Deciphering the role of manganese-alloying on hydrogen embrittlement susceptibility of martensitic steel

Manganese (Mn) is essential alloying element in martensitic advanced high-strength steel, commonly referred as Mn-alloyed steel exhibiting a synergistic blend of high strength and improved formability rendering it a promising material for automotive application. Hydrogen embrittlement (HE) remains a significant challenge in Mn-alloyed steel, however optimal Mn concentration and microstructural optimization can enhance the material's properties. In the present work, HE behavior of three novel series of press-hardend steel (PHS) with varying Mn content were investigated by hydrogen permeation test, thermal desorption spectroscopy, and slow strain rate tensile test. The results suggest that, adding 2.5 wt% Mn improves microstructure by refining prior austenite grain up to 12.55 µm with increased fraction (34.13 %) of grain boundaries, and complex carbides precipitation. The susceptibility to HE in 2.5 wt% Mn-alloyed steel diminishes by 23.83 %, with enhanced H-trapping density of 4.83 (mol/m³) which is ∼3.6 times higher than 1.3 wt% Mn-alloyed steel. The essential distinction in HE mechanism among microstructures of Mn-alloyed PHS is attributed to hydrogen trapping and diffusion, which govern the dispersal and entrapment of hydrogen with in the steel matrix, providing valuable understanding for future microstructural design to enhance HE resistance.