Hydrogen Embrittlement (HE)
Definition
Loss of toughness and ductility in a metal due to absorbed atomic hydrogen, resulting in brittle fracture at stress intensities below the material's normal fracture toughness in a hydrogen-free environment.
- Mechanism
- Atomic hydrogen diffuses into the metal lattice and lowers cohesive strength
- Fracture mode
- Brittle, often intergranular, below normal fracture toughness
- Common sources
- Pickling, electroplating, welding, cathodic overprotection
- Susceptible materials
- High-strength steels, titanium alloys, some nickel alloys
Common questions
How is hydrogen embrittlement told apart from stress corrosion cracking on a fracture surface?+
Both can produce intergranular brittle fracture, so investigators rely on the surrounding history: HE is linked to a hydrogen-charging step such as plating or pickling and can occur without active corrosion, while SCC needs a specific corrosive environment acting alongside sustained tensile stress.
Can hydrogen embrittlement be reversed once a part is charged?+
Low-temperature baking soon after plating or pickling can diffuse much of the absorbed hydrogen back out and restore toughness, which is why aerospace and fastener specifications mandate a bake window measured in hours after the charging process.
Related terms
- Hydrogen-Assisted Cracking (HAC)
- The general term for crack initiation and propagation facilitated by absorbed atomic hydrogen. Encompasses hydrogen embrittlement, sulfide stress cracking, and hydrogen-induced cracking.
- Hydrogen-Induced Cracking (HIC)
- Planar crack arrays that form parallel to the steel rolling direction when high levels of hydrogen are absorbed. Common in pipeline steels...
- Liquid-Metal Embrittlement (LME)
- Brittle fracture of a normally ductile metal when it is in contact with a specific liquid metal. Not hydrogen-related but mechanistically analogous:...
- NACE MR0175/ISO 15156
- The international standard for materials selection and qualification for sour oil-and-gas service. Sets hardness limits, alloy restrictions, and testing requirements to prevent...
- Sulfide Stress Cracking (SSC)
- Hydrogen-assisted cracking specific to H2S-containing environments. Sulfide ions poison the recombination reaction at the steel surface, forcing more atomic hydrogen to enter...