Metal plate strip full-continuous short-process production method

Abstract

A full-continuous short-process production method for a metal plate strip comprises the steps of smelting, tundish induction heating, thin strip continuous casting, rolling, 1 # flying shearing, cooling after rolling, acid-free descaling, 2 # flying shearing and strip steel coiling, and a steel coil without oxide scale on the surface is obtained. The metal plate strip comprises the following components in percentage by weight: 0.01-0.06% of C, less than or equal to 0.15% of Si, less than or equal to 0.85% of Mn, less than or equal to 0.02% of P, less than or equal to 0.005% of S and Alslt; 0.001%, less than or equal to 0.0050% of Ca, and the balance Fe and other unavoidable impurities. The method comprises the following steps: carrying out on-line hot rolling on a cast strip cast by double rollers through an on-line six-roller mill, and carrying out an acid-free descaling process to obtain a steel coil without oxide scale on the surface. Products produced through the method are high in ductility, good in forming performance and high in surface quality, and the purpose that cold is replaced by hot in the field of high-end products can be truly achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of thin strip continuous casting, and in particular to a fully continuous short-process production method for metal strips. Background Art

[0002] Traditional thin strip steel is mostly produced by continuous rolling of ingots with a thickness of 70-200mm through multiple passes. The traditional hot rolling process is: continuous casting + ingot reheating and insulation + rough rolling + finishing rolling + cooling + coiling. That is, first, ingots with a thickness of about 200mm are obtained through continuous casting. After the ingots are reheated and kept warm, rough rolling and finishing rolling are performed to obtain steel strips with a thickness generally greater than 2mm. Finally, the steel strips are laminar cooled and coiled to complete the entire hot rolling production process. If steel strips with a thickness of less than 1.5mm (inclusive) are to be produced, it is relatively difficult and usually the hot-rolled steel strips must be subsequently cold rolled and annealed to complete the process. In addition, the process is long, energy consumption is high, multiple units and equipment are required, and infrastructure costs are high, resulting in high production costs.

[0003] The thin slab continuous casting and rolling process is as follows: continuous casting + soaking and hot rolling + cooling + coiling. The main differences between this process and traditional processes are: the thin slab process significantly reduces the thickness of the cast slab to 50-90mm. Due to its thinness, the cast slab only needs one or two rough rolling passes (for slabs with a thickness of 70-90mm) or no rough rolling (for slabs with a thickness of 50mm). In contrast, the traditional continuous casting process requires repeated rolling passes to reduce the cast slab to the required specifications before finishing rolling. Furthermore, the cast slab does not undergo cooling but directly enters the soaking furnace for soaking and holding, or a small amount of supplementary heating. Therefore, the thin slab process significantly shortens the process flow, reduces energy consumption, reduces investment, and thus reduces production costs. However, the faster cooling rate during continuous casting and rolling of thin slabs leads to increased steel strength and yield ratio, thereby increasing the rolling load. As a result, the thickness specification of the economically produced hot-rolled products cannot be too thin, generally ≥1.5mm, see Chinese patents CN200610123458.1, CN200610035800.2 and CN200710031548.2.

[0004] The recently emerging headless thin slab continuous casting and rolling process (ESP) is an improvement on the semi-headless thin slab continuous casting and rolling process. ESP achieves headless rolling during slab casting, eliminating the need for flame cutting and the heating furnaces used for heat preservation and slab transfer. This significantly reduces the total length of the production line to approximately 190 meters. Slabs cast by the continuous caster range from 90-110 mm thick and 1100-1600 mm wide. The cast slabs pass through an induction heated roller conveyor for heat preservation and heat preservation before undergoing roughing, finishing, layer cooling, and coiling to produce hot-rolled plates. This headless rolling process allows for hot-rolled plates as thin as 0.8 mm, expanding the range of hot-rolled plate specifications. Furthermore, a single production line can produce up to 2.2 million tons per year. This process is rapidly developing and expanding, with several ESP production lines currently in operation worldwide.

[0005] A shorter process than thin slab continuous casting and rolling is thin strip casting and rolling. Thin strip casting is a cutting-edge technology in metallurgy and materials research, with a history of over 160 years since Henry Bessemer proposed the idea in 1865 (U.S. Patent 49053). However, due to the immaturity of related technologies such as manufacturing and control, the technology remained largely stagnant. It wasn't until the mid-20th century that it was realized in the continuous casting and rolling of aluminum, which rekindled its appeal in the steelmaking industry. Its emergence has revolutionized the steel industry, transforming the traditional steel strip production process in the metallurgical industry by integrating continuous casting, rolling, and even heat treatment processes. This allows thin strip blanks to be formed into thin steel strip in a single, online hot rolling process. This significantly simplifies the production process from molten steel to steel strip and shortens the production cycle. With a process line length of only approximately 50 meters, the steel production process is more compact, continuous, efficient, and environmentally friendly. This also reduces equipment investment and significantly lowers production costs, making it a low-carbon, environmentally friendly hot-rolled thin strip production process. Consequently, thin strip continuous casting technology has become a hot topic for development in countries around the world in recent years.

[0006] The typical process flow of the existing twin-roll thin strip continuous casting and rolling technology is as follows: Figure 1As shown in the figure, the molten steel in the ladle 1 is directly poured into a molten pool 7 surrounded by two relatively rotating and rapidly cooling crystallizing rollers 8a, 8b and side sealing devices 6a, 6b through the ladle long nozzle 2, the tundish 3, the submerged nozzle 4 and the distributor 5. The molten steel solidifies on the rotating circumferential surface of the crystallizing rollers 8a, 8b to form a solidified shell and gradually grows, and then forms a 1-5mm thick steel strip 11 at the smallest point (nip point) of the gap between the two casting rollers. The steel strip is guided by the guide plate 9 to the pinch roller 12 and sent to the rolling mill 13 to be rolled into a thin strip, and then cooled by the cooling device 14. After the head is cut by the flying shear device 16, the cut head falls into the flying shear pit 18 along the flying shear guide plate 17. The hot rolled strip after the head is cut enters the coiler 19 to be coiled into a coil.

[0007] Strip steel produced by continuous strip casting, especially thin products less than 1.2mm thick, can directly replace cold-rolled products (hot-rolled instead of cold-rolled) as long as performance allows. This greatly expands the product range of continuous strip casting. Because it does not require multiple cold-rolling thinning processes, its production cost is lower than that of products produced by cold rolling, and its cost-effectiveness is more outstanding. However, most cold-rolled products require thinner thickness, better plate shape, and no iron oxide scale on the surface. Therefore, products used for "hot-rolled" thin strip casting usually undergo traditional wet chemical processing such as pickling, descaling, and oiling to achieve a bright surface and achieve the surface quality of cold-rolled plate. However, the plate shape cannot be compared with cold-rolled products, and its use is limited to some relatively low-end applications. This pickling process requires the disposal of large amounts of acid and waste acid, which has a significant impact on the environment and is relatively expensive. Summary of the Invention

[0008] The purpose of the present invention is to provide a fully continuous short-process production method for metal plates and strips, which effectively improves the shortcomings and problems of the original thin strip continuous casting technology in producing low-carbon steel by using an ultra-short process, fully continuous near-net-shape production method, and has the advantages of high production efficiency, energy saving and environmental protection, low CO2 emissions, and reduced costs; the products produced by the present invention have high elongation, good forming performance, and high surface quality, and can truly realize the "replacing cold with heat" in the field of high-end products, and are green and low-carbon products.

[0009] To achieve the above object, the technical solution of the present invention is:

[0010] A fully continuous short-process production method for metal strips, comprising the following steps:

[0011] 1) Smelting

[0012] Smelted according to the following composition, the weight percentage of the composition is: C: 0.01-0.06%, Si≤0.15%, Mn≤0.85%, P≤0.02%, S≤0.005%, Als<0.001%, Ca≤0.0050%, the balance includes Fe and other unavoidable impurities;

[0013] 2) Induction heating of tundish

[0014] The qualified molten steel is poured into the tundish through the ladle, and the tundish is equipped with an electromagnetic induction heating device;

[0015] 3) Thin strip continuous casting

[0016] The continuous casting adopts twin-roll thin strip casting. Molten steel is injected from the tundish into the distributor and evenly distributed into the molten pool formed by the two crystallization rollers for continuous casting. A cast strip with a thickness of 1.5 to 3 mm is formed at the smallest gap between the two crystallization rollers. The diameter of the crystallization rollers is between 500 and 1500 mm. The crystallization rollers are cooled by water inside. The casting speed of the casting machine is 50 to 150 m / min.

[0017] After the casting strip leaves the crystallization roller, the casting strip temperature is 1400-1480℃, and it directly enters the lower closed chamber. Non-oxidizing cooling gas is passed through the lower closed chamber, and the oxygen concentration in the lower closed chamber is controlled at <5%; the temperature of the casting strip at the outlet of the lower closed chamber is 1100-1300℃.

[0018] 4) Rolling

[0019] The cast strip passes through the pinch rollers in the lower closed chamber and then enters the online six-high rolling mill for rolling in a closed environment. The starting rolling temperature is 1000-1250°C, the rolling reduction rate is 15-80%, the thickness of the steel strip after rolling is 0.3-2.5mm, and the rolling outlet temperature is 850-1100°C. By controlling the oxygen concentration in the lower closed chamber, the thickness of the iron oxide scale of the steel strip after rolling can be controlled to 3-10μm.

[0020] 5) 1# flying shear

[0021] The rolled strip is conveyed to the No. 1 flying shear device via a conveyor roller to cut off the poor quality head. The cut head falls into the flying shear pit along the flying shear guide plate.

[0022] 6) Cooling after rolling

[0023] The strip steel after online hot rolling is cooled by gas atomization cooling at a cooling rate of 10-300°C / s. The gas-water ratio of gas atomization cooling is 15:1-10:1, the gas pressure is 0.5-0.8 MPa, and the water pressure is 1.0-1.5 MPa, and the strip steel is cooled to below 200°C.

[0024] 7) Acid-free descaling

[0025] After cooling, the strip directly enters the acid-free descaling process, including multi-roller crushing, jet descaling, washing and blowing;

[0026] 8) 2# flying shear

[0027] The 2# flying shear is set in front of the coiler to realize coil separation during the continuous production process of strip steel;

[0028] 9) Strip coiling

[0029] After acid-free descaling, the strip steel is finally rolled into a steel coil with no iron oxide scale on the surface.

[0030] Preferably, the molten steel is smelted by an electric furnace or a converter, or further by an LF furnace, a VD / VOD furnace, or a RH furnace.

[0031] Preferably, the non-oxidizing gas in the lower sealed chamber is N2, Ar or CO2 obtained by sublimation of dry ice.

[0032] Preferably, the thickness of the iron oxide scale of the rolled strip is preferably 3 to 6 μm.

[0033] Preferably, the multi-roller crushing is in the form of three-roller crushing, five-roller crushing or seven-roller crushing.

[0034] Preferably, the jet descaling adopts a solid-liquid mixed medium to be sprayed onto the surface of the strip at high speed through a nozzle; the mass percentage of solids in the solid-liquid mixed medium is 10% to 80%; the liquid medium is preferably liquid water, and the solid medium is hard particles, including mineral abrasives or metal materials, with a diameter between 0.1-0.8mm, preferably 0.2-0.5mm; the mineral abrasives are preferably natural garnet, corundum, and corundum, and the metal materials include steel shots, steel sand, and wire cut shots.

[0035] Preferably, the jet direction of the descaling jet is opposite to the traveling direction of the strip steel, and the jet forms an angle of 10° to 75° with the surface of the strip steel, preferably 30° to 60°.

[0036] Preferably, the nozzle port of the jet descaling is 50 to 100 mm away from the strip surface, the nozzle pressure is 5 to 10 MPa, and the nozzle flow rate is 30 to 80 L / min.

[0037] Preferably, the flushing method uses a simple liquid medium, preferably liquid water, and the flushing pressure is usually 0.1 to 10 MPa.

[0038] Preferably, the purging method is compressed air purging with a pressure range of 0.01 to 2 MPa.

[0039] Preferably, the coiling is carried out using a carousel coiler or a double-coil down coiler.

[0040] Preferably, the yield strength of the metal strip is 280-330 MPa, the tensile strength is 380-420 MPa, and the elongation is ≥35%.

[0041] In the chemical composition design of the low carbon steel of the present invention:

[0042] C: C is the most economical and fundamental strengthening element in steel, increasing the strength of steel through solid solution strengthening and precipitation strengthening. For conventional slab continuous casting, casting in the peritectic reaction zone is prone to surface cracks on the slab, and in severe cases, steel leakage accidents may occur. The same is true for thin strip continuous casting. Casting the strip in the peritectic reaction zone is prone to surface cracks, and in severe cases, the strip may break. Therefore, thin strip continuous casting of Fe-C alloys also needs to avoid the peritectic reaction zone, so the C content range used in the present invention is 0.01-0.06%.

[0043] Si: In the present invention, the addition of Si serves as a deoxidizer, improving steel purity. Si also expands the range of ferrite formation, facilitating ferrite rolling. However, excessive Si content can easily lead to the formation of "red scale" defects on the steel sheet after rolling, increasing strength while decreasing elongation. Since the present invention aims for lower strength and higher elongation, a high Si content is not necessary. Therefore, the Si content employed in the present invention is ≤0.15%.

[0044] Mn: Mn is one of the cheapest alloying elements. It improves the hardenability of steel and has a considerable solid solubility in steel. It increases steel's strength through solid solution strengthening while having little effect on its plasticity and toughness. It is the most important strengthening element for increasing steel's strength and also acts as a deoxidizer. However, excessive Mn content can degrade weldability and the toughness of the weld heat-affected zone. Therefore, the Mn content used in this invention is ≤0.85%.

[0045] P: High P contents tend to segregate at grain boundaries, increasing the steel's cold brittleness, impairing weldability, reducing plasticity, and deteriorating cold bending properties. In the thin strip continuous casting process, the cast strip solidifies and cools at extremely rapid rates, effectively suppressing P segregation, thereby effectively avoiding P's disadvantages and fully utilizing its advantages. Therefore, in the present invention, a higher P content than in conventional production processes is employed, while the P content is appropriately relaxed, eliminating the P removal step in the steelmaking process. In actual operation, no deliberate P removal step is required, nor is additional P addition necessary. The P content range is ≤ 0.02%.

[0046] S: S is typically a harmful element in steel, causing hot brittleness and reducing its ductility and toughness. S easily forms MnS in steel. The amount and form of sulfides in steel directly affect the formability of the steel sheet. Therefore, S must be below 0.005%. The amount and form of inclusions significantly impact the deep-drawability of steel sheets. In particular, stripe-shaped sulfide inclusions can easily cause cracking during deformation. Therefore, in the present invention, S is controlled as an impurity element, with a content range of ≤ 0.005%.

[0047] Als: To control inclusions in steel, the present invention requires that Al cannot be used for deoxidation. In the use of refractory materials, the additional introduction of Al should also be avoided as much as possible, and the content of acid-soluble aluminum Als should be strictly controlled: <0.001%.

[0048] Ca: It can change the morphology of sulfides in steel, transforming long MnS inclusions into spherical CaS inclusions, improving the plasticity and toughness of the steel plate, and helping to improve the formability of the steel plate. The present invention controls Ca to less than 0.0050%.

[0049] In the production method of the present invention:

[0050] The tundish is equipped with an electromagnetic induction heating device. This induction heating can effectively stabilize or increase the temperature of the molten steel in the tundish, effectively ensuring that the temperature of the molten steel in the tundish remains within a constant range, thereby ensuring stability throughout the entire process of thin strip continuous casting, from pouring to changing the ladle to final pouring. It can also float inclusions, effectively removing high-melting-point deoxidation products.

[0051] The continuous casting process utilizes twin-roll thin strip casting. Molten steel is injected from the tundish into a distributor, evenly distributed across the molten pool formed by two crystallization rollers. Continuous casting results in a 1.5-3mm thick cast strip at the smallest gap between the two rolls. After exiting the crystallization rollers, the strip, at a temperature of 1400-1480°C, enters a lower confined chamber, where a non-oxidizing cooling gas is passed. This protects the strip from oxidation and also cools it. The oxygen concentration in the chamber is controlled at <5%, and the strip temperature at the exit of the lower confined chamber is 1100-1300°C. The non-oxidizing gas is N2, Ar, or CO2 derived from sublimated dry ice.

[0052] After passing through pinch rollers in the lower confined chamber, the cast strip enters an in-line six-high rolling mill for rolling under closed conditions. The starting rolling temperature is 1000-1250°C, the rolling reduction range is 15-80%, the thickness of the rolled strip is 0.3-2.5 mm, and the rolling outlet temperature is 850-1100°C. Lubricated rolling improves the strip surface quality and reduces rolling wear on the rolls. The oxide scale on the rolled strip is uniformly distributed and relatively thin. By controlling the oxygen concentration in the lower confined chamber, the oxide scale thickness can be controlled to 3-10 μm, preferably 3-6 μm.

[0053] Reasons for choosing a six-high mill: Existing online rolling mills used in thin-strip continuous casting and rolling production lines worldwide are all four-high mills, which can achieve a maximum reduction ratio of no more than 50% per pass. To achieve a higher reduction ratio (>50%) and better plate shape per pass, this invention uses a six-high mill for the first time. Six-high mills have the characteristics of cold rolling mills. Since the cast strip produced by thin-strip continuous casting is inherently thin and has a high aspect ratio, it shares some of the characteristics of cold-rolled strip. Therefore, using a six-high mill for online rolling of the cast strip is relatively easy, resulting in thinner and better-shaped strip products.

[0054] Ultra-thin strip produced by continuous strip casting can achieve a high compression ratio after entering the six-roll mill at a high reduction rate. At higher rolling temperatures, dynamic recrystallization of the material's internal microstructure is easily achieved. Complete dynamic recrystallization can improve the material's performance uniformity. If a traditional four-roll mill is used, the insufficient compression ratio will lead to incomplete dynamic recrystallization, easily causing mixed crystals and affecting performance uniformity.

[0055] After cooling, the steel strip directly enters the acid-free descaling process, which includes multi-roller crushing + jet descaling + flushing + purging and other units. Among them, the multi-roller crushing is in the form of three-roller crushing, five-roller crushing or seven-roller crushing, which can have a descaling effect on the surface of the steel strip; the jet descaling adopts a solid-liquid mixed medium to be sprayed to the surface of the steel strip at high speed through a nozzle. The liquid medium is preferably liquid water, and the solid medium is hard particles, such as natural garnet, corundum, corundum and other mineral abrasives, or metal materials such as steel shot, steel sand, wire cut shot and other metal pellets, with a diameter of 0.1-0.8mm, preferably 0.2-0.5mm, and the mass percentage of solid in the solid-liquid mixed medium is usually selected between 10% and 20%. Adjustable within the range of 80%; the jet direction has a certain angle with the direction of strip travel, and the angle with the horizontal is 10-75°, preferably 30-60°, the nozzle port is 50-100mm away from the strip surface, the nozzle pressure is 5-10MPa, and the nozzle flow rate is 30-80L / min; the flushing method uses a simple liquid medium, preferably liquid water, and its flushing pressure is usually 0.1-10MPa; the purging method is compressed air purging, and the pressure range is 0.01-2MPa to ensure that the strip surface is dry and no scale residue remains.

[0056] The entire acid-free descaling section must be equipped with a medium recovery and processing system (omitted in the figure), which specifically includes a water recovery, filtration and reuse system, a particle recovery, cleaning and reuse system, a granular abrasive and scale collection system, and a water temperature control system.

[0057] After this manufacturing process, the final product has mechanical properties of 280-330 MPa yield strength, 380-420 MPa tensile strength, and 35% or greater elongation. This product has high elongation, good formability, and high surface quality, truly replacing cold with hot in the high-end product market, making it a green, low-carbon product.

[0058] The differences and improvements of the present invention over the prior art are as follows:

[0059] There are many patents for the application of technologies such as six-roller cold rolling and acid-free descaling. However, in the thin-strip continuous casting and rolling technology, the relevant technology described in the present invention has not been proposed or publicly reported, and no similar industrial units are sold on the market.

[0060] The online rolling mills configured in the existing thin-strip continuous casting and rolling production lines in various countries around the world are all four-roll mills, which can achieve a maximum reduction rate of no more than 50% in a single pass.

[0061] In order to achieve a larger single-pass reduction rate (>50%) and better plate shape, the present invention first selects a six-roll mill. The six-roll mill has the characteristics of a cold rolling mill, and the working roll diameter can be smaller. Since the cast strip obtained by thin strip continuous casting is relatively thin in thickness and has a large width-to-thickness ratio, it has some characteristics of cold-rolled strip. Therefore, it is relatively easy to use a six-roll mill to roll the cast strip online, and a strip product with thinner thickness and better plate shape can be obtained.

[0062] The present invention targets ultra-thin strip produced by continuous strip casting. Once the strip enters a six-roll mill, it achieves a high compression ratio at a high reduction ratio. This allows for dynamic recrystallization of the material's internal microstructure at higher rolling temperatures. Complete dynamic recrystallization improves the material's performance uniformity. Using a conventional four-roll mill, the insufficient compression ratio results in incomplete dynamic recrystallization, which can easily lead to mixed crystals and affect performance uniformity.

[0063] In order to reduce the damage to the environment caused by traditional chemical pickling methods, Chinese patent CN103537640B discloses a method for producing hot-rolled pickling-free plates by combining thin strip continuous casting with reduction annealing, which eliminates the cold rolling pickling process. The process is characterized by re-uncoiling the produced thin strip cast and rolled coils and performing reduction annealing on separate lines to remove iron oxide scale. This lack of continuity is essentially different from the jet descaling method used in the present invention. In addition, the present invention is a continuous production method without the need for re-uncoiling.

[0064] Chinese patent CN1387467A discloses a method for producing thin steel strip. After hot rolling, the twin-roll cast steel strip is forcedly cooled to approximately 750°C by water jets before entering a descaling machine for descaling. This method uses high-pressure water jets to remove scale, making it difficult to completely remove the scale. The present invention uses high-pressure water entrained with fine hard particles, spraying them onto the strip surface to achieve better descaling results.

[0065] Chinese patent CN1291922A discloses a stainless steel strip manufacturing apparatus and method. This method directly casts liquid metal into 15-25mm thick stainless steel strip, which is then hot-rolled (optional), annealed (optional), and descaled using shot blasting, wire brushing, or fluid spraying. The strip is then subjected to multi-stand cold rolling, annealing and pickling or bright annealing furnaces, skin-pass cold rolling mills (single stand), and coiling. This method achieves continuous production of stainless steel cold-rolled strip from continuous casting to cold-rolled coils, eliminating many intermediate steps and significantly improving yield and site utilization. The present invention uses twin-roll thin strip casting to produce 1.5-3mm cast strip, which is significantly different from the patent. The patent also does not involve technical means such as tundish induction heating and six-roll online hot rolling.

[0066] Therefore, the present invention is based on the ultra-short process of near-net-shape thin strip continuous casting and rolling technology, combined with green and low-carbon technologies such as tundish induction heating, online six-roll hot rolling, and acid-free descaling, to continuously produce "heat instead of cold" products in the field of high-performance and high-end products with low carbon emissions, and is technologically innovative and advanced.

[0067] Beneficial effects of the present invention:

[0068] (1) The present invention selects a six-roll mill for the first time in the thin strip continuous casting and rolling process, which meets the requirements of matching the thin strip continuous casting process. The six-roll mill has the characteristics of a cold rolling mill. Since the thickness of the cast strip obtained by thin strip continuous casting is relatively thin, the width-to-thickness ratio is large, and it has some characteristics of cold-rolled plate and strip, it is relatively easy to use a six-roll mill to roll the cast strip online, and the process requirements of a larger single-pass reduction rate (>50%) can be achieved, thereby obtaining a strip product with thinner thickness and better plate shape. The ultra-thin specification hot-rolled strip obtained by this method can be as thin as 0.3 mm.

[0069] The products produced by the present invention have high elongation, good forming performance and high surface quality, and can truly realize "replacing cold with heat" in the field of high-end products.

[0070] (2) The present invention utilizes the tundish induction heating technology to effectively stabilize or increase the temperature of the molten steel in the tundish, effectively ensuring that the temperature of the molten steel in the tundish remains within a constant range, thereby ensuring the stability of the entire process of the thin strip continuous casting process from start of pouring to replacement of the ladle to final pouring; it can also cause inclusions to float, thereby effectively removing high-melting-point deoxidation products.

[0071] (3) The present invention is directed to the ultra-thin cast strip produced by continuous strip casting. After entering a six-roll mill, a large reduction ratio can be achieved for the cast strip. At a high rolling temperature, dynamic recrystallization of the internal microstructure of the material is easily achieved. Complete dynamic recrystallization can improve the uniformity of material properties. If a conventional four-roll mill is used, the compression ratio is insufficient, resulting in incomplete dynamic recrystallization, the easy occurrence of mixed crystals, and the impact on performance uniformity.

[0072] (4) The present invention uses an acid-free descaling method to remove the iron oxide scale on the strip surface, making the strip surface bright and achieving the surface quality of cold-rolled sheet, while also significantly improving the metal yield. This method replaces the traditional pickling process and avoids the serious environmental pollution and damage caused by waste acid generated by pickling; the traditional pickling process also significantly reduces the metal yield.

[0073] (5) The present invention adopts an ultra-short process, fully continuous, near-net-shape production method, eliminating many complex intermediate steps in traditional process production. The production line has the advantages of small footprint, simplicity and efficiency, high production efficiency, energy saving and environmental protection; the product has low carbon emissions, low energy consumption, low cost, and excellent performance, and is a low-carbon, green and environmentally friendly product. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 This is a typical process flow diagram of the existing twin-roll thin strip continuous casting and rolling technology;

[0075] Figure 2 This is a schematic diagram of the process layout of the fully continuous short-process production method of metal plates and strips described in the present invention. DETAILED DESCRIPTION

[0076] The present invention will be further described below with reference to the following examples and drawings, but these examples are by no means limiting of the present invention. Any changes made by those skilled in the art in the art in light of this specification will fall within the scope of the claims.

[0077] See also Figure 2, a schematic diagram of the process layout of the fully continuous short-process production method of metal plates and strips according to the present invention, wherein the molten steel in accordance with the chemical composition design of the present invention is directly poured into a molten pool 7 surrounded by two relatively rotating and rapidly cooling crystallizing rollers 8a, 8b and side sealing plate devices 6a, 6b through a ladle 1, a long ladle nozzle 2, a tundish 3, an immersion nozzle 4 and a distributor 5. The molten steel solidifies on the rotating circumferential surface of the crystallizing rollers 8a, 8b, and then forms a solidified shell which gradually grows to form a cast strip 11 with a thickness of 1.5-3 mm at the minimum gap between the two crystallizing rollers (nip point).

[0078] After the cast strip 11 exits the crystallization rollers 8a and 8b, the cast strip temperature is between 1400°C and 1480°C, and the cast strip directly enters the lower closed chamber 10. The lower closed chamber 10 is passed through a non-oxidizing cooling gas to protect the strip steel. The oxygen concentration in the lower closed chamber 10 is controlled at less than 5%. The lower closed chamber 10 provides anti-oxidation protection for the cast strip 11 until the entrance of the rolling mill 13. The temperature of the cast strip 11 at the exit of the lower closed chamber 10 is between 1100°C and 1250°C. The cast strip 11 is then sent to the online six-high rolling mill 13' by the swinging guide plate 9 and the pinch rollers 12 for rolling. The starting rolling temperature is between 1000°C and 1250°C, the rolling reduction ratio range is between 15% and 80%, the thickness of the steel strip after rolling is between 0.3 and 2.5 mm, the rolling exit temperature is between 850°C and 1100°C, and lubrication rolling is used for rolling.

[0079] The rolled strip is conveyed via conveyor rollers 15 to the No. 1 flying shear 16, where the poor-quality ends are removed. The cut ends fall along the shear guide 17 into the shear pit 18. The cut strip then enters the post-rolling cooling zone 20, where it is cooled using atomization at a rate of 10-300°C / s. The atomization cooling method uses an air-to-water ratio of 15:1 to 10:1, an air pressure of 0.5-0.8 MPa, and a water pressure of 1.0-1.5 MPa, cooling the strip to below 200°C. The cooled strip then enters the acid-free descaling process, which includes multi-roll crushing 21, jet descaling 22, flushing 23, and purging 24. The multi-roll crushing system 21, which can be a three-roll, five-roll, or seven-roll crushing system, can effectively break the scale on the strip surface. Jet descaling 22 uses a solid-liquid mixed medium to spray onto the strip surface at high speed through a nozzle. Flushing 23 uses a pure liquid medium. Blowing 24 uses compressed air to ensure that the strip surface is dry and free of scale residue. After acid-free descaling, the strip is finally wound by coiler 19, producing a scale-free coil. When the coil weight reaches the user's specified weight, it is separated by flying shear 25 to ensure continuous production throughout the entire process.

[0080] The composition of the embodiment of the present invention is shown in Table 1, with the remainder including Fe and other unavoidable impurities. The manufacturing process parameters of the embodiment of the present invention are shown in Table 2, and the properties of the final product are shown in Table 3.

[0081] After the above manufacturing process, the final product has mechanical properties of 280-330 MPa yield strength, 380-420 MPa tensile strength, and elongation ≥35%. This product has high elongation, excellent formability, and high surface quality, truly replacing cold with hot in the high-end product market, making it a green, low-carbon product. This ultra-short process, fully continuous, near-net-shape production method effectively overcomes the shortcomings and issues of conventional thin-strip continuous casting technology for producing low-carbon steel, offering advantages such as high production efficiency, energy conservation and environmental protection, low CO2 emissions, and reduced costs.

[0082]

[0083]

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Claims

1. A fully continuous short-process production method for metal strips, characterized in that: The steps include: 1) Smelting The composition is smelted according to the following weight percentages: C: 0.01-0.06%, Si≤0.15%, Mn≤0.85%, P≤0.02%, S≤0.005%, Als<0.001%, Ca≤0.0050%, and the balance includes Fe and other unavoidable impurities; 2) Induction heating of tundish The qualified molten steel is poured into the tundish through the ladle, and the tundish is equipped with an electromagnetic induction heating device; 3) Thin strip continuous casting The continuous casting adopts twin-roll thin strip casting. Molten steel is injected from the tundish into the distributor and evenly distributed into the molten pool formed by the two crystallization rollers for continuous casting. A cast strip with a thickness of 1.5 to 3 mm is formed at the smallest gap between the two crystallization rollers. The diameter of the crystallization rollers is between 500 and 1500 mm. The crystallization rollers are cooled by water inside. The casting speed of the casting machine is 50 to 150 m / min. After the casting strip leaves the crystallization roller, the casting strip temperature is between 1400 and 1480°C and directly enters the lower closed chamber. Non-oxidizing cooling gas is passed through the lower closed chamber, and the oxygen concentration in the lower closed chamber is controlled at <5%. The temperature of the casting strip at the outlet of the lower closed chamber is between 1100 and 1300°C. 4) Rolling The cast strip passes through the pinch rollers in the lower closed chamber and then enters the online six-high rolling mill for rolling in a closed environment. The starting rolling temperature is 1000-1250°C, the rolling reduction rate is 15-80%, the thickness of the steel strip after rolling is 0.3-2.5mm, and the rolling outlet temperature is 850-1100°C. The thickness of the iron oxide scale of the steel strip after rolling is controlled to be 3-10μm. 5) 1# flying shear The rolled strip is conveyed via a conveyor roller to the No. 1 flying shear device to cut off the poor quality head; 6) Cooling after rolling The strip steel after online hot rolling is cooled by gas atomization cooling at a cooling rate of 10-300°C / s. The gas-water ratio of gas atomization cooling is 15:1-10:1, the gas pressure is 0.5-0.8 MPa, and the water pressure is 1.0-1.5 MPa, and the strip steel is cooled to below 200°C. 7) Acid-free descaling After cooling, the strip directly enters the acid-free descaling process, including multi-roller crushing, jet descaling, washing and blowing; 8) 2# flying shear The 2# flying shear is set in front of the coiler to realize coil separation during the continuous production process of strip steel; 9) Strip coiling After acid-free descaling, the strip steel is finally rolled into a steel coil with no iron oxide scale on the surface.

2. The fully continuous short-process production method of metal strip according to claim 1, characterized in that: In step 1), the molten steel is smelted in an electric furnace or a converter, or further in an LF furnace, a VD / VOD furnace, or a RH furnace.

3. The fully continuous short-process production method of metal strip according to claim 1, characterized in that: In step 3), the non-oxidizing gas in the lower sealed chamber is N2, Ar or CO2 obtained by sublimation of dry ice.

4. The fully continuous short-process production method of metal strip according to claim 1, characterized in that: In step 4), the thickness of the iron oxide scale of the rolled strip is 3 to 6 μm.

5. The fully continuous short-process production method of metal strip according to claim 1, characterized in that: In step 7), the multi-roller crushing is in the form of three-roller crushing, five-roller crushing or seven-roller crushing.

6. The fully continuous short-process production method of metal strip according to claim 1, characterized in that: In step 7), the jet descaling adopts a solid-liquid mixed medium to be sprayed onto the surface of the strip at high speed through a nozzle; the mass percentage of solids in the solid-liquid mixed medium is 10% to 80%; the liquid medium is preferably liquid water, and the solid medium is hard particles, including mineral abrasives or metal materials, with a diameter between 0.1 and 0.8 mm, preferably 0.2 to 0.5 mm; the mineral abrasives are preferably natural garnet, corundum, and corundum, and the metal materials include steel shot, steel grit, and wire cut shot.

7. The fully continuous short-process production method of metal strip according to claim 1 or 6, characterized in that: In step 7), the direction of the jet for descaling is opposite to the direction of travel of the strip, and the jet forms an angle of 10° to 75° with the surface of the strip, preferably 30° to 60°.

8. The fully continuous short-process production method of metal strip according to claim 6, characterized in that: In step 7), the nozzle port of the jet descaling is 50 to 100 mm away from the strip surface, the nozzle pressure is 5 to 10 MPa, and the nozzle flow rate is 30 to 80 L / min.

9. The fully continuous short-process production method of metal strip according to claim 1, characterized in that: In step 7), the flushing method uses a simple liquid medium, preferably liquid water, and the flushing pressure is usually 0.1 to 10 MPa.

10. The fully continuous short-process production method of metal strip according to claim 1, characterized in that: In step 7), the purging method is compressed air purging with a pressure range of 0.01 to 2 MPa.

11. The fully continuous short-process production method of metal strip according to claim 1, characterized in that: In step 9), the coiling is carried out using a carousel coiler or a double-coil down coiler.

12. The fully continuous short-process production method of metal strip according to claim 1, characterized in that: The yield strength of the strip steel is 280-330 MPa, the tensile strength is 380-420 MPa, and the elongation is ≥35%.

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