Vanadium or copper alloyed duplex lightweight steelwith enhanced hydrogen embrittlement resistance at room temperature

Abstract

Hydrogen embrittlement is a phenomenon that causes the deterioration of mechanical properties of steel, such as ductility, owing to hydrogen present inside the material and is a crucial factor that determines the reliability of structural materials. Hydrogen embrittlement is controlled by two kinetics—trapping and diffusion of hydrogen present in the material—and these are affected by microstructural factors such as defects and phases. In this study, microstructures of medium-Mn duplex lightweight steel (Fe-0.5C–12Mn–7Al) and lightweight steel containing 0.1 wt% V and 1 wt% Cu were analyzed, and slow strain rate tensile tests were performed after electrochemical hydrogen charging. The correlation between microstructural evolution and hydrogen embrittlement was analyzed by measuring the amount of hydrogen inside the steel through thermal desorption analysis. Resistance to hydrogen embrittlement was improved in the decreasing order of Cu addition, V addition, and no addition of steel. When V is added, the V-rich carbide acts as an effective hydrogen trapping site, improving the resistance to hydrogen embrittlement despite the majority of hydrogen being inside the specimen. When Cu is added, the B2 particles trap hydrogen in a similar way as done by V-rich carbide, and the solute segregation along the boundaries interferes with hydrogen diffusion. Because Cu is an austenite stabilizer, the fraction of FCC, which is a close packed structure, is high. Thus, the amount of hydrogen entering the specimen is the least under Cu addition, and the corresponding steel shows the best resistance to hydrogen embrittlement. Microstructural factors have a significant effect on hydrogen embrittlement, and by adding V and Cu, it is possible to develop a medium-Mn duplex lightweight steel that can accommodate sufficient deformation even when exposed to a hydrogen atmosphere.