MANUFACTURING OF MS INGOT

A steel ingot is a semi-finished solid metal form, which is produced through a continuous casting process.

Mild steel Ingots are the basic raw material for the manufacture of various types of re-rolled products, for e.g. rounds, flats, channels equal and unequal angles etc. A major part of this re-rolled products in the form of cold-twisted deformed bars are used in building construction as reinforcement.

Ingot is the product obtained by pouring liquid steel into cast iron mould of a shape appropriate for the subsequent processing generally by hot rolling or forging into semi-finished or finished products. The shape generally resembles a truncated pyramid or truncated cone. The side surfaces can be corrugated and the corners are more or less rounded. Depending on its subsequent conversion requirements, ingot can be dressed and/or hot scarred or cropped.

The usual cross section of ingot is square, rectangular, round, oval, or polygon. Ingots with square cross section are used for rolling into billets, rails and other structural sections, whereas, ingots with rectangular cross section, are generally used for rolling into flat products. These ingots usually have a width which is two times or higher than the thickness. Round ingots are used for the production of seamless pipes. Polygonal ingots are used to produce tyres, and wheels etc. Low capacity steel melting shops with induction furnaces produce very small cross section ingots which are called as pencil ingots.

Typically ingots used for the production of rolled products have weights in the range of 5 tons to 35 tons. Pencil ingots are used for the rolling of merchant long products and reinforcement bars and have weights typically in the range of 100 kg to 200 kg. Ingots used for the production by forging of the heavy equipment/components can be extremely large ingots weighing even 600 tons and more.

Ingot is a conventional crude steel product, but presently it constitutes a very small percentage of global crude steel production. However, ingots are still fundamental for specific low-alloy steel grades and for special forging applications, where products of large dimension, high quality or small lot size are needed. These large dimension ingots are being used these days in the power engineering industry (e.g. shafts for power generation plants, turbine blades), the oil and gas industry (conveying equipment, seamless tubes), the aerospace industry (shafts, turbines, engine parts), ship building (shafts for engines and drives), tool making and mechanical engineering (heavy forgings, cold, hot and high-speed steels, bearing, drive gears) as well as automotive engineering (shafts, axes).

As the demand of heavy ingot increases nowadays, especially from the power engineering industry and ship industry, there is a tendency of producing extremely large ingots, which are mainly applied for pressure retaining components such as reaction vessels for nuclear power plant and rotating components like drive shafts of gas turbines and generator rotors.

The general macrostructure that is often seen in the steel ingot can be divided into three distinct zones namely (i) the outer chill zone with small crystals of approximately equal size, (ii) the intermediate columnar zone with elongated columnar dendrites, and (iii) the central equiaxed zone with relatively large equiaxed grains. Besides the referred three zones, a region where the outer columnar dendritic structure transfers to the inner equiaxed grain structure is commonly observed. This region is named as the ‘columnar to equiaxed transition’ zone.

As the demand of heavy ingot increases nowadays, especially from the power engineering industry and ship industry, there is a tendency of producing extreme large ingots over 600 t and continuous cast strands with thickness over 450 mm and rounds with diameter up to 800 mm, which are mainly applied for pressure retaining components such as reaction vessels for nuclear power plant and rotating components like drive shafts of gas turbines and generator rotors.