Fracture toughness of laser welds in ship steel

Shipbuilders are showing increasing interest in laser welding as a means of reducing fabrication costs. The nature of the weld zone is very different to that in an arc weld. Careful research is needed to establish the safety of laser welded structures against a range of risk scenarios. This report deals with fracture toughness and defect tolerance. The laser weld is shown to exhibit very unusual behaviour. The lowest toughness is obtained when a crack is located at the heat affected zone (HAZ), but there is no apparent microstructural embrittlement at this location. It is proposed that the effect arises from an elevation of crack tip tensile stresses induced by the strength overmatch of the adjacent weld zone.