GB/T 2518 Continuously Hot-Dip Coated Steel

1. Definition and Scope

GB/T 2518 is the Chinese national standard specifying continuously hot-dip zinc-coated and zinc-iron alloy coated steel sheet and strip. It applies to flat products in thicknesses from 0.17 mm to 4.0 mm, supplied in coils or sheets, intended for further cold forming including roll forming, stamping, and bending. GB/T 2518 is the primary galvanized feedstock standard for roll forming operations in mainland China, functionally equivalent to EN 10346 in Europe, ASTM A653 in North America, and JIS G 3302 in Japan. Major Chinese steel producers (Baosteel, Shougang, Ansteel, HBIS) manufacture GB/T 2518 product on continuous galvanizing lines with capacity exceeding 30 million tonnes per year collectively.

The standard defines steel grades using DC (drawing quality) and S (structural) designations parallel to EN 10346 DX and SxxGD naming. Coating types include pure zinc (Z) and zinc-iron alloy (ZF). Coating mass designations follow the EN convention (+Z275, +ZF120, etc.) expressing total coating mass on both surfaces in g/m². GB/T 2518 was revised to align more closely with EN 10346 grade names and coating designations, facilitating cross-standard specification for export-oriented roll forming manufacturers.

Roll forming manufacturers in China specify GB/T 2518 on domestic purchase orders and on export orders where the customer accepts Chinese standard feedstock. Finished profile tolerances for export may additionally reference EN 10162 or customer-specific drawings. The 2019 revision introduced FA/FB/FC surface quality classes and aligned coating mass codes with EN 10346, reducing specification ambiguity for international procurement teams sourcing from Chinese steel mills.

2. Steel Grades

GB/T 2518 organizes grades into DC series for cold forming and S series for structural applications with defined minimum yield strength.

2.1 DC Grades (Drawing and Forming)

2.2 S Grades (Structural)

2.3 Cross-Standard Grade Equivalents

3. Coating Types and Mass

GB/T 2518 defines two coating types: Z (pure zinc) and ZF (zinc-iron alloy). Coating mass designations follow the +Z or +ZF prefix with the total mass in g/m² on both surfaces.

3.1 Z (Zinc) Coating Mass

3.2 ZF (Zinc-Iron Alloy) Coating

ZF coating is produced by diffusing iron into the zinc layer during a post-coating annealing step. The matte surface accepts paint without spangle telegraphing and provides uniform appearance on visible roll-formed profiles.

4. Mechanical Properties and Tolerances

Mechanical properties apply to the coated product. Thickness and width tolerances follow GB/T 2518 tables, closely aligned with EN 10346 tolerance structures.

4.1 Thickness Tolerance

4.2 Width Tolerance

5. Surface Quality and Treatment

GB/T 2518 specifies surface quality classes and treatment codes aligned with EN 10346 conventions.

5.1 Surface Quality Classes

5.2 Surface Treatment Codes

6. Designation System

GB/T 2518 designation follows: steel grade + coating type and mass + surface quality + surface treatment + dimensions + standard reference.

6.1 Worked Designation Examples

7. Roll Forming Process Considerations

GB/T 2518 coated strip processing on roll forming lines follows the same practices as EN 10346 and JIS G 3302 feedstock. Chrome-plated or polished tool steel rolls prevent zinc pickup. Roll gap is set to measured coil thickness at entry. Lines running both GB/T 2518 and imported EN 10346 feedstock on the same mill use identical roll tools and process parameters when grade and coating mass are equivalent, simplifying multi-source material management.

7.1 Forming Parameters by Grade

7.2 Quality Documentation

Mill quality certificates per GB/T 247 accompany each coil shipment. Roll forming plants archive certificates by heat number and link finished profile batch numbers to feedstock heat numbers for full material traceability required by GB 50018 structural building projects and export CE marking documentation.

7.3 Pre-Painted GB/T 2518 Substrate

Color-coated product per GB/T 12754 uses GB/T 2518 ZF or Z coated substrate. Roll forming lines processing pre-painted coil run at reduced speed (50–70% of bare galvanized speed) to avoid paint cracking at bend radii. Paint damage at bends is evaluated per GB/T 12754 bend test criteria on first-article samples before full production release. ZF substrate is preferred over Z for pre-painted roll forming because the matte zinc-iron alloy surface provides more uniform paint adhesion without spangle pattern telegraphing through the topcoat.

8. Roll Forming Applications

GB/T 2518 is the dominant feedstock specification for roll forming production in China's building construction, infrastructure, solar energy, and industrial equipment sectors.

Chinese roll forming manufacturers supplying export markets maintain dual certification: GB/T 2518 feedstock traceability on mill test certificates and EN 10162 (or customer standard) compliance on finished profile inspection reports. The grade naming alignment between GB/T 2518 and EN 10346 since the 2019 revision simplifies cross-standard procurement for multinational roll forming operations with production facilities in China.

8.1 Domestic Standards Integration