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Hydrogen Embrittlement of Steels
One of the most significant limitations of the use of high strength steel
components is hydrogen embrittlement cracking (HEC). Hydrogen, in the atomic
form, can enter the materials from many sources (1) steel making, (2) welding,
(3) corrosion and (4) cathodic protection. It can produce a range of
deterioration resulting in reduced ductility to brittle fracture.
The following figure shows the reduced ductility of steels as the hydrogen
content increases. Its effect is particularly severe in steels with hardness
values greater than HRC 35. This can cause difficulties with some grades of
high strength bolting materials which can range in hardness from HRC 25 to 40.
There can be particular concern for embrittlement of as carburized parts
which can have surface hardnesses in the range of HRC 45-50. The problem is
magnified further if the steel parts are coated with sacrificial coatings
(e.g. Zn, Cd) which accelerate hydrogen charging.
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