Steel Ductile Iron
also Nodular Iron, Nodular Cast Iron
Ductile (nodular / spheroidal-graphite) iron is a cast iron in which magnesium treatment converts the graphite into spheroids, giving a ferrite/pearlite iron with steel-like strength and real ductility instead of the brittleness of gray iron.
Values for the As Cast condition
Ductile Iron tempers and conditions
Ductile Iron is supplied in 6 conditions, soft to hard. As Cast is the default FabDigit quotes; the values on this page are for it.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
fully ferritic (ASTM A536 60-40-18 / EN GJS-400-18) | Pick when maximum ductility, impact energy and low-temperature toughness matter — pressure pipe, fittings, wind-turbine and safety-critical castings. | 300 | 440 | 20 | 160 HB | 36 W/m·K |
sub-critical stress relief (≈540–650 °C), matrix essentially as-cast | Pick for dimensionally critical machined castings (hydraulic bodies, machine bases) where residual casting stress must be removed without changing strength class. | 320 | 460 | 15 | 180 HB | 3.1 % IACS |
As CastDefault ferritic/pearlitic matrix, no heat treatment (ASTM A536 65-45-12 / EN GJS-450-10) | Default stocked condition: best cost/strength balance for general machinery castings, housings and brackets. | 340 | 480 | 14 | 187 HB | 33 W/m·K |
Normalized and tempered | Pick for higher strength and wear resistance with moderate ductility — gears, crankshafts, sprockets, heavy-duty linkages. | 510 | 730 | 5 | 25 HRC | 30 W/m·K |
Quenched and tempered | Pick for maximum strength and wear life in ductile iron where low elongation is acceptable — dies, rolls, high-load gears and pins. | 700 | 900 | 3 | 34 HRC | 26 W/m·K |
Austempered ductile iron, ausferrite matrix | Pick when you want steel-level strength and fatigue life plus useful ductility and wear resistance at casting cost — suspension arms, track links, gears, ground-engaging tools. | 750 | 1,050 | 7 | 35 HRC | 24 W/m·K |
What is Ductile Iron?
Ductile (nodular / spheroidal-graphite) iron is a cast iron in which magnesium treatment converts the graphite into spheroids, giving a ferrite/pearlite iron with steel-like strength and real ductility instead of the brittleness of gray iron. It is chosen for cast pressure pipe, valve and pump bodies, crankshafts, gears, hubs, brackets and heavy machine bases because it casts and machines easily, damps vibration and costs far less than cast or forged steel. Limits are modest corrosion resistance, low weldability, section-sensitive properties (nodule count and matrix vary with wall thickness), and a stiffness/toughness ceiling well below wrought steel. Ductile Iron has a density of 7.1 g/cm³ (0.257 lb/in³), lighter than 99% of steel grades. It melts at 1,150°C (2,102 °F). Ductile Iron has a yield strength of 340 MPa (49.3 ksi) and a tensile strength of 480 MPa (69.6 ksi) — weaker than 76% of steel grades. Elongation at break is 14% and the elastic modulus is 169 GPa (24.5 Msi).
What is Ductile Iron used for?
- Water and sewer pressure pipe and fittings
- Valve and pump housings
- Engine blocks and crankshafts
- Gearbox housings and gears
- Wheel hubs and steering knuckles
- Machine tool bases and heavy brackets
- Manhole covers and municipal castings
Advantages
- Easy to machine — 68/100, better than 95% of steel grades
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
Limitations
- Low stiffness — 169 GPa (24.5 Msi), worse than 97% of steel grades
- Limited formability — 8/100, worse than 97% of steel grades
- Low fracture toughness — 42 MPa·√m (38.2 ksi·√in), worse than 92% of steel grades
- Low electrical conductivity — 3.1 % IACS, worse than 89% of steel grades
- Poor heat conductor — 33 W/m·K (19.1 BTU/hr·ft·°F), worse than 80% of steel grades
Ductile Iron properties
Typical room-temperature values for Ductile Iron-As Cast; bars are the position among steel grades.
Physical3
Ductile Iron has a density of 7.1 g/cm³ (0.257 lb/in³), lighter than 99% of steel grades. It melts at 1,150°C (2,102 °F).
Mechanical15
Ductile Iron has a yield strength of 340 MPa (49.3 ksi) and a tensile strength of 480 MPa (69.6 ksi) — weaker than 76% of steel grades. Elongation at break is 14% and the elastic modulus is 169 GPa (24.5 Msi).
Thermal6
Ductile Iron is rated for continuous service to 400°C (752 °F). It conducts heat at 33 W/m·K (19.1 BTU/hr·ft·°F), worse than 80% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
Ductile Iron conducts electricity at 3.1 % IACS, worse than 89% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (16/100), better than 79% of steel grades.
Sustainability4
Producing a kilogram of Ductile Iron takes about 21 MJ of energy and emits 1.9 kg of CO₂ — less than 99% of steel grades. Typical recycled content is 85%.
Manufacturability8
Ductile Iron's machinability is good (68/100, better than 95% of steel grades); weldability fair (35/100); formability not recommended (8/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. Ductile Iron is highlighted; hover a dot for its name, or open the interactive family chart.
Working with Ductile Iron
Is Ductile Iron easy to machine?
Machines better than steel of equal hardness — carbide at 150–300 m/min for ferritic/pearlitic grades, dry or with light coolant; watch for hard carbides in thin chilled sections and use CBN on Q&T/ADI.
Can Ductile Iron be welded?
Poor as-welded: use Ni or Ni-Fe electrodes (ENiFe-CI), 200–350 °C preheat, short low-heat beads with peening, then ferritize/stress-relieve to avoid carbides and martensite in the HAZ.
Can Ductile Iron be formed, bent or molded?
A casting alloy — green sand, shell, no-bake or permanent mold with Mg treatment plus late inoculation; feed for shrinkage and keep section modulus consistent since nodule count and matrix are section-sensitive, and it is not cold formed.
Manufacturability
The process limits FabDigit applies to Ductile Iron. Every Ductile Iron part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Better68 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Ductile Iron chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Ctotal carbon; CE typically 4.3–4.6 | 3.2 – 3.9 | 3.6 |
| Sihigher Si strengthens ferrite, lowers toughness | 1.8 – 2.9 | 2.4 |
| Mnkept low for ferritic grades | 0.1 – 0.6 | 0.3 |
| Mgresidual Mg for nodularization | 0.03 – 0.06 | 0.04 |
| P | ≤ 0.05 | 0.03 |
| S | ≤ 0.02 | 0.01 |
| Cuoptional pearlite stabilizer (higher-strength grades) | 0 – 0.8 | 0.2 |
| Nioptional, hardenability/toughness | 0 – 1 | |
| Mooptional, for ADI/Q&T sections | 0 – 0.4 | |
| Fe | balance |
What surface finishes work on Ductile Iron?
No anodizing; shot blast then paint, powder coat, zinc/phosphate or electroless nickel; cement-mortar or fusion-bonded epoxy lining for water pipe; can be flame/induction hardened or nitrided for wear surfaces.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel Ductile Iron in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Trade names
- Nodular IronNodular Cast IronSpheroidal Graphite IronSG IronDuctile Cast IronIron
How much does Ductile Iron cost?
Ductile Iron is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Ductile Iron — frequently asked
What is Ductile Iron used for?
Ductile Iron is typically used for water and sewer pressure pipe and fittings, valve and pump housings, engine blocks and crankshafts, gearbox housings and gears, wheel hubs and steering knuckles and machine tool bases and heavy brackets. In short: stronger than gray iron.
What is the yield strength of Ductile Iron?
Ductile Iron has a typical yield strength of 340 MPa (49.3 ksi) and a tensile strength of 480 MPa (69.6 ksi) — weaker than 76% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is Ductile Iron easy to machine?
Reasonably — machinability is rated good (68/100, better than 95% of steel grades). Machines better than steel of equal hardness — carbide at 150–300 m/min for ferritic/pearlitic grades, dry or with light coolant; watch for hard carbides in thin chilled sections and use CBN on Q&T/ADI.
Can Ductile Iron be welded?
With care — weldability is rated fair (35/100). Poor as-welded: use Ni or Ni-Fe electrodes (ENiFe-CI), 200–350 °C preheat, short low-heat beads with peening, then ferritize/stress-relieve to avoid carbides and martensite in the HAZ.
What surface finishes work on Ductile Iron?
No anodizing; shot blast then paint, powder coat, zinc/phosphate or electroless nickel; cement-mortar or fusion-bonded epoxy lining for water pipe; can be flame/induction hardened or nitrided for wear surfaces.
Can Ductile Iron be formed, bent or molded?
A casting alloy — green sand, shell, no-bake or permanent mold with Mg treatment plus late inoculation; feed for shrinkage and keep section modulus consistent since nodule count and matrix are section-sensitive, and it is not cold formed.
What is the maximum service temperature of Ductile Iron?
Ductile Iron is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between Ductile Iron As Cast and Ductile Iron-ADI?
As Cast is the default condition — default stocked condition: best cost/strength balance for general machinery castings, housings and brackets. ADI: pick when you want steel-level strength and fatigue life plus useful ductility and wear resistance at casting cost — suspension arms, track links, gears, ground-engaging tools. Yield strength is 340 MPa in As Cast versus 750 MPa in ADI.
How much does Ductile Iron cost?
Ductile Iron is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in Ductile Iron?
Yes — Ductile Iron is available for CNC machining and casting & forging; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM A536 — Standard Specification for Ductile Iron Castings — ASTM International (2019)
- ASTM A897/A897M — Austempered Ductile Iron Castings — ASTM International (2022)
- EN 1563 — Founding: Spheroidal graphite cast irons — CEN (2018)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- Ductile Iron Data for Design Engineers — Ductile Iron Society / Rio Tinto Iron & Titanium (2013)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.