scope:

Significant production of niobium steels began about 15 years ago. The early steels contained up to 0.03% Nb and permitted higher yield strengths to be obtained in steels having greatly reduced carbon equivalents. Thus the heat affected zone properties of these steels were excellent and they were widely adopted for welded construction of ships, bridges, pipelines and the like. More recent development has extended the use of niobium strengthening to higher yield strengths, more complex base plate composition, greater thicknesses and to more severe climatic regions such as the Arctic. In addition niobium contents have been increased (in some cases to above 0.10%) steel rolling and heat treating practices have become more sophisticated and welding evaluations are now concerned with all regions of the weld and adjacent base plate. The inclusion of weld metal toughness minimums in several recent specifications focused attention on the potentially detrimental effect of excessive niobium levels in high dilution welds. However recent studies have demonstrated that the behavior of niobium is strongly related to the carbon, titanium and vanadium contents of the base plate and to the characteristics of the welding process and consumables used. The paper summarizes the extensive current usage of niobium strengthened steel in a wide variety of welded constructions