EN24 / AISI 4340 / 34CrNiMo6 Steel
When engineering components are subjected to extreme stress, heavy shock loads, and severe wear, standard carbon steels simply cannot survive. For critical applications ranging from aerospace landing gears to heavy-duty automotive crankshafts engineers globally specify the EN24 / AISI 4340 steel grade family.
As India’s leading alloy steel manufacturer and supplier, Kesari Alloys produces high-integrity EN24, AISI 4340, and 34CrNiMo6 steel designed to meet the most stringent 2026 industrial standards. This guide breaks down the metallurgical profile, mechanical capabilities, and heat treatment protocols of this premier nickel-chromium-molybdenum alloy.
Understanding the Designations: EN24 vs. AISI 4340 vs. 34CrNiMo6
While often used interchangeably in procurement, these designations reflect regional standardization systems for essentially the same high-strength alloy:
- EN24: The British Standard (BS 970) designation, widely recognized across India and the Commonwealth.
- AISI 4340: The American Iron and Steel Institute standard, the dominant specification in global aerospace and defense sectors.
- 34CrNiMo6 (1.6582): The European (DIN/EN) standard, explicitly detailing the core alloying elements.
Regardless of the specific nomenclature on your drawing, this alloy family delivers unparalleled deep hardenability and toughness.
Chemical Composition: The Metallurgical Blueprint
The superior mechanical properties of the EN24 / AISI 4340 family stem from a precisely balanced chemical composition. The synergistic effect of Nickel, Chromium, and Molybdenum creates a steel capable of retaining high strength without sacrificing ductility.
| Element | Symbol | Composition Range (%) | Engineering Function |
|---|---|---|---|
| Carbon | C | 0.35 – 0.45 | Provides the baseline tensile strength and primary hardenability. |
| Nickel | Ni | 1.30 – 1.80 | Significantly improves toughness, impact resistance, and fatigue life. |
| Chromium | Cr | 0.90 – 1.40 | Enhances overall hardness, wear resistance, and depth of hardening. |
| Molybdenum | Mo | 0.20 – 0.35 | Mitigates temper embrittlement and maintains strength at elevated temperatures. |
| Manganese | Mn | 0.45 – 0.70 | Acts as a deoxidizer during melting and improves forgeability. |
Mechanical Properties (Condition T)
In the Indian market, Kesari Alloys frequently supplies EN24 in the “T” condition (hardened and tempered). This pre-treated state offers an optimal balance of machinability and operational strength, allowing manufacturers to bypass secondary in-house heat treatments for many components.
- Tensile Strength: 850 – 1000 N/mm² (MPa)
- Yield Stress: 680 N/mm² (MPa) Minimum
- Elongation: 13% Minimum
- Impact Strength (Izod): ~54 Joules
- Hardness: 248 – 302 HB (Brinell)
For applications demanding even higher tensile profiles, this steel can be heat-treated to conditions U, V, W, or Z, pushing tensile strengths well beyond 1500 MPa.
Heat Treatment Guidelines: 2026 Best Practices
Achieving the maximum potential of 34CrNiMo6 requires strict adherence to thermal processing parameters. Deviations can lead to cracking or suboptimal grain structures.
- Forging: Preheat uniformly to 1150°C. Forging should not continue below 850°C. Due to its air-hardening tendencies, parts must be cooled slowly in ash or sand post-forging to prevent thermal stress cracking.
- Annealing: Heat the material to 840°C – 860°C, hold until the temperature is uniform across the cross-section, and cool slowly in the furnace. This yields a structure suitable for extensive machining operations.
- Hardening: Heat slowly and uniformly to 820°C – 850°C. Quench in agitated oil. (Caution: Water quenching is strictly prohibited for the EN24 / AISI 4340 family due to the high risk of catastrophic cracking).
- Tempering: Transfer to the tempering furnace immediately while the part is still warm to the touch. Temper between 550°C and 660°C (depending on the target hardness condition) and cool in still air.
Surface Hardening Note: Where extreme surface wear resistance is required alongside a tough core, EN24 responds exceptionally well to induction hardening and nitriding.
Critical Industrial Applications
Because of its premium alloying cost, EN24 is reserved for components where failure carries high financial or safety risks. Common applications engineered from Kesari Alloys stock include:
- Automotive & Heavy Commercial Vehicles: High-stress crankshafts, heavy-duty connecting rods, axle shafts, and transmission gears.
- Power Transmission & Machinery: High-torque splined shafts, PTO shafts, drill collars, and heavy machine tool components.
- Aerospace & Defense: Landing gear assemblies, structural brackets, and specialized heavy-caliber ordnance components.
- Fasteners: High-tensile bolts, studs, and nuts used in petrochemical and offshore oil rigs.
Why Source EN24 / AISI 4340 from Kesari Alloys?
Specifying the right grade is only the first step; material integrity is the second. Even minor inclusions or inconsistent heat treatment at the mill level can compromise the entire manufacturing run.
As India’s premier alloy steel manufacturer, Kesari Alloys utilizes advanced melting and refining practices to guarantee pristine internal soundness and strict dimensional tolerances. Whether you require black bar, bright drawn, or custom-forged blocks, our EN24 / AISI 4340 stock delivers the predictable, high-performance machining behavior your CNC lines demand.
Secure your supply chain with India’s most trusted steel manufacturer. Contact the metallurgical team at Kesari Alloys today to discuss your next high-strength project.
Kesari Alloys Private Limited | IBR Approved | ISO 9001 Certified | Bhiwadi, Rajasthan, India Manufacturer & Exporter of Carbon Steel, Alloy Steel & Stainless Steel Ingots, Billets, Blooms & Rolled Bars