Experimental and Fractographic Study of the Hydrogen‐Induced Cracking of 45CrNiMoVA Martensitic Advanced High‐Strength Steel

Hydrogen‐induced cracking (HIC) in high‐strength 45CrNiMoVA steel is investigated using smooth and notched cylindrical specimens by performing uniaxial tensile tests. Specimens with different notch geometries are used to analyze the interacting effects of the stress concentration factor and HIC micromechanism. The results show that hydrogen charging reduces the elongation at fracture and the ultimate tensile strength of smooth tensile specimens. The microscopic fracture mode changes from ductile dimples with some quasicleavage fracture without hydrogen to a mixture of brittle quasicleavage and intergranular cracking with hydrogen. For notched specimens with a lower notch root radius, significant stress concentration occurs at the notch root, which enriches hydrogen in these highly stressed regions. This causes a lower notch tensile strength and greater susceptibility to hydrogen embrittlement. Microfracture observations show that the area fraction of the intergranular cracking surface increases gradually, and the brittle zone moves farther away from the notch root upon decreasing the notch root radius, causing the embrittlement index to remain high. These results will help determine the applicability of existing steel for hydrogen service and also provide guidance for developing new high‐strength martensitic steels that can resist hydrogen embrittlement.