What Does Embrittlement Mean?
Embrittlement is the partial or complete loss of a material's ductility, thus making it brittle. An embrittled product fails by fracture without deforming. Common embrittlement is encountered in galvanized steel, which is related to cold working, aging, and hydrogen absorption.
Embrittlement in steel can be associated with strain aging. This refers to the delayed increase in strength and hardness, impact resistance and loss of ductility. This occurs in susceptible steel due to induced strains by cold working.
Corrosionpedia Explains Embrittlement
The possibility of steel absorbing atomic hydrogen causes hydrogen embrittlement to occur. This is influenced by the steel's previous heat treatment, steel type, thickness of steel and the degree of the previous cold work. It is accentuated by areas of stress concentration like those caused by holes, notches, sharp bends or fillets of small radii, among others.
In galvanized steel, the acidic pickling reaction before galvanization becomes a potential source of hydrogen. Absorbed hydrogen is expelled by the heat of the galvanizing bath. Hydrogen embrittlement is only of concern if steel exceeds an ultimate tensile strength of approximately 1100MPa, or if it has been cold worked severely prior to pickling.
It should be noted that various materials have different embrittlement mechanisms. These include:
- Hydrogen embrittlement (as discussed earlier)
- Sulfide stress cracking: This is the embrittlement caused by the absorption of hydrogen sulfide.
- Liquid metal embrittlement: This is an embrittlement that is caused by liquid metals.
- Metal-induced embrittlement: This is an embrittlement caused by diffusion of metal atoms, either liquid or solid, into the metal.
- Neutron embrittlement: This is an embrittlement caused by neutron radiation.
The primary embrittlement mechanism of plastics is the loss of plasticizers by aging or overheating, and the primary embrittlement mechanism of asphalt is by oxidation, which is severe in warmer climates.