1018 vs 4140 Steel
1018 is a low-carbon mild steel — inexpensive, very machinable, and easy to weld. 4140 is a chromium-molybdenum alloy steel that hardens through heat treatment to much higher strength and toughness. Use 1018 for easy general parts; use 4140 where you need strength, wear resistance, and fatigue life.
| Property | 1018 | 4140 |
|---|---|---|
| Type | Low-carbon (mild) steel | Cr-Mo alloy steel |
| Carbon | ~0.18% | ~0.40% |
| Alloying | — | ~0.8–1.1% Cr, 0.15–0.25% Mo |
| Yield | ~370 MPa (54 ksi) cold-drawn | 415 MPa (annealed) → up to ~1500 MPa Q&T |
| Tensile | ~440 MPa (64 ksi) cold-drawn | 655 MPa (annealed) → up to ~1700 MPa Q&T |
| Density | 7.87 g/cm³ | 7.85 g/cm³ |
| Heat treatable | Limited (case-harden only) | Yes — through-hardening |
| Machinability | Excellent (~78%) | Good (best annealed) |
| Weldability | Excellent | Fair — preheat / post-heat |
| Typical uses | Shafts, pins, brackets, case-hardened parts | Gears, axles, high-strength shafts, tooling |
4140 properties depend heavily on heat treatment (annealed vs quenched & tempered). 1018 values are typical cold-drawn. Confirm against the mill certificate and your heat-treat spec.
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Find suppliersFrequently asked questions
- What is the main difference?
- 1018 is a low-carbon mild steel — soft, cheap, easy to machine and weld. 4140 is a chromium-molybdenum alloy steel that responds to heat treatment, reaching far higher strength and toughness. Pick 1018 for easy general parts; 4140 for strength and wear in heat-treated condition.
- Is 4140 stronger than 1018?
- Much stronger once heat treated — quenched and tempered 4140 can exceed 1500 MPa yield, versus ~370 MPa for cold-drawn 1018. In the annealed state the gap is smaller (≈415 vs 370 MPa yield); the advantage comes from heat treatment.
- Which is easier to machine and weld?
- 1018 — it has excellent machinability (~78% rating) and welds without special precautions. 4140 machines best in the annealed state and usually needs preheat and post-weld heat treatment to avoid cracking, especially after hardening.