Vermicular graphite
Vermicular graphite is worm-shaped graphite in cast iron, giving a mix of good heat conductivity and higher mechanical strength.
Physical-Chemical Mechanism of Action
Vermicular graphite forms by the condensed precipitation of graphite in the melt. It develops into a worm-like structure that lies between flake and spheroidal graphite.
Metallurgical Relevance & Welding Risks
Vermicular graphite improves the thermal conductivity and mechanical load capacity of cast iron. It reduces the occurrence of cracks and increases the toughness of the weld. However, incorrect welding parameters can lead to uneven deformation or excessive stress, which can cause hot cracking.
Shop Practice & Action Guidelines
When welding cast iron with vermicular graphite, it is important to ensure controlled cooling. The cooling shield should be thinner than with other graphite types to make optimal use of thermal conductivity. Recommended cooling times are between 10 and 20 seconds per cm² of weld area.