Production process of low-alloy high-strength structural steel

Abstract

The invention relates to the technical field of production processes of steel for pipe blanks, and discloses a production process of low-alloy high-strength structural steel, which comprises the steps of molten iron pretreatment, converter treatment, CAS, LF refining, VD, continuous casting, casting blank inspection, bar two-line rolling, cold bed slow cooling, and finished product inspection and warehousing. The production process of the low-alloy high-strength structural steel comprises the following steps: S1, a molten iron pretreatment stage: preparing SiFe, medium-carbon MnFe, VFe, V-N alloy and high-AlMnFe, feeding a semi-finished product subjected to rough rolling into an intermediate rolling mill for further rolling so as to achieve a smaller section size and higher dimensional precision, and adjusting a roller gap and rolling reduction according to the requirements of the rolling process in the intermediate rolling process so as to achieve a better rolling effect; and the rolling temperature and the rolling speed are monitored, semi-finished products obtained after intermediate rolling are fed into a finishing mill to be subjected to final rolling so as to produce bar products meeting the requirements of users, and parameters such as the roller gap, the rolling reduction, the rolling temperature and the rolling speed need to be strictly controlled in the finish rolling process so as to ensure the product quality.

Description

Technical Field

[0001] The invention relates to the technical field of production technology of steel for tube blanks, in particular to a production technology of low-alloy high-strength structural steel. Background Art

[0002] The production of low-alloy high-strength structural steel is a complex and delicate process, which involves multiple steps and links. Each link needs to be strictly controlled to ensure the quality of the final product. Low-alloy high-strength structural steel has excellent mechanical properties, welding properties and low-temperature toughness, and is widely used in shipbuilding, bridges, aviation, aerospace, automobiles and other fields. At the same time, this type of steel also has the advantages of light weight, high strength, good corrosion resistance, etc., and is one of the important structural materials in the future. In the production process, each link needs to be strictly controlled to ensure that the product quality meets customer needs.

[0003] When the steel used in the tube billet is produced, if there are impurities on its surface or impurities in the molten iron, it will cause a series of problems such as cracks, scars or inclusions after the steel is smelted or even during subsequent rolling, thus affecting the subsequent use of the steel billet and subsequent rolling of the steel billet. Summary of the invention

[0004] The object of the present invention is to provide a production process of low-alloy high-strength structural steel 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 low-alloy high-strength structural steel production process, including molten iron pretreatment, converter, CAS, LF refining, VD, continuous casting, ingot inspection, bar second-line rolling, cooling bed slow cooling, finished product inspection and warehousing;

[0006] S1. In the hot metal pretreatment stage, SiFe, medium carbon MnFe, VFe, VN alloy, and high AlMnFe are prepared. The alloys must be clean and dry without mixing. Hot metal pretreatment is a convenient and economical method to obtain low-sulfur and low-phosphorus hot metal. The sulfur content in hot metal can be reduced to a very low level through one or two desulfurization treatments;

[0007] S2. Prepare metal raw materials such as scrap steel, molten iron and slag-making materials such as lime and light-burned dolomite. These materials need to be mixed in proportion to ensure that the chemical reaction in the steelmaking process can proceed smoothly. Load the metal raw materials into the converter and add the first batch of slag-making materials;

[0008] S3, CAS stage, CAS technology first uses argon bottom blowing to form a slag-free area on the surface of molten steel, and then inserts an isolation cover into the molten steel to cover the slag-free area, so that the alloy added to the upper part of the isolation cover is isolated from the slag;

[0009] S4, LF refining stage, after the basic smelting of molten steel is completed in the primary refining furnace such as converter or electric arc furnace, the molten steel is tapped into a ladle, and an appropriate amount of alloy, slag, etc. are added to the ladle to prepare for LF refining. At the same time, the LF furnace is ensured to be in good condition, the ladle filled with molten steel is hoisted to the LF refining station, and the Ar gas pipe is connected for argon blowing and stirring. In the LF furnace, slag is removed and the temperature is raised by adding materials such as silicon carbide, calcium carbide, and aluminum particles to form a highly reducing white slag to improve the desulfurization and deoxidation effects;

[0010] S5, VD stage, after LF refining is completed, the refined molten steel is hoisted to the VD treatment station. At this time, the composition, temperature and purity of the molten steel should meet the requirements of VD treatment. The molten steel is poured from the ladle into the molten steel tank in the VD vacuum chamber. During the pouring process, attention should be paid to controlling the flow rate and flow of the molten steel to prevent the molten steel from splashing or generating eddy currents. Argon is blown into the molten steel through the air-permeable bricks at the bottom of the molten steel tank for stirring. The purpose of blowing argon and stirring is to promote the floating and removal of gas and inclusions in the molten steel;

[0011] S6, continuous casting stage, the refined molten steel is poured from the ladle into the tundish, which plays the role of buffering and distributing the molten steel to ensure that the molten steel can flow evenly into the crystallizer. The molten steel flows from the tundish through the water inlet into the crystallizer. The crystallizer is one of the core equipment of the continuous casting machine, which allows the molten steel to be quickly cooled and solidified into the primary shell of the ingot. The molten steel in the crystallizer is cooled by the cooling water and gradually solidifies into the shell. At the same time, the secondary cooling zone further cools and solidifies the ingot to ensure the quality and shape of the ingot;

[0012] S7. During the ingot inspection stage, check whether there are scars, cracks, folds, inclusions, bubbles, iron oxide scale intrusion and other defects that are harmful to the use of the ingot. It is allowed that there are local defects such as thin iron oxide scale, rust and slight pitting and scratches on the ingot surface that do not affect the use, but the depth or height shall not exceed half of the ingot thickness tolerance, and the minimum allowable thickness of the ingot shall be guaranteed;

[0013] S8, bar second-line rolling stage, bar rolling is carried out by feeding the heated billet into the rolling mill for rolling;

[0014] S9, slow cooling stage of the cooling bed. The purpose of slow cooling of the cooling bed is to make the temperature of the steel evenly and slowly drop during the cooling process, so as to avoid defects such as internal stress and cracks in the steel caused by rapid cooling. At the same time, slow cooling also helps to homogenize and refine the internal structure of the steel, thereby improving the mechanical properties and service life of the steel.

[0015] S10: Finished product inspection and warehousing stage, inspection and warehousing operations are carried out.

[0016] Preferably, in the S2, converter stage, the steelmaking raw materials need a narrower composition deviation to improve the purity of the molten steel and control the content of harmful elements in the steel, such as Pb, Sn, As, Sb, Bi, etc. Most low-alloy high-strength steels can be smelted in a top-bottom composite blown converter. This method can not only obtain low-sulfur steel, but also achieve carbon reduction and deoxidation in the later stage. The carbon content of the converter steel can be controlled at a low level, and the iron content in the surface slag is also at a very low level. According to different uses, the molten steel after converter smelting will be refining in a ladle. This step often uses electromagnetic stirring, argon blowing, spraying or vacuum degassing and other process means to achieve degassing, component homogenization and alloying, and modification of inclusion morphology.

[0017] Preferably, in the S3 and CAS stages, argon is blown from the bottom throughout the process, and violent blowing is strictly prohibited. The argon pressure during the steel-out process is controlled according to the target of 0.8-1.2Mpa. The temperature of the molten steel is measured within 2 minutes after entering the station. After normal argon blowing for 2 minutes, a static sampler is used to take a sample. After sampling, the argon is adjusted to a soft blowing state and the steel is covered before leaving the station.

[0018] Preferably, in the S4 and LF refining stages, the argon blowing system is carefully checked before the molten steel enters the LF furnace to ensure that the argon blowing quick connector is reliably connected and leak-free, the large tank must have a good bottom blowing effect, the tank edge is clean, and it meets the process requirements for entering the LF furnace, power is supplied according to the temperature requirements of the steel grade, the molten steel is sampled and the temperature is measured in time, a static sampler is used to take samples, the molten steel is powered on for ≥20 minutes in the LF furnace, the total argon blowing time is ≥40 minutes, white slag is quickly deoxidized, the composition is fine-tuned according to the target value, and it is ensured that the outgoing composition meets the internal control requirements. After refining, 50 to 200 m of pure Ca line is fed for Ca treatment.

[0019] Preferably, in the S5, VD stage, the VD process generally includes steps such as heating, vacuum treatment, stirring and cooling. In the heating stage, the molten steel is heated to an appropriate temperature; in the vacuum treatment stage, the gas and inclusions in the molten steel are removed by vacuuming; in the stirring stage, the stirring device is used to promote uniform mixing of the molten steel; in the cooling stage, the treated molten steel is cooled to an appropriate temperature for subsequent processes. Through VD treatment, the quality and performance of the steel can be significantly improved, so that it has the characteristics of high strength, good toughness and welding performance.

[0020] Preferably, in the S5 and VD stages, harmful gases such as hydrogen and nitrogen in the molten steel can be effectively removed by vacuum treatment to prevent these gases from forming defects such as bubbles or looseness in the steel, thereby improving the density and strength of the steel. The VD stage can also remove non-metallic inclusions in the molten steel, such as oxides and sulfides, which will seriously affect the mechanical properties and processing properties of the steel. The VD equipment consists of a vacuum chamber, a heating device, a stirring device, a gas control system, etc. The vacuum chamber is used to create a vacuum environment, and the heating device is used to maintain the temperature of the molten steel. The stirring device is used to promote uniform mixing of molten steel. The gas control system is used to control the vacuum degree and gas flow rate. When the molten steel enters the VD furnace, argon blowing is started throughout the process, and temperature measurement and sampling are carried out. The total argon blowing time in the VD furnace is not less than 45 minutes. The composition is fine-tuned before vacuuming and controlled according to the target value. All composition adjustments and wire feeding operations after breaking the vacuum are strictly prohibited. The vacuuming target does not exceed 0.5tor, the vacuum maintenance time is not less than 10 minutes, and the soft argon blowing time after breaking the vacuum is not less than 15 minutes. Covering agent or carbonized rice husk is added according to the temperature for insulation when leaving the station.

[0021] Preferably, in the S6, continuous casting stage, the continuous casting machine is the core equipment of the continuous casting link, which is composed of a crystallizer, a vibration device, a billet drawing device, a secondary cooling device, a cutting device, etc. These equipment work together to complete the casting, cooling, solidification and cutting of molten steel. In the production of low-alloy high-strength structural steel, the continuous casting link is usually combined with converter smelting, refining and rolling processes. By optimizing the continuous casting process parameters and equipment configuration, low-alloy high-strength structural steel products with uniform structure and excellent performance can be produced. Argon is blown at the long water nozzle and a sealing ring is added to the water nozzle to protect the pouring. It is strictly forbidden to expose the molten steel in the tundish and crystallizer. The tundish is cut to size as required. The liquid level control of the tundish: not less than 450mm for opening casting and not less than 650mm for normal casting. The tundish is protected by covering agent + carbonized rice husk or composite insulation agent for pouring. The superheat of the molten steel in the tundish does not exceed 40℃ for opening casting furnace and 35℃ for continuous casting furnace. The superheat of the tundish is 15-53℃. Crystallizer protective slag: low carbon steel protective slag is used, and the protective slag is required to be dry. Take at least one sample for each pouring for low-magnification and surface pickling inspection of the ingot.

[0022] Preferably, in the S7, ingot inspection stage, the ingot inspection for low alloy high strength structural steel production is a complex and important task, involving multiple aspects such as chemical composition, mechanical properties, process performance, surface quality and internal quality. Through strict inspection and control, it can be ensured that the quality of the ingot meets national standards and contractual provisions, providing reliable guarantee for subsequent processing and use.

[0023] Preferably, in the S8, second-line rolling stage of bars, quality inspection is carried out on the steel billets entering the production line, including card verification, external dimension measurement, surface quality inspection, etc. The steel billet acceptance is carried out according to the steel billet technical standards and internal control technical conditions. Unqualified steel billets shall not be allowed to enter the furnace. The heated steel billets are initially rolled in the rough rolling mill to reduce their cross-sectional dimensions and increase their length. The semi-finished products after rough rolling are sent to the intermediate rolling mill for further rolling to achieve a smaller cross-sectional dimension and higher dimensional accuracy. During the intermediate rolling process, the roller gap and reduction amount need to be adjusted according to the rolling process requirements, and the rolling temperature and rolling speed need to be monitored. The semi-finished products after the intermediate rolling are sent to the finishing mill for final rolling to produce bar products that meet user needs. During the finishing rolling process, parameters such as roller gap, reduction amount, rolling temperature and rolling speed need to be strictly controlled to ensure product quality.

[0024] Preferably, in the S9, cooling bed slow cooling stage, the cooling rate of the cooling bed slow cooling needs to be controlled within a certain range to ensure that the steel can evenly and slowly reduce the temperature. Too fast cooling rate may cause stress inside the steel, while too slow cooling rate may affect production efficiency. The cooling time of the cooling bed slow cooling depends on the material, specification and production requirements of the steel. In general, the cooling time needs to be long enough to ensure that the internal structure of the steel can be fully transformed and homogenized. When the cooling bed is slow cooling, the selection of cooling medium is also very important. Commonly used cooling media include air, water, etc. Different cooling media have different cooling effects and effects on steel. Therefore, it is necessary to select according to specific circumstances. In the slow cooling process, it is necessary to avoid the rapid cooling of steel. Rapid cooling may cause defects such as stress and cracks inside the steel, affecting the performance and quality of the steel. In the slow cooling process, it is necessary to continuously monitor the temperature changes of the steel. Once an abnormal situation is found, such as too high or too low temperature, it is necessary to take timely measures to adjust. The cooling bed equipment is one of the key equipment in the slow cooling process. Therefore, it is necessary to regularly maintain and service the cooling bed equipment to ensure that it is in good working condition.

[0025] Compared with the prior art, the present invention provides a low-alloy high-strength structural steel production process, which has the following beneficial effects:

[0026] 1. In the production process of low-alloy high-strength structural steel, the semi-finished products after rough rolling are sent to the intermediate rolling mill for further rolling to achieve smaller cross-sectional dimensions and higher dimensional accuracy. During the intermediate rolling process, the roll gap and reduction amount must be adjusted according to the rolling process requirements, and the rolling temperature and rolling speed must be monitored. The semi-finished products after intermediate rolling are sent to the finishing mill for final rolling to produce bar products that meet user needs. During the finishing rolling process, parameters such as roll gap, reduction amount, rolling temperature and rolling speed must be strictly controlled to ensure product quality.

[0027] 2. In the production process of low-alloy high-strength structural steel, the heated billet is initially rolled in a rough rolling mill to reduce its cross-sectional size and increase its length. The semi-finished product after rough rolling is sent to the intermediate rolling mill for further rolling to achieve a smaller cross-sectional size and higher dimensional accuracy. During the intermediate rolling process, the roller gap and reduction amount must be adjusted according to the rolling process requirements, and the rolling temperature and rolling speed must be monitored. The semi-finished product after intermediate rolling is sent to the finishing mill for final rolling to improve the quality of steel through continuous pressing.

[0028] 3. In the slow cooling process of the low-alloy high-strength structural steel production process, it is necessary to avoid rapid cooling of the steel. Rapid cooling may cause stress, cracks and other defects inside the steel, affecting the performance and quality of the steel. In the slow cooling process, it is necessary to continuously monitor the temperature changes of the steel to accurately reduce the occurrence of cracks during cooling. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0030] like Figure 1 As shown, the present invention provides a technical solution: a low-alloy high-strength structural steel production process, including molten iron pretreatment, converter, CAS, LF refining, VD, continuous casting, ingot inspection, bar second-line rolling, cooling bed slow cooling, finished product inspection and warehousing;

[0031] S1. In the hot metal pretreatment stage, SiFe, medium carbon MnFe, VFe, VN alloy, and high AlMnFe are prepared. The alloys must be clean and dry without mixing. Hot metal pretreatment is a convenient and economical method to obtain low-sulfur and low-phosphorus hot metal. The sulfur content in hot metal can be reduced to a very low level through one or two desulfurization treatments;

[0032] S2. Prepare metal raw materials such as scrap steel, molten iron and slag-making materials such as lime and light-burned dolomite. These materials need to be mixed in proportion to ensure that the chemical reaction in the steelmaking process can proceed smoothly. Load the metal raw materials into the converter and add the first batch of slag-making materials;

[0033] S3, CAS stage, CAS technology first uses argon bottom blowing to form a slag-free area on the surface of molten steel, and then inserts an isolation cover into the molten steel to cover the slag-free area, so that the alloy added to the upper part of the isolation cover is isolated from the slag;

[0034] S4, LF refining stage, after the basic smelting of molten steel is completed in the primary refining furnace such as converter or electric arc furnace, the molten steel is tapped into a ladle, and an appropriate amount of alloy, slag, etc. are added to the ladle to prepare for LF refining. At the same time, the LF furnace is ensured to be in good condition, the ladle filled with molten steel is hoisted to the LF refining station, and the Ar gas pipe is connected for argon blowing and stirring. In the LF furnace, slag is removed and the temperature is raised by adding materials such as silicon carbide, calcium carbide, and aluminum particles to form a highly reducing white slag to improve the desulfurization and deoxidation effects;

[0035] S5, VD stage, after LF refining is completed, the refined molten steel is hoisted to the VD treatment station. At this time, the composition, temperature and purity of the molten steel should meet the requirements of VD treatment. The molten steel is poured from the ladle into the molten steel tank in the VD vacuum chamber. During the pouring process, attention should be paid to controlling the flow rate and flow of the molten steel to prevent the molten steel from splashing or generating eddy currents. Argon is blown into the molten steel through the air-permeable bricks at the bottom of the molten steel tank for stirring. The purpose of blowing argon and stirring is to promote the floating and removal of gas and inclusions in the molten steel;

[0036] S6, continuous casting stage, the refined molten steel is poured from the ladle into the tundish, which plays the role of buffering and distributing the molten steel to ensure that the molten steel can flow evenly into the crystallizer. The molten steel flows from the tundish through the water inlet into the crystallizer. The crystallizer is one of the core equipment of the continuous casting machine. It allows the molten steel to cool quickly and solidify into the primary shell of the ingot. The molten steel in the crystallizer is cooled by the cooling water and gradually solidifies into the shell. At the same time, the secondary cooling zone further cools and solidifies the ingot to ensure the quality and shape of the ingot.

[0037] S7. During the ingot inspection stage, check whether there are scars, cracks, folds, inclusions, bubbles, iron oxide scale intrusion and other defects that are harmful to the use of the ingot. It is allowed that there are local defects such as thin iron oxide scale, rust and slight pitting and scratches on the ingot surface that do not affect the use, but the depth or height shall not exceed half of the ingot thickness tolerance, and the minimum allowable thickness of the ingot shall be guaranteed;

[0038] S8, bar second-line rolling stage, bar rolling is carried out by feeding the heated billet into the rolling mill for rolling;

[0039] S9, the slow cooling stage of the cooling bed. The purpose of the slow cooling of the cooling bed is to make the temperature of the steel drop evenly and slowly during the cooling process, so as to avoid defects such as internal stress and cracks caused by rapid cooling. At the same time, slow cooling also helps to homogenize and refine the internal structure of the steel, and improve the mechanical properties and service life of the steel.

[0040] S10: Finished product inspection and warehousing stage, inspection and warehousing operations are carried out.

[0041] S2. In the converter stage, the steelmaking raw materials need a narrower composition deviation to improve the purity of the molten steel and control the content of harmful elements in the steel, such as Pb, Sn, As, Sb, Bi, etc. Most low-alloy high-strength steels can be smelted in a top-bottom composite blown converter. This method can not only obtain low-sulfur steel, but also achieve carbon reduction and deoxidation in the later stage. The carbon content of the converter steel can be controlled at a low level, and the iron content in the surface slag is also at a very low level. According to different uses, the molten steel after converter smelting will be refining in a ladle. This step often uses electromagnetic stirring, argon blowing, spraying or vacuum degassing to achieve degassing, composition homogenization and alloying, and modification of inclusion morphology.

[0042] In the S3 and CAS stages, argon is blown from the bottom throughout the entire process, and violent blowing is strictly prohibited. The argon pressure during the steel-making process is controlled according to the target of 0.8-1.2Mpa. The temperature of the molten steel is measured within 2 minutes after entering the station. After normal argon blowing for 2 minutes, a static sampler is used to take a sample. After sampling, the argon is adjusted to a soft blowing state and the steel is covered before leaving the station.

[0043] During S4 and LF refining stages, 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 air leakage. The large tank must have a good bottom blowing effect and a clean tank edge to meet the process requirements for entering the LF furnace. Power is supplied according to the temperature requirements of the steel grade, the molten steel is sampled and the temperature is measured in time, and a static sampler is used to take samples. The molten steel is powered on for ≥20 minutes in the LF furnace, and the total argon blowing time is ≥40 minutes. The molten steel is quickly deoxidized into white slag, and the composition is fine-tuned according to the target value to ensure that the outgoing composition meets the internal control requirements. After refining, it is fed with 50 to 200 m of pure Ca line for Ca treatment.

[0044] S5, VD stage, the VD process usually includes heating, vacuum treatment, stirring and cooling. In the heating stage, the molten steel is heated to an appropriate temperature; in the vacuum treatment stage, the gas and inclusions in the molten steel are removed by vacuuming; in the stirring stage, the stirring device is used to promote the uniform mixing of the molten steel; in the cooling stage, the treated molten steel is cooled to an appropriate temperature for subsequent processes. Through VD treatment, the quality and performance of steel can be significantly improved, making it have the characteristics of high strength, good toughness and welding performance. These characteristics make low-alloy high-strength structural steel widely used in shipbuilding, bridges, construction, machinery and other fields.

[0045] S5, VD stage, through vacuum treatment, harmful gases such as hydrogen and nitrogen in molten steel can be effectively removed to prevent these gases from forming defects such as bubbles or looseness in steel, thereby improving the density and strength of steel. VD can also remove non-metallic inclusions in molten steel, such as oxides and sulfides, which will seriously affect the mechanical properties and processing properties of steel. VD equipment consists of a vacuum chamber, a heating device, a stirring device, a gas control system, etc. The vacuum chamber is used to create a vacuum environment, the heating device is used to maintain the temperature of the molten steel, and the stirring device is used to control the temperature of the molten steel. The device is used to promote uniform mixing of molten steel. The gas control system is used to control the vacuum degree and gas flow rate. When the molten steel enters the VD furnace, argon blowing is started throughout the process, and temperature measurement and sampling are carried out. The total argon blowing time in the VD furnace is not less than 45 minutes. The composition is fine-tuned before vacuuming and controlled according to the target value. All composition adjustments and wire feeding operations after breaking the vacuum are strictly prohibited. The vacuuming target does not exceed 0.5tor, the vacuum maintenance time is not less than 10 minutes, and the soft argon blowing time after breaking the vacuum is not less than 15 minutes. When leaving the station, covering agent or carbonized rice husk is added according to the temperature for insulation.

[0046] S6, continuous casting stage, the continuous casting machine is the core equipment of the continuous casting link, it is composed of a crystallizer, a vibration device, a billet drawing device, a secondary cooling device, a cutting device, etc. These equipment work together to complete the casting, cooling, solidification and cutting of molten steel. In the production of low-alloy high-strength structural steel, the continuous casting link is usually combined with converter smelting, refining and rolling processes. By optimizing the continuous casting process parameters and equipment configuration, low-alloy high-strength structural steel products with uniform structure and excellent performance can be produced. Argon is blown at the long water nozzle and a sealing ring is added to the water nozzle to protect the pouring. It is strictly forbidden to expose the molten steel in the tundish and crystallizer. The tundish is cut to size as required. The liquid level control of the tundish: not less than 450mm for opening casting and not less than 650mm for normal casting. The tundish is protected by covering agent + carbonized rice husk or composite insulation agent for pouring. The superheat of the molten steel in the tundish does not exceed 40℃ for opening casting furnace and 35℃ for continuous casting furnace. The superheat of the tundish is 15-53℃. Crystallizer protective slag: low carbon steel protective slag is used, and the protective slag is required to be dry. Take at least one sample for each pouring for low-magnification and surface pickling inspection of the ingot.

[0047] S7. During the ingot inspection stage, ingot inspection for low-alloy high-strength structural steel production is a complex and important task, involving chemical composition, mechanical properties, process performance, surface quality and internal quality. Through strict inspection and control, it can be ensured that the quality of the ingot meets national standards and contractual provisions, providing reliable guarantee for subsequent processing and use.

[0048] S8. During the second-line rolling stage of bars, the steel billets entering the production line are subject to quality inspection, including card verification, external dimension measurement, surface quality inspection, etc. The acceptance of steel billets is carried out in accordance with the technical standards of steel billets and the internal control technical conditions. Unqualified steel billets shall not be allowed to enter the furnace. The heated steel billets are initially rolled in the rough rolling mill to reduce their cross-sectional dimensions and increase their length. The semi-finished products after rough rolling are sent to the intermediate rolling mill for further rolling to achieve a smaller cross-sectional dimension and higher dimensional accuracy. During the intermediate rolling process, the roll gap and reduction amount must also be adjusted according to the rolling process requirements, and the rolling temperature and rolling speed must be monitored. The semi-finished products after intermediate rolling are sent to the finishing mill for final rolling to produce bar products that meet user needs. During the finishing rolling process, the roll gap, reduction amount, rolling temperature and rolling speed and other parameters must be strictly controlled to ensure product quality.

[0049] S9. In the slow cooling stage of the cooling bed, the cooling rate of the slow cooling of the cooling bed needs to be controlled within a certain range to ensure that the temperature of the steel can be reduced evenly and slowly. Too fast cooling may cause stress inside the steel, while too slow cooling may affect production efficiency. The cooling time of the slow cooling of the cooling bed depends on the material, specification and production requirements of the steel. Generally speaking, the cooling time needs to be long enough to ensure that the internal structure of the steel can be fully transformed and homogenized. When the cooling bed is slow cooling, the selection of cooling medium is also very important. Common cooling media include air, water, etc. Different cooling media have different cooling effects and effects on steel. Therefore, it is necessary to select according to the specific situation. During the slow cooling process, it is necessary to avoid the rapid cooling of the steel. Rapid cooling may cause defects such as stress and cracks inside the steel, affecting the performance and quality of the steel. During the slow cooling process, it is necessary to continuously monitor the temperature changes of the steel. Once an abnormal situation is found, such as too high or too low temperature, timely measures need to be taken to adjust it. The cooling bed equipment is one of the key equipment in the slow cooling process. Therefore, it is necessary to regularly maintain and service the cooling bed equipment to ensure that it is in good working condition.

[0050] 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 process for producing low-alloy high-strength structural steel, characterized in that: Including hot metal pretreatment, converter, CAS, LF refining, VD, continuous casting, ingot inspection, bar second-line rolling, cooling bed slow cooling, finished product inspection and warehousing; S1, hot metal pretreatment stage, prepare SiFe, medium carbon MnFe, VFe, VN alloy, high AlMnFe, the alloy must be clean and dry, and no mixing is allowed; S2, converter stage, prepare metal raw materials such as scrap steel, molten iron and slag-making materials such as lime and light-burned dolomite. These materials need to be proportioned in proportion to ensure that the chemical reaction in the steelmaking process can proceed smoothly. The metal raw materials are loaded into the converter and the first batch of slag-making materials are added; S3, CAS stage, CAS technology first uses argon bottom blowing to form a slag-free area on the surface of molten steel, and then inserts an isolation cover into the molten steel to cover the slag-free area, so that the alloy added to the upper part of the isolation cover is isolated from the slag; S4, LF refining stage, after the basic smelting of molten steel is completed in the primary refining furnace such as converter or electric arc furnace, the molten steel is tapped into a ladle, and an appropriate amount of alloy and slag are added to the ladle to prepare for LF refining. At the same time, the LF furnace is ensured to be in good condition, the ladle filled with molten steel is hoisted to the LF refining station, and the Ar gas pipe is connected for argon blowing and stirring. In the LF furnace, slag is removed and the temperature is raised by adding silicon carbide, calcium carbide, and aluminum granules to form a highly reducing white slag to improve the desulfurization and deoxidation effects; S5, VD stage, after LF refining is completed, the refined molten steel is hoisted to the VD treatment station. At this time, the composition, temperature and purity of the molten steel should meet the requirements of VD treatment. The molten steel is poured from the ladle into the molten steel tank in the VD vacuum chamber. During the pouring process, attention should be paid to controlling the flow rate and flow of the molten steel to prevent the molten steel from splashing or generating eddy currents. Argon is blown into the molten steel through the air-permeable bricks at the bottom of the molten steel tank for stirring. The purpose of blowing argon and stirring is to promote the floating and removal of gas and inclusions in the molten steel; S6, continuous casting stage, the refined molten steel is poured from the ladle into the tundish, which plays the role of buffering and distributing the molten steel to ensure that the molten steel can flow evenly into the crystallizer. The molten steel flows from the tundish through the water inlet into the crystallizer. The crystallizer is one of the core equipment of the continuous casting machine. It allows the molten steel to cool quickly and solidify into the primary shell of the ingot. The molten steel in the crystallizer is cooled by the cooling water and gradually solidifies into the shell. At the same time, the secondary cooling zone further cools and solidifies the ingot to ensure the quality and shape of the ingot. S7. During the ingot inspection stage, check whether there are scars, cracks, folds, inclusions, bubbles and iron oxide scale pressure defects that are harmful to the use of the ingot. It is allowed that there are thin layers of iron oxide scale, rust and slight pits and scratches on the ingot surface that do not affect the use, but the depth or height shall not exceed half of the ingot thickness tolerance, and the minimum allowable thickness of the ingot shall be guaranteed; S8, bar second-line rolling stage, bar rolling is carried out by feeding the heated billet into the rolling mill for rolling; S9, cooling bed slow cooling stage, the purpose of cooling bed slow cooling is to make the temperature of steel drop evenly and slowly during the cooling process; S10: Finished product inspection and warehousing stage, inspection and warehousing operations are carried out.

2. A process for producing low-alloy high-strength structural steel according to claim 1, characterized in that: In the S2, converter stage, the steelmaking raw materials require a narrower composition deviation to improve the purity of the molten steel and control the content of harmful elements in the steel, such as Pb, Sn, As, Sb, and Bi. Most low-alloy high-strength steels can be smelted in a top and bottom composite blown converter.

3. A low alloy high strength structural steel production process according to claim 1, characterized in that: In the S3 and CAS stages, argon is blown from the bottom throughout the process, and violent blowing is strictly prohibited. The argon pressure during the steel-out process is controlled according to the target of 0.8-1.2Mpa. The temperature of the molten steel is measured within 2 minutes after entering the station. After normal argon blowing for 2 minutes, a static sampler is used to take a sample. After sampling, the argon is adjusted to a soft blowing state and the steel is covered before leaving the station.

4. A process for producing low-alloy high-strength structural steel according to claim 1, characterized in that: During the S4 and LF refining stages, the argon blowing system should be carefully checked before the molten steel enters the LF furnace to ensure that the argon blowing quick connector is reliably connected and leak-free. The large tank must have a good bottom blowing effect and a clean tank edge that meets the process requirements for entering the LF furnace. Power should be supplied according to the temperature requirements of the steel grade, the molten steel should be sampled and the temperature measured in time, and a static sampler should be used to take samples.

5. A process for producing low alloy high strength structural steel according to claim 4, characterized in that: The S5, VD stage, the VD process generally includes heating, vacuum treatment, stirring and cooling steps. In the heating stage, the molten steel is heated to an appropriate temperature; in the vacuum treatment stage, the gas and inclusions in the molten steel are removed by vacuuming; in the stirring stage, the stirring device is used to promote uniform mixing of the molten steel; In the cooling stage, the treated molten steel is cooled to an appropriate temperature for subsequent processes.

6. A process for producing low alloy high strength structural steel according to claim 5, characterized in that: The S5VD stage removes non-metallic inclusions in the molten steel. The VD equipment consists of a vacuum chamber, a heating device, a stirring device, and a gas control system. The vacuum chamber is used to create a vacuum environment, the heating device is used to maintain the temperature of the molten steel, the stirring device is used to promote uniform mixing of the molten steel, and the gas control system is used to control the vacuum degree and gas flow rate.

7. A process for producing low alloy high strength structural steel according to claim 5, characterized in that: In the S6 continuous casting stage, the continuous casting machine is the core equipment of the continuous casting process, which consists of a crystallizer, a vibration device, a billet drawing device, a secondary cooling device, and a cutting device. These devices work together to complete the casting, cooling, solidification and cutting of molten steel.

8. The process for producing low alloy high strength structural steel according to claim 1, characterized in that: During the S8 and second-line rolling stage of bars, quality inspection is carried out on the steel billets entering the production line, including card verification, dimension measurement, and surface quality inspection. The steel billets are accepted according to the technical standards for steel billets and internal control technical conditions, and unqualified steel billets shall not be allowed to enter the furnace.

9. The process for producing low alloy high strength structural steel according to claim 1, characterized in that: In the S9, cooling bed slow cooling stage, the cooling rate of the cooling bed slow cooling needs to be controlled within a certain range to ensure that the temperature of the steel can be lowered evenly and slowly. Too fast a cooling rate may cause stress inside the steel.

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