Nitrogen Solution Behavior In Austenitic Stainless Steel Melts

Recently, with the rapid development of Chinese stainless steel industry, China has become the biggest stainless steel consumption country in the world. AOD is the major refining equipment to produce stainless steel by mixing blowing of argon and oxygen which leads higher costs for the consumption of a lot of argon, while the costs will be decreased remarkable by using nitrogen instead of argon during refining and nitrogen alloying process. Therefore, it's necessary to reseach nitrogen behevors in smelting process of stainless steel and the influences of other elements to the speed of nitriding and denitriding in steel melts, further more, to develop the technology of control nitrogen content in smelting process of stainless steel, and all of the above researches have important social significance.Combining nitrogen content standards (0.02%～0.1%) and smelting process of austenitic stainless steel in a plant., nitrogen behevors were reseached by using theories and research methods of metallurgical thermodynamics and kinetic. The calculating formula of nitrogen solubility in stainless steel melts were established using thermodynamic method based on the equilibrium reaction. According to the laboratory experiments and semi-industrial tests, the rules and influencing factors of nitriding and denitriding were analysed by metallurgical kinetic in smelting process of AOD and LTS. The calculation methods and off-line calculation software were established in each refining process, which can need the demand of control precision in the industrial production.Based on the reseach of nitrogen behevors in stainless steel melts, the models for nitrogen solubility, nitriding and denitriding of AOD, nitriding of LTS were established. The windows of models were also established by Visual Basic.6.0, moreover, the models were proved by part of industrial data.Nitriding behaviors in the austenitic stainless steel melts were researched in the laboratory by bubbling nitrogen gas under different temperature and partial pressure of nitrogen. Under the present experimental conditions, the nitrogen solubility in austenitic stainless steel increases with the increasing of nitrogen pressure and the decreasing of temperature. Based on the experimental results, nitrogen solubility in stainless steel melts was calculated by thermodynamic model. Contrasted with the experimental results in the stainless steel melts, the calculation results were in good agreements with the measured values.Based on the experimental results, the calculation methods of nitriding were established by combination control theory in the stainless steel melts. Contrasted with the experimental results, the calculation results were in good agreements with the measured values. The absolute error is less than 0.01% and the relative error is less than 10%. The calculation methods of denitriding were also established by combination control theory in the stainless steel melts. Contrasted with the experimental results, the denitriding calculation results were also in good agreement with the measured values. The absolute error is less than 0.01% and the relative error is less than 15%.Based on the semi-industrial test results in a plant, nitrogen solubility in stainless steel melts decreases with the increasing of carbon contents. The calculation model of nitrogen solubility was also established. The calculation results were in good agreements with the test results. The absolute error is less than 0.004%. Based on the semi-industrial test results, the calculation methods of nitriding were established by combination control theory in the stainless steel melts. The nitriding calculation results were in good agreements with the test results after deleted some error data. The absolute error is less than 0.01%. The calculation methods of denitriding were also established by combination control theory Contrasted with the test results, the denitriding calculation results were also in good agreements with the test results. The absolute error is less than 0.002%.Based on the industrial production of austenitic stainless steel, the model for nitriding of AOD was established by interface reaction control theory and the model for disnitriding of AOD was established by combination control theory. The data of 75 heats were proved by the model. The number of heats is 70 heats which the absolute error between test result and calculating values from negative 0.01% to 0.01%, and the veracity rate is 97.2%.Based on the industrial production of austenitic stainless steel, the model for nitriding of LTS was established by combination control theory. The data of 88 heats of 316L,304L,304, 301S and 00Cr19Ni10 stainless steel were proved by the model. The number of heats is 84 heats which the absolute error between test result and calculating values from negative 0.006% to 0.006%, and the veracity rate is 95.5%. So the model for nitriding of LTS can be used to guide the industrial production of austenitic stainless steel.In order to make the operation for engineers and operater easily, the windows of models were established by Visual Basic 6.0, and the operating instruction manual was offered. The models'have been fixed on the computers of L3 level. The models can predicted the nitrogen content synchronously by inputing industrial data of production.