Strengthening and hydrogen embrittlement of ultrafine-grained Fe–0.01 mass% C alloy processed by high-pressure torsion

This study was conducted to elucidate the effects of annealing and hydrogenation on the tensile properties of an Fe–0.01 mass% C alloy processed by high-pressure torsion (HPT). By HPT processing, the tensile strength was increased to ∼1500 MPa through grain refinement. Low-temperature annealing further strengthened the HPT-processed specimen because of a simultaneous effect of carbide precipitation and grain refinement. Reduction in the dislocation density and the fraction of low-angle grain boundaries through warm-temperature annealing led to a decrease in hydrogen uptake when the specimens were exposed to high-pressure gaseous hydrogen, and they became less sensitive to hydrogen embrittlement (HE).

► We examined hydrogen embrittlement of ultrafine-grained Fe through annealing.
► Dislocations and low-angle grain boundaries generated by HPT process trap hydrogen.
► Low-temperature annealing hardened HPT-processed Fe because of carbide precipitation.
► Warm-temperature annealing decreased dislocations and low-angle grain boundaries.
► Reduction in hydrogen uptake in warm-annealed Fe led to no hydrogen embrittlement.