Cast Steel vs Cast Iron: Key Differences, Properties & Applications

1. Introduction

Cast steel and cast iron are both ferrous metals produced through melting and casting processes.

Though they share a base element—iron—their properties, applications, and performance characteristics differ significantly due to variations in carbon content and alloying elements.

Choosing between cast steel and cast iron is crucial for engineers, manufacturers, and designers because it directly impacts the strength, machinability, corrosion resistance, and overall lifecycle cost of a component.

This article explores the metallurgy, mechanical behavior, production methods, and end-use suitability of cast steel and cast iron in depth.

2. What Is Cast Iron?

Cast iron is a group of iron-carbon alloys with a carbon content typically between 2.0% and 4.0%, along with varying levels of silicon (1.0–3.0%), manganese, sulfur, and phosphorus.

This high carbon content differentiates it from steel and gives cast iron its distinct physical and mechanical properties.

It is one of the oldest and most widely used ferrous metals in engineering and manufacturing, valued for its excellent castability, vibration damping, and compressive strength.

Historical Context

The use of cast iron dates back to 5th century BC in China, with widespread industrial adoption beginning in the 15th century.

It revolutionized construction, machinery, and transportation, making its way into everything from bridges and pipes to engines and cookware.

Key Types of Cast Iron

Key Characteristics of Cast Iron

• High Carbon Content: Enhances castability and wear resistance but reduces ductility.
• Excellent Castability: Low melting point (≈1150–1200 °C) and good fluidity allow intricate, large, and complex shapes to be cast easily.
• Good Damping Capacity: Particularly in gray iron, which absorbs vibration well, making it ideal for machinery bases.
• Brittleness: Most forms, especially gray and white cast iron, fracture under tensile or impact loads.
• Thermal Conductivity: Effective for heat distribution, making it a good material for engine parts and cookware.
• Corrosion Resistance: Moderate without coatings, though improved with certain alloying elements or surface treatments.

3. What Is Cast Steel?

Cast steel is a category of iron-carbon alloys with a carbon content typically ranging from 0.1% to 0.5%, produced by melting and casting the molten steel into molds to form specific shapes.

Unlike cast iron, cast steel has a lower carbon content, which results in significantly higher ductility, toughness, and weldability.

It is especially favored for applications involving dynamic loads, impact resistance, and wear resistance.

Historical Context

While wrought steel dates back to antiquity, cast steel became widely available in the 19th century following advancements in steel-making processes such as the Bessemer and open-hearth methods.

Today, cast steel is a vital material in structural, automotive, mining, and pressure-containing applications due to its strength and versatility.

Key Types of Cast Steel

Key Characteristics of Cast Steel

• Lower Carbon Content: Typically 0.1–0.5%, resulting in superior ductility and weldability compared to cast iron.
• High Strength & Toughness: Cast steel offers excellent mechanical properties, including high tensile strength and resistance to shock loading.
• Heat Treatable: Unlike cast iron, cast steel can be heat-treated (quenched, tempered, normalized) to enhance hardness, toughness, and wear resistance.
• Weldability: Excellent for fabrication, repair, and joining—ideal for components that may need modification or maintenance.
• Machinability: Generally good, though varies with alloy composition and heat treatment state.
• Corrosion Resistance: Varies widely depending on alloying elements. Stainless grades are highly corrosion-resistant.

4. Comparison Table: Cast Steel vs Cast Iron

5. Common Casting Methods: Cast Steel vs Cast Iron

Casting method selection is pivotal for cost control, dimensional precision, mechanical performance, and production scale.

Cast steel and cast iron share several casting techniques, but each material presents unique challenges due to differences in melting point, solidification behavior, and alloy reactivity.

Casting Methods for Cast Steel

Cast Steel Sand Casting

Sand casting is the most widely used method for producing cast steel parts, especially for medium to large components.

A pattern (wood, metal, or resin) is used to shape a cavity in sand—either green (clay-bound) or chemically bonded.

Because cast steel requires high pouring temperatures (1,450–1,600°C), mold materials and gating systems must be designed to handle thermal shock, erosion, and shrinkage.

Common Parts: Gearboxes, valve bodies, structural brackets.

Cast Steel Investment Casting (Lost Wax)

Investment casting excels at producing intricate shapes with thin walls and tight tolerances. A wax pattern is coated in ceramic slurry, forming a shell that is later dewaxed and fired.

This high-precision process is ideal for cast steel due to its ability to minimize machining, especially for complex aerospace, medical, or energy components.

Common Parts: Turbine blades, medical instruments, military components.

Cast Steel Shell Mold Casting

Shell molding uses a heated metal pattern to cure a resin-coated sand shell. It provides superior surface finish and dimensional consistency compared to traditional sand casting.

For steel, the process is particularly effective when medium-complexity components with high repeatability are needed.

Common Parts: Engine mounts, hydraulic brackets, bearing caps.

Cast Steel Centrifugal Casting

In centrifugal casting, molten steel is poured into a rotating mold.

The high-speed spinning distributes the metal outward against the mold wall, increasing density and reducing defects like inclusions or gas porosity.

Particularly useful for cylindrical or tubular parts, this method produces components with a fine-grained, highly uniform structure.

Common Parts: Steel pipes, sleeves, and rings for oil & gas or rail applications.

Cast Steel Continuous Casting (for Semi-Finished Products)

Although not used for near-net or finished parts, continuous casting is essential in the steel industry to produce billets, blooms, and slabs.

Molten steel is poured into a water-cooled mold, solidifying as it is drawn out. These forms are later processed via forging, machining, or rolling.

Products: Bar stock, structural beams, sheet steel.

Casting Methods for Cast Iron

Cast Iron Green Sand Casting

Green sand casting remains the dominant method for cast iron due to its low cost, recyclability, and adaptability.

The “green” refers to the moisture content in the sand, which is bonded with bentonite clay.

Cast iron’s excellent fluidity and lower melting point (1,100–1,250°C) make it perfectly suited for this process.

Common Parts: Manhole covers, engine blocks, compressor housings.

Cast Iron No-Bake (Resin-Bonded) Sand Casting

In no-bake molding, sand is mixed with a resin and catalyst that cures at room temperature, forming strong, rigid molds.

This process is preferred for large cast iron parts that require better dimensional accuracy and smoother surfaces than green sand can provide.

Common Parts: Large machine bases, industrial housings, impellers.

Cast Iron Shell Mold Casting

Shell mold casting is used less often in iron but remains beneficial when tighter tolerances or smoother finishes are needed. Resin-coated sand forms a thin, semi-rigid shell around the pattern.

Because cast iron flows well, this process ensures minimal flashing and fine edge definition.

Common Parts: Gear housings, valve bodies, decorative ironwork.

Cast Iron Centrifugal Casting

Widely used for ductile iron pipe and cylinder liners, centrifugal casting leverages rotational force to distribute molten metal within a mold.

For cast iron, this enhances nodule formation (in ductile grades), reduces porosity, and promotes grain refinement.

Common Parts: Pipe sections, flywheels, and brake drums.

Cast Iron Lost Foam Casting

Lost foam casting uses a polystyrene pattern embedded in unbonded sand. When molten cast iron is poured in, the foam evaporates, forming the shape with minimal gas entrapment due to iron’s lower reactivity.

This method excels for complex geometries without parting lines or cores.

Common Parts: Engine manifolds, pump housings, ornamental castings.

Key Differences in Casting Characteristics

6. Heat Treatment and Weldability: Cast Steel vs Cast Iron

Heat treatment and weldability are critical factors influencing the performance, service life, and repairability of cast components.

The fundamental metallurgical differences between cast steel and cast iron directly impact how each material responds to thermal processing and welding.

Cast Steel

Heat Treatment:

Cast steel generally contains lower carbon (0.1–0.5%) and is more amenable to a variety of heat treatments to tailor its mechanical properties. Common heat treatments include:

• Annealing: Softens the steel, reduces residual stresses, and improves machinability.
• Normalizing: Refines grain structure by heating above critical temperature (~870–950°C) followed by air cooling; enhances strength and toughness.
• Quenching and Tempering: Rapid cooling (quenching) from the austenitizing temperature (~900–1,000°C) to form martensite, followed by tempering to balance hardness and ductility.
  This process is essential for wear-resistant or high-strength cast steel parts.

These heat treatments allow cast steel to achieve a wide range of mechanical properties, including high tensile strength (400–800 MPa), improved impact toughness, and controlled hardness.

Weldability:

Cast steel’s relatively low carbon content and homogeneous microstructure make it highly weldable. It can be welded using conventional techniques such as:

• Shielded Metal Arc Welding (SMAW)
• Gas Tungsten Arc Welding (GTAW)
• Flux-Cored Arc Welding (FCAW)

However, care must be taken to control preheat and post-weld heat treatment to avoid cracking, especially in alloyed cast steels or thick sections.

The weld metal can closely match the base material properties, allowing effective repair and joining.

Cast Iron

Heat Treatment:

Cast iron, with its high carbon content (2.0–4.0%) and presence of graphite flakes or nodules, reacts differently to heat treatment:

• Annealing: Often applied to malleable iron to reduce hardness and improve ductility.
• Normalizing: Limited use, primarily to modify microstructure in white cast iron.
• Stress Relieving: Reduces residual stresses but does not significantly alter hardness or strength.

Unlike cast steel, cast iron cannot be effectively hardened through quenching due to the presence of graphite, which inhibits martensitic transformation.

Therefore, its mechanical properties are largely fixed after casting and cooling.

Weldability:

Welding cast iron poses significant challenges:

• The presence of graphite flakes (especially in gray cast iron) promotes crack initiation and propagation during welding.
• High carbon equivalent leads to brittleness and risk of hot cracking.
• Thermal expansion mismatch between weld and base metal causes residual stresses.

Welding cast iron often requires:

• Specialized techniques such as preheating (200–400°C), slow cooling, and use of nickel-based filler metals.
• Peening or stress relief after welding to minimize cracking.

8. Corrosion Resistance and Surface Finish: Cast Steel vs Cast Iron

Material behavior in corrosive environments and the achievable surface quality after casting or machining are crucial factors in component durability, performance, and aesthetics.

Cast steel and cast iron, though both ferrous materials, differ notably in corrosion resistance and post-casting finish characteristics due to their composition, microstructure, and carbon content.

Corrosion Resistance

Cast Steel

Cast steel generally has lower intrinsic corrosion resistance than cast iron due to its more reactive, homogeneous microstructure and lower carbon content.

However, it offers greater versatility in corrosion control through alloying and surface treatments.

Characteristics:

• Unalloyed carbon steel castings are prone to uniform rusting when exposed to moisture or oxygen.
• Alloyed cast steels (e.g., with chromium, nickel, or molybdenum) can resist various environments:

• • Stainless steel castings (≥10.5% Cr) exhibit strong corrosion resistance, even in acidic or marine settings.

• Compatible with coatings (galvanizing, painting, epoxy) for enhanced protection.

Cast Iron

Despite being more brittle, cast iron often shows better corrosion resistance in stagnant or mildly corrosive environments, largely due to the protective oxide layer formed by graphite content and surface texture.

Characteristics:

• Gray cast iron forms a stable, passivating oxide layer that slows corrosion—a self-limiting process.
• The graphite matrix acts as a cathode, making cast iron less prone to deep pitting but more susceptible to uniform surface oxidation.
• Ductile iron offers better corrosion performance than gray iron, especially with coatings or epoxy linings.

Surface Finish After Casting and Machining

Cast Steel

• Due to its dense and homogeneous grain structure, cast steel can achieve a smoother surface finish post-machining and polishing.
• As-cast surfaces tend to be rougher than cast iron but can be improved using investment or permanent mold casting.
• Ideal for components requiring tight tolerances or critical sealing surfaces.

Typical finish (as-cast):

• Sand casting: Ra 12.5–25 µm
• Investment casting: Ra 1.6–6.3 µm

Cast Iron

• Cast iron has excellent castability, which often results in better surface replication from molds.
• However, the presence of graphite can create a slightly porous surface texture, especially in gray iron.
• Machinability is superior due to graphite acting as a chip breaker and lubricant, leading to good post-machining finish.

Typical finish (as-cast):

• Green sand casting: Ra 6.3–12.5 µm
• Shell mold casting: Ra 3.2–6.3 µm

9. Advantages and Limitations of Cast Steel vs Cast Iron

Choosing between cast steel vs cast iron depends on a balance of mechanical performance, cost, manufacturability, corrosion resistance, and application-specific demands.

Both materials offer distinct strengths and trade-offs that influence design and procurement decisions.

Cast Steel

Advantages

1. High Ductility & Toughness
   Cast steel exhibits excellent impact resistance and tensile strength, making it suitable for dynamic and high-load applications.
2. Superior Weldability
   Its low carbon content and homogeneous structure allow for easy welding and repair.
3. Wide Alloy Selection
   Can be alloyed with chromium, nickel, molybdenum, etc., to enhance corrosion resistance, hardness, or heat resistance.
4. Heat Treatability
   Mechanical properties can be customized through heat treatment (e.g., quenching, tempering, annealing).
5. Good Fatigue Resistance
   Ideal for cyclic loading and shock conditions (e.g., structural or automotive parts).

Limitations

1. Lower Castability
   Higher shrinkage and poor fluidity make casting intricate or thin-walled shapes more difficult.
2. Higher Cost
   More expensive in terms of energy use, mold complexity, and alloying elements.
3. Surface Finish
   Generally rougher than cast iron in as-cast form and may require additional machining.
4. Corrosion Prone (if unalloyed)
   Requires coatings or alloying for applications in corrosive environments.

Cast Iron

Advantages

1. Excellent Castability
   Flows easily in molds; ideal for complex, thin-walled, or intricate shapes.
2. Superior Machinability
   The graphite microstructure acts as a lubricant, improving machinability and tool life.
3. Good Vibration Damping
   Ideal for machine bases and engine blocks where noise and vibration control are critical.
4. Cost-Effective
   Lower melting point and less energy-intensive processing reduce overall costs.
5. Natural Corrosion Resistance (in stagnant conditions)
   Especially gray iron, which forms a protective oxide layer.

Limitations

1. Brittle Fracture
   Low ductility and poor impact resistance make it unsuitable for dynamic loading or high-stress applications.
2. Poor Weldability
   Difficult to weld due to graphite flakes and high carbon content; repair is often impractical.
3. Lower Tensile Strength
   Cannot match cast steel in load-bearing or structural applications.
4. Limited Heat Treatment Options
   Mostly limited to stress relieving or annealing; mechanical properties are less tunable.

10. Common Applications of Cast Steel vs Cast Iron

The selection between cast steel and cast iron is often driven by performance demands, environmental conditions, and economic constraints.

Cast Iron Applications

Cast iron’s excellent fluidity, castability, and damping properties make it ideal for components with complex geometries, static loads, and noise/vibration sensitivity.

Cast Steel Applications

Cast steel is favored in industries requiring high strength, impact resistance, and structural integrity, particularly under dynamic or extreme service conditions.

11. Conclusion

Both cast iron vs cast steel play essential roles in modern engineering.

Cast iron is ideal for applications requiring excellent castability, machinability, and vibration damping, whereas cast steel excels in high-impact, high-strength, and fatigue-prone environments.

Material choice should be based on performance requirements, operating conditions, and lifecycle costs to achieve optimal functionality and durability.

LANGHE’s Comprehensive Metal Casting Services

LANGHE offers a wide range of professional casting services tailored to meet the diverse needs of industries worldwide.

Our capabilities span multiple casting techniques and metal materials to ensure optimal performance, quality, and cost-efficiency for every project.

Casting Methods We Provide:

• Sand Casting
• Investment Casting (Lost Wax)
• Permanent Mold Casting
• Die Casting
• Centrifugal Casting
• Lost Foam Casting
• Gravity Casting

Materials We Work With:

• Cast Iron (Gray Iron, Ductile Iron, White Iron)
• Cast Steel (Carbon Steel, Low-Alloy Steel, Stainless Steel)
• Aluminum Alloys (AlSi10Mg, A356, etc.)
• Copper-Based Alloys (Brass, Bronze)
• Zinc Alloys
• Specialty Alloys (Heat-resistant, corrosion-resistant grades)

Whether you’re developing complex precision parts or large structural castings, LANGHE is your trusted partner for reliable, high-quality metal casting solutions.

FAQs

Is cast iron stronger than cast steel?

No. Cast steel has higher tensile strength (400–1000 MPa) than ductile iron (400–800 MPa) and far exceeds gray iron (200–400 MPa).

Can cast iron be welded?

Ductile iron can be welded with preheating (200–300°C) but loses 10–20% ductility. Gray iron is difficult to weld due to brittleness. Cast steel welds easily, matching base metal strength.

Which is more machinable?

Gray iron is most machinable (graphite acts as a lubricant), followed by ductile iron. Cast steel is harder to machine, requiring carbide tools.

Why is cast iron used for engine blocks?

Its vibration-damping reduces noise, low-cost suits mass production, and fluidity enables complex water jackets and oil galleries.

When is stainless cast steel necessary?

In corrosive environments (seawater, chemicals) or high-purity applications (pharmaceutical, food processing) where rust or contamination is unacceptable.