What is the difference between ductile iron and gray iron?

Ductile Iron and Grey Cast Iron are two common cast iron materials. The main difference between them lies in the graphite morphology and the resulting performance differences:

Graphite morphology

- Ductile Iron: The graphite exists in a spherical shape. These spherical graphite forms spherical voids in the base metal, which helps to improve the toughness and strength of the material.

- Grey Cast Iron: The graphite exists in a layered shape, forming flake voids. These flake graphite is more likely to cause the material to break, so the toughness of grey cast iron is lower.

Mechanical properties

- Ductile Iron: It has high tensile strength, yield strength and impact toughness, and can withstand large stresses and impact loads.

- Grey Cast Iron: The tensile strength and impact toughness are relatively low, but the compressive strength is good. It is usually used in occasions where it bears pressure but not tension.

Casting performance

- Ductile Iron: The casting performance is good, but slightly worse than that of grey cast iron, because the spheroidization treatment requires a strict casting process.

- Grey Cast Iron: The casting performance is excellent and it is easy to be cast into shape. The requirements for the casting process are relatively low.

Machining performance

- Ductile Iron: It has good machinability and can be machined by various methods such as turning, milling, planing and grinding.

- Grey Cast Iron: Although it can be machined, due to the existence of graphite flakes, problems such as tool wear and rough machined surface may occur during the machining process.

Application industries

- Ductile Iron: Due to its excellent mechanical properties, it is often used to manufacture components that bear complex loads, such as crankshafts, gears, camshafts, etc.

- Grey Cast Iron: Because of its low cost, it is suitable for manufacturing machine tool beds, valves, pump bodies and other components that bear pressure or require vibration damping.

Performance and corrosion resistance

- Ductile Iron: Usually has good performance and corrosion resistance.

- Grey Cast Iron: The performance and corrosion resistance are relatively poor, but in some cases, the graphite flakes can play a certain lubricating role.

In summary, the main difference between ductile iron and grey cast iron lies in the graphite morphology, which leads to their differences in mechanical properties, casting performance, machining performance and application industries. Ductile iron is usually used in occasions that require higher performance, while grey cast iron is suitable for some specific applications because of its low cost and good casting performance.