Steel 18CrMoS4 +AC (Spheroidize annealed)
Heat-treated state · default condition
EN 18CrMoS4
Standard stock condition: softest, most uniform microstructure for high-speed automatic machining and cold forming before carburizing.
Values for the +AC condition
Other 18CrMoS4 tempers and conditions
18CrMoS4 is listed in 9 conditions; see the grade overview at 18CrMoS4.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
+ACDefaultThis page Spheroidize annealed | Standard stock condition: softest, most uniform microstructure for high-speed automatic machining and cold forming before carburizing. | 330 | 520 | 22 | 160 HB | — |
Peeled/turned and ground bright bar | Choose for defect-free, decarb-free surface and h9/h11 tolerance when the outer diameter is left as delivered. | 340 | 540 | 21 | 170 HB | 7.5 % IACS |
Annealed | General soft-annealed bar for rough machining before carburizing; hardness capped for consistent cutting. | 360 | 560 | 20 | 175 HB | — |
Treated for shearability | For coil/bar that will be cold-sheared into slugs for forging or cold heading without cracking. | 360 | 560 | 20 | 180 HB | 7.5 % IACS |
Normalized | Normalized bar/forging stock giving a uniform fine ferrite-pearlite structure and predictable distortion in later carburizing. | 400 | 620 | 18 | 11 HRC | 7.4 % IACS |
Treated to a specified hardness range | Pick when machine shops need a guaranteed narrow hardness band for unattended CNC/automatic turning. | 410 | 620 | 16 | 175 HB | 7.5 % IACS |
Spheroidize annealed then cold drawn | Bright cold-drawn bar: tight tolerance, smooth surface and higher strength for screw-machine parts fed from bar stock. | 530 | 660 | 9 | 200 HB | — |
Restricted hardenability (Jominy band), properties in blank-hardened… | Specify when case depth and core strength must be reproducible batch to batch; mechanicals quoted are for the blank-hardened (direct quench + low temper) test condition. | 740 | 1,030 | 10 | 33 HRC | — |
Carburized and hardened | Final service condition for gears, shafts and injector parts: hard wear-resistant case over a tough, moderately strong core. | 800 | 1,100 | 9 | 60 HRC | — |
What is 18CrMoS4 +AC?
18CrMoS4 +AC is 18CrMoS4 heat treated to +AC — standard stock condition: softest, most uniform microstructure for high-speed automatic machining and cold forming before carburizing. 18CrMoS4 +AC has a yield strength of 330 MPa (47.9 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 78% of steel grades. Elongation at break is 22% and the elastic modulus is 210 GPa (30.5 Msi). 18CrMoS4 +AC has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Advantages
- Easy to machine — 65/100, better than 93% of steel grades
Limitations
- Hard to polish — 45/100, worse than 84% of steel grades
- Low strength — 330 MPa (47.9 ksi), worse than 78% of steel grades
18CrMoS4 +AC properties
Typical room-temperature values for 18CrMoS4 +AC; 15 are specific to this condition. Other listed values are 18CrMoS4 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
18CrMoS4 +AC has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
18CrMoS4 +AC has a yield strength of 330 MPa (47.9 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 78% of steel grades. Elongation at break is 22% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
18CrMoS4 +AC is rated for continuous service to 350°C (662 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
18CrMoS4 +AC conducts electricity at 7.5 % IACS, worse than 67% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 18CrMoS4 +AC takes about 30 MJ of energy and emits 2.1 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 30%.
Manufacturability8
18CrMoS4 +AC's machinability is good (65/100, better than 93% of steel grades); weldability poor (30/100); formability good (60/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 18CrMoS4 +AC
Is 18CrMoS4 easy to machine?
Excellent for automatics in +AC/+AC+C: MnS gives short chips; run carbide at 150–220 m/min, avoid re-annealing after final turning to keep dimensions.
Can 18CrMoS4 be welded?
Poor — sulfur promotes hot cracking and Cr-Mo hardens the HAZ; if unavoidable use low-hydrogen consumables, 200–300 °C preheat and immediate stress relief.
Can 18CrMoS4 be formed, bent or molded?
Spheroidized condition takes moderate cold heading/extrusion; cold-drawn bar has little remaining ductility, so bend generously or normalize first.
What surface finishes work on 18CrMoS4?
Not anodizable; protect with zinc or manganese phosphate, black oxide, Zn-Ni plating or oil; grind case-hardened surfaces to remove distortion and any decarb.
18CrMoS4 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 |
|---|---|---|
| C | 0.15 – 0.21 | 0.18 |
| Si | ≤ 0.4 | 0.25 |
| Mn | 0.6 – 0.9 | 0.75 |
| P | ≤ 0.03 | 0.02 |
| Sdeliberate resulfurization for machinability | 0.02 – 0.04 | 0.03 |
| Cr | 0.9 – 1.2 | 1.05 |
| Mo | 0.15 – 0.25 | 0.2 |
| Fe | balance | — |
18CrMoS4 +AC — frequently asked
What is 18CrMoS4 +AC used for?
18CrMoS4 +AC is typically used for mass-produced gears, shafts machined on automatic lathes, carburized transmission parts and camshaft followers. In short: free-machining 18CrMo4; built for automatic lathes; reduced transverse ductility.
What is the yield strength of 18CrMoS4 +AC?
18CrMoS4 +AC has a typical yield strength of 330 MPa (47.9 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 78% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 18CrMoS4 +AC easy to machine?
Reasonably — machinability is rated good (65/100, better than 93% of steel grades). Excellent for automatics in +AC/+AC+C: MnS gives short chips; run carbide at 150–220 m/min, avoid re-annealing after final turning to keep dimensions.
Can 18CrMoS4 +AC be welded?
Not readily — weldability is rated poor (30/100). Poor — sulfur promotes hot cracking and Cr-Mo hardens the HAZ; if unavoidable use low-hydrogen consumables, 200–300 °C preheat and immediate stress relief.
What surface finishes work on 18CrMoS4 +AC?
Not anodizable; protect with zinc or manganese phosphate, black oxide, Zn-Ni plating or oil; grind case-hardened surfaces to remove distortion and any decarb.
Can 18CrMoS4 +AC be formed, bent or molded?
Spheroidized condition takes moderate cold heading/extrusion; cold-drawn bar has little remaining ductility, so bend generously or normalize first.
What is the maximum service temperature of 18CrMoS4 +AC?
18CrMoS4 +AC is rated for continuous use to about 350°C (662 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 18CrMoS4 +AC and 18CrMoS4-CH?
+AC is the default condition — standard stock condition: softest, most uniform microstructure for high-speed automatic machining and cold forming before carburizing. CH: final service condition for gears, shafts and injector parts: hard wear-resistant case over a tough, moderately strong core. Yield strength is 330 MPa in +AC versus 800 MPa in CH.
Sources
- EN 10084 — Case hardening steels: technical delivery conditions — CEN (2008)
- EN 10277 — Bright steel products: technical delivery conditions — CEN (2018)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol. 4A/4D — Heat Treating (carburizing of Cr-Mo case-hardening steels) — ASM International (2014)
- Case-hardening steel 18CrMo4 / 18CrMoS4 (1.7243 / 1.7244) datasheet — European long-products mills (e.g. Ovako / Deutsche Edelstahlwerke) (2022)
- SAE J404 / AISI 4118 chemical composition — SAE International (2021)
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.