GB/T 25052-2024Dimensions, shape, weight and tolerances for continuously hot-dip coated steel sheet and strip (English PDF)

1 Scope

China's national standard for the dimensions, shape, weight and permissible deviations of continuously hot-dip coated steel sheet and strip. It specifies the thickness, width and length tolerances, the shape tolerances, the weight and the deviations for galvanized, galvannealed, aluminium-zinc and similar hot-dip coated products. Every coated steel product standard specifies the coating, the substrate grade and the mechanical properties, and refers the dimensions to this document rather than restating them - which is why a short standard of tables is cited by all of them. The tolerances are not simply those of uncoated strip with an allowance added, and that is the reason it exists separately. A hot-dip line passes the strip through molten metal and wipes the coating to thickness with air knives, so the coated thickness is the substrate thickness plus a coating whose weight is itself specified separately and varies across the width; the thickness tolerance therefore has to state whether it applies to the coated or the uncoated product, and the standard fixes that. The line also anneals the strip continuously before coating and cools it afterwards, which affects the flatness: coated strip is more prone to edge wave and centre buckle than cold-rolled strip, and the shape tolerances reflect what a hot-dip line can actually hold. And the width tolerance has to accommodate the trimmed and untrimmed conditions, since much coated strip is sold mill edge. The weight tolerance matters commercially because coated strip is sold by weight and the coating is part of that weight - a difference in coating mass within specification is a difference in the steel delivered for the same money. Issued on 23 August 2024 and in force since 1 March 2025, it replaces GB/T 25052-2010.

This document specifies the classification and designation, dimensions, dimensional tolerances, shapes, measurement of dimensions and shapes, weights and numerical rounding of continuously hot-dip coated steel sheets and strips. This document is applicable to continuous hot-dip coated wide strips and their sheared steel plates (hereinafter referred to as steel plates) and slit wide strips with a nominal thickness not exceeding

2 Normative references

The provisions of the following documents constitute the essential clauses of this document through normative references in this text. Among them, for referenced documents with dates, only the versions corresponding to the dates are applicable to this document; for referenced documents without dates, the latest versions (including all amendments) are applicable to this document.

GB/T 8170 Rules of rounding off for numerical values & expression and judgment of limiting values

3 Terms and definitions

The following terms and definitions apply to this document.

3.1 wide strip Steel strip with a rolling width of not less than 600 mm and delivered in coils.

3.2 slit wide strip Steel strip cut longitudinally from a wide strip (3.1) and delivered in coils.

3.3 nominal(specified) thickness Ordering thickness of coated products.

4 Classification and codes

4.1 The classification and codes according to edge state are as follows:

4.2 The classification and codes according to dimensional precision are as follows:

4.3 The classification and codes according to flatness precision are as follows:

4.4 The classification of dimensional precision and flatness precision corresponding to product forms is shown in Table 1.

5 Dimensions...

8 Measurement of dimensions and shapes

8.1 Thickness The wide strips and steel sheets with mill edges shall be measured at a distance of not less than 40 mm from the rolled edge; wide strips and steel sheets with cut edges shall be measured at a distance of not less than 25 mm from the sheared edge.

8.2 Width It shall be measured in a direction perpendicular to the center line of the steel sheet, wide strip or slit wide strip.

9 Weight

9.1 Steel sheets shall be delivered according to theoretical or actual weight, and wide strips and slit wide strips shall be delivered according to actual weight.

9.2 When steel sheets are delivered according to theoretical weight, the theoretical weight shall be calculated based on the nominal dimensions.

9.3 The nominal thickness of the coating is calculated according to formula (1).