Ductile Iron properties
Chemical composition
Section titled “Chemical composition”The carbon content in ductile iron typically ranges between 3.0 % and 4.1 %.
| Element | Minimum (% by mass) | Maximum (% by mass) | Notes |
|---|---|---|---|
| Carbon (C) | 3.0 | 4.1 | Forms graphite nodules; in ferritic compositions 3.0‑3.7 % |
| Silicon (Si) | 1.2 | 2.8 | Promotes graphitization; in ferritic grades 2.2‑2.8 % |
| Manganese (Mn) | 0.03 | 0.8 | Controls pearlitic structure; ≤0.2 % in ductile applications |
| Phosphorus (P) | ≤0.005 | <0.1 | Kept low to avoid brittleness |
| Sulfur (S) | ≤0.005 | <0.03 | Reduced by magnesium treatment |
| Magnesium (Mg) | 0.03 | 0.07 | Typical residual nodulizing element |
| Nickel (Ni) | 0 | 1.0 | Optional to improve strength and hardenability |
| Copper (Cu) | 0 | <0.40 | Increases strength and hardness; decreases ductility |
| Iron (Fe) | Balance | Balance | Metal matrix |
Values vary according to grade and section thickness. The exact chemical composition is at the manufacturer’s discretion, in accordance with EN 1563.
Mechanical properties in tension, compression and hardness
Section titled “Mechanical properties in tension, compression and hardness”The tensile strength of ductile iron ranges from 350 MPa (50.8 ksi) to 1000 MPa (145.0 ksi).
| Property | Minimum (SI) | Maximum (SI) | Unit (SI) | Minimum (Imperial) | Maximum (Imperial) | Unit (Imperial) |
|---|---|---|---|---|---|---|
| Tensile strength | 350 | 1000 | MPa | 50.8 | 145.0 | ksi |
| Yield strength (Rp0.2) | 215 | 790 | MPa | 31.2 | 114.6 | ksi |
| Compressive strength | 229 | 799 | MPa | 33.2 | 115.9 | ksi |
| Elongation (A) | 2 | 29 | % | 2 | 29 | % |
| Hardness (approx. Brinell) | 115 HB | 326 HB | – | – | – | – |
| Young’s modulus (E) | 165 | 180 | GPa | 23.9 | 26.1 | 10⁶ psi |
| Shear modulus (G) | 64 | 71 | GPa | 9.28 | 10.30 | 10⁶ psi |
| Bulk modulus (K) | 119 | 137 | GPa | 17.3 | 19.9 | 10⁶ psi |
| Poisson’s ratio (ν) | 0.27 | 0.28 | – | 0.27 | 0.28 | – |
For grade EN-GJS-500-7, the minimum tensile strength is 500 MPa (up to 30 mm thickness) and the Brinell hardness is maintained between 150 and 230 HB.
Fatigue limit and fracture toughness
Section titled “Fatigue limit and fracture toughness”The fatigue limit of ductile iron is between 180 MPa (26.1 ksi) and 330 MPa (47.9 ksi).
| Property | Minimum (SI) | Maximum (SI) | Unit (SI) | Minimum (Imperial) | Maximum (Imperial) | Unit (Imperial) |
|---|---|---|---|---|---|---|
| Fatigue limit (Endurance limit) | 180 | 330 | MPa | 26.1 | 47.9 | ksi |
| Fracture toughness (KIC) | 22 | 54 | MPa·m½ | 20.0 | 49.1 | ksi·in½ |
These values reflect the remarkable fatigue resistance and damage tolerance that characterize nodular grades compared to other cast irons.
Physical properties
Section titled “Physical properties”The density of ductile iron varies between 7.05 Mg/m³ (440 lb/ft³) and 7.25 Mg/m³ (453 lb/ft³).
| Property | Minimum (SI) | Maximum (SI) | Unit (SI) | Minimum (Imperial) | Maximum (Imperial) | Unit (Imperial) |
|---|---|---|---|---|---|---|
| Density | 7.05 | 7.25 | Mg/m³ | 440 | 453 | lb/ft³ |
| Atomic volume (avg.) | 0.0077 | 0.0080 | m³/kmol | 470 | 488 | in³/kmol |
| Energy content | 60 | 72 | MJ/kg | 6500 | 7800 | kcal/lb |
| Loss coefficient | 0.0006 | 0.0022 | – | 0.0006 | 0.0022 | – |
Thermal properties
Section titled “Thermal properties”The melting point of ductile iron lies between 1403 K (1130 °C) and 1523 K (1250 °C).
| Property | Minimum (SI) | Maximum (SI) | Unit (SI) | Minimum (Imperial) | Maximum (Imperial) | Unit (Imperial) |
|---|---|---|---|---|---|---|
| Melting point | 1403 | 1523 | K | 2066 | 2282 | °F |
| Latent heat of fusion | 270 | 275 | kJ/kg | 116 | 118 | BTU/lb |
| Maximum service temperature | 623 | 723 | K | 662 | 842 | °F |
| Minimum service temperature | 123 | 393 | K | –238 | 248 | °F |
| Specific heat (cp) | 460 | 495 | J/(kg·K) | 0.356 | 0.383 | BTU/(lb·°F) |
| Thermal conductivity | 29 | 44 | W/(m·K) | 54.3 | 82.4 | BTU·ft/(h·ft²·°F) |
| Coefficient of thermal expansion | 10 | 12.5 | 10⁻⁶ /K | 18 | 22.5 | 10⁻⁶ /°F |
The glass transition temperature is not defined and is omitted because it is a crystalline material.
Electrical properties
Section titled “Electrical properties”The electrical resistivity of ductile iron is between 49 × 10⁻⁸ Ω·m and 56 × 10⁻⁸ Ω·m.
| Property | Minimum (SI) | Maximum (SI) | Unit (SI) | Minimum (Imperial) | Maximum (Imperial) | Unit (Imperial) |
|---|---|---|---|---|---|---|
| Electrical resistivity | 49 | 56 | 10⁻⁸ Ω·m | 49 | 56 | 10⁻⁸ Ω·m |
No significant values of dielectric constant or breakdown potential are reported, as it is not a dielectric material.
Corrosion resistance and environmental agents
Section titled “Corrosion resistance and environmental agents”Ductile iron exhibits excellent wear resistance (5/5) and good resistance to fresh water (4/5).
| Agent / Condition | Resistance (1 = poor, 5 = excellent) |
|---|---|
| Flammability | 5 |
| Fresh water | 4 |
| Organic solvents | 5 |
| Oxidation at 500 °C | 4 |
| Seawater | 3 |
| Strong acid | 2 |
| Strong alkalis | 3 |
| UV radiation | 5 |
| Wear | 5 |
| Weak acid | 4 |
| Weak alkalis | 5 |
Intermediate behaviors in marine environments and strong acids require selecting protective coatings or grades alloyed with chromium or nickel for exposed applications.
Applications by industry
Section titled “Applications by industry”Ductile iron is used in water and sewage pipes, where its tensile strength exceeds 420 MPa.
| Industry | Typical applications | Most demanded property |
|---|---|---|
| Water supply and sanitation | Pipes, valves, fittings, hydrants | Mechanical strength + corrosion resistance |
| Automotive | Crankshafts, connecting rods, brake discs, steering knuckles, differential housings | High fatigue resistance and good machinability |
| Industrial and agricultural vehicles | Tractors (frames, axles), class 8 trucks, off-road machinery | Strength/weight ratio and ductility |
| Wind energy | Hubs, structural supports, generator frames | Resistance to dynamic loads and low temperatures |
| Machine tools and capital goods | Press frames, pump bodies, compressors | Stiffness and vibration damping |
| Railway | Bogie components, draw hooks | Impact resistance |
| General industry | Pulleys, large gears, stamping dies | Toughness and wear resistance |
The replacement of forged steel with ductile iron in complex geometry parts reduces machining and material costs without sacrificing mechanical performance.
Comparison with other cast irons
Section titled “Comparison with other cast irons”Compared to gray iron, ductile iron offers at least 10 times greater ductility.
| Property | Ductile iron | Gray iron | Malleable iron |
|---|---|---|---|
| Tensile strength (MPa) | 350 - 1000 | 100 - 400 | 300 - 700 |
| Elongation (%) | 2 - 29 | < 0.5 | 2 - 18 |
| Young’s modulus (GPa) | 165 - 180 | 80 - 140 | 160 - 180 |
| Fracture toughness (MPa·m½) | 22 - 54 | 10 - 20 | 20 - 40 |
| Machinability | Very good | Excellent | Good |
| Relative cost | Medium | Low | Medium‑high |
The spheroidal shape of graphite eliminates the stress concentrators typical of gray iron flakes, giving it a unique combination of strength and ductility similar to some steels, with the added advantage of excellent fluidity in casting.
Variants and standardized designations
Section titled “Variants and standardized designations”Grade EN-GJS-500-7 has a minimum tensile strength of 500 MPa and a minimum elongation of 7%.
| Designation (EN 1563) | Minimum tensile strength (MPa) | Minimum yield strength (MPa) | Minimum elongation (%) | Brinell hardness (HBW) | Equivalent designations (examples) |
|---|---|---|---|---|---|
| EN-GJS-350-22 | 350 (t≤30 mm) | 220 | 22 | ≤ 160 | – |
| EN-GJS-400-15 | 400 | 250 | 15 | 130 - 180 | 60-40-18 (ASTM A536) |
| EN-GJS-450-10 | 450 | 310 | 10 | 140 - 210 | 65-45-12 |
| EN-GJS-500-7 | 500 (t≤30 mm) | 320 | 7 | 150 - 230 | 70-50-05; 80-55-06; FCD500 (JIS) |
| EN-GJS-600-3 | 600 | 370 | 3 | 190 - 270 | 100-70-03 |
| EN-GJS-700-2 | 700 | 420 | 2 | 225 - 305 | – |
| EN-GJS-800-2 | 800 | 480 | 2 | 245 - 335 | – |
For thick sections (30‑60 mm and 60‑200 mm) the minimum properties are reduced as stipulated in the standard. Additional equivalents can be found in ASTM A536, A395 and other regional standards.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the typical tensile strength of ductile iron?
Section titled “What is the typical tensile strength of ductile iron?”The tensile strength of ductile iron ranges from 350 MPa (50.8 ksi) in ferritic grades to 1000 MPa (145 ksi) in heat-treated grades such as ADI. The exact value depends on grade, thickness, and applied heat treatment.
What is the carbon content of this material?
Section titled “What is the carbon content of this material?”The carbon content ranges from 3.0% to 4.1% by mass, although most industrial compositions fall in the 3.2‑3.8% range. This carbon appears mainly as spheroidal graphite nodules, responsible for the high ductility.
What is the density of ductile iron?
Section titled “What is the density of ductile iron?”Its density is between 7.05 g/cm³ and 7.25 g/cm³, equivalent to 440‑453 lb/ft³. This density is slightly lower than that of steel (7.8 g/cm³), which provides an advantage in strength/weight ratios.
Up to what temperature can it work without losing properties?
Section titled “Up to what temperature can it work without losing properties?”The maximum service temperature ranges from 623 K (350 °C) to 723 K (450 °C). Above these values, mechanical strength decreases and surface oxidation accelerates, although grades with high silicon content or nickel alloys can be used for higher temperature applications.
What Brinell hardness does it typically exhibit?
Section titled “What Brinell hardness does it typically exhibit?”Brinell hardness can range from 115 HB to 326 HB (approximately 1150‑3200 MPa indentation hardness). The exact range depends on grade: an EN-GJS-500-7 exhibits between 150 and 230 HB, while high-strength pearlitic grades reach up to 305 HB.
How does its fatigue resistance compare to that of steel?
Section titled “How does its fatigue resistance compare to that of steel?”The fatigue limit of 180‑330 MPa (26‑48 ksi) typically represents between 40% and 55% of its tensile strength, a behavior very similar to that of many structural steels. This ability to withstand cyclic loads makes ductile iron a viable alternative for components such as crankshafts and suspension elements.
References
Section titled “References”- azom.com: https://www.azom.com/properties.aspx?ArticleID=797
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/cast-iron-d_1163.html
- steelnumber.com: https://www.steelnumber.com/en/steel_composition_eu.php?name_id=1522