Degradation Behavior and Optimization Strategies for Metallic Materials in High-Temperature Hydrogen Service: A Review.

This review systematically examines the degradation behavior of metallic materials exposed to high-temperature hydrogen-rich environments, with particular focus on hydrogen metallurgy applications. The major degradation mechanisms, including hydrogen embrittlement, intergranular corrosion, high-temperature creep, carburization, stress corrosion cracking, thermal fatigue, and high-temperature hydrogen attack, are critically analyzed, along with their coupled effects under complex service conditions. The interactions between external service factors and intrinsic material characteristics are discussed to clarify their roles in material degradation and failure. To further clarify these interactions, a synergistic degradation framework is proposed, in which surface-film damage governs hydrogen ingress, high-temperature creep and precipitate evolution generate hydrogen traps and stress concentrators, and carburization, stress corrosion cracking, thermal fatigue, high-temperature hydrogen attack, and erosion jointly accelerate crack initiation and propagation. Particular attention is given to the limitations of conventional materials, such as Cr-Mo steels, austenitic stainless steels, and Fe-Ni alloys, in high-temperature hydrogen-rich environments. Furthermore, recent advances in material optimization strategies are summarized, including alloy design, microstructural regulation, and surface engineering approaches such as diffusion coatings. Nickel-based superalloys are identified as some of the most promising candidates for high-temperature hydrogen applications owing to their superior creep resistance and structural stability. This review highlights current knowledge gaps in the understanding of coupled degradation mechanisms and provides guidance for material selection, performance optimization, and safe operation of key components in hydrogen metallurgy systems.