Comparative study of hydrogen embrittlement in 310S, 304L, and 316L stainless steels under in situ electrochemical hydrogen charging. Part 1: Experimental study

The microstructure and hydrogen embrittlement behavior of the austenitic stainless steels STS310S, STS304L, and STS316L were investigated under hydrogen charging conditions. The steels were charged at various current densities ranging from 0.25 to 15 mA/cm². The analysis was conducted using a slow strain-rate tensile (SSRT) test on notched specimens under in situ electrochemical hydrogen charging. The results indicated that hydrogen embrittlement effects emerged after the elastic region, with mechanical properties deteriorating as the current density increased. The critical current densities for mechanical property degradation were determined to be 5, 2, and 10 mA/cm² for STS310S, STS304L, and STS316L, respectively. Hydrogen concentration increased with current density, following a power-law relationship, with critical hydrogen concentrations of 35.80, 24.00, and 28.80 wppm, respectively. STS310S, with the highest Ni equivalent, retained ductile fracture behavior and demonstrated superior resistance to hydrogen embrittlement. In contrast, STS304L, with the lowest Ni equivalent, exhibited the highest susceptibility, transitioning to brittle fracture with extensive secondary cracking, while STS316L showed intermediate behavior, balancing ductility and brittleness. Fractographic and EBSD analyses confirmed that a higher Ni equivalent stabilizes the FCC phase and mitigates phase transformation to martensite, enhancing resistance to hydrogen embrittlement. These results indicate that alloy composition, particularly the Ni equivalent, plays a crucial role in the development of hydrogen resistant materials.