LAUSR

Abstract A 42CrMo4 steel quenched and tempered at different temperatures was tested via a combination of electrochemical hydrogen transient build-up permeation tests and thermal desorption analysis (TDA). The evolution of the apparent diffusion coefficient, Dapp, versus the applied cathodic current density as microstructural hydrogen traps are progressively filled, was obtained until reaching the value of the lattice diffusion coefficient, DL (hydrogen diffusion in the steel when all its traps are filled). TDA analyses were additionally performed to determine the binding energies related to the different microstructural traps present in the microstructures of these steel grades. Hydrogen binding energies of 11.8, 17 and 27.4 kJ/mol were determined, these values being found not to depend on the tempering temperature. It was also demonstrated that the most energetic peak was associated with dislocations. Furthermore, both hydrogen diffusivities, Dapp and DL, decrease while hydrogen solubility, C0app, (subsurface hydrogen concentration at the entry side when all traps are filled), and the density of hydrogen traps, Nt, increase with the hardness of the steel (hardness varies linearly with the tempering temperature in this 42CrMo4 quenched and tempered steel).