Hydrogen diffusion in 0.2–0.4wt% carbon martensitic and martensitic-austenitic advanced high-strength steels

Hydrogen-tolerant steels are a central part of enabling the green transition and utilisation of steels with ever higher strength levels. However, hydrogen embrittlement is a critical challenge for advanced high-strength steels (AHSSs) with martensitic-austenitic microstructures. Therefore, the hydrogen–microstructure interactions must be understood when developing products for hydrogen applications. Novel AHSSs with optimised retained austenite (RA) structure offer promising candidates for improved hydrogen resistance, such as direct-quenched and partitioned steels. Here, we investigate microstructural effects on hydrogen diffusion utilising the electrochemical permeation method for a range of direct-quenched and partitioned steels and their direct-quenched variants. In agreement with prior research, RA is the key factor affecting diffusion. Al-alloying and increased carbon content in the bulk and in RA are effective decelerators of hydrogen diffusion. By utilising data from prior mechanical testing and microstructural characterisation with the permeation experiments, we gain a more comprehensive understanding of hydrogen-steel interactions in martensitic-austenitic AHSSs. • Characterises hydrogen diffusion in 3rd generation advanced high strength steels. • Increased retained austenite volume fraction slows hydrogen diffusion. • Increased carbon fraction of retained austenite slows hydrogen diffusion. • Aluminium alloying of martensite aids in further slowing hydrogen diffusion.