The addition of a small volume fraction of carbon monoxide (CO) gas to pure gaseous H2 potentially mitigates the susceptibility of steel to hydrogen environment embrittlement (HEE). The effect of environmental gas pressure on the mitigation of HEEs by a mixture of H2 and CO was examined in this study. Fracture toughness tests of an ASTM A106 pipe carbon steel were carried out in H2 gas containing CO. The environmental gas pressures at which the fracture toughness tests were conducted were 0.6, 1.0 and 4.0 MPa. The addition of a certain concentration of CO to H2 gas completely prevented HEE. The CO concentration achieving complete HEE prevention increased with an enhancement of the environmental gas pressure. Molecular dynamics (MD) simulations were further conducted to interpret the experimental results based on the interactions of H2 and CO with the Fe surface in conjunction with the effect of gas pressure. The MD simulations revealed that the dissociation rate of dihydrogen molecules to atomic hydrogen on the Fe surface significantly increased with an elevation of the gas pressure, whereas the adsorption rate of CO on the Fe surface was almost independent of the gas pressure. These results suggest that the increase in the gas pressure relatively promotes hydrogen uptake into the material in the presence of CO, which accounts for the experimental results showing that the CO concentration achieving complete HEE prevention increased with the elevation of the gas pressure.
|Journal||Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science|
|Publication status||Accepted/In press - 2021|
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Mechanics of Materials
- Metals and Alloys