Hydrogen Diffusion Coefficient
Temperature-dependent parameter describing the speed at which hydrogen atoms migrate through the crystal lattice. Because of the small atomic radius, this coefficient is very high in iron, favoring rapid degassing or insertion processes.
The hydrogen diffusion coefficient tells you how fast hydrogen migrates through the steel lattice. This is especially important in welding, because if hydrogen accumulates in the component, it can cause cold cracks, particularly in stiff, thick-walled parts. The danger is greatest when the steel cools quickly and the hydrogen can no longer diffuse out. You must therefore ensure that the weld cools slowly enough for the hydrogen to escape. For critical components, it helps to control the cooling instead of just leaving it to the air.