AIR LEAK THROUGH SNORKEL OF RH DEGASSER A ND ITS EFFECT ON NITROGEN REMOVAL IN MOLTEN STEEL

Experimental and theoretical studies were carried out to understand th e effects of air leak through the snorkel of a RH degasser on desorpti on and absorption of nitrogen in molten steel during vacuum treatment. The pressure and gas composition in steel pipes inserted into the ref ractory of up-and down-legs were examined. Snorkels were sealed with a rgon gas and change of nitrogen content in steel were compared with co nventional treatment without argon gas seal. The outer side pressure o f the down-leg is higher than the inner side one, whereas the pressure distribution of the up-leg is to the contrary. The main gas compositi on in the down-leg is nitrogen and that of the up-leg is argon. These mean that the air leak spot exists in the down-leg. Desorption and abs orption rates of nitrogen are balanced at 20 ppm when snorkels are sea led with argon gas, whereas balance content is 27 ppm for conventional treatment without argon gas seal. The kinetic analysis on nitrogen be havior made clear that the amount of nitrogen gas leak when argon gas was used for sealing snorkels was reduced on the average by one half a nd standard deviation of that value by one fifth compared with the con ventional treatment. The relation between the rate constant for nitrog en removal and nitrogen absorption rate by air leak was shown in order to obtain the aimed final nitrogen content at the fixed treatment tim e.