What refractory materials are used for 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 material is 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 desiliconizer is added, and a forced air cooling pipe is buried in the side wall of the iron channel. For desiliconized 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>1, the formation of 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.
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 physical quantities such as the strength, elastic modulus, thermal conductivity, and linear expansion coefficient of the product.
For sintered products, the higher the high-temperature strength, the smaller the factors that inhibit the generation of cracks. Existing microcracks are easy to grow, the fracture toughness is poor, and they are easy to peel off 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.
How to determine the aggregate size of electric furnace gunning material?
Under the premise of determining the material and binder, the particle size ratio of aggregate is crucial to produce 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 materials is usually 3mm.
The particle size of flame gunning materials is usually smaller than that of semi-dry methods, 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 gunning materials, reduce dust, improve the working environment, and increase the adhesion rate, it has developed from the original crushed aggregate particles to particles plus additives and binders (organic or inorganic), which are pre-mixed and spray-dried for secondary granulation.
Granular polyphosphate and superphosphate are used to replace powdered binders to improve the moisture absorption and agglomeration problem during storage. In order to solve the hydration and oxidation problems of carbon-containing alkaline gunning materials, the waterproofing soaking treatment technology of alkaline aggregate particles and graphite has developed rapidly.
What are the effects of bottom blowing gas supply components on refractory materials?
① The air-permeable bricks of ultra-high power electric furnaces should have good air permeability during use. After steel formation, the air permeability function must be restored within 1 to 2 heats after reuse.
② The air supply components are in contact with molten steel at a high temperature of more than 1630℃ and are 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 intermittently operated. 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-blown 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 uses air-permeable ramming of the furnace bottom.
The refractory material of the furnace bottom must have the following properties: the air permeability of the ramming layer should be maintained for a long time, and the sintering 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 small cracks occur, it will affect the uniformity of air permeability; the air permeable layer must also have high resistance to thermal shock.
What refractory materials are used to adapt to the development of new continuous casting technology?
(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 lot of research has been done 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.
(2) Refractory materials for thin slab continuous casting
Since the crystallizer space is small in thin slab continuous casting, special requirements are placed on the submerged nozzle, so a special shape of thin-walled submerged nozzle has been developed. The submerged nozzle is made of high aluminum carbon refractory containing boron nitride (BN) and zirconium oxide (ZrO2).
What refractory materials are used in AOD furnaces?
AOD argon oxygen furnace is mainly used for melting stainless steel, and in recent years it has been expanded to the production of carbon steel and low alloy steel.
AOD furnace refractory materials should have good thermal shock resistance and slag resistance, mechanical wear resistance, erosion resistance, compact structure, and high strength.
AOD furnace lining materials are mainly magnesia chrome bricks in the United States and the United Kingdom. In 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 rebonded magnesia-chrome bricks fired at ultra-high temperatures and other materials have also been developed.
Magnesia-zirconium bricks are used in the tuyere area. 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.
What refractory materials are used in RH/RH-OB furnaces?
RH refractory lining works under vacuum sealing conditions. Common use conditions include high temperature (about 1600℃) operation, thermal cycle (up to 600℃), gas 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 factor 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 of partition lining according to the use conditions of different parts.
The RH-OB circulation method with oxygen blowing function improves the air extraction capacity, aggravates 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.
Oxygen blowing port bricks use 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 outer lining of the lift pipe.
