14770, Germany;3. BIAS- Bremer Institut fuer Angewandte Strahltechnik, Bremen, D-28359, Germany;1. Key Laboratory of Automobile Materials of Ministry of Education, School of Materials Science and Engineering, Jilin University, No. 5988 Renmin Street, Changchun 130025, PR China;2. Changchun Railway Vehicles Co., Ltd., Changchun 130062, PR China |
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| Abstract: | Hybrid fiber laser-arc welding (HLAW) process was applied to a novel hot-rolled Nb-Ti-Mo microalloyed steels of 8 mm thickness. The steel is primarily used to manufacture automotive and construction machinery components, etc. To elucidate the effect of heat input on geometry, microstructure and mechanical properties, different heat inputs (3.90, 5.20 and 7.75 kJ/cm) were used by changing the welding speeds. With increased heat input, the depth/width of penetration was decreased, and the geometry of fusion zone (FZ) changed to “wine cup-like” shape. In regard to the microstructural constituents, the martensite content was decreased, but granular bainite (GB) content was increased. The main microstructural difference was in the FZ cross-section at 7.75 kJ/cm because of the effect of thermal source on the top and bottom. The microstructure of the top part consisted of GB, grain boundary ferrite, and acicular ferrite, while the bottom part was primarily lath martensite. The hardness distribution was similar for different heat inputs. Hardness in FZ, coarse-grained HAZ and mixed-grained HAZ was higher than the base metal (BM), but for the fine-grained HAZ was similar or marginally less than the base metal (BM). Tensile strain was concentrated in the BM such that the fracture occurred in this region. In summary, the geometry, microstructure, and mechanical properties of weld joints were superior at heat input of 5.20 kJ/cm. |
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| Keywords: | HLAW Heat input Weld joints Microstructure and properties Phase transformation |
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