| Tinplate is a kind of low carbon and low silicon(LCLS) steel, and it is widely used in automobile, appliances and construction and other industries due to its good plasticity and mechanical properties. Deoxidation of this steel is mainly undertaken by aluminum in the production process. The inclusions generated in the reaction has an important influence on processing performance and mechanical performance of steel. In order to ensure the performance of SPHC steel to meet the requirements, Reducing the number of SPHC steel inclusions and controlling inclusions existence has very important significance..This paper takes one steel mill's SPHC steel as an example.In the process of actual trial production, respectively before and after the RH refining liquid steel samples, The number, morphology and composition of inclusions in steel are analysed using metallographic microscope and scanning electron microscopy.The results show that before RH refining, dissolved oxygen content is high in steel, and inclusions in molten steel is mainly FeO kind inclusions. After deoxidation with aluminum, a large number of clusters of Al2O3 inclusionswere to generatedin the liquid steel. The size larger inclusions in RH refining process were rasied and removed due to the effect of blowing argon stirring, while part of the small size of Al2O3 inclusions stayed in the steel and affect the performance of the steel seriously. So it is necessary to adjust the refining slag to reduce and control the form of the inclusions in steel.Use Factsage software for thermodynamic calculation, and find that adding a certain amount of MgO intothe refining slag can reduce the activity of Al2O3 and SiO2 in the refining slag, and improve the stability of the slag;The liquid area of the CaO-SiO2-Al2O3 refining slag will be affected significantly due to the addition of MgO. The second liquid phase area(CaO: 40 ~ 60%, SiO2:0 ~ 20%, Al2O3:40 ~ 50%) that is suitable for SPHC steel smelting will increase as the content of MgO increase firstly, when the content reach a limited value, the area will decrease with the increase of content of MgO and when the content of MgO > 9%, the liquid area will reduce significantly. So the suitable range of the MgO content in this refining slag is 3~7% and the alkalinity is 3 ~ 4. The effect of the addiction of TiO2 on the liquid area of refining slag is also analyzed, and it is concluded that the addiction of TiO2 can increase the liquid area at refining temperature, especially the second liquid phase zone area, but the content of TiO2 in the refining slag at the actual trial production is 1%, and effect of TiO2 is not obvious..Base on the results of thermodynamics calculation, the influence of mass content of MgO in refining slag and inner wall materials of ladle as Magnesia Chrome and Magnesia spinel on the inclusions in steel is studied by experiment. conversion of the Al2O3 inclusions to CaO-MgO-Al2O3 inclusions in steel is analyzed by samples of steel observation. it shows that the inclusions in steel can be controlled by content of refining slag.Analysisthe content of crucible inner-wall, find that the iron oxide, CaO and SiO2 diffusing into the inner wall and reacting with the refractory of crucible is significance to crucible erosion. The erosion degree refining slag to magnesite-chrome crucible is lower. Magnesite-chrome crucible have less effect on the composition of refining slag,And in the magnesite-chrome crucible after the steel-slag reaction, the inclusions' melting point in the steel is lower, thus learned that magnesium chromium is more stable than magnesia spinel crucible, more conducive to control of inclusions in steel. |
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