Grade 60 steel is a high-quality carbon structural steel per GB/T 699-2015, with a carbon content of approximately 0.60%. It can also be used for spring manufacturing per GB/T 1222. It offers good hardenability, and after quenching & tempering or quenching + medium-temperature tempering, it achieves excellent elastic limit and fatigue strength. It is widely used in various springs, clock springs, spring washers, and high-strength shaft components. Based on national standard data, this article systematically introduces the chemical composition, mechanical properties, and CNC machining considerations for Grade 60 steel.
1. Basic Information of Grade 60 Steel
| Parameter | Value |
|---|---|
| Grade | 60 |
| Standard | GB/T 699-2015 High-quality carbon structural steel GB/T 1222 Spring steel |
| Type | High-carbon high-quality carbon structural steel / Spring steel |
| Approximate International Equivalents | AISI/SAE 1060, EN C60, JIS S58C |
| Delivery Condition | Hot-rolled, normalized, annealed |
2. Chemical Composition
| Element | Content Range (%) | Function |
|---|---|---|
| Carbon (C) | 0.57 – 0.65 | Determines hardness after quenching and elastic limit |
| Silicon (Si) | 0.17 – 0.37 | Deoxidizer, improves elastic limit |
| Manganese (Mn) | 0.50 – 0.80 | Improves hardenability and strength |
| Chromium (Cr) | ≤ 0.25 | Residual element |
| Nickel (Ni) | ≤ 0.30 | Residual element |
| Copper (Cu) | ≤ 0.25 | Residual element |
| Phosphorus (P) | ≤ 0.035 | Harmful element, content controlled |
| Sulfur (S) | ≤ 0.035 | Harmful element, content controlled |
3. Mechanical Properties
Mechanical properties in the normalized condition (GB/T 699-2015):
| Property | Value | Test Condition |
|---|---|---|
| Tensile Strength σb | ≥ 675 MPa | Room temperature tensile test |
| Yield Strength σs | ≥ 400 MPa | Room temperature tensile test |
| Elongation δ5 | ≥ 12% | Gauge length 5× diameter |
| Reduction of Area ψ | ≥ 35% | Room temperature tensile test |
| Hardness | ≤ 255 HB | Hot-rolled / annealed condition |
Hardness after quenching + tempering: approximately 40 – 55 HRC, depending on tempering temperature. Oil quenched hardness can reach 58 – 63 HRC.
4. Heat Treatment Process
- Normalizing: Heat to 810 – 830°C, hold, air cool — refines grain structure.
- Annealing: Heat to 770 – 790°C, furnace cool — reduces hardness, improves machinability.
- Quenching: Heat to 790 – 820°C, oil quench or water quench (oil for thin sections, water recommended for thick sections) — obtains high-hardness martensite.
- Tempering: Medium-temperature tempering at 350 – 500°C for springs — achieves excellent elastic limit.
5. Physical Properties
| Parameter | Value |
|---|---|
| Density | 7.81 g/cm³ |
| Melting Point | Approx. 1450°C |
| Specific Heat Capacity | Approx. 478 J/(kg·K) (room temperature) |
| Linear Expansion Coefficient | Approx. 11.5 × 10⁻⁶ /K (20-100°C) |
| Thermal Conductivity | Approx. 48 W/(m·K) (room temperature) |
6. Key Characteristics
- High Elastic Limit: High carbon content yields excellent elastic limit after proper heat treatment.
- Hardenability: Moderate — oil quenching can harden sections up to φ12-15mm.
- Wear Resistance: High surface hardness after quenching provides better wear resistance than medium/low-carbon steels.
- Weldability: Poor — high carbon content leads to weld cracking tendency; preheating and post-heating required.
- Decarburization Sensitivity: High-carbon steel is prone to decarburization during heating; atmosphere control is necessary.
7. Typical Applications
- Compression springs, extension springs, torsion springs
- Automotive suspension springs, clutch springs
- Clock springs, spring washers
- High-strength shafts, pins, guide pillars
- CNC machined precision spring seats and elastic components
8. CNC Machining Performance
The CNC machinability of Grade 60 steel depends on its heat treatment state:
- Annealed condition: Hardness ≤ 255 HB, medium machinability. Use carbide tools; cutting speed 60 – 100 m/min.
- Quenched & tempered condition: Machinability acceptable at 25 – 35 HRC; coated tools recommended.
- Quenched + tempered (high hardness): Difficult to machine above 40 HRC; grinding is preferred.
- Drilling: Use carbide drills, ample cooling, feed rate 0.08 – 0.15 mm/r.
If elastic limit needs to be restored after machining, re-quenching + medium-temperature tempering is required.
9. Comparison with 65Mn Spring Steel
| Comparison Item | Grade 60 Steel | 65Mn |
|---|---|---|
| Carbon Content | 0.57 – 0.65% | 0.62 – 0.70% |
| Manganese Content | 0.50 – 0.80% (normal) | 0.90 – 1.20% (high manganese) |
| Hardenability | Moderate | Better than Grade 60 (manganese improves hardenability) |
| Elastic Limit | Good | Better than Grade 60 |
| Cost | Lower | Slightly higher |
| Application Range | General springs, structural parts | Critical springs, high-stress applications |
Selection advice: Choose Grade 60 steel for light loads, small sections, and cost-sensitive applications; prefer 65Mn for high stress, large sections, or critical springs.
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