Niobium-bearing construction steels and global application trends

The technological development of value-added applications for Nb-microalloyed construction steels continues globally for both low and high yield strength applications. The civil engineering and end user community demands structural bars, shapes, beams and plates with improved properties. Properties such as increased toughness, better fire and seismic resistance, yield-totensile ratio consistency and improved weldability are end user requirements for both low and high yield strength construction applications. Nb-bearing construction steels have been, and will continue to be developed to address these more demanding requirements in both the low and high yield strength construction sector. Various Nb structural steel technologies are applied dependent upon the specification requirements, cost benefit considerations and competitive market conditions. These technologies and market dynamics are described in this paper. For example, several mills within the construction beam sector have adopted a 0.02 to 0.04%Nb chemistry and reduced the C content for lower strength (S355 and S420) steels with improved mechanical property performance and weldability, compared to traditional higher C (peritectic) construction steel grades. Operational cost reductions are also experienced by the steel producer when the Nb, low C, low alloy concept is adopted. Advanced Nb-bearing high strength structural steels have also been developed. Another evolving Nb product segment involves the high C, long product, pre-stressed, concrete wire rod market. Micro additions of 0.005 to 0.020%Nb exhibit improved wire drawability during manufacturing, as well as improved mechanical properties, compared to traditional non Nb-bearing high C steels. Finally, within the low C construction sector, the shift from the high volume, heavier gauge S235 and S275 construction grades to lower C, Nb-bearing S355 lighter gauge steels offers the potential to reduce construction costs with a favorable environmental impact on the carbon footprint. (AU) Copyright © 2015 Companhia Brasileira de Metalurgia e Mineração (CBMM) All rights reserved