Behavior Of Nitrogen In High Nitrogen Steel Melting Processes And Influence Of Nitrogen To The Corrosion Resistance Of Stainless Steels

High nitrogen steels is one kind of stainless steels. The steels contain more than 0.08 % (mass percent) nitrogen in a ferritic matrix or more than 0.4 %(mass percent)nitrogen with an austenitic matrix were defined as high nitrogen steels. High nitrogen steels have many advantages, for example, high strength and toughness, good ductibility and corrosion resistance, low magnetic permeability, and so on. However, the nitrogen solubility in molten steels is very low under atmosphere pressure, so it is more difficult to fabricate than common ones. Development of a cost low and effective technique to smelt high nitrogen steels was always paid attention to.To promote the investigation and application of high nitrogen, through melting of Fe-Cr-V high nitrogen steels and high nitrogen 304 stainless steels at high pressure, it was studied that solubility of nitrogen and the factor of influence to the solution, solution dynamics of nitrogen, the influence of different slags to aluminum deoxidate in the melting process, the behavior of nitrogen in the remelting and curdling process of high nitrogen steels with or without slags, the influence of nitrogen to the Corrosion Resistance of Stainless Steels.Melting of Fe-Cr-V high nitrogen alloys has been experimentally investigated in.MgO crucibles by a high Frequency Vacuum/ Pressurized Induction Furnace at 0.4～1.0 MPa nitrogen atmosphere and 1570～1640℃. The results show that the solubilities of nitrogen in Fe-15Cr-1.0V, Fe-18Cr-1.0V, Fe-18Cr-1.5V and Fe-20Cr-2.0V liquid alloys were 0.595%, 0.736%, 0.776% and 1.02%, respectively with 30CaO-45Al2O3-25SiO2 as top slag. Nitrogen dissolution in these liquid stainless steels follows the Sievert's Law. The slag composition has important effects on nitrogen dissolution and the aluminum deoxidation in liquid stainless steels. At 1873K, 1.0MPa of nitrogen, the concentrations of nitrogen in Fe-18Cr-1.5V were 0.7764%, 0.849% and 0.884% with the top slag of 30CaO-45Al2O3-25SiO2, 40CaO-40Al2O3-20SiO2, and 40CaO-50Al2O3-10SiO2, respectively. The change of alloys composition after melting resulted the difference of nitrogen concentration. The correspondent contents of oxygen were 0.0211%, 0.0179% and 0.0168%. At 1873K, 1.0MPa of nitrogen, nitrogen absorption reaction follows first order reaction. The mass transfer coefficient is about 4.60×10-5m·s-1. The deoxidation experiments were carried out using Al or Fe-50%Al alloy with top slags by the induction furnace at 1.0 MPa nitrogen atmosphere. The result of aluminum deoxidate was influenced by the component of top slags, 20CaF2-80CaO-20Al2O3 has better action than 30CaO-45Al2O3-25SiO2 to aluminum deoxidate; more slags and longer time is better to remove the deoxidate outcome. Under the condition of this experiment, the oxygen content in an Fe-20Cr-1.93V alloys can be decreased to 0.0072% by using Fe-50%Al alloy with 20CaF2-80CaO-20Al2O3 top slags in 40 minutes.It is important programs that overflow of nitrogen in the process of jointing and other remelting of high nitrogen steels. Behavior of nitrogen in the process of remelting of highnitrogen 304 stainless steels was studied. When no slags, the nitrogen content in the remelted steels decreased with the remelting nitrogen pressure, and it doesn't follow the Sievert's Law. When having slags, the nitrogen content in the remelted steels changed indistinctively, the nitrogen content in the remelted steels was 0.4% steadily; and the influence of different slags was also little. The reason why the phenomenon formed is the remelting time was brevity, it cannot achieve thermodynamic balance.Nitrogen can improve the corrosion resistance of stainless steels remarkably. In the solution of 6% FeCl3, the chemical immersion experiment was done to 304 austenitic stainless steels adding nitrogen,then metallographic analysis was done; In the solution of 1mol/L H2SO4+0.5 mol/L NaCl, the anodic polarization curves of 304 austenitic stainless steels adding nitrogen are measured by electrochemical test, the corrosion resistance property of 304 austenitic stainless steels was studied. The results showed that nitrogen which was added to steels can improve the corrosion resistance property of 304 austenitic stainless steels, and when the concentration of nitrogen is 0.388～0.556%, the corrosion resistance property is the best; it will fall if the concentration of nitrogen increase and decrease.