Coated Steel – Galvanized steel:

Coated Steel – Galvanized steel:

Steel sheet coated through a heat process or through electrolysis with a layer of substance to protect the base metal (substrate) against corrosion. The most commonly used material is zinc which can be applied either using the heat process (hot-dip galvanizing) or using electrolysis (electro-galvanizing).

A. Galvanized steel products - Zinc coated galvanized GP and GC steel products are sturdy, light weight, bright and corrosion resistant. The functions of the zinc layer are mainly three folds:

(a) To retain the steel intact with its full initial strength

(b) To provide the surface a more pleasing appearance

(c) To increase the life of any suitable organic finishing system applied over it

In fact, zinc coatings provide the most effective and economic way of protecting steel against corrosion. Zinc coated steel is very environment friendly. Zinc is an integral part of our environment and occurs naturally in rocks, soil, air and water. Zinc is also an essential element for all life, from humans and animals to plants and micro – organisms. All types of zinc coated steel products are recyclable. In the last few decades, both the recycling technology and its capacity has been developed considerably in response to increasing environmental awareness and the cost-effective alternative supplies of raw materials for the steel and zinc industries. Presently, about 80 percent of the zinc is available from zinc coated steel that is recycled in India.

B. Galvanizing process: There are two main processes used in the production galvanized product namely: (i) Hot – dipped galvanizing and (ii) Electrolytic Galvanizing

(i) Hot – dipped Galvanizing – It is one of the basic and efficient corrosion resistant technique for producing galvanized steel. During the galvanizing process, steel coils are previously cleaned and pickled and then dipped into a bath of molten zinc to form a series of zinc / iron alloys integrated with the steel surface. As steel is removed from the bath, a layer of relatively pure zinc is deposited on the top of alloy layers. On solid deification, the zinc assumes a crystalline metallic luster, often known as “spangling”. The spangles can be enhanced and reduced depending on the end use. The life of galvanized coating in steel structures permanently immersed in liquids depends on the corrosion properties of the liquid and the thickness of the galvanized coating in the structure. Hot-dipped galvanizing technology has been greatly improved over the years and by the introduction of the sendzimir process or one of its variants, HDG products are introducing on the market share of electrolytic galvanized products in the western world because it is more cost effective.

(ii) Electrolytic Galvanized Steel - In the electrolytic galvanizing process, zinc ions from the electrolytic is deposited on the strip surface (cathode) under the influence of electric current using either soluble or insoluble anodes. The electrolyte is usually zinc sulfate or zinc chloride or mixed. The electro–galvanized strips are post treated with passivation solutions such as phosphate or chromate. The plating process controls the coating thickness resulting in much thinner coatings as well as double-side coatings. The automobile industries in Japan and the U.S. are using between 35 to 45 percent of the total steel consumed in the form of electro-galvanized steel sheets. These sheets have excellent surface finish and press formability for protection from corrosion of auto body, fuel tanks, exhaust pipes etc.

Types of finished steel products and their terminologies:

Types of finished steel products and their terminologies:

Steel is not a single product. There are currently more than 3,500 different grades of steel with many different properties - physical, chemical, environmental, 75% of which have been developed in the last 20 years. If the Eiffel Tower were to be rebuilt today the engineers would only need one-third of the amount of steel, modern cars have new steels with higher strength reducing the overall shell weight by 25%. Some of the finished steel terminologies have been discussed below:

(1) Annealing: Annealing is a heat treatment process. With this, steel products are reheated to a suitable temperature to remove stresses, resulting from previous processing and to soften them and/or improve their machinability and cold forming properties.

(2) Billet: Billet is a semi-finished steel product with a square cross section up to 155mm x 155mm. This product is either rolled or continuously cast and is further processed by rolling to produce finished products like wire rods, merchant bars and other sections. The range of semi-finished products above 155 mm x 155 mm is called blooms.

(3) Carbon Steel: A type of steel generally having no specified minimum quantity of any alloying element and containing only an incidental amount of any element other than carbon, silicon, manganese, copper, sulfur and phosphorus.

(4) Coated Steel (Galvanized & Color coated): Steel sheet coated through a heat process or through electrolysis with a layer of substance to protect the base metal (substrate) against corrosion. The most commonly used material is zinc which can be applied either using the heat process (hot-dip galvanizing) or using electrolysis (electro-galvanizing). An organic coating (paint, plastic) can also be deposited on the layer of zinc. The zinc-coated steel is often referred to as "galvanized steel".

(5) Electric Sheets: These sheets are produced from steel alloyed with silicon (up to 3.5%) and are used in the manufacture of alternators, transformers and motors. Grain oriented electrical sheets have a high silicon content and are used for the manufacture of large transformers. Non-oriented products are used in electric motors and small transformers.

(6) Flat Steel Products: A flat steel product is a plate product or a (hot or cold) rolled strip product. Typically steel is rolled between sets of rollers to produce the final thickness. Plate products vary in dimensions from 10 mm to 200 mm and thin flat rolled products from 1 mm to 10 mm. Plate products are used for ship building, construction, large diameter welded pipes and boiler applications. Thin flat products find end use applications in automotive body panels, domestic 'white goods' products, 'tin cans' and whole host of other products from office furniture to heart pacemakers.

(7) Long Steel Products: A long product is a rod, a bar or a section - typical rod products are the reinforcing rods for concrete, engineering products, gears, tools etc. are typical of bar products and sections are the large rolled steel joists (RSJ) that are used in building construction projects. Wire-drawn products and seamless pipes are also part of the long products group.

(8) Refining Stand: A stage in the process of making crude steel, during which the crude steel is further refined (i.e., most residual impurities are removed) and additions of other metals may be made before it is cast.

(9) Semi-finished Products: Steel products such as billet, blooms and slabs. These products can be made by direct continuous casting of hot steel or by pouring the liquid steel into ingots, which are then hot rolled into semi-finished products.

(10) Slab: A semi-finished steel product obtained by rolling ingots on a rolling mill or processed through a continuous caster and cut into various lengths. The slab has a rectangular cross section and is used as a starting material in the production process of flat products, i.e., hot rolled coils.

(11) Strip: Flat steel coil products, with widths of less than 600mm for hot rolled products and less than 500mm for cold rolled products.

(12) Thin Strip Continuous Casting: Casting technology that takes liquid steel and casts it into solid strip in one step, thereby eliminating the need for a continuous slab caster and hot strip mill.