GB/T 2518-2019Continuously hot-dip zinc and zinc alloy coated steel sheet and strip (English PDF)

1 Scope

China's national standard for continuously hot-dip zinc and zinc alloy coated steel sheet and strip. It specifies the classification and designation, the order content, the dimensions, the technical requirements, the test methods, the inspection rules and the packaging and marking of galvanized and zinc alloy coated flat steel. Galvanized steel is the largest coated steel product in the world and the reason is electrochemical rather than physical. Zinc is anodic to iron, so the coating does not merely cover the steel - it protects it sacrificially, and a scratch that exposes bare metal does not rust, because the surrounding zinc corrodes preferentially and protects the exposed area. That is why a galvanized panel outlasts a painted one at a cut edge and why the product dominates construction, automotive bodies, appliances and ducting. The standard covers the whole family, which is broader than the name suggests. Pure zinc coatings are the classic product. Zinc-iron alloy, made by annealing the coating after the pot so it converts to a zinc-iron intermetallic, is matt, welds and paints better and is what car bodies use. Zinc-aluminium and zinc-aluminium-magnesium coatings give several times the corrosion life at the same coating weight, which is why they have displaced pure zinc in demanding outdoor use. Each behaves differently in forming, welding and painting. So the requirements cover the substrate grades and their mechanical properties, the coating type and mass and how the mass is expressed and measured, the surface quality and finish, the spangle, the passivation and oiling, the adhesion of the coating under bending, and the dimensional tolerances referred to GB/T 25052. Issued on 10 December 2019 and in force since 1 July 2020, it replaces GB/T 2518-2008.

This Standard stipulates the terms, definitions, classification, codes, designation representation methods, order content, dimensions, shapes, weights, technical requirements, test methods, inspection rules, packaging, marking and quality certificate of continuously hot-dip zinc, zinc-iron alloy, zinc-aluminum alloy and aluminum-zinc alloy coated steel sheet and strip (hereinafter referred to as steel sheet and strip). This Standard is applicable to steel sheets and strips (with the thickness of

0.20 mm ~

6.0 mm) for the automotive, construction and household appliance industry, etc.

2 Normative References

The following documents are indispensable to the application of this document. In terms of references with a specified date, only versions with a specified date are applicable to this document. In terms of references without a specified date, the latest version (including all the modifications) is applicable to this document.

GB/T 223.5 Steel and Iron - Determination of Acid-soluble Silicon and Total Silicon Content - Reduced Molybdosilicate Spectrophotometric Method

GB/T 223.9 Steel and Iron - Determination of Aluminum Content - Chrome Azurol S Photometric Method

GB/T 223.12 Methods for Chemical Analysis of Iron, Steel and Alloy - The Sodium Carbonate Separation - Diphenyl Carbazide Photometric Method for the Determination of Chromium Content

GB/T 223.14 Methods for Chemical Analysis of Iron, Steel and Alloy - The N-Benzoy- N-Phenylhydroxylamine Extraction Photometric Method for the Determination of Vanadium Content

GB/T 223.17 Methods for Chemical Analysis of Iron, Steel and Alloy - The Diantipyrylmethane Photometric Method for the Determination of Titanium Content

GB/T 223.26 Iron, Steel and Alloy - Determination of Molybdenum Content - The Thiocyanate Spectrophotometric Method

GB/T 223.40 Iron, Steel and Alloy - Determination of Niobium Content by the Sulphochlorophenol S Spectrophotometric Method

GB/T 223.59 Iron, Steel and Alloy - Determination of Phosphorus Content - Bismuth Phosphomolybdate Blue Spectrophotometric Method and Antimony Phosphomolybdate Blue Spectrophotometric Method

GB/T 223.60 Methods for Chemical Analysis of Iron, Steel and Alloy - The Perchloric Acid Dehydration Gravimetric Method for the Determination of Silicon Content

GB/T 223.63 Methods for Chemical Analysis of Iron, Steel and Alloy - The Sodium (potassium) Periodate Photometric Method for the Determination of Manganese Content

GB/T 223.64 Iron, Steel and Alloy - Determination of Manganese Content - Flame Atomic Absorption Spectrometric Method

GB/T 223.78 Methods for Chemical Analysis of Iron, Steel and Alloy - Curcumin Spectrophotometric Method for the Determination of Boron Content

3 Terms and Definitions

The following terms and definitions are applicable to this document.

3.1 Hot-dip Zinc Coating Hot-dip zinc coating refers to pure zinc coating obtained by immersing pretreated steel strip in molten zinc solution on continuous hot-dip zinc production line. NOTE. in the molten zinc solution, zinc content is not less than 99%.

3.2 Hot-dip Zinc-iron Alloy Coating Hot-dip zinc-iron alloy coating refers to zinc-iron alloy coating obtained by immersing pretreated steel strip in molten zinc solution on continuous hot-dip zinc production line. NOTE. in the molten zinc solution, zinc content is not less than 99%. Through alloying treatment process, form zinc-iron alloy layer on the entire coating, and iron content in the alloy coating is generally. 8% ~ 15%.

3.3 Hot-dip Zinc-aluminum Alloy Coating Hot-dip zinc-aluminum alloy coating refers to coating obtained by immersing pretreated steel strip in molten zinc-aluminum alloy solution on continuous hot-dip zinc aluminum production line. NOTE. in the molten zinc aluminum alloy solution, the mass fraction of aluminum is approximately 5%; contain a small amount of rare earth; the remaining ingredient is zinc.

3.4 Hot-dip Aluminum-zinc Alloy Coating Hot-dip aluminum-zinc alloy coating refers to coating obtained by immersing pretreated steel strip in molten aluminum-zinc alloy solution on continuous hot-dip aluminum-zinc production line.

3.5 Interstitial Free Steel Interstitial free steel refers to a type of steel, which adds an appropriate amount of titanium or niobium to ultra-low carbon steel, so that the carbon and nitrogen interstitial atoms in the steel are completely fixed into carbide and nitride, and no interstitial atom exists in the steel.

3.6 High Strength Interstitial Free Steel High strength interstitial free steel refers to steel which adds a certain amount of strengthening elements, such as. phosphorus, manganese and silicon, to interstitial free steel, so that the steel has high strength and can maintain good formability.

3.7 Bake Hardening Steel Bake hardening steel refers to a type of steel, which retains a certain amount of solid dissolved carbon and nitrogen atoms, and can enhance the strength by adding strengthening elements, such as. phosphorus and manganese; after processing and baking at a certain temperature, the yield strength is further enhanced due to age hardening.

5 Order Content

5.1 Contracts or orders which order products in accordance with this Standard shall include the following content.

5.2 If order contract does not indicate specific requirements for dimensions, unevenness accuracy, surface treatment type, surface quality, surface structure and packaging mode, then, the supply-side shall supply in accordance with the common accuracy of dimensions and unevenness; surface treatment. oiling (O); surface quality level. common level of surface (FA) in GB/T 25052-2010, and the surface structure and packaging mode appointed by the supply-side. If order contract does not indicate the internal diameter of steel strip, then, it shall be selected by the supply-side.

7 Technical Requirements

7.1 Chemical Composition The chemical composition (smelting analysis) of steel may take the stipulations in Item Nominal Dimensions

7.2 Smelting Method Steel should adopt oxygen converter or electric furnace for smelting. Unless it is otherwise stipulated, the mode of smelting shall be selected by the supply-side.

7.3 Delivery State Steel sheet and strip shall receive hot-dip or hot-dip and flattening (or finishing), then, be delivered.

8 Test Methods

8.1 Generally speaking, the chemical composition test of steel shall be conducted in accordance with the methods in GB/T 4336, GB/T 20123, GB/T 20125 and GB/T 20126, and universal chemical analysis methods. The arbitration shall be conducted in accordance with the stipulations in GB/T 223.5, GB/T 223.9, GB/T 223.12, GB/T 223.14, GB/T 223.17, GB/T 223.26, GB/T 223.40, GB/T 223.59, GB/T 223.60, GB/T 223.63, GB/T 223.64, GB/T 223.78, GB/T 20125 and GB/T 20126.

8.2 The inspection items and test methods of each lot of steel sheets and strips shall comply with the stipulations in Table 20.

9 Inspection Rules

9.1 The inspection and acceptance inspection of steel sheet and strip shall be conducted by the supply-side's quality supervision and inspection department.

9.3 The inspection items, sampling quantity, sampling location and sampling method of steel sheet and strip shall comply with the stipulations in Table 20.

9.4 The re-inspection and determination rules of steel sheet and strip shall comply with the stipulations in GB/T 17505.