Experimental Investigation of the Effect of Surface Markings on the Mechanical Integrity of Weathering Bridge Steels. Final Report for April 24, 2013 - October 31, 2014.

摘要

High-strength low-alloy (HSLA) weathering steels are the conventional material used for nonredundant fracture-critical members in bridge construction. Guidelines have been put in place by state Departments of Transportation (DOTs) to prevent material suppliers from making scribe marks that will remain on the surface of fracture-critical members when in service, due to the possibility of degrading mechanical properties. Currently, any automated scribing marks allowed, namely mechanical milling, are either cut off of the member or subsequently welded over, thereby effectively removing them prior to service. All other markings are either manually die-stamped or spray-painted on. The lack of an automated capability to place markings on weathering steels slows production, and markings are often accidentally removed during sand blasting or shipping, which causes additional problems for the manufacturer and recipient. There is a need to establish safe, automated methods of scribing fracture-critical members such that markings will remain throughout the production process, but will not compromise the integrity over the lifetime of the part. Three automated techniques were of interest in this study as they are often already in the manufacturing process. These include mechanical milling, plasma scribing, and laser scribing. In this study, a microstructural evaluation of 50W weathering steel was conducted to understand and characterize the effect of the three markings on microstructural evolution and mechanical properties. Plasma scribing resulted in the most noticeable surface marking. S-N curves generated through fatigue testing showed no measurable difference in fatigue life between marked and unmarked material.