Nucleation rate during crystallization
The number of new crystal nuclei per time, which influences grain size. A high nucleation rate leads to fine grains, a low rate to coarse grains.
Physicochemical Mechanism of Action
The nucleation rate is the measure of the number of new crystal nuclei forming in a material. This rate directly influences the size of the resulting grains in the metal.
Metallurgical Relevance & Risks in Welding
A high nucleation rate results in fine grains, which improves the toughness and formability of the material. A low rate can lead to coarse grains that reduce hardness and ductility and promote cracking.
Workshop Practice & Action Instructions
To achieve an optimal nucleation rate, control the melting temperature and the cooling step. Too high a temperature can lead to coarse grains (t8/5 > 25 s), while too rapid cooling can lead to fine grains and potential hot cracking (t8/5 < 5 s).