Development and Performance Study of Welding Electrodes for Weathering Bridge Steel

In response to the demand for high-performance bridge steel in complex high-altitude environments, research and development of matching welding electrode for Q500qENH and Q550qENH bridge steel plates were carried out, and their performance was studied. 6 types of welding electrodes with different compositions were designed. Metallographic analysis and impact fracture morphology analysis were conducted on the weld metals, and the influence of the chemical composition of the deposited metals on the structure and properties was explored. The microstructure inside the weld bead was divided into three parts: columnar grain zone microstructure, reheated coarse grain zone microstructure, and reheated fine grain zone microstructure. The main metallographic structures were Acicular Ferrite, Proeutectoid Ferrite, Carbon Free Bainite, Block Ferrite and a small amount of Granular Bainite. The fiber area of the impact specimen had a relatively uniform dimple shaped structure. The crystalline area of the fracture surface was mostly composed of cleavage river patterns and a small amount of dimples. The research results indicated that Acicular Ferrite had a positive effect on the low-temperature toughness of deposited metals. No.3 had the highest proportion of Acicular Ferrite and the best low-temperature impact toughness. The increase in Mn and Si element content led to an increase in the proportion of Proeutectoid Ferrite and Carbon Free Bainite, while the proportion of Acicular Ferrite decreased. These factors had led to a decrease in low-temperature toughness. Ni element could increase the proportion of Acicular Ferrite tissue, which was beneficial for low-temperature toughness. The developed welding electrode matched well with the weathering steel plate, meeting the task requirements of weather resistance index I≥6.5, -40 ℃ kV₂≥60 J, A≥17%.