The effect of the weld fusion zone shape on residual stress in submerged arc welding

A new multiple-electrode submerged arc welding technique has been developed that imparts improved fracture toughness properties in the heat affected zone, produces a narrower weld bead geometry, and can also be employed with lower heat inputs than conventional SAW. This study examines how the difference in the weld fusion zone profile affects residual stresses for weldments of API X70 steel made using the same consumable, heat input and restraint, varying only the shape of the weld fusion zone. The contour method and neutron diffraction have been employed to map and compare longitudinal and transverse residual stresses. Results show peak longitudinal stresses in the weld are within 50 MPa for both, and this is believed to be because they have the same heat input and hence similar heat affected zone size. By contrast, the peak stress in the transverse direction is 120 MPa lower for the new SAW technique. The reduction in transverse stress is attributed to a narrower fusion zone profile. The new SAW technique opens up the possibility of producing high quality narrower welds with lower heat input which could lead to significant reductions in residual stress.