Laser and laser assisted arc welding processes for DH 36 microalloyed steel ship plate

A series of laser and laser assisted metal inert gas (MIG) welds was produced from a common plate. Each weld was mechanically tested, and the welds showed broadly similar properties, except for the autogenous CO2 laser weld metal, which had poorer toughness. This was related to a harder weld metal microstructure. Toughness and hardness were related to the lath width of the ferrite, for the welds involved. The weld metal area/volume was used as an indicator of potential distortion. In this instance, the autogenous CO2 laser weld was superior to the CO2 laser assisted MIG weld which was better than the Nd:YAG laser assisted MIG weld. Each weld was examined using carbon extraction replicas in the TEM, and also using an SEM with an EDAX attachment. A number of inclusions and precipitates were observed, identified and sized. It was concluded that the particles observed were not detrimental in this specific case. A tentative relationship was established between parent plate inclusion size distribution and weld metal inclusion size distribution.