Steel EN24 Q&T-Z
Hardness band
BS EN24 · AISI/SAE 4340
Q&T-Z = q&T condition Z
Maximum-strength condition for small sections and tooling; low ductility and high notch/hydrogen sensitivity.
Values for the Q&T-Z condition
Other EN24 tempers and conditions
EN24 is listed in 12 conditions; see the grade overview at EN24.
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-ZThis page 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 Q&T-Z?
EN24 Q&T-Z is EN24 heat treated to Q&T-Z — maximum-strength condition for small sections and tooling; low ductility and high notch/hydrogen sensitivity. EN24 Q&T-Z has a yield strength of 1,400 MPa (203 ksi) and a tensile strength of 1,650 MPa (239 ksi) — stronger than 96% of steel grades. Elongation at break is 7% and the elastic modulus is 205 GPa (29.7 Msi). EN24 Q&T-Z 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). HR is the default condition FabDigit quotes; Q&T-Z is available on request or by drawing note.
Advantages
- High strength — 1,400 MPa (203 ksi), better than 96% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
Limitations
- Difficult to weld — 10/100, worse than 99% of steel grades
- Limited ductility — 7%, worse than 96% of steel grades
- Difficult to machine — 22/100, worse than 95% of steel grades
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
- Low fracture toughness — 50 MPa·√m (45.5 ksi·√in), worse than 86% of steel grades
EN24 Q&T-Z properties
Typical room-temperature values for EN24 Q&T-Z; 14 are specific to this condition. Other listed values are EN24 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
EN24 Q&T-Z 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 Q&T-Z has a yield strength of 1,400 MPa (203 ksi) and a tensile strength of 1,650 MPa (239 ksi) — stronger than 96% of steel grades. Elongation at break is 7% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
EN24 Q&T-Z is rated for continuous service to 200°C (392 °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 Q&T-Z 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 Q&T-Z 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 Q&T-Z's machinability is poor (22/100, worse than 95% of steel grades); weldability not recommended (10/100); formability poor (30/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with EN24 Q&T-Z
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.
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.
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 |
EN24 Q&T-Z — frequently asked
What is EN24 Q&T-Z used for?
EN24 Q&T-Z is typically used for drive shafts, industrial axles and forgings. In short: workhorse Q&T English bar.
What is the yield strength of EN24 Q&T-Z?
EN24 Q&T-Z has a typical yield strength of 1,400 MPa (203 ksi) and a tensile strength of 1,650 MPa (239 ksi) — stronger than 96% of steel grades. Strength varies by condition: see the 12 listed tempers.
Is EN24 Q&T-Z easy to machine?
Not especially — machinability is rated poor (22/100, worse than 95% 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 Q&T-Z be welded?
Not readily — weldability is rated not recommended (10/100). 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 Q&T-Z?
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 Q&T-Z 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 Q&T-Z?
EN24 Q&T-Z is rated for continuous use to about 200°C (392 °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.
Can FabDigit make parts in EN24 Q&T-Z?
Yes — EN24 Q&T-Z 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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.