Effect of Tempering Temperature on Strength and Hydrogen Embrittlement Resistance of 2 GPa Hot-Stamped Steel
摘要
The lightweight potential of ultra-high-strength hot-stamped steel is limited, as its susceptibility to hydrogen embrittlement (HE) increases with rising strength. This study systematically investigated the effect of tempering temperatures (100, 170, and 250 °C, holding 20 min, respectively, named QT100, QT170, and QT250) on the mechanical properties and HE resistance of 2000 MPa grade steel. The results revealed that the dislocation density decreased from 3.11 × 1016 m−2 of QT100 sample to 1.13 × 1016 m−2 of QT250 sample, resulting in the weakening of the dislocation strengthening effect, and the ultimate tensile strength (UTS) decreased from 2226 to 1770 MPa. The precipitation of fine ε-carbide in the QT170 sample produced significant precipitation strengthening, which maintained the UTS of 2020 MPa. However, the precipitation strengthening effect of the QT250 sample was weakened due to the coarsening of ε-carbide and the formation of spherical Fe3C, resulting in significant strength loss (ΔUTS = 456 MPa). Under low hydrogen flux (1 mA/cm2), ε-carbides and retained austenite synergistically trapped diffusible hydrogen, resulting in a significantly lower HE sensitivity index (IHE) of 2.22% for the QT170 sample compared to the QT100 sample (57.14%). For the QT250 sample, the low dislocation density suppressed hydrogen enrichment at crack tips, with an IHE of 2.22%. Under a high hydrogen flux of 5 mA/cm2, the trap in the QT170 sample was saturated, and the IHE increased sharply to 44.44 %, accompanied by intergranular fracture. In contrast, the large amount of ε-carbides and Fe3C particles in the QT250 served as effective hydrogen traps, immobilizing more hydrogen atoms and effectively suppressing local hydrogen enrichment, thereby maintaining a relatively low IHE of 22.22%.