Carbon steel flat bar is the rectangular-section bar stock that shows up in fabricating shops, structural assemblies, machinery frames, brackets, gussets, and tool-and-die work. It cuts cleanly, drills cleanly, welds cleanly, and welds back into assemblies without surprises. Huaxia-Steel ships hot-rolled flat bar directly from the mill, in the standard rectangular sizes and the project-specific mill-direct cuts most fabrication shops actually order. Same shipping chain as our other bar and plate products: mill-direct pricing, dual-certified standard coverage, and the MTC chain your QA team expects.
Product Overview
Flat bar is produced by hot-rolling a rectangular billet or coil edge through a succession of stands until the desired width and thickness are achieved. The hot-rolled surface carries a thin mill-scale layer; further surface treatments — pickled, cold-drawn, machined, polished — are applied downstream according to the end use. Flat bar is sold by its width (across the flat) and thickness (the rolled dimension). Length is usually 6 m or 12 m, cut-to-length available on order.
Typical applications include:
- Steel structures: bracing, gusset plates, base plates, ladder rungs.
- General fabrication: brackets, supports, frame elements, machine bases.
- Industrial equipment: clamps, fixtures, wear strips, cutting edges.
- Construction: stairs, handrails, ladder cages, balcony frames.
- Tool-making: rule die blanks, blade bodies, knife blanks, tool shanks.
- Forging stock: reheat and forge into finished forged parts.
- Plates and welding applications: assembly backing, weld-prep backing strips.
Specifications
| Attribute | Typical Range |
|---|---|
| Section shape | Rectangular, sharp corners or slight radius; rolled edges |
| Width | 10 mm to 200 mm (intermediate sizes on request) |
| Thickness | 3 mm to 50 mm (above 50 mm treated as plate; see plate product page) |
| Length | Standard 6 m, 9 m, 12 m; cut-to-length 1-12 m |
| Steel grade | Q195, Q235, Q275, Q345, Q355, SS400, A36, S235JR, S275JR, S355JR, A572 Gr.50, SAE 1018, SAE 1020, SAE 1045 |
| Surface condition | Hot-rolled black (mill scale), hot-rolled + shot-blasted, pickled + oiled, cold-drawn to size |
| Edge condition | Mill edge (slight radius), slit edge (square cut), deburred on request |
| Mill test certificate | EN 10204 3.1 mill cert; 3.2 independent witness on request |
| Width tolerance | +/- 1.5 mm for hot-rolled; +/- 0.3 mm for cold-drawn |
| Thickness tolerance | +/- 0.3 mm at 6 mm; +/- 0.5 mm at 10 mm; +/- 1.0 mm at 25 mm; +/- 1.5 mm at 50 mm (per EN 10058 / ASTM A6) |
| Length tolerance | + 50 mm / 0 mm for mill lengths; +/- 2 mm for cut-to-length |
| Straightness | 1 mm / m or 2 mm / m typical |
| Bundle packaging | Strapped bundles, plastic sleeve, six-sided wrap on heavy export orders |
Standard Sizes and Stock
The table below captures the most common size range we ship ex-stock. Other sizes can be mill-direct scheduled with 30-45 days FOB from order entry.
| Width x Thickness (mm) | Length | Stock Status |
|---|---|---|
| 20 x 3, 20 x 5, 20 x 6, 20 x 8, 20 x 10 | 6 m | Ex-stock |
| 25 x 3, 25 x 5, 25 x 6, 25 x 8, 25 x 10 | 6 m | Ex-stock |
| 30 x 3, 30 x 5, 30 x 6, 30 x 8, 30 x 10, 30 x 12 | 6 m | Ex-stock |
| 40 x 4, 40 x 5, 40 x 6, 40 x 8, 40 x 10, 40 x 12 | 6 m | Ex-stock |
| 50 x 5, 50 x 6, 50 x 8, 50 x 10, 50 x 12, 50 x 16 | 6 m / 12 m | Ex-stock |
| 60 x 5, 60 x 6, 60 x 8, 60 x 10, 60 x 12, 60 x 16 | 6 m / 12 m | Ex-stock |
| 75 x 6, 75 x 8, 75 x 10, 75 x 12, 75 x 16 | 6 m / 12 m | Ex-stock |
| 80 x 6, 80 x 8, 80 x 10, 80 x 12, 80 x 16, 80 x 20 | 6 m / 12 m | Ex-stock |
| 100 x 6, 100 x 8, 100 x 10, 100 x 12, 100 x 16, 100 x 20, 100 x 25 | 6 m / 12 m | Ex-stock |
| 120 x 8, 120 x 10, 120 x 12, 120 x 16, 120 x 20, 120 x 25 | 12 m | Mill-direct |
| 150 x 10, 150 x 12, 150 x 16, 150 x 20, 150 x 25 | 12 m | Mill-direct |
| 200 x 10, 200 x 12, 200 x 16, 200 x 20, 200 x 25, 200 x 30 | 12 m | Mill-direct |
Standards and Grade Coverage
| Standard | Grade | Yield (MPa) | Tensile (MPa) | Elongation | Typical Use |
|---|---|---|---|---|---|
| GB/T 700 | Q235 | 235 | 370-500 | 26 % | General structural |
| GB/T 700 | Q275 | 275 | 410-540 | 22 % | Higher strength structural |
| GB/T 1591 | Q345 | 345 | 470-630 | 21 % | Heavy structural, machinery |
| GB/T 1591 | Q355 | 355 | 470-630 | 22 % | EN-equivalent structural |
| ASTM A36 | A36 | 250 | 400-550 | 23 % | General structural |
| ASTM A572 | Gr.50 | 345 | 450 min | 21 % | High-strength low-alloy |
| EN 10025-2 | S235JR | 235 | 360-510 | 26 % | EU general structural |
| EN 10025-2 | S275JR | 275 | 410-560 | 23 % | EU higher strength |
| EN 10025-2 | S355JR | 355 | 470-630 | 22 % | EU heavy structural |
| JIS G3101 | SS400 | 245 | 400-510 | 21 % | General structural |
| SAE J403 | 1018 | 220 | 400 | 25 % | Machining, case-hardening |
| SAE J403 | 1020 | 240 | 430 | 22 % | Machining, welding |
| SAE J403 | 1045 | 310 | 565 | 16 % | Heat-treated applications |
Surface Conditions Explained
Hot-rolled black (as-rolled mill scale)
The standard finish on most flat bar shipments. Black mill scale is a thin oxide layer formed during the rolling process; it gives modest atmospheric corrosion resistance but is generally removed for further processing. Most structural applications accept as-rolled.
Hot-rolled + shot-blasted
Mill scale removed mechanically by steel-shot blasting. Provides a clean, slightly rough grey finish ready for painting or galvanizing.
Pickled + oiled (P&O)
Mill scale removed by acid pickling (sulfuric or hydrochloric bath), then neutralized and coated with a rust-preventive oil. P&O flat bar is the standard for downstream cold-drawing and machining.
Cold-drawn to size (rectangular)
Flat bar drawn through dies for tighter dimensional tolerance, smoother finish, and higher mechanical strength. Cold-drawn flat bar typically has +/- 0.05-0.2 mm tolerance on thickness and width. Tensile and yield rise by 20-40 % compared to hot-rolled. Suitable for precision parts where close tolerance and surface finish are critical.
Turned and polished (ground flat stock)
For tool-room applications, flat bar can be supplied as precision-ground stock with very tight thickness tolerance (typically +/- 0.025 mm), machined edges, and a polished finish. Often sold as “precision flat stock” or “ground flat stock” per ASTM A109 or similar.
Quality Assurance
Each shipment ships with a mill test certificate (EN 10204 3.1 as standard; 3.2 with independent witness on request), traceable to heat number and bundle. Each bundle carries a label with heat number, grade, size, length, and piece count.
- Chemistry: C, Mn, Si, P, S verified per heat.
- Tensile: yield, ultimate, elongation per ASTM A370 / ISO 6892-1.
- Dimensional: width, thickness, length, straightness, edge radius on every bundle.
- Visual: surface defects, decarburization (on heat-treated grades), and edge condition.
- Decarburization: check on cold-drawn and ground-flat-stock products when specified.
- UT / MT: ultrasonic or magnetic-particle examination available for higher-strength grades.
Applications and Engineering Notes
Steel stair stringers and handrails: 75 x 6 mm or 100 x 8 mm Q235/A36 in 6 m lengths is the typical stair-stringer and railing flat bar. Hot-rolled + shop-painted is the standard route for visible surfaces.
Cutting edges and blade bodies: 1018 or 1020 in cold-drawn 25 x 6 mm or 50 x 10 mm is the standard rule-die and knife-blank blank stock for heat treatment and grinding downstream.
Heavy structural reinforcement: Q345/S355JR/A572 Gr.50 flat bar in 100 x 12 mm to 200 x 25 mm is the high-strength reinforcement for crane boom sections, trailer chassis, and mining equipment.
Machine tool bases and bed plates: Annealed or normalized flat bar in Q235/Q275 at 50 x 12 mm and above serves as foundation stock for machine bases, welded into fabricated frames.
Forging stock: SAE 1045 in 50 x 50 mm to 150 x 150 mm hot-rolled black feeds the forging industry for blanking and upsetting. We commonly stock 1045 in cut lengths with MTC.
Galvanized and architectural: Pre-galvanized flat bar (sheet-fed, like the square tube process) is available for trim, support, and exposed architectural framing. Cold-drawn and zinc-plated for fasteners (per ASTM A108).
Ordering Information
When requesting a quotation, please specify:
- Width and thickness (or thickness x width; flat bar is usually called by width).
- Length in meters.
- Steel grade (Q235 / S235JR / A36 / SAE 1020 / etc.).
- Surface condition: hot-rolled black, shot-blasted, pickled + oiled, cold-drawn, ground flat stock.
- Edge condition: mill edge, slit edge, deburred.
- Tolerance (standard mill tolerance, or tighter). Cold-drawn is significantly tighter than hot-rolled.
- Special requirements: decarburization limit, ultrasonic test, sub-size impact test.
- Mill test certificate level: 3.1 or 3.2.
- Packaging and marking: bundle size, container vs. break-bulk.
- Quantity in metric tons.
- Destination port and Incoterm.
Packaging and Shipment
- Container: 20-ft container accommodates roughly 22-26 metric tons; 40-ft HC holds roughly 25-28 metric tons for short lengths; heavier flat stock tends to be break-bulk or in 40-ft HC bundles.
- Break-bulk: strapped bundles with steel banding, plastic sleeve, corner protection, six-sided wrap on heavy export orders.
- Lead time: ex-stock sizes ship 7-15 working days after order. Mill-direct sizes ship 20-35 working days.
- Documents: commercial invoice, packing list, MTC, country of origin, B/L, insurance, and any FTA certificate requested.
Frequently Asked Questions
What is the difference between “mill edge” and “slit edge”?
Mill edge is the as-rolled edge with a slight natural radius. Slit edge is square-cut from a wider coil, giving a sharper corner but slightly rougher surface. For visible architectural applications, request slit-edge deburred.
How precise is cold-drawn flat bar?
Cold-drawn flat bar typically runs +/- 0.05-0.2 mm tolerance on thickness and width depending on size. Tensile and yield rise 20-40 % over hot-rolled because of work hardening. For precision applications like hydraulic packings, jigs, or tool shanks, cold-drawn is the standard.
Is hot-rolled flat bar suitable for welding?
Yes. Most low-carbon and medium-carbon flat bar grades (Q235, A36, S275JR, SAE 1020) weld cleanly with conventional E7018 or ER70S-6 consumables. Higher-carbon grades (SAE 1045) require preheating and post-weld stress relief.
What is the typical MOQ on a mill-direct size?
Around 5-10 metric tons for cold-drawn sizes; 15-25 metric tons for hot-rolled non-stock thicknesses. Below MOQ, we may ship from stock-warehouse with a small premium.
Can you dual-certify ASTM and EN grades?
Yes. Many of our flat bar grades are dual-certified (ASTM A36 + EN S235JR; ASTM A572 Gr.50 + EN S355JR; SAE 1020 + EN 1C20). One heat number covers both standards’ requirements.
Can you supply flat bar with holes or special cuts?
We can supply flat bar with end cropping and miter cuts; complex hole patterns and machined features are sourced through a downstream fabricator and consolidated at our facility. Please share drawings for evaluation.
Request a Quotation
Send your size list, grade, surface condition, and destination port to [email protected]. We return a mill-direct offer with MTC, packaging, and the lead time you can schedule into your project’s procurement plan.
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