A bottom-blowing nozzle of a converter, being featured by a wide range of flow rate controllability and a low wearing rate, has been studied with the view of developing a top- and bottom-blowing converter which is capable of producing a wide variety of steel.
(1)When an inert gas is injected into the steel bath through the bottom-blowing nozzle, a so-called mushroom (solidified iron) having extremely small pores is formed atop the nozzle by the cooling effect of gas.
(2) When a stable mushroom is formed atop the nozzle, the flow rate controllability and the wear rate of the nozzle are improved.
(3) In order to form a stable mushroom atop the nozzle, it is most effective to use a nozzle consisting of multiple small-diameter pipes.
(4) There is a proper range for the diameter of individual pipes. On the basis of the heat transfer model it has been established that, for the specified diameter, there is the minimum value both for the distance between neighboring pipes and for the gas flow rate to form a stable mushroom atop the nozzle.
(5) This bottom-blowing nozzle allows to control the bottom gas flow rate over a wide range and ultimately makes it possible to control the iron content in slag (T.Fe) widely. In a low carbon region, the iron content can be reduced by bottom gas injection with the full flow rate. In a high carbon region, the nozzle can be used at a low gas flow rate to increase the iron content and ensure proper dephosphorization of the same level as in a top-blowing converter. Thus, this process is applicable for the production of all grades of plain carbon steel.