The Principle and Practice on Melting High Nitrogen Steel (HNS) by Blowing Ammonia Gas

摘要

During the HNS melting process, the absorption reaction of Nitrogen in the liquid steel by blowing NH_3 and N_2 respectively was investigated. Under the normal pressure, the content of nitrogen increased due to the existence of the elements such as [Cr] and [Mn] in melting process. In order to obtain higher content of nitrogen in steel, high pressure of nitrogen should be kept, additionally, the liquid steel should be deoxidized and desulfurized because the [O] and [S]as surface activity element is not favorable to absorb nitrogen in the melting process. Therefore, it is difficult to achieve higher nitrogen content in steel melt within a short melting time under the normal pressure. The present work is based on the metallurgical thermodynamics. A coupling reaction of NH_3 with [O] , NH_3+3/2[O] = [N] + 3/2H_2O, can enhance generation of activity nitrogen atom in liquid steel. Nitrogen atom is absorbed more easily than nitrogen molecule. At the same time, blowing ammonia gas can remove the oxygen from liquid steel and decreased the inclusion in the steel. Experiments of HNS melting in ten-kilogram induction furnace indicated that, the absorption efficiency of nitrogen by blowing NH_3 increase 30% ～80% than blowing N_2 under the condition of the same content of alloys and the same mole of nitrogen which is blown. The technical melting process by blowing NH_3 under normal pressure is available in the industry production of HNS.