Spheroidal Graphite Nucleus
A microscopic nucleation site, usually based on sulfides or oxides, that initiates the radial growth of graphite spherulites in cast iron.
Physical-Chemical Mechanism of Action
The spheroidal graphite core forms in the molten pool through the crystallization of sulfides or oxides. These cores serve as anchor points for the radial growth of graphite spherulites, leading to a fine graphitized microstructure.
Metallurgical Relevance & Welding Risks
A fine graphitic microstructure increases toughness and scale resistance of cast iron. However, too many spheroidal graphite cores can make the material too soft, reducing mechanical strength. When welding, this can lead to distortion or spalling.
Workshop Practice & Action Guidelines
To ensure a homogeneous microstructure, cool the cast iron at a constant rate. Cooling position and temperature control are critical. When welding, careful pre-treatment is required to avoid porosity and stabilize the microstructure.