This project developed and tested the mechanical, fracture toughness, weathering, and welding properties of a new “super” weathering (SW), cost-competitive steel for transportation infrastructure applications. The new steel’s compositions were modifications of the composition of an ASTM A710 Grade B 70-ksi-yield, copper-precipitation-strengthening, hot-rolled and air-cooled steel, previously developed at Northwestern University, that showed excellent fracture properties at low temperatures and a corrosion loss about 40% less than that in A709 HPS70W steel (as measured in automotive accelerated SAE J2334 test at Bethlehem Steel/Arcelor Mittal). To increase the weatherability of steel phosphorus appears to be the most potent element to enhance the corrosion resistance of steel. However, phosphorus also increases the steel’s brittleness. Consequently addition of phosphorus to A710 Grade B steel (developed previously at Northwestern University) and mitigation of the steel embrittlement by addition of specific amount of titanium to keep phosphorous from migration to the grain boundaries was the approach taken in this IDEA project. Other elements, such as chromium and molybdenum, which enhance steel weathering, were also added. Four steels were designed and tested. The steels were very ductile and fracture-tough to -100°F, thus significantly outperforming the requirements of ASTM A709 bridge steel standard. No brittle heat-affected zone was formed as result of high-power laser welding simulation, thus indicating that the steels could be easily welded without pre- or post-welding heat-treatment. The accelerated studies indicated that developed steels have better weathering characteristics than A588 weathering steels that are currently used for bridge construction. The production of the newly developed steels does not require special processing or thermal treatment; therefore, these steels can be produced by any steel manufacturer in any steel-plate sizes.
The contractor's final report is available.