Effects of hydrogen and nitrogen gas mixture on nitrogen absorption rate in low carbon steel melt

To clarify the effects of blowing a H₂-N₂ mixture onto the surface of molten steel containing various oxygen contents on the absorption reaction of nitrogen in the molten steel, experimental studies were carried out using a 20 kg induction furnace. Blowing of the H₂-N₂ mixture accelerates the nitrogen absorption rate because the oxygen concentration at the gas-metal interface is decreased by the reducing effect of the hydrogen gas. The apparent chemical reaction rate of nitrogen absorption in the present work was evaluated at almost the same reaction rate as that of desorption of nitrogen in previous works. Furthermore, a mathematical model for the nitrogen absorption and desorption reactions in a RH degasser was developed in order to estimate the contribution of each nitrogen reaction site during decarburization and killing treatment with injection of pure N₂ gas or the H₂-N₂ mixture in the molten steel. Using the mathematical model, it was estimated that a larger increase in the nitrogen concentration during decarburization treatment could be achieved by applying a 30% H₂-N₂ mixture to the injection gas in the RH degasser than by applying pure N₂ gas.