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Steel and Composite Structures
  Volume 39, Number 4, May25 2021 , pages 401-417

Experimental study of welding effect on grade S690Q high strength steel butt joint
Cheng Chen, Sing Ping Chiew, Mingshan Zhao, Chi King Lee and Tat Ching Fung

    This study experimentally reveals the influence of welding on grade S690Q high strength steel (HSS) butt joints from both micro and macro levels. Total eight butt joints, taking plate thickness and welding heat input as principal factors, were welded by shielded metal arc welding. In micro level, the microstructure transformations of the coarse grain heat affected zone (CGHAZ), the fine grain heat affected zone (FGHAZ) and the tempering zone occurred during welding were observed under light optical microscopy, and the corresponding mechanical performance of those areas were explored by micro-hardness tests. In macro level, standard tensile tests were conducted to investigate the impacts of welding on tensile behaviour of S690Q HSS butt joints. The test results showed that the main microstructure of S690Q HSS before welding was tempered martensite. After welding, the original microstructure was transformed to granular bainite in the CGHAZ, and to ferrite and cementite in the FGHAZ. For the tempering zone, some temper martensite decomposed to ferrite. The performed micro-hardness tests revealed that an obvious "soft layer" occurred in HAZ, and the HAZ size increased as the heat input increased. However, under the same level of heat input, the HAZ size decreased as the plate thickness increased. Subsequent coupon tensile tests found that all joints eventually failed within the HAZ with reduced tensile strength when compared with the base material. Similar to the size of the HAZ, the reduction of tensile strength increased as the welding heat input increased but decreased as the thickness of the plate increased.
Key Words
    welded high strength steel; heat-affected zone; light optical microscopy; micro-hardness test; microstructure; tensile strength
Cheng Chen: School of Civil Engineering and Geomatics, Southwest Petroleum University, Xindu Street No.8, China
Sing Ping Chiew and Mingshan Zhao: Singapore Institute of Technology, 10 Dover Drive, Singapore
Chi King Lee: School of Engineering and Information Technology, University of New South Wales Canberra, Canberra 2600, Australia
Tat Ching Fung: School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Ave, Block N1, Singapore

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