Hydrogen-induced crack
A hydrogen-induced crack is a delayed cold crack caused by trapped hydrogen. It occurs under high residual stresses and in martensitic microstructures.
How it works physically and chemically
Hydrogen-induced cracks happen when hydrogen gets into the metal and sits between the crystal structure as atoms. Under high residual stresses, that trapped hydrogen can weaken the material and lead to cracks.
Why it matters in welding and the risks
Hydrogen-induced cracks are especially nasty because they can show up later. They occur when the metal is under high stress and has a martensitic structure. That can cause cold cracks that are hard to spot and can damage the part.
Shop practice and what to do
To avoid hydrogen-induced cracks, it's important to dry the metal well before welding. You can do that with high preheat and a slow cooling process. Also use materials with low hydrogen pickup and watch your welding parameters to keep stresses down.