Effect of austenitizing time on hydrogen embrittlement resistance of a 2.0 GPa grade hot-stamping steel

Hot-stamping steel has become a core material for automotive lightweighting and safety enhancement due to its excellent strength and safety characteristics. However, the problem of hydrogen embrittlement (HE) seriously restricts its development and application. This work systematically investigated the influence of different holding times (100 s, 180 s, 300 s) at 930 °C austenitizing temperature on the microstructure and properties of a 2.0 GPa grade hot-stamping steel. The results indicated that prolonging the holding time led to an increase in prior-austenite grain size from 3.97 μm to 4.6 μm, coarsening of (Ti, Nb, Mo)C precipitates, dissolution of Cu-rich phases, and a significant decrease in dislocation density. Consequently, the ultimate tensile strength decreased from 2020 MPa (100 s) to 1902 MPa (300 s). Slow strain rate tensile tests revealed that the susceptibility to HE increased with extended holding time. After charging at a current density of only 1 mA/cm 2 , the longer austenitizing time resulted in grain coarsening and a reduction in beneficial hydrogen traps, such as dislocations and fine particles. This facilitated greater hydrogen accumulation at grain boundaries, causing the fibrous zone of the 300 s held specimen to exhibit intergranular fracture characteristics. This study clarifies the significant impact of austenitizing time on material properties and provides an important basis for optimizing hot-stamping processes to enhance HE resistance while maintaining high strength.