Comparative Study on the Weldability and Low-Temperature Toughness of Thick TMCP Steel for Offshore Wind Power Substructures According to Grade and Welding Position

As the demand for eco-friendly energy increases, offshore wind power structures are gradually becoming larger to increase power generation capacity, which in turn requires the use of thick TMCP steels and the securing of structural integrity. In this study, multi-pass FCAW was applied to 40 mm thick S355ML and S420ML steels in 2G and 3G welding positions, and the welding conditions for each experiment were designed to simulate actual industrial site construction conditions. After the experiments, tensile, low-temperature impact, and hardness tests were performed on the welded joints, and a comparative analysis was conducted on whether the relevant standards were satisfied and their major characteristics. As a result of the tensile test, tensile strengths exceeding the standard requirements were measured under all conditions, and base metal fracture occurred. In addition, the low-temperature impact test conducted at −50 °C exceeded the standard requirement of 27 J, ensuring sufficient low-temperature toughness, and the Vickers hardness test results were measured to be less than the reference value of 380 HV10. Through this study, the structural integrity and mechanical reliability of multi-pass FCAW welded joints for thick TMCP steel plates were secured.