Abstract: Microalloying with Niobium or Vanadium is commonly used in long high strength (> 50 ksi) steels, usually in compositions with carbon around 0.10% and about 1% manganese. In addition to requirements from standards (eg. ASTM A572), the use of low C + microalloying allows adequate combination of mechanical properties, mainly strength, ductility and toughness, especially when compared to high carbon low strength steels (eg. ASTM A36). This paper analyzes the possibility of Nb substituting V in standard long structural products, with examples in beams, sections and flats, with different dimensions. All products were focused on 50 ksi with base chemical composition of carbon between 0.07% and 0.17% and manganese between 0.8% and 1.5%. Vanadium was the standard microalloying elements in those products, with contents between 0.010% and 0.060%V. First, several trial heats with Nb replacing V were produced, followed by a number of large scale production heats. V was replaced with Nb with a ratio of 1 part of Nb for 2 parts of V, and all cost comparison used this ratio in addition to the alloy prices. The final Niobium content in those products then varies from 0.005% to 0.030%Nb. Provided that Nb was fully soluble after reheating, direct rolling was applied without the need of specific thermomechanical rolling practices. In addition to substantial cost advantages in terms of alloy costs, the use of Niobium showed improvement in the Yield to Tensile strength ratio in many of the products. No issues were found in casting or rolling.
Authors:Rafael A. Mesquita, Yan Wang, Bryan Williams, John Heerema, Steve Jansto, and Bhaskar Yalamanchili
Keywords: Case Study, Long Products, Beams, Sections, Vanadium Microalloying, Niobium Microalloying, Substitution