1018 vs 4140: differences explained
1018 vs 4140 steel: cold-drawn 1018 ≈ 370 MPa yield, not hardenable, weldable; 4140 ≈ 415 MPa annealed and 900–1600 MPa heat-treated, hardenable to 55 HRC, hard to weld. Full table and when each is right.
Overview
1018 and 4140 are the two bar steels every North American shop keeps in the rack, and they sit at opposite ends of the decision: 1018 is the cheap, weldable, low-carbon steel for parts that carry little stress; 4140 is the chromoly alloy that can be heat-treated to three or four times the strength. The chemistry tells the story — 1018 has 0.18 % carbon and no alloying, 4140 has 0.40 % carbon plus 1 % Cr and 0.2 % Mo — and everything downstream follows: hardenability, strength, machinability, weldability and price.
Many designers reach for 4140 by reflex; many others use 1018 where it will later fail. The table gives the numbers in the conditions actually sold (cold-drawn 1018; annealed, pre-hard and Q&T 4140), and the verdict says which to buy for which job.
1018 vs 4140 side by side
| Property | 1018 | 4140 |
|---|---|---|
| Type | plain low-carbon steel | Cr-Mo low-alloy steel (chromoly) |
| UNS | G10180 | G41400 |
| Carbon | 0.15–0.20 % | 0.38–0.43 % |
| Alloying | Mn 0.60–0.90 % | Mn 0.75–1.00, Cr 0.80–1.10, Mo 0.15–0.25 % |
| Usual supply condition | cold-drawn (CRS) bar | annealed, or pre-hardened 28–32 HRC (HT/PH) |
| Yield, as supplied | ≈ 370 MPa (54 ksi) cold-drawn; ≈ 220 MPa hot-rolled | ≈ 415 MPa (60 ksi) annealed; ≈ 690–760 MPa pre-hard |
| Tensile, as supplied | ≈ 440 MPa (64 ksi) | ≈ 655 MPa annealed; ≈ 930–1000 MPa pre-hard |
| Max. heat-treated tensile | ≈ 500 MPa (cannot through-harden) | ≈ 1770 MPa (257 ksi) tempered 205 °C |
| Hardness, as supplied | ≈ 126 HB | ≈ 197 HB annealed; 28–32 HRC pre-hard |
| Max. hardness | carburized case 58–62 HRC only | 54–59 HRC as-quenched; 50 HRC in service |
| Through-hardening | no | yes, to ≈ 50–75 mm in oil |
| Elongation | ≈ 15 % cold-drawn, 25 % hot-rolled | ≈ 25 % annealed; 10–16 % Q&T |
| Impact toughness | high (soft) | good at ≤ 40 HRC; falls at high hardness |
| Machinability (vs B1112) | ≈ 70–78 % | ≈ 65 % annealed; ≈ 55–60 % pre-hard |
| Weldability | excellent, no preheat | poor: 250–350 °C preheat + post-weld temper |
| Carbon equivalent | ≈ 0.30 | ≈ 0.80 |
| Fatigue strength (rotating bend, typical) | ≈ 200 MPa | ≈ 450–550 MPa (Q&T) |
| Surface hardening | carburize/carbonitride | induction/flame (50–55 HRC), nitride (55–60 HRC) |
| Relative price per kg (bar, 2026) | 1.00 | ≈ 1.6–2.0 (pre-hard ≈ 2.0–2.5) |
| EN equivalent | C15 / C22 (near) | 42CrMo4 (identical) |
| Typical use | spacers, pins, brackets, fixtures, low-stress shafts | shafts, gears, bolts, tooling, hydraulic rods, high-stress parts |
Which should you choose?
Use 4140 when the part carries real stress, will be heat-treated, or must resist wear and fatigue: shafts, gears, bolts above Grade 5, hydraulic rods, tooling, anything that would bend or wear in 1018. Buy it pre-hardened (28–32 HRC) to skip heat treatment.
Use 1018 when the part is a spacer, pin, bracket, fixture, guide or low-stress shaft, or when it must be welded: it is half the price, machines to a bright finish, welds with no preheat, and can be carburized for a hard skin if a wear surface is needed.
The common mistake is welding 4140 like 1018 — it cracks — and the opposite one is using 1018 for a shaft that then yields or fatigues. If in doubt and the part is not welded, 4140 pre-hard is the safe choice; if it is welded, 1018 or a weldable 4130.
- Welded assemblies, brackets, weldments
- Spacers, bushings, pins, dowels, keys
- Fixtures, jigs, prototypes, low-stress shafting
- Parts to be carburized for a hard surface
- Cost-driven, high-volume machined parts
- Shafts, axles, spindles under torsion/bending
- Gears, sprockets, splines
- High-strength bolts, studs, tie rods
- Hydraulic cylinder rods, pistons
- Tooling, fixtures under wear, punches
- Parts needing 30–50 HRC through the section
Frequently asked questions
Which is stronger, 1018 or 4140?
4140 — even annealed it exceeds cold-drawn 1018 (≈ 415 vs 370 MPa yield), pre-hard 4140 is about twice as strong, and Q&T 4140 reaches 900–1600 MPa yield. 1018 cannot be strengthened by heat treatment.
Can 1018 be hardened like 4140?
No. 1018's 0.18 % carbon is too low to form hard martensite through the section. It can only be case-hardened (carburized) for a thin 58–62 HRC skin over a soft core.
Is 4140 harder to machine than 1018?
Somewhat: annealed 4140 rates about 65 % versus 70–78 % for cold-drawn 1018, and pre-hard 4140 (28–32 HRC) about 55–60 %. In practice 4140 pre-hard gives better chip control and surface finish than 'gummy' 1018 with carbide tooling.
Can I weld 4140 like 1018?
No. 1018 welds with no preheat by any process. 4140 (CE ≈ 0.8) needs 250–350 °C preheat, low-hydrogen filler and post-weld tempering, and pre-hard/Q&T 4140 loses its properties in the heat-affected zone. Use 4130 for welded chromoly structures.
How much more does 4140 cost than 1018?
Roughly 1.6–2× per kilogram for annealed bar and 2–2.5× for pre-hardened bar, depending on size and market. The premium is small next to the cost of a failed shaft.
What are 1018 and 4140 called in Europe?
1018 has no exact EN twin — C15/C22 or S235JRC bright bar are the substitutes. 4140 is identical to EN 42CrMo4 (1.7225), JIS SCM440 and GB 42CrMo.
Related comparisons
Verified against ASTM A29/A29M-20 and A108-18. Last checked: September 2026.