Influence of nanotwins on hydrogen embrittlement of TWIP (twinning-induced plasticity) steel processed by high-pressure torsion

摘要

Recent studies suggested that nanotwinned metallic materials can exhibit a good combination of high strength and high ductility. However, few studies examined the strength and ductility of nanotwinned alloys under hydrogen atmosphere. In this study, nanotwins are introduced in a TWIP (twinning-induced plasticity) steel by application of high-pressure torsion (HPT) followed by annealing. The nanotwinned austenitic TWIP steel exhibited a high tensile strength as -1.4 GPa but without ductility after hydrogen charging. Unlike nanotwinned alloy, the HPT-processed sample, which experienced a phase transformation to a bimodal martensitic structure, exhibited both high strength (～1.6 GPa) and high uniform ductility (6%) after hydrogen charging. It was concluded that twin boundaries act mainly as crack initiation sites and propagation paths but not as effective barriers for dislocation accumulation to enhance the ductility of the TWIP steels under hydrogen atmosphere.