Carbon steel grade
EN 8
A medium-carbon unalloyed engineering steel, supplied normalised or hardened and tempered.
What is EN 8?
EN 8 is an unalloyed medium-carbon engineering steel. It contains 0.36 to 0.44 percent carbon and 0.6 to 1.0 percent manganese. It is supplied normalised or hardened and tempered. Typical uses include shafts and machined components that require a defined proof stress but do not require a hardened case or corrosion resistance. The grade responds to quench hardening.
EN 8 and 080M40 are designations for the same steel. EN 8 originated in the 1955 edition of BS 970 and remains common in workshop terminology. The 1991 edition designated the grade as 080M40. In the six-character designation for carbon and carbon-manganese steels, the first three digits represent the mean manganese content multiplied by one hundred. The letter identifies the basis of supply: A for chemical analysis, H for hardenability and M for mechanical properties. The final two digits represent the mean carbon content multiplied by one hundred. The designation 080M40 therefore identifies steel with mean manganese and carbon contents of 0.80 percent and 0.40 percent, respectively, supplied to a mechanical property specification.
The mechanical properties depend on the heat-treatment condition rather than the chemical analysis alone. An order that specifies only EN 8 defines the composition but does not define the required strength.
Laxcon Steels lists EN 8 in its grades reference as a carbon steel grade. The same steel is written EN8, 080M40, C45 and 1045.
What is the chemical composition of EN 8?
Composition limits in weight percent are carbon 0.36 to 0.44, manganese 0.6 to 1.0, sulphur 0.06 maximum, phosphorus 0.06 maximum and silicon 0.05 to 0.35.
Composition, weight percent, balance iron.
| Element | Symbol | Minimum % | Maximum % |
|---|---|---|---|
| Carbon | C | 0.36 | 0.44 |
| Manganese | Mn | 0.6 | 1.0 |
| Sulphur | S | 0.06 | |
| Phosphorus | P | 0.06 | |
| Silicon | Si | 0.05 | 0.35 |
Mechanical properties
BS 970 specifies EN 8 mechanical properties by condition letter rather than by one strength range for all forms. Condition R is commonly specified for hardened and tempered bar. It requires a tensile strength of 700 to 850 N/mm squared, a minimum yield stress of 465 N/mm squared, a minimum elongation of 16 percent and a hardness of 201 to 255 Brinell. Condition Q specifies a tensile strength of 625 to 775 N/mm squared. These values apply within a limiting ruling section. This is the largest bar diameter for which the specified property is guaranteed at the centre rather than only at the surface.
The following values apply to EN 8 in BS 970 condition R, as published by UK stockholders working to the standard. Yield stress, proof stress and impact values apply up to a 19 mm limiting ruling section.
| Property | Specified value |
|---|---|
| Tensile strength | 700 to 850 N/mm squared |
| Yield stress | 465 N/mm squared minimum |
| 0.2 percent proof stress | 450 N/mm squared minimum |
| Elongation | 16 percent minimum, 12 percent if cold drawn |
| Impact, KCV | 28 joules minimum |
| Hardness | 201 to 255 Brinell |
Bars from the same cast can have substantially different yield properties if one remains normalised and another receives treatment to condition R. Both remain EN 8. The heat-treatment condition must therefore be stated when mechanical properties are specified.
Heat treatment and hardenability
Normalising uses a temperature of 830 to 860 degrees Celsius followed by cooling in still air. Hardening uses a temperature of 820 to 860 degrees Celsius, followed by soaking through the section and quenching in oil or water. Tempering is then performed at 550 to 660 degrees Celsius for one hour per 25 mm of section to obtain the required strength condition. Full annealing uses 680 to 710 degrees Celsius followed by furnace cooling. Forging begins at about 1050 degrees Celsius and stops before the steel cools below 850 degrees Celsius.
EN 8 has limited through-section hardenability because it contains no alloying elements that increase hardenability. Carbon controls the potential hardness of martensite, while alloying controls the depth at which martensite forms. A light section can transform throughout during quenching and can meet the specified tempered properties at its centre. The centre of a heavy section cools too slowly and forms ferrite and pearlite instead. It consequently remains softer even when the surface meets the specified hardness. A longer soak or a more severe quench does not remove this section-size limit. EN 8 also responds to flame and induction hardening when a wear-resistant surface is required over an unchanged core.
Machining and welding
EN 8 has predictable machining behaviour in the normalised condition. Machinability decreases as tempered strength increases, so machining commonly precedes final heat treatment. EN 8 M and EN 8 DM are resulphurised versions used where chip breaking has priority over toughness. They contain 0.12 to 0.20 percent sulphur, compared with a maximum of 0.06 percent in plain EN 8. Their manganese content is increased to bind the sulphur as manganese sulphide inclusions, to 1.0 to 1.3 percent in EN 8 M and 0.9 to 1.3 percent in EN 8 DM. These inclusions improve chip breaking but reduce transverse ductility and weldability.
Welding behaviour depends on the carbon equivalent. Using the midpoints of the EN 8 composition limits and the International Institute of Welding formula, carbon plus manganese over six plus chromium, molybdenum and vanadium over five plus nickel and copper over fifteen, the carbon equivalent is about 0.53. Values above roughly 0.45 require preheating, low-hydrogen consumables and controlled interpass temperature. EN 8 is therefore weldable when a controlled procedure is used. Welding without these controls can produce untempered martensite in the heat-affected zone. Welding a hardened and tempered bar without post-weld tempering also removes the specified heat treatment locally. Stockholder guidance identifies a practical section threshold of around 18 mm, above which post-weld heat treatment is required to prevent cracking.
Applications
EN 8 is used for shafts, spindles, studs, keys, keyways, axles, machine tool parts, lightly loaded gears, bolts, tie rods and pins. It also serves in turned and milled components that carry load without high contact stress. Components with guide surfaces or cam faces may receive local flame hardening where a hard track is required on a tough body.
Where EN 8 is not the right choice
EN 8 is unsuitable for heavy sections that require uniform through-section hardness. Its composition does not provide sufficient hardenability for the centre of a thick quenched bar to reach the surface hardness. Such a part can yield through a soft core while satisfying a surface hardness test. Longer soaking or a colder quench does not correct this limitation. EN 19 provides the usual alloyed alternative. EN 24 applies to heavier sections or applications that require toughness at strength.
EN 8 is also unsuitable when the design requires a hard, wear-resistant case over a tough core. It can receive local surface hardening, but its core carbon content is too high for effective carburising. EN 36C and SAE 8620 belong to the appropriate case-hardening grade family. EN 8 has no corrosion resistance. Wet or humid service requires protection by paint, plating or oil. A martensitic stainless steel such as AISI 410 or 420 is appropriate when corrosion exposure rather than mechanical load controls material selection.
Other carbon steel grades
Reviewed 2026-08-18. Composition from the Laxcon Steels grade reference, which covers 500+ grades: see EN 8 in the full table, the carbon steel family, or the equivalents reference.