Steel EN24
BS EN24 · AISI/SAE 4340
EN24 is the British Standard high-strength nickel-chromium-molybdenum through-hardening steel, closely equivalent to AISI 4340 and 34CrNiMo6, supplied quenched and tempered in condition classes U through Z.
Values for the HR condition
EN24 tempers and conditions
EN24 is supplied in 12 conditions, soft to hard. HR is the default FabDigit quotes; the values on this page are for it.
Compare all 12 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
full/spheroidise annealed (condition A) | Softest condition for deep machining, cold forming or thread rolling before hardening. | 470 | 750 | 22 | 217 HB | — |
HRDefault Hot rolled | Cheapest raw stock for parts that will be heat treated after rough machining. | 520 | 850 | 15 | 22 HRC | — |
Cold rolled | Thin flat product with tight thickness and smooth surface; strength from cold work, heat treat after blanking. | 700 | 900 | 9 | 26 HRC | 7.8 % IACS |
Cold drawn | Bright, size-accurate bar for shafts machined to near-final size before hardening; best surface of the untreated forms. | 720 | 900 | 11 | 26 HRC | 7.8 % IACS |
Quenched and tempered | The standard stock condition (EN24T): best strength/toughness/machinability compromise for shafts, gears and general engineering parts. | 740 | 930 | 15 | 28 HRC | — |
Q&T condition U | One step above T when slightly higher strength is required with near-equal toughness. | 800 | 1,000 | 14 | 31 HRC | 7.8 % IACS |
austenitised ~860 °C, air cooled | Uniform grain and high strength without quench distortion; usually followed by tempering for stock relief. | 860 | 1,280 | 12 | 39 HRC | — |
Q&T condition V | Common for high-duty gears, torsion bars and heavy-duty shafting. | 900 | 1,080 | 13 | 34 HRC | 7.8 % IACS |
Q&T condition W | High-strength condition for aerospace/heavy machine parts; machining becomes noticeably harder. | 990 | 1,150 | 12 | 36 HRC | 7.7 % IACS |
Q&T condition X | Used where high yield strength dominates; watch notch sensitivity and plating hydrogen embrittlement. | 1,070 | 1,230 | 11 | 40 HRC | — |
Q&T condition Y | Near-top standard strength band for highly stressed bolts, rods and aerospace fittings. | 1,130 | 1,300 | 10 | 42 HRC | — |
Q&T condition Z | Maximum-strength condition for small sections and tooling; low ductility and high notch/hydrogen sensitivity. | 1,400 | 1,650 | 7 | 49 HRC | — |
What is EN24?
EN24 is the British Standard high-strength nickel-chromium-molybdenum through-hardening steel, closely equivalent to AISI 4340 and 34CrNiMo6, supplied quenched and tempered in condition classes U through Z. Default Q&T bar gives 520 MPa yield, 850 MPa tensile, 15 % elongation and 240 HB (22 HRC), with deep hardenability that suits heavy shafts, axles and forgings machined from solid. Weldability is restricted and cold formability low (score 30), so bending is done only in the annealed state, and the steel has no corrosion resistance and needs plating, phosphating or paint. 25CrMo4/4130 is the choice when welding matters more than strength. EN24 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). EN24 has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 850 MPa (123 ksi) — stronger than 67% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi).
What is EN24 used for?
- Drive shafts
- Industrial axles
- Forgings
Advantages
- Polishes to a fine finish — 70/100, better than 87% of steel grades
EN24 properties
Typical room-temperature values for EN24-HR; bars are the position among steel grades.
Physical3
EN24 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
EN24 has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 850 MPa (123 ksi) — stronger than 67% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
EN24 is rated for continuous service to 400°C (752 °F). It conducts heat at 42 W/m·K (24.3 BTU/hr·ft·°F), worse than 56% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
EN24 conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (15/100), better than 75% of steel grades.
Sustainability4
Producing a kilogram of EN24 takes about 34 MJ of energy and emits 2.3 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 30%.
Manufacturability8
EN24's machinability is fair (50/100, worse than 53% of steel grades); weldability poor (30/100); formability poor (30/100).
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. EN24 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with EN24
Is EN24 easy to machine?
Machinable at 248–302 HB with rigid setups, carbide tooling and generous coolant; above ~350 HB use coated carbide/CBN, low feeds and consider grinding for finishing.
Can EN24 be welded?
Restricted weldability — preheat 250–350 °C, low-hydrogen consumables (or matching Ni-Cr-Mo filler), and temper immediately after welding; cracking risk high in the hardened conditions.
Can EN24 be formed, bent or molded?
Hot forge 1150–850 °C then normalise or anneal; cold forming only in the annealed condition and limited to gentle bends.
Manufacturability
The process limits FabDigit applies to EN24. Every EN24 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Better50 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Fair30 / 100 |
|---|---|
| Weldability | Better30 / 100 |
EN24 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 | 0.36 – 0.44 | 0.4 |
| Si | 0.1 – 0.4 | 0.25 |
| Mn | 0.45 – 0.7 | 0.58 |
| Ni | 1.3 – 1.7 | 1.5 |
| Cr | 1 – 1.4 | 1.2 |
| Mo | 0.2 – 0.35 | 0.27 |
| S0.015–0.040 for 817M40; 0.050 max for free-machining 816M40 variant | ≤ 0.04 | 0.02 |
| P | ≤ 0.04 | 0.02 |
| Fe | balance |
What surface finishes work on EN24?
No anodising; protect by black oxide, phosphating, zinc or hard chrome plating, nitriding for surface wear — bake plated parts above 1000 MPa strength to relieve hydrogen.
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).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel EN24 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
How much does EN24 cost?
EN24 is a standard-cost steel ($$), cheaper than about 61% 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.
EN24 — frequently asked
What is EN24 used for?
EN24 is typically used for drive shafts, industrial axles and forgings. In short: workhorse Q&T English bar.
What is the yield strength of EN24?
EN24 has a typical yield strength of 520 MPa (75.4 ksi) and a tensile strength of 850 MPa (123 ksi) — stronger than 67% of steel grades. Strength varies by condition: see the 12 listed tempers.
Is EN24 easy to machine?
Reasonably — machinability is rated fair (50/100, worse than 53% of steel grades). Machinable at 248–302 HB with rigid setups, carbide tooling and generous coolant; above ~350 HB use coated carbide/CBN, low feeds and consider grinding for finishing.
Can EN24 be welded?
Not readily — weldability is rated poor (30/100). Restricted weldability — preheat 250–350 °C, low-hydrogen consumables (or matching Ni-Cr-Mo filler), and temper immediately after welding; cracking risk high in the hardened conditions.
What surface finishes work on EN24?
No anodising; protect by black oxide, phosphating, zinc or hard chrome plating, nitriding for surface wear — bake plated parts above 1000 MPa strength to relieve hydrogen.
Can EN24 be formed, bent or molded?
Hot forge 1150–850 °C then normalise or anneal; cold forming only in the annealed condition and limited to gentle bends.
What is the maximum service temperature of EN24?
EN24 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 EN24-HR and EN24-CD?
HR is the default condition — cheapest raw stock for parts that will be heat treated after rough machining. CD: bright, size-accurate bar for shafts machined to near-final size before hardening; best surface of the untreated forms. Yield strength is 520 MPa in HR versus 720 MPa in CD.
How much does EN24 cost?
EN24 is a standard-cost steel ($$), cheaper than about 61% 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.
Can FabDigit make parts in EN24?
Yes — EN24 is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- BS 970-1: Wrought steels — 817M40 (EN24) — BSI (1991)
- GB/T 3077 Alloy structural steels — 40CrNiMoA — SAC (2015)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels (AISI 4340) — ASM International (1990)
- ASM Handbook Vol.19: Fatigue and Fracture — ASM International (1996)
- MMPDS-17 typical properties, 4340 steel — Battelle/FAA (2022)
- EN24T / 817M40 hardened & tempered bar datasheets — West Yorkshire Steel / Interlloy (2023)
- 40CrNiMoA — Mysteel / 1688 (2026)
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.