C40

Carbon Steel

C40

Introduction:

C40 Carbon Steel is a high-quality carbon structural steel with an average carbon content of about 0.4%, classified as non-alloy steel according to European standards. It offers high strength, good machinability, and medium cold deformation plasticity, but exhibits poor weldability and hardenability.

C40 is typically used in a normalized or quenched and tempered condition, suitable for manufacturing parts with large loads or wear-resistant surfaces.

Properties of the Grade:

High strength and hardness.
Good machinability.
Medium cold deformation plasticity.
Poor weldability and hardenability.

Standards and Equivalent Grades Available:

China: GB 3077: 40
USA: ASTM A29: 1040
Japan: JIS G4051: S40C
UK: BS970: 080M40
France: NFA 33-101: AF60-C40

Uses/Applications of the Grade:

Machinery components: Shafts, gears, axles, and machine parts.
Automotive parts: Axles and transmission components.
Structural applications: High-load components requiring strength and durability.
Tools and dies: Parts subject to wear and stress.

Chemical Composition:

Element	Min (%)	Max (%)
Carbon (C)	0.37	0.44
Silicon (Si)	–	0.40
Manganese (Mn)	0.50	0.80
Phosphorus (P)	–	0.045
Sulfur (S)	–	0.045
Chromium (Cr)	–	0.40
Molybdenum (Mo)	–	0.10
Nickel (Ni)	–	0.40

Mechanical Properties:

Property	Value
Tensile Strength (MPa)	≥570
Yield Strength (MPa)	≥335
Elongation (%)	≥19
Reduction of Area (%)	≥45
Impact Charpy-V (J)	≥47

Physical Properties:

Property	Value
Density	7.85 g/cm³
Tensile Strength	530-680 MPa
Yield Strength	300-400 MPa
Elongation	18-22%
Hardness (HB)	150-190

Forging:

Initial Forging Temperature: 1200°C.
Final Forging Temperature: 850°C.
Forging Ratio: Above 4:1.
Post-Forging Treatment: Slowly cooled after forging.

Heat Treatment:

Annealing: Heat to 840-870°C, cool in furnace (hardness < 187 HBW).
Normalizing: Heat to 840-890°C, cool in air (hardness ~207 HBW).
Hardening: Heat to 810-850°C, quench in water or oil.
Tempering: Heat to 520-620°C.

Dimensional Tolerances:

Surface Finish	Tolerance
Black-Forged	(0, +5mm)
Black-Rolled	(0, +1mm)
Turned	(0, +3mm)
Grinding	Best h9
Polished	Best h11
Peeled	Best h11
Cold Drawn	Best h11

Machinability:

Good machinability due to its balanced hardness and strength.

Corrosion Resistance:

Limited corrosion resistance. Surface protection is recommended for applications in corrosive environments.

Weldability:

Poor weldability due to high carbon content. Pre-heating and post-weld heat treatment are required.

Available Form:

Round Bars.

Conclusion:

C40 Carbon Steel is a medium carbon steel known for its good balance of strength, toughness, and machinability. It is widely used in machinery and automotive components due to its durability. However, its weldability is limited, requiring special procedures for welding. Proper heat treatment can enhance its mechanical properties, making it ideal for high-load applications.

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C40