The 120t converter in Benxi Iron and Steel Co. has been built with magnesia-carbon bricks since 1990s. The service life of the converter has risen greatly and has reached the level of 10,000 times.
Converter lining is composed of bottom, body (straight section) and cap (cone section). Steel mouth bricks are built at the junction of body (straight section) and cap (cone section). The lining of all parts includes working layer, permanent layer and heat insulation layer. Masonry Requirements for Bottom of Furnace, the principle is to meet the requirements of combined blowing and ensure the spherical surface. At the same time, the gaps and fillers in each layer should meet the requirements of use.The masonry principles of the furnace body (straight section) and the furnace cap (cone section) are: horizontal, vertical, back tight, solid and round. The masonry of steel outlet should satisfy the center alignment of outer flange.
2.Application of Magnesium Carbon Bricks in Converter Lining
Although magnesia-carbon bricks have the advantages of high fireproof, good slag invasion resistance, strong thermal vibration resistance and low creep at high temperature, the use environment still has a great influence on its use effect. Specifically, there are the following aspects:
- Loading system: that is to determine the reasonable load of converter, appropriate molten iron, scrap ratio. In order to determine the charging capacity of converter, we should not only consider a suitable volume ratio, but also maintain a suitable depth of molten pool. In order to ensure that the bottom of the furnace is not impacted by oxygen jet, the depth of the molten pool must exceed the maximum penetration depth of oxygen jet to the molten pool.
- Furnace Volume Ratio: Appropriate furnace volume ratio has certain influence on converter steelmaking operation. If the furnace capacity ratio is too large, the cost of
steelmaking will be increased; if the furnace capacity ratio is too small, splashing will occur easily, which will reduce the service life of the lining and is not conducive to improving the productivity of converter. Therefore, the furnace volume ratio determined in design should be maintained in the process of converter production.
- Oxygen supply system: Determining scientific and reasonable oxygen supply system, ensuring impurity removal speed, bath heating speed, slagging speed, controlling splashing and removing gas and inclusions in steel, and reasonably controlling end-point carbon and temperature have important effects on strengthening smelting of converter, enlarging steel varieties, improving steel quality and increasing lining service life.
- Slag-making system: The condition of converter slag has a great influence on lining erosion. Establishing a reasonable slagging system can not only ensure the smooth operation of converter smelting and reduce the consumption of raw materials, but also slow down the erosion of converter slag on lining and improve the service life of lining.
- Raw material quality: The quality of raw materials for converter steelmaking has a certain impact on the lining life. Specifically, there are:
Hot metal: Hot metal is the main material for converter steelmaking.
Scrap steel: Scrap steel is used to balance the heat of converter.
Slag-making material: Lime is the main slag-making material in steelmaking. Its effective calcium oxide, burning rate and activity index have a great impact on the use effect, and must meet the requirements.
Slag adjusting agent: In order to ensure a certain content of magnesium oxide in slag and reduce the loss of magnesium content in furnace lining, slag adjusting agent should be added in the slag making process. Therefore, it is required to have certain magnesium content in slag adjusting agent, and the impurity content should meet the requirements.
Fluxing aids: Ferromanganese ore, iron oxide scale or iron ore are commonly used as fluxing AIDS because of the supply reasons of fluorite and the side effects of its use.
- Temperature regime: Temperature control in steelmaking process and terminal temperature control also have great influence on erosion rate of converter lining. So,on the premise of satisfying the requirement of molten steel casting, the lower the temperature control in steelmaking process and the terminal temperature are, the better the lining life will be.
3.Maintenance of Converter Lining
- Slag splashing for furnace protection
The end slag used for slag splashing should be “spatterable, sticky and corrosion resistant”. Therefore, the composition, temperature and fluidity of slag should be adjusted firstly. When splashing slag, proper gun position, pressure and flow rate should be adopted, and sufficient splashing time should be ensured.
- Repair lining in time
The front, rear and both sides of trunnion of converter are vulnerable parts. It must be repaired during the service of converter. The principle of repairing is: timely repairing and repairing without serious erosion of lining can improve the effect of repairing furnace, including front and rear face and both sides of trunnion. If the erosion is serious, the repairing effect will be greatly reduced. The condition of tapping port not only affects the safety of its use, but also affects the quality of steel. It must be replaced in time.
Magnesium-carbon bricks are widely used in various metallurgical furnaces because of their simple production process, excellent physical and chemical properties, no pollution to the environment and simple construction methods. Magnesium-carbon bricks were used in converter masonry in the early 1990s in Benxi Iron and Steel Works. Through continuous improvement, the average furnace life of converter has increased from about 1,000 times to 9425 times in 2003, and the maximum furnace life has reached 10328 times.