NEW MGO-CAO BASED REAGENT FOR LADLE TREATMENT OF STEEL

A new method for steel desulphurisation and non-metallic inclusion control using magnesium produced from its oxide in situ in steel melts has been developed. This involves the pneumatic injection into the steel ladle of a granular product (average size 0.5 mm dia.) which consists essentially of fine aluminium particles encapsulated by a coating comprising a combination of calcium and magnesium oxides based on the formula (by weight): 50.27%MgO, 20.86%CaCO3, 18.18%Al, and 10.69%CaF2. At steelmaking temperatures the free energy diagram predicts that the aluminium will reduce MgO and release magnesium gas for desulphurisation and deoxidation and such a reaction has been confirmed by earlier laboratory experiments. In the present work 180 kg of the reagent described above was injected with a Scaninject lancers injection system into 40 t of aluminium killed SAE 1513 steel contained in an alumina ladle at 1570-degrees-C, and for comparison purposes an identical cast was treated in exactly the same way with CaSi. Both treatments achieved high levels of desulphurisation and clean steels. Inclusion studies revealed almost identical inclusion distributions for both treatments, and microchemical analyses in the scanning electron microscope showed that the inclusions present were typical of those expected in calcium and magnesium treated aluminium killed steels.