Hydrogen trapping in Ferrovac E‐iron, mild steel and 4340 steel

Hydrogen diffusion rates through Ferrovac E‐iron, mild steel and 4340 steel have been studied using an electrochemical permeation cell. Thermal‐mechanical processing included cold rolling and annealing and, in case of 4340 steel, quench and tempering. Apparent diffusion coefficients were determined from the slope of plots of log [(P‐P0)√t] versus 1/t where P, P0 and t are the permeation rate at time t, the initial permeation rate and the time, respectively. Apparent diffusion coefficients are dependent on processing. Cold rolling and quenching produce trap sites that are annihilated during annealing and tempering, respectively. These traps are associated with lattice imperfections. In addition, the steels have trap sites at the interface between different phases. Both types of traps behave reversibly.