Square steel production process

Abstract

The invention relates to the technical field of square steel production, and discloses a square steel production process which comprises molten iron, a converter, CAS, LF, continuous casting and bar two-line rolling. In the molten iron preparation stage, alloy is required to be clean and dry without mixing, C, S, Mn, P, S, Al and Si are added into molten steel, in the converter stage, it is ensured that the carbon content and temperature in the molten steel need to meet preset requirements, in the CAS stage, whole-course bottom argon blowing is adopted, sudden blowing is strictly prohibited, and the stability and continuity of the molten steel in the casting process can be ensured by accurately controlling the tundish liquid level. And when the liquid level is too low, the waste blanks can be timely picked out, so that the defects caused by insufficient molten steel can be avoided. Meanwhile, casting protection measures such as a covering agent and carbonized rice husks are adopted, so that heat loss and oxidation of molten steel can be further reduced, the uniformity and quality of a casting blank are improved, and defects caused by unstable casting are reduced. And meanwhile, the service life of the tundish and the crystallizer can be prolonged by protecting casting.

Description

Technical Field

[0001] The invention relates to the technical field of square steel production, in particular to a square steel production process. Background Art

[0002] In the field of steel production, square steel, as an important basic material, is widely used in many industries such as construction, machinery, and automobiles. With the continuous advancement of technology and the intensification of market competition, higher requirements are placed on the production process and product quality of square steel.

[0003] In the steel production process, hot delivery and opening of continuous casting billets are key links to ensure steel quality and production efficiency. The precise control of scientific composition and microstructure is crucial to the mechanical properties and processing performance of the final product. However, in the actual production process, problems such as poor castability of molten steel and surface quality defects are often encountered, which directly affect the product yield and market competitiveness. Summary of the invention

[0004] The object of the present invention is to provide a square steel production process to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions: a square steel production process, including molten iron, converter, CAS, LF, continuous casting, and two-line rolling of bars;

[0006] S1. During the molten iron preparation stage, the alloy must be clean and dry and no mixing is allowed;

[0007] S2. During the converter stage, ensure that the carbon content and temperature in the molten steel meet the predetermined requirements. Carbon (C) is one of the main elements in steel and has an important influence on the hardness, strength and toughness of steel. Phosphorus (P) is a harmful element in steel. It will drastically reduce the plasticity and toughness of steel, especially the low-temperature toughness, making the steel brittle at low temperatures and causing cold brittleness. Therefore, the phosphorus content needs to be strictly controlled during the steelmaking process to meet the performance requirements of the steel.

[0008] S3. In the CAS stage, argon is blown from the bottom throughout the process, and violent blowing is strictly prohibited. The argon pressure during the steel-making process is controlled at the target of 0.8-1.2Mpa;

[0009] S4. In the LF stage, by controlling the oxygen and sulfur content, temperature and composition in the molten steel, high-quality molten steel with low oxygen and sulfur content is produced;

[0010] S5. During continuous casting, argon is blown through the long nozzle and a sealing ring is added to the nozzle to protect the casting. It is strictly forbidden to expose the molten steel in the tundish and crystallizer;

[0011] S6, the second-line rolling of bars includes ingot inspection - entering the furnace, heating - 800 rolling - continuous rolling - sawing - cooling bed - stacking slow cooling - grinding - finished product inspection - warehousing.

[0012] Preferably, the molten iron preparation stage includes the following steps:

[0013] S1.1. Prepare high carbon ferromanganese or medium carbon ferromanganese, high carbon ferrochrome, high AlMnFe, synthetic slag, and provide accurate alloy composition and required quantity to the alloy worker in front of the furnace during steelmaking;

[0014] S1.2. Lime requirements: CaO ≥ 88%, activity ≥ 300ml.

[0015] Preferably, the converter stage comprises the following steps:

[0016] S2.1. Classify, clean and pre-treat scrap steel, scrap iron, molten steel and other raw materials to ensure that the quality of the raw materials meets the requirements, and prepare other auxiliary raw materials and desulfurizers;

[0017] S2.2, loading raw materials and desulfurizer into the converter steelmaking furnace;

[0018] S2.3, start the converter and heat it to high temperature. Under high temperature conditions, the raw materials undergo oxidation-reduction reactions to remove impurities and harmful elements such as sulfur and phosphorus;

[0019] S2.4, oxygen is introduced into the converter to cause oxidation-reduction reaction of impurities and carbon in the raw materials, thereby accelerating the smelting process, producing alloy elements, adjusting the composition of the molten steel, and adding deoxidation alloy into the ladle for deoxidation alloying when 1 / 4 of the steel is discharged;

[0020] S2.5. When the molten steel is transferred from the converter to the ladle, measures should be taken to prevent the slag from entering the ladle. The maximum thickness of the slag in the ladle should be controlled to ≤50mm. Slag is a by-product produced during the smelting process. If it enters the ladle, it will affect the quality of the steel. The thickness of the slag should be strictly controlled.

[0021] Preferably, the CAS stage includes the following steps:

[0022] S3.1. The ladle containing the molten steel is transported to the refining station and argon is blown into the bottom of the ladle;

[0023] S3.2. Measure the temperature of molten steel within 2 minutes after entering the station. After blowing argon for 2 minutes, use a static sampler to take samples.

[0024] S3.3. After sampling, adjust the argon gas to the soft blowing state and cover it before leaving the station. CAS treatment can significantly reduce large inclusions in molten steel and improve the quality of steel.

[0025] Preferably, the LF stage comprises the following steps:

[0026] S4.1. Ensure the bottom blowing effect of the large tank, the tank edge is clean, and meets the process requirements for entering the LF furnace;

[0027] S4.2. Carefully check the argon blowing system before the molten steel enters the LF furnace to ensure that the argon blowing quick connector is connected reliably and without leakage;

[0028] S4.3. Power is supplied according to the temperature requirements of the steel grade, and the molten steel is sampled and the temperature is measured in time. Static samplers are used to take samples. Different temperatures need to be controlled during the LF refining process depending on the steel grade. Power supply heating is to meet this temperature requirement. At the same time, sampling and temperature measurement are important means of monitoring the refining process, which can timely discover and solve problems, ensure that the temperature of the molten steel meets the process requirements, and improve the stability and controllability of the refining process. At the same time, problems in the molten steel can be discovered in time through sampling and temperature measurement, providing a basis for subsequent adjustments;

[0029] S4.4. During the process of adding refined slag, add appropriate amount of calcium carbide and aluminum powder to make white slag. The white slag keeping time is ≥15min, and the total argon blowing time of LF is ≥40min. White slag is a high-basicity, low-oxidizing slag with good desulfurization and dephosphorization capabilities. White slag can be made by adding appropriate amount of calcium carbide and aluminum powder, and kept for a certain time to ensure the refining effect. At the same time, long-term argon blowing and stirring can promote material exchange and chemical reaction between molten steel and slag, improve the desulfurization and dephosphorization efficiency of molten steel, and reduce the content of harmful impurities. At the same time, long-term argon blowing and stirring can also promote the uniformity and stability of molten steel;

[0030] S4.5. Equipped with carbon wire and alloy bulk materials, fine-tune the composition according to the target value. The outgoing composition meets the internal control requirements. The outgoing Al control target is: 0.033-0.045%. Feed 150-250m of pure Ca wire before leaving the station. After feeding the wire, soft blowing is ≥10min. The overheat of the tundish is controlled by the target value of ≤40℃ for the start-casting furnace and ≤35℃ for the continuous casting furnace. The outgoing temperature reference is: 1574±5℃ for the start-casting furnace and 1559±5℃ for the continuous casting furnace.

[0031] Preferably, the continuous casting stage comprises the following steps:

[0032] S5.1. Argon is blown at the long nozzle, and a sealing ring is added to the nozzle to protect the casting. It is strictly forbidden to expose the molten steel in the tundish and crystallizer;

[0033] S5.2, middle ladle liquid level control: start casting> 400mm, normal casting> 600mm, change to large ladle> 650mm; when the liquid level in the middle ladle of the continuous casting furnace is lower than 400mm, the billets must be picked out and treated as waste billets. The middle ladle uses covering agent + carbonized rice husk (or composite insulation agent) to protect the casting. By accurately controlling the liquid level in the middle ladle, the stability and continuity of the molten steel during the casting process can be ensured. When the liquid level is too low, timely picking out the waste billets can avoid defects caused by insufficient molten steel. At the same time, the use of protective casting measures such as covering agents and carbonized rice husks can further reduce the heat loss and oxidation of molten steel, improve the uniformity and quality of the billets, and reduce defects caused by unstable casting. At the same time, protective casting can also extend the service life of the middle ladle and crystallizer;

[0034] S5.3, Crystallizer protective slag: Medium carbon steel protective slag; the protective slag is required to be dry, and the depth of the tundish outlet immersed in the crystallizer liquid level is: 90-110mm. Use protective slag suitable for medium carbon steel and ensure that it is dry, which can effectively reduce the friction and adhesion between the ingot and the crystallizer. At the same time, the protective slag can also absorb inclusions and gases in the molten steel. Controlling the depth of the tundish outlet immersed in the crystallizer liquid level can ensure the uniform distribution and stable solidification of the molten steel in the crystallizer, improve the surface quality and internal quality of the ingot, and reduce defects caused by friction and adhesion. At the same time, the use of protective slag can also increase the service life of the crystallizer and casting efficiency;

[0035] S5.4. The billet continues to be cooled by spraying water in the secondary cooling zone to ensure that the billet is completely solidified.

[0036] S5.5. The molten steel gradually solidifies into a billet shell along the periphery of the crystallizer. When the molten steel level rises to a certain height and the billet shell solidifies to a certain thickness, the straightening machine pulls the billet out. When the crystallizer liquid level fluctuation exceeds ±7.5mm, the billet is cut off. No less than one low-power sample is taken for each pouring. The molten steel gradually solidifies into a billet shell in the crystallizer. This is a key step in the continuous casting process. The straightening machine pulls the billet out after the billet shell solidifies to a certain thickness, which can ensure the continuity and stability of the billet. At the same time, strict control of the crystallizer liquid level fluctuation can avoid billet defects caused by liquid level fluctuation. Taking low-power samples for each pour can timely discover and evaluate the quality problems of the billet, improve the continuity and stability of the billet, and reduce defects caused by solidification and pulling out. At the same time, the control of liquid level fluctuation and the sampling of low-power samples can ensure that the quality of the billet meets the standards and requirements.

[0037] 8. Preferably, the second-line rolling of the bar comprises the following steps:

[0038] S6.1. Residual element requirements for billet: Cr≤0.10%, Cu≤0.05%, Ni≤0.05%, Mo≤0.05%, As≤0.03%, B≤0.001%;

[0039] S6.2. Put the billet into the heating furnace. If the accident time is more than 20 minutes, the heating temperature should be reduced in time. The heating furnace should be strictly controlled according to the heating temperature and furnace time in the production process control regulations of this steel grade. Ensure that the overall temperature of the billet is uniform to prevent the visible positive and negative sides. If the positive and negative sides are obvious, the rolling should be stopped immediately to wait for the temperature, increase the gas volume of the burner, and steel can be tapped only after the temperature is normal. During the rolling process, high-pressure water descaling should be turned on, and the descaling working pressure should not be less than 12Mpa. To ensure the dephosphorization effect of high-pressure water descaling, the descaling pressure needs to be confirmed when taking over. If the iron oxide scale is not removed cleanly, the steel production should be stopped immediately, and the fitter should be arranged to check the nozzle and pressure. The steel can be produced only after the treatment is completed; the surface iron oxide scale should be removed cleanly to avoid surface defects such as pitting caused by the rolling and pressing of the iron oxide scale, ensure the uniformity of heating, avoid quality problems caused by uneven temperature, improve the overall quality and surface finish of the steel, start high-pressure water descaling, effectively remove the iron oxide scale on the steel surface, and avoid the iron oxide scale being pressed into the steel surface during the rolling process, forming defects such as pitting;

[0040] S6.3. When rolling the square billet, there shall be no visible reconnection and scarring on the surface, no cracks, fissures, folds and subcutaneous bubbles on the surface. The rolling temperature shall be ≥1000℃. The sharp corners and burrs on the rolling groove, baffle, guide and roller shall be polished clean. Those that cannot be polished clean shall be replaced in time. When changing rolls and taking over, the 800 rolling mill roll groove shall be checked for severe wear and loss of meat. Special attention shall be paid to checking the surface of the push bed and the "vertical roller" to avoid scratches and abrasions on the red steel surface by the push bed, which may cause defects such as discontinuity and shallow folding on the surface of the finished product. , the shearing length of the 400t shear should be carried out according to the operating procedures. When producing large square billets, the 400t shear must clean the head and fishtail defects. The wear of the rolling groove should be checked during the shift inspection and mid-term shutdown, whether there are serious cracks and meat loss; whether the cooling water pipe nozzle is aligned with the rolling groove, whether the connecting hose is leaking, etc.; check whether the guide is centered, whether there is iron clamping, wire drawing, guide roller jamming, etc., and stop or replace it in time if any abnormality is found. The material shape and size of each frame should be measured every hour during the rolling process. If folds and scratches are found on the online pickling surface of each batch during the rolling process, the machine should be stopped for inspection. The sampling post personnel should record the online pickling surface conditions of each batch with defects in the MES system. The length of the head and tail of the hot saw should be strictly carried out in accordance with the requirements of the operating procedures. The length can be increased but it must not be shorter than the required length. The finishing team arranges personnel to check the sawing condition of the tail of the cooling bed every hour. If there is any incomplete sawing, the sawing length of the corresponding batch should be increased by about 50-200mm. The round steel cooling bed is equipped with teeth, and the number of teeth is not less than 3. If the square steel rolls together in the second and third sections, the number of teeth should be appropriately increased.

[0041] S6.4. Cool the steel billet. After the square steel is put on the chain, each steel bar should be separated by a distance of not less than 150mm to prevent cold bending;

[0042] S6.5, Square steel stacking and slow cooling: The upper longitudinal edge is less than 200mm away from the lower tail end, and the upper transverse end is less than 200mm beyond the lower edge. The stacking density and slow cooling conditions are properly controlled to ensure uniform heat dissipation of the steel during the slow cooling process to avoid internal stress concentration and deformation;

[0043] S6.6. Before grinding the steel billet, the six digits after the furnace number should be drawn on the end with a white paint pen. During finishing and grinding, operators at all positions must operate carefully, not bend the finished product, not scratch the surface, clean the ears, scratches, burrs and flash on the surface of the finished product, and inspect the surface quality of the finished product. The scratches, cracks, folds, scars, ears, burrs and flash on the surface must be ground clean;

[0044] S6.7. Inspection and acceptance of steel materials require that the surface should not have visually visible reconnections and scars, cracks, fissures, folds and subcutaneous bubbles. If there are any defects that are not allowed on the surface, they should be removed. The removal width should not be less than 6 times the depth, and the length should not be less than 10 times the depth. After grinding, the defective parts should be smooth and without edges and corners. The grinding depth should not be greater than 1.5mm. The grinding depth is calculated from the actual size. After grinding, follow the contract requirements and sign a label or paint the color on one end of each steel.

[0045] S6.8. When warehousing and delivery are carried out, hot-rolled state delivery is required. If the user has special requirements, the user contract or technical agreement shall be implemented, and the inspection and acceptance shall be carried out in accordance with the provisions of the user contract or technical agreement.

[0046] Preferably, the auxiliary raw materials added in S2.1 have the following component addition requirements: C 0.36wt%-0.38wt%, Si≤0.09wt%, Mn 0.66wt%-0.83wt%, P≤0.024wt%, S≤0.024wt%, Cr 0.31wt%-0.39wt%, Al 0.025wt%-0.060wt%. By adding appropriate amounts of elements such as C, Si, Mn, Cr, etc., the hardness, strength, hardenability and wear resistance of the steel can be significantly improved while maintaining relatively good plasticity and toughness. Elements such as Si, Mn, Al are used as deoxidizers and desulfurizers, which help to remove harmful elements such as oxygen and sulfur in the steel, thereby improving the quality and performance of the steel. The addition of elements such as Cr can also improve the corrosion resistance and antioxidant effect of the steel and extend the service life of the steel.

[0047] Preferably, during the converter stage, it is ensured that C ≥ 0.08% and P ≤ 0.013% in the molten steel, the molten steel entering the furnace is not lower than 1550°C, and when tapping, the steel is required to contain C0.31%-0.34%, Mn0.62%-0.69%, Cr0.26-0.34%, P≤0.020, Al0.026%-0.049, and deoxidizer, high carbon Mn-Fe, high carbon Cr-Fe, and high aluminum Fe-Mn-Al are added to the molten steel.

[0048] Compared with the prior art, the present invention provides a square steel production process, which has the following beneficial effects:

[0049] 1. The square steel production process can ensure the stability and continuity of molten steel during the casting process by accurately controlling the liquid level of the tundish. When the liquid level is too low, timely picking out the scrap billet can avoid defects caused by insufficient molten steel. At the same time, the use of protective casting measures such as covering agents and carbonized rice husks can further reduce the heat loss and oxidation of molten steel, improve the uniformity and quality of the billet, and reduce defects caused by unstable casting. At the same time, protective casting can also extend the service life of the tundish and crystallizer.

[0050] 2. The square steel production process strictly follows the heating temperature and furnace time control regulations of the steel production process control regulations to ensure uniform heating, avoid quality problems caused by uneven temperature, and improve the overall quality and surface finish of the steel. At the same time, high-pressure water descaling is used to effectively remove the iron oxide on the surface of the steel, avoiding the iron oxide being pressed into the steel surface during the rolling process, forming defects such as pitting.

[0051] 3. The square steel production process can significantly improve the hardness, strength, hardenability and wear resistance of steel by adding appropriate amounts of elements such as C, Si, Mn, Cr, etc., while maintaining relatively good plasticity and toughness. Elements such as Si, Mn, Al, etc. are used as deoxidizers and desulfurizers, which help to remove harmful elements such as oxygen and sulfur in steel, thereby improving the quality and performance of steel. The addition of elements such as Cr can also improve the corrosion resistance and antioxidant effect of steel and extend the service life of steel.

[0052] 4. The square steel production process can ensure that the steel has excellent properties, such as high strength, high toughness, and good corrosion resistance, by precisely controlling the composition of the molten steel. Reasonable composition control can reduce energy consumption and waste emissions during the smelting process, while improving smelting efficiency. According to the purpose and requirements of the final product, by adjusting the composition of the molten steel and the type and amount of added alloys, steel that meets specific performance requirements can be produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a schematic diagram of the process of the present invention;

[0054] Figure 2 It is a schematic diagram of the two-line rolling process for bars of the present invention. DETAILED DESCRIPTION

[0055] like Figure 1-2 As shown, the present invention provides a technical solution: a square steel production process, including molten iron, converter, CAS, LF, continuous casting, and two-line rolling of bars;

[0056] S1. During the molten iron preparation stage, the alloy must be clean and dry and no mixing is allowed;

[0057] S2. During the converter stage, ensure that the carbon content and temperature in the molten steel meet the predetermined requirements. Carbon (C) is one of the main elements in steel and has an important influence on the hardness, strength and toughness of steel. Phosphorus (P) is a harmful element in steel. It will drastically reduce the plasticity and toughness of steel, especially the low-temperature toughness, making the steel brittle at low temperatures and causing cold brittleness. Therefore, the phosphorus content needs to be strictly controlled during the steelmaking process to meet the performance requirements of the steel.

[0058] S3. In the CAS stage, argon is blown from the bottom throughout the process, and violent blowing is strictly prohibited. The argon pressure during the steel-making process is controlled at the target of 0.8-1.2Mpa;

[0059] S4. In the LF stage, by controlling the oxygen and sulfur content, temperature and composition in the molten steel, high-quality molten steel with low oxygen and sulfur content is produced;

[0060] S5. During continuous casting, argon is blown through the long nozzle and a sealing ring is added to the nozzle to protect the casting. It is strictly forbidden to expose the molten steel in the tundish and crystallizer;

[0061] S6, the second-line rolling of bars includes ingot inspection - entering the furnace, heating - 800 rolling - continuous rolling - sawing - cooling bed - stacking slow cooling - grinding - finished product inspection - warehousing.

[0062] The following steps are included in the hot metal preparation stage:

[0063] S1.1. Prepare high carbon ferromanganese or medium carbon ferromanganese, high carbon ferrochrome, high AlMnFe, synthetic slag, and provide accurate alloy composition and required quantity to the alloy worker in front of the furnace during steelmaking;

[0064] S1.2. Lime requirements: CaO ≥ 88%, activity ≥ 300ml.

[0065] The following steps are included in the converter stage:

[0066] S2.1. Classify, clean and pre-treat scrap steel, scrap iron, molten steel and other raw materials to ensure that the quality of the raw materials meets the requirements, and prepare other auxiliary raw materials and desulfurizers;

[0067] S2.2, loading raw materials and desulfurizer into the converter steelmaking furnace;

[0068] S2.3, start the converter and heat it to high temperature. Under high temperature conditions, the raw materials undergo oxidation-reduction reactions to remove impurities and harmful elements such as sulfur and phosphorus;

[0069] S2.4, oxygen is introduced into the converter to cause oxidation-reduction reaction of impurities and carbon in the raw materials, thereby accelerating the smelting process, producing alloy elements, adjusting the composition of the molten steel, and adding deoxidation alloy into the ladle for deoxidation alloying when 1 / 4 of the steel is discharged;

[0070] S2.5. When the molten steel is transferred from the converter to the ladle, measures should be taken to prevent the slag from entering the ladle. The maximum thickness of the slag in the ladle should be controlled to ≤50mm. Slag is a by-product produced during the smelting process. If it enters the ladle, it will affect the quality of the steel. The thickness of the slag should be strictly controlled.

[0071] The CAS stage includes the following steps;

[0072] S3.1. The ladle containing the molten steel is transported to the refining station and argon is blown into the bottom of the ladle;

[0073] S3.2. Measure the temperature of molten steel within 2 minutes after entering the station. After blowing argon for 2 minutes, use a static sampler to take samples.

[0074] S3.3. After sampling, adjust the argon gas to the soft blowing state and cover it before leaving the station. CAS treatment can significantly reduce large inclusions in molten steel and improve the quality of steel.

[0075] The LF phase includes the following steps:

[0076] S4.1. Ensure the bottom blowing effect of the large tank, clean tank edge, and meet the process requirements of entering the LF furnace, which can ensure the uniformity and stability of the molten steel during the refining process. At the same time, the cleanliness of the tank edge is also an important factor affecting the refining effect. A clean tank edge can reduce the chance of impurities and secondary oxidation, improve refining efficiency, and ensure the purity and quality of the molten steel;

[0077] S4.2. Carefully check the argon blowing system before the molten steel enters the LF furnace to ensure that the argon blowing quick connector is connected reliably and without leakage. The argon blowing system is a key equipment in the LF refining process, used to stir the molten steel and promote chemical reactions. Checking and ensuring the integrity and reliability of the argon blowing system can avoid leakage or uneven stirring during the refining process, ensure that the molten steel in the refining process can be evenly heated and the chemical reaction can be fully carried out, thereby improving the quality of the molten steel and the refining efficiency;

[0078] S4.3. Power is supplied according to the temperature requirements of the steel grade, and the molten steel is sampled and the temperature is measured in time. Static samplers are used to take samples. Different temperatures need to be controlled during the LF refining process depending on the steel grade. Power supply heating is to meet this temperature requirement. At the same time, sampling and temperature measurement are important means of monitoring the refining process, which can timely discover and solve problems, ensure that the temperature of the molten steel meets the process requirements, and improve the stability and controllability of the refining process. At the same time, problems in the molten steel can be discovered in time through sampling and temperature measurement, providing a basis for subsequent adjustments;

[0079] S4.4. During the process of adding refined slag, add appropriate amount of calcium carbide and aluminum powder to make white slag. The white slag keeping time is ≥15min, and the total argon blowing time of LF is ≥40min. White slag is a high-basicity, low-oxidizing slag with good desulfurization and dephosphorization capabilities. White slag can be made by adding appropriate amount of calcium carbide and aluminum powder, and kept for a certain time to ensure the refining effect. At the same time, long-term argon blowing and stirring can promote material exchange and chemical reaction between molten steel and slag, improve the desulfurization and dephosphorization efficiency of molten steel, and reduce the content of harmful impurities. At the same time, long-term argon blowing and stirring can also promote the uniformity and stability of molten steel;

[0080] S4.5. Equipped with carbon wire and alloy bulk, fine-tune the composition according to the target value, and the exit composition meets the internal control requirements. The exit Al control target is: 0.033-0.045%. Feed 150-250m of pure Ca wire before exiting the station, soft blowing ≥10min after feeding the wire, the middle package superheat is ≤40℃ for the start-casting furnace and ≤35℃ for the continuous casting furnace. The exit temperature reference is: 1574±5℃ for the start-casting furnace and 1559±5℃ for the continuous casting furnace. By equipping with carbon wire and alloy bulk, the composition of the molten steel can be fine-tuned according to the target value to meet the internal control requirements. The operation of feeding the Ca wire before exiting the station can further purify the molten steel and remove inclusions. The soft blowing operation is to promote the floating and removal of gas and inclusions in the molten steel. At the same time, the control of the tundish superheat and the exit temperature is also an important factor in ensuring the quality of the molten steel and the stability of the continuous casting process, ensuring that the composition of the molten steel meets the internal control requirements and improving the purity and quality of the molten steel. At the same time, by controlling the superheat of the tundish and the exit temperature, the stability of the continuous casting process and the product quality can be ensured. The Ca line feeding and soft blowing operations can further reduce the inclusion and gas content in the molten steel and improve the quality of the molten steel.

[0081] The continuous casting stage includes the following steps:

[0082] S5.1. Blow argon at the long nozzle and add a sealing ring to the nozzle to protect the casting. It is strictly forbidden to expose the molten steel in the tundish and the crystallizer. Blowing argon at the long nozzle can effectively prevent the molten steel from being secondary oxidized during the casting process. At the same time, adding a sealing ring to the nozzle can further enhance the protection effect, ensure that the molten steel is not polluted by the outside world during the casting process, improve the purity and quality of the ingot, and reduce the inclusions and defects caused by oxidation;

[0083] S5.2, middle ladle liquid level control: start casting> 400mm, normal casting> 600mm, change to large ladle> 650mm; when the liquid level in the middle ladle of the continuous casting furnace is lower than 400mm, the billets must be picked out and treated as waste billets. The middle ladle uses covering agent + carbonized rice husk (or composite insulation agent) to protect the casting. By accurately controlling the liquid level in the middle ladle, the stability and continuity of the molten steel during the casting process can be ensured. When the liquid level is too low, timely picking out the waste billets can avoid defects caused by insufficient molten steel. At the same time, the use of protective casting measures such as covering agents and carbonized rice husks can further reduce the heat loss and oxidation of molten steel, improve the uniformity and quality of the billets, and reduce defects caused by unstable casting. At the same time, protective casting can also extend the service life of the middle ladle and crystallizer;

[0084] S5.3, Crystallizer protective slag: Medium carbon steel protective slag; the protective slag is required to be dry, and the depth of the tundish outlet immersed in the crystallizer liquid level is: 90-110mm. Use protective slag suitable for medium carbon steel and ensure that it is dry, which can effectively reduce the friction and adhesion between the ingot and the crystallizer. At the same time, the protective slag can also absorb inclusions and gases in the molten steel. Controlling the depth of the tundish outlet immersed in the crystallizer liquid level can ensure the uniform distribution and stable solidification of the molten steel in the crystallizer, improve the surface quality and internal quality of the ingot, and reduce defects caused by friction and adhesion. At the same time, the use of protective slag can also increase the service life of the crystallizer and casting efficiency;

[0085] S5.4. The billet continues to be cooled by spraying water in the secondary cooling zone to ensure that the billet is completely solidified.

[0086] S5.5. The molten steel gradually solidifies into a billet shell along the periphery of the crystallizer. When the molten steel level rises to a certain height and the billet shell solidifies to a certain thickness, the straightening machine pulls the billet out. When the crystallizer liquid level fluctuation exceeds ±7.5mm, the billet is cut off. No less than one low-power sample is taken for each pouring. The molten steel gradually solidifies into a billet shell in the crystallizer. This is a key step in the continuous casting process. The straightening machine pulls the billet out after the billet shell solidifies to a certain thickness, which can ensure the continuity and stability of the billet. At the same time, strict control of the crystallizer liquid level fluctuation can avoid billet defects caused by liquid level fluctuation. Taking low-power samples for each pour can timely discover and evaluate the quality problems of the billet, improve the continuity and stability of the billet, and reduce defects caused by solidification and pulling out. At the same time, the control of liquid level fluctuation and the sampling of low-power samples can ensure that the quality of the billet meets the standards and requirements.

[0087] The second-line rolling of bars includes the following steps:

[0088] S6.1. Residual element requirements for billets: Cr≤0.10%, Cu≤0.05%, Ni≤0.05%, Mo≤0.05%, As≤0.03%, B≤0.001%. The content limits of these residual elements ensure the purity of the steel and the stability of the chemical composition, improve the mechanical properties, corrosion resistance and weldability of the steel, and reduce the quality problems caused by excessive elements;

[0089] S6.2. Put the billet into the heating furnace. If the accident time is more than 20 minutes, the heating temperature should be reduced in time. The heating furnace should be strictly controlled according to the heating temperature and furnace time in the production process control regulations of this steel grade. Ensure that the overall temperature of the billet is uniform to prevent the visible positive and negative sides. If the positive and negative sides are obvious, the rolling should be stopped immediately to wait for the temperature, increase the gas volume of the burner, and steel can be tapped only after the temperature is normal. During the rolling process, high-pressure water descaling should be turned on, and the descaling working pressure should not be less than 12Mpa. To ensure the dephosphorization effect of high-pressure water descaling, the descaling pressure needs to be confirmed when taking over. If the iron oxide scale is not removed cleanly, the steel production should be stopped immediately, and the fitter should be arranged to check the nozzle and pressure. The steel can be produced only after the treatment is completed; the surface iron oxide scale should be removed cleanly to avoid surface defects such as pitting caused by the rolling and pressing of the iron oxide scale, ensure the uniformity of heating, avoid quality problems caused by uneven temperature, improve the overall quality and surface finish of the steel, start high-pressure water descaling, effectively remove the iron oxide scale on the steel surface, and avoid the iron oxide scale being pressed into the steel surface during the rolling process, forming defects such as pitting;

[0090] S6.3. When rolling the square billet, there shall be no visible reconnection and scarring on the surface, no cracks, fissures, folds and subcutaneous bubbles on the surface. The rolling temperature shall be ≥1000℃. The sharp corners and burrs on the rolling groove, baffle, guide and roller shall be polished clean. Those that cannot be polished clean shall be replaced in time. When changing rolls and taking over, the 800 rolling mill roll groove shall be checked for severe wear and loss of meat. Special attention shall be paid to checking the surface of the push bed and the "vertical roller" to avoid scratches and abrasions on the red steel surface by the push bed, which may cause defects such as discontinuity and shallow folding on the surface of the finished product. , the shearing length of the 400t shear should be carried out according to the operating procedures. When producing large square billets, the 400t shear must clean the head and fishtail defects. The wear of the rolling groove should be checked during the shift inspection and mid-term shutdown, whether there are serious cracks and meat loss; whether the cooling water pipe nozzle is aligned with the rolling groove, whether the connecting hose is leaking, etc.; check whether the guide is centered, whether there is iron clamping, wire drawing, guide roller jamming, etc., and stop or replace it in time if any abnormality is found. The material shape and size of each frame should be measured every hour during the rolling process. If folds and scratches are found on the online pickling surface of each batch during the rolling process, the machine should be stopped for inspection. The sampling post personnel should record the online pickling surface conditions of each batch with defects in the MES system. The length of the head and tail of the hot saw should be strictly carried out in accordance with the requirements of the operating procedures. The length can be increased but it must not be shorter than the required length. The finishing team arranges personnel to check the sawing condition of the tail of the cooling bed every hour. If there is any incomplete sawing, the sawing length of the corresponding batch should be increased by about 50-200mm. The round steel is laid on the cooling bed with teeth, and the number of teeth is not less than 3. If square steel rolls together in the second and third sections, the number of teeth should be appropriately increased. The rolling temperature should be ≥1000℃ to ensure the plasticity and deformation ability of the steel during the rolling process, reduce the rolling force and energy consumption, and improve the rolling efficiency;

[0091] S6.4. Cool the steel billet. After the square steel is put on the chain, each steel bar should be separated by a distance of not less than 150mm to prevent cold bending;

[0092] S6.5, Square steel stacking and slow cooling: The upper longitudinal edge is less than 200mm away from the lower tail end, and the upper transverse end is less than 200mm beyond the lower edge. The stacking density and slow cooling conditions are properly controlled to ensure uniform heat dissipation of the steel during the slow cooling process to avoid internal stress concentration and deformation;

[0093] S6.6. Before grinding the steel billet, the six digits after the furnace number should be drawn on the end with a white paint pen. During finishing and grinding, operators at all positions must operate carefully, not bend the finished product, not scratch the surface, clean the ears, scratches, burrs and flash on the surface of the finished product, and inspect the surface quality of the finished product. The scratches, cracks, folds, scars, ears, burrs and flash on the surface should be ground clean. The defects on the surface of the finished product should be cleaned and ground to ensure the surface quality of the finished product and improve the market competitiveness and customer satisfaction of the product;

[0094] S6.7. Inspection and acceptance of steel materials require that the surface should not have visually visible reconnections and scars, cracks, fissures, folds and subcutaneous bubbles. If there are any defects that are not allowed on the surface, they should be removed. The removal width should not be less than 6 times the depth, and the length should not be less than 10 times the depth. After grinding, the defective parts should be smooth and without edges and corners. The grinding depth should not be greater than 1.5mm. The grinding depth is calculated from the actual size. After grinding, follow the contract requirements and sign a label or paint the color on one end of each steel.

[0095] S6.8. When warehousing and delivery are carried out, hot-rolled state delivery is required. If the user has special requirements, the user contract or technical agreement shall be implemented, and the inspection and acceptance shall be carried out in accordance with the provisions of the user contract or technical agreement.

[0096] The auxiliary raw materials added in S2.1 have the following composition requirements: C 0.36wt%-0.38wt%, Si≤0.09wt%, Mn0.66wt%-0.83wt%, P≤0.024wt%, S≤0.024wt%, Cr0.31wt%-0.39wt%, Al0.025wt%-0.060wt%. By adding appropriate amounts of C, Si, Mn, Cr and other elements, the hardness, strength, hardenability and wear resistance of the steel can be significantly improved while maintaining relatively good plasticity and toughness. Si, Mn, Al and other elements are used as deoxidizers and desulfurizers, which help to remove harmful elements such as oxygen and sulfur in the steel, thereby improving the quality and performance of the steel. The addition of elements such as Cr can also improve the corrosion resistance and antioxidant effect of the steel and extend the service life of the steel.

[0097] During the converter stage, ensure that C ≥ 0.08% and P ≤ 0.013% in the molten steel, and the temperature of the molten steel entering the furnace is not lower than 1550℃. When tapping, the steel is required to contain C0.31%-0.34%, Mn0.62%-0.69%, Cr0.26-0.34%, P≤0.020, and Al0.026%-0.049. Deoxidizer, high carbon Mn-Fe, high carbon Cr-Fe, and high aluminum Fe-Mn-Al are added to the molten steel. By precisely controlling the composition of the molten steel, it can be ensured that the steel has excellent properties, such as high strength, high toughness, and good corrosion resistance. Reasonable composition control can reduce energy consumption and waste emissions during the smelting process, and at the same time improve smelting efficiency. According to the use and requirements of the final product, by adjusting the composition of the molten steel and the type and amount of added alloys, steel that meets specific performance requirements can be produced.

[0098] The above generally describes the present invention in detail, but it is obvious to a person skilled in the art that some modifications or improvements can be made to the present invention. Therefore, modifications or improvements that do not depart from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. A square steel production process, characterized in that: Including hot metal, converter, CAS, LF, continuous casting, and bar second-line rolling; S1. During the molten iron preparation stage, the alloy must be clean and dry and no mixing is allowed; S2. During the converter stage, ensure that the carbon content and temperature in the molten steel meet the predetermined requirements; S3. In the CAS stage, argon is blown from the bottom throughout the process, and violent blowing is strictly prohibited. The argon pressure during the steel-making process is controlled at the target of 0.8-1.2Mpa; S4. In the LF stage, by controlling the oxygen and sulfur content, temperature and composition in the molten steel, high-quality molten steel with low oxygen and sulfur content is produced; S5. During continuous casting, argon is blown through the long nozzle and a sealing ring is added to the nozzle to protect the casting. It is strictly forbidden to expose the molten steel in the tundish and crystallizer; S6, the second-line rolling of bars includes ingot inspection - entering the furnace, heating - 800 rolling - continuous rolling - sawing - cooling bed - stacking slow cooling - grinding - finished product inspection - warehousing.

2. A square steel production process according to claim 1, characterized in that: The molten iron preparation stage comprises the following steps: S1.

1. Prepare high carbon ferromanganese or medium carbon ferromanganese, high carbon ferrochrome, high AlMnFe, synthetic slag, and provide accurate alloy composition and required quantity to the alloy worker in front of the furnace during steelmaking; S1.

2. Lime requirements: CaO ≥ 88%, activity ≥ 300ml.

3. A square steel production process according to claim 1, characterized in that: The converter stage comprises the following steps: S2.

1. Scrap steel, scrap iron and molten steel are classified, cleaned and pre-treated to ensure that the quality of the raw materials meets the requirements, and other auxiliary raw materials and desulfurizers are prepared; S2.2, loading raw materials and desulfurizer into a converter steelmaking furnace; S2.3, start the converter and heat it to high temperature. Under high temperature conditions, the raw materials undergo oxidation-reduction reactions to remove impurities and harmful elements such as sulfur and phosphorus; S2.4, oxygen is introduced into the converter to cause oxidation-reduction reaction between impurities and carbon in the raw materials, thereby accelerating the smelting process, producing alloy elements, adjusting the composition of the molten steel, and adding deoxidation alloy into the ladle for deoxidation alloying when 1 / 4 of the steel is discharged; S2.

5. When molten steel is transferred from the converter to the ladle, measures should be taken to prevent slag from entering the ladle. The maximum thickness of slag in the ladle should be controlled to ≤50mm.

4. A square steel production process according to claim 1, characterized in that: The CAS stage includes the following steps: S3.

1. The ladle containing the molten steel is transported to the refining station and argon is blown into the bottom of the ladle; S3.

2. Measure the temperature of molten steel within 2 minutes after entering the station. After blowing argon for 2 minutes, use a static sampler to take samples. S3.

3. After sampling, adjust the argon gas to the soft blowing state and cover it before leaving the station.

5. A square steel production process according to claim 1, characterized in that: The LF stage includes the following steps: S4.

1. Ensure the bottom blowing effect of the large tank, the tank edge is clean, and meets the process requirements for entering the LF furnace; S4.

2. Carefully check the argon blowing system before the molten steel enters the LF furnace to ensure that the argon blowing quick connector is connected reliably and without leakage; S4.

3. Supply power according to the temperature requirements of the steel grade, sample and measure the temperature of the molten steel in time, and use a static sampler to take samples; S4.4, during the process of adding refined slag, add appropriate amount of calcium carbide and aluminum powder to make white slag, the white slag keeping time is ≥15min, and the total argon blowing time of LF is ≥40min; S4.

5. Equipped with carbon wire and alloy bulk materials, fine-tune the composition according to the target value. The outgoing composition meets the internal control requirements. The outgoing Al control target is: 0.033-0.045%. Feed 150-250m of pure Ca wire before leaving the station. After feeding the wire, soft blowing is ≥10min. The overheat of the tundish is controlled by the target value of ≤40℃ for the start-casting furnace and ≤35℃ for the continuous casting furnace. The outgoing temperature reference is: 1574±5℃ for the start-casting furnace and 1559±5℃ for the continuous casting furnace.

6. A square steel production process according to claim 1, characterized in that: The continuous casting stage comprises the following steps: S5.

1. Argon is blown at the long nozzle, and a sealing ring is added to the nozzle to protect the casting. It is strictly forbidden to expose the molten steel in the tundish and crystallizer; S5.2, tundish liquid level control: start casting> 400mm, normal casting> 600mm, change to large ladle> 650mm; when the liquid level of the tundish in the continuous casting furnace is lower than 400mm, the blanks must be picked out and treated as waste. The tundish is protected by covering agent + carbonized rice husk (or composite insulation agent) for casting; S5.3, Crystallizer protection slag: medium carbon steel protection slag; the protection slag is required to be dry, and the depth of the tundish outlet immersed in the crystallizer liquid level is 90-110mm; S5.

4. The billet continues to be cooled by spraying water in the secondary cooling zone to ensure that the billet is completely solidified; S5.

5. The molten steel gradually solidifies into a billet shell along the periphery of the crystallizer. When the molten steel level rises to a certain height and the billet shell solidifies to a certain thickness, the billet is pulled out by the straightening machine. When the crystallizer liquid level fluctuation exceeds ±7.5mm, the billet is cut off. Take not less than one low-magnification sample for each casting.

7. A square steel production process according to claim 1, characterized in that: The second-line rolling of bars comprises the following steps: S6.

1. Residual element requirements for billet: Cr≤0.10%, Cu≤0.05%, Ni≤0.05%, Mo≤0.05%, As≤0.03%, B≤0.001%; S6.

2. Put the billet into the heating furnace. If the accident time is greater than 20 minutes, the heating temperature should be lowered in time. The heating furnace should be strictly controlled in accordance with the heating temperature and furnace time control in the production process control regulations of this steel grade to ensure uniform temperature of the entire billet and prevent visible positive and negative surfaces. If the positive and negative surfaces are obvious, the rolling should be stopped immediately to wait for the temperature to rise, and the gas volume of the burner should be increased. Steel can only be tapped after the temperature is normal. High-pressure water descaling should be turned on during rolling. The descaling working pressure should not be less than 12Mpa. The dephosphorization effect of high-pressure water descaling should be ensured. The descaling pressure should be confirmed when taking over. If the iron oxide scale is not removed cleanly, the steel should be stopped immediately, and the fitter should be arranged to check the nozzle and pressure. Steel can only be tapped after the treatment is completed. The surface iron oxide scale should be removed cleanly to avoid surface pitting defects caused by the rolling and pressing of the iron oxide scale. S6.

3. When rolling square billets, the surface must not have visible reconnection and scarring, cracks, fissures, folds and subcutaneous bubbles. The rolling temperature should be ≥1000℃. The sharp corners and burrs on the rolling groove, baffle, guide and roller must be polished clean. Those that cannot be polished clean must be replaced in time. When changing rolls and taking over, the 800 rolling mill roll groove should be checked for severe wear and loss of meat. Pay special attention to checking the surface of the push bed and the "vertical roller" to avoid scratches and abrasions on the red steel surface by the push bed, which will cause intermittent and superficial folding defects on the surface of the finished product. The shearing length of the 400t shear should be carried out according to the operating procedures. When producing large square billets, the 400t shear must cut the head and fishtail defects cleanly. The wear of the rolling groove should be checked during the handover inspection and mid-term shutdown to see if there are serious cracks and loss of meat; whether the cooling water pipe nozzle is aligned with the rolling groove, Check whether the connecting hose is leaking; check whether the guide is aligned, whether there is iron clamping, wire drawing, or guide roller jamming. If any abnormality is found, stop the machine for processing or replace it in time. During the rolling process, the material shape and size of each frame should be measured every hour. If folding or scratches are found on the online pickling surface of each batch during the rolling process, the machine should be stopped for inspection. The sampling post personnel should record the online pickling surface conditions of each batch with defects in the MES system. The length of the head and tail of the hot saw should be strictly carried out in accordance with the requirements of the operating procedures. The length can be increased but must not be shorter than the required length. The finishing team arranges personnel to check the sawing of the tail of the cooling bed every hour. If there is any uncut, the sawing length of the corresponding batch should be increased by about 50 to 200 mm. The round steel cooling bed is equipped with teeth, and the number of teeth is not less than 3. If square steel rolls together in the second and third sections, the number of teeth should be appropriately increased. S6.

4. Cool the steel billet. After the square steel is put on the chain, each steel bar should be separated by a distance of not less than 150mm to prevent cold bending; S6.5, Square steel stacking and slow cooling: The upper longitudinal edge is less than 200mm away from the lower tail end, and the upper transverse end is less than 200mm beyond the lower edge; S6.

6. Before grinding the steel billet, the six digits after the furnace number should be drawn on the end with a white paint pen. During finishing and grinding, operators at all positions must operate carefully, not bend the finished product, not scratch the surface, clean the ears, scratches, burrs and flash on the surface of the finished product, and inspect the surface quality of the finished product. The scratches, cracks, folds, scars, ears, burrs and flash defects on the surface must be ground clean; S6.

7. Steel materials shall be inspected and accepted. There shall be no visible reconnection and scarring on the surface, no cracks, fissures, folds and subcutaneous bubbles on the surface. If there are any defects on the surface, they shall be removed. The width of the removal shall not be less than 6 times the depth, and the length shall not be less than 10 times the depth. After grinding, the defective part shall be smooth and without edges and corners. The grinding depth shall not be greater than 1.5mm. The grinding depth is calculated from the actual size. After grinding, follow the contract requirements and sign a label or paint the color on one end of each steel. S6.

8. When warehousing and delivery are carried out, hot-rolled state delivery is required. If the user has special requirements, the user contract or technical agreement shall be implemented, and the inspection and acceptance shall be carried out in accordance with the provisions of the user contract or technical agreement.

8. A square steel production process according to claim 3, characterized in that: The auxiliary raw materials added in S2.1 have the following component addition requirements: C 0.36wt%-0.38wt%, Si≤0.09wt%, Mn 0.66wt%-0.83wt%, P≤0.024wt%, S≤0.024wt%, Cr0.31wt%-0.39wt%, Al0.025wt%-0.060wt%.

9. A square steel production process according to claim 1, characterized in that: During the converter stage, ensure that C ≥ 0.08% and P ≤ 0.013% in the molten steel, the molten steel entering the furnace is not lower than 1550°C, and when tapping, the steel is required to contain C0.31%-0.34%, Mn0.62%-0.69%, Cr0.26-0.34%, P≤0.020, Al0.026%-0.049, and add deoxidizer, high carbon Mn-Fe, high carbon Cr-Fe, and high aluminum Fe-Mn-Al to the molten steel.

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