At present, ladle is gradually large-scale, and its high smelting temperature and long smelting time, the use conditions are more and more stringent, which puts forward higher requirements for refractory materials used in ladle. Due to the special position and environment of the breathable brick in the ladle, the requirement of its life, success rate of blowing and breathable amount is high. At present, the breathable brick at the bottom of the ladle has become the bottleneck factor limiting the life of the ladle. High blow-through rate, oxygen free cleaning and synchronization with the service life of ladle lining or bottom refractory are the common goals of users, breathable brick manufacturers and researchers.
1. Damage analysis of breathable brick
The intermittent operation process of the breathable brick for ladle is steel connection, air blowing refining, steel pouring, slag pouring, oxygen cleaning. The above process is repeated in the use of the breathable brick until the end of life. Among the many factors that affect the service life of the breathable brick, the heat stripping and oxygen cleaning are the important reasons leading to the damage of the breathable brick, and the blowing stirring time and stirring intensity also have a very significant influence on the damage of the breathable brick. The main reasons for the re-entry of molten steel and frequent replacement of the breathable brick are spalling, clamping steel in the slit and failure to blow.
In field use, it is often found that the lower part of the heating surface of the slit corundum spinel breathable brick in contact with molten steel is prone to transverse cracks, resulting in thermal spalling from the transverse cracks, which greatly reduces the service life of the breathable brick. The erosion and penetration of liquid steel and slag are one of the important reasons leading to the damage of the breathable brick. The erosion and penetration of molten steel and slag form a reaction metamorphic layer on the working face of the breathable core, which leads to the structure spalling. Severe penetration will block the airway, reduce the blowing rate and service life.
The microstructure analysis of the residual brick after use shows that the slit and crack of the permeable brick used in LF refining process have obvious slag erosion and penetration, and the slit and crack of the permeable brick used in LF+VD refining process have liquid steel penetration. In the course of periodic operation, the expansion of the slit mouth and the crack caused by thermal shock will aggravate the penetration erosion of molten steel or slag, and lead to the occurrence of spalling phenomenon. After plugging the slit of the breathable brick, it must be cleaned by blowing oxygen, which directly affects the blowing rate and service life of the breathable brick.
2. Research progress of breathable brick material
In order to improve the performance and service life of the slit breathable brick, some countermeasures are taken from the aspects of raw materials and manufacturing technology. 1) From the perspective of erosion resistance and erosion resistance, raw materials with good thermal shock resistance must be selected; 2) From the perspective of permeability resistance, it is necessary to choose a material that is not easy to be wet by molten steel at the working temperature. Under high temperature and vacuum, the stability order of several refractory oxides is as follows: Al₂O₃ > CaO > MgO > Cr₂O₃, and the wetting Angle order is as follows: ZrO₂ > Al₂O₃ > MgO.