A six-stand tandem cold rolling production method of wide 65Mn high carbon steel strip

Abstract

The application discloses a six-stand cold continuous rolling production method for wide 65Mn high-carbon steel strips, and aims at the problems of large strip deformation resistance and easy brittle fracture of welds, the method comprises the following steps: in the smelting and continuous casting stage, inclusion spheroidization is performed, and a dynamic light pressing device is used to apply a mechanical pressing amount to control low-multiple segregation; in the hot rolling and cooling stage, a U-shaped cooling mode is implemented to make the head and tail temperatures of the strip higher than the middle part; in the laser welding stage, the welding line energy is controlled, and post-welding heat treatment is performed to convert the microstructure of the strip weld into tempered sorbite; in the pickling stage, three-stage acid liquid concentration gradient pickling and dynamic matching of the strip passing speed are performed; in the cold continuous rolling stage, the expected value of the rolling force mutation of the strip weld when passing through the stand is calculated in advance, and the compensation amount of the tension and the correction value of the work roll bending force increment are fed forward to the stand; the application improves the cold plasticity of the material, offsets the rolling force fluctuation, prevents the strip from being broken, and guarantees the stability of the production process.

Description

Technical Field

[0001] This invention relates to the field of metallurgy and steel rolling technology, specifically to a six-stand cold continuous rolling production method for wide 65Mn high carbon steel strip. Background Technology

[0002] 65Mn high-carbon steel, due to its high proportion of carbon and manganese, possesses high yield strength, but exhibits high deformation resistance at room temperature and poor cold plasticity. In conventional smelting and continuous casting processes, center segregation and porous micropores easily form within the continuously cast slab. Simultaneously, during hot rolling and coiling processes, the head and tail of the strip are prone to premature hardening phase transformation due to faster natural heat dissipation. These structural defects, arising from the metallurgical origins of the material and temperature fluctuations during hot rolling, weaken the overall macroscopic plasticity of the strip, increasing the risk of strip breakage during subsequent high-pressure cold continuous rolling.

[0003] In the cold continuous rolling production process, laser welding is required to splice the head and tail of the strip steel to achieve continuous rolling. Due to the high carbon equivalent of 65Mn strip steel, under conventional welding processes and natural cooling conditions, the cooling rate of the strip steel weld and heat-affected zone is relatively fast. Its thermodynamic cooling trajectory will enter the martensitic phase transformation region, generating a high-hardness and extremely brittle martensitic structure. This microstructure results in large residual stress at the grain boundaries of the strip steel weld, leading to insufficient physical toughness in the weld area. During the large reduction deformation process of six-stand cold continuous rolling, brittle fracture is very likely to occur.

[0004] Furthermore, when the spliced ​​strip weld enters the cold continuous rolling mill, the microstructural differences between the strip base material and the strip weld can cause abrupt changes in macroscopic rheological resistance. Existing rolling control systems mainly rely on static tension distribution and basic roll gap settings, and cannot provide feedforward intervention for transient stress changes at the strip weld. Abrupt changes in rheological resistance can cause fluctuations in the rolling normal pressure between stands and cause disturbances and deflections in the work rolls. This equipment stress imbalance disrupts the uniformity of the strip's transverse thickness, easily causing local stress concentration in the rolling deformation zone, which in turn leads to transverse tearing of the strip when passing through the weld. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a six-stand cold continuous rolling production method for wide 65Mn high-carbon steel strip, aiming to solve the technical problem of strip breakage caused by large deformation resistance and microstructural stress concentration in the weld zone during the cold rolling stage of wide 65Mn high-carbon steel strip.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a six-stand cold continuous rolling production method for wide 65Mn high-carbon steel strip, comprising the following steps: The raw materials are provided, and the chemical composition and mass fraction of the raw materials are as follows: carbon: 0.64%~0.69%, silicon: 0.25%~0.35%, manganese: 0.95%~1.05%, chromium: 0.13%~0.20%, and controlled impurities P≤0.015% and S≤0.01%; In the smelting and continuous casting stages, the raw materials are smelted into molten steel. In the refining stage, a calcium treatment agent is added to the molten steel to react and achieve spheroidization of inclusions. Subsequently, the molten steel is injected into a continuous casting machine and drawn to form a continuous casting slab. A dynamic light reduction device below the crystallizer is used to apply mechanical reduction to the continuous casting slab during the solidification process to control low-magnification segregation. In the hot rolling and cooling stage, the continuously cast slab is heated and then rolled into strip steel in a hot continuous rolling mill. After rolling, the strip steel enters the laminar flow cooling zone, and the cooling water is adjusted to implement a U-shaped cooling mode so that the cooling temperature of the head and tail of the strip steel is higher than that of the middle of the strip steel. Then the strip steel is coiled up. During the laser welding stage, the coiled strip steel is uncoiled and fed into a fiber solid-state laser welding machine to splice the head and tail of the strip steel. The welding speed is controlled synchronously and the annealing inductor is turned on to perform post-weld heat treatment, which prolongs the cooling time of the strip steel weld and the local heat-affected zone, and transforms the microstructure of the strip steel weld area into tempered sorbite structure. During the pickling stage, the welded strip steel is continuously fed into a pickling tank group with a three-level acid concentration gradient. The threading speed is dynamically adjusted within the range of 60~150m / min according to the thickness of the iron oxide scale on the surface of the strip steel to control the residence reaction time of the strip steel in the pickling tank group, thereby removing the residual iron oxide scale on the surface of the strip steel. In the six-stand cold continuous rolling stage, the pickled strip enters the UCMW six-stand cold continuous rolling mill, which includes the first to sixth stands, for cold plastic deformation. Each stand from the first to the sixth stand rolls the strip according to a set basic reduction command and a progressively increasing tension distribution pattern between stands. Before the strip weld reaches the stand, the expected value of the rolling force mutation that will occur when the strip weld passes through each stand is calculated in advance. When the strip weld is about to enter any of the stands as the current stand, the front tension compensation and back tension compensation are added to the current stand in advance according to the expected value of the rolling force mutation, and the work roll bending force increment correction value is output to the work roll bending hydraulic cylinder of the current stand. This is combined with the intermediate roll shifting action to perform dynamic compensation for the weld. After being rolled on the sixth stand, the strip is coiled into finished products.

[0007] Furthermore, in the smelting and continuous casting stages, a calcium treatment process is implemented in the later stage of LF refining, feeding calcium wire or calcium-silicon wire into the molten steel that has completed deoxidation and alloying, controlling the non-metallic inclusion rating to level 1.0 or below; maintaining the superheat of the molten steel entering the crystallizer in the range of 15~25℃; the dynamic light reduction device includes multiple sector-shaped hydraulic cylinders, when the solidification heat transfer model calculates that the solidification phase fraction at the center of the continuously cast slab reaches the two-phase region range of 0.3 to 0.7, driving the sector-shaped hydraulic cylinders to apply a total mechanical reduction of 8mm to the continuously cast slab.

[0008] Furthermore, during the hot rolling and cooling stages, the furnace exit temperature of the continuously cast slab is controlled at 1210~1250℃, the initial rolling temperature is controlled at 1040~1080℃, and the final rolling temperature is controlled at 880~920℃. The U-shaped cooling mode implemented is as follows: the number and timing of the opening and closing of the cooling manifold spray valves are adjusted according to the surface temperature distribution of the strip. The cooling temperature of the head 20-meter area and the tail 20-meter area of ​​the strip is controlled to be 20~30℃ higher than that of the middle area of ​​the strip. The final coiling temperature is controlled at 600~640℃.

[0009] Furthermore, in the laser welding stage, the welding input power of the fiber solid-state laser welding machine is set to 5kW, and the welding travel speed is limited to 2.5m / min; the post-weld heat treatment power of the annealing inductor is set to 8-10kW; by combining the welding travel speed of 2.5m / min with the post-weld heat treatment power of 8-10kW, the actual cooling rate of the strip weld is limited to below the critical martensite cooling rate, which promotes the diffusion-type phase transformation of the supercooled austenite into the tempered sorbite structure.

[0010] Furthermore, in the pickling stage, the pickling tank group includes a No. 1 pickling tank, a No. 2 pickling tank, and a No. 3 pickling tank arranged sequentially along the strip's travel direction; the acid concentration in the No. 1 pickling tank is controlled at 60~75 g / L, the acid concentration in the No. 2 pickling tank is controlled at 100~125 g / L, and the acid concentration in the No. 3 pickling tank is controlled at 140~165 g / L; the acid temperature in the No. 1, No. 2, and No. 3 pickling tanks is uniformly maintained at 80~85℃. When the head or tail of the strip passes through the No. 1, No. 2, and No. 3 pickling tanks, the threading speed is adjusted to the lower limit of 60 m / min; when the middle of the strip passes through the No. 1, No. 2, and No. 3 pickling tanks, the threading speed is adjusted to the upper limit of 150 m / min. After the strip steel leaves the No. 3 acid tank, the residual acid liquid adhering to the surface of the strip steel is physically squeezed by rubber-coated squeezing rollers, and the surface wear of the rubber-coated squeezing rollers is controlled to be less than 5mm.

[0011] Furthermore, in the basic reduction command and gradually increasing tension distribution mode between stands in the six-stand cold continuous rolling stage, the reduction rate of the first stand is controlled in the range of 12%~12.5%, the reduction rate of the second stand is controlled in the range of 14.8%~15.5%, the reduction rate of the third stand is controlled in the range of 11.5%~13%, and the reduction rate of the sixth stand is controlled in the range of 2.1%~6.3%. The uncoiling unit tension at the entrance of the first stand is set to 6 kg / mm², the unit tension between the first and second stands is set to 6~10 kg / mm², the unit tension between the second and third stands is set to 8~13 kg / mm², the unit tension between the third and fourth stands is set to 10~15 kg / mm², the unit tension between the fourth and fifth stands is set to 11~16 kg / mm², and the unit tension between the fifth and sixth stands is set to 12~17 kg / mm².

[0012] Furthermore, the specific steps for calculating in advance the expected value of the sudden change in rolling force that will occur when the strip weld passes through each stand include: Obtain the static deformation resistance of the strip base material region and the local deformation resistance of the tempered sorbite structure in the strip weld region. Subtract the static deformation resistance from the local deformation resistance to obtain the deformation resistance difference at the current stand. The expected value of the sudden change in rolling force is equal to the product of the actual width of the strip, the square root of the product of the effective radius of the work roll after being flattened under load and the absolute reduction of the strip, and the deformation resistance difference.

[0013] Furthermore, the logic of pre-adding the pre-tension compensation amount and the post-tension compensation amount to the current rack includes: The forward tension compensation amount of the current stand is obtained by multiplying the pre-calibrated forward tension influence coefficient and the expected value of the rolling force mutation by the product of the actual strip width and the exit thickness of the strip when it leaves the current stand; the backward tension compensation amount of the current stand is obtained by multiplying the pre-calibrated backward tension influence coefficient and the expected value of the rolling force mutation by the product of the actual strip width and the entry thickness of the strip when it enters the current stand; when it is determined that the strip weld is about to reach the current stand and the time to reach it is 0.5 seconds, a command is sent to the AC variable frequency motor to superimpose the forward tension compensation amount and the backward tension compensation amount; after the strip weld leaves the current stand, the forward tension compensation amount and the backward tension compensation amount linearly and smoothly decay to zero within a 0.5-second time window.

[0014] Furthermore, the coordination logic between the work roll bending force increment correction value and the intermediate roll shifting action includes: The actual radius of the intermediate roll at any lateral coordinate is formed by superimposing the basic radius of the intermediate roll at the midpoint of the roll body with the first, second, and third compensation terms of the lateral coordinate with the midpoint of the roll body as the origin to form a topological roll profile curve. A static roll gap crown reference is established by adjusting the axial roll position of the intermediate roll. The work roll bending force increment correction value is obtained by multiplying the expected value of the rolling force mutation by the dynamic bending roll compensation coefficient. It is applied by the work roll bending hydraulic cylinder to offset the work roll disturbance deflection. After the strip weld exits the current stand, the work roll bending force increment correction value smoothly decays to the basic set value.

[0015] Furthermore, the six-stand cold continuous rolling stage also includes the implementation of lubrication cooling and parameter closed-loop control, the specific steps of which are as follows: An emulsion with a mass concentration of 2.5% to 4.0% and a supply temperature of 50 to 60°C is sprayed onto the work rolls of each stand. An infrared scanning thermometer collects real-time data on the surface temperature distribution of the strip along its width. The increase in the emulsion spray flow rate in a specific area is determined by the product of the local temperature deviation of the strip and a preset flow rate adjustment coefficient. An instruction to increase the valve opening is sent to the proportional adjustment valve at the corresponding width position. Before the strip is coiled after being rolled on the sixth stand, a high-pressure airflow is sprayed through a compressed air purging device to blow away the emulsion droplets on the surface of the strip.

[0016] This invention provides a six-stand cold continuous rolling production method for wide 65Mn high-carbon steel strip. It has the following beneficial effects: 1. This invention limits the cooling rate of the strip weld to below the critical martensite cooling rate by setting the linear energy input of the fiber solid-state laser welding machine and coordinating it with an annealing inductor to perform post-weld heat treatment. This technical feature induces a diffusion-type phase transformation of the supercooled austenite in the strip weld region, converting it into a fine-grained tempered sorbite structure. This eliminates residual stress at the grain boundaries of the strip weld, providing the wide 65Mn high-carbon steel strip with the physical toughness to withstand the large deformation of six-stand cold continuous rolling, and reducing the risk of brittle fracture of the strip through the weld.

[0017] 2. This invention introduces a dynamic feedforward compensation mechanism for weld seams based on microstructure differences in the six-stand cold continuous rolling stage. By calculating in advance the expected value of the rolling force mutation when the strip weld seam passes through each stand, the tension compensation amount is superimposed on the stand in advance, and the work roll bending force increment correction value is applied simultaneously. The above-mentioned coordinated compensation actions directly offset the rolling pressure fluctuation and work roll disturbance deflection caused by the sudden change in strip rheological resistance, maintain the uniformity of the strip transverse thickness in the rolling deformation zone, and prevent transverse tearing of the strip weld seam due to local stress concentration.

[0018] 3. This invention employs inclusion spheroidization and dynamic light reduction processes during the continuous casting stage, and implements U-shaped temperature control at the head and tail of the strip in the hot-rolled laminar cooling zone. Mechanical reduction displaces residual molten steel from the center of the continuously cast slab to close loose micropores, while controlled localized high-temperature cooling suppresses the premature hardening phase transformation of the high-carbon, high-manganese material in the head and tail regions of the strip. The combination of these process features improves the cold-state macroscopic plasticity of the strip from the material metallurgical source, providing a metal matrix with uniform microstructure and low segregation for subsequent continuous pickling and cold rolling processes. Attached Figure Description

[0019] Figure 1 This is a flowchart of the overall process of the production method of the present invention. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0021] Please see the appendix Figure 1 This invention provides a six-stand cold continuous rolling production method for wide 65Mn high-carbon steel strip, comprising: Raw materials: The following chemical composition by mass fraction: carbon: 0.64%~0.69%, silicon: 0.25%~0.35%, manganese: 0.95%~1.05%, chromium: 0.13%~0.20%, and controlled impurities P≤0.015%, S≤0.01%. Addressing the technical problem of high deformation resistance and brittle fracture of wide 65Mn high-carbon steel strip during cold rolling, this embodiment provides a multi-process collaborative production method. The overall process is as follows: During the smelting and continuous casting stages, a calcium treatment agent is added in the LF refining process to spheroidize inclusions in the molten steel, controlling the non-metallic inclusion rating to level 1.0 or below. The thickness of the continuously cast slab is set to 230 mm, and a dynamic light reduction device is installed below the crystallizer with a reduction amount of 8 mm to control low-magnification segregation. Regarding the physical distribution of the reduction roller system and the water distribution in the secondary cooling zone, those skilled in the art can make adaptive configurations based on the conditions of conventional continuous casting machines. The configuration of the physical distribution of the reduction roller system and the water distribution in the secondary cooling zone is a well-known technology in the field and will not be described in detail here.

[0022] During the hot rolling and cooling stages, the continuously cast slab enters the hot continuous rolling mill after exiting the heating furnace for multi-pass rolling. After rolling, the strip temperature control process is implemented. Specifically, a U-shaped cooling mode is implemented, that is, by adjusting the opening and closing sequence of the cooling water spray above the conveyor roller table, the cooling temperature of the head and tail 20 meters of the strip is 20-30°C higher than that of the middle of the strip. Finally, the coiling temperature is controlled at 600-640°C.

[0023] In the laser welding stage, after the strip is uncoiled, it is fed into a fiber solid-state laser welding machine for head-to-tail splicing. To avoid the formation of hard and brittle martensite in the 65Mn strip at the conventional welding cooling rate, this embodiment uses the method of controlling the input power of the fiber solid-state laser welding machine, the welding travel speed, and simultaneously activating the induction heating annealing module to extend the local cooling time of the strip weld and heat-affected zone. Through the matching of specific parameters, the microstructure of the strip weld area avoids the martensitic phase transformation zone and is transformed into fine-grained tempered sorbite, thereby reducing the hardness of the strip weld area and improving its toughness.

[0024] During the pickling stage, the welded strip steel is continuously fed into a group of pickling tanks with three levels of acid concentration gradient; the acid concentration of the first to the third pickling tank increases step by step, and the residual oxide scale on the surface of the strip steel is removed by a threading speed of 60~150m / min.

[0025] In the six-stand cold rolling stage, the strip enters the UCMW six-stand cold rolling mill. Large reduction is performed in the first three stands, and precise control of strip shape and thickness is performed in the last three stands. During this cold rolling process, to prevent strip breakage due to local deformation resistance differences in the weld area, a dynamic weld compensation mechanism is activated. The specific compensation steps include: Based on the microstructure differences between the strip base material zone and the strip weld zone, the expected value of the rolling force mutation that will occur when the strip weld passes through each stand is calculated in advance; the strip weld tracking signal is acquired, and when the tracking signal indicates that the strip weld is about to enter the current stand, the front tension compensation amount and the rear tension compensation amount are added to the current stand in advance according to the expected value of the rolling force mutation; simultaneously, the work roll bending force increment correction value is output to the bending roll actuator of the current stand, and in conjunction with the intermediate roll shifting action, a roll gap space is formed in the rolling deformation zone to adapt to the local stress changes of the strip weld; after the strip weld leaves the current stand, the tension compensation amount and the bending roll force increment correction value are controlled to smoothly decay to the basic set value; after the strip is rolled on the last stand, it is coiled and quality inspected.

[0026] To address the issue of microcracks and strip breakage that easily occur in wide 65Mn high-carbon steel strips during the subsequent high-pressure, six-stand cold rolling process, it is necessary to improve the material's plasticity by controlling the morphology of non-metallic inclusions and the segregation within the continuously cast slab before the cold rolling process. The specific process implementation steps are as follows: S110 involves the execution of primary refining in an electric arc furnace and refining in an LF furnace. After the raw materials are smelted in the electric arc furnace, the molten steel is transported to the LF refining furnace for secondary metallurgy. In the later stage of LF refining, a calcium treatment process is implemented, in which calcium wire or calcium silicon wire is fed into the deoxidized and alloyed steel at a constant rate. The free oxygen and sulfur elements in the molten steel react with the calcium elements, transforming the long strip-shaped manganese sulfide inclusions and the sharp-angled alumina inclusions in the molten steel into spherical calcium aluminate inclusions. With the bottom blowing argon gas stirring operation, the spherical inclusions are made to float to the top layer of steel slag, and the non-metallic inclusion rating of the final product is controlled to be 1.0 or below. For the power supply and slag-making control of the electric arc furnace and the conventional deoxidation and desulfurization operations of the LF furnace, those skilled in the art can configure them according to conventional metallurgical manuals. The relevant slag-making and deoxidation operations are well-known technologies in this field and will not be described in detail here.

[0027] S120 is used for continuous casting tundish temperature control; refined molten steel is injected into the tundish of the continuous casting machine. By adjusting the heating device or billet speed of the tundish, the superheat of the molten steel entering the crystallizer is maintained in the range of 15~25℃; limiting the superheat of the molten steel to the range of 15~25℃ can increase the proportion of equiaxed crystals in the central region of the continuously cast slab and reduce central segregation.

[0028] S130 executes dynamic light reduction and low-magnification defect control in continuous casting. After initial cooling in the crystallizer, molten steel is drawn to form a continuously cast slab with a thickness set at 230mm. The dynamic light reduction device includes multiple sector-shaped hydraulic cylinders. These sector-shaped hydraulic cylinders are arranged along the secondary cooling zone of the continuous casting machine. The drawing speed, slab thickness, and cooling water volume of each section of the secondary cooling zone are collected in real time. The solidification heat transfer model is used to calculate the solidification fraction inside the slab. When the solidification fraction at the center of the slab reaches the two-phase region range of 0.3 to 0.7, the cylinders are driven to activate the corresponding... The sector-shaped hydraulic cylinder within the effective range applies a total mechanical reduction of 8 mm to the continuously cast slab. The 8 mm physical deformation generated by the sector-shaped hydraulic cylinder can compensate for the volume solidification shrinkage caused by the transformation from liquid to solid phase inside the continuously cast slab. The mechanical extrusion action displaces the residual molten steel enriched with carbon and manganese elements in the center of the continuously cast slab, and closes the loose micropores in the center of the continuously cast slab. After the reduction operation is completed, the low-magnification C-type segregation of the continuously cast slab is controlled to level 1.5 or below, and the low-magnification defects are controlled to level 0.5 or below, thereby meeting the high-strength feeding requirements of the subsequent six-stand cold continuous rolling.

[0029] To address the issue of high carbon and manganese content in wide 65Mn high-carbon steel strip leading to easy hardening, and to provide raw materials with uniform microstructure before subsequent six-stand cold rolling, the microstructure evolution of the strip is controlled by regulating the temperature gradient along the strip's length during hot rolling. The specific process steps are as follows: In the heating and multi-pass hot rolling stages, the continuously cast slab prepared in the previous process is fed into a heating furnace for heating, with the furnace exit temperature controlled at 1210~1250℃. The slab then enters the hot continuous rolling mill, with the initial rolling temperature controlled at 1040~1080℃ and the final rolling temperature controlled at 880~920℃. High-temperature austenitization facilitates the solid solution of carbon and manganese elements. After hot rolling, the strip thickness is controlled between 2.1~2.5mm. The allocation of reduction schedules and roll speed matching between the roughing and finishing mills can be configured by those skilled in the art based on conventional hot continuous rolling mills; the relevant rolling procedures are well-known in the field and will not be elaborated upon here.

[0030] During the laminar flow cooling and U-shaped temperature control stages, the hot-rolled strip enters the laminar flow cooling zone and is cooled using a front-end centralized cooling mode. To meet the toughness requirements of the base material structure for the subsequent laser splicing process, a U-shaped cooling mode is implemented in the laminar flow cooling zone. Temperature measuring instruments acquire the surface temperature distribution of the strip along its length in real time, and adjust the number and timing of the opening and closing of the cooling manifold spray valves above and below the output roller table based on the surface temperature distribution of the strip. By changing the cooling water flow rate in local areas of the strip, the cooling temperature of the head 20-meter area and the tail 20-meter area of ​​the strip is controlled to be 20-30°C higher than that of the middle area of ​​the strip.

[0031] During the coiling and grain size control stage, the strip steel after U-shaped cooling enters the coiler, and the overall coiling temperature of the strip steel is controlled at 600~640℃. The head and tail of the strip steel are kept at a higher temperature. On the one hand, this compensates for the natural heat loss of the head and tail of the strip steel during the operation of the output roller table and the coiling operation, and prevents the 65Mn strip steel from undergoing a hardening phase transformation due to excessively rapid local cooling. On the other hand, the artificially created temperature gradient changes the phase transformation driving force of different sections of the strip steel, so that the base material areas of the head and tail of the strip steel that will be used for laser splicing have a stable thermodynamic basis. After the coiling operation is completed, the overall grain size of the strip steel reaches grade 8.0 or above, the microstructure is uniformly distributed and there is no obvious mixed crystal or banded structure, which meets the feeding requirements of subsequent continuous pickling and high-pressure continuous rolling of six stands.

[0032] To address the technical problem of strip breakage due to excessive hardness at the weld seam during the six-stand cold rolling process of wide 65Mn high-carbon steel strip, this embodiment implements a laser welding process based on the coordinated control of preheating and annealing before cold rolling; the specific process steps are as follows: During the strip head-to-tail splicing and preheating stage, the strip is uncoiled and fed into a fiber solid-state laser welding machine for head-to-tail splicing. Inside the fiber solid-state laser welding machine, along the strip's travel direction, a preheating inductor, a laser welding head, and an annealing inductor are arranged sequentially. After the strip is centered and clamped, the preheating inductor heats the area to be welded. The strip clamping and centered mechanism and the protective gas purging circuit of the fiber solid-state laser welding machine can be configured by those skilled in the art based on conventional fiber solid-state laser welding machines. Mechanical centeredness and gas protection operations are well-known technologies in the field and will not be elaborated upon here.

[0033] During the laser welding and line energy input stage, the laser welding head outputs a high-energy laser beam to perform penetration welding on the strip steel. To match the metallurgical characteristics of 65Mn strip steel, the welding input power of the fiber solid-state laser welding machine is set to 5kW. At the same time, the welding travel speed of the laser welding head is limited to 2.5m / min. By limiting the welding input power and welding travel speed, the welding line energy input to the strip steel weld is controlled. Maintaining a stable input of welding line energy can ensure the full fusion of the strip steel weld and avoid expanding the heat-affected zone due to excessive heat input.

[0034] During the post-weld heat treatment and microstructure transformation stage, the strip weld enters the working area of ​​the annealing inductor as the equipment operates; the annealing inductor is turned on simultaneously, and the post-weld heat treatment power of the annealing inductor is set to 8-10KW; 65Mn strip contains 0.64%~0.69% carbon and 0.95%~1.05% manganese. The high content of carbon and manganese causes the continuous cooling transformation curve of the strip to shift to the right; under conventional high-speed welding and natural cooling conditions, brittle lamellar martensite is easily generated at the strip weld, leading to cracking of the strip weld and strip breakage during subsequent cold continuous rolling.

[0035] In this embodiment, the low welding travel speed of 2.5 m / min is combined with the high-power post-weld heat treatment of 8-10 KW to reduce the cooling rate of the strip weld and heat-affected zone after welding. The slow cooling process changes the local thermodynamic cooling trajectory of the strip, so that the microstructure of the strip weld area avoids the martensitic phase transformation zone and is completely transformed into a fine-grained tempered sorbite structure. The tempered sorbite structure has toughness, which reduces the risk of micro-cracks at the strip weld and meets the rolling requirements of six-stand cold continuous rolling.

[0036] In the six-stand cold continuous rolling production process, the microstructure of the strip weld determines whether the strip can withstand high-pressure continuous rolling; the welding parameters of the fiber solid-state laser welding machine change the thermodynamic cooling trajectory of 65Mn strip, and the specific phase transformation control mechanism is as follows: During the austenitization and elemental solution stages, the temperature of the strip to be welded rises locally above the austenitization temperature under the high-energy focusing of the fiber solid-state laser welding machine. 0.64%~0.69% of the carbon and 0.95%~1.05% of the manganese in the 65Mn strip are completely dissolved in the austenite lattice at high temperatures. Due to the high content of carbon and manganese, the stability of austenite is increased, causing the continuous cooling transformation curve of the 65Mn strip to shift to the right. The principle of solid solution diffusion in the austenite lattice can be derived by those skilled in the art with reference to the theory of metal materials science. The principle of solid solution diffusion is a well-known technology in this field and will not be elaborated further here.

[0037] During the cooling rate control phase, the strip weld moves away from the laser welding head as the equipment operates and enters the working area of ​​the annealing inductor. Under natural cooling conditions, the strip weld transfers heat to the surrounding room-temperature base strip, experiencing a significant temperature gradient, with a cooling rate exceeding the critical martensite cooling rate. The cooling trajectory enters the martensitic transformation zone below the continuous cooling transformation curve, generating lamellar martensite with high hardness and poor toughness. To avoid martensitic transformation, the annealing inductor outputs 8-10KW of heat treatment power, forming a heating zone around the strip weld. The combination of a welding travel speed of 2.5m / min and 8-10KW of post-weld heat treatment power increases the dwell time of the strip weld within the annealing inductor heating zone and replenishes the heat lost by the strip weld.

[0038] During the microstructure phase transformation stage, the increase in residence time and the supplementation of heat limit the actual cooling rate of the strip weld to below the critical martensite cooling rate. The actual cooling trajectory of the strip weld changes, and the curve of the strip weld temperature decreasing with time no longer intersects with the martensite initiation line, but passes through the pearlite transformation zone of the continuous cooling transformation curve, which promotes the diffusion-type phase transformation of supercooled austenite.

[0039] Ultimately, the supercooled austenite at the strip weld transforms into a fine-grained tempered sorbite structure; the tempered sorbite structure eliminates the residual stress at the grain boundaries of the strip weld, providing sufficient toughness to withstand the large reduction deformation of the six-stand cold continuous rolling; the strip weld breakage rate is controlled, ensuring the stability of the six-stand cold continuous rolling production process for wide 65Mn high carbon steel strip.

[0040] After laser welding, the surface of the 65Mn strip still contains iron oxide scale generated during the hot rolling stage. After undergoing U-shaped cooling and laser welding thermal cycles, the iron oxide scale structure at the head, tail, and weld area of ​​the strip is relatively dense. In order to remove the iron oxide scale from the surface of the strip and provide an oxide-free metal matrix for subsequent six-stand cold continuous rolling, a three-stage gradient pickling process is implemented on the strip. The specific process steps are as follows: During the strip threading and acid temperature control stages, the welded strip is continuously fed into a continuous pickling unit. Inside the continuous pickling unit, three acid tanks (No. 1, No. 2, and No. 3) are arranged sequentially along the strip's travel direction. These tanks contain hydrochloric acid pickling solution. Graphite steam heaters and associated temperature sensors are installed inside each of the three acid tanks. The temperature sensors acquire the acid temperature and adjust the steam flow rate to the graphite steam heaters, maintaining the acid temperature in the three tanks at a uniform range of 80-85°C. Limiting the acid temperature to 80-85°C ensures the acid's chemical reaction rate while preventing excessive acid evaporation and over-pickling of the strip substrate.

[0041] In the three-stage gradient pickling and concentration control stage, the strip steel passes sequentially through the No. 1, No. 2, and No. 3 acid tanks with progressively increasing concentrations. The acid addition pipes and valves control the acid concentrations in the No. 1, No. 2, and No. 3 acid tanks. The acid concentration in the No. 1 acid tank is controlled at 60~75g / L, the acid concentration in the No. 2 acid tank is controlled at 100~125g / L, and the acid concentration in the No. 3 acid tank is controlled at 140~165g / L.

[0042] Due to the high carbon and manganese content of 65Mn strip steel, the strip matrix is ​​highly sensitive to hydrogen embrittlement. When the strip steel enters the first acid bath, the iron oxide scale on the surface is thick and relatively loose. At this time, using a low-concentration acid solution of 60~75g / L can prevent the acid from reacting too quickly with the strip surface and releasing excessive hydrogen gas, thus reducing the risk of hydrogen embrittlement caused by hydrogen penetration into the strip matrix. When the strip steel enters the second acid bath, the loose iron oxide scale on the surface has been peeled off, and a medium-concentration acid solution of 100~125g / L is used. The concentrated acid solution dissolves the inner layer of iron oxide scale. When the strip enters the No. 3 acid tank, the surface of the strip has residual bottom oxides as well as special oxides formed at the head, tail, and weld areas of the strip due to high-temperature cooling. At this time, a high-concentration acid solution of 140~165g / L is used to remove the residual oxides on the surface of the strip and expose the metal substrate of the strip. The stepped concentration configuration matches the concentration of the acid solution with the thinning state of the iron oxide scale on the surface of the strip, protecting the strip substrate while removing the iron oxide scale.

[0043] During the strip threading speed control and squeezing operation stage, the strip threading speed in the No. 1, No. 2, and No. 3 acid tanks is controlled between 60 and 150 m / min. The threading speed is dynamically adjusted according to the thickness of the iron oxide scale on the strip surface and the actual acid concentration in the No. 1, No. 2, and No. 3 acid tanks. When the iron oxide scale on the strip surface is thick or the acid concentration is low, the threading speed is reduced to prolong the pickling reaction time. When the iron scale is thin or the acid concentration is high, the strip threading speed is increased to prevent over-pickling. After the strip exits the No. 3 pickling tank, the residual acid adhering to the surface of the strip is physically squeezed by rubber-coated squeeze rollers. The surface wear of the rubber-coated squeeze rollers is controlled to be less than 5mm to ensure that the rubber-coated squeeze rollers apply uniform contact pressure to the surface of the strip and prevent the acid from being carried into the subsequent rinsing process. The surface of the strip after the three-stage gradient pickling is smooth, which meets the high-strength feeding requirements of the UCMW six-stand cold rolling mill.

[0044] In the continuous pickling process, to ensure that the iron oxide scale on the surface of the 65Mn strip is removed, and to avoid over-pickling or hydrogen embrittlement defects in the strip substrate, it is necessary to adjust and inspect parameters such as acid temperature, strip threading speed, and the condition of the rubber-coated squeeze rolls. The specific parameter adjustment and quality inspection steps are as follows: During the acid temperature control stage, the 65Mn strip steel contains high levels of carbon and manganese, making the strip steel matrix highly sensitive to temperature-induced changes in the pickling reaction rate. Platinum resistance temperature sensors are distributed inside the No. 1, No. 2, and No. 3 acid tanks, as well as in the acid circulation pipeline. These sensors collect the acid temperature in real time and send the data to the programmable logic controller (PLC). The continuous pickling unit is equipped with a heating actuator, which includes a graphite heat exchanger connected to the acid circulation pipeline and controls the entry of high-temperature steam into the graphite. The pneumatic regulating valve of the heat exchanger; when the platinum resistance temperature sensor detects that the acid temperature in the No. 1, No. 2, and No. 3 acid tanks is below 80°C, the programmable logic controller outputs an analog signal to open the pneumatic regulating valve, increasing the flow of high-temperature steam; when the acid temperature reaches 85°C, the opening of the pneumatic regulating valve is reduced; through continuous closed-loop control, the acid temperature in the No. 1, No. 2, and No. 3 acid tanks is stabilized in the range of 80~85°C, maintaining the stable dissolution capacity of the acid on the iron oxide scale on the strip steel surface.

[0045] During the strip threading speed adjustment stage, the residence time of the strip in the pickling tank directly determines the pickling quality. This residence time is determined by the threading speed of the tension rollers. The continuous pickling unit is equipped with a strip threading speed adjustment mechanism, which includes an AC variable frequency motor driving the front and rear tension rollers. Based on the U-shaped cooling mode implemented in the hot rolling process, the cooling temperature at the head and tail of the strip is higher than that in the middle, resulting in a greater iron oxide scale thickness at the head and tail than in the middle. When the strip enters the continuous pickling unit, the temperature is adjusted in real-time within the No. 1, No. 2, and No. 3 pickling tanks. The acid concentration data is used to send speed commands to the AC variable frequency motor. When the head or tail of the strip with a thicker iron oxide scale passes through the No. 1, No. 2, and No. 3 acid tanks, a command is sent to the AC variable frequency motor to adjust the threading speed to the lower limit of 60 m / min, extending the chemical reaction time between the strip surface and the acid. When the middle part of the strip with a thinner iron oxide scale passes through the No. 1, No. 2, and No. 3 acid tanks, the threading speed is adjusted to the upper limit of 150 m / min. The dynamically matched threading speed prevents local under-acidification or over-acidification of the 65Mn strip.

[0046] During the strip surface drying control stage, after the strip exits the No. 3 acid tank and rinsing tank, residual acid and cleaning water adhere to the strip surface. At the rinsing tank outlet, rubber-coated squeeze rollers are arranged in pairs along the strip's travel direction. Hydraulic cylinders provide clamping force to the rubber-coated squeeze rollers, ensuring they are tightly fitted to the upper and lower surfaces of the strip. To prevent uneven wear of the rubber-coated squeeze rollers from causing localized acid residue on the strip surface, displacement sensors monitor the roll gap closure of the rubber-coated squeeze rollers in real time, calculating the wear amount on the surface. When the surface wear of the rubber-coated squeeze rollers reaches 5mm, an early warning is issued and a roll replacement procedure is triggered. By controlling the surface wear of the rubber-coated squeeze rollers to less than 5mm, uniform contact pressure is applied along the strip width direction, preventing watermarks or rust spots from appearing on the strip surface.

[0047] During the strip surface quality inspection stage, before the strip enters the UCMW six-stand cold rolling mill, the surface of the strip is scanned by a surface quality inspection unit. The surface quality inspection unit includes a linear CCD camera and an image processing computer. The linear CCD camera captures the reflected light image of the strip surface, and the image processing computer compares it with the grayscale threshold of a normal metal substrate to identify whether there are residual unwashed iron oxide scale or pitting defects caused by over-pickling on the strip surface. The qualified clean strip enters the UCMW six-stand cold rolling mill to perform a high-pressure cold rolling process.

[0048] After continuous pickling, the 65Mn strip enters the UCMW six-stand cold rolling mill. Because the 65Mn strip contains high levels of carbon and manganese, it exhibits significant resistance to deformation during cold plastic deformation at room temperature. To ensure the strip is rolled to the target finished thickness without breakage, a basic reduction command is issued to each stand via a parameter allocation model. The specific parameter configuration is as follows: During the strip reduction distribution stage, the UCMW six-stand cold rolling mill is equipped with hydraulic reduction cylinders as reduction actuators. Based on the control logic of thinning in the front stand and shaping in the rear stand, and combined with the target finished thickness of the strip, displacement commands are issued to the hydraulic reduction cylinders of each stand. The first to third stands undertake the main thickness reduction task, with the reduction rate of the first stand controlled in the range of 12% to 12.5%, the reduction rate of the second stand controlled in the range of 14.8% to 15.5%, and the reduction rate of the third stand controlled in the range of 11.5% to 13%. The fourth to sixth stands perform precision control of strip shape and thickness, with the reduction rate of the fourth and fifth stands gradually decreasing, and the reduction rate of the sixth stand at the end controlled in the range of 2.1% to 6.3%.

[0049] The reduction rate of each stand is determined by dividing the difference between the entry thickness of the strip entering the stand and the exit thickness of the strip exiting the stand by the entry thickness of the strip entering the stand. The main reduction is concentrated in the first three stands of the six-stand cold rolling mill, when the strip enters the mill and the work hardening degree is relatively low. This utilizes the plasticity of the 65Mn strip in the initial stage and reduces rolling energy consumption. The smaller reduction in the last three stands restricts the lateral metal flow of the strip at the end of the rolling process, leaving room for adjustment of the strip shape and thickness.

[0050] During the tension distribution stage between stands, the six-stand cold rolling mill uses the AC variable frequency motors that drive the work rolls of the stands as the tension actuators between stands. As the strip undergoes work hardening during rolling, the deformation resistance of the strip gradually increases. A progressively increasing tension distribution mode between stands is established to reduce the normal rolling pressure in the deformation zone by utilizing tension. The specific parameters are configured as follows: the uncoiling unit tension at the entrance of the first stand is set to 6 kg / mm², the unit tension between the first and second stands is set to 6~10 kg / mm², the unit tension between the second and third stands is set to 8~13 kg / mm², the unit tension between the third and fourth stands is set to 10~15 kg / mm², the unit tension between the fourth and fifth stands is set to 11~16 kg / mm², and the unit tension between the fifth and sixth stands is set to 12~17 kg / mm².

[0051] The gradually increasing tension distribution from the inlet to the outlet of the six-stand cold rolling mill offsets the increase in rolling force caused by work hardening of the 65Mn strip. The increasing rear tension balances the transmission load between stands, preventing the rolling load of a single stand from exceeding the limit or the strip from breaking between stands. For the specific mechanical transmission structure and the closed-loop drive parameter settings of the AC variable frequency motor of the UCMW six-stand cold rolling mill, those skilled in the art can operate according to the transmission control manual of a conventional six-roll continuous rolling mill. The relevant mechanical transmission structure and the closed-loop drive parameters of the AC variable frequency motor are well-known technologies in the field and will not be described in detail here. During the rolling process of the strip receiving basic reduction and tension distribution, when the strip weld enters the six-stand cold rolling mill, a subsequent dynamic compensation command for the weld will be superimposed on the basic distribution value.

[0052] During the rolling process where the strip undergoes basic reduction and tension distribution, the strip weld enters the rolling deformation zone of a six-stand cold continuous rolling mill. After prior laser welding and annealing, the weld area of ​​the 65Mn strip transforms into tempered sorbite, while the base material retains its original microstructure. This difference in microstructure leads to different macroscopic rheological resistances between the strip weld and the base material during cold plastic deformation. To prevent strip breakage due to differences in rheological resistance when the strip weld enters the mill stand, the rheological resistance analysis and the expected value of the rolling force mutation are calculated before the strip weld reaches the mill stand. The specific calculation steps are as follows: In the analytical calculation stage of rheological resistance difference, the static deformation resistance of the 65Mn strip base material region and the local deformation resistance of the tempered sorbite structure in the strip weld region are obtained; the static deformation resistance of the strip base material region and the local deformation resistance of the strip weld region are pre-calibrated and stored by material tensile tests; the deformation resistance difference at the current stand is obtained by subtracting the static deformation resistance of the strip base material region from the local deformation resistance of the tempered sorbite structure in the strip weld region.

[0053] In the stage of calculating the expected value of the sudden change in rolling force of the weld seam, after obtaining the difference in deformation resistance, the additional rolling force load applied to the work rolls of the stand when the strip weld seam passes through the current stand is calculated in combination with the rolling parameters of the current stand. The expected value of the sudden change in rolling force caused by the strip weld seam passing through the current stand is equal to the product of the actual width of the strip, the square root of the product of the effective radius of the work roll after being flattened under load and the absolute reduction of the strip, and the difference in deformation resistance. The absolute reduction of the strip is obtained by subtracting the exit thickness of the strip from the inlet thickness of the strip entering the current stand.

[0054] The expected value of the sudden change in rolling force transforms the microstructure difference into an additional load benchmark for the current stand stress, providing calculation input conditions for subsequent implementation of dynamic tension compensation and bending roll force compensation between stands; for the effective radius of the work roll after being flattened under load, those skilled in the art can refer to the conventional elastic flattening calculation model for solution, the solution of the effective radius of the work roll after being flattened under load is a well-known technology in the field, and will not be elaborated here.

[0055] After obtaining the expected value of the sudden change in rolling force caused by the strip weld passing through the current stand, in order to eliminate the impact of the sudden change in rolling force on the stable operation of the strip, dynamic feedforward compensation is implemented on the front tension and back tension of the current stand. The specific execution logic and steps are as follows: During the tension compensation calculation stage, based on the expected value of the rolling force mutation, the front tension compensation and rear tension compensation of the current stand are calculated respectively. The front tension compensation and rear tension compensation are control increments for specific strip weld materials. The front tension compensation of the current stand is obtained by multiplying the pre-calibrated front tension influence coefficient and the expected value of the rolling force mutation by the actual width of the strip and the exit thickness of the strip when it leaves the current stand. The rear tension compensation of the current stand is obtained by multiplying the pre-calibrated rear tension influence coefficient and the expected value of the rolling force mutation by the actual width of the strip and the entry thickness of the strip when it enters the current stand. The front tension influence coefficient and the rear tension influence coefficient are fitted, calibrated and stored based on the previous 65Mn strip cold rolling test data. Through the calculation, the expected value of the rolling force mutation is converted into incremental control commands for the front and rear tensions of the current stand.

[0056] During the strip weld tracking and compensation triggering stage, the strip weld identification device installed at the entrance of the six-stand cold rolling mill and the length measuring encoder installed on the conveyor rollers collect the physical position of the strip weld in real time; the remaining time for the strip weld to reach each stand is calculated based on the strip threading speed; when it is determined that the strip weld is about to reach the current stand and the time to reach it is 0.5 seconds, the feedforward tension compensation command is triggered.

[0057] During the tension compensation execution and attenuation stage, the pre-tension compensation amount and post-tension compensation amount are sent to the AC variable frequency motor driving the work roll of the drive stand; the AC variable frequency motor superimposes the pre-tension compensation amount and post-tension compensation amount on the original basic tension setting value, increasing the strip tension in the rolling deformation zone; the increased strip tension offsets the rolling force fluctuation caused by the difference in the rheological resistance of the microstructure of the 65Mn strip weld, preventing the strip weld from wavy deformation or instantaneous strip breakage at the current stand.

[0058] When the strip weld seam passes the current stand and the length encoder indicates that the strip weld seam has left the current stand, a tension recovery command is sent to the AC variable frequency motor. The front tension compensation and the rear tension compensation are linearly and smoothly decayed to zero within a 0.5-second time window. The front tension and the rear tension of the current stand are restored to the basic tension set value. For the signal acquisition principle of the strip weld seam identifier and the torque control logic of the AC variable frequency motor, those skilled in the art can refer to the conventional cold rolling automation control manual for programming and configuration. The distance conversion of the length encoder and the motor torque control are well-known technologies in this field and will not be described in detail here.

[0059] While implementing dynamic feedforward tension compensation, the expected change in rolling force caused by the strip weld will cause elastic flattening and elastic bending of the rolls in the current stand; the elastic deformation of the rolls will cause changes in the roll gap shape between the work rolls, thus generating strip shape defects such as edge waves or center waves at the strip weld; in order to maintain the transverse thickness uniformity and strip shape straightness at the strip weld, the intermediate roll topology roll shifting and dynamic bending roll of the work rolls are coordinated to compensate. The specific parameter configuration and compensation logic are as follows: In the topology roll configuration and basic plate shape setting stage, the UCMW six-stand cold continuous rolling mill is equipped with an intermediate roll that can move along the axial direction; the outer surface of the intermediate roll is ground with a topology roll profile curve; the actual radius of the intermediate roll at any transverse coordinate is composed of the basic radius of the intermediate roll at the midpoint of the roll body, and the first term compensation, second term compensation, and third term compensation of the transverse coordinate with the midpoint of the roll body as the origin.

[0060] When the upper and lower intermediate rolls move in opposite directions along the axial direction, the topological roll profile curves of the upper and lower intermediate rolls are superimposed on each other. After the two cubic polynomial curves are superimposed, a parabolic roll gap convexity is formed between the work rolls. By adjusting the axial roll position of the intermediate rolls, the roll gap convexity required for rolling wide 65Mn high carbon steel strip is provided. Before the strip enters the current stand, the axial roll position of the intermediate rolls is locked at the target position according to the actual width of the strip, and a static roll gap convexity reference is established.

[0061] During the dynamic roll bending force compensation stage, the rolling force increases when the strip weld reaches the current stand. This increased rolling force disrupts the static roll gap crown reference. To counteract the additional roll bending caused by the increased rolling force, a work roll bending force increment correction value is issued to the work roll bending hydraulic cylinder of the current stand. This work roll bending force increment correction value is obtained by multiplying the expected value of the sudden change in rolling force by the dynamic roll bending compensation coefficient. The dynamic roll bending compensation coefficient is obtained through offline calibration or finite element simulation calculation of the UCMW six-stand cold continuous rolling mill, and a mapping relationship is constructed based on the current axial roll shifting position of the intermediate roll, pre-stored as a multidimensional data table.

[0062] The hydraulic cylinder of the work roll bending roll applies the work roll bending force increment correction value and applies a reverse bending moment at both ends of the work roll. The reverse bending moment cancels out the work roll disturbance deflection caused by the sudden change in rheological resistance at the strip weld, and maintains the roll gap space in the rolling deformation zone to adapt to the local stress change of the strip weld. After the strip weld leaves the current stand, the work roll bending force increment correction value and the tension compensation amount synchronously and smoothly decay to the basic set value. The coordinated compensation action ensures the transverse thickness accuracy and strip shape quality of the 65Mn high carbon steel strip when passing through the weld, and prevents transverse tearing and strip breakage due to local stress concentration at the strip weld.

[0063] In the six-stand cold continuous rolling process of wide 65Mn high-carbon steel strip, the strip undergoes cold plastic deformation, generating deformation heat and frictional heat in the rolling deformation zone. To reduce the frictional resistance in the rolling deformation zone and control the thermal expansion crown of the rolls, lubrication cooling and closed-loop parameter control are implemented during the rolling process. The specific process execution steps are as follows: In the lubricating and cooling fluid preparation and supply stage, emulsion is used as the lubricating and cooling medium; the mass concentration of the emulsion is configured to be 2.5%~4.0%, and the supply temperature of the emulsion is maintained at 50~60℃; by limiting the emulsion concentration and temperature within the range, a uniform lubricating oil film can be established between the strip surface and the work roll, providing the boundary lubrication conditions required for rolling with large reduction, and preventing thermal scratches or roll sticking defects on the strip surface.

[0064] During the multi-zone injection and flow closed-loop regulation stage, segmented multi-zone injection manifolds are arranged along the axial direction of each frame's work rolls; each injection section of the multi-zone injection manifold is independently connected to a proportional regulating valve; an infrared scanning thermometer installed at the frame outlet collects real-time data on the surface temperature distribution of the strip along its width; when the surface temperature of a local area of ​​the strip exceeds the set target temperature threshold, a valve opening increase command is sent to the proportional regulating valve at the corresponding width position.

[0065] The increase in emulsion spray flow rate in a specific area is determined by the product of the local temperature deviation of the strip and the preset flow rate adjustment coefficient. The local temperature deviation of the strip is obtained by subtracting the target temperature threshold from the actual surface temperature collected by the infrared scanning thermometer. The preset flow rate adjustment coefficient is calibrated by fitting the previous mill thermal balance test data and input in advance. Increasing the emulsion spray flow rate in a local area can specifically cool the local high-temperature area of ​​the work roll and prevent the work roll from uneven thermal expansion due to local overheating. The closed-loop regulation of the emulsion flow rate maintains the stability of the thermal crown of the work roll. Combined with the intermediate roll topology and dynamic bending roll compensation of the work roll, it ensures the flatness of the strip when passing through the weld and under conventional rolling conditions.

[0066] In the post-rolling purging and residual liquid recovery stage, after the strip leaves the sixth stand at the end, residual emulsion adheres to the upper and lower surfaces of the strip. The compressed air purging device sprays high-pressure airflow onto the strip surface to blow away the emulsion droplets. This removes the residual emulsion and prevents it from carbonizing at high temperatures during the subsequent strip annealing process, thus avoiding residual carbon spots on the strip surface. After purging, the strip enters the coiler for winding, completing the six-stand cold continuous rolling production process.

[0067] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for producing wide 65Mn high-carbon steel strip using a six-stand cold continuous rolling mill, characterized in that, Includes the following steps: The raw materials are provided, and the chemical composition and mass fraction of the raw materials are as follows: carbon: 0.64%~0.69%, silicon: 0.25%~0.35%, manganese: 0.95%~1.05%, chromium: 0.13%~0.20%, and controlled impurities P≤0.015% and S≤0.01%; In the smelting and continuous casting stages, the raw materials are smelted into molten steel. In the refining stage, a calcium treatment agent is added to the molten steel to react and achieve spheroidization of inclusions. Subsequently, the molten steel is injected into a continuous casting machine and drawn to form a continuous casting slab. A dynamic light reduction device below the crystallizer is used to apply mechanical reduction to the continuous casting slab during the solidification process to control low-magnification segregation. In the hot rolling and cooling stage, the continuously cast slab is heated and then rolled into strip steel in a hot continuous rolling mill. After rolling, the strip steel enters the laminar flow cooling zone, and the cooling water is adjusted to implement a U-shaped cooling mode so that the cooling temperature of the head and tail of the strip steel is higher than that of the middle of the strip steel. Then the strip steel is coiled up. During the laser welding stage, the coiled strip steel is uncoiled and fed into a fiber solid-state laser welding machine to splice the head and tail of the strip steel. The welding speed is controlled synchronously and the annealing inductor is turned on to perform post-weld heat treatment, which prolongs the cooling time of the strip steel weld and the local heat-affected zone, and transforms the microstructure of the strip steel weld area into tempered sorbite structure. During the pickling stage, the welded strip steel is continuously fed into a pickling tank group with a three-level acid concentration gradient. The threading speed is dynamically adjusted within the range of 60~150m / min according to the thickness of the iron oxide scale on the surface of the strip steel to control the residence reaction time of the strip steel in the pickling tank group, thereby removing the residual iron oxide scale on the surface of the strip steel. In the six-stand cold continuous rolling stage, the pickled strip enters the UCMW six-stand cold continuous rolling mill, which includes the first to sixth stands, for cold plastic deformation. Each stand from the first to the sixth stand rolls the strip according to the set basic reduction command and the gradually increasing tension distribution pattern between stands. Before the strip weld reaches the stand, the expected value of the rolling force change that will occur when the strip weld passes through each stand is calculated in advance. When the strip weld is about to enter any of the stands as the current stand, the front tension compensation amount and the back tension compensation amount are added to the current stand in advance according to the expected value of the rolling force change, and the work roll bending force increment correction value is output to the work roll bending hydraulic cylinder of the current stand. This is combined with the intermediate roll shifting action to perform dynamic compensation for the weld. After being rolled on the sixth stand, the strip steel is coiled into finished products.

2. The method for producing wide 65Mn high-carbon steel strip using a six-stand cold continuous rolling mill according to claim 1, characterized in that, During the smelting and continuous casting stages: In the later stage of LF refining, a calcium treatment process is implemented, in which calcium wire or calcium silicon wire is fed into the molten steel that has completed deoxidation and alloying, and the non-metallic inclusion rating is controlled to 1.0 or below. The superheat of the molten steel entering the crystallizer is maintained in the range of 15~25°C; The dynamic light reduction device includes multiple sector-shaped hydraulic cylinders. When the solidification heat transfer model is used to calculate that the solidification fraction at the center of the continuously cast slab reaches the two-phase region range of 0.3 to 0.7, the sector-shaped hydraulic cylinders are driven to apply a total mechanical reduction of 8 mm to the continuously cast slab.

3. The method for producing wide 65Mn high-carbon steel strip using a six-stand cold continuous rolling mill according to claim 1, characterized in that, During the hot rolling and cooling stages: The continuous casting slab exit temperature is controlled at 1210~1250℃, the initial rolling temperature is controlled at 1040~1080℃, and the final rolling temperature is controlled at 880~920℃. The U-shaped cooling mode implemented is as follows: the number of opening and closing of the cooling manifold spray valves and the opening sequence are adjusted according to the temperature distribution of the strip surface. The cooling temperature of the head 20-meter area and the tail 20-meter area of ​​the strip is controlled to be 20-30°C higher than that of the middle area of ​​the strip. The final coiling temperature is controlled at 600-640°C.

4. The method for producing wide 65Mn high-carbon steel strip using a six-stand cold continuous rolling mill according to claim 1, characterized in that, During the laser welding stage: The welding input power of the fiber solid-state laser welding machine is set to 5kW, and the welding travel speed is limited to 2.5m / min; The post-weld heat treatment power of the annealing inductor is set to 8-10KW; By combining a welding travel speed of 2.5 m / min with a post-weld heat treatment power of 8-10 KW, the actual cooling rate of the strip weld is limited to below the critical martensite cooling rate, which promotes the diffusion-type phase transformation of the supercooled austenite into the tempered sorbite structure.

5. The method for producing wide 65Mn high-carbon steel strip using a six-stand cold continuous rolling mill according to claim 1, characterized in that, During the pickling stage: The pickling tank group includes a No. 1 pickling tank, a No. 2 pickling tank, and a No. 3 pickling tank arranged sequentially along the strip's travel direction; the acid concentration in the No. 1 pickling tank is controlled at 60~75g / L, the acid concentration in the No. 2 pickling tank is controlled at 100~125g / L, and the acid concentration in the No. 3 pickling tank is controlled at 140~165g / L; the acid temperature in the No. 1, No. 2, and No. 3 pickling tanks is uniformly maintained at 80~85℃; When the head or tail of the strip passes through the No. 1 acid tank, the No. 2 acid tank, and the No. 3 acid tank, the strip threading speed is adjusted to the lower limit of 60m / min. When the middle of the strip passes through the No. 1 acid tank, the No. 2 acid tank, and the No. 3 acid tank, the strip threading speed is adjusted to the upper limit of 150m / min. After the strip steel leaves the No. 3 acid tank, the residual acid liquid adhering to the surface of the strip steel is physically squeezed by rubber-coated squeezing rollers, and the surface wear of the rubber-coated squeezing rollers is controlled to be less than 5mm.

6. The method for producing wide 65Mn high-carbon steel strip using a six-stand cold continuous rolling mill according to claim 1, characterized in that, In the basic reduction command and the gradually increasing tension distribution pattern between stands in the six-stand cold continuous rolling stage: The reduction rate of the first rack is controlled in the range of 12% to 12.5%, the reduction rate of the second rack is controlled in the range of 14.8% to 15.5%, the reduction rate of the third rack is controlled in the range of 11.5% to 13%, and the reduction rate of the sixth rack is controlled in the range of 2.1% to 6.3%. The unwinding unit tension at the first rack inlet is set to 6 kg / mm², the unit tension between the first and second racks is set to 6-10 kg / mm², the unit tension between the second and third racks is set to 8-13 kg / mm², the unit tension between the third and fourth racks is set to 10-15 kg / mm², the unit tension between the fourth and fifth racks is set to 11-16 kg / mm², and the unit tension between the fifth and sixth racks is set to 12-17 kg / mm².

7. The method for producing wide 65Mn high-carbon steel strip using a six-stand cold continuous rolling mill according to claim 1, characterized in that, The specific steps for calculating the expected sudden change in rolling force that will occur when the strip weld passes through each stand include: Obtain the static deformation resistance of the strip base material region and the local deformation resistance of the tempered sorbite structure in the strip weld region. Subtract the static deformation resistance from the local deformation resistance to obtain the deformation resistance difference at the current frame. The expected value of the sudden change in rolling force is equal to the product of the actual width of the strip, the square root of the product of the effective radius of the work roll after being flattened under load and the absolute reduction of the strip, and the difference in deformation resistance.

8. The method for producing wide 65Mn high-carbon steel strip using a six-stand cold continuous rolling mill according to claim 1, characterized in that, The logic for pre-adding the pre-tension compensation and post-tension compensation to the current rack includes: The current stand front tension compensation amount is obtained by dividing the product of the pre-calibrated front tension influence coefficient and the expected value of the rolling force mutation by the product of the actual strip width and the exit thickness of the strip exiting the current stand. The back tension compensation amount of the current stand is obtained by dividing the product of the pre-calibrated back tension influence coefficient and the expected value of the rolling force mutation by the product of the actual width of the strip and the entry thickness of the strip into the current stand. When it is determined that the strip weld is about to reach the current frame and the time to reach it is 0.5 seconds, a command is sent to the AC variable frequency motor to superimpose the front tension compensation amount and the rear tension compensation amount; after the strip weld leaves the current frame, the front tension compensation amount and the rear tension compensation amount linearly and smoothly decay to zero within a 0.5-second time window.

9. A method for producing wide 65Mn high-carbon steel strip using a six-stand cold continuous rolling mill according to claim 1, characterized in that, The coordination logic between the work roll bending force increment correction value and the intermediate roll shifting action includes: The actual radius of the intermediate roll at any lateral coordinate is composed of the basic radius of the intermediate roll at the midpoint of the roll body, and the superposition of the first, second, and third compensation terms of the lateral coordinate with the midpoint of the roll body as the origin. The static roll gap convexity reference is established by adjusting the axial roll position of the intermediate roll. The incremental correction value of the work roll bending force is obtained by multiplying the expected value of the sudden change in rolling force with the dynamic bending roll compensation coefficient. It is applied by the work roll bending hydraulic cylinder to counteract the work roll disturbance deflection. After the strip weld exits the current frame, the incremental correction value of the work roll bending force smoothly decays to the basic set value.

10. A six-stand cold continuous rolling production method for wide 65Mn high-carbon steel strip according to claim 1, characterized in that, The six-stand cold continuous rolling stage also includes the implementation of lubrication cooling and parameter closed-loop control, the specific steps of which are as follows: An emulsion with a mass concentration of 2.5% to 4.0% and a supply temperature of 50 to 60°C is sprayed onto the work rollers of each frame. The infrared scanning thermometer collects real-time surface temperature distribution data of the strip steel along the width direction. The increase in emulsion spray flow rate in a specific area is determined by the product of the local temperature deviation of the strip steel and the preset flow rate adjustment coefficient. The valve opening is increased by sending a command to the proportional control valve at the corresponding width position. Before the strip is coiled after being rolled on the sixth stand, a high-pressure airflow is sprayed through a compressed air purging device to blow away the emulsion droplets on the surface of the strip.

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