Damage mechanism in which atomic hydrogen picked up during pickling, electroplating, welding or corrosion collects at stressed regions and causes brittle cracking, often hours or days after assembly. Steels above about 39 HRC are most at risk. Plated high-strength fasteners and springs get a relief bake, commonly 190 to 220 °C for 4 to 24 hours, started within a few hours of plating.
Grade 8 bolts are back from zinc, they go in the oven for the hydrogen embrittlement bake within the hour.
Start the relief bake within about four hours of plating. Parts that sit over a weekend before baking may already be damaged.
Also heard as
- HE
- hydrogen-assisted cracking
Related terms
Rockwell hardness
The standard shop hardness test that presses a diamond or ball into a part and reads depth as a number.
Quench crack
A crack that forms during or soon after quenching from thermal and transformation stress in hardened steel.
Tempering
Reheating hardened steel below its lower critical temperature to trade some hardness for toughness.
Cert
Shop word for the certificate of heat treatment that states what was done to a lot and the results.