A review has been carried out on the status of particular microalloying elements in plate used for the construction of naval ships. The potential problem area tends to be the heat affected zone (HAZ) toughness where the presence of niobium imparts no beneficial effects. Vanadium has been excluded historically on the basis of cost, but current trends indicate that the ferroniobiumferrovanadium cost differential has been decreasing. In addition, vanadium is known to reduce the incidence of transverse slab cracking, and this could potentially reduce through costs as the scarfing loss to remove the cracks can account for a yield loss of y3%. A detailed through cost evaluation is required to establish the exact status. In addition, a tentative relationship exists between the HAZ toughness effect of the microalloying element and its effect on the susceptibility to induce transverse slab cracking. Overall, the benefits improve in the order of niobium, vanadium and titanium. If cost is factored into these effects, then the microalloying element with the most potentially positive benefits is titanium. The effects of multimicroalloying have been briefly reviewed and this is clearly an area where further work is required. Although molybdenum has been extensively used in linepipe steels, its potentially positive effects as a microalloying element, and on transverse slab cracking in ship plate steels, has never been fully enough explored. This is related to its higher ferroalloy cost.

Virtual fabrication technology (VFT) weld modeling software has been mainly used in thick-structure welding simulation. Recently both U. S. and European shipyards have shown strong interests in using the software to predict and control welding distortion of thin-plate ship panels. It is more complicated to simulate the welding of thin structures than thick structures because buckling distortion often occurs during the welding of thin structures. To evaluate the effectiveness of VFT for predicting distortion in thin structures, a bead-on-plate specimen, a butt joint of two large plates, and a long T stiffener were analyzed with VFT welding modeling software. By comparing the predicted distortions with those obtained by measurement, it was found that VFT can accurately predict welding-induced distortions of thin structures. Sensitivity studies show that pre-deformation induced by upstream fabrication processes and heat input are important factors influencing predicted distortions. Both distortion trends and magnitudes for thin structures are influenced by predeformation and heat input. 99

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

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