Experimental Kinetics Study On Refining High Nitrogen Steels By High-pressure And Bottom-blowing Nitrogen

The steels containing more than 0.08wt% nitrogen in a ferrite matrix or more than 0.4wt% nitrogen in an austenitic matrix were defined as high nitrogen steels. The performance and quality of HNS have a distinctive improvement compared with other general steels. It has a good toughness. High strengthen, good anti-erosion and anti-wear, wriggle performance and fatigue intensity have also increased. However adding nitrogen in molten steels is very difficult under atmosphere pressure so the development of a low cost and effective technique to make high nitrogen steels have being paid more and more attention.According to the results of thermodynamics calculation, the mechanics of reaction for adding nitrogen reaction is dicussed. On the bais of reaction model, dynamic model of adding nitrogen reaction is established. With experiments, the nitrogen content in steel is obtained under different conditions, and the main kinetic factors are determined.Analysis and calculation based on the experital results indicate that, there are a lot of influencing factors on refining high nitrogen steels in techniques of high-pressure and bottom-blowing nitrogen; pressure is the most significant factor, the second is alloy content, the third is the time of blowing, and the last is the temperature. The adding nitrogen reaction isn't first-order reaction and second-order reaction, the reaction is controlled by interface chemical reaction and diffusion in the liquid phase boundary layer, and the reaction rate constant and the apparent activation energy are also obtained. The apparent mass transfer coefficient was measured under different conditions.There are four factors which are pressure in the furnace, nitrogen flux that blow from bottom, temperature and blowing time to influence kinetic of adding nitrogen. The relation between content of nitrogen and flux of nitrogen that blow from bottom is better in line when flux of gas is 0.15 -0.20 m³Â·h^-1. It mainly benefits for kinetic of adding nitrogen when molten temperature is 1920K. Content of nitrogen in steel is adding at 25 minutes after beginning air refining when the temperature rises which is nearly saturation or saturation already at 35 minutes, and is already reaching saturation at 45 minutes. But owing to the influence of thermodynamics, solubility of nitrogen is decreasing when the temperature rises. The influence of pressure to kinetic of adding nitrogen is slight, so the pressure is 1.15-1.20MPa when steel of 18Cr18Mn-0.9N is smelted.