Method for stably producing high-carbon steel hot-rolled steel plate

Abstract

The invention provides a method for stably producing a high-carbon steel hot-rolled steel plate, which optimizes and improves the toughness of hot-rolled strip steel through parameter control and process cooperation of the procedures of molten steel refining, slab continuous casting, slab heating, descaling rough rolling, finish rolling, coiling, slow cooling and transverse cutting, optimizes the straightening process of transverse cutting, and improves the yield of the high-carbon steel hot-rolled steel plate. And the common processing fracture problem of the type of steel is effectively improved.

Description

Technical Field

[0001] This application relates to the field of iron and steel metallurgy technology, and in particular to a method for the stable production of hot-rolled high-carbon steel plates. Background Technology

[0002] High-carbon steel refers to steel with a carbon content greater than 0.6%, which is higher than that of ordinary carbon steel. It is commonly used in the processing of products such as knives, measuring tools, and springs. Compared with ordinary low-carbon steel, it has the characteristics of high strength, high hardness, easy quenching, and poor toughness after hot rolling. Due to these performance characteristics, the manufacturing and deep processing of high-carbon steel also presents many problems, among which the most common is the problem of cold working cracking or even fracture. Summary of the Invention

[0003] This application provides a method for the stable production of hot-rolled high-carbon steel plates, which improves the problems such as breakage that easily occur in hot-rolled high-carbon steel coils during subsequent processing.

[0004] This application provides a method for the stable production of hot-rolled high-carbon steel plates. The method includes: obtaining molten steel from a converter; performing LF refining and RH extreme refining on the molten steel to obtain refined molten steel, wherein the LF refining time is not less than 30 min, the RH extreme refining vacuum time is not less than 20 min, and the sum of the mass percentages of P and S elements in the refined molten steel is not higher than 0.02%; continuously casting the refined molten steel to obtain a continuously cast slab; charging the continuously cast slab into a heating furnace with an inlet temperature ≥300℃ and an outlet temperature of 1100~1200℃; descaling and rough rolling the heated continuously cast slab to obtain an intermediate slab, wherein the rough rolling is performed in 5~7 passes, the thickness of the intermediate slab is ≤35mm, and the intermediate slab is reversed at both ends using a hot coil box. The intermediate billet is finished by a seven-stand finishing mill to obtain a finished billet. The final rolling temperature of the finished billet is controlled at 900-1000℃. The finished billet is then coiled to obtain a steel coil. The coiling temperature is set at 650-750℃. During the coiling process, the fine-tuning feedback water at the very end of the shielded layer cooling system is used, and the first three sets of layer cooling manifolds are turned on for cooling. Only the front and rear sets of layer cooling side spray devices are turned on, and the rest of the side spray devices are turned off. A hot head control process of 25℃~35℃ is used for the preset area within 50 meters of the head and the preset area within 50 meters of the tail of the steel coil. The edge shielding technology is implemented for the layer cooling manifolds to regulate the edge cooling intensity of the strip. After the steel coil is quickly removed from the line, it is placed in a warehouse and slowly cooled in a slow cooling pit for more than 2 days. When the temperature of the steel coil is lower than 50℃, it is cross-cut.

[0005] According to the embodiments of this application, the phosphorus content of the converter steel is ≤0.010% by mass, and argon gas is introduced for stirring during the LF refining process, with an argon gas stirring flow rate of 0.3~0.5 m³ / h. 3 / (t·min), the vacuum degree of RH ultimate refining is ≤67Pa.

[0006] According to the embodiments of this application, during the continuous casting process, the casting speed is controlled at 0.8~1.4m / min, a low-flow cooling mode is adopted, and electromagnetic stirring is used. The thickness of the continuously cast slab is 200~240mm. Optionally, the specific water volume of the low-flow cooling mode is 0.8~1.2L / kg, the current of the electromagnetic stirring is 250~350A, the stirring frequency is 5~10Hz, and the cooling water temperature difference of the continuous casting crystallizer is controlled at 5~8℃.

[0007] According to the embodiments of this application, the total time the continuously cast slab spends in the heating furnace is 200 to 300 minutes. The heating furnace is divided into a preheating section, a heating section, and a soaking section. The temperature of the preheating section is controlled at 600 to 800°C, the temperature of the heating section is controlled at 1000 to 1150°C, and the temperature of the soaking section is the same as the furnace exit temperature.

[0008] According to the embodiments of this application, descaling includes rough descaling and rough rolling body descaling. Rough rolling body descaling is only started in the first pass of rough rolling. The reduction in the first pass of rough rolling is 30~40mm, and the reduction in each subsequent pass decreases by 5~8mm. The heat preservation temperature of the hot rolling box is maintained at 950~1000℃.

[0009] According to an embodiment of this application, during the finishing rolling process, the inter-stand water and roll gap spray water are normally activated, with only the F6 stand activating the side spray water. The side spray water pressure is 0.8~1.2MPa. The entire coil is rolled using a speed-increasing method, with an initial rolling speed of 1.2~1.5m / s and a final rolling speed of 3.0~3.5m / s, and a speed increase rate of 0.1~0.2m / (s). 2 ).

[0010] According to an embodiment of this application, the edge shielding technology is implemented using an arc-shaped guide plate. The guide plate is made of high-temperature resistant stainless steel, and the distance between the guide plate and the edge of the strip is 5~10mm. The temperature fluctuation range controlled by the hot head is ≤±5℃.

[0011] According to the embodiments of this application, the lining material of the slow cooling pit is high-temperature resistant insulation cotton, and the cooling rate of the temperature in the slow cooling pit from 600~700℃ to below 50℃ is ≤10℃ / h. After the steel coil is taken out of the slow cooling pit, it naturally cools to the target temperature.

[0012] According to an embodiment of this application, the cross-cutting includes controlling the inlet and outlet roll gaps to be greater than a preset thickness of the steel plate for a 6-12 meter area at the head and tail of the steel coil. After the head passes through, the roll gap value is adjusted to be equal to the steel plate thickness. Subsequently, the roll gap is adjusted in real time according to the plate shape. Optionally, the preset thickness is 3 mm during the cross-cutting process. The working roll hardness of the cross-cutting straightener is HRC55-60, the straightening speed in the head area is 30-50 m / min, and the straightening speed is increased to 80-120 m / min after the head passes through.

[0013] According to the embodiments of this application, the high-carbon steel hot-rolled steel plate is a high-carbon steel hot-rolled steel plate with a carbon content of 0.6% to 1.0%.

[0014] This application provides a method for the stable production of hot-rolled high-carbon steel plates. By optimizing the smelting and hot rolling processes, the toughness of the hot-rolled strip is improved. At the same time, the straightening process of cross-cutting is optimized, which effectively improves the common processing fracture problem of this type of steel. Detailed Implementation

[0015] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0016] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0017] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0018] The inventors of this application noticed during the production of hot-rolled high-carbon steel plates that the rapid cooling of the head, tail, and outer ring caused extreme fluctuations in the performance of the steel plates, making them prone to breakage during processes such as cross-cutting and straightening. This was particularly pronounced in winter when temperatures were low, with broken fragments often breaking into the rough straightening machine, causing the straightening rollers to jam and damage the steel, which had a significant impact on production.

[0019] Cracking in high-carbon steel has many causes, generally considered to be related to low steel cleanliness, uneven hot-rolled microstructure, and improper processing methods. To reduce cracking and fracture during subsequent processing, it is necessary to optimize the process by addressing potential fracture risks in both preceding and following stages. Existing processes primarily reduce cracks in the hot-rolled substrate, with few methods specifically addressing the root causes of processing-related cracking. Alternatively, annealing the hot-rolled coil before further processing can be effective but significantly increases costs.

[0020] In view of the above problems, this application provides a method for stable production of hot-rolled high-carbon steel plates, which can improve the problems such as breakage that easily occur in hot-rolled high-carbon steel coils during subsequent processing.

[0021] This application provides a method for the stable production of hot-rolled high-carbon steel plates, the method comprising the following steps: The molten steel from the converter is obtained and subjected to LF refining and RH extreme refining to obtain refined molten steel. The LF refining time is not less than 30 minutes, the vacuum time of RH extreme refining is not less than 20 minutes, and the sum of the mass percentages of P and S elements in the refined molten steel is not higher than 0.02%. Refined molten steel is continuously cast to obtain continuously cast slabs; The continuously cast slab is charged into the heating furnace by hot charging, with a furnace temperature ≥300℃ and a furnace exit temperature of 1100~1200℃. The heated continuous casting slab is descaled and rough rolled to obtain an intermediate slab. The rough rolling is carried out in 5 to 7 passes. The thickness of the intermediate slab is ≤35mm. The head and tail of the intermediate slab are reversed in a hot rolling box. The intermediate billet is finished by a seven-stand finishing mill to obtain a finished billet. The final rolling temperature of the finishing mill is controlled at 900-1000℃. The finishing billet is coiled into a steel coil at a temperature of 650-750℃. During the coiling process, the fine-tuning feedback water at the very end of the shielded cooling system is used, and the first three sets of cooling manifolds are turned on for cooling. Only the front and rear sets of cooling side spray devices are turned on, while the rest are turned off. A hot head control process of 25℃~35℃ is used for the preset area within 50 meters of the head and the preset area within 50 meters of the tail of the steel coil. Edge shielding technology is implemented on the cooling manifolds to regulate the cooling intensity of the strip edge.

[0022] After the steel coils are quickly removed from the production line, they are placed in a slow cooling pit and cooled slowly for more than 2 days. When the temperature of the steel coils is below 50℃, they are then cross-cut.

[0023] This application provides a method for the stable production of hot-rolled high-carbon steel plates. The method covers steel refining, slab continuous casting, slab heating, descaling rough rolling, finish rolling, coiling, slow cooling and cross-cutting processes. Each process is controlled by parameters and coordinated with the process to form a complete technical solution.

[0024] In the steel refining process, converter steel is first obtained and subjected to dual refining treatments: LF refining and RH extreme refining, to obtain refined steel that meets the requirements. The LF refining time is strictly controlled to be no less than 30 minutes to fully remove non-metallic inclusions from the steel through slag formation and adsorption. The RH extreme refining vacuum time is no less than 20 minutes to efficiently remove gaseous components such as H and N from the steel. Finally, the sum of the mass percentages of P and S elements in the refined steel is controlled to be no higher than 0.02%, improving the cleanliness of the steel from the source.

[0025] To further optimize the refining effect, in some embodiments, the phosphorus content of the converter steel should be ≤0.015% by mass; argon gas is introduced for stirring during the LF refining process, and the argon gas stirring flow rate is controlled at 0.3~0.5 m³ / h. 3 / (t·min), the effect of inclusion removal is enhanced by airflow disturbance; the vacuum degree of RH extreme refining needs to reach ≤67Pa to ensure complete gas removal.

[0026] In the slab continuous casting process, the above-mentioned refined molten steel is fed into a continuous casting machine for continuous casting. In some embodiments, the casting speed is controlled at 0.8~1.4m / min, a small flow cooling mode is adopted, and electromagnetic stirring is used. The thickness of the continuously cast slab is 200~240mm.

[0027] The continuous casting speed adopts a constant control mode, maintained at 0.8~1.4m / min, to avoid uneven solidification caused by speed fluctuations; to reduce surface longitudinal cracks and subcutaneous bubble defects caused by sudden speed changes; for high carbon steel such as 80CrV2 steel, the fluidity of molten steel decreases due to the addition of chromium, and a constant casting speed can be adapted to its solidification characteristics.

[0028] For example, the casting speed is controlled at 0.8 m / min, 0.9 m / min, 1.0 m / min, 1.1 m / min, 1.2 m / min, 1.3 m / min, 1.4 m / min or any two of the above values.

[0029] In the continuous casting process, a special protective slag for high-carbon steel is used to optimize heat transfer and lubrication within the crystallizer. For example, the characteristics of this special protective slag for high-carbon steel are as follows: basicity of 0.75~0.8, melting point of 900-950℃, and viscosity of 0.1~0.2 Pa·s at 1100℃~1300℃.

[0030] In some embodiments, the specific water volume in the low-flow-rate cooling mode is controlled at 0.8~1.2L / kg to slow down the cooling rate and prevent edge overcooling cracking. The low-flow-rate cooling mode solves the core problem of edge overcooling cracking in high-carbon steel continuous casting billets by controlling the cooling intensity of the crystallizer and the secondary cooling zone.

[0031] For example, the specific water volume in the low-flow cooling mode is controlled at 0.8 L / kg, 0.9 L / kg, 1.0 L / kg, 1.1 L / kg, 1.2 L / kg, or any two of the above values.

[0032] During continuous casting, a special protective slag for high-carbon steel is used to optimize heat transfer and lubrication within the crystallizer; Optionally, the electromagnetic stirring current is 250~350A and the stirring frequency is 5~10Hz. The electromagnetic stirring forces convection through the convection of the melt to refine the grains, breaking the columnar crystal growth trend of high carbon steel continuous casting billets, increasing the equiaxed crystal ratio, improving the plasticity and toughness of the billets, and reducing the risk of cracking during the rolling process. The cooling water temperature difference of the continuous casting crystallizer is controlled at 5~8℃ to ensure stable heat transfer in the crystallizer and further reduce surface defects.

[0033] Continuously cast slabs with a thickness of 200–240 mm show good compatibility with the subsequent 5–7 passes of rough rolling. By rationally allocating the reduction, the intermediate slab thickness can be reduced to ≤35 mm, decreasing the rolling load and force in the finishing rolling process and preventing equipment failures due to excessive load on the finishing mill. For 80CrV2 steel, a thicker slab allows for extended soaking time, ensuring complete dissolution of vanadium carbides and preventing undissolved carbides from becoming crack initiations during rolling.

[0034] For example, the thickness of the continuously cast slab is 200 mm, 210 mm, 220 mm, 230 mm, 240 mm or any value between the two mentioned above.

[0035] In the slab heating process, the continuously cast slab is fed into the heating furnace by hot charging, with an inlet temperature of ≥300℃, making full use of the residual heat of the continuously cast slab to reduce energy consumption; the outlet temperature is controlled at 1100~1200℃ to ensure that the slab enters the temperature range of complete austenitization and improves plasticity.

[0036] For example, the furnace exit temperature is 1100°C, 1120°C, 1140°C, 1150°C, 1160°C, 1180°C, 1200°C, or any value between the two above.

[0037] In some embodiments, to achieve uniform heating of the slab, the heating furnace is divided into three sections: a preheating section, a heating section, and a soaking section. The preheating section temperature is controlled at 600–800°C, allowing the slab to heat up slowly from the surface inwards. This avoids excessive thermal stress inside the slab due to rapid heating, preventing defects such as cracks and deformation. Simultaneously, it gradually removes residual moisture and adsorbed gases from the slab surface, providing stable conditions for subsequent high-temperature heating. The heating section temperature is controlled at 1000–1150°C, rapidly increasing the slab temperature so that the slab quickly enters the suitable temperature range for plastic deformation, improving heating efficiency and shortening the overall furnace time. The soaking section temperature is consistent with the furnace exit temperature, ensuring uniform temperature throughout the slab. The total furnace time for the continuously cast slab is 200–300 minutes, ensuring sufficient dissolution of carbides and homogenization of the microstructure.

[0038] For example, the preheating zone temperature is 600°C, 620°C, 640°C, 650°C, 660°C, 680°C, 700°C, 720°C, 740°C, 750°C, 760°C, 780°C, 800°C, or any value between the two above.

[0039] For example, the heating section temperature is 1000℃, 1020℃, 1040℃, 1050℃, 1060℃, 1080℃, 1100℃, 1120℃, 1140℃, 1150℃ or any value between the above two.

[0040] For example, the total time the continuously cast slab spends in the heating furnace is 200 min, 210 min, 220 min, 230 min, 240 min, 250 min, 260 min, 270 min, 280 min, 290 min, 300 min, or any value between the two above.

[0041] In the descaling and rough rolling process, the heated continuously cast slab first undergoes descaling to remove the iron oxide scale generated on the surface, preventing it from being pressed into the steel plate and forming defects. It is then fed into a four-high roughing mill for rough rolling, using a 5-7 pass rolling process to obtain an intermediate slab with a thickness ≤35mm. During the rough rolling process, a hot coil box is used to reverse the head and tail of the intermediate slab, balancing the temperature distribution at both ends.

[0042] In some embodiments, the descaling process is divided into rough descaling and rough rolling body descaling. Rough rolling body descaling is only started in the first pass of rough rolling. The reduction in the first pass of rough rolling is 30~40mm, and the reduction in each subsequent pass decreases by 5~8mm. The heat preservation temperature of the hot rolling box is maintained at 950~1000℃.

[0043] Because a thick and dense scale of iron oxide forms on the surface of the slab after heating, if it is not removed in time, it is easily pressed into the strip matrix during subsequent rolling, forming surface pits, pits, and other defects. Rough descaling refers to the process of removing the primary iron oxide scale formed on the surface of the slab during heating before it enters the roughing mill. Specifically, this can be achieved by using a high-pressure water descaling device installed in front of the roughing mill to impact the surface with high-pressure water.

[0044] Descaling of the roughing mill body is only initiated in the first pass. This not only removes the iron oxide scale completely before it is fully pressed together, ensuring the surface quality of the steel plate, but also avoids heat loss caused by repeated descaling in subsequent passes, effectively reducing the temperature drop of the intermediate billet and maintaining temperature stability during the roughing process.

[0045] The roughing rolling process employs a reduction of 30-40 mm in the first pass, with subsequent passes decreasing by 5-8 mm each time. By applying a larger reduction in the early stages of roughing rolling, the slab structure can be fully broken down, internal porosity defects can be compacted, and the density of the strip can be improved. At the same time, completing most of the deformation in the roughing rolling stage can significantly reduce the rolling load of the subsequent finishing mill, avoiding problems such as high rolling force, difficulty in shape control, and thickness accuracy fluctuations caused by excessive reduction in the finishing rolling stage, thus achieving a reasonable load match between roughing and finishing rolling.

[0046] The hot rolling box maintains a temperature of 950~1000℃, which can effectively keep the intermediate billet after rough rolling warm, reduce the temperature difference between the head and tail of the intermediate billet, suppress the excessive temperature drop caused by the tail due to long-term residence, further optimize the temperature uniformity of the intermediate billet, provide stable temperature and uniform structure billet conditions for finishing rolling, and ensure the stable performance of the strip throughout its entire length.

[0047] For example, the heat preservation temperature of the hot roll box is 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C or any value between the above two.

[0048] In the finishing rolling process, the intermediate billet is fed into a seven-stand finishing mill for continuous finishing rolling to obtain the finished billet. During the finishing rolling process, the final rolling temperature is strictly controlled at 900-1000℃ to ensure dynamic recrystallization during rolling and refine the austenite grains.

[0049] For example, the final rolling temperature is 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C or any value between the above two.

[0050] To ensure the quality and efficiency of finishing rolling, in some embodiments, the present invention further limits the finishing rolling parameters: inter-stand water and roll gap spray water are normally turned on, only the F6 stand is turned on with side spray water, and the side spray water pressure is controlled at 0.8~1.2MPa, which reduces the intrusion of foreign objects on the surface and reduces the temperature drop at the edges; the whole coil adopts an accelerating rolling mode, with an initial rolling speed of 1.2~1.5m / s and a final rolling speed increased to 3.0~3.5m / s, and the speed increase rate is controlled at 0.1~0.2m / (s). 2 The rolling force at the tail end is reduced through speed optimization. The F6 stand refers to the sixth stand of the finishing mill.

[0051] During the finishing rolling process of strip steel, the temperature drop at the tail end is usually significantly greater than that at the head and middle, resulting in a lower tail temperature and increased deformation resistance. If constant speed rolling is used, problems such as excessive rolling force at the tail end, uneven rolling load, strip shape fluctuation, and decreased dimensional accuracy are likely to occur. This application addresses this issue by gradually increasing the running speed of the strip during the rolling process through speed-increasing rolling. This effectively shortens the residence time of the strip tail end between stands, reduces the temperature drop at the tail end, and makes the temperature of the strip more uniform along its entire length. This reduces the deformation resistance and rolling force at the tail end, avoiding problems such as motor overload, accelerated roll wear, and excessive strip thickness deviation caused by excessive rolling force at the tail end. Simultaneously, the speed increase rate is controlled at 0.1~0.2 m / (s). 2 This process enables smooth speed increase and impact-free transition, avoiding tension fluctuations, strip deviation, or plate shape defects caused by sudden speed changes. While ensuring rolling stability, it further improves the uniformity of strip thickness and consistency of microstructure properties throughout the entire length of the strip.

[0052] In the coiling process, after finishing rolling, the finished billet is fed into the coiler for coiling, and the coiling temperature is set at 650-750℃. During the coiling process, the fine-tuning feedback water at the very end of the shielded cooling system is only turned on for cooling by the first three sets of cooling manifolds; only the front and rear sets of cooling side spray devices are turned on, and the remaining side spray devices are turned off; a 30℃ hot head control process is used for the first 50 meters and the last 50 meters of the steel coil; at the same time, edge shielding technology is implemented for the cooling manifolds to regulate the cooling intensity of the strip edge.

[0053] For example, the winding temperature is 650°C, 660°C, 670°C, 680°C, 690°C, 600°C, 710°C, 720°C, 730°C, 740°C, 750°C, or any value between the two above.

[0054] In some embodiments, edge shielding is achieved using an arc-shaped guide plate. The guide plate is made of high-temperature resistant stainless steel, and its distance from the edge of the strip is controlled at 5~10mm. The guide plate reduces the amount of cooling water contacting the edge through its guiding effect. The temperature fluctuation range of the hot head control needs to be ≤±5℃ to ensure accurate temperature compensation at the head and tail and improve the overall temperature uniformity of the steel coil.

[0055] In the slow cooling process, the steel coil is quickly removed from the production line after being coiled and placed in the warehouse. It is then sent to the slow cooling pit for slow cooling for no less than 2 days. Once the temperature of the steel coil drops below 50°C, subsequent cross-cutting is carried out. After the steel coil leaves the slow cooling pit, forced cooling methods such as air cooling or water cooling are strictly prohibited to avoid stress cracking caused by sudden temperature changes.

[0056] To enhance the slow cooling effect, nitrogen gas with a purity of ≥99.9% is introduced into the slow cooling pit for protection to prevent oxidation of the steel coil. The cooling rate of the temperature in the slow cooling pit from 600~700℃ to below 50℃ is controlled at ≤10℃ / h. The residual stress inside the steel coil is released by slow cooling, thereby optimizing the microstructure and properties.

[0057] For example, the cooling rate is 1℃ / h, 2℃ / h, 3℃ / h, 4℃ / h, 5℃ / h, 6℃ / h, 7℃ / h, 8℃ / h, 9℃ / h, 10℃ / h or any value between the above two.

[0058] The head and tail of a steel coil experience rapid heat dissipation and significant temperature drops in the laminar cooling zone, which can lead to problems such as low temperature, hardened microstructure, and reduced toughness, resulting in brittle fracture during subsequent cross-cutting and straightening. This application addresses this issue by implementing pre-controlled temperature supplementation of 25°C to 35°C in a pre-defined area within a 50-meter zone at both ends. This increases the final cooling temperature of the head and tail areas, reduces the temperature difference between the head, tail, and middle sections of the steel coil, and makes the temperature distribution along the entire length of the strip more uniform. This reduces uneven microstructure, excessive hardness, and insufficient toughness caused by excessively low temperatures at the head and tail, significantly lowering the risk of breakage and fragmentation during subsequent processing and ensuring smooth strip threading and straightening.

[0059] For example, the temperature of the hot head control process is 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, or any value between the two above.

[0060] The pre-set area within 50 meters of the head of the steel coil refers to the strip area extending inward from the outermost end of the coil along the length of the strip after the coil is formed, with a pre-set distance ≤ 50 meters; similarly, the pre-set area within 50 meters of the tail refers to the strip area extending outward from the innermost end of the coil, with a pre-set distance ≤ 50 meters.

[0061] For example, a hot-head control process is applied to the head portion of the steel coil at 5 meters, 10 meters, 15 meters, 20 meters, 25 meters, 30 meters, 35 meters, 40 meters, 45 meters, or 50 meters. The tail portion of the steel coil at 5 meters, 10 meters, 15 meters, 20 meters, 25 meters, 30 meters, 35 meters, 40 meters, 45 meters, or 50 meters is also treated with hot-head control.

[0062] The edges of strip steel have a large heat exchange area and a much faster cooling rate than the middle, which easily leads to problems such as overcooling, hardening of the microstructure, and increased internal stress. These are the main causes of edge cracking and processing cracking in hot-rolled high-carbon steel plates. By implementing edge shielding on the laminar flow cooling manifold, the cooling intensity at the edges of the strip steel is reduced, and the temperature drop rate at the edges is slowed down. This makes the cooling rate of the edges and the middle of the strip steel more consistent, thereby reducing the temperature gradient and microstructure difference, reducing edge internal stress, improving the toughness of the strip steel edges, avoiding edge hardening and brittleness, and preventing edge cracking or strip breakage during subsequent straightening and cross-cutting, thus improving the overall processing stability of the steel plate.

[0063] In some embodiments, cross-cutting includes a 6-12 meter area at the head and tail of the steel coil, controlling the inlet roll gap and outlet roll gap to be greater than a preset thickness of the steel plate thickness, adjusting the roll gap value to be equal to the steel plate thickness after the head passes through, and subsequently adjusting it in real time according to the plate shape.

[0064] In the cross-cutting process, during the cross-cutting process, for the head and tail 6-12 meters of the steel coil, which has a fast cooling rate and poor toughness, the inlet roll gap and outlet roll gap are controlled to be greater than the preset thickness of the steel plate. After the head passes through, the roll gap value is adjusted to be equal to the thickness of the steel plate. Subsequently, the straightening parameters are adjusted in real time according to the shape of the plate.

[0065] In some embodiments, the preset thickness is set to 3mm, that is, the roll gap in the head and tail areas needs to be greater than the steel plate thickness + 3mm. By increasing the roll gap, the straightening force of the straightener on the strip in this area is reduced, thereby effectively avoiding the risk of brittle fracture. The reason is that after the head and tail of the steel coil are cooled and coiled, the cooling rate is much faster than that in the middle area. Its internal structure is harder and its toughness is significantly reduced. If the same roll gap as the middle area (that is, the roll gap is equal to the steel plate thickness) is used for straightening, the larger straightening force will cause the strip to bear stress exceeding its toughness limit, which can easily cause brittle fracture, edge breakage, or even machine jamming in the head and tail areas.

[0066] Meanwhile, the hardness of the work rolls of the cross-cutting straightener is strictly controlled between HRC55 and 60. On the one hand, a hardness of HRC55 to 60 ensures that the work rolls have excellent wear resistance, enabling them to withstand the friction and extrusion forces during the straightening process of high-carbon steel (especially 80CrV2 steel, which contains chromium and vanadium and has high hardness) for a long time. This avoids defects such as wear, scratches, and dents on the surface of the work rolls, extends the service life of the roll system, reduces equipment maintenance costs, and ensures the stability of straightening accuracy during long-term production. On the other hand, this hardness range allows the work rolls to have appropriate toughness, avoiding increased brittleness and easy breakage of the roll body due to excessive hardness. At the same time, it ensures that the roll body is not prone to plastic deformation, maintaining the preset roll gap accuracy and straightening arc for a long time. This prevents strip shape defects such as edge waviness and center waviness after straightening due to roll deformation, ensuring the surface quality and dimensional accuracy of the steel plate.

[0067] Furthermore, the straightening speed adopts a segmented control mode. During the straightening of the head area of ​​the steel coil, the speed is controlled in a low-speed range of 30~50m / min; after the head area has completely passed through the straightening machine, the straightening speed is increased to a high-speed range of 80~120m / min. This segmented speed control takes into account both processing quality and production efficiency, and also specifically addresses the problem of brittle fracture in the head area: as the part of the whole coil of strip steel with the worst toughness and prone to cracking, low-speed straightening can prolong the stress time of the strip steel in the straightening machine, so that the straightening force is evenly transmitted to all parts of the strip steel, avoiding local stress concentration, and at the same time, it is convenient for operators to observe the head straightening status in real time, adjust parameters in a timely manner, and minimize the risk of strip breakage; after the head has passed, the middle area of ​​the strip steel has a uniform structure and good toughness, and high-speed straightening can significantly improve the efficiency of cross-cutting, shorten the production cycle, and adapt to the needs of large-scale batch production.

[0068] For example, the straightening speed in the head region of the steel coil is 30 m / min, 35 m / min, 40 m / min, 45 m / min, 50 m / min or any value between the above two.

[0069] For example, after the head region has completely passed through the straightening machine, the straightening speed is 80m / min, 85m / min, 90m / min, 95m / min, 100m / min, 105m / min, 110m / min, 115m / min, 120m / min or any value between the above two.

[0070] In some embodiments, the high-carbon steel hot-rolled sheet is a high-carbon steel hot-rolled sheet with a carbon content of 0.6% to 1.0%. Exemplarily, the high-carbon steel hot-rolled sheet is an 80CrV2 hot-rolled sheet or a 75Cr1 hot-rolled sheet. The composition of the 80CrV2 hot-rolled sheet, by mass percentage, is as follows: C, 0.78% to 0.82%, Cr, 1.1% to 1.2%, V, 0.18% to 0.22%, Ti ≤ 0.02%, (P+S) ≤ 0.02%.

[0071] In summary, this application effectively reduces the content of harmful elements such as phosphorus and sulfur, as well as the levels of gases and inclusions, through precise control of the dual refining process, thereby improving the cleanliness of molten steel, reducing crack initiation sources at the source, and lowering the risk of fracture during subsequent processing. The synergistic effect of constant casting speed, electromagnetic stirring, and precise cooling control during continuous casting reduces the segregation of the continuously cast billet and the incidence of internal cracks, providing high-quality billets for subsequent rolling. The application of processes such as hot coil box reversal, segmented heating, and accelerated rolling controls the temperature difference between the head and tail of the intermediate billet within 30℃, reduces the rolling force at the tail of the finishing roll, and minimizes the fluctuation range of longitudinal properties of the steel plate. The cooling process combines a special layer cooling mode with edge shielding technology, controlling the temperature difference between the inner and outer rings of the steel coil within 25℃, reducing the hardness difference between the edge and the center, and solving the performance difference problem caused by uneven cooling. Without the need for an additional annealing process, targeted adjustments to the cross-cutting and straightening parameters reduce the straightening breakage rate, improve production efficiency, and lower overall production costs.

[0072] Example The following embodiments describe the disclosure of this application in more detail. These embodiments are for illustrative purposes only, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0073] Example 1 A method for stable production of high-carbon steel hot-rolled steel plates includes: 1) Steelmaking: A double refining process is adopted, with LF refining for 55 minutes to fully remove inclusions, and RH ultimate vacuum time for 24 minutes to reduce gas composition. The chemical composition of the cast steel is as follows: C: 0.80%, Si: 0.22%, Mn: 0.41%, P: 0.009%, S: 0.005%.

[0074] 2) Slab Continuous Casting: High-carbon steel-specific protective slag is used in continuous casting. The casting speed is kept constant at 1.0 m / min to avoid cracking caused by large speed fluctuations. A low-flow-rate cooling mode is employed to prevent excessive edge cooling and slab cracking. Electromagnetic stirring is used to reduce slab segregation and internal cracks. The specific water flow rate for the low-flow-rate cooling mode is 1.1 L / kg, the electromagnetic stirring current is 300 A, the stirring frequency is 8 Hz, and the cooling water temperature difference in the continuous casting crystallizer is controlled between 5 and 8℃.

[0075] 3) Slab heating: The thickness of the continuous casting slab is 230mm. It is charged into the heating furnace by hot charging. The furnace temperature is 460℃ and the furnace temperature is 1150℃. The total furnace time is 240 minutes.

[0076] 2) Rough rolling: After exiting the furnace, the billet passes through a four-high roughing mill in seven passes. Only the first pass is used for descaling the billet body to ensure thorough removal of surface oxide scale while minimizing temperature drop. The intermediate billet thickness is 34mm, with increased roughing reduction to decrease rolling force in the finishing stage. Hot-rolled coiling is employed, reversing the head and tail of the intermediate billet to reduce temperature drop at the finishing tail and decrease rolling force.

[0077] 3) Finishing rolling: A seven-stand finishing mill is used for rolling, with a final rolling temperature of 950℃. The inter-stand water spray and roll gap spray are turned on normally, while the side spray is only turned on on the F6 stand to reduce the intrusion of foreign objects on the surface and minimize the temperature drop at the edges. The entire coil is rolled at an increasing speed to reduce the rolling force at the tail end.

[0078] 5) Winding: The winding temperature is set at 720℃. A higher winding temperature reduces the cooling water flow, minimizing uneven cooling. For the final fine-tuning feedback water of the shielded layer cooling system, only the first three sets of layer cooling manifolds are activated for cooling. Simultaneously, only the front and rear sets of side sprayers for layer cooling are activated, with the rest closed. A 30℃ hot-head control is used at the head and tail of the coil to improve temperature uniformity at the head and tail and within the coil itself. Edge shielding technology is employed on the layer cooling manifolds to intercept and drain a small amount of edge layer cooling water, reducing edge cooling of the strip.

[0079] 6) Slow Cooling: After the steel coils are quickly removed from the production line and put into the warehouse, they are slowly cooled in a slow cooling pit for more than 2 days. After leaving the slow cooling pit, it is strictly forbidden to cool the steel coils with air or water. When the temperature of the steel coils is below 50℃, cross-cutting and other deep processing should be carried out as soon as possible to improve the machinability of the strip by utilizing the internal residual heat.

[0080] 7) Cross-cutting: During cross-cutting and other processing, reduce straightening within the first 10 meters and the last 6 meters. Specifically, ensure that the inlet and outlet roll gaps are greater than the thickness + 3mm to prevent brittle breakage at the beginning and end within the straightening machine. After the first 10 meters, increase the straightening force to control the roll gap value and thickness to be approximately equal. Subsequent adjustments should be made based on the actual plate shape.

[0081] The steel plate produced in Example 1 has small differences in microstructure and properties between the edges and the middle, high dimensional accuracy, and no cracking problems occurred during leveling and subsequent cold working processes. It also has a good straightening shape.

[0082] Example 2 A method for stably producing high-carbon hot-rolled steel plates is similar to that in Example 1, except that the steel grade produced is 75Cr1: the chemical composition of the cast steel is as follows: C: 0.75%, Si: 0.26%, Mn: 0.62%, P: 0.01%, S: 0.004%. The steel plates produced have small differences in microstructure and properties between the edges and the middle, high dimensional accuracy, and no cracking problems occurred during leveling and subsequent cold working processes. Furthermore, the straightened plates have good shape.

[0083] Example 3 A method for stable production of hot-rolled high-carbon steel plates is similar to that in Example 1, except that the slab is heated to 550°C upon entering the furnace and 1180°C upon exiting, with a total furnace time of 220 minutes. The produced steel plates exhibit minimal differences in microstructure and properties between the edges and the center, high dimensional accuracy, and no cracking issues during leveling and subsequent cold working processes, while also demonstrating good straightening shape.

[0084] Example 4 A method for stable production of hot-rolled high-carbon steel plates is similar to that in Example 1, except that the rough rolling is performed in 5 passes with an intermediate billet thickness of 32 mm. The produced steel plates exhibit minimal differences in microstructure and properties between the edges and the center, high dimensional accuracy, and no cracking issues occur during leveling and subsequent cold working processes, while also demonstrating good straightening shape.

[0085] Example 5 A method for stable production of hot-rolled high-carbon steel plates is similar to that in Example 1, except that the final rolling temperature during finishing is 910℃. The produced steel plates exhibit minimal differences in microstructure and properties between the edges and the center, high dimensional accuracy, and no cracking issues occur during leveling and subsequent cold working processes, with excellent straightening shape.

[0086] Example 6 A method for stable production of hot-rolled high-carbon steel sheets is similar to that in Example 1, except that the coiling temperature is 680℃. The produced steel sheets exhibit minimal differences in microstructure and properties between the edges and the center, high dimensional accuracy, and no cracking issues occur during leveling and subsequent cold working processes, with good straightening shape.

[0087] Comparative Example 1: A method for producing hot-rolled high-carbon steel plates is similar to that in Example 1, except that: only LF refining is performed in the molten steel smelting, the molten steel has a high content of inclusions and gases, and the produced steel coils are prone to breakage when leveling, straightening or opening.

[0088] Comparative Example 2: A method for producing hot-rolled high-carbon steel plates is similar to that in Example 1, except that the LF refining time for molten steel is only 20 minutes and the RH ultimate vacuum time is 10 minutes. The molten steel contains more inclusions and gases, and the produced steel coils are prone to breakage when leveling, straightening or opening.

[0089] Comparative Example 3: A method for producing hot-rolled high-carbon steel plates is similar to that in Example 1, except that: no protective slag is used in continuous casting, or the casting speed fluctuates from 0.8 m / min to more than 1.0 m / min in the same casting cycle, which causes micro-cracks or slag entrapment in the continuous casting billet. After rolling, the cracks extend inward, and cracking occurs in the subsequent cold working process.

[0090] Comparative Example 4: A method for producing hot-rolled high-carbon steel plates is similar to that in Example 1, except that the slab heating temperature reaches 1250°C, the furnace time exceeds 400 minutes, and the number of brittle fractures occurs during the leveling process after the steel coil cools.

[0091] Comparative Example 5: A method for producing hot-rolled high-carbon steel plates is similar to that in Example 1, except that: the roughing descaling unit is fully open, the intermediate billet thickness is 45mm, the tail temperature is lower, and the strip breaks at the tail during finishing rolling.

[0092] Comparative Example 6: A method for producing hot-rolled high-carbon steel plates is similar to that in Example 1, except that: the water spray on the finishing rolling side is fully turned on, the surface quality is normal, but there are more micro-cracks on the side corresponding to the water spray after cooling, and the number of fractures in subsequent processing is more.

[0093] Comparative Example 7: A method for producing hot-rolled high-carbon steel sheets is similar to Example 1, except that the coiling temperature is 580°C, the hot-rolled steel coil has many edge cracks on both sides, and multiple fractures occur during subsequent processing.

[0094] Comparative Example 8: A method for producing hot-rolled high-carbon steel sheets is similar to Example 1, except that: the head and tail coiling temperatures are controlled in a normal mode, the head temperature is 50°C lower than the target temperature, the edge shielding process is not used, the inner ring has slight edge cracks, and it breaks during subsequent processing.

[0095] Comparative Example 9: A method for producing hot-rolled high-carbon steel plates is similar to that in Example 1, except that: when the strip is cut horizontally, the roll gap is smaller than the thickness when the strip is threaded, and the head of the strip breaks inside the straightening machine.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for stable production of high-carbon steel hot-rolled steel plates, characterized in that, The method includes: Molten steel is obtained from a converter and subjected to LF refining and RH extreme refining to obtain refined molten steel. The LF refining time is not less than 30 minutes, the RH extreme refining vacuum time is not less than 20 minutes, and the sum of the mass percentages of P and S elements in the refined molten steel is not higher than 0.02%. The refined molten steel is continuously cast to obtain a continuously cast slab. The continuously cast slab is hot-charged into a heating furnace with a furnace temperature ≥300℃ and a furnace exit temperature of 1100~1200℃. The heated continuous casting slab is descaled and rough rolled to obtain an intermediate slab. The rough rolling is performed in 5 to 7 passes. The thickness of the intermediate slab is ≤35mm. The head and tail of the intermediate slab are reversed using a hot rolling box. The intermediate billet is finished by a seven-stand finishing mill to obtain a finished billet, and the final rolling temperature of the finishing mill is controlled at 900-1000℃. The finished billet is coiled into a steel coil at a temperature of 650-750℃. During the coiling process, the fine-tuning feedback water at the very end of the shielded cooling system is used, and the first three sets of cooling manifolds are turned on for cooling. Only the front and rear sets of cooling side spray devices are turned on, while the rest are turned off. A hot-head control process of 25℃~35℃ is used for the preset area within 50 meters of the head and the preset area within 50 meters of the tail of the steel coil. Edge shielding technology is implemented on the cooling manifolds to regulate the cooling intensity at the edges of the strip. After the steel coil is quickly removed from the production line, it is placed in a slow cooling pit and cooled slowly for more than 2 days. When the temperature of the steel coil is below 50°C, it is then cross-cut.

2. The method according to claim 1, characterized in that, The phosphorus (P) content of the molten steel in the converter is ≤0.010% by mass. Argon gas is introduced for stirring during the LF refining process, with a flow rate of 0.3~0.5 m³ / h. 3 / (t·min), the vacuum degree of RH ultimate refining is ≤67Pa.

3. The method according to claim 1, characterized in that, During the continuous casting process, the casting speed is controlled at 0.8~1.4m / min, a low-flow cooling mode is adopted, and electromagnetic stirring is used. The thickness of the continuously cast slab is 200~240mm. Optionally, the specific water volume of the low-flow cooling mode is 0.8~1.2L / kg, the electromagnetic stirring current is 250~350A, the stirring frequency is 5~10Hz, and the cooling water temperature difference of the continuous casting crystallizer is controlled at 5~8℃.

4. The method according to claim 1, characterized in that, The total time the continuously cast slab spends in the heating furnace is 200-300 minutes. The heating furnace is divided into a preheating section, a heating section, and a soaking section. The temperature of the preheating section is controlled at 600-800℃, the temperature of the heating section is controlled at 1000-1150℃, and the temperature of the soaking section is the same as the furnace exit temperature.

5. The method according to claim 1, characterized in that, The descaling includes rough descaling and rough rolling body descaling. Rough rolling body descaling is only started in the first pass of rough rolling. The reduction in the first pass of rough rolling is 30~40mm, and the reduction in each subsequent pass decreases by 5~8mm. The heat preservation temperature of the hot rolling box is maintained at 950~1000℃.

6. The method according to claim 1, characterized in that, During the finishing rolling process, the inter-stand water and roll gap spray water are normally activated, except for the F6 stand which has side spray water activated at a pressure of 0.8~1.2MPa. The entire coil is rolled using an accelerating method, with an initial rolling speed of 1.2~1.5m / s and a final rolling speed of 3.0~3.5m / s, and a speed increase rate of 0.1~0.2m / (s). 2 ).

7. The method according to claim 1, characterized in that, The edge shielding technology is achieved using an arc-shaped guide plate made of high-temperature resistant stainless steel. The distance between the guide plate and the edge of the strip is 5~10mm, and the temperature fluctuation range controlled by the hot head is ≤±5℃.

8. The method according to claim 1, characterized in that, The lining material of the slow cooling pit is high-temperature resistant insulation cotton. The cooling rate of the temperature in the slow cooling pit from 600~700℃ to below 50℃ is ≤10℃ / h. After the steel coil is taken out of the slow cooling pit, it cools naturally to the target temperature.

9. The method according to claim 1, characterized in that, The cross-cutting includes cutting a 6-12 meter section at the head and tail of the steel coil. The inlet and outlet roll gaps are controlled to be greater than a preset thickness of the steel plate. After the head passes through, the roll gap value is adjusted to be equal to the steel plate thickness. Subsequent adjustments are made in real time according to the plate shape. Optionally, the preset thickness is 3 mm during the cross-cutting process. The working roll hardness of the cross-cutting straightener is HRC55-60, the straightening speed in the head area is 30-50 m / min, and the straightening speed is increased to 80-120 m / min after the head passes through.

10. The method according to claim 1, characterized in that, The high-carbon steel hot-rolled plate is a high-carbon steel hot-rolled plate with a carbon content of 0.6% to 1.0%.