EN24T (sometimes called 817M40T) is an alloy steel through-hardening alloy commonly used in engineering and industrial applications requiring extreme strength, hardness, and wear resistance. It is a nickel-chromium-molybdenum steel available in tender-hardened and tempered T form, providing a rare combination of tensile strength, great ductility, excellent machinability, and reliable mechanical properties.
This paper is a detailed, easy-to-read overview of EN24T alloy steel – technical composition, mechanical specifications, typical uses, heat treatment information, and industry applicability as applicable to engineers, architects, and people involved in procurement.
EN24T / 817M40T Steel Overview and Specification
EN24T, the British standard BS970:1955, and since catalogued as 817M40T, is a medium-to-high alloy steel with strong chemical composition and heat-treatable properties. Rigid material supplied in a hardened and tempered condition is indicated by T in EN24T to provide optimum strength and manufacturability.
International counterparts are:
- German DIN: 934NiCrMo6
- French AFNOR: 35NCD6
- European steel number: 1.6582
- American SAE (AISI): 4340
- European Standard EN 10277-5
This wide similarity enables EN24T to be easily acquainted with international engineering teams and to be similar to other alloy steels of comparable use worldwide.
Chemical Composition of EN24T
EN24T performs well because it contains accurate alloying elements. Average chemical analysis is given as follows:
- Carbon (C): 0.36 – 0.44%
- Silicon (Si): 0.10 – 0.40%
- Manganese (Mn): 0.45 – 0.70%
- Chromium (Cr): 1.00 – 1.40%
- Molybdenum (Mo): 0.20 – 0.35%
- Nickel (Ni): 1.30 – 1.70%
- Phosphorus (P): [?] 0.035%
- Sulphur (S): [?] 0.040%
Mechanical Properties in “T” Condition
EN24T has a characteristic balanced mechanical profile. Common properties in the hardened and tempered condition of T are:
- Tensile Strength: 850 – 1,000 N/mm2
- Yield Strength: Approx. 680 N/mm2
- Proof Stress (0.2%): 680 N/mm2 minimum
- Brinell Hardness: 248 – 302 HB
- Elongation: minimum (with section size) = ~9%.
- Impact Resistance: Good dynamical loading toughness.
These values indicate the appropriateness of EN24T for high-stress, precision-engineering parts where strength and ductility are important.
Heat Treatment and Machinability
The performance of EN24T is to a great extent affected by the heat treatment process:
Hardened and Tempered (T) Condition
It is the normal supply condition, where the supply is in the strongest form and is easily machineable without any additional work.
Case Hardening
To achieve surface wear-resistant characteristics, EN24T may be subjected to surface case hardening (flame or induction hardening) to make the surface hard, whilst maintaining a tough core.
Annealing & Normalising
Annealing eliminates internal stresses and enhances softness for further machining, where high strength is not required at the moment.
Stress Relieving
This is an optional measure to reduce distortions after welding or heavy machining.
The T condition also makes EN24T suitable for machining operations, enabling engineers to produce quality parts with less time spent on processing.
Supply Forms and Sizes
EN24T/817M40T is available in various supply conditions to meet various engineering requirements. These include:
- Bright Drawn Bar
- Hot Rolled Bar
- Turned and Polished Bar
- Forged Blocks (cold sawn to specifications)
- Custom cut-to-length options
Diameters range from 10mm to 310mm, and bespoke sizes are available on request.
Key Advantages of EN24T Steel
EN24T / 817M40T has a number of impressive advantages:
High Strength & Toughness
EN24T is an alloy in the heat-treatable state, making it extremely strong and shock-resistant and suited for heavy-duty mechanical components.
Wear and Fatigue Resistance
Nickel, chromium, and molybdenum are additives that increase wear resistance and fatigue resistance under cyclic loading.
Machinability and Weldability
EN24T is reasonably machinable with proper tempering and can be welded using standard industrial processes; however, special attention should be given to the post-weld heat treatment.
Versatility
The flexibility of steel in heat treatment and its ability to be formed into various shapes qualify it for a wide range of engineering industries.
Typical Applications of EN24T
The profile of strength and durability of EN24T provides it with the opportunity to be used in critical components of various industries:
Automotive and Motorsport
- Transmission shafts
- Axles and couplings
- Powerful bolts and rivets.
The Construction and Heavy Machinery
- Gears and pinions
- Tool holders and fixtures
- Pump rods and spindles
High-Performance Engineering and Aerospace
- Aircraft landing gear
- Load-bearing rotating parts
- Mechanical assemblies of high torque.
These applications demonstrate why EN24T will be an engineering steel of choice in situations requiring high mechanical performance.
Conclusion: Why Choose EN24T / 817M40T?
A perfect combination of high tensile strength, machinability, and toughness, EN24 T (817M40T) alloy steel can be used in precision engineering for automotive, aerospace, heavy machinery, and industrial applications.
Its all-purpose supply shapes and its high mechanical qualities, combined with solid international equivalency, contribute to its prominence in engineering circles, where engineers expect reliability and performance from a material under harsh working conditions.
EN24T alloy steel is a good candidate for your specification if your application requires high loads, impact resistance, and reliable mechanical performance.
