Niobium-Bearing Structural Beam, Section and Seismic Rebar Development

by Steven G Jansto, David D Jarreta

Publisher - CBMM - Reference Metals Company, CBMM - Metal Prime Technology Pte Ltd

Category - General Novel

Value-added niobium (Nb) bearing microalloyed structural steels continue to be researched, developed and commercially implemented throughout the world. There is a shift in progress for several structural applications in the plate and beam segment to Nb-bearing grades at less than 0.10%C replacing non-Nb bearing grades at 0.15-0.22%C grades with superior toughness. In view of the recent demand for alternative high strength lower carbon structural beam chemistries and associated economic and processing cost factors, the low carbon low alloy (LCLA©) niobium-microalloy approach has been developed and applied for the production of large structural beams with improved mechanical properties. The Nb-microalloyed structural beam steels for building and bridge applications exhibit outstanding notch-toughness even at -40oC compared to other traditional microalloy design systems. The LCLA© approach is under development and implementation for several long product light and medium shapes for construction applications as well. One of the most important steel products widely applied in civil construction is weldable and non-weldable reinforcing steel bar. The application of Nb bearing rebar has increased in popularity for the 345, 390 and 490 grades. However, there exists a compelling need for development of even higher quality rebar for seismic applications driven by recent catastrophic earthquakes in Haiti, Peru and China. Niobium value added rebar research projects are in progress around the world with a focus on the development of a family of S500 and S600 Nb-Mo grades with superior toughness, fatigue resistance, fire resistance and less yield to tensile ratio variation compared to current grades. Successful high quality production of these higher strength-elongation Nb-steel grades, regardless of the microalloy addition type, will require changes in melting and hot rolling practices to consistently manufacture these value added S500 and S600 reinforcing bar grades for earthquake as well as typhoon resistant applications.

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