Examination of Hydrogen Diffusivity in Carbon Steels Using a Newly Developed Hydrogen Permeation System

Background: Hydrogen energy has received increased attention because of environmental needs and because it is an attractive replacement for fossil fuels. However, the presence of hydrogen in steels is known to be prejudicial to their global performance due to reduced ductility and unpredictable failures. Objective: To understand the diffusivity of hydrogen in carbon steels, a new hydrogen permeation system was developed to reveal hydrogen diffusion characteristics in carbon steels. Methods: Hydrogen gas was applied directly to one of the chambers to determine if hydrogen would permeate through the steel plate and into the other chamber. The hydrogen gas charged into the chamber at a pressure of 0.7 MPa after air removal using a vacuum pump, and fresh air was charged into the other chamber at atmospheric pressure before the measurement of the penetrated hydrogen. Results: Hydrogen did not diffuse substantially through a steel plate heated to less than 50 °C, but it did diffuse effectively through a carbon steel plate heated to more than 100 °C. The amount of hydrogen that diffused through the steel plate increased nonlinearly with increasing plate temperature and charging time. However, the diffusion amount saturated at 100 °C even after more than 2 h of charging, and hydrogen penetration through the steel plate stopped. In particular, the hydrogen atoms trapped in the steel plate interrupted the penetration of newly charged hydrogen atoms. Conclusion: By using newly proposed system, it is now possible to accurately quantify the diffusion amount of the hydrogen in the carbon steels, and hydrogen charging of the carbon steels was found to be irreversible. Based upon the results, hydrogen trapping system and hydrogen embrittlement characteristics were proposed.