Effect of Gradient Microstructure Induced by Pre-Torsion on Hydrogen Embrittlement of Pure Iron

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Building a gradient structure can achieve overall improvement of multiple properties of metal materials. However, the investigation on hydrogen embrittlement (HE) behavior of gradient structure alloys has not been reported so far. This study investigated HE of pure iron with gradient microstructure induced by pre-torsion. The results reveal that with an increase in pre-torsion angle, the resistance to HE of alloys decreases. Fracture surface observation demonstrates that hydrogen uncharged samples present ductile cup-shape fracture, whereas hydrogen charged samples exhibit brittle spiral patterns, mainly depending on pre-torsion level. Additionally, microscopical hydrogen-assisted cracking mechanism of gradient structured pure iron has been proposed.