JPS6150905B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the tuyere of a steelmaking furnace having a tuyere, the tuyere surrounding area, slag line, general wall, VAD,
This article relates to a method for producing highly corrosion-resistant magnesia-lime refractories with improved thermal and structural spalling properties, which are lining furnace materials used in slag lines of molten steel containers for special refining such as VOD. Conventionally, when the steelmaking conditions were relatively high basicity operation, the furnace structure was relatively open, and in the case of intermittent operation, CaO% was about 10 to 40%.
% of Magdro or Mag Lime bricks are used. In the case of high basicity slag operation, 3CaO・
Since it produces high melting point minerals such as SiO ₂ and 2CaO/SiO ₂ , it has less penetration of slag components and has excellent corrosion resistance.Bricks with a high CaO content are also thought to have excellent spalling resistance. This is because However, the raw material composition of the conventional Magdro bricks that are actually manufactured uses fine powder of magnesia clinker because lime-based raw materials are easily digested and difficult to use as fine powder in the manufacturing process. As far as the matrix part is concerned, it is the same as magnesia brick. Therefore, if such Magdro bricks are used in an actual furnace,
Slag components produce low-melting substances such as CaO・MgO−SiO ₂ (monticerite) and 3CaO・MgO・2SiO ₂ (melvinite), which easily penetrate deep into the brick matrix, resulting in structural spalling. This often results in peeling and wear. Furthermore, with regard to thermal spalling, since the matrix portion is made of magnesia, results as excellent as expected were not obtained. In addition, in recent years, single lime bricks or high lime bricks with CaO of 50% or more have been used in actual furnaces by using high-purity, dense electrofused or sintered lime clinker as raw materials. For example, like a lime brick, the matrix
CaO quality bricks have the _above -mentioned 3CaO and
In order to generate high melting point minerals such as SiO ₂ and 2CaO/SiO ₂ , the slag components remain on the surface of the brick and do not penetrate deeply, and are also resistant to thermal spalling, resulting in good durability. show. However, when a large amount of Al ₂ O ₃ and Fe ₂ O ₃ is present in the slag, CaO forms low-melting minerals such as CaO・Al ₂ O ₃ and 2CaO・Fe ₂ O ₃ , resulting in a decrease in corrosion resistance. have. In this case, a matrix with a high MgO ratio has better corrosion resistance than a CaO matrix. As a result of a detailed study of the advantages and disadvantages of mag-lime bricks and calcareous bricks, the present inventor has developed mag-lime bricks that have high corrosion resistance and excellent thermal and structural spalling properties. Successful. The present invention improves the corrosion resistance and further improves the thermal and structural spalling properties of a basic brick whose matrix portion is made of magnesia. That is, the coarse grain and intermediate grain portions are single or a combination of two or more of dolomite clinker, synthetic magdo clinker, electrofused or sintered lime clinker, electrofused or sintered magnesia clinker, and the fine powder portion is electrofused or sintered magnesia clinker. For the basic formulation consisting of sintered magnesia clinker, electrofused or sintered lime clinker, or
It is characterized by adding 5 to 20% of CaO to mag-lime clinker, which has a total content of CaO and MgO of 95% or more based on analysis, with a particle size of 0.5 mm or less, and then kneading, molding, and baking it. Mag-lime clinker is manufactured by electrofusion or sintering, and the CaO/MgO ratio is CaO50~100MgO0~
50, and refers to mag lime clinker, which is made by uniformly mixing lime raw materials and magnesia raw materials in advance and treating it at high temperature in an electric furnace or kiln. In addition, analysis shows that minor components other than CaO and MgO include Fe ₂ O ₃ of 1% or less, SiO ₂ of 1% or less, and Al ₂ O ₃
is limited to 1.5% or less. The microstructure of mag-lime clinker has a mottled structure in which MgO solids are uniformly scattered and distributed in CaO solids, and this clinker is similar to the properties of lime clinker.
It also has the properties of MgO clinker. Although the object of the present invention can be sufficiently achieved by using lime clinker, it is even more effective if mag lime clinker is used. First, let's talk about the case where lime clinker is applied. For the basic composition mentioned above, lime clinker is used at a particle size of 5 to 20%, preferably 5 to 10%, with the maximum particle size being 0.5 mm and 80% or more being 0.2 mm or less. %Added. When brick tissue is observed under a microscope, there are some periclase-periclase bonds in the matrix, but most of the periclase is bonded by CaO crystals. The thermal spalling properties of the bricks are far superior to those without lime clinker, and this effect is even more pronounced when a dense brick structure is created through particle size structure and high-temperature firing. This exists in the pericles gap
This is thought to be because CaO has the property of softening slightly at high temperatures, absorbing the expansion and contraction of periclase, and improving thermal spalling properties. Regarding slag resistance, CaO between periclase is 3CaO・
Since it generates SiO ₂ , 2CaO・SiO ₂ , it suppresses the penetration of slag components into the interior of the brick, which is better than conventional Magdro bricks, and also prevents structural spalling due to slag absorption. It is much better than the existing bricks. The amount of lime clinker added is 5 to 20% by weight as CaO, but the reason why the lower limit was set at 5% is as follows.
If it is less than 5%, it will not be possible to improve the spalling resistance or prevent slag penetration.The reason why the upper limit was set at 20% is that the particle size structure of firebricks generally The proportion of fine particles of 0.5 mm or less is in the range of 20 to 40%, but the proportion of CaO due to the addition of lime clinker is 1/2 of the fine particles.
It is desirable that the amount be less than 1/2, because if it is more than 1/2, the corrosion resistance will be significantly lowered. The reason why the maximum particle size was set to 0.5 mm and the particle size of 0.2 mm or less was set to 80% or more will be explained. From the purpose of the present invention, it is desirable that the particle size of the lime clinker and maglime clinker be 0.2 mm or less, but these clinkers tend to absorb moisture in the air and become hydroxides. If a 0.2mm sieve is used in the sieving process for producing fine powder, the sieves tend to become clogged, reducing sieving efficiency, and as a result, the clinker absorbs moisture from the air. and hydroxide [Ca
(OH) ₂ ]. This Ca(OH) ₂
Bricks manufactured by adding the fine clinker powder produced in large amounts will decompose the hydrates again during firing and release water, which will inhibit the sintering of the bricks. Therefore, assuming the maximum particle size of clinker to be 0.5 mm,
If a 0.5 mm sieve is used, the sieving process can be speeded up and the formation of hydroxides can be almost ignored. Furthermore, if the particle size is 0.2 mm or less at least 80%, it is possible to sufficiently improve the matrix made up mostly of periclase, which is the object of the present invention, so the lower limit was set at 80%. Of course as mentioned above
If it is 100%, the invention will be even more effective. Another reason for setting the maximum grain size to 0.5 mm is that when the maximum grain size exceeds 0.5 mm, lime clinker or mag-lime clinker
mm), and as a result, the clinker particles selectively react with harmful components such as Al ₂ O ₃ and Fe ₂ O ₃ that invade the brick structure from the slag components, and the low-melting minerals This is because this will cause a decrease in erosion resistance, and if the grain size is 0.5 mm or less, this effect will be suppressed to a minimum. Next, when 5 to 20% of fine powder of Mag-Lime clinker is added as CaO, the microstructure of the brick matrix is such that particles of Mag-Lime clinker form cross-links between periclase. , the outside of the particle is a CaO solid, and the inside has a skeletal MgO solid,
The bricks have high hot strength and improved spalling resistance, and as with the case of adding lime clinker, there was less slag infiltration and structural spalling resistance was also improved. The reason why the MgO% of the mag-lime clinker is limited to 50% is that if it exceeds 50%, the spalling resistance effect of CaO decreases. lime clinker, mag lime clinker
As for the small amounts of Fe ₂ O ₃ , SiO ₂ , and Al ₂ O ₃ , it is better to reduce the amount as much as possible. That is, Fe ₂ O ₃ is 1% or less, preferably 0.5
% or less, SiO ₂ is 1% or less, preferably 0.5% or less, Al ₂ O ₃ is also 1.5% or less, preferably 1.0
% or less. The reason is that these small amounts of components contain CaO・Al ₂ O ₃ ,
This is because low melting point minerals such as 2CaO and Fe ₂ O ₃ are formed between the CaO and MgO crystals in the matrix, reducing hot strength and corrosion resistance. Next, the present invention will be explained by examples. Table 1 shows quality examples of the fused lime clinker and fused mag lime clinker used, and Table 2 shows quality examples of mag lime bricks manufactured using fused lime clinker A and fused mag lime clinker D. showed that. Electrified lime clinker A is made into a fine powder with a particle size of 0.5 mm or less, and 5% is added to the blend of regular Magdro bricks.
Or, after adding 10% and kneading with a binder used for ordinary lime-based basic bricks such as attacking polypropylene, and molding under high pressure,
It was fired at a temperature of 1,500°C or higher, and after firing it was coated with wax or impregnated with tar to give it resistance to digestion. As a result, the quality of the bricks is improved by a slight decrease in apparent porosity and densification in proportion to the amount of lime, resulting in improved compressive strength and
A high value was also obtained for hot bending strength at 1480℃. Furthermore, as shown in the drawing, the elastic modulus was reduced due to the effect of lime, indicating that thermal spalling properties were improved. In addition, in the drawings, indicates Magdro Brick, and indicates the present invention. After removing the slag from these bricks using a rotary erosion furnace, we conducted a rapid cooling erosion test in which cold air was blown into the furnace, and it was found that the inventive product had little penetration of slag components and structural spalling was the cause. There were almost no cracks. When the product of the present invention was used in the tuyere, the area around the tuyere, and the slag line of Company A's 90 ^ton AOD furnace, it showed less cracking and peeling caused by structural spalling than conventional Magdro bricks, and it was resistant to cracking and peeling due to structural spalling. Improvement in spalling property was observed. In addition, tests were conducted on the slag line of Company B's VOD furnace with conventional Magdro bricks, and good results were obtained with few cracks and peeling, so the product continues to be used.

【table】

【table】

【table】 [Brief explanation of the drawing]

The drawing is a chart showing the elastic modulus of the Magdro bricks described in Examples and the products of the present invention.

Claims (1)

[Claims] 1. The coarse grain and intermediate grain portion of the magnesia-lime refractory compound are single or a combination of two or more of dolomite clinker, synthetic magne clinker, lime clinker, and magnesia clinker, and the fine grain portion is composed of magnesia clinker. CaO/MgO ratio is 100 to 50/0 to the basic formulation
50. Electro-fused or sintered lime clinker or electro-fused or sintered mag-lime clinker whose minor components are analytically less than 1% Fe ₂ O ₃ , less than 1% SiO ₂ , and less than 1.5% Al ₂ O ₃ , Grain size is 0.5mm and 0.2
A method for producing a magnesia-lime refractory, which comprises adding 5 to 20% CaO%, kneading, molding, and firing at a temperature of 1500°C or higher.