The main differences between cast iron and ductile iron lie in the graphite morphology and alloying element content.
Cast iron typically contains between 2% and 4% carbon, while ductile iron, through a spheroidizing process, distributes the graphite in spherical shapes. This results in superior strength and toughness compared to ordinary cast iron.
Chemical Composition Differences
Ordinary cast iron has a carbon content of 2.5% to 4% and a silicon content of 0.6% to 3%. It may also contain elements such as manganese, phosphorus, and sulfur. Ductile iron, on the other hand, requires the addition of spheroidizing agents such as rare earth elements, magnesium. Adjusting alloying elements promotes graphite spheroidization while also controlling silicon and manganese content to optimize performance.
Microstructure and Performance Differences
Ordinary cast iron graphite is flaky or flocculent, with a ferrite/pearlite matrix, resulting in lower strength and toughness. Ductile iron graphite is spherical, and the matrix can be manipulated to be either ferrite or pearlite, resulting in significantly improved overall mechanical properties.
Strength Properties
The strength of ductile iron is primarily reflected in two key indicators: tensile strength and yield strength.
Tensile Strength: Different grades of ductile iron have a wide range of tensile strengths, as shown below:
QT400-18: Tensile strength ≥ 400 MPa
QT450-10: Tensile strength ≥ 450 MPa
QT700-2: Tensile strength ≥ 700 MPa
Austenitic-bainitic ductile iron: Tensile strength can reach over 1000 MPa.
Yield Strength:
The conditional yield strength of QT450-10 is ≥ 250 MPa.
The conditional yield strength of QT700-2 is ≥ 420 MPa.
Special Treatments to Enhance Strength:
Austempered ductile iron (ADI) features a bainite and retained austenite structure, significantly improving tensile strength and wear resistance. It can replace forged steel in the manufacture of automotive tow hooks, bushings, and crankshafts. II. Toughness
The toughness of ductile iron is primarily reflected in its elongation and impact toughness:
Elongation:
QT700-2: Elongation ≥ 2%
QT450-10: Elongation ≥ 10%
QT400-18: Elongation ≥ 18%
Austenitic-bainitic ductile iron: Elongation 3%-8%.
Impact toughness:
QT800-2A: Room temperature impact energy ≥ 10 J
QT400-15: Impact energy absorption remains ≥ 100 J/cm² at -20°C
Bainitic ductile iron: Fracture toughness reaches 60 MPa·m², reaching the level of low-alloy steel. Low-Temperature Performance:
Ferritic ductile iron maintains excellent toughness even at low temperatures, making it suitable for cold-region equipment such as wind turbine hubs and polar engineering machinery.
Applications:
Automotive: Crankshafts, gears, pistons, and other key components.
Pipeline Engineering: Urban water supply/drainage networks, oil and gas pipelines.
Heavy Machinery: Wind turbine hubs and engineering machinery components.
Other Applications: Agricultural machinery, internal combustion engines, wear-resistant parts, etc.
Of course, the excellent performance of ductile iron is primarily due to its spherical graphite morphology, which enables matrix strength utilization to reach 70-90%, far exceeding that of ordinary cast iron. This structural feature enables it to withstand high pressure and external loads, adapting to complex construction conditions and diverse operating environments. If you require custom ductile iron castings, consider working with Mulan Group. With 12 years of experience in ductile iron casting production and processing, Mulan Group serves customers in over 30 countries and has received widespread recognition. We look forward to your consultation and cooperation.
Here is our Custom Castings Display：
