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Help CenterFlat Steel & Flat Steel Bar，20×3、25×4、30×4、40×4、40×5、50×5、50×6、60×6、80×8、100×10
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1. Basic Product Definition
Flat bar is long shaped steel with standard rectangular cross-section and slightly blunt edges. Its specification is uniformly marked as width × thickness (mm), such as 40×4, 50×6. The density is 7.85g/cm³ and goods are delivered by theoretical weight. It is split into hot rolled flat bar and cold drawn flat bar. Featuring neat cross-section and superior processing performance, it is a universal basic section steel for construction, electric power and machinery industry. It can be used as finished products directly or blanks for welded pipes and thin steel sheets.
2. Applicable Standards
Domestic National Standards
GB/T 704-2016 Hot Rolled Flat Bars — Dimensions, Shape, Weight and Permissible Deviations
GB/T 3078-2014 Cold Drawn Structural Steel Products
GB/T 700 for carbon structural steel Q235B, GB/T 1591 for high strength low alloy steel Q355B
International Export Standards
ASTM A36, EN10025 S235JR/S355JR, JIS G3101 SS400, DIN 17100
3. Specification Parameters
Dimension Range
Width: 12mm–300mm
Thickness: 3mm–60mm
Standard fixed lengths: 6m, 9m, 12m; custom lengths like 2m/3m/10m or arbitrary cutting lengths are available
Regular Common Sizes
20×3, 25×4, 30×4, 40×4, 40×5, 50×5, 50×6, 60×6, 80×8, 100×10
Delivery Form
Supplied in straight fixed-length bars; small sizes can be provided in coils. Pre-processing services including cutting, punching and bending are available upon customers’ demand.
4. Common Grades & Chemical Composition
Q235B (General grade for construction & earthing)
C≤0.22%, Si≤0.35%, Mn≤1.40%, S≤0.045%, P≤0.045%
Q355B (High strength for load-bearing structures)
Low carbon low alloy steel with increased manganese content, better low-temperature toughness, suitable for bridges and equipment bases.
45# / 40Cr (Machining parts for quenching & tempering)
Medium carbon steel with high hardness and strength after heat treatment, used as blanks for molds, shafts and mechanical accessories.
Surface treatment types
Black hot rolled flat bar, hot-dip galvanized flat bar, electro-galvanized flat bar, polished bright flat bar
5. Core Mechanical Properties
Q235B Hot Rolled Flat Bar
Yield Strength Re ≥235MPa
Tensile Strength Rm: 370–500MPa
Elongation after fracture A ≥22%
Advantages: good ductility, easy welding, no cracks during cold bending, stable conductivity
Q355B High Strength Flat Bar
Minimum yield strength reaches 355MPa. Smaller cross-section can be adopted under the same bearing capacity, with excellent impact resistance and low-temperature performance.
6. Complete Production Process
Steel billet heating → High-temperature rough and finish rolling to form hot rolled flat bar / Cold drawing processing from wire rod for cold drawn flat bar → Straightening and fixed-length cutting → Surface grinding or galvanizing treatment → Random inspection of dimension and mechanical property → Bundling, marking and warehousing
7. Product Classification
By Production Process
Hot Rolled Flat Bar: Ample stock, cost-effective, specially used for engineering structures, earthing and lightning protection
Cold Drawn Flat Bar: High dimensional precision and smooth surface, applied for precision mechanical accessories
By Surface Treatment
Black Finish Flat Bar: Original oxidized surface with the lowest cost
Hot-dip Galvanized Flat Bar: Thick zinc coating, anti-corrosion for outdoor and earthing projects
Electro-galvanized Flat Bar: Thin zinc coating for indoor rust prevention and decoration
Polished Bright Flat Bar: Smooth appearance for hardware decorative components
By Material & Application
Ordinary carbon flat bar, high strength low alloy flat bar, medium carbon flat bar for machinery, stainless steel flat bar
8. Product Advantages
Standard size with tiny tolerance, uniform width, thickness and length, reducing processing loss without massive secondary cutting
Excellent comprehensive processing performance: weldable, bendable, punchable, drillable and cuttable, fit for all processing scenarios
Stable conductive performance; galvanized versions resist acid and alkali, hardly rust under long-term outdoor service
Full range of specifications with sufficient stock, supporting customized size, galvanization and pre-processing
Complete export certificates, shipped from Tianjin Port with full set of material documents for customs clearance
9. Main Application Fields
Steel structure construction: Purlin, support bracket, embedded parts, guardrail, stair treads for workshops
Electric power lightning protection engineering: Earthing flat bar, lightning strip, conductive connecting parts for iron towers
Machinery manufacturing: Equipment base, connecting rod, fixture, tool blanks, agricultural machinery accessories
Transportation infrastructure: Bridge reinforcement parts, vehicle frames, small marine structural components
Municipal hardware: Storage racks, pipe supports, fences, raw materials for fasteners
10. Surface Quality & Packaging
Surface Standard
No cracks, folds, delamination or severe scarring on surface; slight iron oxide scale is acceptable; zinc coating is uniform without peeling; flat cutting ends free of burrs.
Packaging Methods
Conventional straight bars: 2–3 tons per bundle, fastened with multiple steel straps. Metal tags hung on both ends marked with specification, grade, heat batch number and weight
Export sea freight package: Wrapped with waterproof plastic cloth and rainproof tarpaulin, moisture-proof agent can be added to avoid rust during sea transportation
Galvanized flat bars are packed separately with isolation protection to prevent scratch on zinc coating
11. Delivery Supporting Information
Loading Port: Tianjin Port, Lead Time: 5–7 working days
Payment Term: 30% TT advance deposit + 70% balance against copy of Bill of Lading
Attached Documents: Original mill test certificate, factory inspection report, Certificate of Origin (CO), FTA Certificate of Origin are available
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