EN3B is a low-carbon mild steel usually supplied as bright drawn or turned bar, with a clean surface and close size. It machines and welds easily and can be case hardened, but it is not hardened through. It is used for general engineering parts such as pins, spacers, bushes, brackets and lightly loaded shafts.
Quick facts
- Type
- Low-carbon mild steel
- Carbon
- About 0.15–0.25%
- Supply
- Bright drawn, turned or ground bar; also black bar
- Tensile strength
- About 400–560 MPa bright drawn
- Machinability
- Good; free-cutting EN1A machines faster
- Weldability
- Very good
Equivalent grades
| Standard | Grade |
|---|---|
| Old BS 970 | EN3B |
| BS 970 | 070M20 (close) |
| IS 1570 / IS 2062 bars | C15 / C20 (close) |
| AISI / SAE | 1018 / 1020 (close) |
| EN | C22 / 1.0402 (close) |
Equivalents are close, not identical. Name the grade and standard on the drawing.
Typical chemical composition
| Element | % |
|---|---|
| Carbon (C) | About 0.15–0.25 |
| Manganese (Mn) | About 0.5–0.9 |
| Silicon (Si) | Up to about 0.35 |
| Sulphur, phosphorus | 0.05 max each |
Values are typical. The exact limits depend on the standard and supplier; ask for the mill test certificate when it matters.
Typical uses
- Pins, spacers, bushes and collars
- Brackets, studs and fixtures
- Lightly loaded shafts and spindles
- Welded machine frames and parts
- Case-hardened parts that need a hard skin and soft core
EN3B or EN8?
| EN3B | EN8 | |
|---|---|---|
| Carbon | About 0.15–0.25% | About 0.35–0.45% |
| Strength | Lower | Higher |
| Hardening | Case hardening only | Can be hardened; induction hardening |
| Typical use | General parts, welded parts | Shafts, studs, gears |
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Questions
- Can EN3B be hardened?
- Not through-hardened in a useful way, because the carbon is too low. It can be case hardened (carburised) to give a hard surface on a soft, tough core.
- What is bright bar?
- Steel bar that has been cold drawn, turned or ground after hot rolling, so it has a clean, smooth surface and close size tolerance (often h9–h11). It saves machining.
- EN3B or EN1A for turned parts?
- EN1A is a free-cutting steel and machines much faster on CNC and automatic lathes, but welds poorly. EN3B suits parts that will be welded or need slightly better toughness.
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 18 October 2026.