Quick Answer
Cast iron vs cast steel — cast iron is cheaper, easier to cast, and excellent for damping and wear resistance. Cast steel is stronger, tougher, and weldable but harder to cast and more expensive. For OEM buyers, the decision depends on application: static structural parts favor cast iron; dynamic, impact-loaded, or welded parts favor cast steel.
Material Overview
Cast Iron
Cast iron is iron with >2% carbon. Common grades: gray iron, ductile (nodular) iron, white iron. Gray iron is most common for general applications.
Key characteristics:
- Carbon content: 2–4%
- Strength: moderate (tensile 150–400 MPa for gray, up to 700 MPa for ductile)
- Hardness: high, wear-resistant
- Damping: excellent (vibration absorption)
- Castability: easy (low shrinkage, fluid melt)
- Cost: lower than steel
- Machinability: good (gray iron easy, ductile harder)
- Weldability: poor (gray iron cracks, ductile weldable with care)
Cast Steel
Cast steel is iron with <2% carbon, often with alloying elements (Mn, Cr, Ni, Mo). Grades: carbon steel castings, low-alloy steel, stainless steel castings.
Key characteristics:
- Carbon content: 0.1–1.0%
- Strength: high (tensile 400–800+ MPa, up to 1200 MPa for alloy)
- Hardness: moderate to high (heat-treatable)
- Damping: poor compared to iron
- Castability: harder (higher shrinkage, fluidity issues)
- Cost: higher than iron
- Machinability: moderate (harder than gray iron)
- Weldability: good (carbon and low-alloy steel weldable)
Material Comparison Table
| Property | Gray Iron | Ductile Iron | Cast Carbon Steel | Cast Alloy Steel |
|---|---|---|---|---|
| Tensile strength (MPa) | 150–400 | 400–700 | 400–600 | 600–1200 |
| Yield strength (MPa) | — | 250–550 | 200–400 | 400–1000 |
| Hardness (HB) | 150–250 | 160–300 | 150–250 | 200–400 |
| Damping capacity | Excellent | Good | Poor | Poor |
| Castability | Excellent | Good | Moderate | Harder |
| Cost (relative) | Low | Medium | Medium–High | High |
| Weldability | Poor | Moderate | Good | Good |
| Machinability | Excellent | Good | Moderate | Moderate–Hard |
Mechanical Properties
Cast steel is significantly stronger and tougher than cast iron. For high-stress, impact-loaded, or fatigue-critical applications, steel is necessary.
Cast iron (especially gray iron) excels at:
- Vibration damping (engine blocks, machine bases)
- Wear resistance (sliding surfaces, brake components)
- Thermal stability (heat resistance, low distortion)
Cost Comparison
Cast iron is cheaper due to:
- Lower melting temperature (energy cost)
- Better fluidity (fewer defects, higher yield)
- Simpler alloy composition
Cast steel is more expensive due to:
- Higher melting temperature
- More complex alloying
- More casting defects requiring rework
Machinability
Gray iron is one of the most machinable metals — it cuts easily, breaks chips cleanly, and does not gum up tools. Cast steel is harder to machine, requiring more power and slower speeds.
Weldability
Gray iron welds poorly — cracks from thermal stress and carbon migration. Ductile iron can be welded with proper preheat and filler. Cast steel welds well with standard procedures.
Buyer decision: If welding is required in assembly, cast steel is preferred. If welding is not needed, cast iron may save cost.
Application Fit
Cast iron applications:
- Engine blocks, cylinder heads
- Machine bases, frames
- Pump housings, valve bodies
- Brake rotors, drums
- Manifold, pipe fittings
Cast steel applications:
- High-stress structural parts
- Impact-loaded components (crusher parts, mining equipment)
- Welded assemblies
- Pressure vessels, high-pressure fittings
- Aerospace and defense critical parts
Before finalizing the sourcing decision, many OEM buyers also compare Sand Casting Process, Material Selection for Cast Parts, Welding Services, and Casting Tolerances to clarify process fit, cost trade-offs, tolerance expectations, and supplier risk.
If you need application-specific guidance, drawing review, or a quotation, you can Contact YCUMETAL.
FAQ
Which is stronger?
Cast steel. Ductile iron approaches steel strength but steel alloys can exceed 1000 MPa.
Which is cheaper?
Cast iron. Material and casting cost are lower.
Can I weld cast iron?
Gray iron: generally not recommended. Ductile iron: weldable with proper technique and preheat. Cast steel: weldable.
Which is better for vibration?
Gray iron has excellent damping; ideal for engine blocks and machine bases.