Steel C40 +AC (Spheroidize annealed)
Heat-treated state
EN C40 · AISI/SAE 1040 · JIS S40C · GB 40
Choose for cold heading, deep drawing or fine machining where a spheroidized carbide structure is needed.
Values for the +AC condition
Other C40 tempers and conditions
C40 is listed in 11 conditions; see the grade overview at C40.
Compare all 11 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
+ACThis page 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 +AC?
C40 +AC is C40 heat treated to +AC — choose for cold heading, deep drawing or fine machining where a spheroidized carbide structure is needed. C40 +AC has a yield strength of 320 MPa (46.4 ksi) and a tensile strength of 500 MPa (72.5 ksi) — weaker than 81% of steel grades. Elongation at break is 33% and the elastic modulus is 205 GPa (29.7 Msi). C40 +AC 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). +N is the default condition FabDigit quotes; +AC is available on request or by drawing note.
Advantages
- Conducts heat well — 52 W/m·K (30 BTU/hr·ft·°F), better than 98% of steel grades
- Ductile — tolerates forming and impact — 33%, better than 96% of steel grades
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- High electrical conductivity — 10.5 % IACS, better than 89% of steel grades
- Easy to machine — 62/100, better than 89% of steel grades
Limitations
- Low strength — 320 MPa (46.4 ksi), worse than 81% of steel grades
C40 +AC properties
Typical room-temperature values for C40 +AC; 22 are specific to this condition. Other listed values are C40 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
C40 +AC 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 +AC has a yield strength of 320 MPa (46.4 ksi) and a tensile strength of 500 MPa (72.5 ksi) — weaker than 81% of steel grades. Elongation at break is 33% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
C40 +AC is rated for continuous service to 400°C (752 °F). It conducts heat at 52 W/m·K (30 BTU/hr·ft·°F), better than 98% of steel grades. Thermal expansion is 11.3 µm/m·K (6.28 µin/in·°F).
Electrical3
C40 +AC conducts electricity at 10.5 % IACS, better than 89% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of C40 +AC 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 +AC's machinability is good (62/100, better than 89% of steel grades); weldability fair (45/100); formability good (62/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with C40 +AC
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.
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.
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 | — |
C40 +AC — frequently asked
What is C40 +AC used for?
C40 +AC 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 +AC?
C40 +AC has a typical yield strength of 320 MPa (46.4 ksi) and a tensile strength of 500 MPa (72.5 ksi) — weaker than 81% of steel grades. Strength varies by condition: see the 11 listed tempers.
Is C40 +AC easy to machine?
Reasonably — machinability is rated good (62/100, better than 89% 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 +AC be welded?
With care — weldability is rated fair (45/100). 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 +AC?
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 +AC 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 +AC?
C40 +AC 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.