Heat stress
In actual production, the ladle temperature reaches more than 1000℃, and the molten steel temperature reaches more than 1600℃. The temperature difference between the two when in contact will produce large thermal stress, which in turn causes a very large thermal shock.
The ladle is in a repetitive working environment. The thermal stress caused by the frequent temperature changes of the air brick when it contacts the molten steel and the ladle is one of the reasons for the damage of the air brick. The key factor for the thermal stress of the air brick is the change of temperature, and the temperature changes of different parts of the air brick are different.
The difference between the thermal stress generated by the internal parts of the air brick and the temperature change at the same position is compared. It is found that the thermal stress near the working surface exceeds the bonding strength of the air brick itself to a certain extent. The air brick is subjected to a strong thermal shock, resulting in layered peeling of the working surface of the air brick, which leads to the destruction of the air brick.
The temperature field formed at the bottom of the ladle when the molten steel enters and exits the ladle and the stress field generated by the molten steel are numerically simulated and analyzed, and numerical detection is performed.
The study found that, if the ladle is to reach a “quasi-steady state”, the preheated ladle needs to be subjected to several thermal cycles. Since the stress of the working layer near the ladle wall at the bottom of the ladle is higher than that near the center, in order to reduce the thermal stress generated there, an insulation device can be added near the ladle wall to alleviate this phenomenon.
Mechanical wear
There are roughly three situations in which turbulence scours the Ladle porous plug bricks.
- When the air bricks are higher than the seat bricks, the main reason for the damage to the air bricks is that the molten steel in the ladle forms a vortex that produces a huge shear effect and scouring effect on the side of the air bricks. Therefore, the scouring force is one of the reasons for the great damage to the seat bricks of the air bricks. In a normal working environment, the air seat bricks are used only once, and the structure above the seat bricks will be washed away after one time;
- When the air bricks are level with the seat bricks, the seat bricks protect the air bricks from erosion and damage. The vortex formed by the molten steel first scours the seat bricks, causing the shear force of the air bricks to decrease accordingly;
- When the air bricks are lower than the seat bricks, cold steel is easily accumulated on the working surface during normal work. Since the viscosity of the remaining cold steel is relatively large, it has a certain obstruction to the blowing, so the blowing pressure needs to be increased to meet the refining requirements. In this way, the scouring force of the air flow on the air bricks is correspondingly increased, and the shear and impact strength is large, making them more easily damaged. In order to meet the requirements of off-furnace refining for blow-through rate and service life, the air-permeable brick must have excellent anti-scouring ability and high-temperature mechanical properties.
When there are differences in refining conditions, the aggregate and matrix are properly proportioned to reduce the impact of erosion and penetration on the blow-through rate and service life of the air-permeable brick.
Mechanical stress
During use, the working surface of the air bricks at the bottom of the ladle is in direct contact with the high-temperature molten steel. Under the condition of cyclic use, the temperature in the ladle is always in a state of change.
For example, when the refractory material at the bottom of the ladle is used, a temperature difference will occur from high temperature to low temperature. Since the expansion coefficient of the original layer of the refractory material is different from that of the metamorphic layer, the air bricks are subjected to shear stress, resulting in transverse cracks or even fractures in the air brick structure.
Chemical attack
The working layer of the air brick is in contact with the steel slag and molten steel for a long time, and the molten slag continuously erodes and penetrates into the air brick. The oxides such as MnO, MgO, SiO2, FeO, Fe2O3 in the molten steel and slag react with the refractory materials in the air brick.
The physical erosion caused by the melting and peeling of the working layer of the air brick by molten steel, and the chemical erosion caused by the continuous penetration of slag and molten steel into the air brick during the smelting process are the two main reasons for the damage of the air brick. Therefore, in order to improve the thermal shock resistance and slag resistance of the material, it is necessary to improve the toughness and permeability of the air brick.
