Steel Ductile Iron vs Gray Iron
Steel · grade comparison
Steel Ductile Iron and Gray Iron are both steel grades. Ductile Iron is the stronger of the two: yield strength 340 MPa (49.3 ksi) against 165 MPa (23.9 ksi) for Gray Iron, about 106% more; tensile strength follows at 480 MPa (69.6 ksi) vs 220 MPa (31.9 ksi). Ductile Iron is the more ductile: elongation 14% versus 0.5% for Gray Iron. Ductile Iron is stiffer (169 GPa vs 103 GPa) and Gray Iron conducts heat better (46 W/m·K vs 33 W/m·K). On the shop floor, Gray Iron machines more easily (excellent vs good) and Ductile Iron welds better (fair vs poor).
Ductile IronChoose it when strength drives the design, or when the part is bent, formed or impact-loaded.
Gray IronChoose it when the part is machined in volume.
Ductile Iron vs Gray Iron: propertiesHow to read these bars
- One bar per material. A full bar is the highest value among all steel grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
How to read these bars
- One bar per material. A full bar is the highest value among all steel grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
Mechanical
Strength, stiffness, ductility and hardness at room temperature.
Elastic (Young's) Modulus
Shear Modulus
Bulk Modulus
Poisson's Ratio
Tensile Strength (Ultimate)
Yield Strength (0.2% offset)
Elongation at Break
Reduction in Area
Compressive Strength
Shear Strength
Fatigue Strength (Endurance Limit)
Fracture Toughness (K_IC)
Charpy V-Notch Impact (RT)
Hardness, Vickers
Same in both: Hardness, Brinell 187 HB · Hardness, Rockwell B 90 HRB
Physical
Density and transition temperatures.
Density
Liquidus Temperature
Same in both: Melting Point (Solidus) 1,150°C2,102 °F
Thermal
How each material carries heat and how hot it can run.
Thermal Conductivity
Thermal Expansion (CTE, 20–100 °C)
Min Service Temperature
Same in both: Specific Heat Capacity 460 J/kg·K0.11 BTU/lb·°F · Latent Heat of Fusion 220 J/g94.6 BTU/lb · Max Service Temperature (continuous) 400°C752 °F
Electrical
Conductivity and insulation.
Electrical Conductivity
Electrical Resistivity
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Corrosion Resistance
Same in both: Galvanic Potential (seawater, vs SCE) -0.61 V
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Machinability Rating (AISI 1212 = 100 %)
Weldability
Formability (cold)
Castability
Brazeability / Solderability
Polishability
Sustainability
Primary-production footprint per kilogram.
Embodied Energy (primary production)
Embodied Carbon (primary production)
Typical Recycled Content
Same in both: Embodied Water 40 L/kg4.8 gal/lb
Common Calculations
Ratios derived from the values above.
Specific Strength (UTS / density)
Specific Stiffness (E / density)
Modulus of Resilience
Thermal Diffusivity
Thermal Shock Resistance Index
Strength versus weight
Yield strength against density for every steel grade in the FabDigit library; the compared grades are highlighted. Up and left is stronger for its weight.
Manufacturing and finishing
| Capability | Ductile Iron | Gray Iron |
|---|---|---|
| Default condition | As Cast | As Cast |
| Relative cost | $$ Standard | $$ Standard |
| Min. machined wall | 0.8 mm | 0.8 mm |
| Best machined surface | Ra 1.6 µm | Ra 1.6 µm |
Both are offered for CNC machining and Casting & forging. Both take the same 38 finishes: AlCrN, AlTiN, Black Oxide, CVD Al2O3, CVD TiCN, CVD TiN, Cerakote, Chrome Plating, Copper Plating, CrN, DLC, E-Coating and 26 more.
Ductile Iron vs Gray Iron — frequently asked
Is Ductile Iron stronger than Gray Iron?
Yes. Ductile Iron has a typical yield strength of 340 MPa (49.3 ksi) against 165 MPa (23.9 ksi) for Gray Iron — about 106% more. Tensile strength is 480 MPa (69.6 ksi) vs 220 MPa (31.9 ksi).
Which is cheaper, Ductile Iron or Gray Iron?
Both sit in the same relative cost tier ($$, standard); the part price will be decided by machining time, tolerance and quantity rather than by the material.
Which is easier to machine, Ductile Iron or Gray Iron?
Gray Iron. Its machinability rates excellent (85/100) against good (68/100) for Ductile Iron; for welding the order is Ductile Iron first (fair, 35/100) then Gray Iron (poor, 25/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in Ductile Iron and Gray Iron side by side — material, machining time, tolerance and finish in one quote. Certified material data ships with the order on request.
Typical handbook values for the conditions named above, normalised for comparison. Hardness on non-Brinell scales is converted approximately for charting only. Request certified data with your order for design-critical properties.