Niobium and heat affected zone mythology

The myth that niobium levels should be restricted in steel specifications for structural and line pipe applications, to avoid unacceptably low HAZ toughness, is considered herein and effectively dispelled. Furthermore it is demonstrated that control of carbon level and the judicious use of primary alloying elements should always allow steelmakers to identify attractive compositional options which more effectively utilise the unique properties of niobium to provide optimum combinations of plate and HAZ mechanical properties. The latter objective becomes possible because the important factors that control HAZ toughness in HSLA steels microalloyed with niobium are now more thoroughly appreciated; this should ensure that steels supplied for individual projects are metallurgically tailored to be compatible with the welding processes appropriate to the envisaged application. (AU) Copyright © 2013 Companhia Brasileira de Metalurgia e Mineração (CBMM) All Rights Reserved