Cast Carbon Steel: Properties and Key Applications

Cast carbon steel is a category of steel characterized by its high carbon content and the method of its production, which involves casting molten metal into molds. This steel grade is primarily classified as a low-carbon or medium-carbon steel, depending on its carbon content, which typically ranges from 0.05% to 0.30%. The primary alloying element in cast carbon steel is carbon (C), which significantly influences its hardness, strength, and ductility. Other elements may include manganese (Mn), silicon (Si), and small amounts of sulfur (S) and phosphorus (P), which can affect the steel's mechanical properties and performance.

Comprehensive Overview

Cast carbon steel is known for its excellent machinability and weldability, making it a popular choice in various engineering applications. Its significant characteristics include good tensile strength, wear resistance, and the ability to be heat-treated to enhance its properties. The inherent properties of cast carbon steel allow it to be used in applications where strength and durability are paramount.

Advantages of Cast Carbon Steel:
- High Strength: Offers good tensile and yield strength, making it suitable for structural applications.
- Cost-Effective: Generally less expensive than alloy steels and stainless steels.
- Versatile: Can be easily cast into complex shapes, reducing the need for extensive machining.

Limitations of Cast Carbon Steel:
- Corrosion Susceptibility: Prone to rusting and corrosion if not properly treated or coated.
- Lower Toughness: Compared to alloy steels, it may exhibit lower toughness, especially at low temperatures.
- Limited High-Temperature Performance: Not ideal for applications requiring high-temperature resistance.

Historically, cast carbon steel has played a crucial role in the development of industrial machinery and infrastructure, being widely used in the manufacturing of components such as gears, shafts, and frames.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	C10, C20, C30	USA	Closest equivalents to low and medium carbon steels
AISI/SAE	1020, 1045	USA	Minor compositional differences; 1020 is low carbon, 1045 is medium carbon
ASTM	A216	USA	Specification for castings of carbon steel
EN	1.0402, 1.0503	Europe	Equivalent grades for low and medium carbon cast steel
DIN	G20Mn5, G40Mn2	Germany	Designations for cast carbon steels with specific manganese content
JIS	SCW 40	Japan	Japanese standard for carbon steel castings

The differences between equivalent grades can significantly affect performance. For instance, while AISI 1020 and 1045 are often considered similar, the higher carbon content in 1045 provides improved hardness and strength, making it more suitable for applications requiring enhanced mechanical properties.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
C (Carbon)	0.05 - 0.30
Mn (Manganese)	0.30 - 0.90
Si (Silicon)	0.10 - 0.40
P (Phosphorus)	≤ 0.04
S (Sulfur)	≤ 0.05

The primary role of carbon in cast carbon steel is to enhance hardness and strength through solid solution strengthening and the formation of carbides. Manganese improves hardenability and tensile strength, while silicon acts as a deoxidizer and can enhance the steel's resistance to oxidation.

Mechanical Properties

Property	Condition/Temper	Typical Value/Range (Metric - SI Units)	Typical Value/Range (Imperial Units)	Reference Standard for Test Method
Tensile Strength	Annealed	370 - 480 MPa	54 - 70 ksi	ASTM E8
Yield Strength (0.2% offset)	Annealed	210 - 310 MPa	30 - 45 ksi	ASTM E8
Elongation	Annealed	20 - 30%	20 - 30%	ASTM E8
Hardness (Brinell)	Annealed	120 - 180 HB	120 - 180 HB	ASTM E10
Impact Strength	Charpy V-notch, -20°C	20 - 40 J	15 - 30 ft-lbf	ASTM E23

The combination of these mechanical properties makes cast carbon steel suitable for applications that require good strength and ductility, such as structural components and machinery parts. Its ability to be heat-treated further enhances its performance in demanding environments.

Physical Properties

Property	Condition/Temperature	Value (Metric - SI Units)	Value (Imperial Units)
Density	Room Temperature	7.85 g/cm³	490 lb/ft³
Melting Point/Range	-	1425 - 1540 °C	2600 - 2800 °F
Thermal Conductivity	Room Temperature	50 W/m·K	29 BTU·in/(hr·ft²·°F)
Specific Heat Capacity	Room Temperature	0.46 kJ/kg·K	0.11 BTU/lb·°F
Electrical Resistivity	Room Temperature	0.00001 Ω·m	0.00001 Ω·in

The density of cast carbon steel contributes to its strength, while its thermal conductivity is essential for applications involving heat transfer. The specific heat capacity indicates how much energy is required to raise the temperature, which is crucial in thermal applications.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Atmospheric	Varies	Ambient	Fair	Prone to rust without protection
Chlorides	Varies	Ambient	Poor	Risk of pitting corrosion
Acids	Varies	Ambient	Not Recommended	Highly susceptible
Alkaline	Varies	Ambient	Fair	Moderate resistance

Cast carbon steel exhibits fair resistance to atmospheric corrosion but is susceptible to rusting if not properly coated or maintained. In chloride environments, it is prone to pitting, while exposure to acids can lead to rapid degradation. Compared to stainless steels, cast carbon steel's corrosion resistance is significantly lower, making it less suitable for marine or chemical applications.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	400 °C	752 °F	Beyond this, properties may degrade
Max Intermittent Service Temp	500 °C	932 °F	Short-term exposure only
Scaling Temperature	600 °C	1112 °F	Risk of oxidation at this temperature
Creep Strength considerations	300 °C	572 °F	Begins to lose strength

At elevated temperatures, cast carbon steel can experience oxidation and loss of mechanical properties. The maximum continuous service temperature indicates the upper limit for prolonged exposure, while the scaling temperature highlights the risk of surface degradation.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
MIG	ER70S-6	Argon/CO2	Good for thin sections
TIG	ER70S-2	Argon	High-quality welds
Stick	E7018	N/A	Suitable for thicker sections

Cast carbon steel is generally considered to have good weldability, particularly with the right filler metals. Preheating may be required for thicker sections to avoid cracking, and post-weld heat treatment can enhance the integrity of the weld.

Machinability

Machining Parameter	Cast Carbon Steel	AISI 1212	Notes/Tips
Relative Machinability Index	70	100	Good machinability, but varies with carbon content
Typical Cutting Speed (Turning)	30-50 m/min	60-80 m/min	Adjust based on tooling and setup

Cast carbon steel offers good machinability, particularly in lower carbon grades. Optimal cutting speeds and tooling can enhance performance, while higher carbon content may require more robust tooling due to increased hardness.

Formability

Cast carbon steel can be formed through both cold and hot processes. Cold forming is suitable for thinner sections, while hot forming is preferred for thicker materials. The material exhibits work hardening, which can affect bend radii and forming limits.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Annealing	600 - 700 °C / 1112 - 1292 °F	1 - 2 hours	Air or water	Softening, improved ductility
Quenching	800 - 900 °C / 1472 - 1652 °F	30 minutes	Oil or water	Hardening, increased strength
Tempering	400 - 600 °C / 752 - 1112 °F	1 hour	Air	Reducing brittleness, improving toughness

Heat treatment processes significantly alter the microstructure of cast carbon steel, enhancing its mechanical properties. Annealing softens the material, while quenching increases hardness. Tempering is essential to relieve stresses and improve toughness.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection (Brief)
Automotive	Engine Blocks	High strength, good machinability	Durability and performance
Construction	Structural Beams	High tensile strength, weldability	Load-bearing applications
Machinery	Gearboxes	Wear resistance, toughness	Reliability under stress
Oil & Gas	Pipeline Components	Corrosion resistance, strength	Safety and integrity

Other applications include:
* - Heavy machinery components
* - Agricultural equipment
* - Tooling and fixtures

Cast carbon steel is chosen for these applications due to its balance of strength, machinability, and cost-effectiveness, making it suitable for a wide range of industrial uses.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	Cast Carbon Steel	AISI 4140	Stainless Steel 304	Brief Pro/Con or Trade-off Note
Key Mechanical Property	Good tensile strength	Higher strength	Lower strength	4140 offers better strength but at a higher cost
Key Corrosion Aspect	Fair resistance	Good resistance	Excellent resistance	Stainless steel is superior in corrosive environments
Weldability	Good	Fair	Excellent	Stainless steel requires special techniques
Machinability	Good	Fair	Poor	Cast carbon steel is easier to machine
Formability	Good	Fair	Poor	Stainless steel is less formable
Approx. Relative Cost	Low	Medium	High	Cost is a significant factor in selection
Typical Availability	High	Medium	High	Cast carbon steel is widely available

When selecting cast carbon steel, considerations include cost-effectiveness, availability, and specific application requirements. While it offers good mechanical properties and machinability, its susceptibility to corrosion may necessitate protective coatings or treatments in certain environments. Understanding the trade-offs between cast carbon steel and alternative materials is crucial for optimal material selection in engineering applications.