Is EN24 the same as 4340?

They are close equivalents (nickel-chromium-molybdenum steels with about 0.40% carbon) and are often used interchangeably.

Why choose EN24 over EN19?

EN24's nickel lets it harden more deeply and stay tougher, which matters in large sections and for shock loads. For smaller parts EN19 is usually enough and cheaper.

Can EN24 be nitrided?

Yes. Nitriding gives a hard, wear-resistant surface with very little distortion, which suits shafts and gears that are already finished to size.

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EN24 steel

Also called: 817M40, 34CrNiMo6, AISI 4340, 40Ni6Cr4Mo3, SNCM439, EN24 material

EN24 is a nickel-chromium-molybdenum alloy steel (817M40), close to AISI 4340. Its nickel lets it harden deeply and stay tough, so it is used for heavily loaded, larger-section parts such as heavy shafts, gears and axles.

Quick facts

Type: Low-alloy nickel-chromium-molybdenum steel
Main alloys: About 1.5% nickel, 1.2% chromium, 0.25% molybdenum
Usually supplied: Hardened and tempered (condition T or above)
Tensile strength: About 850–1000 MPa in condition T; much higher in harder conditions
Strength in big sections: Better than EN19 (deeper hardening)
Weldability: Poor: preheating and post-weld treatment needed

Equivalent grades

Standard	Closest grade
BS 970 (old / current)	EN24 / 817M40
IS 1570 (India)	40Ni6Cr4Mo3
DIN / EN 10083	34CrNiMo6 (1.6582) is the usual European substitute
AISI / SAE	4340
JIS	SNCM439

Close equivalents, not identical: 34CrNiMo6 has slightly less carbon. Name the grade and standard on the drawing if it matters.

Typical chemical composition (817M40)

Element	%
Carbon (C)	0.36–0.44
Silicon (Si)	0.10–0.35
Manganese (Mn)	0.45–0.70
Nickel (Ni)	1.30–1.70
Chromium (Cr)	1.00–1.40
Molybdenum (Mo)	0.20–0.35

Heat treatment

Hardening: about 830–850 °C, quench in oil
Tempering: about 550–660 °C for the usual T–V conditions; lower for very high strength
Can be nitrided or induction hardened for a wear-resistant surface
Deep hardening means less difference between surface and core in thick parts

Typical uses

Heavy-duty shafts, axles and spindles
Highly stressed gears
Crankshafts and connecting rods
Landing-gear, defence and oil-tool parts
Large bolts and studs

EN19 or EN24?

	EN19	EN24
Alloys	Cr, Mo	Ni, Cr, Mo
Hardening depth	Good	Deeper
Toughness	Good	Better
Cost	Lower	Higher (nickel)
Best for	Small and medium sections	Large, heavily loaded sections

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Questions

Is EN24 the same as 4340?: They are close equivalents (nickel-chromium-molybdenum steels with about 0.40% carbon) and are often used interchangeably.
Why choose EN24 over EN19?: EN24's nickel lets it harden more deeply and stay tougher, which matters in large sections and for shock loads. For smaller parts EN19 is usually enough and cheaper.
Can EN24 be nitrided?: Yes. Nitriding gives a hard, wear-resistant surface with very little distortion, which suits shafts and gears that are already finished to size.

The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 8 October 2026.