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Help CenterFlat Steel & Flat Steel Bar，Q195、Q235A、Q235B、Q355A、Q355B、SS400
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1. Product Overview
Flat Bar (Flat Steel) refers to rectangular solid steel bar with smooth blunted edges, divided into hot rolled flat bar and cold drawn precision flat bar, stainless steel grades are excluded. Manufactured via high-temperature hot rolling of steel billets or cold drawing of wire rods, it features neat cross-section and burr-free edges with excellent performance for welding, bending, punching and cutting. It serves as universal basic section steel for steel structures, machinery fittings, guardrails, earthing strips and embedded parts, and can also act as blanks for welded pipes and thin plate rolling.
Production Process
Hot Rolled Flat Bar: Steel billet heating → Multi-pass vertical hot rolling → Cooling & straightening → Cut to fixed length → Full dimensional & visual inspection → Marking & bundling
Cold Drawn Flat Bar: Hot rolled wire rod / small flat blank → Pickling, phosphating & lubrication → Multi-pass cold drawing finishing → Optional annealing → Cut & surface polishing
2. Executive Standards & Main Material Grades
2.1 Applicable Standards
GB Hot Rolled Standard: GB/T 704 Dimensions, Shape, Weight and Tolerance of Hot Rolled Flat Steel
GB Cold Drawn Standard: GB/T 905 Cold Drawn Round, Square and Flat Steel
Carbon Structural Steel: GB/T 700; HSLA Steel: GB/T 1591; Quality Carbon Steel: GB/T 3077
ASTM Standard: ASTM A36, ASTM A572 Gr50
EN Standard: EN 10025 (S235JR, S355JR)
JIS Standard: JIS G3101 (SS400)
2.2 Common Grades & Service Conditions
| Grade | Material Type | Mechanical Features | Core Applications |
|---|---|---|---|
| Q235B / S235JR / SS400 / A36 | Mild Carbon Steel | Cost-effective, easy machining | Building supports, guardrails, earthing strips, simple machinery bases, fences |
| Q355B / S355JR / A572 Gr50 | HSLA High Strength Steel | High yield strength, heavy load capacity | Bridge stiffeners, heavy-duty equipment bases, steel structure connecting plates, vehicle parts |
| 20# / 35# / 45# Quality Carbon Steel | Medium Carbon Machining Steel | Quench-temperable, wear resistant | Machine tool guide rails, mold base plates, gear blanks, fastener blanks |
3. Supply Specifications & Dimensional Parameters
3.1 Size Range (Marked as Width × Thickness, Unit: mm)
Width: 12mm–300mm; regular stock: 20/30/40/50/60/80/100/120/150mm
Thickness: 3mm–60mm; regular stock: 3/4/5/6/8/10/12/14/16/20mm
Standard fixed length: 6m, 9m, 12m; custom non-standard length 1–12m available
Bundle weight: 2–5 tons per bundle; 24–29 tons loading capacity per 40HC container
Side Edge: Hot rolled blunted edge; cold drawn precision right-angle edge, burr-free
3.2 Dimensional Tolerance
Hot rolled flat bar adopts negative tolerance rolling: width tolerance ±0.5mm for width ≤100mm, ±0.8mm for width＞100mm; thickness tolerance ±0.2~±0.6mm. Straightness ≤2mm/m for hot rolled, ≤0.8mm/m for cold drawn precision flat bar; camber and twist strictly controlled for automatic cutting lines.
3.3 Theoretical Weight Formula
Weight per meter (kg/m) = Width(mm) × Thickness(mm) × 7.85 ÷ 1000
4. Delivery Condition & Optional Surface Treatments
Hot Rolled Black Finish: Economical base type with uniform mill scale, ready for painting or galvanizing
Shot Blasted & Pickled Bright Finish: Scale-free clean grey surface, no polishing required before welding & spraying
Cold Drawn Bright Precision Finish: Ultra-high dimensional accuracy, smooth surface for direct assembly without machining
Hot-dip Galvanized Flat Bar: Zinc coating ≥85μm, superior salt spray resistance for outdoor guardrails, power earthing and coastal anti-corrosion projects
5. Standard Mechanical Properties
1. Q235B Mild Carbon Flat Bar
Min Yield ReL≥235MPa, Tensile Rm 370–500MPa, Min Elongation A≥26%, no cracks or delamination after 180° cold bend test
2. Q355B HSLA High Strength Flat Bar
Min Yield ReL≥355MPa, Tensile Rm 470–630MPa, Min Elongation A≥21%, anti-deformation under heavy load
3. 45# Medium Carbon Flat Bar
Min Yield≥355MPa, Min Tensile≥600MPa, can be quenched & tempered to improve hardness for wear-resistant machinery parts
6. Core Product Advantages
High Material Utilization: Negative tolerance rolling reduces cutting loss compared with steel plate, less secondary processing & lower raw material cost
Comprehensive Machinability: Suitable for bending, roll forming, plasma/laser cutting, drilling, stamping and welding for all manufacturing industries
Neat Cross-section & Smooth Edges: Vertical hot rolling eliminates collapsed sides and burrs, no secondary edge trimming needed
Complete Strength Grades: Mild carbon, HSLA and medium carbon options for light decorative to heavy load applications
Diverse Anti-corrosion Options: Black mill scale, pickled bright, cold drawn polished, hot-dip galvanized finishes fit indoor, open-air and coastal corrosive environments
Dual-purpose Raw Material: Used directly as finished structural parts or blanks for welded pipe & thin plate rolling
7. Main Application Fields
7.1 Building & Steel Structure Engineering
Steel structure connecting plates, factory support brackets, embedded fixing parts, stair stiffener plates, secondary purlin materials
7.2 Power & Municipal Works
Substation earthing strips, photovoltaic support connectors, transmission tower reinforcement plates, road guardrails, isolation fences
7.3 Machinery & Equipment Manufacturing
Machine tool bases, guide rails, fixture base plates, agricultural machinery parts, forklift accessories, stamping blanks
7.4 Bridge & Transportation
Bridge stiffeners, bearing base plates, carriage frames, road anti-collision reinforcement components
7.5 Hardware & Deep Processing Blanks
Welded pipe blanks, small stamping parts, storage rack supports, door & window reinforcing strips
8. Packaging, Marking & Delivery Terms
Seaworthy Export Packaging: Neatly stacked flat bars tightly bundled with multi-layer high-strength steel strips, iron corner protectors fitted at both ends to avoid collision scratches. Galvanized flat bars fully wrapped by waterproof plastic film and tarpaulin, placed on wooden skids for moisture proof.
Product Marking: Paper tag attached to each bundle marked with grade, width×thickness dimension, fixed length, heat number, executive standard and net weight. Original complete Mill Test Certificate (MTC) delivered with each shipment.
Lead Time: 5–7 days for standard hot rolled stock; 7–12 days for customized cold drawn precision, hot-dip galvanized and special length flat bar.
Logistics & Shipment: Loading at Tianjin Port, full truck or 40HC container export, FOB Tianjin / CFR / CIF trade terms acceptable.
9. Storage, Machining & Operation Precautions
Warehouse must be dry and ventilated; cover with waterproof tarpaulin for outdoor storage. Long-term rain exposure causes zinc layer peeling on galvanized flat bar.
Store separately by dimension and grade, place on wooden skids to avoid surface scratch and rust from ground moisture.
Avoid heavy pressure stacking for cold drawn precision flat bar to prevent bending deformation and assembly tolerance deviation.
Remove mill scale and anti-rust oil before welding to guarantee pore-free, sound weld joints.
Prioritize hot-dip galvanized flat bar for long-term outdoor and coastal projects to extend anti-corrosion service life by 5–10 years.
Quench & temper heat treatment is recommended for 45# medium carbon flat bar used in wear-resistant components to boost hardness and abrasion resistance.
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