Mechanical properties of HSLA-65 hybrid laser arc welds

High strength steels are finding increasing use in the shipbuilding industry to decrease the weight of vessels for improved maneouverability and fuel efficiency, increased payloads and decreased fabrication costs. High strength low alloy (HSLA) steel, such as HSLA-65, provides a unique combination of strength, weldability and toughness that makes it a particularly attractive choice for many shipbuilding applications. However, as HSLA-65 is a thermomechanically processed steel, it can be susceptible to grain coarsening and softening in the heat affected zone (HAZ) during welding. Low heat input welding procedures such as hybrid laser arc welding are desirable because they minimise HAZ softening and can tolerate gaps between the workpieces better than conventional laser welding. In this paper, the mechanical properties of hybrid laser arc welds, used to join 9.1 mm thick HSLA-65 plates in a single pass, were evaluated. Hardness maps indicated that softening did not occur in the HAZ. Transverse tensile fracture occurred in the base metal, away from the welds, confirming that the fusion zone and HAZ had higher strength than the base metal. Subsized Charpy impact toughness specimens, notched in the HAZ, were typically less tough than the base metal. However, the fracture path typically deviated away from the HAZ, into either the base metal or along the fusion line.