Effects of Mo and V on the Hydrogen Assisted Cracking of Tempered Martensitic Steels

摘要

Hydrogen damage of two tempered martensitic steels with different molybdenum and vanadium contents is investigated. Firstly, structural and mechanical characterizations are performed, followed by electrochemical charging and permeation tests. These experiments allowed establishing relationships between composition, structure, hydrogen diffusion and trapping. As expected, we verified that the steel with higher molybdenum and vanadium contents presents significantly higher apparent hydrogen solubility and lower apparent diffusion coefficient. These results confirm that these alloying elements play an important role in the interactions between hydrogen and the martensitic structure. Afterwards, mechanical testing with several notches geometries were completed with hydrogen pre-charged specimens (with only deep trapped hydrogen) and under hydrogen flux (with trapped and mobile hydrogen). These tests aim to investigate separately the impact of trapped and mobile hydrogen in the hydrogen damage. Finally, a damage graph relating the observed fracture surface morphologies with the stress concentration factors, the average hydrogen flux and concentrations is proposed in order to qualitatively access the hydrogen stress cracking resistance of the steels.