Regarding the use of refractory materials in ladle linings, domestic scholars have summarized the development and use of ladle refractories. The effect of refractory castables on molten steel can be divided into direct and indirect effects. The direct effect is that the refractory material reacts directly with the molten steel, or the refractory material enters the molten steel due to mechanical erosion (flaking); the indirect effect is that the refractory material first reacts with the ladle slag After the reaction, the ladle slag reacts further with molten steel. Ladle refractories of different materials have different degrees of influence on the shape, quantity and composition of inclusions in steel through direct and indirect interaction with molten steel. So what are the reasons and selection methods of refractory materials used in ladle linings?
Chromium corundum castable
Two different ladle lining bricks of magnesia calcium and magnesia carbon are used for LF refining, and the tapping volume is 120t. The main components of the molten steel measured by the electric spark method at the beginning of the soft blowing are lime, calcium carbide and high-purity silicon carbide in the steel. The added amounts of quartz sand, manganese alloy and low-grade silicon carbide are the same. The content of aluminum low-titanium ferrosilicon is more than that of magnesium-calcium lining, while the content of Al2O3 in quartz sand is only 0.73%, the content of Al in manganese alloy is less than 0.01%, and the content of Al in low-aluminum and low-titanium ferrosilicon alloy is 0.02%. For molten steel weighing 120t, the effect is small, so it can be considered that the reason for such a huge difference in aluminum content in molten steel is caused by refractory materials, which directly leads to the difference in Al2O3 content in subsequent inclusions.
When using different magnesia cladding, the number of inclusions in steel and the change of average diameter. It can be seen that before the start of soft blowing, when using magnesia-calcium lining, the number density of inclusions in steel is 5-10 pcs/mm2 higher than that of magnesia-carbon lining, and both tend to be stable after the start of soft blowing The value is about 8 pieces/mm2. When using magnesia-carbon lining, the average size of inclusions is relatively high, and reaches a peak of about 2.5μm at the beginning of soft blowing; when using magnesia-calcium lining, the average size of inclusions is about 2.5μm, and then stabilizes at About 1.0μm.
It can be seen that the content of Al2O3 is particularly obvious in the composition change. After slagging, the content of Al2O3 in the inclusions was about 1%, and then the increase in Al2O3 content in the magnesia-carbon lining heats was significantly lower than that of the magnesia-calcium heats. The Al2O3 content of the former was always less than 4%, while the latter was less than 4%. Gradually increase to 10%; when using magnesia-carbon lining, the SiO2 content in inclusions is higher than that of magnesia-calcium heats. It can be seen that the MnO content in the steel inclusions of the two furnaces has a difference of about 5% in the first three stages, and is basically the same at the end of soft blowing; while the CaO content difference is about 2%, the difference is relatively small. The main reason for the increase of CaO content in the smelting process is the involvement of refining slag. A small amount of refining slag will cause the rapid increase of CaO content.
Generally speaking, when using different linings, the number density of inclusions in the steel tends to be stable after the start of soft blowing, and will remain at about 8/mm2, while the average size of the inclusions changes differently. When using magnesia-carbon lining, the average size of inclusions is relatively high, reaching a peak of about 2.5μm at the beginning of soft blowing; when using magnesia-calcium lining, the average size of inclusions after slagging is about 2.5μm. Afterwards, they stabilized at around 1.0μm.
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