Effect of plasma marking on the fatigue properties of grade 50W steel

Abstract: High-strength low-alloy (HSLA) weathering steels are the conventional material used for nonredundant fracture-critical members in bridge construction. Guidelines from state departments of transportation (DOTs) prevent material suppliers from scribing marks which remain on the surface of fracture-critical members when in service due to the possibility of degrading mechanical properties. Currently, any automated scribe marking, namely mechanical milling, is either cut from the end of the part, or welded over, thereby effectively removing it before service. All other markings are either manually die-stamped, or spray-painted on, which can be accidentally removed during sand blasting or shipping. Safe automated methods of scribing fracture-critical members are needed such that markings will remain throughout the production process but will not compromise the integrity over the lifetime of the part. In this study, a microstructural evaluation of 50W (or 345W) weathering steel was conducted to characterize the effect of plasma markings on microstructure and mechanical properties. S-N curves generated through fatigue testing showed no measurable difference in fatigue life between marked and unmarked material.