Residual Carbon Activity
Residual carbon activity is the fraction of free carbon atoms in a metal that are available for diffusion processes and phase transformations. High activity can lead to increased toughness and improved mechanical properties.
Physicochemical mechanism of action
Residual carbon activity refers to the number of free carbon atoms in the metal matrix that are not bound and thus available for chemical reactions such as diffusion or phase transformations. These atoms can move and form new bonds, influencing the mechanical properties of the material.
Metallurgical relevance & risks in welding
High residual carbon activity can lead to increased toughness and improved mechanical properties, especially in high-temperature zones. However, it can also increase the risk during phase transformations such as martensite formation, which can lead to crack-susceptible weld areas. It is important to control residual carbon activity in the material to achieve an optimal balance between toughness and crack resistance.
Workshop practice & action instructions
To control residual carbon activity, specific temperatures and times must be maintained during welding. For example, during martensite formation, a cooling method should be applied (t8/5 < 5 s) to avoid the formation of hard, brittle phases. For rigid steels with high residual carbon activity, it is important to ensure controlled cooling using water cooling or other coolants.