Grades and technical requirements Galvanized

Grades and technical requirements Galvanized
1、 Nomenclature grades of Galvanized steel sheet and steel strip
Common brands DX51D + Z, DX52D + Z, DC51D + Z, DC52D + Z, S350GD + Z and so on. Grades of Galvanized steel sheet or steel strip consists of five parts: the product usage code, steel grade code, Characteristics of steel , hot-dip galvanizing code (D), +, zinc coating class code , the Named Methods of details  brand  as follows:
A） Galvanized sheet using Cold forming :
For example: DX51D + Z (or ZF \ AZ), DC51D + Z (or ZF AZ), DD52D + Z (or ZF AZ) DX: The first letter D is flat steel for cold forming, the second letter If it is X, it means that the rolling state of the substrate is not defined; if the second letter is C, it means that the substrate is a cold-rolled ; if the second letter is D, it means that the substrate is a hot-rolled substrate;
51 ~ 57: two digits that the steel grade serial number; after two digits D is hot-dip galvanized code;
Z indicates that the coating is pure zinc, ZF indicates galvanized iron alloy and AZ indicates aluminized zinc.
So: DX51D + Z says the product use for cold forming, flat steel, not specified substrate status, steel grade serial number 51, pure zinc coating, hot-dip products. B) Other galvanized grades naming example
Characteristics are not specified, D is hot-dip galvanized, and + Z is zinc-plated
HX340LAD + ZF: It is used for high-strength flat steel for cold forming. It does not specify the state of the substrate. The minimum yield strength is 340Mpa. The type of steel is high-strength low-alloy steel, zinc-iron alloy plating and hot-dip galvanized steel. HC340 / 590DPD + Z: that the product is used for cold forming, high strength flat steel, the provisions of the substrate for the cold-rolled substrate, the minimum yield strength value of 340Mpa, provides the minimum tensile strength of 590Mpa, steel type duplex steel, Pure zinc plating hot-dip products.
2 Steel grades Galvanized steel sheet and steel strip in Table 2
Table 2 common used brands and characteristics of galvanized sheet
3 Code of Surface Quality Normal Grade Surfaces FA Higher Surfaces FB Advanced Surfaces
4 Coating types, coating surface structure, surface treatment code in Table 3
5 Size, shape and tolerance of Galvanized steel coils and strip.
(1) Nominal size range of galvanized steel sheet and strip is shown in Table 4-1
(2) Size tolerances of Galvanized steel sheet and steel strip
For the steel sheet and strip with the specified minimum yield strength of not less than 260 MPa and less than 360 MPa and grades DX51D + Z (ZF) and S550GD + Z (ZF) of the steel plates and strips , the thickness deviation is in accordance with Table 4-2
6 Recommended Galvanized weight and The corresponding coating code of Steel and steel sheet in Table 5
7 Surface treatment（1）（C5）Chromic acid passivation (C) and chromic acid-free passivation (C5)
The surface treatment can reduce the white rust on the surface of the product during transportation and storage, During Chromium-free passivation treatment should limit the passivation film squadron human health harmful hexavalent chromium components;
（2） Chromic Acid Passivation + Oiled (CO) and Chromium-Free Passivated + Oiled (CO5) This surface treatment further reduces the generation of white rust on the surface of the product during shipping and storage.
（3） （PO）Phosphating (P) and phosphating + oiling (PO)
This surface treatment reduces the generation of white rust on the surface during transport and storage of the product and improves the formability of the steel sheet.
（4） Fingerprint resistant film (AF) and chromium free fingerprinted film (AF5)
Surface treatment can reduce the surface white rust during transport and storage, chromium-free passivation should be restricted passivation film Squadron human harmful hexavalent chromium composition.
（5） Oiling treatment (O)
Reduce white rust during the storage and transportation ,The anti-rust oil is generally not used as a follow-up processing rolling oil and stamping lubricants
（6） No treatment (U)
When ordering, it must be stated in the contract. In this case, the surface of steel sheet and steel strip will be more easily to form white rust and black spots on the surface during transportation and storage. Users should be cautious in the selection.
四、Classification of Galvanized sheet
1 Classification as galvanized substrate (1) galvanized carbon steel
Continuous aluzinc steel coil mostly use mild steel, the carbon content of 0.10% -0.20%, galvanized features and industrial pure iron is very similar. In the ordinary low-carbon steel as a substrate for hot-dip galvanizing, the composition of the most influential elements are carbon and silicon. In general, the higher the carbon content in the steel, the stronger the zinc-iron reaction, the greater the iron loss, and the thicker the resulting alloy coating, making the coating brittle, poor plasticity, poor adhesion of the coating. In addition, the high carbon content of steel will also affect the surface quality of the coating, often with missing plating point, but also easy to form zinc tumor.
With the development of the automotive industry, more and more requirements are put forward on cold forming properties such as deep drawing of general carbon steel. The carbon content in the steel is expected to be as low as possible. For example, the carbon content of a stamping steel is generally less than 0.10%, and the commonly used carbon The content of carbon is not more than 0.04% (such as K08Al), while the content of ultra-deep-drawn steel (such as interstitial-free IF steel) is up to 0.005%.
(2) High-strength Prepainted steel coil In order to meet the needs of the automobile manufacturing industry such as weight reduction, energy conservation and safety, one of the major users of hot-dip galvanized steel sheets, the hot-dip galvanized steel sheets for automobiles, which are based on high-strength steel sheets, have been rapidly developed. At present,in abroad have developed or are being developed high strength steel IF high strength steel, bake hardened steel, low alloy high strength steel, dual phase steel and phase change induced plastic, carbon and manganese high strength steel, martensitic steel, The achievable intensity levels are shown in Figure 1.
Figure 1 Relationshi betweenyield strength and elongation of All types of high-strength steel.
IF without gap atomic deep drawing steel; IS isotropic steel ;Mild mild steel; BH bake hardened steel; CMn carbon manganese high strength steel ;HSLA high strength low alloy steel ;DP duplex steel ;CP complex steel ;TRIP phase Variable induction plastic steel; MART martensitic steel
2 Classification according to the coating (1) the classification according to of zinc spangle A Galvalume steel coil with large zinc spangle.
This is one of the most original production of galvanized steel, as we all know, zinc ore and lead ore total symbiosis, in the smelting of zinc, it is impossible to remove all lead impurities, the content of 0.05% or more can be formed large zinc spangle.
Each zinc spangle, the crystallization center is raised, the edge is concave, the surface is uneven appearance, which is not conducive to its subsequent processing and coating. In addition, due to the low amount of lead in zinc solid solution, it will be precipitated in the grain boundary when cooling, resulting in stress and electrochemical corrosion at the grain boundaries, galvanic intergranular corrosion, reducing its corrosion resistance. Therefore, in recent years, people have gradually got to know it. The galvanized sheet with large zinc spangle will be gradually eliminated.