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Help CenterFlat Steel & Steel Flat Bar，10#、20#、35#、45#、40Cr、42CrMo、20CrMnTi
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1. Product Definition & Overview
Flat steel bar is a long structural section steel with solid rectangular cross-section, whose width is obviously larger than thickness. It is mainly divided into hot rolled flat bar and cold drawn flat bar. Produced by high-temperature hot rolling or room-temperature precision cold drawing, it features neat vertical edges, stable uniform metallographic structure, outstanding weldability, bending, punching and cutting performance. It can be directly used as finished structural components or raw blanks for welded pipes and thin plates, widely adopted in steel structure construction, mechanical manufacturing, power grounding, guardrail engineering, shipbuilding and hardware processing industries as universal basic raw material.
2. Executive Standards
Chinese National Standards
GB/T 704-2016 Hot rolled flat steel – Dimensions, shape, mass and permissible deviations
GB/T 905 Cold drawn steel bars
GB/T 700 Carbon structural steels
GB/T 1591 High strength low alloy structural steels
GB/T 3077 Alloy structural steels
GB/T 13912-2022 Hot-dip galvanized steel products
International General Standards
ASTM A36 / A572 Gr50 Carbon & HSLA structural flat bar
EN 10025 S235JR, S355JR European structural steel standard
JIS G3101 SS400 Japanese general structural steel
ASTM A276 Stainless steel flat bar specification
3. Product Classification
3.1 Classification by Production Process
(1) Hot Rolled Flat Steel Bar
Heated steel slabs are formed through multi-pass high-temperature rolling, laminar cooling and straightening. With mill black oxide surface, moderate cost and full-size stock availability. Suitable for general structural frames, embedded parts, guardrails and subsequent painting/galvanizing treatment.
(2) Cold Drawn Bright Flat Steel Bar
Hot rolled blanks are pickled for descaling then precision cold drawn at room temperature. Ultra-precise dimension tolerance, smooth bright surface without oxide scale, no secondary polishing required. Mainly applied to precision machinery parts, mold accessories and high-finish assembly components.
3.2 Classification by Material Grade
Mild Carbon Flat Bar: Q195, Q235B, A36, SS400, S235JR Soft, excellent weldability, cost-effective for civil construction, ordinary supports and grounding strips.
High Strength Low Alloy Flat Bar: Q355B/C/D, A572 Gr50, S355JR High yield strength, strong impact resistance, suitable for heavy-load frames, bridge components and marine engineering structures.
Medium & High Carbon Alloy Flat Bar: 20#, 35#, 45#, 40Cr, 65Mn High hardness and wear resistance, used for machinery molds, shaft blanks, spring base parts.
Stainless Steel Flat Bar: 201, 304, 316L Superior acid, alkali and seawater corrosion resistance, applied to chemical equipment, food machinery and coastal anti-corrosion structures.
3.3 Classification by Surface Treatment
Mill Black Finish Flat Bar: Original hot rolled surface, for indoor temporary structures and secondary anti-rust treatment.
Pickled Bright Flat Bar: Descaled clean grey surface, convenient for welding and spraying without thick oxide interference.
Hot-Dip Galvanized Flat Bar: Thick uniform zinc coating with strong adhesion, long-term anti-corrosion for outdoor, power grounding and coastal projects.
Polished Mirror Flat Bar: High-gloss polished surface for decorative frames and precision assembly.
4. Specification Range
Standard Width: 12mm, 16mm, 20mm, 25mm, 30mm, 40mm, 50mm, 60mm, 80mm, 100mm, 120mm, 150mm, 200mm, 250mm, 300mm
Standard Thickness: 3mm, 4mm, 5mm, 6mm, 8mm, 10mm, 12mm, 14mm, 16mm, 20mm, 25mm, 30mm, 40mm, 50mm, 60mm
Standard Fixed Length: 6m, 9m, 12m; customizable length from 1m to 12m, ultra-long cutting available
Dimension Tolerance: Comply with GB/T 704 negative tolerance standard, uniform cross-section without thickness/width deviation
Surface Quality: Straight vertical side edges free of burrs, collapse, cracks, scars and delamination; consistent straightness ≤2mm/m for hot rolled products
Theoretical Weight Formula: Weight per meter (kg/m) = Width(mm) × Thickness(mm) × 0.00785
5. Core Mechanical Properties
Q235B Mild Flat Bar: Yield strength ≥235MPa, tensile strength 370–500MPa, elongation ≥26%, qualified 180° cold bending without cracks
Q355B HSLA Flat Bar: Yield strength ≥355MPa, tensile strength 470–630MPa, outstanding low-temperature impact toughness
45# Medium Carbon Flat Bar: High tensile strength, good hardenability for heat treatment and mold processing
Galvanized Flat Bar: Zinc coating passes bending adhesion test, no zinc peeling or flaking after repeated twisting
6. Production Process Flow
Hot Rolled Flat Bar Process
Steel slab heating (1100–1250℃) → High-pressure water descaling → Multi-pass continuous rolling → Laminar controlled cooling → Straightening & leveling → Fixed-length cutting → Edge trimming → Surface dimension inspection → Marking, bundling & warehousing
Cold Drawn Bright Flat Bar Process
Hot rolled blank incoming → Acid pickling & phosphating lubrication → Multi-pass precision cold drawing → Straightening → Surface finishing polishing → Fixed-length cutting → Finished product inspection → Packaging & delivery
Galvanized Flat Bar Additional Process
Finished flat bar surface activation → Hot-dip galvanizing → Zinc layer homogenization → Surface finishing → Coating thickness inspection
7. Core Product Advantages
Neat Solid Cross-Section: Vertical 90° edges reduce secondary trimming loss, higher material utilization rate than steel plates.
Excellent Comprehensive Machinability: Supports free cutting, bending, welding, punching and drilling, compatible with automatic processing lines.
Complete Material & Surface Options: Cover mild carbon, high-strength alloy, stainless steel and multiple anti-corrosion finishes to match all indoor, outdoor and corrosive working conditions.
Stable Dimensional Consistency: Strict rolling tolerance control ensures uniform batch size for standardized component assembly.
Strong Structural Bearing Capacity: Flat wide surface provides large welding contact area, improving structural connection stability and load performance.
Sufficient Stock & Flexible Customization: Full standard sizes in stock, supporting non-standard width/thickness, special fixed-length cutting, galvanizing and polishing customized processing.
8. Main Application Fields
Steel Structure Construction: Building support frames, embedded foundation parts, stair tread supports, factory workshop beam connectors
Power & Electrical Engineering: Lightning protection grounding strips, substation grounding network, equipment earthing conductors
Mechanical Manufacturing: Machine base frames, mold blanks, fixture accessories, automobile chassis structural parts
Guardrail & Traffic Works: Road safety barriers, stadium fence frames, slope protection structural components
Ship & Offshore Engineering: Ship cabin supports, deck connecting parts, coastal anti-corrosion structural strips
Hardware & Decoration: Iron craft frames, decorative metal supports, assembly equipment brackets
9. Selection & Usage Guidelines
Indoor short-term structural projects select black hot rolled flat bar for optimal cost performance; paint or spray anti-rust coating after installation.
Outdoor exposed, humid and power grounding projects must adopt hot-dip galvanized flat bar to prevent rust failure.
Precision machinery and high-finish assembly parts prefer cold drawn bright or polished flat bar to eliminate secondary polishing procedures.
Heavy-load, long-span and low-temperature environment structures shall use Q355B low alloy high strength flat bar instead of ordinary Q235 grade.
Marine, chemical acid-base corrosive working conditions require stainless steel flat bar or extra-thick zinc galvanized flat bar.
Store finished flat bars in dry ventilated warehouse with rain and moisture protection; separate galvanized and black finished products to avoid surface cross-contamination and scratch damage.
10. Packaging, Quality Documents & Customization Services
10.1 Standard Packaging
Flat bars are bundled with multiple steel straps, separated by wooden blocks at bottom to avoid bending and scratch deformation. Plastic film wrapping for dustproof protection. Export orders adopt professional moisture-proof, rust-proof seaworthy wooden pallet packaging suitable for long-distance ocean transportation.
10.2 Complete Factory Quality Certification Documents
Full set of original delivery papers including factory material certificate, spectral chemical composition report, mechanical performance test report, dimensional inspection record and factory qualification certificate. Third-party SGS and BV inspection is supported to meet domestic engineering acceptance and overseas export customs clearance requirements.
10.3 Customization Services
Support non-standard width & thickness customization, arbitrary fixed-length cutting, special edge finishing, hot-dip galvanizing, pickling and mirror polishing processing. Multi-standard compliance certificates (GB, ASTM, EN, JIS) can be issued for global construction, machinery and power engineering manufacturers.
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