Steel 18CrMo4 +AC (Spheroidize annealed)
Heat-treated state · default condition
EN 18CrMo4
Standard as-supplied bar and wire state: spheroidize annealing gives the lowest hardness and best machining and cold forming before the user carburizes and quenches.
Values for the +AC condition
Other 18CrMo4 tempers and conditions
18CrMo4 is listed in 6 conditions; see the grade overview at 18CrMo4.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
+ACDefaultThis page Spheroidize annealed | Standard as-supplied bar and wire state: spheroidize annealing gives the lowest hardness and best machining and cold forming before the user carburizes and quenches. | 350 | 570 | 22 | 170 HB | — |
Normalized | Common delivery state for forgings and hot-rolled bar: normalizing gives a uniform structure and slightly higher strength than annealed while easing later carburizing. | 420 | 640 | 19 | 12 HRC | 7.7 % IACS |
Spheroidize annealed and cold drawn | Pick bright cold-drawn bar for close size tolerance and good surface on automatic-lathe parts and later carburizing; work hardening lifts strength to 700 MPa but drops elongation to 10%. | 550 | 700 | 10 | 210 HB | — |
Hardenability-guaranteed (Jominy band), carburized and hardened core… | Order with the guaranteed Jominy hardenability band for gears and shafts: carburizing, quenching and low tempering give a 58–62 HRC case over a strong, tough core. | 680 | 950 | 11 | 30 HRC | — |
Carburized + hardened + low tempered | Final state of finished gears and shafts: carburized, hardened and low tempered to a 0.5–1.5 mm wear-resistant case over a tough core, so allow stock for grinding. | 700 | 1,000 | 9 | 60 HRC | — |
Quenched and tempered | Choose quenched and tempered when the part runs through-hardened instead of carburized: moderate strength with good toughness for small and medium shafts and fasteners. | 780 | 1,000 | 12 | 33 HRC | — |
What is 18CrMo4 +AC?
18CrMo4 +AC is 18CrMo4 heat treated to +AC — standard as-supplied bar and wire state: spheroidize annealing gives the lowest hardness and best machining and cold forming before the user carburizes and quenches. 18CrMo4 +AC has a yield strength of 350 MPa (50.8 ksi) and a tensile strength of 570 MPa (82.7 ksi) — weaker than 74% of steel grades. Elongation at break is 22% and the elastic modulus is 210 GPa (30.5 Msi). 18CrMo4 +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
- Forms and bends easily — 70/100, better than 86% of steel grades
18CrMo4 +AC properties
Typical room-temperature values for 18CrMo4 +AC; 15 are specific to this condition. Other listed values are 18CrMo4 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
18CrMo4 +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
18CrMo4 +AC has a yield strength of 350 MPa (50.8 ksi) and a tensile strength of 570 MPa (82.7 ksi) — weaker than 74% of steel grades. Elongation at break is 22% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
18CrMo4 +AC is rated for continuous service to 400°C (752 °F). It conducts heat at 43 W/m·K (24.8 BTU/hr·ft·°F), better than 51% of steel grades. Thermal expansion is 11.6 µm/m·K (6.44 µin/in·°F).
Electrical3
18CrMo4 +AC conducts electricity at 7.7 % IACS, worse than 65% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 18CrMo4 +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%.
Manufacturability7
18CrMo4 +AC's machinability is good (60/100, better than 83% of steel grades); weldability good (68/100); formability very good (70/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 18CrMo4 +AC
Is 18CrMo4 easy to machine?
Machining is best in the spheroidize-annealed or cold-drawn condition, with coated carbide at 120–180 m/min. Once carburized and quenched, only grinding or hard turning with CBN is practical.
Can 18CrMo4 be welded?
Carbon equivalent is about 0.55, so the steel is weldable with 150–250 °C preheat and low-hydrogen consumables, followed by stress relief at 550–650 °C. Do not weld on carburized surfaces.
Can 18CrMo4 be formed, bent or molded?
The +AC condition suits cold heading, cold extrusion and thread rolling. Hot forge at 1100–850 °C and normalize after forging to refine the structure.
What surface finishes work on 18CrMo4?
Corrosion protection is required: black oxide, phosphating, zinc or nickel plating, or paint. Carburized gear teeth are ground after hardening and can be shot peened to improve fatigue life.
18CrMo4 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 | — |
| SLow/controlled-sulfur grades also specify S 0.020-0.040 | ≤ 0.04 | — |
| Cr | 0.9 – 1.2 | 1.05 |
| Mo | 0.15 – 0.25 | 0.2 |
| Fe | balance | — |
18CrMo4 +AC — frequently asked
What is 18CrMo4 +AC used for?
18CrMo4 +AC is typically used for gears, shafts, case-hardened pins, camshafts and chain components. In short: weldable case-hardening steel; tough core, 58–62 HRC case; direct 4118/SCM418 equivalent.
What is the yield strength of 18CrMo4 +AC?
18CrMo4 +AC has a typical yield strength of 350 MPa (50.8 ksi) and a tensile strength of 570 MPa (82.7 ksi) — weaker than 74% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is 18CrMo4 +AC easy to machine?
Reasonably — machinability is rated good (60/100, better than 83% of steel grades). Machining is best in the spheroidize-annealed or cold-drawn condition, with coated carbide at 120–180 m/min. Once carburized and quenched, only grinding or hard turning with CBN is practical.
Can 18CrMo4 +AC be welded?
Yes — weldability is rated good (68/100). Carbon equivalent is about 0.55, so the steel is weldable with 150–250 °C preheat and low-hydrogen consumables, followed by stress relief at 550–650 °C. Do not weld on carburized surfaces.
What surface finishes work on 18CrMo4 +AC?
Corrosion protection is required: black oxide, phosphating, zinc or nickel plating, or paint. Carburized gear teeth are ground after hardening and can be shot peened to improve fatigue life.
Can 18CrMo4 +AC be formed, bent or molded?
The +AC condition suits cold heading, cold extrusion and thread rolling. Hot forge at 1100–850 °C and normalize after forging to refine the structure.
What is the maximum service temperature of 18CrMo4 +AC?
18CrMo4 +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.
Sources
- EN 10084 — Case hardening steels: technical delivery conditions — CEN (2008)
- EN 10277 — Bright steel products: technical delivery conditions — CEN (2018)
- GB/T 3077 (20CrMo ) — SAC (2015)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- Machinery's Handbook (machinability ratings) — Industrial Press (2020)
- Case hardening steel 18CrMo4 / 1.7243 data sheet — European long-products producers (2022)
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.