EN8
EN8 Bright Bar
The standard medium carbon shafting steel — hardens through the section.
Also known as 080M40 · AISI 1040 · C40 · EN8A
Overview
What EN8 is, and where it belongs
EN8 is the default medium carbon engineering steel across Indian industry, and for good reason. At 0.36–0.44% carbon it has enough carbon to respond properly to hardening and tempering, letting a designer choose the final strength of the part rather than accept whatever the mill supplied.
In the as-supplied cold drawn condition it already delivers 600–750 MPa tensile — enough for a great many shafts and pins with no heat treatment at all. When more is needed, oil quenching and tempering takes it well past 850 MPa with useful toughness retained through the whole cross section, not just at the surface.
That through-hardening behaviour is the essential difference from the case hardening grades. A carburised 16MnCr5 gear has a hard skin over a soft core. A hardened and tempered EN8 shaft is uniformly strong all the way through — which is what a torque carrying shaft actually needs.
Chemistry
Chemical composition
As per BS 970 Part 1 : 080M40, certified against our mill supplier’s EN8A specification. Values are percentage by weight.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.330 | 0.440 |
| Silicon | Si | 0.050 | 0.400 |
| Manganese | Mn | 0.600 | 1.000 |
| Phosphorus | P | — | 0.060 |
| Sulphur | S | — | 0.060 |
A dash in the minimum column means only an upper limit applies to that element.
Properties
Mechanical properties
Typical values in the Cold Drawn condition. Certified values for your consignment appear on the test certificate.
- Tensile Strength
- 600 – 750 MPa
- Yield Strength
- 450 – 520 MPa
- Elongation (A5)
- 10 – 16%
- Hardness
- 179 – 229 HB
- Impact (Izod)
- 28 J typical
Availability
Sizes and tolerances
We draw EN8 across the range below. Exact availability for a given size is confirmed on enquiry.
Round bar
6 – 65 mm
Nominal diameter
Hex bar
7 – 46 mm
Across flats (AF)
Tolerance bands
All bands are ISO 286 ‘h’ — the bar is never above nominal size. See exact values for your size.
Where it is used
Typical applications
- Drive shafts and axles
- Spindles and machine shafts
- Couplings and connecting rods
- Studs, bolts and tie rods
- Gears in light duty service (through hardened)
Application guides
Cross reference
International equivalents
Nearest designations under other standards. Equivalents are close but rarely identical — check the specific requirement that matters for your part.
Full equivalents chart| Standard | Designation |
|---|---|
| BS (UK) | 080M40 / EN8 |
| AISI / SAE (USA) | 1040 |
| DIN (Germany) | C40 / 1.0511 |
| JIS (Japan) | S40C |
| IS (India) | C40 / 40C8 |
Processing
Heat treatment guidelines
Indicative parameters. Actual cycles depend on section size, furnace and the properties your drawing calls for.
- 01Normalising830 – 860 °C, cool in still air
- 02Annealing830 – 850 °C, furnace cool to below 500 °C
- 03Hardening820 – 860 °C, quench in oil
- 04Tempering550 – 660 °C, air cool. Higher tempering temperature gives lower strength and higher toughness.
Index relative to AISI 1212 = 100. Higher is faster to machine.
Machines acceptably in the cold drawn condition. Higher carbon means more tool wear than the low carbon grades, and no free-machining sulphur means a continuous chip. Where the part is turning-intensive, EN8M gives the same mechanical class with far better machinability.
Weldability: Fair
Related grades
Chemical composition and mechanical properties shown are as per the applicable standard and are indicative. Actual values for your consignment are certified in the Mill Test Certificate supplied with each dispatch. Available sizes and tolerances are confirmed at the time of enquiry.
Need EN8?
Send us the size and quantity — Round 6–65 mm · Hex 7–46 mm. We will confirm availability and come back with a price.