Is EN8 the same as C45?

They are close but not the same. EN8 (080M40) has about 0.40% carbon and C45 about 0.45%. In India they are often used interchangeably for general parts; if it matters, name the exact grade and standard on the drawing.

What is the hardness of EN8?

About 150–210 HB as supplied, and about 200–255 HB when hardened and tempered. With induction hardening the surface can reach around 50–55 HRC.

Yes. It can be hardened and tempered, and its surface can be induction or flame hardened. Only small sections harden all the way through.

Yes, with care: preheat, use low-hydrogen electrodes and let it cool slowly, otherwise it can crack near the weld.

What is the difference between EN8 and EN9?

EN9 (070M55) has more carbon, about 0.55%, so it is harder and wears better but is less tough and harder to weld. EN8 is the more general-purpose grade.

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EN8 steel

Also called: 080M40, 40C8, C40 / C45, AISI 1040 / 1045, EN8 material, EN8 bar

EN8 is a medium-carbon steel with about 0.4% carbon, known today as 080M40. It is strong, cheap and machines well, and it is one of the most used steels in India for shafts, axles, pins, studs and general machine parts.

Quick facts

Type: Medium-carbon (unalloyed) steel
Carbon: About 0.36–0.44%
Typical hardness: About 150–210 HB as supplied; about 200–255 HB hardened and tempered
Tensile strength: About 550 MPa as supplied; 700–850 MPa hardened and tempered
Machinability: Good, especially in the normalised condition
Weldability: Fair: needs preheating

Equivalent grades

Standard	Closest grade
BS 970 (old / current)	EN8 / 080M40
IS 1570 (India)	40C8
DIN / EN 10083	C40 (1.0511); C45 (1.0503) is often supplied in its place
AISI / SAE (USA)	1040; 1045 is often used in its place
JIS (Japan)	S40C; S45C

Equivalents are close, not identical: the limits of each standard differ slightly. In India EN8 and C45 are often sold and used interchangeably; if the exact grade matters, name the standard on your drawing and ask for the mill test certificate.

Typical chemical composition (080M40)

Element	%
Carbon (C)	0.36–0.44
Silicon (Si)	0.10–0.40
Manganese (Mn)	0.60–1.00
Sulphur (S)	0.050 max
Phosphorus (P)	0.050 max

Typical mechanical properties

Condition	Tensile strength	Yield strength	Hardness
Normalised / as rolled	About 550 MPa min	About 280 MPa min	About 150–210 HB
Hardened and tempered	About 700–850 MPa	About 465 MPa min	About 200–255 HB

Values depend on the bar size (bigger sections are softer after hardening) and on the supplier. Use them for guidance only.

Heat treatment

Normalising: heat to about 830–860 °C and cool in air
Hardening: heat to about 830–860 °C and quench in oil or water, then temper
Tempering: about 550–660 °C for a tough, machinable hardened-and-tempered condition
Surface hardening: induction or flame hardening gives a hard wearing surface, typically around 50–55 HRC, over a tougher core
EN8 hardens fully only in small sections; thick parts stay softer in the middle

Machining and welding

EN8 machines well in the normalised condition and is easy to turn, mill, drill and thread. A free-machining version with added sulphur (EN8M) cuts faster and gives better chips, at some cost to toughness.

Because of its carbon content, EN8 can crack near a weld if it cools too fast. Preheating (often around 150–250 °C, depending on thickness), low-hydrogen electrodes and slow cooling are normally used. For parts that need a lot of welding, a low-carbon steel is a better choice.

Typical uses

Shafts, axles and spindles
Pins, studs, bolts and keys
Couplings, gears and sprockets for moderate loads
Hydraulic rams and rods (often hard-chrome plated)
General machine parts and forgings

When to choose another grade

Higher strength and toughness: EN19 (42CrMo4) or EN24 (34CrNiMo6)
A hard wearing surface with a tough core, such as gears: case-hardening steel EN353 or 20MnCr5
Easy welding and fabrication: mild steel (IS 2062)
Corrosion resistance: stainless steel such as SS304 or SS410

Available forms

Round bars, black (hot rolled) and bright (drawn or peeled)
Hexagon and square bars
Flats and plates
Forgings

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Questions

Is EN8 the same as C45?: They are close but not the same. EN8 (080M40) has about 0.40% carbon and C45 about 0.45%. In India they are often used interchangeably for general parts; if it matters, name the exact grade and standard on the drawing.
What is the hardness of EN8?: About 150–210 HB as supplied, and about 200–255 HB when hardened and tempered. With induction hardening the surface can reach around 50–55 HRC.
Can EN8 be hardened?: Yes. It can be hardened and tempered, and its surface can be induction or flame hardened. Only small sections harden all the way through.
Can EN8 be welded?: Yes, with care: preheat, use low-hydrogen electrodes and let it cool slowly, otherwise it can crack near the weld.
What is the difference between EN8 and EN9?: EN9 (070M55) has more carbon, about 0.55%, so it is harder and wears better but is less tough and harder to weld. EN8 is the more general-purpose grade.

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.