Nitrogen aging
Nitrogen aging increases yield strength and reduces ductility of plain carbon steels by precipitating fine nitrides in the ferrite lattice. Mechanical deformation accelerates this process.
Physicochemical mechanism of action
Nitrogen aging is a long-term metallurgical process in which nitrogen in the steel crystal structure is bound as fine nitrides (N). These nitrides grow over time and cause a change in the ferrite lattice. Deformation of steel under pressure accelerates the formation of these nitrides, as it converts mechanical energy into chemical energy.
Metallurgical relevance & risks in welding
Nitrogen aging can lead to an increased yield strength and lower elongation of the material. This can cause stress buildup and possibly cracks or fractures in the material, especially in unalloyed steels. In welding, these effects can be amplified if the material is under mechanical stress.
Workshop practice & instructions
To minimize the effects of nitrogen aging, it is important to avoid unalloyed steels during welding and forming. When selecting materials, look for alloyable steels that are less susceptible to these aging processes. If the material is already aged, heat treatment (tempering) can help normalize the structure and restore ductility.