Hydrogen Embrittlement : Causes, Effects & Prevention
Department of Metallurgical and Materials EngineeringNIT – Rourkela, 769008
Embrittlement is a loss of ductility of a material, or making it brittle.
If embrittlement occurs due to the effect of hydrogen absorption then it known as Hydrogen Embrittlement.
It is more susceptible to BCC and HCP structured metals as compare to FCC structured metals. As Little as 0.0001 weight percent of hydrogen can cause cracking in steel.
Hydrogen may be introduced during :
 During Melting & Entrapped during Solidification,
 Anodic Reaction during Corrosion,
 Hydrogen Gas Welding & Moistured
The Chief characteristics of Hydrogen Embrittlement :
 Strain Rate Sensitivity increases,
 Susceptibility to Delayed Fracture
Hydrogen Embrittlement is enhanced by slow strain
rates. At low temperatures and high temperatures
hydrogen embrittlement is negligible, but it is most
severe at Room Temperature for example steel.
Slow bend test and Notched and Unnotched tension
tests will detect hydrogen Embrittlement by a drastic
decrease in ductility, but notched–impact tests are
of no use for detecting the phenomenon.
The exact mechanism of hydrogen embrittlement is not well known. The initial causes is the same: penetration of atomic hydrogen into the metal structure.
Most of the mechanisms that have been proposed for hydrogen embrittlement are based on slip interference by dissolved hydrogen. This slip interference may be due to accumulation of hydrogen near dislocation sites or microvoids, but the precise mechanism is still in doubt.
Hydride-Induced Embrittlement, HIE (Second-phase mechanism)
Hydrogen-Enhanced Decohesion Mechanism,HEDE (brittle fracture)
Hydrogen Enhanced Localized Plasticity-Mechanism, HELP (ductile fracture)
Reducing Corrosion Rate
Hydrogen embrittlement occurs frequently during pickling operations where corrosion of the base metal produces vigorous hydrogen evolution. By careful inhibitor additions, base-metal corrosion can largely be eliminated during pickling with a susequent decrease in hydrogen pickup.
Using Clean Steel
Rimmed steels tend to have numerous voids, and the subtitution of killed steel greatly increases the resistance to hydrogen interstitials for embrittlement because of the Less number of voids in this material.
Hydrogen embrittlement is an almost reversible process, especially in steels. That is, if the hydrogen is removed, the mechanical properties of the treated material are only slightly different from those of hydogen-free steel. A common way of removing hydrogen in steels is by baking at relatively low temperatures at 200-300 F.
Practicing Proper Welding
Low-hydrogen welding rods should be specified for welding if hydrogen embrittlement is a problem. Also, it is important to maintain dry conditions during welding since water and water vapor are major sources of hydrogen.
The materials most susceptible to hydrogen embrittlement are the very high-strength steels. Alloying with Ni or Mo reduces susceptibility. Because, Nickel-containing steels and Nickel-base alloys have very low hydrogen diffusion rates and best way to prevent from hydrogen embrittlement.
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