Hydrogen trapping and embrittlement of a high-carbon steel after quenching and high-temperature tempering

High-carbon steels after quenching and tempering face hydrogen embrittlement (HE) risk due to their high strength and low ductility. This study investigates hydrogen trapping behavior and HE susceptibility in a quenched and tempered high-carbon steel by means of thermal desorption spectroscopy (TDS), hydrogen microprinting technique (HMT), and slow strain rate tensile (SSRT) tests. Results demonstrate that dislocations act as the primary reversible hydrogen trapping sites, and hydrogen uptake decreases with the decrease of dislocation density from 3.26 × 10¹² cm⁻² in the as-quenched specimen to 4.74 × 10⁸ cm⁻² in the specimen tempered at 600 ℃. Cementite/matrix interfaces act as irreversible hydrogen trapping sites, where hydrogen adsorption is governed by heterogeneous strain fields near the interfaces. SSRT results reveal that the specimen tempered at 540 ℃ exhibits high HE susceptibility, with elongation decreasing from 8.9 % to 3.6 % after hydrogen charging. In contrast, the specimen tempered at 600 ℃ retains superior ductility under identical charging conditions, with elongation decreasing from 15.4 % to 12.9 %. HE susceptibility of the experimental steel shows an exponential dependence on hydrogen content, with the fracture mode transitions driven by synergistic hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE) mechanisms. This work indicates that optimizing dislocation density and interfacial strain states can effectively mitigate HE risk of high-carbon steels.