Influence of hydrogen on the cohesion and charge density distribution in bcc iron matrix by DFT calculations

Hydrogen-induced delayed fracture is a critical failure mode in low-alloy steels, particularly impacting equipment reliability in petrochemical, hydrogen energy, and related fields, with a lack of effective early warning technologies. Using first-principles calculations based on density functional theory (DFT), this study investigates body-centered cubic (bcc) iron matrix models with hydrogen concentrations of 0, 4.17%, and 6.25% to explore hydrogen's influence on cohesion. DFT results show hydrogen doping causes severe lattice distortion and plastic deformation along the [001] direction, reducing matrix cohesion and inducing fracture trend. From the simulation results, it was found that a higher concentration of hydrogen atoms does not necessarily reduce the cohesion of the matrix, but rather the increase in local charge density caused by hydrogen atoms is the intrinsic driving factor that induces a decrease in cohesion in the bcc iron matrix. Notably, higher hydrogen concentrations do not necessarily reduce cohesion. Instead, the increased local charge density from hydrogen is the critical driver for cohesion decrease. This work reveals the electronic mechanism of hydrogen-induced cohesion reduction, providing a theoretical basis for developing hydrogen-induced fracture warning technologies.