Examining hydrogen trapping in steels by using advanced microscopy and modelling techniques

Abstract

The presence of hydrogen in high-strength steels leads to hydrogen embrittlement (HE), causing premature cracking and posing challenges for hydrogen infrastructure amid the global push for decarbonization. With hydrogen crucial for net-zero emissions, addressing HE is imperative for a secure and environmentally sound hydrogen economy. One strategy involves introducing hydrogen traps into alloy microstructures, limiting HE. While promising, a comprehensive atomic-scale understanding is vital. This study combines advanced microscopy and modeling to investigate hydrogen distribution in steel microstructures. A difference in trapping mechanisms is observed between titanium carbide (TiC) ferritic steel and Ti(Mo)C, formed with the addition of a small amount of Molybdenum. Findings highlight the importance of additional carbon vacancies in Ti(Mo)C, enabling hydrogen transit within the carbide's interior.

Beyond investigating hydrogen trapping within steel precipitates, this study explores hydrogen interactions with pearlitic steel, crucial for steel gas pipes. Hydrogen shows a predilection for the interior regions of ferrite and cementite phases in pearlite, but does not accumulate at interfaces, a different result to what had been predicted in the literature. This complex interplay underscores the significance of understanding hydrogen behavior in steel microstructures.

Atomic-scale simulations are now standard for theoretical understanding, covering defect concentrations. However, addressing intermediate concentrations is challenging. To overcome this, a computationally streamlined approach, inspired by cluster expansion and ensemble statistics techniques, bridges the gap, offering an effective means to tackle complexities associated with intermediate concentration levels. This innovation is crucial for designing HE-resistant alloys and creating safer materials in the hydrogen era, aligning with global net-zero targets.