Development of Alloy Bullets Shooting Method into Molten Steel in Ladle

The bullets shooting method has been developed as one of the alloy adding technologies into ladle. The charactristic of this method is that it is very effective for adding the elements whose properties are distinctive in terms of high vapour pressure, low specific weight, and high affinity with oxygen. By utilizing this method, several effects have been obtained. These are as follows. 1) The shooting method of aluminium gives a much higher aluminium yield of addtion compared with the conventional method, and the amount of aluminium addtion becomes 80% of that in the convetional method for killed steel. In addition to this effect the scatter in soluble aluminium content in products has been reduced to about 1/3 and the steel quality has been improved. 2) SCAT is a comprehensive system of calcium adding technique by utilizing the shooting method, and gives a high and stable yield of calcium. By adopting SCAT the shape and distribution of inclusions in steel are altered, and this results in the improvement of mechanical properties such as low temperature thoughness, elongation and notch impact toughness in T and Z directions, and toughness in welded zone. 3) It has become possible to control baron content in steel precisely by utilizing the shooting method combined with other technical developments, and thereby to obtain the tergetted mechanical properties. Further development in ladle treatments is expected and especially the bullets shooting method will take a significant part in this area.