817M40T / EN24T Alloy Steel
High tensile strength, good machinability and weldability.
817M40T / EN24T Alloy Steel
817M40T (EN24T) is a high-performance 1.1/2% Nickel Chromium Molybdenum through-hardening alloy steel known for its exceptional strength, toughness, and wear resistance. Favoured across a broad spectrum of engineering and industrial applications, this steel offers an excellent combination of high tensile strength, good ductility, and outstanding machinability in its hardened and tempered “T” condition.
| BS970: 1955 | BS970: 1991 | Description |
|---|---|---|
| EN24T | 817M40T | Bright / Black 1.1/2% nickel chromium molybdenum steel |
| International Specification Comparison | |
|---|---|
| BRITISH BS 970:1991 | 817M40T |
| BRITISH BS 970:1955 | EN24T |
| GERMAN DIN | 934NiCrMo6 |
| FRENCH AFNOR | 35NCD6 |
| SWEDISH SS | 2541 |
| AMERICAN SAE | 4340 |
| EUROPEAN STEEL NO. | 1.6582 |
| EUROPEAN STEEL NAME | 34CrNiMo6 |
| EUROPEAN STANDARD | EN 10277-5 |
| Mechanical Properties | |
|---|---|
| Tensile Strength N/MM2 Min Rm | 850 / 1000 |
| Yield Stress N/MM2 Min Rm | 700 |
| Elongation A Mrn % on 5.65,SO | 9 |
| Izod Min | 54 |
| Kcv Min | - |
| Proof Stress 0.2% N/MM2 Min | 680 |
| Brinell Hardness | 248 / 302 |
| Chemical Analysis | |
|---|---|
| Car | 0.36 / 0.44 |
| Sil | 0.10 / 0.40 |
| Mang | 0.45 / 0.70 |
| Phos | 0.035 max |
| Sul | 0.040 max |
| Chr | 1.00 / 1.40 |
| Moly | 0.20 / 0.35 |
| Nick | 1.30 / 1.70 |
Key Features and Advantages
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High Tensile Strength: 817M40T / EN24T Alloy Steel is typically supplied in the hardened and tempered condition, offering tensile strength up to 1000 N/mm², making it ideal for high-stress components that must maintain dimensional stability under load.
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Wear Resistance: Thanks to its Nickel-Chromium-Molybdenum alloy composition, EN24T delivers excellent abrasion and wear resistance, even in harsh working environments.
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Toughness & Shock Resistance: Its superior impact properties make this steel particularly suited for dynamic and load-bearing components that operate under high torque or shock loading.
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Machinability: Supplied in the “T” condition, 817M40T machines well with minimal effort, allowing components to be produced quickly and accurately with no need for further treatment.
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Weldability: This grade offers good weldability using standard methods, provided correct procedures are followed (including post-weld heat treatment where necessary).
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Versatility of Supply: Available in bright drawn, hot rolled, and turned bar forms, as well as forged blocks which can be cold sawn to size, EN24T gives engineers and manufacturers the flexibility they need to meet diverse application requirements.
| Size Range Summary | ||
|---|---|---|
| Rounds | IMP | 3/8" - 3" dia |
| MM | 10mm - 310mm dia | |
Common Applications
Due to its reliable mechanical performance, 817M40T / EN24T is widely used in demanding engineering and mechanical applications. Typical uses include:
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Transmission shafts and drive axles
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Heavy-duty gears and pinions
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Studs, bolts, and high-strength fasteners
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Crankshafts and couplings
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Tool holders and fixtures
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Spindles, splined shafts, and pump rods
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Aircraft landing gear and high-load aerospace components
Its versatility makes it a go-to alloy for the automotive, aerospace, offshore, and general engineering sectors.
| Properties | |
|---|---|
| MACHINEABILITY | 40 |
| WELDABILITY | Pre / post heat precaution required |
| HARDENABILITY | High strength up to 100mm dia |
| SELECTION GUIDEAND USAGE EXAMPLES | Popular direct hardening steel with good tensile. ductility, shock and wear resistance properties |
Heat Treatment and Hardening
EN24T responds well to a range of heat treatment options:
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Hardened & Tempered (“T” Condition): Supplied with excellent strength and machinability. No further heat treatment is typically required.
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Case Hardening: Surface hardness can be further increased for specific wear-resistant applications using flame or induction hardening techniques.
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Annealing & Normalising: Soft annealed forms can be supplied upon request for applications requiring subsequent heat treatment.
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Stress Relieving: Recommended after welding or heavy machining to reduce internal stresses and maintain dimensional stability.
Supply Conditions and Forms
At Midland Special Steels, we supply 817M40T / EN24T in the following conditions:
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Bright drawn bar
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Hot rolled bar
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Turned and polished bar
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Forged blocks, which we can cold saw to your exact size requirements
All material can be cut to length and delivered in either standard or bespoke sizes to suit your production schedule.
Standards and Designations
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British Standard: BS 970: 817M40
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European Equivalent: 34CrNiMo6
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Werkstoff Number: 1.6582
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International Equivalents: AISI 4340 / ASTM 4340
All material is supplied with full certification and traceability, ensuring you meet compliance requirements for safety-critical or regulated industries.
Additional Services Available
Midland Special Steels is committed to helping customers get the most from their materials. We offer a range of value-added services, including:
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Cutting to length
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Centreless grinding
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Heat treatment options
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Ultrasonic and non-destructive testing (NDT)
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Bespoke machining solutions
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Next-day delivery and scheduled dispatch
If you require your material pre-machined or processed to reduce production time, just let us know — we can tailor our services to your needs.
Speak to the Experts
With decades of experience supplying high-grade alloy steels to industry leaders across the UK and beyond, Midland Special Steels is your trusted partner for EN24T / 817M40T alloy bar and block. Whether you need a one-off bar for a prototype or regular scheduled deliveries for production, we’re here to help.
