High-throughput evaluation of Mo effect on hydrogen embrittlement behavior of ultra-high strength steel

Abstract

The susceptibility of high-strength hot-stamping steels to hydrogen embrittlement (HE) remains a critical challenge for their widespread adoption in automotive applications. In this study, we introduce a novel high-throughput methodology to assess the influence of molybdenum (Mo) content on the HE behavior of 32MnB5 steel. By integrating diffusion couple to create a Mo compositional gradient (0–0.6 wt%) and fabricating an array of microcantilevers via focused ion beam (FIB) milling, we employed nanoindentation to evaluate fracture toughness under both hydrogen-charged and hydrogen-free conditions. Microstructural characterization via electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) revealed that increasing Mo content slightly induces grain refinement and reduces localized stress concentrations, enhancing grain boundary cohesion and thereby increasing fracture toughness. Under hydrogen-charged conditions, however, hydrogen significantly reduces fracture toughness, with Mo exerting dual competing effects on the plastic component of fracture (J_plastic): grain refinement and reduction of localized stress concentrations enhance J_plastic, while lattice distortion exacerbates hydrogen-induced dislocation pinning, diminishing J_plastic. Consequently, J_plastic shows no significant variation with Mo content in the presence of hydrogen, yet overall, HE susceptibility decreases with higher Mo levels due to dominant elastic contributions. This high-throughput approach provides a robust alternative for rapidly screening alloy compositions to mitigate HE in advanced high-strength steels.