Interstitial diffusion
Interstitial diffusion is the rapid exchange of atoms through interstices in the lattice, without occupying regular sites. This affects the composition and properties of the material.
Physicochemical Mechanism of Action
Interstitial diffusion describes the process where atoms or ions move through the gaps between the lattice lines of a crystal. These atoms can be smaller foreign atoms that penetrate the lattice and stabilize there without having to occupy regular lattice sites.
Metallurgical Relevance & Risks in Welding
Interstitial diffusion is crucial for the formability and strength of steels. Excessive diffusion rates can lead to a coarsening of the lattice, which increases toughness but reduces durability. At incorrect welding temperature or too slow cooling, the material can coarsen and its mechanical properties degrade.
Workshop Practice & Instructions
To ensure an optimal diffusion rate, it's important to set the welding temperature and time precisely. For steels with high carbon content, the cooling steps should be done slowly (t8/5 > 25 s) to avoid a uniform coarsening of the lattice. For low carbon content, a faster cooling process (t8/5 < 5 s) may be appropriate to avoid glass-hard microstructures.