45# Carbon Steel: Medium-Carbon Structural Steel for High-Strength Mechanical Applications
45# carbon steel (equivalent to AISI 1045, UNS G10450, or JIS S45C) is a medium-carbon structural steel widely used in machinery manufacturing due to its balanced strength, hardness, and machinability. With a carbon content of 0.42-0.50%, it offers superior mechanical properties after heat treatment while maintaining good weldability and formability. This article explores its chemical composition, mechanical characteristics, heat treatment processes, industrial applications, and performance advantages.
1. Chemical Composition (GB/T 699-2015 Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | 0.42 – 0.50% | Primary hardening element; increases tensile strength and hardness |
| Silicon (Si) | 0.17 – 0.37% | Deoxidizer; improves strength and elastic limit |
| Manganese (Mn) | 0.50 – 0.80% | Enhances hardenability and strength; counteracts sulfur’s negative effects |
| Phosphorus (P) | ≤ 0.035% | Impurity; reduces ductility and toughness when excessive |
| Sulfur (S) | ≤ 0.035% | Impurity; improves machinability but reduces weldability |
| Chromium (Cr) | ≤ 0.25% | Trace element; slightly improves hardenability |
| Nickel (Ni) | ≤ 0.25% | Trace element; minor impact on mechanical properties |
| Copper (Cu) | ≤ 0.25% | Trace element; improves corrosion resistance slightly |
2. Mechanical Properties (After Normalizing)
- Tensile Strength (σb): ≥ 600 MPa (87,000 psi)
- Yield Strength (σs): ≥ 355 MPa (51,500 psi)
- Elongation (δ5): ≥ 16% (indicates moderate ductility)
- Reduction of Area (ψ): ≥ 40% (good toughness for structural use)
- Brinell Hardness (HB): 170-210 (as-rolled condition)
- Impact Toughness (Akv): ≥ 39 J at room temperature
3. Heat Treatment Processes
| Treatment Type | Temperature Range | Cooling Medium | Resulting Hardness (HB) | Application Purpose |
|---|---|---|---|---|
| Normalizing | 830-860°C | Air cooling | 170-210 | Refine grain structure; improve machinability |
| Annealing | 790-810°C | Furnace cooling | ≤ 197 | Reduce hardness; enhance ductility for cold working |
| Quenching | 820-850°C | Water or oil | 55-62 HRC | Maximize hardness for wear-resistant components |
| Tempering | 500-650°C | Air cooling | 180-300 | Reduce brittleness; achieve desired strength-toughness balance |
4. Typical Industrial Applications
Machinery Components
Gears, shafts, spindles, and axles in automotive and industrial machinery — quenched and tempered for high wear resistance and fatigue strength.
Fasteners & Hardware
High-strength bolts, nuts, and studs (Grade 8.8/10.9) — carbon content ensures required hardness after heat treatment.
Tooling & Molds
Dies, punches, and plastic injection molds — surface hardened for extended tool life in production environments.
Construction & Infrastructure
Bridge components, crane wheels, and railway tracks — normalized or quenched-and-tempered for structural integrity under heavy loads.
5. Comparison with Other Carbon Steels
| Grade | Carbon Content | Key Properties | Typical Applications |
|---|---|---|---|
| 20# Steel | 0.17-0.23% | Low strength, high ductility, excellent weldability | Low-stress components, cold-formed parts, weldments |
| 45# Steel | 0.42-0.50% | Balanced strength-toughness, good machinability, heat-treatable | Shafts, gears, fasteners, structural parts requiring medium strength |
| 60# Steel | 0.57-0.65% | High hardness, lower ductility, prone to cracking if welded | Spring steel, high-wear components, hand tools |
6. Machining & Processing Guidelines
- Machining: Use high-speed steel (HSS) or carbide tools; recommended cutting speed 20-30 m/min for turning (adjust based on hardness).
- Welding: Preheat to 150-250°C for thick sections (>25mm); use low-hydrogen electrodes (E7018) to minimize cracking risk.
- Forging: Heat to 1100-1200°C; avoid forging below 800°C to prevent cracking. Anneal after forging to relieve stresses.
- Surface Treatment: Case hardening (carburizing) can achieve 58-62 HRC surface hardness while retaining a tough core.
- Quality Control: Verify hardness (HB/HRc) and microstructure post-heat-treatment; ultrasonic testing for critical components.
7. Request a Carbon Steel Quote
For customized 45# carbon steel products — including hot-rolled bars, cold-drawn shafts, or precision-machined components — contact our team with your specifications. We provide mill-certified materials, heat treatment services, and global shipping solutions tailored to your project requirements.