EN24

Element Carbon (C) Silicon (Si) Manganese (Mn) Nickel (Ni) Chromium (Cr) Molybdenum (Mo) Sulphur (S) Phosphorus (P) Percentage (%) 0.36 – 0.44 0.10 – 0.35 0.45 – 0.70 1.30 – 1.70 0.90 – 1.40 0.20 – 0.35 ≤ 0.040 ≤ 0.035

The hardness of EN24 depends on its heat treatment condition. In its most commonly used hardened and tempered state, EN24 typically achieves a hardness of: 28–36 HRC (Rockwell Hardness) when tempered for toughness Up to 55–60 HRC when fully hardened and tempered for maximum strength With surface treatments like nitriding or induction hardening, EN24 can reach even higher surface hardness levels—up to 60–65 HRC—while maintaining a tough, impact-resistant core. This makes it ideal for applications that need both a hard-wearing surface and internal strength.

AISI / SAE: 4340 DIN (Germany): 1.6511 or 34CrNiMo6 DIN (Germany): 1.6511 or 34CrNiMo6 UNI (Italy): 40NiCrMo7 AFNOR (France): 35NCD6 BS (UK): 817M40 (old British Standard designation for EN24) JIS (Japan): SNCM8

EN24 is a versatile alloy steel that responds well to various heat treatment processes, allowing it to achieve a wide range of mechanical properties. Here’s how it’s typically treated: Annealing Heat to 820–850°C, then allow to cool slowly in a furnace. Purpose: Softens the steel for easier machining and improves ductility. Normalizing Heat to 850–880°C, then cool in still air. Purpose: Refines the grain structure and relieves internal stresses. Hardening (Quenching) Heat to 820–860°C, then quench in oil. Purpose: Increases hardness and tensile strength. Tempering Reheat after quenching to 250–650°C, depending on desired properties, then air cool. Purpose: Reduces brittleness and increases toughness. Lower tempering temperatures retain more hardness; higher temperatures increase toughness. Nitriding (Optional) Heat to 500–530°C in a nitrogen-rich environment. Purpose: Hardens the surface (up to 60–65 HRC) without affecting the core toughness. Induction Hardening (Optional) Localized surface heating followed by rapid quenching. Purpose: Provides a hard, wear-resistant surface with a tough core—ideal for components like shafts and gears.

Hardening (Quenching) Process: Heat the steel uniformly to 820–860°C. Hold at temperature until it’s fully heated through. Quench in oil to rapidly cool the material. This process creates a hardened structure (martensite), increasing the steel’s hardness up to 55–60 HRC, depending on the cooling rate and section size. After hardening, EN24 becomes very hard but also brittle. To improve toughness and reduce brittleness, it must be tempered—this involves reheating to 250–650°C, depending on the desired final properties.

EN24 can be challenging due to its high strength and alloy content (especially nickel, chromium, and molybdenum). These elements make it prone to cracking during and after welding, particularly in the hardened and tempered condition. Key Considerations: Not recommended in hardened condition – Welding should ideally be done in the annealed or normalized state. Preheating is essential – Heat the material to 200–300°C before welding to reduce thermal shock and the risk of cracking. Post-weld heat treatment (PWHT) – After welding, slow cooling followed by stress relieving or tempering at around 600–650°C helps restore ductility and reduce residual stresses. Use low-hydrogen electrodes or filler rods – These minimize the risk of hydrogen-induced cracking.

EN24 offers moderate to good machinability, especially when it's supplied in the annealed or normalized condition. In these softer states, the steel can be cut, drilled, turned, and milled with standard high-speed steel (HSS) or carbide tools. Annealed EN24: Easier to machine, ideal for roughing and general machining operations. Hardened EN24 (quenched and tempered): More difficult to machine due to higher hardness. Requires rigid setups, slower speeds, and specialized tooling (e.g., carbide inserts). Coolant: Use of appropriate cutting fluids or coolant is essential to avoid overheating and improve tool life. Tool Wear: Machining hardened EN24 can lead to faster tool wear, so proper tool material and geometry are important.

Property Value Density 7.85 g/cm³ Melting Point ~1425–1460°C Thermal Conductivity ~42.6 W/m·K (at 100°C) Electrical Resistivity ~0.45 µΩ·m Modulus of Elasticity ~205 GPa Specific Heat Capacity ~460 J/kg·K Poisson’s Ratio ~460 J/kg·K Thermal Expansion Coefficient ~12.3 x 10⁻⁶ /°C (20–100°C)

Property Value Corrosion Resistance Moderate, improves with heat treatment and alloying elements Hardness 250-280 HfB annealed; 55-60 HRC hardened Tensile Strength High, typically 850-1100 MPa Toughness Excellent with proper heat treatment