1. What refractory materials are used for the pre-desiliconization of molten iron?
Compared with blast furnace slag, desiliconized slag has a high iron oxide content. The original Al2O3-SiC-C iron channel refractory materials used were severely corroded in the slag line. Therefore, the material is changed in the slag line, the size of the iron channel is enlarged in the part where the siliconized is added, and forced air cooling pipes are buried in the side walls of the iron channel. For de-siliconized slag with high iron oxide, SiC, and C are oxidized and corroded. Al2O3-MgO refractory materials can be used instead. The corrosion resistance mainly depends on the amount of liquid phase generated by the slag formation reaction. Experiments have confirmed that when MgO/Al2O3>l, the formation of the liquid phase is inhibited. The reason is that the reaction of FeO in the desiliconized slag with Al2O3-MgO will generate high melting point minerals.
2. What are the disadvantages of sintered refractory oxide products?
It is generally believed that the thermal mechanical damage of sintered refractory oxide products is mainly caused by microcracks, and the generation and growth of microcracks depend on the physical quantities of the product such as strength, elastic modulus, thermal conductivity, linear expansion coefficient, etc. For sintered products, the higher the high-temperature strength, the smaller the factors that inhibit the generation of cracks. The existing microcracks are easy to grow, the fracture toughness is poor, and it is easy to peel and damage at high temperatures. The key weakness of high-temperature fired refractory products such as fired magnesia bricks and fired magnesia-chrome bricks is that they have poor thermal shock resistance and are easy to absorb slag defects.
3. How to determine the aggregate particle size of electric furnace gunning material?
Under the premise that the material and binder are determined, the aggregate particle size ratio is crucial to manufacture high-quality gunning materials. The larger the critical particle size, the better the corrosion resistance, but the poor fluidity and high rebound rate during the gunning operation.
The critical particle size of semi-dry gunning material is usually 3mm. The particle size of flame gunning material is usually smaller than that of semi-dry method, preferably 0.5~0.05mm. The particle grading has developed from the early two- and three-level batching to multi-level batching. In recent research on alkaline flame gunning materials, Nippon Steel of Japan believes that spherical aggregate particles are better. It has a small specific surface area, strong anti-hydration performance, and good fluidity during spraying. In order to improve the fluidity of the gunning material, reduce dust, improve the working environment, and increase the adhesion rate, foreign countries have developed from the original crushing of aggregate particles to particles plus additives and binders (organic or inorganic), premixed, and spray-dried for secondary granulation. Granular polyphosphates and superphosphates are used to replace powdered binders to improve the problem of moisture absorption and agglomeration during storage. In order to solve the hydration and oxidation problems of carbon-containing alkaline gunning materials, the soaking treatment technology of alkaline aggregate particles and graphite waterproofing has developed rapidly.
4. What are the effects of bottom blowing gas supply components on refractory materials?
① Ultra-high power electric furnace permeable bricks should have good air permeability during use. After steel formation, the air permeability function must be restored within 1~2 furnaces after reuse.
② The gas supply element is in contact with molten steel at a high temperature of more than 1630℃ and is washed by high-speed stirring molten steel. The material is required to have sufficient strength and high-temperature mechanical properties.
③ The electric furnace is operated intermittently. The temperature difference caused by repeated heating and cooling varies greatly. Thermal stress inside the material causes peeling. The material is required to have good thermal shock resistance and peeling resistance.
The refractory material for the contact (direct stirring) device is composed of a nozzle (stainless steel pipe) and a magnesium carbon material (magnesium carbon brick), and the air plug is in the center of the furnace bottom. The composition of the bottom blowing refractory material is filled with magnesium castables between the nozzle and the tube brick, and between the tube brick and the magnesium seat brick, and the furnace bottom uses amorphous magnesium dry ramming material.
The refractory material for the non-contact (indirect stirring) device adopts air-permeable ramming of the furnace bottom. The furnace bottom refractory material must have the following properties: the air permeability of the ramming layer should be maintained for a long time, and the sintered layer must be very thin and maintain good air permeability even at high temperatures, and the raw materials must be of high purity; the air permeable layer should have good stability, and if fine cracks are generated, the air permeability will be affected. The air permeable layer must also have high thermal shock resistance.
5. What refractory materials are used to adapt to the development of new continuous casting technologies?
(1) Refractory materials for horizontal continuous casting
The development of horizontal continuous casting determines the working performance of the separation ring between the tundish and the crystallizer, which directly affects the production capacity of the horizontal continuous casting machine. A large amount of research has been conducted on the materials of separation rings for horizontal continuous casting at home and abroad, and fused quartz, high aluminum, ZrO2, Si3N4, BN, Si3N4-BN and Sialon separation rings have been developed successively.
(2) Refractory materials for thin slab continuous casting
Since the crystallizer space is small, thin slab continuous casting has special requirements for immersion nozzles, so a thin-walled immersion nozzle with a special shape has been developed. The material of the submerged nozzle is a high-aluminum carbon refractory containing boron nitride (BN) and zirconium oxide (ZrO2).
6. What refractory materials are used in AOD furnaces?
AOD argon oxygen furnaces are mainly used for melting stainless steel, and in recent years, they have been expanded to the production of carbon steel and low alloy steel.
The refractory materials for AOD furnaces should have good thermal shock resistance and slag resistance, mechanical wear resistance, erosion resistance, dense structure, and high strength.
The lining material of AOD furnaces is mainly magnesia-chrome bricks in the United States and the United Kingdom. In my country and Western European countries, attention is paid to the development of magnesia-calcium bricks and dolomite carbon bricks and magnesia-dolomite bricks with corresponding carbon content. High purity and low impurities are required in terms of materials.
In recent years, dense recombined magnesia-chrome bricks and other materials fired at ultra-high temperatures have also been developed. Magnesia-zirconium bricks are used in the tuyere. Comprehensive masonry is also used to reduce the erosion rate of the furnace lining, such as ultra-high temperature fired dolomite bricks in the tuyere area; ceramic-bonded dolomite bricks on the steel outlet side of the furnace wall; and cheap asphalt-bonded dolomite bricks in other parts of the furnace cap and furnace bottom.
7. What refractory materials are used in RH/RH-OB furnaces?
RH refractory linings work under vacuum sealing conditions. Common use conditions include high temperature (about 1600℃) operation, thermal cycle (up to 600℃), air pressure cycle (from atmospheric pressure to 66.66Pa), high-speed molten steel flow (1m/s when passing through the submerged pipe), and contact with corrosive slag (calcium silicate, calcium aluminate and ferrite) and iron oxide melt.
According to the erosion factors of the working lining of the RH/RH-OB device, the lining usually adopts high-quality magnesia-chrome bricks or alkaline ramming integral lining or adopts a comprehensive lining with partitioned lining according to the use conditions of different parts.
The RH-OB circulation method with oxygen blowing function improves the air extraction capacity, intensifies the splashing of molten steel in the vacuum chamber, strengthens the refining operation, and oxygen blowing sharply accelerates the damage of refractory materials. Magnesia bricks, magnesia-chrome bricks, high-alumina bricks and high-alumina castables are generally used. Refractory materials must have excellent corrosion resistance and thermal shock resistance.
RH/RH-OB vacuum degassing devices have recently adopted high-purity high-chromium fired magnesia-chrome bricks. The oxygen blowing port bricks are semi-recombined magnesia-chrome bricks; high-temperature fired direct-bonded magnesia-chrome bricks are used in high-corrosion areas such as the lift pipe, bottom, and middle and lower linings. Special-grade high-alumina ramming materials and high-quality castables are used for the lift pipe outer lining.