Black steel bars: round, flat, square and hexagonal
Black steel bar is the solid carbon steel long product behind machined parts, brackets, shafts, forgings and fabricated frames, supplied round, flat, square and hexagonal. ULAMEX supplies merchant and engineering bar in S235JR and S275JR, hot-rolled and bright cold-drawn, to EN 10025-2 and EN 10277, with a 3.1 certificate on request. This guide covers the forms, the black and bright conditions, grades, standards, uses and protection.
What black steel bar is
Black steel bar is solid carbon steel rolled or drawn into a straight length, used wherever a solid section is machined, forged, bent or welded rather than a hollow tube or a flat plate. The term black refers to the dark mill-scale surface a hot-rolled bar carries, uncoated and ready to be worked. It is the everyday workshop material for supports, brackets, pins, shafts and machined parts, cheaper and stronger for the price than stainless, and used wherever corrosion is controlled by a coating or a dry environment rather than by the metal itself.
Bar forms
| Form | Typical use |
|---|---|
| Round bar | Shafts, pins, axles, spacers, turned and forged parts |
| Flat bar | Supports, brackets, base plates, frames and edging |
| Square bar | Frames, gates, grilles, machined and decorative parts |
| Hexagonal bar | Nuts, fasteners and machined fittings |
Round and flat bar are the most widely used, for shafts, supports and general fabrication, while square bar suits gates and frames and hexagonal bar is the stock for nuts and fittings.
Black and bright bar
Carbon bar is supplied in two conditions, and the choice depends on the surface and the tolerance the part needs.
| Condition | Character and use |
|---|---|
| Black (hot-rolled) | Dark mill-scale surface, looser tolerance, economical for general and structural work |
| Bright (cold-drawn) | Smooth scale-free surface, tighter tolerance, for machining and close-fit parts |
| Peeled / ground | Larger round bar turned or ground to a clean, accurate diameter |
Bright cold-drawn bar is drawn through a die to a smooth surface and a close size, so it is used where the part is machined or fitted; black hot-rolled bar is the economical choice for general fabrication, forging and welded work.
Grades for black steel bar
Bar is supplied in structural, engineering and free-cutting grades, and the grade is matched to the job.
| Grade | Best for |
|---|---|
| S235JR (1.0038) | General structural and fabrication bar |
| S275JR (1.0044) | Higher-strength structural bar |
| C45 (1.0503) | Engineering bar for shafts and harder-wearing parts |
| 11SMn30 (1.0715) | Free-cutting bar for high-volume machined parts |
S235JR is the everyday mild steel bar, S275JR the higher-strength structural choice, C45 a medium-carbon engineering grade for shafts and wear parts, and free-cutting 11SMn30 for parts turned in volume. For the full structural grade detail see our guide to structural steel S235, S275 and S355.
Standards and tolerances
Black steel bar is supplied to a material grade and a dimensional tolerance standard for each form.
| Standard | Scope |
|---|---|
| EN 10025-2 | Grades and delivery conditions for non-alloy structural steel |
| EN 10277 | Technical delivery conditions for bright (cold-drawn, peeled, ground) bar |
| EN 10060 | Tolerances for hot-rolled round bar |
| EN 10059 | Tolerances for hot-rolled square bar |
| EN 10061 | Tolerances for hot-rolled hexagonal bar |
| EN 10058 | Tolerances for hot-rolled flat bar |
State the grade, form, dimensions and condition (black or bright) with an enquiry, add the tolerance class and the 3.1 certificate requirement where the part needs them, so the delivered bar matches the part.
How to specify black steel bar
Round bar is specified by diameter, flat bar by width and thickness, square bar by side, and hexagonal bar by across-flats size, all supplied in standard mill lengths. Give the grade, form and dimensions, state black or bright, and add the tolerance class and any certificate requirement. Stating the condition matters as much as the size, because black bar and bright bar of the same nominal dimension differ in surface and tolerance, and the machinist or fabricator works to that.
Bar weight and pricing
Steel bar is priced and shipped by weight, so the mass per metre matters for both cost and handling. Carbon steel has a density of about 7.85 g/cm3, which gives a round bar a mass of roughly 0.00617 times the diameter in millimetres squared, in kilograms per metre. A 20 mm round bar is about 2.47 kg/m, and a 40 mm round bar about 9.87 kg/m. Flat bar mass in kilograms per metre is the width times the thickness in millimetres times 0.00785, so a 40 by 10 mm flat is about 3.14 kg/m. Give the dimensions and lengths with an enquiry and the desk returns the weight and the price together.
Applications
Black steel bar is the general-purpose solid stock of the workshop. Fabricators use flat and square bar for supports, brackets, frames, gates, grilles and edging, and round bar for pins, spacers and balustrade parts. Machine shops turn bright and engineering bar into shafts, axles, spacers, bushes and fittings. Forges heat round and square bar to make hooks, brackets and forged components. Construction uses flat and round bar for cleats, ties, brackets and fixings within steel frames, and blacksmiths use square and round bar for gates, railings and ironwork.
Machining and forging bar
Carbon bar machines and forges more easily than stainless. Bright cold-drawn bar machines cleanly, free-cutting 11SMn30 suits high-volume turning, and medium-carbon C45 gives harder, more wear-resistant shafts and can be heat treated. For forging, hot-rolled round and square bar is heated and worked to shape. Bar is drilled and welded with standard mild-steel filler, so it fabricates with ordinary workshop equipment, without the tooling and contamination precautions that stainless needs.
Protecting black steel bar
Bare carbon bar rusts, so any bar left exposed or damp is protected. Indoor dry parts can be primed or oiled; exposed parts are painted over a cleaned and primed surface, or hot-dip galvanised for long-life outdoor protection. Bright bar is often supplied lightly oiled to hold its finish in storage. Where galvanising is chosen, see our guide to galvanised steel. Where the part must resist corrosion without a coating, a stainless steel bar is the alternative.
Black steel versus stainless bar
Black carbon bar and stainless bar suit different jobs. Carbon bar is cheaper, stronger for the price and easier to machine, forge and weld, so it is the default for structural, machined and fabricated parts where corrosion is handled by a coating. Stainless bar resists corrosion in the metal itself, so it is chosen for food, marine, chemical and visible parts that must not rust and cannot be coated. Many projects use both, carbon bar for the hidden and coated work and stainless where corrosion or hygiene demand it. ULAMEX supplies both from one source.
Black steel bars from ULAMEX
ULAMEX has supplied carbon steel since 1988, and bar is a core part of the range.
| What you get | Detail |
|---|---|
| Forms | Round, flat, square and hexagonal bar |
| Conditions | Black (hot-rolled), bright (cold-drawn), peeled and ground |
| Grades | S235JR, S275JR, C45 and free-cutting 11SMn30 |
| Standards | EN 10025-2 and EN 10277, with EN 10058, 10059, 10060 and 10061 tolerances |
| Terms | 3.1 certificate on request, no minimum order on stocked SKUs, dispatch 2 to 7 working days |
Need black steel bar for a project? Send the grade, form, dimensions and condition, and ULAMEX will return a non-binding quotation. See our guides to structural sections and stainless steel bar, and our supply capabilities, or contact the export desk at [email protected] or +48 504 424 761.
Frequently asked questions
What is the difference between black and bright bar?
Black bar is hot-rolled with a dark mill-scale surface and a looser tolerance, and suits general and structural work. Bright bar is cold-drawn to a smooth, scale-free surface and a tighter tolerance, and is used for machining and close-fit parts.
What forms is black steel bar available in?
Round, flat, square and hexagonal. Round and flat bar are the most widely used, square bar suits gates and frames, and hexagonal bar is the stock for nuts and fittings.
What grades is black steel bar available in?
S235JR and S275JR structural grades, C45 medium-carbon engineering bar, and free-cutting 11SMn30 for high-volume machined parts. S235JR is the everyday mild steel bar.
Does black steel bar rust?
Yes, bare carbon bar rusts, so exposed or damp bar is protected by priming, painting or hot-dip galvanising. Bright bar is often lightly oiled for storage. Where a part must resist corrosion without a coating, stainless bar is the alternative.
What standards apply to black steel bar?
Grades to EN 10025-2, bright products to EN 10277, and hot-rolled tolerances to EN 10060 (round), EN 10059 (square), EN 10061 (hexagonal) and EN 10058 (flat).
Does black steel bar come with a material certificate?
Yes. A 3.1 inspection certificate to EN 10204 is supplied on request, giving the cast analysis and mechanical properties for traceability, with no minimum order quantity on stocked SKUs.
Which bar is best for machining?
Bright cold-drawn bar for clean, close-tolerance machining, free-cutting 11SMn30 for high-volume turning, and C45 where the finished shaft needs to be harder and can be heat treated.
How much does steel bar weigh per metre?
Carbon steel is about 7.85 g/cm3, so a round bar weighs roughly 0.00617 times the diameter in millimetres squared, in kg/m: a 20 mm round is about 2.47 kg/m. A flat bar weighs width times thickness in millimetres times 0.00785, so a 40 by 10 mm flat is about 3.14 kg/m.