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The investigation of the role of retained austenite (RA) in mediating hydrogen embrittlement (HE) within quenching and partitioning (Q&P) steels presents considerable complexity, primarily due to the intricate interplay with adjacent phases. Notably, there is a scarcity of comprehensive research examining the influence of deformed microstructures on HE resistance. This study aims to reveal the factors that govern HE resistance by manipulating the morphology and distribution of RA alongside its neighboring phases. Two model microstructures are designed by varying annealing temperatures within the austenitic and intercritical regimes, respectively. Electrochemical hydrogen pre-charging followed by interrupted uniaxial tensile deformations is adopted to probe the impact of these deformed microstructures on HE susceptibility. This approach facilitates a nuanced understanding of strain localization during deformation, assessed through digital image correlation analysis and examinations of the progression of hydrogen-induced crack formation. The findings reveal that RA stability, irrespective of its morphological attributes, exhibits superior characteristics in intercritically annealed steel due to its compositional effects. Furthermore, the observed prevalent strain partitioning within the ferrite matrix significantly enhances the extrinsic mechanical stability of RA. In particular, the enhanced RA stability, coupled with the predominance of transgranular fracture mechanisms, markedly improves the HE resistance. Therefore, this study not only sheds light on the complex interrelations governing RA and HE resistance in Q&P steels but also provides critical insights for the advancement of material design strategies aimed at optimizing HE resistance. • The RA stability attributed to its composition was superior in IA-QP. • The mechanical stability of RA was greater due to strain partitioning in the ferrite. • For A-QP, the distinct PAGBs served as susceptible sites for hydrogen segregation. • The strain partitioning in the ferrite altered the crack propagated path in IA-QP. • The increased RA stability and transgranular fracture enhanced the HE resistance. [ABSTRACT FROM AUTHOR]

The investigation of the role of retained austenite (RA) in mediating hydrogen embrittlement (HE) within quenching and partitioning (Q&P) steels presents considerable complexity, primarily due to the intricate interplay with adjacent phases. Notably, there is a scarcity of comprehensive research examining the influence of deformed microstructures on HE resistance. This study aims to reveal the factors that govern HE resistance by manipulating the morphology and distribution of RA alongside its neighboring phases. Two model microstructures are designed by varying annealing temperatures within the austenitic and intercritical regimes, respectively. Electrochemical hydrogen pre-charging followed by interrupted uniaxial tensile deformations is adopted to probe the impact of these deformed microstructures on HE susceptibility. This approach facilitates a nuanced understanding of strain localization during deformation, assessed through digital image correlation analysis and examinations of the progression of hydrogen-induced crack formation. The findings reveal that RA stability, irrespective of its morphological attributes, exhibits superior characteristics in intercritically annealed steel due to its compositional effects. Furthermore, the observed prevalent strain partitioning within the ferrite matrix significantly enhances the extrinsic mechanical stability of RA. In particular, the enhanced RA stability, coupled with the predominance of transgranular fracture mechanisms, markedly improves the HE resistance. Therefore, this study not only sheds light on the complex interrelations governing RA and HE resistance in Q&P steels but also provides critical insights for the advancement of material design strategies aimed at optimizing HE resistance. • The RA stability attributed to its composition was superior in IA-QP. • The mechanical stability of RA was greater due to strain partitioning in the ferrite. • For A-QP, the distinct PAGBs served as susceptible sites for hydrogen segregation. • The strain partitioning in the ferrite altered the crack propagated path in IA-QP. • The increased RA stability and transgranular fracture enhanced the HE resistance. [ABSTRACT FROM AUTHOR]