High-strength steel fasteners are essential in numerous industrial sectors, especially in the automotive industry. They must ensure the integrity of systems subjected to various mechanical and environmental stresses throughout their lifetime, as a fastener failure can have catastrophic consequences. One cause of fastener failure is hydrogen embrittlement (HE), with hydrogen sources being either internal (during manufacturing stages) or external (related to the environment). In high-strength steels, above a certain hardness range, the applied load on the fastener can lead to the diffusion of hydrogen into the stressed area, gradually causing crack initiation and propagation [1]. Preventing failures and managing the risk of HE are fundamental concerns in the automotive industry.
Hydrogen embrittlement has been studied for many years. Several mechanisms have been proposed, involving a reduction in cohesive energy, facilitated dislocation emission, or localized slip. Moreover, the presence of crystalline defects affects hydrogen diffusion and can particularly promote the segregation of this solute at preferential sites following its adsorption and absorption. These models have shown that HE-related damage issues are linked to hydrogen diffusion and segregation processes. The phenomena of solute diffusion and trapping are significantly influenced by the material's microstructure, composition, and local stress state.
In the present work, the Incremental Step Loading Technique and Slow Strain Rate Tests were performed directly on fasteners under cathodic polarization. Subsequently, the results from the different microstructures (bainitic and martensitic), the different levels of hardness, and the presence or absence of a coating were compared.
[1] Brahimi S.V., Y. S. (2017). Alloy and composition dependence of hydrogen embrittlement, susceptibility in high-strength steel fasteners. Philosophical Transactions. Series A, Mathematical,Physical, and Engineering Sciences.
Hydrogen Embrittlement, Martensitic steel, Bainitic steel, Fasteners