Ductile (Spheroidal Graphite) Cast Iron

This cast iron is also called ductile (spheroidal) cast iron. It’s an iron-carbon casting material whose graphite is spherical in structure. When a certain amount of chemical elements are added to the molten iron, the graphite solidifies in a spherical form instead of flakes. The figure below shows the appearance of the spherical graphite under a microscope.

Its name in the Turkish standards is Ductile (Spheroidal Graphite) Cast Iron, known by the abbreviation “DDK.”

Microstructure of ductile cast iron (Above) a) Ferritic structure b) Pearlitic structure

Chemical composition of ductile cast iron

Mg is used extensively in industry. When iron is alloyed with magnesium or other special elements, the graphite within the iron solidifies in a spherical shape, turning it into a material with high-strength properties. This material, known as ductile cast iron, is the strongest and toughest of the cast iron types.

Cast iron is brittle. Ductile cast iron (DCI), however, is ductile, unlike other cast irons. In addition to cast iron’s well-known properties such as castability, machinability, load-bearing capacity, and production characteristics, this cast iron also has a wide strength range, wear resistance, fatigue resistance, toughness, and ductility.

Magnesium Addition

In ductile (spheroidal graphite) cast iron, magnesium is added to the molten metal so the graphite takes on a spherical shape.

High Strength and Ductility

The spherical graphite structure gives ductile cast iron much higher strength and ductility than grey cast iron.

Use as a Steel Alternative

In some applications, ductile cast iron is preferred as a lower-cost alternative to forged steel.

Mechanical properties of ductile cast iron

The mechanical properties of ductile cast iron are quite good. Its corrosion resistance is high. It’s easy to use in machining. Ductile cast iron is used as a replacement for grey cast iron, cast steel, and non-ferrous metal alloys in many applications. Ductile cast iron is known by names such as “nodular cast iron, ductile iron, fonte sphéroïdale graphite, kugelgraphit gusseisen, spherulitic graphite iron” in many countries.

Where ductile cast iron is used

Where is ductile cast iron used:

Mining and Metallurgy: Crusher housings, conveyor elbows, slurry pump housings, aluminum and lead melting crucibles, slag ladles, press machines, molding flasks, hot rolling mill rolls.

Machine manufacturing: Hydraulic presses, cylinders, forging press heads and cylinders, crank press gears, bending machine frames, axles, various gears.

Agriculture: Tractor parts, front wheel forks, transmission housings, pedals.

Construction: Crane parts, concrete mixer parts, road construction machinery.

Chemistry: Drying drums, valves, pumps, plastic extrusion cylinders, plastic mixers, refinery valves.

Transportation: Aircraft construction, differential gear housing, flywheels, gearboxes, gear selector forks, wheel molds.

Power: Compressor housings and heads, gas turbine compressor casings, control rings, water turbine castings, burner housings, heat-resistant furnace parts.

Related Questions

The graphite inside it exists as round spheres rather than sharp-edged flakes. The spherical shape prevents stress concentration within the material, giving the cast iron a flexibility and impact resistance not seen in other types.

Magnesium creates a chemical effect during solidification that encourages the graphite to grow in a spherical shape rather than flakes. This change fundamentally improves the material’s mechanical properties, making it more durable.