Hydrogen Diffusion Trapping

Hydrogen can enter the weld during welding and cause cracks. When it gets trapped at lattice defects or dislocations in the microstructure, this is called diffusion trapping. That's not inherently bad, because it holds the hydrogen in place and prevents it from moving freely through the material. The problem is when you have too much hydrogen in the weld. Then trapping doesn't help anymore, and you get cold cracks, often only after cooling. The risk is especially high with hard or high-strength materials. In practice, this means you have to keep the hydrogen source dry. So clean filler materials and base material, free of grease, and don't introduce moisture into the weld. If you work with low-hydrogen electrodes or appropriate shielding gases, you're on the safe side. You can't actively promote trapping, but you can choose the boundary conditions so that hydrogen doesn't cause damage.