Industrial experience for nitrogen control in the production of interstitial-free (IF) steel

Interstitial Free steel is a microalloyed steel that contains significantly low concentrations of interstitial elements such as carbon and nitrogen. In this context, nitrogen control in liquid steel is a major issue particularly in cases where the nitrogen content in hot metal or other charged material is high. This paper describes the practice of IF steel production at No. 3 steelmaking plant of WISCO using hot metal containing high nitrogen due to hot metal desulphurization treatment with nitrogen as the carrier gas. By adapting new technology for nitrogen removal in a combined blown converter and an RH vessel as well as controlling nitrogen pick-up during transfer operations, final product can be generated with an average nitrogen content of about 18 ppm and with some values as low as 10 ppm.