Mechanical properties of weathering steels at elevated temperatures

Weathering steels are high strength low alloy steels, with a resistance to corrosion provided through their alloying elements to form a dense layer of rust to stop further corrosion. While their mechanical material properties are well-known at ambient temperature, they have not been studied when exposed to high temperatures (as found in fires) and then cooled. This research examines mechanical properties such as Young's modulus, E, yield stress, σ_y, ultimate stress, σ_u, fracture toughness, and surface hardness for weathering steel (A588) and compares them to A709/A992 non-weathering steel. Such a comparison is done at ambient (as a control) and for temperatures ranging from 20 °C (70 °F), to 815 °C (1500 °F). Cooling by air and cooling by water examines the post-fire residual strength. Results show that A588 steel specimens have a slightly larger reduction in σ_u at elevated temperatures compared to A709 steel specimens. Steel specimens heated up to 649 °C (1200 °F) and allowed to cool in either air or water can be expected to possess residual (post-fire) mechanical properties that are comparable to their original ambient temperature mechanical properties. Steel specimens heated to 815 °C (1500 °F) and cooled in water can experience significant increases in their residual ambient temperature σ_y and σ_u values, but also increasingly brittle behavior.