AISI 1045 Carbon Steel: Medium-Tensile Cold-Rolled & Hot-Rolled Bar Stock for Machining and Structural Applications
AISI 1045 carbon steel is a medium-carbon, medium-tensile grade widely utilized in industrial applications requiring a balance of strength, machinability, and wear resistance. With a nominal carbon content of 0.45%, this non-alloy steel offers excellent response to heat treatment (quench-and-temper) while maintaining good weldability in normalized or annealed conditions. This article provides a technical breakdown of its chemical composition, mechanical properties, processing methods, and optimal use cases in manufacturing, automotive, and machinery sectors.
1. Chemical Composition (ASTM A29/A29M Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | 0.43 – 0.50% | Primary hardening element; increases tensile strength and wear resistance via heat treatment |
| Manganese (Mn) | 0.60 – 0.90% | Enhances hardenability and deoxidation; counteracts sulfur’s negative effects |
| Phosphorus (P) | ≤ 0.040% | Impurity; minimized to prevent embrittlement and reduce cold-shortness |
| Sulfur (S) | ≤ 0.050% | Impurity; controlled for improved machinability (free-machining variants may exceed this) |
| Silicon (Si) | 0.15 – 0.35% | Deoxidizer; improves strength without significantly reducing ductility |
2. Mechanical Properties (Typical Values)
| Condition | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Hardness (HB) | Impact Toughness (J) |
|---|---|---|---|---|---|
| Hot Rolled (As-Rolled) | 565 – 700 | 310 – 450 | 16 – 22 | 170 – 210 | 20 – 35 |
| Cold Drawn (Normalized) | 620 – 780 | 370 – 520 | 12 – 18 | 190 – 230 | 25 – 40 |
| Quench & Tempered (850°C oil quenched, 540°C tempered) | 700 – 900 | 500 – 700 | 10 – 15 | 200 – 280 | 30 – 50 |
3. Heat Treatment Processes
- Normalizing: Heat to 870-920°C, air cool. Refines grain structure after hot rolling, improving machinability and mechanical uniformity. Typical hardness: 170-210 HB.
- Annealing: Heat to 790-845°C, furnace cool. Softens material for cold working (e.g., bending, forming). Typical hardness: 140-180 HB.
- Quenching: Austenitize at 830-860°C, oil or water quench. Achieves maximum hardness (55-62 HRC) but requires tempering to reduce brittleness.
- Tempering: Reheat quenched parts to 400-650°C. Balances hardness and toughness; 540°C temper yields ~200 HB with optimal impact resistance.
- Stress Relieving: Heat to 550-650°C, air cool. Reduces residual stresses after machining or welding without significant softening.
4. Machining & Fabrication Guidelines
- Machinability (Normalized Condition): Rated at 65% of AISI 1212 (free-machining steel). Use high-speed steel (HSS) or carbide tools with sulfurized cutting oils for optimal surface finish.
- Weldability: Fair (preheat recommended for sections >25mm). Use E7018 electrodes; post-weld stress relief at 550-600°C for critical applications.
- Forging: Hot forge at 950-1200°C; avoid working below 850°C to prevent cracking. Anneal post-forging if cold working is required.
- Surface Hardening: Responds well to flame or induction hardening (50-55 HRC case depth). Carburizing not recommended due to sufficient bulk carbon content.
5. Primary Application Sectors
Automotive Components
Axles, crankshafts, connecting rods, and steering knuckles. Quench-and-tempered 1045 offers a cost-effective alternative to alloy steels for medium-stress parts.
Machinery & Equipment
Gears, sprockets, bolts, and hydraulic shafts. Normalized or cold-drawn 1045 provides wear resistance for dynamic load applications.
Construction & Infrastructure
Anchor bolts, structural pins, and base plates. Hot-rolled 1045 bars are used in bridges and buildings for high-strength fasteners.
Tooling & Fixtures
Jigs, dies, and arbors. Flame-hardened 1045 resists wear in low-volume production tools where alloy steels are unnecessary.
6. Comparison with Related Carbon Steel Grades
| Grade | Carbon (%) | Key Properties | Typical Applications |
|---|---|---|---|
| AISI 1045 | 0.43-0.50 | Balanced strength/machinability; heat-treatable | Shafts, gears, automotive parts |
| AISI 1018 | 0.15-0.20 | High ductility, low strength; excellent weldability | Cold-headed fasteners, chains |
| AISI 1060 | 0.55-0.65 | Higher hardness; reduced weldability | Spring clips, hand tools |
| AISI 1095 | 0.90-1.03 | Maximum hardness; brittle without tempering | Knives, blades, leaf springs |
7. Selection & Handling Recommendations
- Corrosion Resistance: Not corrosion-resistant; apply protective coatings (zinc plating, black oxide) or use in dry environments. Avoid outdoor exposure without treatment.
- Heat Treatment Control: Quenching cracks risk increases with section thickness >75mm. Use water for small parts, oil for complex geometries to minimize distortion.
- Material Certification: Verify mill test reports (MTR) for sulfur/phosphorus levels if weldability is critical. Low-residual variants (e.g., 1045 “modified”) improve machinability.
- Storage: Store in dry conditions with rust inhibitors. Hot-rolled bars may develop surface scale; shot blasting recommended before machining.
8. Request a Carbon Steel Quote
Need AISI 1045 carbon steel in rounds, flats, or hex bars? Baoli Iron & Steel supplies hot-rolled, cold-drawn, and precision-ground 1045 bars with custom lengths and heat treatment options. Contact our team for competitive pricing, lead times, and technical support tailored to your project requirements.