Compacted graphite
Cast iron graphite morphology featuring worm-like, rounded particles that offer higher mechanical strength than flake graphite and better thermal conductivity than spheroidal graphite. It is produced by controlled under-dosing of nodulizing agents.
You get compact graphite if you deliberately dose the modification in the melt just barely. The particles stay small and roundish, that gives decent strength and conducts heat well. When welding, the part is stable because it doesn't pull hot cracks and the component doesn't overheat so quickly. But watch out: If you catch too much when modifying, the structure tips over to spheroidal graphite, and heat conduction gets worse. You can only find the right setting by controlling the melt – it must not get too hot, otherwise you lose the effect. When cooling, you have to ensure uniform conditions so the structure remains stable.