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COST EFFECTIVE ALLOY OPTIMIZATION DESIGN STRATEGY FOR STRENGTH AND DUCTILITY PROPERTIES OF STRUCTURAL STEELS

Autoria

Stalheim, Douglas Glenn; Barbosa, Ronaldo Antonio Neves Marques; Rodriguez-Ibabe, Jose Maria; Wang, Houxin

DOI

10.5151/9785-9785-32230

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Resumo

 

Major costs in the production of both flat and long commodity grade structural steel products include alloy, labor and energy. Flat and long commodity grade structural steels such as ASTM A36, ASTM A527Gr50, S235, S275, S355 and other equivalent world societal standards represent over 500 million annual tons worldwide. These simple commodity grades consist of a minimum of three base common alloying elements, carbon, manganese, silicon and then can be supplemented with microalloying elements of either vanadium or niobium. Since 2016 raw material costs for two of the five alloying elements in these commodity grade structural steels, FeMn and FeV, have risen significantly. For steel plants producing hundreds of thousands and in some cases over a million tons annually of these common structural steel grades because of the significant alloy cost increase for Mn and V alloy additions has squeezed profitability of these grades. These grades typically represent the base loading for cost controls in most all steel plants and hence a significant cost increase in two of the five elements used for these grades has a negative effect on overall production costs. However, with a proper strategy for alloy designs working in conjunction with the mills existing processing capabilities to achieve the desired end metallurgy/mechanical properties, alloy costs and operational efficiencies can be realized. Cost savings of US $2/ton to US $20/ton or in some cases higher in a mill producing typically from 200,000 tons up to 1 million tons annually can represent cost saving in alloy of US $400,000 up to US $20 million annually. Because of the significant opportunity for cost savings going to the financial bottom line, potential opportunities for alloy optimization is something that cannot be ignored and must be explored. Many worldwide commodity flat and long products structural steel producers have already taken steps in alloy optimization of their production and have realized significant cost savings. An understanding of what creates strength and ductility for any given structural steel microstructure is what is needed to achieve these cost savings. Strength and ductility for any structural steel are obtained from three metallurgical mechanisms or “building blocks”: a) grain size refinement, b) solid solution and c) precipitation. If better engineering of these contributions from the three metallurgical “building blocks” can be realized for a mill processing capabilities, alloy costs can be minimized resulting in significant annual cost savings. The correct use of these factors brings in addition process/mechanical property stability resulting in corresponding reductions in yield losses and additional operational cost savings. Use of practical metallurgical modeling tools along with mill data to determine process control capabilities can also assist in alloy designs for cost optimization.

Palavras-chave

Optimization, Strategy, Niobium, Vanadium, Microstructural Modeling