A production method for reducing the incidence of longitudinal cracks in peritectic steel

Abstract

This invention discloses a production method for reducing the incidence of longitudinal cracks in peritectic steel, relating to the field of steel production and smelting technology. The method employs a mold flux with a basicity of 1.5-1.6 and a viscosity of 0.08-0.10 Pa·s at 1300℃; the taper of the right-angle mold is 1.2-1.3%; the flow rate of the primary cooling water in the wide inner arc direction of the peritectic steel billet in the mold is V1 = the width of the copper plate water tank × v1, where v1 is 1.35-1.4 L / (min·mm); the inlet temperature of the primary cooling water in the mold is 30-36℃. This method minimizes and offsets the volume shrinkage of the peritectic reaction, reduces the air gap between the copper plate and the billet shell, and ultimately significantly reduces the incidence of longitudinal cracks in the casting furnace from 70% to no more than 10%.

Description

Technical Field

[0001] This invention relates to the field of steel production and smelting technology, and in particular to a production method for reducing the incidence of longitudinal cracks in peritectic steel. Background Technology

[0002] In a broad sense, peritectic steel refers to steel with a carbon content in the molten steel range of 0.09-0.17%, which undergoes a peritectic reaction when cooled from the liquid phase to 1495℃. Because the peritectic reaction occurs during solidification, the billet shell contracts rapidly, creating air gaps and resulting in uneven cooling, making it highly susceptible to longitudinal cracks. To control longitudinal cracks in ordinary steel grades, the peritectic region is often avoided; that is, the carbon content in the molten steel is controlled at ≥0.17% or ≤0.10% to reduce the formation of longitudinal cracks.

[0003] To ensure that the steel plates meet the special performance requirements, such as strength, impact, and elongation, the carbon content of many special steels (such as EH36) can only be controlled at 0.11-0.14% after comprehensive consideration. This range happens to be the core area of ​​the peritectic region, where the peritectic reaction is extremely strong and the probability of longitudinal cracks is the highest.

[0004] To reduce the incidence of longitudinal cracks in peritectic steel, common methods include optimizing the molten steel composition to avoid the peritectic zone, reducing casting speed, and performing finishing on the cast billet. However, optimizing the molten steel composition while maintaining plate performance inevitably increases costs; reducing casting speed affects production efficiency; finishing the cast billet affects logistics and transportation; and reducing hot charging of the billet increases rolling costs. Additionally, steel mills can use ultra-weak cooling in the crystallizer to reduce longitudinal cracks in peritectic steel, but this method can lead to other problems such as thinner billet shells and increased heat flux in the crystallizer, causing adhesion alarms within the crystallizer and resulting in more serious steel leakage problems, thus negating the purpose of longitudinal crack control.

[0005] Therefore, optimizing and improving the production and processing technology of these special steels, so that they can meet special performance requirements and ensure production costs and efficiency while reducing the probability of longitudinal cracks, is a key technical challenge in producing these special steels. Summary of the Invention

[0006] Based on the mechanism of longitudinal cracking in peritectic steel, this invention provides a production method to reduce the incidence of longitudinal cracks in peritectic steel slabs. This method achieves uniform shell growth within the crystallizer, forms a stable protective slag film to fill the air gaps generated by the peritectic reaction, reduces the cooling intensity of the crystallizer, and ultimately significantly reduces the formation of longitudinal cracks. Simultaneously, it avoids the problem of adhesion alarms, preventing more serious steel leakage issues. This method meets the requirements of reducing costs and improving production efficiency in hot-charged slab rolling, while also reducing the risk of cracked and scrapped slabs. Specifically, it is achieved through the following technologies.

[0007] A production method for reducing the incidence of longitudinal cracks in peritectic steel involves using a mold protective slag with an alkalinity of 1.5-1.6 and a viscosity of 0.08-0.10 Pa·s at 1300℃; the taper of the right-angle mold is 1.2-1.3%; the flow rate of the first cooling water in the wide inner arc direction of the peritectic steel billet in the mold is V1 = the width of the copper plate water tank × v1, where v1 is 1.35-1.4 L / (min·mm); and the inlet temperature of the first cooling water in the mold is 30-36℃.

[0008] Most existing peritectic steel smelting technologies use mold flux with a basicity of less than 1.5, and the taper of the mold is generally no more than 1.15%. The cooling water (primary cooling water) of the mold is also relatively large, and the inlet water temperature is relatively low. This is due to restrictions to prevent steel leakage.

[0009] Increasing the alkalinity of the mold flux can reduce its viscosity, which facilitates the flow of liquid flux into the air gap between the copper plate and the billet shell, increases the thickness of the liquid flux, and improves the heat transfer uniformity of the mold flux. However, increasing the alkalinity of the mold flux can cause adhesion alarms.

[0010] Increasing the taper of the crystallizer helps to offset volume shrinkage after peritectic reaction in peritectic steel, improves heat transfer uniformity, and reduces longitudinal cracks; however, as the taper of the crystallizer increases, the problem of increased corner cracks in the cast billet will occur.

[0011] When peritectic reaction occurs violently, adjusting or reducing the cooling water flow and inlet temperature of the crystallizer can easily lead to liquid level fluctuations, causing risks such as steel leakage. This also indicates that arbitrarily reducing the cooling water flow and inlet temperature of the crystallizer will not only fail to reduce longitudinal cracks but may also cause problems such as adhesion alarms or even steel leakage, making it technically very difficult to implement. Reducing the cooling water flow and increasing the inlet temperature, using a weak cooling method, can reduce the cooling intensity and improve cooling uniformity, thereby minimizing the volume shrinkage of the peritectic reaction and improving the uniformity of billet shell growth. However, reducing the cooling water flow and increasing the inlet temperature will result in a thinner billet shell, increasing the probability of steel leakage.

[0012] This invention simultaneously selects a high-alkalinity, low-viscosity mold protective slag, increases the taper of the mold, reduces the amount of cooling water in the wide inner arc section of the mold cooling water, and increases the cooling water inlet temperature. By utilizing the synergistic effect of these readjusted process parameters, it not only reduces the incidence of longitudinal cracks, but also ensures that the incidence of adverse effects such as adhesion alarms and steel leakage is at a quality controllable level.

[0013] It should be noted that when adjusting the cooling water volume of the crystallizer, a better heat transfer effect can be achieved by mainly adjusting the water volume in the inner arc section of the wide face.

[0014] Furthermore, the flow rate of the cold water in the narrow face direction of the peritectic steel billet is V2 = narrow face thickness × copper plate water tank width × v2, where v2 is 1.85-1.95 L / (min·mm), and the flow rate of the cold water in the outer arc direction of the wide face is V3 = copper plate water tank width × v3, where v3 is 1.70-1.80 L / (min·mm).

[0015] Based on adjusting and reducing the cooling water volume in the inner arc section of the wide face of the crystallizer, the present invention also adjusts and reduces the cooling water volume on the side and the outer arc section of the wide face, which can further improve the cooling effect.

[0016] Furthermore, the main chemical components of the crystallizer protective slag, by mass fraction, include: CaO 42.5%, SiO2 27.45%, Al2O3 2.01%, F 10.59%; and a viscosity of 0.09 Pa·s at 1300℃.

[0017] This invention achieves a dual effect of slowing down heat transfer and ensuring lubrication by adjusting the main components of the crystallizer protective slag.

[0018] Furthermore, the intermediate container is purged with argon gas, and the superheating temperature is 20-30℃.

[0019] The tundish of this invention is purged with argon gas, which replaces the oxygen in the tundish, reducing Al loss in the molten steel, decreasing the formation of Al2O3 inclusions, and preventing the mold flux from becoming deformed and sticky, thus affecting heat transfer. The tundish superheating temperature has been optimized to facilitate the formation of a stable mold flux.

[0020] Furthermore, the flow rate of argon gas introduced into the intermediate liner via the insertion of the stopper rod is 10-15 L / min, and the flow rate of argon gas at the upper water inlet is 12-20 L / min.

[0021] This invention significantly reduces the likelihood of blockage at the top and submerged entry nozzles by increasing the flow rates of argon gas in the stopper rod and the top nozzle, thus ensuring good fluidity of molten steel, maintaining a constant casting speed in continuous casting, and stabilizing the quality of the cast billet.

[0022] Furthermore, the molten steel is soft-blown and then fed with calcium iron wire.

[0023] Generally, the duration of a soft blowjob can be adjusted as needed. For example, you can choose to blowjob for 8-10 minutes.

[0024] Furthermore, the dosage of calcium iron wire is 1.1-1.3 kg / t.

[0025] Specifically, the amount of calcium iron wire used is 1.2 kg / t.

[0026] This invention modifies the oxidation products in molten steel to form a low-melting-point 12CaO·7Al2O3. By using soft blowing to float inclusions, the fluidity of the molten steel is ensured, preventing insufficient flow of molten steel into the sides of the crystallizer. This, in turn, avoids poor melting of the protective slag due to insufficient heat provided by the molten steel to the protective slag on both sides, as well as an excessively thin and uneven liquid slag layer.

[0027] Furthermore, in the metal raw materials input for smelting, the mass ratio of molten iron to scrap steel is (2.8-3.0):1.

[0028] This invention achieves a more reasonable heat balance by selecting appropriate mass ratios of molten iron and scrap steel, avoiding insufficient temperature after carbon oxidation and preventing problems such as high oxygen and low carbon content in the tapped steel, and severe over-oxygenation in the molten steel.

[0029] Furthermore, the iron-to-steel ratio (mass ratio) can be selected as 800-805 kg / t, that is, the ratio of molten iron to scrap steel is approximately 2.9:1.

[0030] Furthermore, the carbon content of the molten steel after smelting is 0.05-0.07% by mass fraction.

[0031] This invention increases the carbon content of the steel, thereby reducing the oxygen content in the molten steel, which in turn reduces the amount of deoxidizer needed, and significantly reduces inclusions generated by deoxidation.

[0032] Optionally, the oxygen content of the steel is 320-420 pp.

[0033] Compared with the prior art, the advantages of the present invention are: 1. This invention provides a mold protective slag with high alkalinity and low viscosity, while increasing the taper of the mold and reducing the amount of cooling water in the mold, increasing the inlet water temperature, thereby minimizing and offsetting the volume shrinkage of the peritectic reaction, reducing the air gap between the copper plate and the billet shell, and ultimately significantly reducing the incidence of longitudinal cracks in the casting furnace from 70% to no more than 10%.

[0034] 2. By using a suitable iron-to-steel ratio, ensure carbon-temperature balance at the smelting endpoint, reduce oxygen levels in the tapped steel, and decrease oxidation inclusions caused by deoxidation. Calcium treatment of the molten steel modifies inclusions, while soft blowing promotes their flotation, reducing their concentration. Argon gas is used to replace air in continuous casting, reducing the oxidizing atmosphere in the tundish, decreasing the chance of secondary oxidation, and reducing the likelihood of Al2O3 formation leading to mold deformation. Argon gas is blown through the tundish nozzle and stopper rod to prevent Al2O3 from adhering to the inner wall of the nozzle, thus preventing poor steel flow. Through these measures, inclusions in the molten steel are significantly reduced, steel fluidity is significantly improved, and the incidence of longitudinal cracks in peritectic steel tends to stabilize and decrease. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In some embodiments of the present invention, the production method for reducing the incidence of longitudinal cracks in peritectic steel employs a mold protective slag with an alkalinity of 1.5-1.6 and a viscosity of 0.08-0.10 Pa·s at 1300°C; the taper of the right-angle mold is adjusted to 1.2-1.3%, and the flow rate of the first cooling water in the wide inner arc direction of the peritectic steel billet is V1 = the width of the copper plate water tank × v1, where v1 is 1.35-1.4 L / (min·mm); the inlet temperature of the first cooling water in the mold is also adjusted to 30-36°C.

[0037] In some implementation cases, the cooling water (primary cold water) flow rate of other parts of the right-angle crystallizer was further optimized. Specifically, the primary cold water flow rate V2 in the narrow face direction of the peritectic steel billet of the right-angle crystallizer is V2 = narrow face thickness × copper plate water tank width × v2, where v2 is 1.85-1.95 L / (min·mm), and the primary cold water flow rate V3 in the outer arc direction of the wide face is V3 = copper plate water tank width × v3, where v3 is 1.70-1.80 L / (min·mm).

[0038] In some implementation cases, the main chemical components of the mold flux by mass fraction include: CaO 42.5%, SiO2 27.45%, Al2O3 2.01%, F 10.59%; the viscosity of the mold flux at 1300℃ is 0.09 Pa·s.

[0039] In some implementation cases, the tundish is purged with argon gas before the molten steel is transferred to the right-angle crystallizer, and the superheat temperature is 20-30℃.

[0040] Furthermore, the flow rate of argon gas introduced into the intermediate liner via the insertion of the stopper rod is 10-15 L / min, and the flow rate of argon gas at the upper water inlet is 12-20 L / min.

[0041] In some implementation cases, molten steel is soft-blown and calcium iron wire is added.

[0042] In some implementation cases, the dosage of calcium iron wire (calcium content ≥30%) is 1.1-1.3 kg / t.

[0043] In some implementation cases, the mass ratio of molten iron to scrap steel in the metal raw materials input for smelting is (2.8-3.0):1.

[0044] In some implementation cases, the carbon content of the molten steel after smelting is 0.05-0.07% by mass fraction.

[0045] Specifically, the peritectic steel smelting method provided in the following specific embodiments is as follows: (1) A 150t converter is used for smelting. The total amount of molten iron and scrap steel charged is 158-163t. In order to achieve good heat balance in the converter, molten iron and scrap steel are added in a mass ratio of (2.8-3.0):1. For ease of comparison, the total amount of molten iron and scrap steel charged in the following specific implementation methods is 160t.

[0046] (2) The carbon content at the end of the converter (the carbon content of the tapped steel) should be 0.05-0.07%, and spot blowing should be avoided as much as possible. The number of spot blowing (or supplementary blowing) should be ≤1 to prevent the molten steel from being over-oxygenated.

[0047] (3) After the molten steel enters the LF furnace (Ladle Furnace), add 2.2-2.5 kg / t of aluminum (Al content ≥99.5%) for deoxidation and to maintain the Al content in the ladle at 0.040% (considering RH aluminum loss of 0.005%). White slag is produced in the refining furnace, and the white slag is maintained for ≥10 min. The composition at the outlet is controlled according to the target value.

[0048] For ease of comparison, the following specific implementation methods all use 2.4 kg / t of aluminum and a white slag retention time of 12 min.

[0049] (4) Maintain RH ultimate vacuum (<67 Pa) for ≥15 min. After vacuum treatment, perform calcium treatment.

[0050] For ease of comparison, the RH ultimate vacuum (<67 Pa) holding time in the following specific implementation methods is 16 min.

[0051] In some implementation cases, the amount of calcium-iron wire (calcium content ≥30%) used is 1.1-1.3 kg / t, the soft blowing argon time after calcium treatment is ≥8 min, and the slag surface is required to have obvious fluctuations but the molten steel surface is not exposed.

[0052] For ease of comparison, the following specific implementation methods all use 1.2 kg / t of calcium-iron wire (calcium content ≥ 30%); the soft blowing argon time after calcium treatment is 10 min; the soft blowing requires that there be obvious fluctuations on the slag surface but no exposed steel surface.

[0053] (5) Baking the intermediate bread; baking time 2-3 hours, baking temperature ≥1100℃.

[0054] For ease of comparison, the baking time for the intermediate bread in the following specific implementation methods is 2.5 hours and the baking temperature is 1150℃.

[0055] Before pouring, argon gas is used to purge the tundish to reduce the oxidizing atmosphere inside.

[0056] Argon purging is performed as follows: insert a stopper rod into the intermediate drum and introduce argon gas at a flow rate of 10-15 L / min, and introduce argon gas at the top water outlet at a flow rate of 12-20 L / min.

[0057] For ease of comparison, the following specific implementation methods use an argon flow rate of 12 L / min and an argon flow rate of 15 L / min at the water inlet.

[0058] The superheat of the tundish is controlled at 20-30℃. For ease of comparison, the superheat of the tundish is controlled at 28℃ in the following specific implementation methods.

[0059] (6) Inject the intermediate ladle into a right-angle crystallizer and cool to form.

[0060] Crystallizer cooling water settings: The flow rate of the first cooling water in the inner arc direction of the wide face is V1 = the width of the copper plate water tank (mm) × v1, where v1 is 1.35-1.4L / (min·mm), and the inlet water temperature is controlled at 30-36℃.

[0061] Optionally, when setting the cooling water for the crystallizer, the flow rate of the first cooling water in the narrow face direction of the peritectic steel billet of the right-angle crystallizer can also be adjusted as follows: V2 = narrow face thickness × copper plate water tank width × v2, where v2 is 1.85-1.95 L / (min·mm); the flow rate of the first cooling water in the outer arc direction of the wide face is V3 = copper plate water tank width × v3, where v3 is 1.70-1.80 L / (min·mm); the side taper setting of the crystallizer is: pulling speed 1.25 m / min, taper 1.3%.

[0062] The immersion nozzle has an insertion depth of 125mm and does not require adjustment of the slag line.

[0063] The crystallizer protective slag uses ultra-high basicity (≥1.5) and low viscosity (1300℃, ≤0.10pa.s).

[0064] In the peritectic steel smelting method provided in the following specific embodiments, the main chemical components of the mold protective slag are CaO 42.5%, SiO2 27.45%, Al2O3 2.01%, and F 10.59% by mass fraction; and the viscosity at 1300℃ is 0.09 Pa·s.

[0065] In some embodiments of the present invention, the present invention simultaneously selects a high-alkalinity, low-viscosity crystallizer protective slag, which increases the taper of the crystallizer, reduces the cooling water volume in the wide inner arc section of the crystallizer cooling water, and increases the cooling water inlet temperature; by utilizing the synergistic effect of these readjusted process parameters, the incidence of longitudinal cracks is reduced without increasing the probability of adhesion alarms.

[0066] It should be noted that in some embodiments of the present invention, when adjusting the cooling water volume of the crystallizer, a better heat transfer effect can be achieved mainly by adjusting the water volume in the inner arc section of the wide face. Based on this, the present invention also adjusts and reduces the cooling water volume in the outer arc sections of the narrow and wide faces.

[0067] In some embodiments of this invention, the tundish is purged with argon gas to replace the oxygen in the tundish, reducing Al loss in the molten steel, decreasing the formation of Al2O3 inclusions, and preventing the mold flux from becoming sticky and affecting heat transfer. The tundish overheating temperature is optimized to facilitate the formation of a stable mold flux.

[0068] In some embodiments of the present invention, by increasing the flow rate of argon gas in the stopper rod and the argon gas at the top nozzle, the present invention greatly reduces the probability of blockage at the top nozzle and the submerged entry nozzle, ensuring good fluidity of molten steel, maintaining a constant casting speed in continuous casting, and stabilizing the quality of the cast billet.

[0069] In some embodiments of this invention, the oxidation products in the molten steel are modified to form a low-melting-point 12CaO·7Al2O3. By using soft blowing to float inclusions, the fluidity of the molten steel can be ensured, preventing insufficient flow of molten steel into both sides of the crystallizer. This avoids poor melting of the protective slag due to insufficient heat provided by the molten steel to the protective slag on both sides, as well as an excessively thin and uneven liquid slag layer.

[0070] In some embodiments of the present invention, the present invention selects molten iron and scrap steel in appropriate mass ratios to make the heat balance more reasonable, avoids insufficient temperature after carbon oxidation and blowing, and avoids problems such as high oxygen and low carbon in the tapped steel and severe over-oxygenation of molten steel.

[0071] In some embodiments of the present invention, the present invention reduces the oxygen content in the molten steel by increasing the carbon content of the steel, thereby reducing the amount of deoxidizer used and significantly reducing the inclusions generated by deoxidation.

[0072] Examples: Steel grade parameters for each example.

[0073] For ease of comparison, this invention uses EH36, a typical peritectic steel with a wide cross-section (i.e., cross-section ≥ 2000 mm) produced by the applicant, as the research object. Specifically, the steel parameters selected for each embodiment are shown in Table 1 below.

[0074] Table 1

[0075] The specific process parameters for each steel grade in the embodiments are shown in Table 2 below. The main chemical components of the mold flux used, by mass fraction, include: CaO 42.5%, SiO2 27.45%, Al2O3 2.01%, F 10.59%; the viscosity of the mold flux at 1300℃ is 0.09 Pa·s.

[0076] Table 2

[0077] The proportion of longitudinal cracks and the number of times steel was exposed due to adhesion in each embodiment are shown in Table 3 below.

[0078] Table 3

[0079] As can be seen from the test results in Table 3 above, the present invention can significantly reduce the incidence of longitudinal cracks in peritectic steel without increasing the probability of adhesion alarms.

[0080] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A production method for reducing the incidence of longitudinal cracks in peritectic steel, characterized in that, A mold flux with an alkalinity of 1.5-1.6 and a viscosity of 0.08-0.10 Pa·s at 1300℃ is used; the taper of the right-angle mold is 1.2-1.3%; the flow rate of the first cooling water in the inner arc direction of the wide face of the peritectic steel billet is V1 = width of the copper plate water tank × v1, where v1 is 1.35-1.4 L / (min·mm); the flow rate of the first cooling water in the narrow face direction of the peritectic steel billet is V2 = thickness of the narrow face × copper plate water tank. The tank width × v2, where v2 is 1.85-1.95 L / (min·mm); the flow rate of the first cold water in the outer arc direction of the wide surface V3 = the width of the copper plate tank × v3, where v3 is 1.70-1.80 L / (min·mm); the inlet temperature of the first cold water in the crystallizer is 30-36℃; the peritectic steel is peritectic steel EH36 with a cross-section ≥2000mm; the chemical composition of the protective slag of the crystallizer by mass fraction includes: CaO 42.5%, SiO2 27.45%, Al2O3 2.01%, F 10.59%.

2. The production method for reducing the incidence of longitudinal cracks in peritectic steel according to claim 1, characterized in that, The intermediate container is purged with argon gas, and the superheating temperature is 20-30℃.

3. The production method for reducing the incidence of longitudinal cracks in peritectic steel according to claim 2, characterized in that, The flow rate of argon gas introduced into the intermediate tundish via the insertion stopper is 10-15 L / min, and the flow rate of argon gas at the top water inlet is 12-20 L / min.

4. The production method for reducing the incidence of longitudinal cracks in peritectic steel according to claim 1, characterized in that, The molten steel is gently blown and then fed with calcium iron wire.

5. The production method for reducing the incidence of longitudinal cracks in peritectic steel according to claim 4, characterized in that, The dosage of calcium iron wire is 1.1-1.3 kg / t.

6. The production method for reducing the incidence of longitudinal cracks in peritectic steel according to claim 5, characterized in that, The dosage of calcium iron wire is 1.2 kg / t.

7. The production method for reducing the incidence of longitudinal cracks in peritectic steel according to claim 1, characterized in that, In the metal raw materials input for smelting, the mass ratio of molten iron to scrap steel is (2.8-3.0):

1.

8. The production method for reducing the incidence of longitudinal cracks in peritectic steel according to claim 1, characterized in that, The carbon content of the molten steel after smelting is 0.05-0.07% by mass fraction.

Images