Loading Rate Effect on Fracture Toughness of 2.25Cr1Mo0.25V Hydrogen-Vessel Steel

Hydrogen embrittlement is a critical issue for metals, inducing mechanical property degradation and structural service life decay. 2.25Cr1Mo0.25V steel, with excellent hydrogen embrittlement resistance, is widely employed in hydrogen storage vessels. Clarifying its hydrogen- and loading rate-dependent mechanical behaviors thus holds particular significance for safe in-service performance. This work systematically investigates the quasi-static and dynamic fracture toughness of the steel in hydrogen-free and hydrogen-charged conditions. Wide loading rate tests were carried out on compact tensile specimens via a universal testing machine and the self-developed bi-directional electromagnetic-driven Hopkinson bar technique. The fracture process was monitored via high-speed camera and strain gauge techniques for accurate fracture toughness determination. Results demonstrate that fracture toughness is remarkably loading rate-dependent, and so is hydrogen embrittlement degree. Microstructural observations confirm that hydrogen embrittlement is more pronounced under quasi-static loading, reflected by enhanced fracture and crack propagation; a fracture mode transition from ductile to cleavage fracture is identified with increasing loading rate. A mechanism is proposed: under dynamic loading, crack propagation outpaces hydrogen diffusion, preventing timely hydrogen migration to the crack tip, thereby mitigating the hydrogen embrittlement effect.