1. Causes of damage to refractory bricks in ladle refractory materials
1. Ladles are used to transport high-temperature molten steel. During transportation, high-temperature molten steel and slag at around 1680℃ scour and erode them, especially the slag line, which is a serious factor in determining the service life of a tank.
2. LF and other off-furnace refining treatments seriously damage unfired bricks.
3. When the converter taps and molten steel flows out, the lining is subjected to drastic temperature changes, which causes cracks and peeling of refractory bricks in the lining.
4. When the ladle is loaded with molten steel in the converter, the high-temperature molten steel has a strong mechanical scouring on its bottom, which makes the lining material in this part prone to damage caused by thermal shock.
2. Damage mechanism of refractory materials in ladle
The damage mechanism of refractory materials in ladle is mainly caused by erosion and penetration of high-temperature slag. The slag line of the ladle is mainly melted, and the side wall is cracked and thermally peeled due to the penetration of slag. The melting rate is related to the slag temperature, viscosity and reaction rate of the material. The high temperature of the molten steel, the long retention time in the ladle, the low viscosity of the slag, the pore penetration of the matrix material, the liquid phase penetration and the diffusion in the solid phase, make the composition and structure of the material surface change qualitatively, form a metamorphic layer with a high degree of solubility, which is easy to peel off and accelerate the damage of the lining refractory bricks. The lining of the ladle with the same or different chemical composition of the refractory material has different damage rates due to its different organizational structure and performance. The ladle cannot operate continuously, resulting in a decrease in the lining temperature or even a cold ladle, which is also prone to lining structure peeling, reducing the service life of the ladle.
The erosion of slag on refractory materials is not limited to the dissolution of the surface, but the slag can also invade (penetrate) the interior of the refractory materials, expand its reaction area and depth, and undergo qualitative changes in its composition and structure near the surface of the material, forming a metamorphic layer with high solubility, accelerating damage. The proportion of this invasion is roughly proportional to the porosity. Therefore, even if the chemical composition of the refractory materials is the same, their melting loss rates are significantly different due to their different organizational structures.
The higher the open porosity of the refractory material, the faster the slag invasion rate, and the invasion ratio is approximately proportional to the porosity. Even if the apparent porosity of the refractory material is the same, the erosion rate will also change if the shape, size and distribution of the pores are different.
3. Characteristics of refractory materials for ladle lining
According to the above analysis, refractory materials for ladle lining should have the following characteristics: dense and uniform organizational structure; micro-expansion at high temperature, good volume stability; high strength, and a small ratio of medium-temperature strength to high-temperature strength.
During the use of refractory materials, slag easily penetrates from the heating surface to the deep inside, significantly reducing the porosity near the working surface and densifying it, forming a very thick metamorphic layer. When the temperature changes drastically, cracks parallel to the working surface are generated at the junction between the metamorphic layer and the original refractory brick layer, causing the bricks to peel off and be damaged. To reduce the structural peeling of refractory materials, the depth of slag penetration can be reduced from the following aspects:
(1) Improve the resistance of refractory materials to slag penetration;
(2) Reduce the porosity of refractory materials and reduce the erosion channel of slag;
(3) Slag reacts with refractory materials to form a high-melting-point compound retaining wall to prevent slag penetration;
(4) Increase the viscosity of slag. The higher the viscosity of slag, the worse its erosion to refractory materials.
