The effect of hydrogen release at room temperature on the ductility of steel wire rods for pre-stressed concrete

The present study investigated the variation of reduction in area at fracture with the storage time of a high-carbon steel wire rod for pre-stressed concrete. The steel used in this study was an 11-mm diameter, hot-rolled and controlled-cooled wire rod produced without vacuum degassing. The wire hydrogen content and its reduction in area were measured for storage times up to 960 h at room temperature. The hydrogen content decreased from 1.85 ppm immediately after cooling to nearly 0.55-0.60 ppm after 216 h and then stabilized, while the reduction in area increased from 20% to around 37% during this same period of time. Analysis of the hydrogen content variation over time suggests that the release of hydrogen is responsible for an increase in the ductility of the steel. It was also shown, by comparing the results from two models regarding the amount of hydrogen release from the wire, that this phenomenon may be controlled by diffusion when reversible traps are present.