AbstractA time dependent permeation method has been used to measure the diffusivity, permeability, and solubility of hydrogen in hot rolled low carbon steels. The measurements cover the temperature range 200–600°C which includes the onset of hydrogen trapping effects. The results have been interpreted using Oriani's model to explain the effects of microstructure on the trapping. The results show that the initial microstructure of the steel affects significantly the behaviour of the hydrogen atoms. Of the three possible trapping sites, namely, dislocations, interstitial atoms, and precipitated particles, it seems that the most effective traps are the interfaces between coarse particles and the matrix.MST/973