A method for producing a clad strip by a hot continuous rolling process and a clad strip

Abstract

A method for preparing a clad plate strip by adopting a hot continuous rolling process and the clad plate strip, which sequentially comprises: slab heating, rough rolling, clad blank preparation, clad rolling, controlled cooling and coiling; wherein the slab is subjected to surface polishing after phosphorus removal by rough rolling, then preliminarily clad with a to-be-clad plate strip, welded to form a clad blank, and then enters a finishing rolling unit for clad rolling; the slab surface polishing, to-be-clad coil preliminary cladding and welding are all carried out in an atmosphere protection cover, and N2, CO2 or mixed gas of the two is passed through the atmosphere protection cover; the slab is carbon steel; and the to-be-clad plate strip comprises titanium, copper or stainless steel. The present application adopts the hot continuous rolling process to produce the clad plate strip on line, and the clad plate strip combines the excellent properties of corrosion resistance, electrical conductivity, heat dissipation, beauty and high strength of the base plate, and realizes the maximum degree of lower cost and wider application range; the product has the characteristics of good corrosion resistance, heat dissipation performance, easy cold forming processing, beautiful appearance and coating-free.

Description

Technical Field

[0001] This invention relates to the field of coating material manufacturing, and specifically to a method for preparing coated strips using a hot continuous rolling process, and the coated strips themselves. Background Technology

[0002] With increasing demands for aesthetics, corrosion resistance, conductivity, and heat dissipation, single-material applications are insufficient to meet diverse performance requirements. Composite sheets, prepared from multiple metals using various processes, combine the advantages of multiple metals to meet the needs of engineering applications. Currently, common composite sheets include copper-clad, aluminum-clad, titanium-steel, and stainless steel-steel composites. Copper-clad sheets are composite strips formed by coating a copper layer onto the surface of steel strips, and structurally include both copper-steel and copper-steel-copper structures. Copper-clad, aluminum-clad, and titanium-clad sheets combine the strength of steel with the excellent heat dissipation, corrosion resistance, lightweight, conductivity, and aesthetics of copper, aluminum, and titanium, while significantly reducing costs. In particular, copper-clad materials combine the strength of steel with the lubricity and self-sealing properties of copper, and have been widely used in heat sinks, corrosion-resistant pipes, appliance panels, military applications, and electronic components.

[0003] In the field of clad sheet production, there are already many related patents or disclosed technologies. For example, Chinese Patent Publication No. CN101660087 discloses "an aluminum-steel-aluminum composite material and its preparation method", which involves surface treating aluminum and steel and then cold rolling them into high-precision aluminum strips and steel strips respectively, followed by cold rolling again into high-precision aluminum-steel-aluminum composite strips, and then annealing them at a temperature of 650-850℃ for 1-4 hours.

[0004] Chinese Patent Publication No. CN102019727 discloses "Aluminum-coated steel strip for coolers and its preparation method, and the steel strip and aluminum alloy strip used therein"; Chinese Patent Publication No. CN114248508B discloses "An aluminum-coated sheet and strip for kitchenware and its production method," which is an aluminum-coated sheet and strip with a tensile strength ≥320MPa and an elongation ≥28%. Both patents use conventional room temperature cold rolling lamination processes. After lamination and rolling, a bell-type annealing process is required within the range of 500-560℃ to obtain the desired steel-aluminum bonding performance. The production process is complex, including surface treatment of the coating layer and substrate, room temperature cold rolling, annealing, and leveling, not including the substrate production and preparation processes.

[0005] Chinese patent publication CN201645923U discloses "A Copper-Clad Copper Strip" and CN201721090U discloses "Copper-Carbon Steel Composite Plate." The former does not specify a method, only stipulating that the Cu content in the copper-clad strip is 5-20%; the latter involves cleaning the surfaces of copper and steel plates, stacking them together, heating, and then rolling, which is inefficient. This invention relates to a hot continuous rolling process for preparing clad materials and corresponding equipment. It achieves the preparation of clad strips during the production of hot-rolled steel coils, which is not only highly efficient but also eliminates subsequent processes such as uncoiling, pickling, slitting, cladding rolling, and annealing, resulting in lower costs. Furthermore, the width is consistent with conventional hot-rolled steel coils, significantly wider than clad strips prepared by existing processes. Currently, some copper-steel composite manufacturers produce copper-clad materials with a width not exceeding 200mm, primarily used in the production of cartridge cases and warheads for the military industry.

[0006] The Chinese patent publication CN105215536A discloses an "explosive welding method for titanium / aluminum / steel multilayer composite plates." This process is limited to the production of thick-gauge cladding materials, produced sheet by sheet, with no change in total thickness before and after lamination, resulting in low efficiency and limited production capacity. Furthermore, the cladding materials prepared by this process have poor sheet shape, generate significant noise during production, and are heavily dependent on weather conditions.

[0007] Chinese Patent Publication No. CN113106327B discloses a "High Corrosion-Resistant Strip Steel and its Manufacturing Method," which relates to a technology for preparing stainless steel-steel cladding materials by hot continuous rolling of composite billets. This technology involves complex billet assembly techniques, including surface pickling, polishing, welding, and vacuuming, followed by conventional hot continuous rolling processes to complete the strip steel production. The preparation process of the composite billet is complex and the production cost is high.

[0008] The comparison results show that current coating material preparation technologies mainly involve aluminum coating, copper coating, titanium-steel coating, and stainless steel-steel coating. These technologies suffer from problems such as cumbersome production processes, high costs, or narrow application widths. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing clad strip using a hot continuous rolling process, and the clad strip itself. This method utilizes a hot continuous rolling process to produce the clad strip online, which combines the excellent properties of the cladding, such as corrosion resistance, electrical conductivity, heat dissipation, and aesthetics, with the high strength of the substrate. This maximizes cost reduction and broadens the application range. The product is suitable for the production and processing of structural components in fields such as corrosion resistance, heat dissipation, electrical conductivity, or decoration. It features good corrosion resistance, heat dissipation performance, ease of cold forming, attractive appearance, and is paint-free.

[0010] To achieve the above objectives, the technical solution of the present invention is as follows:

[0011] A method for preparing clad strip using a hot continuous rolling process includes, in sequence: slab heating, rough rolling, cladding slab preparation, cladding rolling, controlled cooling, and coiling; wherein,

[0012] After rough rolling and descaling, the slab is surface-polished, then initially laminated and welded with the strip to be coated to form a coated slab, which is then put into the finishing mill for cladding rolling; the surface polishing of the slab, the initial lamination of the strip to be coated and the welding are all carried out in an atmosphere protection hood, which is filled with N2, CO2 or a mixture of the two.

[0013] The slab is made of carbon steel; the strip to be coated includes titanium, copper, or stainless steel.

[0014] Preferably, the strip to be coated is initially in contact with and bonded to the surface of the polished slab, and the front end of the strip to be coated is welded to the slab to form a coated blank.

[0015] The structure of the cladding strip includes single cladding and double cladding on both the upper and lower sides of the substrate.

[0016] Preferably, the material of the strip to be covered is copper, titanium, or stainless steel.

[0017] Preferably, the coating thickness in the coated strip does not exceed 10% of the total thickness of the coated strip.

[0018] Preferably, laser welding or resistance welding is used for welding.

[0019] Preferably, the atmosphere protection cover maintains a positive pressure relative to the outside. Preferably, the concentration of the protective gas inside the atmosphere protection cover is above 95% before the cladding blank enters the atmosphere protection cover.

[0020] Preferably, a temperature measuring device and an online heating device are installed before the clad billet enters the finishing mill. When the temperature of the clad billet is detected to be lower than the set finishing mill start temperature, the clad billet is immediately heated to replenish the temperature until the finishing mill start temperature is met. The heating method includes resistance radiation heating, electromagnetic induction heating or open flame heating.

[0021] Preferably, the slab is obtained through hot metal pretreatment, smelting, refining and casting; preferably, the smelting adopts a converter top and bottom combined blowing process.

[0022] Preferably, before preparing the cladding blank, the strip to be clad needs to be pre-treated to remove surface stains and ensure that there is no oil.

[0023] Furthermore, the slab heating temperature is above 1200℃, the roughing rolling end temperature is above 1000℃; the finishing rolling start temperature is 900~1010℃, the finishing rolling end temperature is 840~910℃, the post-rolling cooling rate is ≥30℃ / s, and the coiling temperature is 520℃~600℃.

[0024] Furthermore, the deformation amount in the roughing stage is controlled to be ≥80%, and the deformation amount in the finishing stage is controlled to be ≥70%.

[0025] Preferably, for substrates with a Ti content of 0.04% or more, a two-stage cooling process is adopted for post-rolling cooling. In the first stage, the substrate is cooled to 660±20°C at a cooling rate of ≥30°C / s, followed by air cooling for 1 to 8 seconds. Then, in the second stage, the substrate is cooled to 520 to 600°C at a cooling rate of ≥10°C / s before winding.

[0026] Preferably, when the material to be covered is copper, the finishing temperature RT of the rough rolling of the slab, i.e. the substrate, is controlled at 1000 to 1080°C.

[0027] Preferably, the chemical composition of the slab by weight percentage is: C: 0.04-0.11%, Si≤0.10%, Mn: 0.3-1.8%, P≤0.018%, S≤0.008%, Al: 0.01-0.04%, N≤0.005%, Ti: 0.01-0.15%; and Ca: 0.001-0.004%, B: 0.0005-0.003% are selectively added, with the balance being Fe and other unavoidable impurities.

[0028] This invention utilizes the combination of high-temperature slab and strip to be coated during hot continuous rolling, eliminating the need for pickling, slitting and annealing of the substrate in conventional coating material rolling, resulting in a shorter process and higher efficiency.

[0029] The key to the production of the clad sheet and strip described in this invention lies in achieving preliminary bonding between the cladding and the substrate between rough rolling and finish rolling to form a cladding blank. The key to the cladding material is its excellent interfacial bonding performance, ensuring that the cladding and substrate do not separate during subsequent processing.

[0030] At high temperatures, oxidation is inevitable in metallic materials, and the formation of an oxide layer severely deteriorates interfacial bonding, making cladding difficult. Hot continuous rolling temperatures are extremely high, generally above 800°C; while the rough rolling and even the billet heating temperatures before finishing rolling are even higher. Under such high temperatures, the key to cladding rolling is solving the high-temperature oxidation problem. To address the oxidation problem in hot continuous rolling cladding, this invention employs an atmosphere protection shield. The shield is filled with CO2, N2, or a mixture of both as a protective gas. During the preparation of the cladding billet, the concentration of the protective gas is controlled to be above 95%, thereby avoiding direct contact between the interface to be clad and O2 during the cladding process and solving the oxidation problem at high temperatures.

[0031] Besides high-temperature oxidation, preparing clad billets under hot continuous rolling requires surface treatment. Interfacial bonding involves two levels: physical bonding and metallurgical bonding. Physical bonding is generally mechanical interlocking with fewer bonding points and limited strength; while metallurgical bonding is atomic-level bonding with higher strength. Surface treatment during cladding rolling involves grinding the substrate surface to improve interfacial bonding strength. This removes oxide layers and stains, increases surface roughness, creates numerous sharp protrusions, and increases surface hardness. During the deformation process of rolling and cladding, the hardened surface layer breaks down, exposing the fresh substrate. The base layer and the cladding layer form atomic-level metallurgical bonds locally; simultaneously, the sharp protrusions increase the physical interlocking points between the base layer and the cladding layer, making it easier for them to improve interfacial bonding strength through mechanical interlocking. Therefore, this invention incorporates clad billet preparation equipment on the hot continuous rolling mill, including an online grinding device, which can treat the substrate surface before cladding to improve interfacial bonding strength.

[0032] Furthermore, the preparation of the clad billet requires careful selection of the appropriate operating position and timing based on the equipment and production characteristics of the hot strip mill, ensuring the preparation is completed without affecting normal hot strip mill production. Hot strip mill production includes processes such as billet heating, tapping, descaling, side pressing, rough rolling, finish rolling, and coiling. Of these processes, only the interval between rough rolling and finish rolling offers sufficient time and operating space. In other processes, the billet material is constantly in motion, making it inconvenient to stop, and the operating space is limited. Additionally, the temperature before rough rolling is generally above 1100℃ or even higher, resulting in an exponentially higher oxidation rate for the billet compared to other processes, making oxidation control extremely difficult. Moreover, the rough rolling deformation rate is generally low and does not meet the high deformation rate required for interfacial bonding. Therefore, this invention selects the interval between rough rolling and finish rolling to prepare the clad billet.

[0033] Online preparation of cladding blanks also requires consideration of the cladding material selection in conjunction with the hot continuous rolling production process. The hot continuous rolling mill process involves high temperatures, typically between 950-1100℃ before roughing and finishing. If the cladding material has a low melting point, it is prone to melting during cladding blank preparation, making cladding rolling impossible. Therefore, the melting point of the cladding material cannot be lower than 950℃. The cladding strips described in this invention primarily use Cu, Ti, and stainless steel, which have relatively high melting points, as cladding materials. Cu has a melting point of 1083℃, stainless steel has a melting point similar to the base material, and Ti has an even higher melting point of 1660℃.

[0034] This invention fully considers the oxidation control of the cladding interface at high temperatures, surface treatment, cladding billet preparation processes, and the characteristics of different cladding types. Combined with the production equipment and process characteristics of hot strip rolling mills, it has developed an online hot strip rolling preparation technology for clad sheets and coils. The production of clad sheets and strips can be achieved by supplementing existing hot strip rolling production line equipment with appropriate cladding billet preparation equipment.

[0035] The purpose of surface grinding after rough rolling and descaling of the slab is twofold: firstly, to remove the oxide layer on the surface, and secondly, to increase roughness and surface hardness, which is beneficial for improving the copper-steel bonding strength during the cladding rolling process. After high-temperature rolling deformation, the cladding slab achieves physical bonding between the strip to be clad and the substrate. During the high-temperature rolling and subsequent coiling and holding processes, the strip and substrate materials undergo interdiffusion, further enhancing the interfacial bonding strength. This results in a clad strip with excellent bonding performance.

[0036] The strip to be coated needs to undergo surface treatment (such as degreasing and cleaning) beforehand, primarily to remove surface stains, especially oil. Pre-polishing the surface can further improve the interfacial bonding strength. The strip to be coated can be made of copper, titanium, stainless steel, etc., selected according to specific requirements. After lamination and winding, the coated strip is rolled into a coil. It can also be further flattened and cut as needed to form the coated sheet.

[0037] The surface grinding of the slab, the initial application of the coating, and the laser welding are all carried out in an atmosphere protection chamber. The atmosphere protection chamber is filled with protective gases such as N2, CO2, or a mixture of the two, thereby reducing the oxidation of the intermediate slab at high temperatures and improving the bonding strength between the coating and the substrate.

[0038] In this invention, the coating materials, i.e., the strip to be coated, are Cu, Ti, and stainless steel. Stainless steel and Ti have melting points that are the same as or higher than the substrate, so there are no special requirements for temperature control; the hot rolling process of the substrate can be referenced based on performance requirements. However, Cu, with a melting point of only 1083℃, falls between the roughing and finishing temperature ranges of a hot rolling mill. Therefore, when the coating material is copper, attention needs to be paid to the temperature control of the substrate during the coating preparation process.

[0039] When the surface cladding material is copper, the rough rolling end temperature RT of the substrate should be controlled between 1000 and 1080℃. Too low a rough rolling end temperature will result in a too low finishing rolling end temperature, which on the one hand increases the deformation resistance of the copper-clad steel billet, increasing the mill load, and on the other hand reduces the cooling rate after finishing rolling, which is detrimental to fine grain strengthening and precipitation strengthening, leading to lower strength of the copper-clad strip. Too high a rough rolling end temperature will affect the copper-steel bonding strength, as the oxidation rate increases with higher temperatures. Although an atmosphere protection is provided, the higher the temperature, the more difficult the atmosphere protection becomes. Furthermore, since the melting point of copper is 1083℃, a rough rolling end temperature exceeding 1080℃ will cause localized melting of the copper strip surface, affecting the uniformity of the surface cladding thickness. Therefore, controlling the rough rolling end temperature RT between 1000 and 1080℃ is more appropriate. If the actual production rough rolling end temperature is too high, it is recommended to stop cooling on the roller table and wait until the temperature drops below 1080℃ before preparing the cladding billet.

[0040] In addition, to ensure the grain refinement effect of recrystallization to improve strength and toughness, the cumulative deformation in the rough rolling stage is required to be ≥80%; at the same time, to ensure the interfacial bonding strength between the cladding material and the substrate, the deformation in the finishing rolling stage is required to be ≥70%; and the cladding plate is required to be cooled intensively after exiting the mill to obtain a high cooling rate and achieve fine grain strengthening, with a cooling rate of ≥30℃ / s after finishing rolling.

[0041] Compared with existing processes, the hot continuous rolling online preparation process for cladding materials described in this invention achieves simultaneous cladding and rolling in conventional hot continuous rolling mills by supplementing them with online cladding billet preparation equipment. This eliminates the need for pickling, slitting, and annealing processes after cladding rolling of the substrate, simplifying the production process and resulting in higher production efficiency and lower costs. Furthermore, the hot continuous rolling process produces clad strips with wider widths, meeting the needs of more application areas.

[0042] Steel plates typically improve their strength through solid solution strengthening, precipitation strengthening, dislocation strengthening, and grain boundary strengthening. The slab described in this invention requires high strength, high formability, good interfacial bonding performance, and lower cost. The chemical composition of the steel (by weight percentage) is: C: 0.04-0.11%, Si≤0.10%, Mn: 0.3-1.8%, P≤0.018%, S≤0.008%, Al: 0.01-0.04%, N≤0.005%, Ti: 0.01-0.15%; with selective addition of 0.001-0.004% Ca, 0.0005-0.003% B, and the remainder being Fe and unavoidable impurity elements.

[0043] This invention relates to slab steel grades, achieving the desired high strength through rolling process control while ensuring the bonding strength between the cladding material and the slab. Mn provides solid solution strengthening, while C, in addition to solid solution strengthening, also exhibits phase transformation strengthening, and further enhances strength through carbide precipitation with Ti. Adding 0.001-0.004% Ca to the steel alters the sulfide morphology, suppresses the hot brittleness of S, and improves toughness. The selective addition of 0.0005-0.003% B is because in Ti-containing steel, B forms BN with N, which fixes and consumes N, thereby reducing the bonding between N and Ti and promoting the formation of more TiC from Ti and C, thus achieving better precipitation strengthening.

[0044] To fully utilize the precipitation strengthening effect of Ti, for slabs containing more than 0.04% Ti, the billet heating temperature should be above 1230℃, and a two-stage cooling process should be adopted for the finished rolled clad strip. Cooling should be paused for 1–8 seconds within the range of 640–680℃, where Ti exhibits optimal precipitation, thus promoting precipitation strengthening in the ferrite region. Subsequently, cooling should be accelerated to the coiling temperature for coiling to obtain higher clad strip strength. Excessive dwell time will increase production difficulty, reduce production efficiency, and form excessive ferrite structure, reducing strength.

[0045] The coated sheet obtained by the method of the present invention consists of a substrate and a coating, wherein the coating includes a single coating or a double coating on both the upper and lower surfaces of the substrate; the chemical composition of the substrate by weight percentage is: C: 0.04-0.11%, Si≤0.10%, Mn: 0.3-1.8%, P≤0.018%, S≤0.008%, Al: 0.01-0.04%, N≤0.005%, Ti: 0.01-0.15%; and Ca: 0.001-0.004%, B: 0.0005-0.003% are selectively added, with the balance including Fe and other unavoidable impurities.

[0046] Furthermore, the chemical composition of the substrate contains the remainder of Fe and other unavoidable impurities.

[0047] Preferably, the coating thickness in the coated strip does not exceed 10% of the total thickness of the coated strip.

[0048] The clad strip of the present invention has a yield strength of 355-850MPa, a tensile strength of 490-900MPa, an elongation of more than 12%, excellent cold forming performance, and meets the bending requirements of 180° and D=1a.

[0049] The width of the cladding strip described in this invention is 700–1800 mm.

[0050] Currently, coated steel sheets and strips are mainly produced using room temperature cladding rolling technology. Taking copper cladding as an example, the basic process flow is as follows: pickling of steel coils → slitting → cleaning and grinding of the surface to be coated on the strip → room temperature rolling → annealing → finishing and straightening (edge ​​trimming) → performance testing → delivery.

[0051] Compared with existing processes, the clad strip of this invention is produced using a hot continuous rolling process, which simultaneously achieves cladding and rolling on a conventional hot continuous rolling mill. This eliminates the need for pickling, slitting, and annealing of the substrate after cladding and rolling, resulting in higher production efficiency and lower costs. Moreover, the clad strip rolled by the hot continuous rolling process has a wider width, which can meet the needs of more application fields.

[0052] Existing coating material preparation technologies are complex, costly, or fail to meet the performance requirements of this invention. For example, explosive lamination is only applicable to thick plate products and has low production efficiency; while the hot rolling technology for preparing stainless steel-steel coating materials disclosed in Chinese patent CN113106327B involves a complex billet assembly process, which is lengthy and has high production costs.

[0053] Existing copper-clad laminates utilize copper's heat dissipation and electrical conductivity properties, primarily for military applications and electronic components. According to the "Standard for Copper-Steel Composite Plates for Bullets and Ammunition" (GJB1458B-2015), existing copper-clad substrates can be classified into two strength levels: 235MPa and 345MPa, with F11 and F18 steels being the main substrate materials. Copper-clad laminates prepared using existing copper cladding processes have a ferrite (F11) matrix or a ferrite and pearlite matrix with grain boundaries (F18), with substrate grain sizes mostly exceeding 10μm. This results in not only relatively low strength and performance but also low production efficiency, and widths are mostly below 200mm, making it difficult to meet the requirements of many application areas.

[0054] The clad strips with strength grades of 355–850 MPa prepared using the process described in this invention have a lamination rolling temperature exceeding 900°C. During such high-temperature deformation, the grains of the matrix material are constantly undergoing a deformation-recovery-recrystallization process, resulting in a sufficiently refined matrix microstructure. This microstructure refinement effect is preserved to room temperature during the rapid cooling process after finishing rolling, further refining the room-temperature microstructure and improving the strength and toughness of the material.

[0055] Furthermore, during the deformation process of the cladding strip, part of the deformation energy is converted into heat, promoting the diffusion of cladding atoms such as Cu and Ti, as well as elements like Cr and Ni in stainless steel, into the substrate. The diffusion of cladding atoms first occurs along the grain boundaries and then diffuses from the grain boundaries into the interior of the grains, inhibiting the growth behavior of substrate grains at high temperatures. This results in grain refinement, and the refinement effect is more pronounced closer to the cladding, thus achieving high strength.

[0056] This invention, based on a lower C-Mn content, combines controlled rolling and controlled cooling processes to ultimately obtain clad strips with yield strengths of 355–850 MPa and tensile strengths of 490–900 MPa, elongation exceeding 12%, and excellent cold-forming performance, meeting the requirements for 180° bending with D=1a. It also exhibits good interfacial bonding strength and stamping / stretching performance. It is suitable for manufacturing various structural components in corrosion-resistant, heat-dissipating, electronic, and decorative fields.

[0057] Compared with the prior art, the present invention has the following advantages:

[0058] 1. This invention employs a hot continuous rolling process to achieve online preparation of clad sheets and strips, which is particularly suitable for the online preparation of clad materials with high melting points, such as copper, titanium, and stainless steel. It can perform both single-sided and double-sided cladding, offering high efficiency and producing clad sheets with high bonding strength and good surface quality. Combined with specific substrate compositions, different strength and dimensional specifications can be obtained, and it also possesses excellent cold bending processing characteristics, which are difficult to achieve with existing clad sheet and strip preparation technologies.

[0059] 2. The online hot continuous rolling process for producing coated strips and sheets described in this invention is short, efficient, and low-cost. Compared with existing conventional room temperature lamination rolling processes, it eliminates pickling, slitting, and subsequent annealing heat treatment, significantly reducing production costs.

[0060] 3. The process described in this invention is simple, flexible, and easy to operate. The thickness and type of the cladding on the upper and lower surfaces of the laminated board rolls prepared using this process can be selected according to requirements, thereby enabling the production of multiple specifications and types of cladding materials on a single production line.

[0061] 4. The clad strip prepared using the process described in this invention exhibits better interfacial bonding performance. The clad material not only achieves initial physical bonding at the interface during rolling deformation, but also realizes interdiffusion of alloying elements between the cladding and the substrate during the high-temperature rolling and subsequent coiling and heat preservation processes, forming a metallurgical bond, thereby further improving the interfacial bonding strength. It also possesses excellent stamping and deep-drawing processing performance, high strength, and high surface quality, making it suitable for the fabrication and processing of structural components in fields such as corrosion resistance, heat dissipation, electronics, and decoration.

[0062] 5. The clad strip of this invention has low manufacturing cost and is easy to form and process. Its substrate adopts only a simple low C-Mn composition design, and high strength is obtained through Ti precipitation strengthening combined with the adjustment of the rolling process; and better corrosion resistance and heat dissipation performance are achieved through surface cladding. Compared with existing weathering steel, it has better corrosion resistance, and the surface cladding improves the cold working formability of the strip, which can meet the requirements of 1a and 180° cold bending.

[0063] 6. The coated strip produced using the process described in this invention possesses excellent corrosion resistance of the coating material (i.e., the strip to be coated, such as Cu, Ti, stainless steel, etc.), resulting in a longer service life. It also exhibits good appearance quality, allowing for use without painting and reducing coating costs. Furthermore, the coating thickness accounts for no more than 10% of the total thickness, leading to lower overall costs.

[0064] 7. The method described in this invention enables online preparation of cladding materials on a hot strip mill production line. Simultaneously, by utilizing controlled cooling and coiling of the cladding coil after rolling, cladding strips with different strengths and cladding specifications can be obtained. The cladding strips prepared by this method achieve a yield strength of 355–850 MPa, a tensile strength of 490–900 MPa, an elongation of ≥12% or even higher, and excellent plasticity, thus meeting the application requirements for higher strength. The cladding strips combine the comprehensive performance of the cladding and the substrate, while also offering high production efficiency and lower cost.

[0065] 8. The clad strips prepared using the process described in this invention are wider. Depending on the hot rolling mill, their width can reach 700–1800 mm, far exceeding the width of conventional clad strips which is less than 500 mm or even narrower. Furthermore, the width range can be further expanded according to the characteristics of the equipment, thereby meeting the needs of more application fields. Attached Figure Description

[0066] Figure 1 This is a schematic diagram of an embodiment of the method described in this invention. Detailed Implementation

[0067] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0068] The method for preparing clad strip using a hot continuous rolling process according to the present invention comprises, in sequence: slab heating, rough rolling, cladding slab preparation, cladding rolling, controlled cooling, and coiling; wherein,

[0069] After rough rolling and descaling, the slab is surface-polished, then initially laminated and welded with the strip to be coated to form a coated slab, which is then put into the finishing mill for cladding rolling; the surface polishing of the slab, the initial lamination of the copper coil to be coated and the welding are all carried out in an atmosphere protection hood, which is filled with N2, CO2 or a mixture of the two gases.

[0070] The slab is made of carbon steel; the strip to be coated includes titanium, copper, or stainless steel.

[0071] See Figure 1The upper and lower sheet metal strips 100 and 200 to be coated are located on the uncoilers 2 and 2' above and below the conveyor roller table 1, respectively. They are guided to the upper and lower surfaces of the slab 300 by the atmosphere protection hood 4 through hydraulic support plates 3 and 3'. The upper and lower sheet metal strips 100 and 200 to be coated and the conveyor roller table 1 are respectively equipped with uncoiling pressure rollers 5 and 5' and coating pressure rollers 6. The surface of the high-temperature slab 300 after rough rolling is ground by the grinding roller belt 7. The end of the grinding roller belt 7 is equipped with a dust collection device to remove the debris generated during grinding. Clean up promptly to avoid leaving any residue on the slab 300; a high-pressure descaling box 8 is installed in front of the grinding roller belt 7, and the intermediate slab of the high-temperature slab 300 is descaled again before grinding; the upper and lower strips to be coated 100 and 200 initially contact and adhere to the surface of the ground slab 300 under the action of the coating pressure roller 6, and the ends of the upper and lower strips to be coated 100 and 200 are welded to the slab 300 by the online welding machine 9 to obtain the coated steel billet; the coated steel billet is rolled by the finishing mill 10 to form the coated strip.

[0072] A temperature control system 11 is installed in front of the finishing mill 10. When the temperature of the clad steel billet is detected to be lower than the set finishing mill start temperature, the clad steel billet is immediately heated until the finishing mill start temperature is met.

[0073] Welding can be performed using laser welding or resistance welding, and can be moved synchronously with the cladding blank. The atmosphere protection system consists of a semi-enclosed atmosphere protection hood and an external gas supply device. The protective gas can be N2, CO2, or a mixture of both. It is required that the atmosphere protection hood maintains a positive pressure relative to the outside, and the concentration of the protective gas is controlled at above 95% to exhaust air and reduce oxidation.

[0074] The temperature control system consists of temperature feedback and online heating device. When the temperature of the cladding blank is too low, it will be heated to compensate for the temperature. The heating method can be resistance radiation heating, electromagnetic induction heating or open flame heating, depending on the cost and equipment characteristics.

[0075] The chemical composition of the substrate of the clad strip in this embodiment of the invention is shown in Table 1. Different specifications of copper strip, titanium strip, and stainless steel strip are selected for the cladding. The production process parameters of the embodiment are shown in Tables 2 and 3. During production, the billet heating temperature is controlled above 1200℃, the rough rolling end temperature is above 1000℃ (not exceeding 1080℃ when cladding with copper), the finish rolling start temperature is 900-1010℃, the finish rolling end temperature is 840-910℃, and the coiling temperature is 520-600℃. For substrates with a Ti content of 0.04% or higher, the intermediate cooling stop temperature is controlled at 640-680℃ and held for 1-8 seconds. The deformation amount during rough rolling is required to be ≥80%, the deformation amount during finish rolling is required to be ≥70%, and the post-rolling cooling rate is required to be ≥30℃ / s. The cladding thickness accounts for ≤10% of the strip thickness.

[0076] Coated strips with thicknesses ranging from 2.0 to 8.0 mm and surface coating thicknesses ranging from 45 to 357 μm were prepared. For ease of description, the upper and lower coatings in the examples are of equal thickness. In actual production, different coating thicknesses can be selected for the upper and lower surfaces according to requirements. The final product thickness can also be further adjusted according to user needs and rolling mill capacity. The product performance is shown in Table 4.

[0077] According to the substrate steel composition design range and rolling process control method described in this invention, the yield strength of the clad strip in the embodiments reaches 355-850 MPa, the tensile strength reaches 490-900 MPa, the elongation is ≥12%, the width is 700-1800 mm, and it has good plasticity. The clad strip has good interfacial bonding performance and surface quality, and excellent cold bending processing performance, adapting to the cold forming requirements of structural components in corrosion resistance, heat dissipation, electronics, and decoration fields. The process involved in this invention can produce wide, high-strength clad strips of different specifications as needed, with good appearance, achieving a paint-free application effect, reducing painting processes and costs. The cladding thickness and type are selected according to the operating conditions, resulting in lower overall costs.

[0078] Furthermore, the specifications, types, and varieties of coatings mentioned above are merely illustrative examples. For ease of description, the upper and lower coatings in the embodiments are of equal thickness. In practical applications, appropriate production processes can be used to combine coatings of different thicknesses with the substrate according to actual needs, thereby producing more coating strips that meet the requirements. In addition to Ti, other reinforcing elements such as Nb, V, and Mo can also be selected as needed for the substrate.

[0079] Table 1. Substrate chemical composition (wt%) of the clad sheet strip in the embodiments

[0080] Example 1 0.078 0.031 0.31 0.0120 0.0063 0.025 0.0028 0.014 - - Example 2 0.069 0.029 0.41 0.0138 0.0061 0.035 0.0029 0.024 - - Example 3 0.041 0.075 0.74 0.0091 0.0031 0.013 0.0028 0.037 0.0028 - Example 4 0.056 0.075 0.71 0.0082 0.0078 0.028 0.0041 0.039 0.0020 - Example 5 0.075 0.092 0.80 0.0177 0.0021 0.040 0.0050 0.081 0.0037 - Example 6 0.081 0.029 0.680 0.0098 0.0031 0.039 0.0041 0.057 0.0028 - Example 7 0.064 0.043 1.79 0.0096 0.0006 0.029 0.0013 0.122 0.0025 0.0029 Example 8 0.108 0.049 1.23 0.0195 0.0015 0.036 0.0014 0.144 0.0013 0.0006

[0081] Table 2 Process parameters for the production of coated sheet and strip

[0082]

[0083]

[0084] Table 3 Process parameters for the production of coated sheet and strip

[0085]

[0086] Table 4 Mechanical Properties of Coated Strips

[0087]

[0088]

Claims

1. A method for preparing clad strip using a hot continuous rolling process, characterized in that, sequentially... include: Slab heating, rough rolling, clad slab preparation, cladding rolling, controlled cooling, and coiling; among these processes... After rough rolling and descaling, the slab is surface-polished, then initially clad and welded with the strip to be clad to form a clad slab, which is then put into the finishing mill for cladding rolling; the surface polishing of the slab, the initial cladding and welding of the strip to be clad are all carried out in an atmosphere protection hood, which is filled with N2, CO2 or a mixture of the two gases. The slab is made of carbon steel; the strip to be coated includes titanium, copper, or stainless steel. The slab heating temperature is above 1200℃, the rough rolling end temperature is above 1000℃; the finish rolling start temperature is 900~1010℃, the finish rolling end temperature is 840~910℃, the post-rolling cooling rate is ≥30℃ / s, and the coiling temperature is 520℃~600℃.

2. The method for preparing clad strip using a hot continuous rolling process as described in claim 1, characterized in that, The strip to be coated is initially in contact with and bonded to the surface of the polished slab, and the front end of the strip to be coated is welded to the slab to form a coated blank.

3. The method for preparing clad strip using a hot continuous rolling process as described in claim 1 or 2, characterized in that, The structural types of the cladding strip include single cladding and double cladding on both the upper and lower surfaces of the substrate.

4. The method for preparing clad strip using a hot continuous rolling process as described in claim 1 or 2, characterized in that, The coating thickness in the coated strip does not exceed 10% of the total thickness of the coated strip.

5. The method for preparing clad strip using a hot continuous rolling process as described in claim 3, characterized in that, The coating thickness in the coated strip does not exceed 10% of the total thickness of the coated strip.

6. The method for preparing clad strip using a hot continuous rolling process as described in claim 1 or 2, characterized in that, Welding is performed using laser welding or resistance welding.

7. The method for preparing clad strip using a hot continuous rolling process as described in claim 1, characterized in that, The atmosphere protection shield maintains a positive pressure relative to the outside.

8. The method for preparing clad strip using a hot continuous rolling process as described in claim 7, characterized in that, Before the clad preform enters the atmosphere protection hood, the concentration of the protective gas inside the atmosphere protection hood is above 95%.

9. The method for preparing clad strip using a hot continuous rolling process as described in claim 1, characterized in that, Temperature measuring devices and online heating devices are installed before the clad billet enters the finishing mill. When the temperature of the clad billet is detected to be lower than the set finishing mill start temperature, the clad billet is immediately heated until the finishing mill start temperature is met. The heating methods include resistance radiation heating, electromagnetic induction heating or open flame heating.

10. The method for preparing clad strip using a hot continuous rolling process as described in claim 1, characterized in that, The slab is obtained through molten iron pretreatment, smelting, refining and casting.

11. The method for preparing clad strip using a hot continuous rolling process as described in claim 10, characterized in that, The smelting process employs a converter top and bottom combined blowing process.

12. The method for preparing clad strip using a hot continuous rolling process as described in claim 1, characterized in that, Before preparing the cladding blank, the strip to be clad needs to be surface treated to remove surface stains.

13. The method for preparing clad strip using a hot continuous rolling process as described in claim 1, characterized in that, When the material to be covered is copper, the finishing temperature of the rough rolling of the slab is controlled at 1000~1080℃.

14. The method for preparing clad strip using a hot continuous rolling process as described in claim 1 or 13, characterized in that, The deformation amount in the roughing stage should be ≥80%, and the deformation amount in the finishing stage should be ≥70%.

15. The method for preparing clad strip using a hot continuous rolling process as described in claim 1 or 13, characterized in that, For substrates with a Ti content of 0.04% or higher, a two-stage cooling process is adopted for post-rolling cooling. In the first stage, the substrate is cooled to 660±20℃ at a cooling rate of ≥30℃ / s, followed by air cooling for 1~8s. Then, in the second stage, the substrate is cooled to 520~600℃ at a cooling rate of ≥10℃ / s before winding.

16. The method for preparing clad strip using a hot continuous rolling process as described in claim 14, characterized in that, For substrates with a Ti content of 0.04% or higher, a two-stage cooling process is adopted for post-rolling cooling. In the first stage, the substrate is cooled to 660±20℃ at a cooling rate of ≥30℃ / s, followed by air cooling for 1~8s. Then, in the second stage, the substrate is cooled to 520~600℃ at a cooling rate of ≥10℃ / s before winding.

17. The method for preparing clad strip using a hot continuous rolling process as described in claim 1, 10, 11, 12, or 13, characterized in that, The chemical composition of the slab by weight percentage is as follows: C: 0.04~0.11%, Si≤0.10%, Mn: 0.3~1.8%, P≤0.018%, S≤0.008%, Al: 0.01~0.04%, N≤0.005%, Ti: 0.01~0.15%; and Ca: 0.001~0.004%, B: 0.0005~0.003% are selectively added, with the balance being Fe and other unavoidable impurities.

18. The method for preparing clad strip using a hot continuous rolling process as described in claim 14, characterized in that, The chemical composition of the slab by weight percentage is as follows: C: 0.04~0.11%, Si≤0.10%, Mn: 0.3~1.8%, P≤0.018%, S≤0.008%, Al: 0.01~0.04%, N≤0.005%, Ti: 0.01~0.15%; and Ca: 0.001~0.004%, B: 0.0005~0.003% are selectively added, with the balance being Fe and other unavoidable impurities.

19. The method for preparing clad strip using a hot continuous rolling process as described in claim 15, characterized in that, The chemical composition of the slab by weight percentage is as follows: C: 0.04~0.11%, Si≤0.10%, Mn: 0.3~1.8%, P≤0.018%, S≤0.008%, Al: 0.01~0.04%, N≤0.005%, Ti: 0.01~0.15%; and Ca: 0.001~0.004%, B: 0.0005~0.003% are selectively added, with the balance being Fe and other unavoidable impurities.

20. The method for preparing clad strip using a hot continuous rolling process as described in claim 16, characterized in that, The chemical composition of the slab by weight percentage is as follows: C: 0.04~0.11%, Si≤0.10%, Mn: 0.3~1.8%, P≤0.018%, S≤0.008%, Al: 0.01~0.04%, N≤0.005%, Ti: 0.01~0.15%; and Ca: 0.001~0.004%, B: 0.0005~0.003% are selectively added, with the balance being Fe and other unavoidable impurities.

21. A coated sheet obtained by the method according to any one of claims 1, 10-20, characterized in that, It includes a substrate and a coating; the coating includes a single coating or a double coating on both sides of the substrate; the chemical composition of the substrate by weight percentage is: C: 0.04~0.11%, Si≤0.10%, Mn: 0.3~1.8%, P≤0.018%, S≤0.008%, Al: 0.01~0.04%, N≤0.005%, Ti: 0.01~0.15%; and selectively adds Ca: 0.001~0.004%, B: 0.0005~0.003%, with the balance including Fe and other unavoidable impurities.

22. The cladding strip as described in claim 21, characterized in that, The chemical composition of the substrate is in the balance of Fe and other unavoidable impurities.

23. The cladding strip as described in claim 21 or 22, characterized in that, The coating thickness in the coated strip does not exceed 10% of the total thickness of the coated strip.

24. The cladding strip as described in claim 21 or 22, characterized in that, The clad sheet has a yield strength of 355~850MPa, a tensile strength of 490~900MPa, an elongation of over 12%, excellent cold forming performance, and meets the bending requirements of 180° and D=1a.

25. The cladding strip as described in claim 23, characterized in that, The clad sheet has a yield strength of 355~850MPa, a tensile strength of 490~900MPa, an elongation of over 12%, excellent cold forming performance, and meets the bending requirements of 180° and D=1a.

26. The cladding strip as described in claim 21 or 22, characterized in that, The width of the cladding strip is 700~1800mm.

27. The cladding strip as described in claim 23, characterized in that, The width of the cladding strip is 700~1800mm.

28. The cladding strip as described in claim 24, characterized in that, The width of the cladding strip is 700~1800mm.

29. The cladding strip as described in claim 25, characterized in that, The width of the cladding strip is 700~1800mm.

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