Secondary steelmaking

The objective of secondary steelmaking is to make the steel of desired chemistry and cleanliness by performing the following treatments in “Ladle”:

a) To stir the molten steel by purging inert gas through the bottom of the ladle.

b) To inject slag forming powder either through a lance for further refining

c) To produce clean steel either by removing inclusions or modify them by suitable injecting    materials     

d) To carry-out deoxidation and degassing.

Secondary steelmaking in ladles has become an integral part of steelmaking. Ladles have additional heating facility and are called Ladle furnaces (LF).

There are several practices adopted for degassing, like vacuum tank degasser, stream degassing and recirculation degassing. In recirculation degassing steel is made to flow from the ladle into a separate degassing chamber and then returned after exposure to the vacuum. In one of the recirculation degassing practice metal circulation is achieved by dipping the degassing vessel into the ladle, the liquid steel is raised into the vessel, degassed and returned into the ladle.

In another practice a refractory lined vessel is equipped with two legs (called snorkels) for dipping into the ladle containing molten steel. Pressure is reduced and argon gas is passed into one of the snorkel, thereby molten steel is raised into the vessel and recirculates back into the ladle through the other snorkel. Details are given in lectures 25 and 26.