Study On Nitrogen Behavior In VOD Steelmaking Process For316L Austenitic Stainless Steel

Nitrogen is the impartment alloy elements in the stainless steel, and it has an impartment effect on property. Recently, it is a research hotspot that nitrogen behavior in the molten stainless steel and the control technology during the smelt processing. In this paper, using the methods of thermodynamics and kinetic for metallurgical reaction, investigating the control condition and processing route of316L austenitic stainless steel line at Baosteel, based on VOD in refine, the nitrogen dissolution behavior was studied in the molten. Further, the FactSage thermodynamic soft are introduced in nitrogen solubility of316L austenite stainless steel at VOD refining stage. Thermal simulation laboratory and industrial test site were also conducted. Finally, based on above simulation and experimental study, the nitrogen software of VOD refinging was developed, and then applied to the Baosteel industrial production, and which provide the basis for controlling the Nitrogen content during the VOD in refine.The model was set up for increasing and decreasing nitrogen though calculating dissolution behavior in solten. The result show using the methods of thermodynamics that logarithmic function of solubility, initial nitrogen content and end point nitrogen content to blowing time has a linear relation. The partial pressure of nitrogen is the main factor affecting nitrogen solubility. With the partial pressure of nitrogen increasing, the nitrogen solubility increasing gradually, this tend is independent of temperature. The nitrogen solubility is about0.208%at1600℃,100kPa partial pressure of nitrogen. For control nitrogen austenitic (w (N)=0.05%-0.1%) and Nitrogen austenitic (w(N)=0.1%～0.4%) stainless steel, can produce in316L. For high nitrogen austenitic stainless steel (w(N)>0.4%), must use pressure production process for smelting.The result shows using the methods of kinetic that blowing argon flow rate increases, rate of nitrogen removal in molten steel more; argon blowing time is longer, the more low nitrogen content in molten steel, to reach equilibrium. Using a large flow of argon gas, to reduce nitrogen content in molten steel, the large flow of argon blowing time, can shorten the time of blowing argon.Laboratory blowing N result shows that the total gas spray of molten steel should be controlled between0.3L·min-1, the nitrogen partial pressure should be controlled in the66.7kPa, can achieve the ideal nitrogen blowing nitriding steel. The temperature of the molten steel suitably low to blow nitrogen nitrogen can increase in molten steel. For steel nitrogen blowing nitrogen, the temperature of molten steel should be controlled at around1500℃.It is obtained from FactSage thermodynamic soft that the nitrogen solubility reduce with carbon content and temperature of melt steel increasing, but increase with partial pressure of blowing nitrogen increment. The partial pressure is a master factor for nitrogen solubility, and then temperature, the effect of carbon content is minimal. For control nitrogen austenitic (w(N)=0.05%-0.1%), it is feasible in decarbonization stage of VOD refining, But only on vacuum case pressure at30kPa above condition, the middle nitrogen content (w(N)=0.10%-0.40%) of316L austenite stainless is produce at the stage of decarbonization, charging and opening vacuum. At different blowing condition, the measured value of nitrogen content is anastomotic with calculation result of FactSage thermodynamic soft.The316L austenitic stainless steel with argon nitrogen removal experiment shows that having the function relation between nitrogen content in molten steel with argon blowing time. When the control in argon gas is at0.1NL·min-1or0.3NL·min-1, end point nitrogen content of molten steel with argon blowing time is into two relations.Industrial test in Baosteel shows that nitrogen purging time should be controlled in316L austenitic stainless steel control nitrogen partial pressure of nitrogen increase around7min.In this paper, the research and development of VOD refining control software was applied to Baosteel industrial production. And the result shows that most measured values around the calculation value fluctuation, The measured content of molten steel in nitrogen value of the relative error of calculated values and below10%, and the model is reliable. The field application results of soft are obvious.