Abstract
The expansion of transportation networks into canyon and mountainous regions has significantly increased the efforts in optimising the existing manufacturing processes and developing advanced structural materials. Although novel materials such as high-entropy alloys have emerged, steels remain the most widely used due to their superior load-bearing capacity. Structural steels offer an excellent balance of strength and ductility; however, their application often requires welding, which can compromise mechanical performance. Welding thick steel sections is particularly desirable for enhancing service reliability and structural stability, yet achieving defect-free joints with conventional techniques remains challenging. Narrow-gap welding has gained attention as a promising solution, enabling the joining of thick plates with reduced filler material and lower heat input. In this study, the double-wire narrow-gap welding technique was applied to a 40 mm thick dissimilar NM 450-ZG30SiMn steel joint using gas metal arc welding. The microstructural evolution and mechanical properties of the weld were systematically investigated. Hardness profile, tensile strength, and fatigue properties were evaluated and correlated with microstructural features. Failure mechanisms were analyzed, with particular focus on the effect of the soft zone, stress concentration, and tensile residual stresses on fatigue strength. The study demonstrates the implications of dynamic fatigue testing in ensuring the quality and structural integrity of welded joints for the demanding structural applications. The details of this work will be presented at the conference.