8 factors affecting the service life of large ladle refractory lining

1. Temperature of ladle

In previous articles, we have made an in-depth analysis of the influence of ladle temperature on the service life of refractory materials. The analysis shows that the higher the temperature of molten steel in ladle, the faster the dissolution corrosion and the lower the service life. The increase of molten steel temperature in ladle significantly increases the corrosion rate. An important process of ladle refining is the improvement of ladle temperature through the input of heat energy such as arc heating, electromagnetic mixing heating, adding heating agent or blowing oxygen, which leads to the acceleration of the corrosion rate of ladle lining and the decrease of service life.

2, the moment when the molten steel stays in the ladle

The lingering time of molten steel in ladle can be divided into steel drawing time (2 ~ 7min), refining time, lingering time and pouring time. The degree of corrosion of refractory lining in these periods is not the same. In the process of steel extraction, the impact force of molten steel on the lining leads to local erosion loss, and the reaction corrosion between slag and refractory is also very intense due to strong stirring. In the cleaning process, the longer the cleaning time, the more slag and refractory reaction, the greater the amount of corrosion, that is, the lower the service life of the ladle, the service life of the lining decreases linearly with the extension of the cleaning time. During the stay period, the time is prolonged, the interface reaction layer is thickened, the reaction and the product have to be dispersed for a long time, and the corrosion is controlled by the dispersion. According to the dispersion kinetics equation, the corrosion amount is proportional to the square root of the stay time, so the corrosion of the coated refractory is slower during the stay.

3. The influence of steel slag on ladle

The influence of steel slag on the service cycle of ladle refractory is mainly manifested in three aspects:

1) Influence of slag alkalinity;

The alkalinity in the slag, that is, the CaO/SiO2 share, reflects the erosion of the slag to different refractory materials and the viscosity and liquefaction temperature of the slag itself. These studies should be analyzed from the slag atlas. Due to the change of CaO/SiO2 in the slag, it leads to the change of liquid phase amount, liquefaction temperature, slag viscosity and chemical composition, and these changes interact with the ladle wall refractory to generate a lower temperature liquid phase, which enters the slag body, resulting in the corrosion consumption of the refractory.

2) The effect of slag oxidation;

At present, magnesia-carbon brick is used in refining ladle slag line. Magnesia-carbon brick is easy to oxidize and is greatly affected by oxidation of slag. The stronger the oxidation of slag, the easier it is to oxidize and erode magnesia-carbon brick.

3) Influence of slag viscosity.

The penetration depth of slag to refractory is inversely proportional to the square root of slag viscosity. Therefore, the slag viscosity decreases, resulting in the addition of diffusion depth, that is, the slag viscosity decreases, which will make the refractory reaction disintegration layer thicker, resulting in the addition of corrosion. The refractoriness of the refractory layer infiltrated by slag decreases, the sintering density increases, and the thermal expansion and other performance differences between the refractory layer and the original layer of refractory are increased. During the intermittent use of ladle, the slag impregnated layer cracks and falls off, and then the refractory lining loss is formed.

4, the effect of vacuum treatment

Many precision equipment with vacuum processing function, such as LF-VD, VOD, RH and DH. Vacuum conditions have a great influence on the loss of refractories, especially carbon-containing refractories. According to the principle of chemical equilibrium, under vacuum conditions, the following reactions will be promoted to the right to form internal gasification of refractory materials: MgO+C=Mg↑+CO↑, 4MgO+2Al=3Mg↑+MgAl2O4, MgO+Si=Mg↑+SiO↑, 5MgO+B4C=5Mg↑+CO↑+2B2O2↑.

5, the impact of ultra-high temperature

According to the principle of chemical balance, increasing the temperature makes the reaction go to the right, which forms the same result as the vacuum condition, that is, at ultra-high temperature, the magnesia carbon brick lining containing additives such as aluminum powder and silicon powder will not have a good application effect, or even worse. Therefore, in the use of refined ladle, ultra-high temperature and the time at high temperature should be controlled.

6, the effect of blowing argon mixing

Argon blowing causes the oxygen concentration on the surface of ladle slag to decrease, and argon itself is not corrosive to the furnace lining, so argon blowing can reduce the oxidation of carbon-containing refractory materials. Therefore, the effect of argon blowing on the corrosion of refractory lining is not very serious

7. The impact of intermittent operation

In the process of ladle filling - transport - refining - stay - pouring - slag turning - repair - waiting (preheating) replacement, the temperature of ladle can change continuously from room temperature to 1700℃, and this temperature fluctuation will cause great stress on the refractory lining. Refractory materials are brittle materials at low temperatures, and under such temperature shaking conditions, cracks and falls off simply occur, and then lead to abnormal losses and reduced service life of the lining. Therefore, in order to reduce the fall off and abnormal loss, the ladle turnover should be accelerated and the ladle preheating and insulation should be strengthened to avoid the temperature drop when the ladle is waiting for steel connection, which can improve the ladle life by more than 30%.

8, the impact of different equipment

General ladle, LF, LF-VD, VOD due to their different refining conditions, resulting in the difference in corrosion rate: ladle: LF: LF-VD: VOD≈1:2:4:8; Or the difference in service life is: ladle: LF: LF-VD: VOD=(100 ~ 130) : (50 ~ 70) : (20 ~ 30) : (12 ~ 20)≈8:4:2:1, that is, the single consumption of refractory material is 2.5, 5, 10 and 20kg/t.

The above differences in corrosion rates are reflected in key parts such as slag lines, which account for only a small part of the lining. If the repair protection is carried out with a small number of repair materials, the service life will be improved, and the unit consumption of refractory materials will be greatly reduced. Therefore, the non-uniformity of metallurgical lining corrosion brings great room for reducing the unit consumption of refractory materials.

The impact of ladle operation on the service cycle of refractory materials is mainly concentrated in the above 8 aspects, which optimize the structure of refractory materials, reduce the single consumption of refractory materials, and extend the service cycle of refractory materials.