Microstructure and Hardness Properties of a S690QL Steel Welded Joint

Offshore structures, including oil and gas platforms, wind turbines, and wave energy converters, are subject to harsh environmental conditions and high-stress cyclic loading. The reliability and safety of these structures are critical, and the performance of welded joints is a key factor in ensuring their structural integrity. Employing precise welding techniques are essential to minimize degradation of the mechanical properties of welded joints, particularly in preventing the formation of brittle phases and ensuring long-term service reliability. To accomplish this, a thorough examination of the hardness properties of two different S690QL steel welded joints was conducted using Vickers hardness testing. Additionally, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) was used to complement the hardness assessments. Thicker joints show lower hardness values in the heat-affected zone due to slower cooling rates. Conversely, higher hardness values in the upper sections of welds imply the influence of increased heat input during final tempering steps. This research underscores the significance of precise heat treatment techniques in mitigating residual stresses, controlling the characteristics of the heat-affected zone and enhancing mechanical properties, thus contributing to improve structural integrity and safety.