Studies On Behaviors Of Inclusions In High-quality Tinned Substrate

High-quality tinned substrate requires higher mechanical properties such as strength,hardness,elongation and plastic strain ratio.It is important to control inclusions during the production high-quality tin plate.A series of basic research was carried out on the evolution of inclusions in tinned substrate.And the results which provided a theoretical basis for further improving the quality of tinned substrate,was applied to the production of tinned substrate in a Steel Company.The main contents are as follows.(1)The evolutions of inclusions during refining,continuous casting and rolling processes were studied from the thermodynamic point of view.The evolution mechanism of inclusions during refining process was proposed.The deformation mechanism was proposed during rolling process based on the composition and morphology of inclusions.(2)A mass-transfer model was developed to investigate the mass transfer occurring among molten steel,slag,inclusions and the refractory during LF refining.The reactions between slag and metal and those between inclusions and metal and refractory erosion were considered.The calculated results agreed with the operational results.The average composition of inclusions can not enter the low melting point area with soft blowing time for 4 min.The average composition of inclusions can not enter the low melting point area when the soft blowing time extended to 8min.The calculated results and industrial sampling results showed that Mg content in the molten steel mainly came from refractory erosion,which accounted for the total amount of 82.9%.(3)Liquid paraffin floating in the water was used to simulate the liquid inclusions floating in the molten steel.The collision of liquid inclusions during floating and the behavior at the interface of slag/steel were studied.Under a certain wettability of the system,a low viscosity slag was favorable for the inclusion to pass through the interface.The effect of wettability on the velocity of inclusions was studied by physical simulation.The wettability has a significant influence on the velocity of particle floating up,and the drag coefficient decreases when the particles and water are non wetting for Re<1.The wettability has no obvious influence on the velocity of particle floating for Re>500.Non wetting inclusions have higher removal rates than wetting inclusions in the tundish.Complete fusion of liquid calcium aluminate inclusions in molten steel occurred after the collision,and the shape of the inclusion became spherical.Fusion did not occurred between CaS and high melting point of calcium aluminate inclusions.and adhered in the shape of cluster,which hindered the further degeneration of calcium aluminate.(4)The flux entrainment into the molten steel and the influence factors were studied.Based on the principle of dimensional analysis,a critical velocity formula was obtained by fitting the measured data from PIV.The mechanism of non Newtonian fluid flux which is favorable to restrain the flux entrainment and lubricate in the mold were studied.A new nozzle for higher speed was designed.An evaluation index of the nozzle structure was proposed.