Synopsis 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 A120~ in the molten powder pool. 2) A1203 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 A1203. 5) Design of optimum powder viscosity by consideration of A1203 absorption during continuous casting. The results obtained were as follows: (1) The A1203 content of the molten powder pool increases with the elapse of casting time in accordance with the A1203 absorption capacity of the powder, but after some time, reaches a constant value that matches the A1203 absorption capacity of the powder. (2) The A1203 absorption rate of the molten powder increases as the basicity index B; of the powder increases. (3) The viscosity of the molten powder generally increases with increasing A1203 content. (4) To uniformize heat removal through the mold during casting, it is effective to control the parameter iV over the range of 1.0 to 3.5, where 2 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 A1203 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 mediumcarbon aluminum-killed steel slabs and to realize the hot direct rolling of unconditioned slabs.

Synopsis:Behavior of hydrogen in steel in the steel-making and strand casting processes was studied. The results are summarized as follows:(1) The optimum procedure of sampling and analysis of hydrogen in liquid steel is determined.(2) Diffusible and non-diffusible hydrogen in cast slabs can be analyzed separately by the methods of glycerine extraction and vacuum heating extraction respectively.(3) Hydrogen content in liquid steel is about 2-4 ppm before tapping and increases abruptly during tapping. The amount of hydrogen increase is closely related to the humidity of atmosphere.(4) Segregation of hydrogen is observed at the center of slabs, the amount of which is affected by the nondiffusible hydrogen content in cavitiees.(5) Non-diffusible hydrogen content is confirmed to be proportional to the total volume of cavities which are formed during solidification.(6) The degree of hydrogen segregation at the center of slabs decrease with an increase of the thickness of equiaxed structure zone in slabs, because cavities in the zone are scattered uniformly and finely.

No abstract

No abstract

No abstract