Kinetics Basic Study Of Refining High Nitrogen Steels By High-pressure And Bottom-blowing Nitrogen

High Nitrogen Steels is defined as nitrogen content beyond the solubility limit at one atm. The performance and quality of HNS have a distinct improve compared with other general steels. It has a well toughness, high strengthen, good anti-erosion and anti-wear, wriggle performance and fatigue intensity have also increased.Many refining techniques have successively been developed abroad in the 1980s, such as high-pressure plasma arc melting, pressure-electro-slag-remelting, counterpressure foundry and powder metallurgy etc. But China is inferior to foreign countries in this aspect, this paper studies the thermodynamics and kinetics factors which influence nitrogen solubility and puts forward adding-nitrogen kinetics model by high-pressure and bottom-blowing nitrogen, explores a new refining technique suitable to large-scale production in order to develop the potential of HNS.The results show that high-pressure and bottom-blowing nitrogen technique is a feasible method to produce HNS. Carbon, silicon, sulphur and phosphorus etc. can decrease nitrogen solubility; chromium, manganese, vanadium etc. can increase nitrogen solubility. Nitrogen solubility change with temperature in liquid state Fe alloys exists a fold point, different variable rules in different state, but nitrogen solubility increasing with temperature is the whole tendency. Generally, nitrogen solubility in HNS increases with high pressure, actually it abides by Sieverts rule in low-pressure scope, a difference comes when high pressure and high content alloys elements. We can utilize Cr equivalence method to predict nitrogen content with different pressure.The paper establishes adding-nitrogen kinetics model by high-pressure and bottom-blowing nitrogen through analyzing the controlling steps which affect add-nitrogen velocity. The model shows that transferring mass coefficient has a direct proportion to mix strength. Increasing nitrogen quantity can bring about nice kinetics conditions. It can improve bubble dispersion degree, increase contact area between liquid and gas state, shorten transferring mass distance, improve transferring mass coefficient and increase nitrogen absorption velocity. Oxygen and sulphur performance more activity than nitrogen, which occupy the room provided for nitrogen absorption, to obstacle nitrogen solution. Mass transfer in liquid state as the limited step influence adding-nitrogen velocity on condition that a low oxygen and sulphur content; with oxygen and sulphur content increasing interface reactor and mass transfer in liquid state control the adding-nitrogen velocity together. So we should confine their content. Additionally nitrogen bubble is subject to flee when HNS is solidification, which demands to maintenance a high pressure all the time when solidification.