Development of a hydrogen absorption model to determine absorption kinetics and diffusion coefficients by means of carrier gas hot extraction

Precise description of the hydrogen charged state of mechanical test specimens including the spatial and energetic hydrogen distribution is considered to be essential for understanding the mechanisms of hydrogen embrittlement. Here, a simple hydrogen absorption model for hydrogen charging in liquids was developed for cylindrical specimens. The absorption model is based on an approximate solution of Fick's laws of diffusion and allows determining hydrogen diffusion coefficients and surface concentrations by measuring the total amount of absorbed hydrogen as a function of the cylinder height. Total hydrogen contents after charging of several cylinders consisting of quenched and tempered steel 42CrMo4 (1.7225) were measured by carrier gas hot extraction and the applicability of the absorption model on the measurement was demonstrated by mathematical fitting. The diffusion coefficient for this material was determined to be D=3.810−11m2/s and the hydrogens surface concentration increases with increasing charging time.