Two free-cutting steels, one key difference: carbon. 230M07, the BS 970 free-cutting grade, machines fastest and costs the least; EN8M trades a little machinability for medium-carbon strength and the ability to harden. Here is how to pick the right one for your turned components.
Both 230M07 and EN8M are free-cutting steels, so both turn and thread cleanly. The difference is carbon. 230M07 is low-carbon (0.15% C max), so it is softer, easier to cut and cheaper, which suits high-volume turned parts under modest load. EN8M carries far more carbon (0.35–0.45%), so it reaches medium-carbon strength and can be hardened in light sections, at some cost to machinability. Choose 230M07 when the part only has to be machined; choose EN8M when the same turned part must also carry a working load.
230M07 and EN8M are often shortlisted together because both are bought for one job: making turned parts quickly. Both have sulphur added to break the chip, so both belong to the free-cutting family rather than to plain structural steel. Where they part company is the carbon content, and carbon decides nearly everything else — strength, hardness, hardenability, and how fast the bar can be cut. Getting the choice right is the difference between paying for strength you do not need (and machining slower than necessary) and specifying a soft grade that bends or wears out under load. The sections below set the two side by side and give a step-by-step way to decide.
| Property | 230M07 | EN8M |
|---|---|---|
| Type | Free-cutting low-carbon (resulphurised) | Free-cutting medium-carbon (resulphurised) |
| Carbon (C) | 0.15% max | 0.35 – 0.45% |
| Manganese (Mn) | 0.90 – 1.30% | 1.00 – 1.40% |
| Silicon (Si) | 0.05% max | 0.05 – 0.35% |
| Sulphur (S) | 0.25 – 0.35% | 0.12 – 0.20% |
| Phosphorus (P) | 0.090% max | 0.06% max |
| Tensile strength | 370 – 480 N/mm² min (cold drawn, size-dependent) | 550 – 700 MPa normalised; higher when quenched & tempered |
| Hardness | ~126 – 180 HB (typical) | ~152 – 250 HB depending on condition |
| Hardenability | Not hardenable — carbon too low | Through-hardenable in small / light sections |
| Machinability | Highest — the free-cutting benchmark | High, but below 230M07 (more carbon to cut) |
| Weldability | Poor (high sulphur) | Poor (high sulphur + medium carbon) |
| Relative cost | Lower | Higher |
| BS 970 / equivalents | 230M07 (BS 970) · EN1A (equivalent) · AISI 1213 · 11SMn30 | 212M36 / EN8M · AISI 1140, 1146 · 36SMn14 |
| Typical applications | High-volume turned parts, fasteners, pins, bushes, fittings | Turned parts needing strength: spindles, studs, shafts, light-duty gears |
230M07 and EN8M are both supplied with a heat-wise mill test certificate. Mechanical figures are typical and condition-dependent.
In a free-cutting steel, sulphur and manganese form manganese-sulphide inclusions that break the chip — that is what both grades share. Carbon does something different: it controls how strong and hard the steel can become. With carbon capped at 0.15%, 230M07 stays soft however you treat it, which is exactly why it cuts so fast and finishes so cleanly, but also why it cannot be hardened and carries little load. EN8M, at 0.35–0.45% carbon, behaves like a medium-carbon EN8 with machinability added: it reaches higher strength in the normalised state and can be quenched and tempered in light sections to raise hardness further.
That extra carbon is not free. More carbon means a tougher cut, so EN8M machines a little slower and wears tooling faster than 230M07, and the bar costs more per tonne. The engineering question is therefore simple: is the part going to be stressed or hardened? If not, the carbon in EN8M is wasted money and lost machining speed. If yes, 230M07 is not strong enough and EN8M earns its place.
The reason to reach for EN8M over 230M07 is almost always load. 230M07, in the cold-drawn condition, gives a tensile strength of roughly 370–480 N/mm² minimum, rising as bar diameter falls, but that comes from work hardening during drawing, not from carbon, and it cannot be raised by heat treatment. Once you machine away the cold-worked surface, the core is soft. For a pin, a bush or a low-stress fitting that is fine; for a spindle or a stud that carries a real working load, it is not.
EN8M behaves like a medium-carbon EN8 with machinability added. In the normalised condition it reaches the medium-carbon strength band, and because it carries 0.35–0.45% carbon it can be quenched and tempered in light sections, or flame- and induction-hardened on a wear face, to lift hardness where the part needs it. That is the practical dividing line: if the drawing carries a hardness specification or a proof load, 230M07 is ruled out and EN8M, or a through-hardening alloy, is the answer. All mechanical values are condition-dependent and certified on the mill test certificate.
Both grades are bought to be machined, but 230M07 is the faster cut. It carries more sulphur (0.25–0.35% against EN8M's 0.12–0.20%) and far less carbon, so it sits at the top of the carbon-steel machinability scale and is one of the grades the industry uses as a 100% reference point. EN8M is still a free-cutting steel and machines well above a plain EN8, but its higher carbon makes the cut tougher and the rating lower.
On a single part the difference looks small. Across a production run it compounds: higher feeds and speeds, longer tool life between regrinds, fewer chip-clearance stoppages, and a cleaner thread finish all lower the cost per piece on 230M07. That is why high-volume turned work — fasteners, pins, connector bodies — defaults to 230M07 unless the part needs strength that only EN8M can give. Specify EN8M for what it adds in strength, not for machining, because in machining 230M07 is the faster, cheaper grade.
Ambhe Ferro rolls both grades in the forms that suit turned work — bright bar (cold drawn, or turned and polished), hexagon, and hot-rolled round. Bright bar runs from 22 to 63.5 mm, hexagons from 23.5 to 52.5 mm across flats, and rounds from 23.5 to 80 mm diameter; non-standard sizes are frequently available make-to-order. Standard length is 5–6 m, with cut-to-length on request, and the minimum order is 5 MT per size, with smaller quantities through approved stockists.
Every dispatch of 230M07 or EN8M carries a heat-wise mill test certificate, with third-party inspection (SGS, BV, TÜV) on request. If you are unsure which grade your component needs, send the drawing or the load and hardness requirement with your enquiry and we will recommend the grade before quoting. Full details are on the 230M07 steel reference page and the EN8M steel page.
Tell us the grade, form, size, and tonnage. Ambhe Ferro responds with pricing, availability, and lead time — and a mill test certificate on every heat.