Mitigating hydrogen-assisted intergranular cracking via pearlite decoration along prior austenite grain boundaries in hot-rolled Fe-0.2C-6.8Mn-3.0Al steel

Hydrogen enrichment at grain boundaries and the consequent intergranular cracking have long been recognized as the primary causes of hydrogen embrittlement (HE) in high-strength steels. Accordingly, engineering the grain-boundaries to eliminate or suppress hydrogen enrichment at these sites represents an effective strategy for enhancing HE resistance. In the present work, the grain-boundary microstructure of a hot-rolled and annealed Fe–0.2C–6.8Mn–3.0Al medium-Mn steel (A740) was tailored through optimized thermomechanical processing, whereby varying amounts of pearlite were introduced along prior austenite grain boundaries (PAGBs). As a result, three derivative samples, namely T550, WR10, and WR15, were fabricated, exhibiting comparable mechanical properties but progressively increasing pearlite contents at the PAGBs. Slow strain rate tensile (SSRT) tests were employed to evaluate the HE susceptibility of the samples. The results demonstrate that HE sensitivity decreases markedly with pearlite formation at PAGBs. Hydrogen microprint tests were further employed to characterize hydrogen distribution, revealing that hydrogen is predominantly and relatively uniformly distributed within prior austenite grains. Notably, the PAGBs decorated with pearlite no longer act as preferential sites for hydrogen accumulation. Consequently, hydrogen-induced intergranular cracking is effectively suppressed, leading to a significant improvement in HE resistance. These findings provide a novel strategy for the microstructural design of hydrogen-resistant medium-Mn steels.