Welding of niobium containing microalloyed steels

This paper reviews a selection of the more important contributions of the past decade on the influence of niobium on various aspects of the weldability of high strength low alloy steels. It is apparent that niobium has insignificant effects on many aspects of weldability, but that considerable controversy has existed in relation to its influence on weld metal and heat affected zone toughness. The apparently contradictory observations of various earlier authors have been carefully examined and rationalized i n the light of all the relevant data now available in the world literature. It is concluded that the complex role of niobium can best be understood when its overall effects are examined in relation to its influence on transformation temperature, and in this context, the importance of carbon content and cooling rate following welding is emphasized. Finally, it is suggested that the most judicious use of niobium will only be made when the liaison between the steelmaker and the end user is improved. It is therefore proposed that all steel compositions should be tailored, not simply with a view t o obtaining optimum base plate mechanical properties, but with equal consideration t o the end product and in particular, to the welding process envisaged for use in practice. (AU)