The Difference Between Ductile Iron and Cast Iron

Ductile iron castings are used in nearly every major industrial sector that demands high strength, ductility, toughness, wear resistance, and resistance to nodular cast iron. They withstand severe thermal and mechanical shocks, as well as extreme temperatures—both high and low—and exhibit excellent corrosion resistance and dimensional stability. To meet the varying demands of different application conditions, ductile iron is available in a wide range of grades, each offering an extensive spectrum of mechanical and physical properties.

The Difference Between Ductile Iron and Cast Iron

Ductile iron is an abbreviation for spheroidal graphite cast iron, an iron-carbon alloy with a carbon content exceeding 2%. Industrial cast irons typically contain 2% to 4% carbon. In cast iron, carbon primarily exists in the form of graphite, though it may occasionally appear as cementite. Besides carbon, cast iron also contains trace amounts of elements such as silicon (1%–3%), manganese, phosphorus, and sulfur. Additionally, alloyed cast irons may include elements like nickel, chromium, molybdenum, aluminum, copper, boron, and vanadium. Among these, carbon and silicon are the key design elements that significantly influence the microstructure and mechanical properties of cast iron.

Cast iron can be classified into:

1. Gray cast iron contains a high carbon content (2.7% to 4.0%), with carbon primarily existing in the form of flaky graphite. Its fracture surface appears gray, hence the name "gray cast iron." It has a low melting point (1145–1250°C), exhibits minimal shrinkage during solidification, and its compressive strength, along with hardness, gradually approaches that of common carbon steel. Additionally, it offers excellent vibration damping properties. Gray cast iron is widely used in manufacturing structural components such as machine tool beds, cylinder blocks, and housings.

2. White cast iron. It has low carbon and silicon content, with carbon primarily existing in the form of cementite. The fracture surface appears silvery white. During solidification and contraction, it is prone to shrinkage defects and cracking. This type of iron exhibits high hardness and brittleness, making it unsuitable for directly withstanding heavy impact loads. It is mainly used as a billet for malleable cast iron and for manufacturing wear-resistant components.

3. Malleable cast iron. It is White mouth After annealing, the cast iron develops a flake-like distribution of graphite, resulting in what is known as ductile cast iron. This material features uniform microstructure and properties, offering excellent wear resistance, as well as superior ductility and toughness. It is widely used to produce parts of intricate shapes that can withstand heavy dynamic loads.

4. Ductile iron. Gray cast iron is transformed into molten iron through a spheroidal graphite process, resulting in graphite that forms spherical shapes—hence the term "ductile iron." Compared to conventional gray cast iron, ductile iron boasts higher strength, as well as superior toughness and ductility. It is widely used in the manufacturing of internal combustion engines, automotive components, and agricultural machinery.

5. Vermicular graphite cast iron. Gray cast iron is produced by treating molten iron with a vermicularizing process, resulting in worm-like graphite flakes. Its mechanical properties are comparable to those of ductile cast iron, while its casting performance falls somewhere between that of gray cast iron and ductile cast iron. It is used to manufacture automotive components.

6. Alloying for Cast Iron: Typically, cast iron is produced by carefully adding适量 of alloying elements—such as silicon, manganese, phosphorus, nickel, chromium, molybdenum, copper, aluminum, boron, vanadium, tin, and others—to achieve desired properties. These alloying elements alter the matrix structure of the cast iron, endowing it with enhanced characteristics like heat resistance, wear resistance, corrosion resistance, low-temperature performance, or even non-magnetic qualities. Such alloys are widely used in manufacturing components for mining equipment, chemical machinery, precision instruments, and other applications.