Kwangyang Works of POSCO produces cold rolled coil amounting to about 30 percent of its total annual production. Cold rolled coils are mainly applied in automotive and home electric appliances. These customers are sensitive to the surface defects caused by non-metallic inclusions. Therefore, slag making technologies have been improved to cope with these customers' cleanliness needs. The technology makes it possible to absorb alumina inclusions from the molten steel and to withhold the reoxidation of the molten steel. The process of slag control for clean steel is as follows: BOF: The amount of BOF slag allowed to enter the ladle is controlled by slag checkball, plug, pneumatic stopper and transfer car cutting. In order to obtain clean steel, it is necessary to minimize the amount of ladle slag which is inflown from BOF. Slag modifier is added to the ladle at the early stage of tapping of BOF. It modifies the carry over BOF slag to form the low melting point slag CaO-Al_2O_3-SiO_2 ternary diagram and to dilute the concentration of FeO + MnO (wt percent) in the ladle slag. Al-base slag deoxidizer is added to the ladle in a few minutes after the tapping of BOF. The standard amount of addition varies depending on free [O] at the BOF end point. BAP: The ladle slag is stirred by Ar top and bottom bubbling at the BAP (B/S). (B/S) Because it makes a major effect on the efficiency of slag deoxidation. RH : In order to remove the alumina inclusion in steel, the synthetic slag is added to the RH vessel after deoxidation. To make extremely clean steel, it is necessary to prevent the reoxidation of the steel by the control of ladle slag. In Kwangyang Works, the technologies of slag modification and deoxidation had been applied to produce ultra low carbon steel. As a result, the amount of non-metallic inclusions
展开▼
