1045 Carbon Steel
1045 is a medium-carbon steel known for its balanced combination of strength, ductility, and machinability. It is one of the most commonly used carbon steels in industrial applications, valued for its versatility and cost-effectiveness in manufacturing components that require moderate strength and wear resistance.
Basic Information
Definition: 1045 is a medium-carbon steel (0.45% nominal carbon content) that can be heat-treated to enhance its mechanical properties. It is a non-alloy steel, meaning it contains primarily iron and carbon with minimal alloying elements, making it economical for general-purpose use.
Corresponding Standards: Defined by ASTM A29/A29M (Hot-rolled and cold-finished alloy steel bars) and SAE J403 (Chemical composition of SAE carbon steels). International equivalents include:
European: C45 (EN 10083-2)
Chinese: 45# steel (GB/T 699)
Japanese: S45C (JIS G4051)
Key Characteristics: Moderate strength, good machinability in the annealed state, and the ability to be heat-treated for higher hardness and wear resistance.
Chemical Composition
1045’s composition is simple, with carbon as the primary alloying element to achieve its mechanical properties:
Element Content Range Role in the Steel
Carbon (C) 0.43–0.50% Provides strength and hardness; the medium carbon content balances strength and ductility.
Manganese (Mn) 0.60–0.90% Enhances hardenability and strength; reduces brittleness from sulfur impurities.
Phosphorus (P) ≤0.040% Controlled to avoid brittleness, especially in cold-worked or heat-treated parts.
Sulfur (S) ≤0.050% Minimized to prevent hot shortness during forging or rolling.
Iron (Fe) Balance Base metal providing structural integrity.
Physical Properties
Density: ~7.85 g/cm³ (standard for carbon steels).
Melting Point: ~1430–1450°C.
Thermal Conductivity: ~45 W/(m·K) at room temperature.
Coefficient of Thermal Expansion: ~11.7×10⁻⁶/°C (20–100°C), typical for medium-carbon steels.
Elastic Modulus: ~205 GPa, ensuring rigidity in structural applications.
Mechanical Properties
1045’s mechanical properties vary significantly with heat treatment, allowing it to be tailored to specific applications:
Property Annealed State Normalized State Quenched & Tempered (550°C)
Tensile Strength (Rm) 570–700 MPa 630–770 MPa 850–1000 MPa
Yield Strength (Rp0.2) 310–380 MPa 350–420 MPa 700–800 MPa
Elongation (A) 15–25% 15–20% 12–18%
Hardness 160–200 HB 180–230 HB 25–32 HRC
Heat Treatment Effect: Quenching (from 820–860°C) and tempering increases strength and hardness while maintaining reasonable ductility. Higher tempering temperatures reduce hardness but improve toughness.
Wear Resistance: Moderate in the annealed state; improved after heat treatment (e.g., carburizing or induction hardening) for applications requiring abrasion resistance.
Heat Treatment
1045 is often heat-treated to enhance its performance for specific applications:
Annealing
Purpose: Soften the steel for machining, reduce internal stress, and improve ductility.
Process: Heat to 815–845°C, hold for 1–2 hours, then cool slowly in the furnace. Results in hardness of 160–200 HB.
Normalizing
Purpose: Refine grain structure, improve uniformity, and enhance machinability.
Process: Heat to 860–900°C, hold, then air cool. Achieves hardness of 180–230 HB with better strength than annealed steel.
Quenching and Tempering
Quenching: Heat to 820–860°C, then water or oil quench to form martensite (as-quenched hardness ~50–55 HRC).
Tempering: Reheat to 200–650°C (depending on desired hardness) to reduce brittleness. Common for applications needing 25–35 HRC.
Surface Hardening
Induction Hardening: Localized heating and quenching to harden surface layers (up to 55 HRC) while keeping cores tough.
Carburizing: Not typically used, as 1045’s carbon content is already sufficient for moderate surface hardness.
Processing Performance
Machinability: Good in the annealed or normalized state, suitable for turning, milling, drilling, and threading with high-speed steel or carbide tools. Hardened 1045 (HRC >35) is more challenging and requires harder tooling.
Weldability: Moderate—welding can be done with low-hydrogen electrodes, but preheating (150–200°C) and post-weld annealing are recommended to avoid cracking, especially in thick sections.
Formability: Fair in the annealed state for bending, stamping, or cold heading, though less ductile than low-carbon steels (e.g., 1018). Hot forming is easier and preferred for complex shapes.
Forging: Excellent—forged at 1100–1200°C, followed by annealing or normalizing to restore properties.
Application Fields
1045 is widely used in general engineering applications requiring moderate strength and wear resistance:
Mechanical Components:
Shafts, gears, and axles for machinery (balances strength and machinability).
Bolts, nuts, and fasteners requiring higher strength than low-carbon steels.
Automotive Industry:
Steering components, crankshafts, and connecting rods (after heat treatment for strength).
Axle parts and heavy-duty fasteners.
Tooling and Fabrication:
Die blocks, punches, and fixtures (when surface-hardened for wear resistance).
Saws, blades, and cutting tools (after heat treatment for edge hardness).
Structural Applications:
Supports, brackets, and levers in industrial equipment.
Hydraulic and pneumatic cylinder rods (often chrome-plated for corrosion resistance).
Advantages and Limitations
Advantages
Balanced Properties: Offers a good mix of strength, ductility, and machinability for general use.
Cost-Effective: Less expensive than alloy steels while providing higher strength than low-carbon grades.
Heat Treatable: Can be customized via heat treatment to meet specific hardness or toughness requirements.
Widely Available: Easily sourced in various forms (bars, plates, sheets) globally.
Limitations
Corrosion Resistance: Poor—susceptible to rust in humid environments, requiring coatings (painting, plating) for protection.
Low Alloy Content: Inferior to alloy steels (e.g., 4140) in strength, hardenability, and fatigue resistance for critical applications.
Welding Complexity: Requires pre- and post-weld treatments to avoid cracking, unlike low-carbon steels.
Comparison with Similar Steels
Steel Grade Carbon Content Tensile Strength (Annealed) Key Advantage
1045 0.43–0.50% 570–700 MPa Balanced strength, machinability, and cost.
1018 0.18% 400–550 MPa Superior ductility and weldability, lower strength.
4140 0.40% 650–800 MPa Higher strength and hardenability (alloy steel).
45# (China) 0.42–0.50% 560–700 MPa Nearly identical to 1045, common in Asian markets.
In summary, 1045 carbon steel is a versatile, economical material ideal for applications requiring moderate strength and machinability. Its ability to be heat-treated and widespread availability make it a staple in manufacturing, bridging the gap between low-carbon steels (for formability) and high-alloy steels (for extreme strength).