Study On Deoxidation By Hydrogen And Natural Gas In Molten Steel

In steel-making process, the properties of steel products are greatly effected by the oxygen and it's form in the steel. With the progressing of society and developing of science and technology, demands for the quality of steel have been increased. New requirements are put forward on deoxidation process. How to decreased the oxygen content and improve the degree of cleanness of steel have attracted more and more attention. For these reasons, deoxidation process was constantly improved and explored for a long time.Generally, the main deoxidation method of steel melts is performed by adding deoxidizers such as Al and ferrosilicon. In this process, deoxidation product remained in steel melt and effected the properties of steel directly. It is well known that many efforts have been made to remove the deoxidation products from molten steel. But the pollution could not be avoided yet. Therefore, reducing the pollution of deoxidation has become a development tendency of deoxidation process.Hydrogen has strong deoxidizing capability. The deoxidation product (H2O) is easily removed from the melt and no non-metallic inclusions are generated. The bad effect of remained inclusions in liquid steels on the properties of steel should be avoided by deoxidation using hydrogen. Therefore, it is great significant to develop the deoxidation by hydrogen for cleanness improvement of steel. However, the deoxidation effect, mechanism and kinetics law by hydrogen need to be studied more systematically.In this subject, the thermodynamic calculations of deoxidizing capabilities of hydrogen and nature gas were carried out respectively. The mechanism and influence factors of deoxidation were discussed. On the conditions of calculations in this subject, the oxygen in the molten steel mainly reacted with hydrogen molecule in the hydrogen bubble in the deoxidation process. During the deoxidation by nature gas, carbon and hydrogen were decomposed from natural gas. Oxygen content was decrease by reaction with carbon and hydrogen. At the same time, the carbon content was increased for carbon solution.Based on the thermodynamic calculation, the experiment of deoxidation effects and kinetics law by hydrogen and methane were studied by measuring the influence of gas flow rate, orifice diameter of submerged lance and gas compound in laboratory scale experiment. Lower oxygen content can be obtained by hydrogen deoxidation. In addition, the retarding for nitrogen desorption by surface-active elements such as oxygen was minished by hydrogen blowing. The nitrogen content was still decreased at high oxygen content. Hydrogen deoxidation obeyed first-order kinetics and reaction is mainly controlled by the mass transfer of oxygen in the liquid boundary layers. The value of total reaction rate constant was between 0.0363～0.0494s^-1 under the present condition. Based on theoretical analysis and experiments, deoxidation by hydrogen in the end of converter blowing for various carbon content steel was presented, which can be used in low carbon, high cleanness steel production.In the deoxidation process by methane, oxygen removed by carbon was the main deoxidation reaction. It is about 60 percent of whole removal amount of oxygen during gas blowing for 15min. Lower oxygen content can be obtained. Furthermore, the rate deoxidation and carburization increased by increasing the content of methane in the gas phase. The value of critical oxygen content below which the carbon decomposed from methane was mainly dissolved in the melt for carburization is between 0.01～0.02%. According to the character of deoxidation by methane. deoxidation by nature gas after oxygen blowing in UHP electric arc furnace melting was presented, which can be used in medium and high carbon, high cleanness, low nitrogen steel production.In order to apply deoxidation by hydrogen in the practical production, the kinetics of hydrogen desorption from steel melt by blowing argon gas has been studied in laboratory experiment for hydrogen content increasing after hydrogen blowing. The result showed that the rate of hydrogen desorption was controlled by mass transfer of hydrogen atoms in liquid phase. The value of total reaction rate constant was between 0.0022～0.0052s^-1 under the present condition. It was deduced that the rate of hydrogen desorption could be increased by strengthening stirring and increasing the area of the reaction surface.Relationship between the size distribution and number of inclusions with varying initial oxygen content as a function of added aluminum was studied for the improvement in cleanness of the steel by hydrogen deoxidation, the inclusions in steel samples were observed by optical microscope in this subject. The result showed that the size distribution and number of inclusion after deoxidation with alumina were dominated by the content of oxygen and deoxidizing alloy , and decreased by decreasing deoxidizing alloy amount and supersaturation degree for hydrogen deoxidation.Lastly, hydrogen gas injection method in the RH degasser was developed. Refining effect and feasibility were analyzed for the process. The mathematical model for hydrogen deoxidation in the RH degasser was developed. The analysis of the process by the model clarified that the dissolved oxygen could be removed efficiently by hydrogen gas injection in RH degasser. The oxygen content in steel could be decreased to final demand by increasing the process time. During the hydrogen injection, the rate of decarburization and nitrogen removal from liquid steel were increased efficiently. Hydrogen gas injection method in the RH degasser can be used for high cleanness, ultra low carbon nitrogen steel production.