Both are cast iron, and both start from similar raw materials. The difference is the shape of the graphite inside the metal, and that one detail changes how the part behaves.

• Gray iron (FC25 / JIS FC250): graphite forms as thin flakes. The flakes absorb vibration and make the iron easy to machine, but they also act as tiny cracks, so the metal is brittle.
• Ductile iron (JIS FCD, also called nodular or spheroidal graphite iron): magnesium treatment turns the graphite into small spheres. Without sharp flake edges, the iron can bend and stretch before it breaks.

Choose FC25 gray iron when…

the part must stay stable and quiet: machine bases, brake drums and discs, cylinder liners, pump and valve bodies, flywheels. These parts carry load mainly in compression and benefit from damping and easy machining.

Choose ductile iron when…

the part takes impact, bending or tension: brackets, crankshafts, gears, suspension and hydraulic parts. Ductile iron can often replace steel castings or forgings at lower cost.

Raw castings plus machining from one supplier

Songhua supplies FC25 gray iron and ductile iron raw castings through our partner foundry, using gravity casting. We can then machine them in-house on 5-axis CNC equipment. One order covers casting, machining and inspection, with no hand-off between suppliers.

Request a quote with your drawing, material grade and annual volume.