Abstract
Refining process with a little quantity of slag in the top and bottom blowing converter (LD-OTB) has been found very promising one through the experiments of using low sulfur and low phosphorus hot metal. Desulfurization and dephosphorization of the hot metal was carried out using a 350 t torperdo car after desiliconization practice and phosphorus content was reduced to the level less than 0.02%. The hot metal, charged into 240 t top and bottom blowing converter was refined at a little quantity of slag less than 8 kg/t in burnt line consumption. A little quantity of slag refining process brought us such good features as lowering the critical carbon content (C*) which decarborization rate decreases in the top and bottom blowing converter, increasing manganese content and reducing hydrogen content at turn down.
However, the increase of iron loss into exhaust gas was observed to some extent in spite of the slag volume decrease and the pretreatment of desiliconization might have a tendency toward the shortage of heat in high temperature heat. One of the countermeasures for these two problems was tested by super soft blowing which was the extreme high lance height practice. The super soft blowing was found out very effective not only for preventing the increase of iron loss into exhaust gas with assistance of bottom stirring, but also for compensating the heat by controlling the post combustion of CO gas.
