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Kinetic Prediction Model for the Composition of Non-metallic Inclusions in Stainless Steel

Author: LiMing
Tutor: JiangZhouHua
School: Northeastern University
Course: Iron and steel metallurgy
Keywords: Stainless Steel Non-metallic Inclusions Composition Kinetic Model
CLC: TF764.1
Type: Master's thesis
Year: 2012
Downloads: 5
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Abstract


Nowadays, the control of non-metallic inclusions’ type and shape has become one of the main research directions. The scholars have conducted relevant research on the variation of inclusion, but rare references are to discuss topic of the kinetic model of inclusions formation in ferritic stainless steel. Through the study of generation thermodynamics and the behavior of inclusion, the present study focuses on the CaO-Al2O3-SiO2composite inclusions in ferritic stainless steels.Based on the previous relevant study, the purpose of the present study is to investigate the mathematical model on generation thermodynamics and inclusions’behavior and establish the kinetic model of inclusions formation in ferritic stainless steels.Based on the relevant thermodynamic data, the interaction coefficient method is used to calculate the activity of elements in molten steel. The high-level sub-regular solution model and GA-BP training learning method are used to calculate the activity of the elements in the SiO2-Al2O3-CaO-MgO slag. The poppers of all these thermodynamic calculation are to provide the relevant data for the kinetic prediction model.Using Matlab2011b, the author established the kinetic prediction model as a visual interface. The main methods are the two-film theory and unreacted core model. The former is to build the slag-steel reaction model and the other is for the steel-inclusion reaction. After the literature investigation, the empirical equation between the mass transport coefficient and stirring intensity was obtained. Based on reasonable assumptions, the kinetic model on the composition of CaO-Al2O3-SiO2composite inclusions in ferritic stainless steels has been established.Based on the kinetic analysis, the author has simulated the AOD working station aimed at the practical production for430stainless steel in this paper. The present experiment focus on the composition changes of inclusions which purpose is to amend and validate present model. Using computer simulation as the main measure and applied the theory and researching methods of metallurgical thermodynamics and dynamics.By graph method, the mass transfer coefficient of element Si on the steel side was obtained. With a comparison with the experiment data, the amended formula kx=(14DxV8g/dc2)0.5was obtained. As a result, km, Si=0.003000m/s,0.004000m/s,0.00480m/s, which was possible to obtain the calculated result which showed a close agreement with experimental results. It provides a remarkably modification to the model establishing.From the final results of the steel sample obtained here, it accords to the430target composition.In terms of inclusions’ size and morphology, the inclusions are, basically, in a spherical shape with sizes from1.05to1.35μm. No large inclusion type was found. It indicated that under experiment stirring condition, no vigorous stirring accrued which might lead the fierce collision.From analysis of the composition results of inclusions here obtained by SEM, the composition of CaO-Al2O3-SiO2composite inclusions at different stirring intensity showed a remarkable agreement with the calculated results obtained by model, expect the results in some inclusions. It means that this kinetic model built by author shows a certain reliability on inclusion formation for CaO-Al2O3-SiO2composite inclusions and provides a credible theory evidence for the kinectic study on inclusions.

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CLC: > Industrial Technology > Metallurgical Industry > Steelmaking > A variety of steel smelting > Special-purpose steel > Stainless steel
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