Hydrogen uptake and diffusion kinetics in a quenched and tempered low carbon steel: experimental and numerical study

To better understand hydrogen uptake kinetics, electrochemical permeation tests have been performed in a quenched and tempered low-alloy steel. Hydrogen uptake and transport has been studied with three different surface roughness, in four different solutions (1 M H2SO4, 1 M H2SO4+As2O3, 0.1 M NaOH and 3.5% NaCl) and two different hydrogen charging current densities (1 and 5 mA/cm2). A strong effect of the charging solution, current density and surface roughness has been demonstrated. In 1 M H2SO4 + As2O3 solution and 5 mA/cm2, hydrogen recombination on the surface of the samples is strongly reduced and interstitial diffusion prevails due to the trap saturation (DL≈Dapp). However, in 1 M H2SO4, 0.1 M NaOH and 3.5% NaCl, hydrogen transport is dominated by trapping and detrapping processes (DL>Dapp). Permeation transients are numerically reproduced through Finite Element simulations and compared to the experimental results. The relationship between hydrogen diffusion kinetics at the microstructural level and surface effects is clearly established by a mapping strategy obtained from the wide range of experimental results, combined with a numerical approach.