Because of the addition of significant quantities of aluminum and manganese,the great challenge of casting 20Mn23Al nonmagnetic steel is to design a mold slag that is chemically compatible with this steel composition.A new mold slag with low melting point and low basicity was proposed.The initial slag(the base mold slag)and two corresponding mold slags sampled after 8 min and 15 min were investigated,and the changes of mold slag composition and properties of molten slag were discussed.The results showed that the slag quickly changed in chemical composition to a slag that contained a small quantity of silica and a larger quantity of alumina,and the basicity increased obviously;the heat flux density through the slag film decreased slightly compared with the slag film at 0 min,8 min and 15 min;the mold slag used for nonmagnetic steel was precipitated as CaF2 crystals.The casting experiment shows that the slab has good surface quality without longitudinal face cracks and slag inclusions;the Al2O3 content in the molten slag pool increased with time at the beginning stage,and it can approach equilibrium state after about 600 s.
YU Xiong WEN Guang-hua TANG Ping MA Fan-jun WANG Huan
Due to the high content of the Al-TRIP steel, Al reacts with SiO2 in the mold slag during the casting process, which results in the increase of wAl2O3/wSiO2 ratio and the Al2O3 content, respectively; the characteristic of heat transfer through the slag film is then changed, which influences the smooth operation of the continuous casting process. The heat flux simulator of mold slag film was used to study the change tendency of the heat flux density through slag film and the results were discussed; at the same time, the characteristics of the crystals in the No.15 mold slag were determined by BSE and XRD. The results obtained show that heat flux density decreases with the increase of wAl2O3/wSiO2 ratio. Heat flux density increases with the increase of Li2O and/or B2O3 content in the mold slag which contains 30% of Al2O3. Compared with the heat flux density of common slag of peritectic steel, a suitable mold slag containing 4% of B2O3 and 4% of Li2O is designed. The heat flux density is 0.645 MW/m2 when wAl2O3/wSiO2=1.46. Under this experimental condition, the CaF2 crystals precipitate in the mold slag used for Al-TRIP steel.
