The Effect of NbC Precipitates on Hydrogen Embrittlement of Dual-Phase Steels

New grades of dual-phase (DP) steels with ultimate tensile strength (UTS) up to 1500 MPa have been developed using a continuous annealing process. This study investigates the effects of over-aging temperature and NbC precipitates on the microstructure and hydrogen embrittlement of these DP steels. Increasing the over-aging temperature promotes carbide coarsening, which reduces tensile strength, but simultaneously stabilizes retained austenite by inhibiting martensite transformation and enhances ductility through the TRIP effect. Compared to the reference DP steel, the Nb-added DP steel exhibits further strength enhancement due to fine-grain strengthening and precipitation strengthening. Results from slow strain rate tensile (SSRT) and thermal desorption spectroscopy (TDS) tests demonstrate that the Nb-added DP steel possesses superior resistance to hydrogen embrittlement. This improvement is primarily attributed to the hydrogen trapping effect of NbC precipitates, complemented by their grain refinement capability.