Difference Between HDG Steel and EG Steel
When we talk about galvanized steel, generally we have two items in mind: one is hot dipped galvanized steel (HDG steel), and the other is electro galvanized steel (EG steel, also known as cold galvanized steel). They are very different in the fabrication process but relatively similar in the final finish. So, how to distinguish them? What is the difference between them then? Continue reading to get more details now.
What Is Galvanization?
Before we move ahead, it is essential to understand what galvanization is.
Galvanization or galvanizing is one of the most widely used manufacturing processes of applying a layer of zinc to the surface of steel so as to prevent corrosion and rust. The zinc acts as a protective barrier for the steel, achieving the purpose of enhancing the anti-corrosion ability and extending the life of the base metal to a considerable extent. Therefore, galvanized steel is also called zinc-coated steel.
According to this galvanizing method, galvanized steel can be divided into hot dipped galvanized steel and electro galvanized steel.
Difference Between Hot Dipped Galvanized Steel and Electro Galvanized Steel
There exist many differences between hot-dip galvanizing steel and electro galvanizing steel caused of the technical process during the production. Let’s review them one by one.
Manufacturing Process
Hot Dipped Galvanized (HDG): it is to immerse the total steel into the melted zinc solution at about 500°C to obtain a protective layer, thus serving the purpose of corrosion protection. In this way, both sides of the base metal are fully galvanized to enhance the corrosion resistance. The production process of HDG is as follows:
Steel Preparing → Degreasing → Water Washing → Pickling → Rust Removing → High-temperature Annealing → Hot-dip Galvanizing → Cooling → Oiling → Packing
Electro Galvanized (EG): electro galvanizing uses the electrolysis equipment to attach a zinc film to the steel surface at room temperature. Unlike hot-dip galvanizing, it can be electroplated either on one side of steel or fully galvanized. The production process of EG is as follows:
Steel Preparing → Degreasing → Erosion → Polishing → Electro Galvanizing → Hydrogen Removal → Passivation → Packing
Zinc Coating Thickness
The zinc content is greatly varied due to the different equipment used when fabricating. Hot dipped galvanization is said to have a normal coat thickness of about 40% thicker than electro galvanization.
The thickness range of hot-dip galvanized steel is very large, which can reach 45～300g/m2. Because it is often operated at a very high temperature, the zinc can easily penetrate into the base metal and is closely adhered to. But at the same time, the surface of the hot-dip galvanized coating is uneven and rough.
Electro galvanized steel has a very low zinc content, about 3 ~ 50 g/m2. Here, the coating thickness is mainly determined by the electrolyte temperature and current density. This process can apply a protective coating with exceptionally uniform and thin zinc thickness.
Anti-corrosion Performance
It is well known that the metal performance of resisting corrosion and rust outside is largely related to the zinc content applied to it. Generally, the thicker the zinc layer, the stronger the corrosion resistance. Therefore, in terms of their making method and zinc content, it can be inferred that HDG steel is more resistant than EG steel.
Spangle
Hot-dipped galvanized steel has a fairly distinct characteristic compared to other galvanized steel as it has a mottled, crystalline-like pattern known as “spangle”. And these spangles can be divided into big spangles, small spangles, and zero spangles.
Electro galvanized steel has no spangles. There are only two kinds of EG steel: fingerprint-resistant and fingerprint-intolerant.
Ductility
The ductility of hot-dip galvanizing steel is greater than that of cold galvanizing steel. Because the high temperature will soften the base metal and reduce the deformation resistance, it is easy for deep processing and welding. In contrast, electro galvanized steel that has high hardness itself and is often processed at room temperature, will be easily broken due to the pressing of the machine.
Adhesion
Hot-dip galvanized steel has a stronger adhesion due to the hot melting and mutual penetration. On the contrary, the galvanized layer of electro galvanized steel is an electroplated layer, and the zinc layer is independently layered with the steel substrate. This makes it easy to peel off over time.
Service Life
Hot dipped galvanized steel is known to have a very long lifespan between 20 to 50 years.
The life expectancy of electro galvanized steel is very low as compared to the former, several years only. What’s more, if the pickling is insufficient and the air is humid, dezincification and oxidation will occur within a few weeks in severe cases.
Appearance
In comparison to the appearance, EG steel is much prettier than HDG steel.
The surface of the hot-dip galvanized steel is dark, rough, and not so eye-catching. Sometimes there are lots of “pimples” on the surface of HDG products. And when the production temperature of hot-dip galvanizing is very high, the appearance will turn gray, and knocking will cause the zinc-iron alloy layer to fall off into small pieces.
However, electro galvanizing steel often comes with an excellent finish: smooth, dense, beautiful, and bright. Especially when you see the electro galvanized finish in the sun, you even can notice the reflecting light from it, like a mirror reflecting the sun.
Color
Generally, the color of hot-dip galvanizing is silvery gray while the electro galvanizing is silvery white.
Application
Hot-dip galvanized steel has higher corrosion protection and larger production capacity so it is more suitable for use in outdoor projects. Therefore, HDG products are widely used in many industries such as automobiles, construction, aerospace, electronics, business, mining, etc. Typical examples include:
Scaffolding,
Building roofing slab,
Kitchenware,
Highway fencing,
Piping,
Grating, etc.
The EG products tend to be more used in indoor projects that require less corrosion protection and a smooth finish or tight tolerances. Typical examples include:
Automotive exterior panels,
Packaging materials for cans,
Cable inner and outer sheath,
Instrument telecommunication parts,
Torch, etc.
Price
Firstly, the price of hot-dip galvanizing is a bit higher and more practical than that of cold galvanizing. But when purchasing, the total cost will be highly affected by the zinc coating thicknesses, quantities, sizes, packaging, freight, taxes, economic condition (war, inflation, deflation, etc), and so on. So remember to communicate more with your GI steel suppliers.
Secondly, the charging standard is also different: hot-dip galvanizing steel is charged according to the thickness of the material and zinc coating, whereas most cold-galvanizing steel is charged according to the square meter.
Contact Wanzhi Steel for More Details Now
If you still have some confusion about HDG & EG steel, contact us immediately. Our technical consultants are ready to serve you.
About Wanzhi
Wanzhi Steel is a professional steel manufacturer and supplier in China with more than 18 years’ experience. We can produce galvanized steel, galvalume steel, stainless steel, PPGI & PPGL steel products. All can be available in a wide variety of sizes, diameters, designs, and coating thicknesses, satisfy your specific demands. Come to contact us for more details!
