Mold powder technology for continuous casting of aluminum-killed steel was developed to produce the clean and crack free steel slabs.
The following items were investigated:
1) Mass balance of Al₂O₃ in the molten powder pool.
2) Al₂O₃ absorption capacity o f the molten powder.
3) Uniformization of heat removal through the mold during continuous casting.
4) Change in powder viscosity with absorption of Al₂O₃.
5) Design of optimum powder viscosity by consideration of Al₂O₃ absorption during continuous casting.
The results obtained were as follows:
(1) The Al₂O₃ content of the molten powder pool increases with the elapse of casting time in accordance with the Al₂O₃ absorption capacity of the powder, but after some time, reaches a constant value that matches the Al₂O₃ absorption capacity of the powder.
(2) The Al₂O₃ absorption rate of the molten powder increases as the basicity index B_i of the powder increases.
(3) The viscosity of the molten powder generally increases with increasing Al₂O₃ content.
(4) To uniformize heat removal through the mold during casting, it is effective to control the parameter ηV over the range of 1.0 to 3.5, where η is the viscosity of the molten powder in poise at 1300°C and V is the casting speed of the machine in m/min.
(5) A method for designing the optimum powder viscosity that allows for the absorption of Al₂O₃ during casting has been established by the combination of the results mentioned above.
(6) Powders designed by the above method have been applied to continuous slab casters to prevent the longitudinal surface cracking of medium-carbon aluminum-killed steel slabs and to realize the hot direct rolling of unconditioned slabs.