Steel C40
EN C40 · AISI/SAE 1040 · JIS S40C · GB 40
C40 is an unalloyed medium-carbon quality steel (~0.40 % C) in the EN 10083 / 1.0511 family, with equivalents C40E, 1040, S40C and Ck40; strength comes from quenching and tempering rather than alloying additions.
Reference datasheet — C40 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the +N condition
C40 tempers and conditions
C40 is supplied in 11 conditions, soft to hard. +N is the default FabDigit quotes; the values on this page are for it.
Compare all 11 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Choose for cold heading, deep drawing or fine machining where a spheroidized carbide structure is needed. | 320 | 500 | 33 | 143 HB | 10.5 % IACS |
Hot rolled | Lowest-cost as-rolled stock for non-critical parts that will be machined and later heat treated. | 320 | 550 | 25 | 156 HB | — |
Annealed | Softest condition, for maximum cold formability and easy rough machining before heat treatment. | 350 | 520 | 30 | 149 HB | 52 W/m·K |
+NDefault Normalized | Default stock condition: uniform fine ferrite–pearlite grain, balanced strength/toughness, good base for machining or later Q&T. | 375 | 590 | 28 | 170 HB | — |
Q&T | Use when maximum toughness and easy machining are wanted from a tempered martensitic structure. | 435 | 620 | 28 | 192 HB | — |
Quenched and tempered | Standard EN delivery condition for shafts and machine parts needing ~650–800 MPa with useful toughness. | 500 | 720 | 18 | 18 HRC | — |
Induction hardened | Select for shaft journals, splines and slideways needing a hard wear surface over a tough tempered core. | 500 | 720 | 16 | 54 HRC | 9 % IACS |
Cold drawn | Pick for close tolerance, straight bright bar with raised yield strength and good chip control on screw machines. | 530 | 620 | 12 | 180 HB | — |
Q&T 25–30 HRC (≈255–290 HB) | Common shaft/gear-blank hardness band: good strength with parts still readily machinable. | 700 | 880 | 17 | 28 HRC | — |
Q&T 28–32 HRC (≈270–310 HB) | Typical specified band for medium-duty shafts, couplings and gear blanks in small sections. | 780 | 950 | 15 | 30 HRC | — |
Q&T 32–36 HRC (≈300–340 HB) | Upper practical Q&T band for C40 in thin sections where wear and strength outweigh toughness. | 900 | 1,080 | 13 | 34 HRC | — |
What is C40?
C40 is an unalloyed medium-carbon quality steel (~0.40 % C) in the EN 10083 / 1.0511 family, with equivalents C40E, 1040, S40C and Ck40; strength comes from quenching and tempering rather than alloying additions. Engineers choose it for shafts, gears and machine parts that need more strength than mild steel, and it is stocked as hot-rolled and cold-drawn bar, forgings and normalized plate — 375 MPa yield, 590 MPa tensile, 28 % elongation and about 170 HB in the default condition. Limits are restricted weldability (CE ≈ 0.55), no corrosion resistance, and service temperature capped near 400 °C. For through-hardening of thicker sections, 42CrMo4/4140 is the usual step up. C40 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F). C40 has a yield strength of 375 MPa (54.4 ksi) and a tensile strength of 590 MPa (85.6 ksi) — weaker than 70% of steel grades. Elongation at break is 28% and the elastic modulus is 205 GPa (29.7 Msi).
What is C40 used for?
- shafts
- gears
- spindles
- connecting rods
- bolts
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- Ductile — tolerates forming and impact — 28%, better than 89% of steel grades
- Conducts heat well — 50 W/m·K (28.9 BTU/hr·ft·°F), better than 87% of steel grades
- High electrical conductivity — 10 % IACS, better than 83% of steel grades
Limitations
- Low fracture toughness — 55 MPa·√m (50.1 ksi·√in), worse than 82% of steel grades
C40 properties
Typical room-temperature values for C40-+N; bars are the position among steel grades.
Physical3
C40 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
C40 has a yield strength of 375 MPa (54.4 ksi) and a tensile strength of 590 MPa (85.6 ksi) — weaker than 70% of steel grades. Elongation at break is 28% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
C40 is rated for continuous service to 400°C (752 °F). It conducts heat at 50 W/m·K (28.9 BTU/hr·ft·°F), better than 87% of steel grades. Thermal expansion is 11.3 µm/m·K (6.28 µin/in·°F).
Electrical3
C40 conducts electricity at 10 % IACS, better than 83% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of C40 takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
C40's machinability is good (55/100, better than 62% of steel grades); weldability fair (40/100); formability fair (45/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. C40 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with C40
Is C40 easy to machine?
Machines well at 55–65 % of 1212; best in the annealed/normalized or cold-drawn state — above ~30 HRC use carbide and reduce speed; sulphurized oil improves finish.
Can C40 be welded?
Weldable with care only: CE ≈ 0.55, so preheat 150–250 °C, use low-hydrogen electrodes and post-weld stress relief/temper to avoid HAZ martensite cracking.
Can C40 be formed, bent or molded?
Hot forge at 1100–1200 °C then normalize; cold bending needs generous radii (≥2t) and is best in the annealed or spheroidized condition.
C40 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CEN 10083-2 C40; AISI 1040 = 0.37–0.44 | 0.37 – 0.44 | 0.4 |
| Si | ≤ 0.4 | 0.25 |
| MnAISI 1040: 0.60–0.90 | 0.5 – 0.8 | 0.65 |
| PC40E ≤0.030 | ≤ 0.05 | |
| SC40E ≤0.035 | ≤ 0.05 | |
| Crresidual | ≤ 0.4 | |
| Niresidual | ≤ 0.4 | |
| Moresidual; Cr+Ni+Mo ≤0.63 | ≤ 0.1 | |
| CuGB/T 699 residual limit | ≤ 0.25 | |
| Fe | balance |
What surface finishes work on C40?
No inherent corrosion protection — apply phosphate+oil, black oxide, zinc plating, hard chrome or paint; grinds and polishes to a fine finish but rusts quickly if left bare.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel C40 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- AISI / SAE
- 1040
- EN / DIN / Werkstoff-Nr.
- 1.0511C40ECk40
- GB (China)
- 40
- JIS
- S40C
How much does C40 cost?
C40 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
C40 — frequently asked
What is C40 used for?
C40 is typically used for shafts, gears, spindles, connecting rods and bolts. In short: workhorse quench-and-temper carbon steel; stronger than mild steel; cheaper than alloy 4140.
What is the yield strength of C40?
C40 has a typical yield strength of 375 MPa (54.4 ksi) and a tensile strength of 590 MPa (85.6 ksi) — weaker than 70% of steel grades. Strength varies by condition: see the 11 listed tempers.
Is C40 easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machines well at 55–65 % of 1212; best in the annealed/normalized or cold-drawn state — above ~30 HRC use carbide and reduce speed; sulphurized oil improves finish.
Can C40 be welded?
With care — weldability is rated fair (40/100). Weldable with care only: CE ≈ 0.55, so preheat 150–250 °C, use low-hydrogen electrodes and post-weld stress relief/temper to avoid HAZ martensite cracking.
What surface finishes work on C40?
No inherent corrosion protection — apply phosphate+oil, black oxide, zinc plating, hard chrome or paint; grinds and polishes to a fine finish but rusts quickly if left bare.
Can C40 be formed, bent or molded?
Hot forge at 1100–1200 °C then normalize; cold bending needs generous radii (≥2t) and is best in the annealed or spheroidized condition.
What is the maximum service temperature of C40?
C40 is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between C40 +N and C40-CD?
+N is the default condition — default stock condition: uniform fine ferrite–pearlite grain, balanced strength/toughness, good base for machining or later Q&T. CD: pick for close tolerance, straight bright bar with raised yield strength and good chip control on screw machines. Yield strength is 375 MPa in +N versus 530 MPa in CD.
How much does C40 cost?
C40 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- EN 10083-2 Steels for quenching and tempering – Non-alloy steels (C40, 1.0511) — CEN (2006)
- ASTM A29/A29M & SAE J403 (AISI 1040) — ASTM / SAE (2020)
- JIS G4051 Carbon steels for machine structural use (S40C) — JSA (2016)
- ASM Handbook Vol.1: Properties and Selection – Irons, Steels and High-Performance Alloys — ASM International (1990)
- Machinery's Handbook, 31st ed. (machinability ratings, heat treatment) — Industrial Press (2020)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.