Qingdao TTWY International Trade Co.,Ltd

In traditional metallurgical furnace use graphite electrode, the electric arc furnace refining operations refer to removing the phosphorus, sulfur, aluminium, silicon, manganese and carbon from steel. In recent times, dissolved gases, especially hydrogen and nitrogen, have been recognized as a concern. Traditionally, refining operations were carried out following meltdown i.e. once a flat bath was achieved. The availability of oxygen determines this refining reaction. At the end of melting, oxygen is sprayed to reduce the carbon content in the bath to the level required for tapping. Most compounds to be removed during the refining process have a higher affinity for oxygen than carbon. Therefore, oxygen will preferentially react with these elements to form oxides, which will float out of the steel and enter the slag.

In modern electric arc furnace operations, especially those that operate with molten steel and residual slag "hot heel", such as metallurgical furnace use graphite electrode for metal smelting, most of the heat may blow oxygen into the molten pool. As a result, some smelting and refining operations are carried out simultaneously.

Phosphorus and sulfur are usually present in the furnace charge at a concentration higher than that normally allowed in steel, and therefore must be removed. Unfortunately the conditions favorable for removing phosphorus are the opposite of those promoting the removal of sulfur. Therefore, once these materials are pushed into the slag stage, they may be reduced to steel. Phosphorus retention in the slag is a function of the molten pool temperature, slag basicity and FeO content in the slag. At higher temperatures or lower FeO content, phosphorus will be returned from the slag to the molten pool. Phosphorus removal is usually performed as early as possible during heating. Hot heel exercises are very good for phosphorus removal, because oxygen can be sprayed into the molten pool when the oxygen temperature is very low. In the early stages of heating, the slag will contain the high FeO content brought about by the previous heating, thus helping to remove phosphorus. Blast furnace slag alkalinity (that is, high lime content) is also conducive to phosphorus removal, but care must be taken not to let the slag be saturated with lime. This will lead to an increase in slag viscosity, which will make the slag less effective. Sometimes fluorspar is added to help fluidize the slag. Stirring the bath with inert gas is also beneficial because it can renew the slag/metal interface, thereby improving the reaction kinetics.

Generally, if a particular steel grade requires low phosphorus content, scrap should be selected to make it low in melting. The partition of phosphorus in the slag to phosphorus in the bath ranges from 5 to 15. Phosphorus in EAF is reduced by 20% to 50%.

http://www.ttwycasting.com/