Mechanical behavior of high strength S690-QT steel welded sections with various heat input energy

• Published in: Engineering structures 2018-11, Vol.175, p.245-256
• Main Authors: Liu, Xiao, Chung, Kwok-Fai, Ho, Ho-Cheung, Xiao, Meng, Hou, Zhao-Xin, Nethercot, David A.
• Format: Article
• Language: English
• Subjects: Aluminum; Automatic welding; Base plates; Butt welding; Construction materials; Deformation; Design engineering; Digital imaging; Ductility; Energy; Gas metal arc welding; Gauges; Heat; High strength; High strength steel; Image resolution; Line heat input energy; Material properties; Mechanical properties; Metals; Plates; Reduced ductility; Reduction; Steel; Strain gauges; Strength reduction; Tensile tests; Thermal energy; Weld metal; Welded sections; Welding; Welding machines; Welding parameters; Yield strength
• ISSN: 0141-0296; 1873-7323
• DOI: 10.1016/j.engstruct.2018.08.026

•S690-QT steels suffer reduction in mechanical properties after welding.•Tensile tests on welded sections with different heat input energy are conducted.•Typical heat input energy of welded sections ranges from 1.0 to 5.0 kJ/mm.•Almost all coupons of the welded sections fracture within the HAZs.•For 1.0 kJ/mm, there is almost no reduction in the mechanical properties.•For 5.0 kJ/mm, only 70% of the yield strength of the base plates is attained. Over the past two decades, there were a number of experimental investigations into mechanical properties as well as structural behaviour of high strength S690-QT steel welded sections. It is evident now that, similar to structural aluminium, these welded sections will suffer from a significant reduction in their mechanical properties, i.e. both yield and tensile strengths as well as ductility, due to change in microstructures if welding is not properly controlled. Owing to a lack of detailed understanding on effects of various welding procedures and parameters onto the mechanical properties of these steel welded sections, many design and construction engineers have serious concerns on adopting these S690-QT steel materials in buildings and bridges. This project aims to investigate and quantify effects of various line heat input energy onto the mechanical properties of the S690-QT steel welded sections through a series of carefully planned and executed standard tensile tests. A total of 12 standard tensile tests on cylindrical coupons of welded sections were conducted, and full range deformation characteristics of these coupons were obtained through use of strain gauges and measurements on high resolution digital images. Both welding methods, namely, GMAW and SAW, were employed to prepare full penetration butt-welded sections with various line heat input energy. It should be noted that GMAW was performed with a robotic welding system while SAW was performed with an automated welding machine to attain high quality welding consistently. Additional standard tensile tests on 3 reference coupons machined from the base plates, and another 3 reference coupons machined from the weld metal were also conducted to provide basic material properties for direct comparison. It was shown that in almost all coupons of the welded sections tested in the present study, fracture occurred within the heat affected zones of the welded sections without any failure in neither the weld metal nor the base plates. For welded sections prepared wi