Compact graphite
Vermicular graphite is a mix of flake and nodular graphite in cast iron, boosting heat conductivity and offering higher strengths. It forms from different arrangements of graphite flakes and cores.
Physicochemical mechanism of action
Vermicular graphite in cast iron consists of a mixture of lamellar graphite (arranged in layers) and spheroidal graphite (rounded). This different arrangement affects the thermal conductivity and mechanical strength of the material.
Metallurgical relevance & risks in welding
Vermicular graphite improves thermal conductivity, which allows faster cooling of the weld. This reduces the risk of hot cracking and increases the toughness of the weld. However, too fast cooling can lead to glass-hard martensite, which increases hardness but reduces durability.
Workshop practice & instructions
When welding cast iron with vermicular graphite, it is important to ensure controlled cooling. Use a suitable shielding material and pay attention to the cooling rate. An optimal cooling time of 10 to 20 seconds after welding ensures a balanced grain structure and improves the mechanical properties of the weld.