Hydrogen diffusion and trapping in X70 pipeline steel

In this investigation, the hydrogen permeation experiment was used to determine the parameters for diffusion, and the hydrogen microprint technique was used to visualize the diffusion path in X70 pipeline steels. The samples in mid-layer at the segregation zone and top-layer of the steel were used in this study. The diffusion parameters from the hydrogen permeation experiment enabled us to determine that the calculated density of total, reversible, and irreversible hydrogen trapping sites in the top layer of the steel decreases for larger grains. However, the irreversible and total trapping sites of the mid-layer showed an initial growth and subsequent decay with grain growth due to the inclusions in mid-layer. The observations from the hydrogen microprint experiment allowed us to conclude that the preferential hydrogen diffusion increases in the order of grains, grain boundaries, triple junctions and cementites with cementites being the easiest path for hydrogen diffusion. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.