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What are the measures to improve the purity of continuous casting steel

Purity refers to the quantity, shape and distribution of non-metallic inclusions in steel. The inclusion in steel shall be reduced to the required level according to the steel grade and product quality,

We should start from the following five aspects:

① Reduce [O] content in steel as much as possible.

② Prevent the molten steel from interacting with air.

③ Reduce the interaction between molten steel and refractory materials.

④ Reduce slag entrainment in molten steel.

⑤ The improved flow promotes the floating of inclusions in molten steel.

In terms of process operation, the following measures shall be taken:

(1) Slag free tapping: slag retaining balls are adopted for the converter and eccentric bottom tapping is adopted for the electric furnace to prevent a large amount of slag from falling into the ladle.

(2) Ladle refining: select the appropriate refining method according to the steel grade, to uniform the temperature, fine tune the composition, reduce the oxygen content, remove gas inclusions, etc.

(3) Non oxidation casting: after the molten steel is treated by ladle, the total oxygen content in the steel can be reduced from 130ppm to below 20ppm. If the injection flow from ladle to tundish is not protected or poorly protected, the total oxygen content in tundish steel will rise to the range of 60-100ppm, which will return to the level before external refining, and the effect of external refining will be wasted.

(4) Tundish metallurgy: the tundish adopts large capacity, and the addition of retaining walls and dams is an effective measure to promote the floating of inclusions. For example, for 6T tundish, the scrap rate of slab inclusion is 12%, and the inclusion is 0.82 pieces / m2; 12t tundish + retaining wall, 0 scrap inclusion in slab, 0.04 inclusions / m2.

(5) Submerged nozzle + casting mold powder: the mold powder shall be able to fully absorb inclusions. The submerged entry nozzle material, nozzle shape and insertion depth shall be favorable for the floating and separation of inclusions.

We Changxing Refractory Material Co.,LTD is professional manufacturer and supplier of refractory materials for more than 30 years. Our high quality casting powder are good sold to many countries say South Africa, Bangladesh, Indonesia, Malaysia, etc.

Article Source: improve the purity of continuous casting steel Company name: Henan Changxing Refractory Materials Co.,Ltd More refractory products:https://www.cxrefractories.com/en-product-solution Email:[email protected] Website:https://www.cxrefractories.com

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What are the prominent problems in the tundish

At present, there are many problems in the tundish used in China, especially in the tundish used for billet caster.

The specific performance is as follows:

(1) The shape of tundish cavity is unreasonable. Due to the unreasonable shape of the inner cavity, the flow of molten steel in the tundish is unreasonable and the residence time is short, which can not purify the molten steel. The distance from the drop point of the large ladle injection into the tundish to the tundish nozzle is short, or the distance from each nozzle is too different; The volume at the drop point of the ladle is too small, resulting in serious steel slag mixing and lining scouring, affecting the service life of the tundish and polluting the molten steel.

(2) The capacity of tundish is small and the depth of molten pool is shallow, so it is not suitable for high-speed caster. The molten steel stays in the tundish for a short time, which makes it difficult to purify the molten steel and remove inclusions; It is difficult to maintain constant casting speed when changing the package; During pouring, the steel slag in the tundish is agitated seriously, which makes it difficult to float the inclusions and easy to enter the mold, especially when changing the tundish.

(3) The position of tundish nozzle clogging is not properly designed, especially the nozzle on both sides is too close to the two sides, which is easy to cause unsmooth pouring of the two side nozzles.

(4) The tundish nozzle control device is too thin and unreliable, which makes it difficult to accurately control the flow of molten steel, making it difficult to stabilize the liquid level of the mold and often causing out of control accidents.

(5) The large deformation of tundish and the problems of design and manufacturing accuracy result in insufficient centering accuracy of multiple water outlets.

(6) The lifting device of tundish is ineffective, and most of them can not be lifted, which brings difficulties to the continuous casting process and causes many defects of the slab.

(7) The distance from the bottom of tundish to the upper mouth of crystallizer is improperly selected. Most of the distance is too high, which makes it difficult to align the nozzle, and also makes the nozzle too long, which increases the refractory consumption per ton of steel nozzle.

(8) Insufficient attention has been paid to the quick change technology of submerged entry nozzle.

The above tundish can only be used at low casting speed, which is not suitable for the requirements of high casting speed. Modern tundish should not only adapt to the conditions of constant speed casting at high drawing speed, high steel throughput and strength, and intense agitation in the tundish, but also play the role of purifying molten steel and removing inclusions.

The specific measures adopted include:

(1) Optimize the shape of the inner cavity of the tundish, make the liquid steel flow reasonably in the tundish, expand the volume of the large ladle at the drop point of the tundish and optimize the distance from the drop point of the large ladle to each water inlet under the condition of adapting to the high pulling speed;

(2) Tundish with large capacity deep melting bath;

(3) Prevent deformation of tundish shell;

(4) Adopt firm and reliable tundish nozzle control device;

(5) Adopt reliable tundish lifting device under load;

(6) Optimize the distance from the tundish to the upper mouth of the crystallizer.

Article Source: What are the prominent problems in the tundish Company name: Henan Changxing Refractory Materials Co.,Ltd More refractory products:https://www.cxrefractories.com/en-product-solution Email:[email protected] Website:https://www.cxrefractories.com

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Measures to increase the life of tundish

1. The working layer of tundish adopts dry material

Under the condition that the technological conditions and the material and masonry form of tundish refractory are fixed, the life of tundish mainly depends on the chemical erosion, high temperature melting loss and mechanical erosion of the molten steel in the working layer of tundish. The tundish dry material has strong erosion resistance and erosion resistance, which can meet the requirements of long continuous pouring time.

2. The lining is made of magnesia refractory

Magnesium refractory adsorb the inclusion in steel is very strong, and good erosion resistance, erosion resistance, can meet the requirements of high number of continuous casting furnace, but also improve the quality of molten steel. After use, it is observed that the lining slag line of the middle bag is the thinnest, and other parts are 30 ~ 40mm. After a pouring time is completed, it is easy to disassemble the middle bag.

3. Use a current stabilizer

Because the steel flow directly impacts the tundish from the large tundish, the erosion of tundish is very serious, which is likely to cause the penetration of tundish. For this reason, it is decided to use the current stabilizer. The material of the current stabilizer is magnesium carbon, and the structure of the current stabilizer is a container structure with hollow cavity. The bottom of the inner cavity of the current stabilizer is large, and the mouth is small. The continuous casting tundish current stabilizer with this structure can prevent liquid steel from slagging obviously and stably, the tundish steel water quality is high, and the tundish refractory material consumption is low.

4. Raise the water level of the intermediate steel envelope

The original minimum liquid level requirement for tundish pouring was 600mm, but now it must be greater than 700mm. After the liquid level of molten steel is raised, the stagnation time of molten steel in tundish is prolonged. In a deep molten pool, the resistance between molten steel from ladle to flow stabilizer is large, and the flow velocity of the contact surface of flow stabilizer is small, thus the impact on the flow stabilizer is small, and the continuous pouring time of flow stabilizer is improved. The tundish life is also improved.

5. Improve slag overflow operation

The original slag overflow mouth close to the pouring point, slag overflow is difficult. With the increase of the number of continuous casting furnace, slag quantity is large and can not be discharged in time, slag line erosion on the lining is serious, and affect the quality of molten steel. For this reason, the position and shape of the slag overflow mouth is changed, and the assessment system is formulated. The slag thickness should not exceed 30mm, and the slag thickness should be controlled below 30mm in time when the rhythm is appropriate, so as to prevent serious erosion of the slag line of the wall and the occurrence of the wall through the steel. At the same time, the large contractor should strengthen the operation, and avoid a large amount of slag into the tunbale, which will cause serious erosion of the slag line of the bale wall.

6. Improve the service life of tundish water outlet

Improve the level of production scheduling, reduce the choke flow caused by equal steel and other reasons, stabilize the temperature of molten steel stage, reduce the secondary pouring caused by operation problems, so as to improve the service life of tundish water outlet, and then improve the life of tundish.

7. Improve the deoxidation process of molten steel

In order to improve the deoxidation effect, the amount of deoxidizer is increased, and the ladle is fed with silicon calcium wire for inclusion denaturation of molten steel. The process not only improves the deoxidation effect of the converter steel, reduces the oxide inclusion in the steel, but also improves the pouring ability of the steel and eliminates the flow of the tundish nozzle caused by the poor fluidity of the steel. At the same time, the free oxygen content in the molten steel is reduced, which reduces the erosion to the water mouth of the tundish and prolonging the life of the tundish.

8. Reasonable temperature regime

In order to ensure the normal pouring ability of molten steel, the water superheat of intermediate clad steel is strictly controlled within 10 ~ 25℃. In order to improve the success rate of the first furnace, the steel output temperature of the converter is 30 ~ 40℃ higher than the normal pouring temperature. According to the lower limit control the water temperature of the intermediate steel envelope, the qualified rate increased from 80% to 95%.

9. Make sure you bake

When baking tundish, the burner in the middle of the oven should be directly facing the center of the current stabilizer to ensure the baking effect of the current stabilizer. Specific requirements for baking tundish: medium fire baking shall be no less than 30min, and large fire baking shall be no less than 1h. Medium fire baking means that the flame reaches the bottom of the bag but does not launch, and large fire baking means that the gas valve is fully or basically open, the flame reaches the bottom of the bag and rebounds, the air volume is suitable, and the flame temperature reaches the highest. Once the fire starts, the dry lining tundish shall not cease fire or reduce the flame in the middle to ensure that the temperature of the middle bag wall reaches more than 1000℃.

10. Improve the production organization model

Make reasonable use of production organization mode, arrange the use of tundish in a planned way, avoid the waste of tundish, make reasonable use of tundish according to the order of masonry in normal circumstances, and give full play to the service life of tundish.

11. Reasonable production system

The connection of molten steel between converter and continuous casting is a necessary condition to ensure the normal production of continuous casting. The molten steel for continuous casting is required to be on time, the information transmission of production scheduling is increased, and the production organization is reasonable to ensure the stability of the water level of tundish steel, and at the same time, the liquid level of tundish is guaranteed within the required range, so as to ensure the service life of tundish.long water mouth) in order to avoid the oxidation of molten steel.

Article Source: Measures to increase the life of tundish Company name: Henan Changxing Refractory Materials Co.,Ltd More refractory products:https://www.cxrefractories.com/en-product-solution Email:[email protected] Website:https://www.cxrefractories.com

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Tundish Coating

Introduction:

Coating for tundish is a substitute for refractory thermal insulting plates to realize high-efficiency continuous casting, which is characterized by easy smearing, no cracks, corrosion resistance and easy disintegration, etc. Compared with thermal insulting plate, this refractory product not only reduces the consumption of refractory per ton of steel, but also improves the purity and property of molten steel.

Specific Application: Easy to be painted, used for wall and bottom of tundish. Max. Thickness: 5 cm.

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