Casting Of Ingots

After the molten steel has been poured from the steel making furnace it has to be converted in solid shapes known as ingot. The ingot is further processed by rolling it into shapes, casting it into semi-finished forms, or forging. For removing the need for ingot the shaping procedure is being rapidly replaced by continuous casting, thus improving efficiency. The molten metal is poured (teemed) from the ladle into ingot moulds in which the metal solidifies. Moulds are generally made of cupola iron or blast-furnace iron, with 3.5 percent carbon, and are tapered in order to facilitate the removal of the solid metal. The bottoms of the moulds may be closed or open; if open, the mould is placed on a flat surface. The taper might be such that the big end is down.

The cooled ingots are removed (stripped) from the moulds and lowered into soaking pits, where they are reheated to a uniform temperature of about 1200oC for subsequent processing by rolling. Ingots might be rectangular, square or round in cross-section, and their weights ranges from a few hundred kgf of 40 tons.

Certain reactions take place during the solidification of an ingot, which in turn have important influences on the quality of the steel. For example, significant amounts of oxygen and other gases can dissolve in the molten metal during steel making. However, much of these gases are rejected during solidification of the metal because the solubility limit of gases in the metal reduced sharply as its temperature reduced. The rejected oxygen combines with carbon, composing carbon monoxide that causes porosity in the solidified ingot.Three types of steel are produced depending on the amount of gas evolved during solidification. These types are following: semi-killed, killed & rimmed.