Residual stress distributions have been established on thin (4 mm thick) plates made from a ferritic steel designated grade DH-36, which is relevant to ship construction. The influence of welding speed (thus energy input) and stiffener dimensions on the residual stress distributions have been studied. The residual stresses in the vicinity of the welds have been measured using the neutron diffraction technique. Increasing the weld speed reduces the weld width and subsequently the width of the high tensile strain region in the vicinity of the butt weld. However, within the practicable limits examined, the weld speed has little effect on the overall stress distribution. It has also been found that the stiffener thickness has relatively little influence on the resultant residual stress distribution.

The current trend in ship construction is to reduce the thickness of the ship panels, in order to minimize weight and maximize vessel speed. The ship panels of interest consist of 4 mm thick butt welded plates. This reduction in panel thickness may lead to excessive plate distortion during welding, resulting in significant additional costs during assembly. A ferritic-pearlitic DH-36 steel is used, in which phase transformations during welding may affect the distortion and stress states observed. Two large plates, representative of ship panels, have been butt welded using a metal inert gas (MIG) process. The temperature histories have been recorded during welding and the resulting distortion profile has been obtained using digital photography. Neutron diffraction measurements have been performed to determine the residual stress state in the plates before welding, due to e.g. processing and laser cutting, and after butt welding of the plates. Reference matchsticks from the weld, heat affected zone (HAZ) and parent plate have been taken from similar locations in nominally identical plates and measured to obtain the strain/stress free lattice parameter, α0. A Rietveld analysis has been performed on the diffraction data. Post welding, hardness surveys have indicated the microstructural variation in the weld, parent plate and HAZ. Results from these on-going studies are presented which identify the key factors responsible for thin plate distortion.