On the Protection of Molten Steel from Nitrogen Absorption in Steelmaking Process

Abstract

For the purpose of producing low nitrogen steel by making use of low nitrogen content (712 ppm) of the molten steel at the end point of improved oxygen converter, conditions for protecting molten steel from nitrogen absorption between the end point of converter and casting are investigated.
(1) In the case of low carbon steel, the combination of tapping without adding deoxidizer and ladle metallurgy with consideration of the amount of slag and sealing suppresses the total nitrogen pick up 39 ppm.
(2) The relationship between the order of rate formula of nitrogen absorption and conditions ([N], [O] and P_N2) is considered. For the steps of reblowing and tapping of low nitrogen molten steel, rate formula of second order would be more suitable. The influence of [%C] on the nitrogen absorption during reblowing and tapping is explained on the result.
(3) In the case of high carbon steel, method of using dry ice for preventing nitrogen absorption during tapping are developed. The optimum condition of using dry ice are studied. It has been possible to produce stably the high carbon steel wire materials of low nitrogen content (2±2 ppm) by using this technique.