Mechanical properties and simulated behavior in industrial atmosphere of welded joints of Q500qENH bridge weathering steels

The CO₂ gas shielded arc welding test of Q500qENH bridge weathering steel was carried out by horizontal transverse butt welding. The metallographic structure of the welded joint was observed by an OM, and the mechanical properties of the welded joint were tested by a hardness tester and tensile testing machine. The corrosion behavior of deposited metal in the industrial atmosphere was simulated through a cyclic immersion test. The structure and chemical composition of the rust layer were characterized by SEM and XRD, respectively. The corrosion weight loss rate of the deposited metal was measured. Finally, the corrosion resistance of the rusted specimen was evaluated by an electrochemical test. The results show that Q500qENH has a low hardening tendency and cold crack sensitivity during welding. The tensile strength of the joint is higher than 650 MPa, and it has good bending resistance and low-temperature impact toughness. The corrosion products at the deposited metal after cyclic immersion in the corrosive solution for 48 h are α-FeOOH and γ-FeOOH. After 96 h of corrosion, a large amount of black Fe₃O₄ is generated in the rust layer, which then gradually decreases. The phase of the rust layer transforms into a stable lamellar α-FeOOH, which has a relatively dense structure and excellent corrosion resistance. In addition, Al₂O₃ inclusions and Si-rich phases in the rust layer will cause the formation of porosity, micro-cracks, and pores in the rust layer, which will adversely affect the compactness of the rust layer.