The advantage of grain refinement in the hydrogen embrittlement of Fe–18Mn–0.6C twinning-induced plasticity steel

•Grain refinement improved the resistance to H embrittlement of Fe–Mn–C TWIP steel.•The H concentration segregated at grain boundaries was reduced by grain refinement.•Junctions of twin–twin and twin–grain boundaries were also reduced in fine grains.•The H migration to twin junctions during tensile tests was inactive in fine grains.

The effect of grain size on hydrogen embrittlement (HE) was investigated using Fe–18Mn–0.6C twinning-induced plasticity (TWIP) steel without Al through slow tensile tests and thermal desorption analyses. The grain refinement improved the resistance to HE of TWIP steel by suppressing a ductile to brittle transition. The high ductility of fine-grained specimens resulted from the low densities of twin boundaries, twin–twin junctions, and twin–grain boundary junctions, which are hydrogen-enriched during tensile tests, due to inactive mechanical twinning.