On hydrogen-induced damage in cold-drawn lean-duplex wires

Abstract Wire manufactures have recently started to produce a less-expensive class of high-strength wires referred to as lean-duplex. They are more attractive to the construction industry, which seeks alternatives to eutectoid prestressing steel and are able to enhance structural durability at a reasonable cost. Their suitability for prestressing is still poorly addressed in terms of sensitivity to hydrogen embrittlement, the root cause of stress corrosion damage. Hence, this paper assesses the resistance to hydrogen-induced stress corrosion (H-SCC) of one of this new generation of wires. In order to determine such resistance, two types of tensile tests were carried out with wires in the as-received condition and fatigue precracked, in air and in an aqueous solution of 20% ammonium thiocyanate (FIP solution) at 50 °C. The former was used to set out the collapse time under constant load in FIP solution and the latter (that is to say, the slow strain rate test) to observe and assess the failure mode in inert and aggressive environments. This provided additional insights from the damage mechanisms that govern the failure of the wires. Lastly, the damage tolerance of the tested lean-duplex wires was analyzed in the as-received condition and embrittled by hydrogen. Comparisons with similar data corresponding to cold-drawn eutectoid and high-alloyed duplex stainless steels wires were made. Although the lifetime of lean-duplex wires is limited (contrary to that of high-alloyed duplex wires), it exceeds that of eutectoid wires, currently used for prestressing purposes, by more than 10 times.