Alternative materials to HY-80, quenched and tempered structural alloy steel, like the microalloyed steels HSLA-80 and ULCB, allow the suppression of the quenching and tempering heat treatment and offer better weldability due to their extra-low C content. In the HSLA-80 steel copper precipitation is one of the main hardening mechanisms available, while in the ULCB steel the contribution of the bainitic transformation plus solid solution hardening is vital. The aim of this work was to determine the continuous cooling austenite transformation (CCT) diagrams of both steels and its performance during age hardening. It was verified that both alloys developed a bainitic microstructure with low C content, commonly designed by the literature as "granular" bainite. The hardenability of the ULCB steel was greater than the HSLA-80 due to the presence of Nb, B and Mo in the first alloy. The age hardening behavior of these alloys was slightly different between each other. The HSLA-80 steel developed maximum hardness during a 600 • C age hardening, while for the ULCB steel this occurred at a 500 or 600 • C age hardening and took less time. Both steels showed a significant hardness decrease during the 700 • C age hardening, that was probably due to overaging and tempering effects.

Hot strip structural steel coil used in construction, engineering, transport, structural applications and other applications are widely used in yield strengths from 300 -700 MPa. However, structural design engineers are now not only requiring various strength levels but also other mechanical properties, primarily good formability, toughness and weldability. To produce a balanced approach to a cost effective structural steel, hot strip coil requires an understanding of utilization of an optimized alloy composition designed for the layout/equipment capabilities of a given hot strip mill to produce the desired metallurgy for optimum mechanical property performance. The term "cost effective" does not just focus on alloy design, but also ease of overall processing from steelmaking, casting, rolling and cooling, stable mechanical properties with a statistically normal distribution, no downgrades/rejections and a product that the end user recognizes as being superior to others. The desired metallurgy is simply understanding what will be the optimum microstructure and cross sectional grain size/distribution needed to meet the mechanical property requirements. This paper is a follow up paper that previously described optimum base alloy designs along with steelmaking/casting processing considerations and will focus on proper reheating, rolling and cooling metallurgy/processing strategies to produce quality cost effective hot strip structural steel coil.

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