Steel 1018 vs 4140: Low Carbon vs Alloy Steel for CNC
1018 is the economical choice for low-stress parts with easy machinability and weldability. 4140 provides significantly higher strength and through-hardenability for demanding applications like shafts and gears.
Side-by-Side Property Comparison
| Property | Carbon Steel 1018 | Alloy Steel 4140 |
|---|---|---|
| Tensile Strength | 440 MPa (64 ksi) | 655 MPa (95 ksi) |
| Yield Strength | 370 MPa (54 ksi) | 415 MPa (60 ksi) |
| Hardness | 126 HB | 197 HB |
| Density | 7.87 g/cm³ | 7.85 g/cm³ |
| Machinability Rating | 78/100 | 66/100 |
| Thermal Conductivity | 51.9 W/m·K | 42.6 W/m·K |
| Melting Point | 1,480–1,526 °C | 1,416–1,460 °C |
| Tolerance | ±0.02 mm | ±0.02 mm |
Key Differences
| Property | Carbon Steel 1018 | Alloy Steel 4140 | Winner |
|---|---|---|---|
| Tensile Strength | 440 MPa | 655 MPa | Alloy |
| Machinability | 78/100 | 66/100 | Carbon |
| Weldability | Excellent | Good (preheat needed) | Carbon |
| Hardenability | Case only | Through-hardenable | Alloy |
| Cost | ~$0.50/lb | ~$1.00/lb | Carbon |
| Fatigue Strength | Moderate | Excellent | Alloy |
Which Material Should You Choose?
Choose Carbon Steel 1018 when:
- Low-stress structural parts
- Pins, spacers, and fixtures
- Parts requiring welding
- Case-hardened components
- Budget-conscious projects
Choose Alloy Steel 4140 when:
- High-strength shafts and gears
- Toolholders and collets
- Oil and gas components
- Through-hardened parts
- Fatigue-critical components
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