Nucleation
Nucleation is the beginning of a phase transformation where small, stable atom groups form. These determine the final grain size and can lead to porosity.
Physico-chemical Mechanism of Action
During welding, the metal near the heat front forms from small, stable atom groups. These groups determine the grain size and can lead to pores if they are not properly conditioned.
Metallurgical Relevance & Welding Risks
Insufficient nucleation can lead to fine grains and increased toughness. This can affect the strength and ductility of the weld. Furthermore, it can lead to porosity, which reduces mechanical strength and promotes cracking.
Workshop Practice & Instructions
To ensure optimal nucleation, it is important to keep the melting process continuous. This can be achieved by proper selection of welding method and parameters. Too rapid cooling can interrupt nucleation and lead to fine grains, while too slow cooling results in coarse grains and porosity.