What is coated steel?
Coated steel is a steel that has an extra finish applied to the natural steel surface. The extra coating or finish applied can be tin, chrome, zinc, paint or plastic. The application of the coating is done in order to protect the surface of the steel from oxidation and it is also used to enhance the appearance of the material. Coated steel can be divided into several different categories. These include hot-dip galvanized, galvannealed, galvalume, galfan, electrolytic zinc (electro-galvanized) and pre-painted steel.

History of Galvanizing
Galvanization refers the process of coating steel with zinc. Galvanizing was named after its founder, Italian scientist Luigi Galvani. Galvanization was originally the process of electrical shock. The process was discovered as Galvani touched a frog¡¯s leg with forceps and saw the muscles twitch. The use of the word galvanize in today¡¯s terms refers mainly to the chemical process of hot dip galvanizing. In the process steel or iron is coated with zinc. The zinc reduces the chances of corrosion.

Hot Dip Galvanized steel
Hot-dip galvanized steel is carbon steel that is coated with a thin zinc layer on both sides using a hot-dip continuous line. The coated zinc layer is tightly bound to the steel in a molten bath of zinc at a temperature of around 460 Celsius. Galvanized steel can be used in a wide variety of applications where rust resistance is needed. One of the big identifying characteristics of galvanized steel is the spangle or visible crystallization pattern on the steel¡¯s surface.

Galvannealed steel
Galvannealed steel is carbon steel that has been coated with a zinc coating on both sides using a hot-dip continuous line. When the steel leaves the molten zinc bath the molten zinc coating is sent to an in-line heat treatment. This converts it into an iron-zinc alloy as the iron is diffused from the steel into the coating. Galvannealed steel is different from hot-dip galvanized steel as it has no visible spangle and it appears matte compared to the highly metallic appearance of galvanized steel. The reddish-orange appearance on of the surface of the steel is because of the iron spread over the coated layer particularly when the iron content ranges 8 to 11 percent.

Galvalume steel
Galfan steel is carbon steel that has been coated with a mixture of aluminum and zinc on both sides using a hot-dip continuous line. The composition of the coating layer is 95 percent zinc and 5 percent aluminum. It is more corrosion resistant than normal hot-hip galvanized and generally cheaper to produce than galvalume steel thus making it the preferred material for use in areas that needs long term resistance to atmospheric corrosion.

Galfan steel
Galfan steel is carbon steel that has been coated with a mixture of aluminum and zinc on both sides using a hot-dip continuous line. The composition of the coating layer is 95 percent zinc and 5 percent aluminum. It is more corrosion resistant than normal hot-hip galvanized and generally cheaper to produce than galvalume steel thus making it the preferred material for use in areas that needs long term resistance to atmospheric corrosion.

Electro-galvanized steel
Electro-galvanized steel is carbon steel that is coated with pure zinc coating by applying an electric current. This causes the positively charged zinc anodes to attach to the negatively charged steel. This process helps to smooth the surface even after painting. The final product has a similar appearance to cold rolled steel but it is darker and it has similar mechanical properties to the base material of cold rolled coil.

Pre-painted steel
Pre-painted steel is a steel that has received a layer of paint after a treatment. In many cases the pre-painted steel also has a layer of primer applied. The paint can be applied to uncoated steel or steel that has a metallic coating. In order to achieve maximum corrosion resistance a metallic coated steel is used. These include galvalume, galfan, galvannealed and galvanized steel. Pre-painted steel technology has been developing fast over the past twenty years. Advances in fade, chalk resistance, flexibility, hardness in painting materials and many more has widened the use of the pre-painted steel in many industries such as the automotive, appliance, construction and furniture industries.

Why use coated steel?
The major benefit that the use of coated steel gives is its improved corrosion resistance. There are many different types of corrosion in low carbon steel. It can be localized corrosion due to certain conditions in the environment or the corrosion can spread over the entire surface of the steel. Uniform corrosion is a form of corrosion that is uniformly spread over the steel and is clearly visible. In addition there are several other forms of corrosion of low carbon steel including crevice corrosion, poultice corrosion, erosive corrosion, fretting corrosion. The need for corrosive resistant steel increased to cope with a wide variety of corrosive factors present in daily living conditions. With coated steel technology advancing fast, there are many different options available to meet the needs of various different industries.