Study On Mould Fluxes In High-Speed Slab Continuous Casting For Panzhihua Iron And Steel Co.

The conduction of high speed slab casting is an important developing tactic for Panzhihua Iron & Steel Co (PISCO). Mould fluxes, used in the hot running of high speed continuous caster were all imported from abroad, of which, those for low-carbon steel worked well, but those for plain carbon steel and low alloy steel didn't work very well, the breakout alert happened frequently. This situation severely blocked the output of caster and the development of new products in PISCO. Based on the investigation about the research and application of high speed continuous casting mould fluxes, considered the equipment and process parameters of the caster in PISCO, (CaO/SiO₂),CaF₂,Na₂O,MnO and Li₂O were selected as main factors, five-factor and five-level two-order regression design was selected. The relationships among composition and melting, viscosity, crystallizing and mineral property were comprehensively researched in this paper. And the manufacturing process for high speed continuous casting mould fluxes was also studied. The trial in steel plant was carried out based on the lab experiments. Some results are as follows: When R(CaO/Si₂O)<1.0, melting temperature decreases as R increases; When R(CaO/Si₂O)>1.0, melting temperature increases slowly; The increase of R(CaO/Si₂O) can decrease the viscosity and elevate the break temperature and crystallization ratio. Melting temperature, viscosity, break temperature and crystallization ratio decreases as the content of CaF₂ increases, however, when quantity of CaF₂ is more than 10%, the influence of CaF₂ on reducing melting temperature becomes weak, and when quantity of CaF₂ is more than 9%, the influence of CaF2 on viscosity reducing becomes weak. If content of Na₂O and MnO increases, the smelting temperature, viscosity and crystallization ratio increases gradually; but when Na₂O>10%, the influence of Na₂O on the smelting temperature,viscosity and break temperature is not evident, and when MnO>4%, the influence of MnO on the smelting temperature,viscosity and break temperature is not evident. When content of Li₂O increases, melting temperature, viscosity and break temperature decreases gradually, while crystallization ratio increases gradually; When Li₂O<2.5%, the influence of Li2O increasing on reducing of melting temperature is significant, when Li₂O>2.5%, the influence is not evident; When Li₂O<3.5%, the influence of Li₂O increasing on reducing of viscosity is evident, when Li2O>3.5%, the influence is not evident. When low carbon steel containing high [Al]s cast, in order to avoid Al₂O₃ inclusion entering into mould fluxes to change physical and chemical property of mould fluxes, R(CaO/Si2O) should be given between 0.95¹.05. In the manufacturing of high speed continuous casting mould fluxes, The adding raw materials of fluxes should be below 200 meshes ; graining balls should be more than two kinds of dimensional specification; density of slurry should be between 50%～65%; the mode of binding materials using at spraying process for granule fluxes can be selected as "clinker + modifying agent+ H type binder materials". Higher pressure of slurry pump, smaller diameter of sprayer nozzle and enough heat exchange in the tower can get smaller size of granules of fluxes with lower moisture and higher density. The application in steel plant show that, the developed mould fluxes for low carbon Al-killed steel and plain carbon steel have good spreadability and liquidity. As the fluxes used, the liquid level in the mould was stable, slag rims did not exist. The mould fluxes for low carbon Al-killed steel behaved stable when the casting speed was between 1.70 ～1.72m/min, and the consumption of mould fluxes was about 0.40Kg/t, which was higher than the mould fluxes imported. And at high casting speed, the consumption of this mould flux decreased slowly, which indicated that it still has more space to elevate casting speed. The cast slab surface quality was good, and the unconditioning ratio accounted for 96.4%. The physic-chemical performance of the mould fluxes kept stable after absorbing Al2O3 inclusions. The mould fluxes for plain carbon steel was stable at the casting speed of 1.40～1.45m/min, and the depth of liquid slag pool was about 10～15mm. The consumption reached 0.55Kg/t, which was better than those fluxes from some other domestic factories. The surface quality of casting slab was good, surface quality defects such as slag and gas entrapment didn't exist, the oscillation mark was uniform and the unconditioning ratio accounted for 100%. After experiment research and steel plant practice, some physical and chemical properties of mould fluxes for low-carbon Al-killed steel was concluded as follows: melting temperature is between 1080¹140℃,viscosity at 1300℃is between 0.15⁰.20Pa.S, basicity is between 0.95¹.05. And a suggested physical and chemical property of mould fluxes for plain carbon steel is as follows: melting temperature is between 1120¹160℃,viscosity at 1300℃is between 0.10⁰.15Pa.S, basicity is between1.15¹.25.