The electrochemical permeation technique allows characterization of the hydrogen fugacity during cathodic hydrogen charging, and this has been done for pure iron.

Q&T 630–780 MS steels exhibited hydrogen-assisted fracture at a stress equal to the ultimate tensile strength for a hydrogen fugacity greater than ∼ 100 atm, but there was no subcritical crack growth, and no hydrogen influence at a lower applied stress.

The hydrogen influence on MS 900–1400 MPa AHSS, for high hydrogen fugacity, was manifest as (i) a decrease in the yield strength by solid solution softening and (ii) hydrogen-assisted fracture at an applied stress equal to the ultimate tensile strength; but there was no subcritical crack growth, and there was no hydrogen-influenced fracture process at a lower applied stress.

A Pt counter electrode should not be used during cathodic hydrogen charging.

There was little influence of hydrogen on the mechanical and fracture properties MS 900–1400 MPa AHSS for conditions that simulated the most aggressive conditions for an automobile in service.

As-quenched 4340 (1700 MPa yield strength) and as-quenched 3.5NiCrMoV (1270 MPa yield strength) show subcritical crack growth due to hydrogen.