Pickling-free continuous production method for hot-dip galvanized aluminum magnesium alloy plate strip

Abstract

The invention discloses a pickling-free continuous production method for a hot-dip galvanized aluminum magnesium alloy plate strip. The pickling-free continuous production method comprises the steps of smelting, tundish induction heating, thin strip continuous casting, six-roller rolling, head cutting, reduction annealing, hot dipping, coil dividing and coiling. The temperature of tundish molten steel is effectively guaranteed to be kept within a constant range through tundish electromagnetic induction heating, and therefore the stability of the whole process of casting starting, large ladle replacement, final casting and the like in the thin-strip continuous casting process is guaranteed; the cast strip is subjected to hot rolling through an online six-roller mill to obtain ultra-thin hot-rolled strip steel; the strip steel is subjected to reduction annealing at the temperature of 800-1100 DEG C through waste heat of the strip steel, and oxide scale on the surface of the strip steel is removed; and the outlet temperature of reduction annealing is controlled, then the strip steel penetrates through a heat preservation section of 450-470 DEG C and directly enters a zinc pot with zinc-aluminum-magnesium alloy liquid to be subjected to zinc-aluminum-magnesium alloy hot-dip plating, and finally the strip steel is cooled and coiled to obtain the hot-dip-plated zinc-aluminum-magnesium alloy strip. 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 is truly achieved.

Description

Technical Field

[0001] The invention relates to a hot-dip galvanized aluminum-magnesium alloy strip manufacturing technology, and in particular to a pickling-free continuous production method for hot-dip galvanized aluminum-magnesium alloy 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 process flow of thin slab continuous casting and rolling is: continuous casting + slab insulation and soaking + hot rolling + cooling + coiling.

[0004] The main differences between the thin slab continuous casting and rolling process and the traditional process are:

[0005] The thickness of the thin slab casting is greatly reduced to 50-90mm. Due to the thinness of the casting, the casting only needs to undergo 1-2 rough rolling passes (when the casting thickness is 70-90mm) or no rough rolling (when the casting thickness is 50mm). The continuous casting casting of the traditional process needs to undergo repeated multiple rolling passes to be thinned to the required specifications before finishing rolling. Moreover, the casting of the thin slab casting is not cooled, but directly enters the soaking furnace for soaking and insulation, or a small amount of warming. Therefore, the thin slab casting process greatly 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.

[0006] 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.

[0007] A process flow that is shorter than thin slab continuous casting and rolling is the thin strip continuous casting and rolling process.

[0008] Continuous strip casting is a cutting-edge technology in metallurgy and materials research. Since Henry Bessemer proposed the idea in 1865 (U.S. Patent 49053), it has a history of over 160 years. 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 revolutionized the steel industry, transforming the traditional strip production process by integrating continuous casting, rolling, and even heat treatment. This allows the production of thin strip blanks through a single in-line hot rolling process, resulting in a single thin strip. This significantly simplifies the entire process from molten steel to strip and shortens production cycles. With a process line length of only approximately 50 meters, the steel production process is more compact, continuous, efficient, and environmentally friendly. Furthermore, it reduces equipment investment and significantly lowers production costs, making it a low-carbon and environmentally friendly hot-rolled thin strip production process. Therefore, thin strip continuous casting technology has become a hot spot for development in countries around the world in recent years.

[0009] The typical process flow of the existing twin-roll thin strip continuous casting and rolling technology is as follows: Figure 1 As shown:

[0010] 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 head cutting enters the coiler 19 to be coiled into a coil.

[0011] 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

[0012] The purpose of the present invention is to provide a method for continuous production of hot-dip galvanized aluminum-magnesium alloy plates and strips without pickling, which can truly realize "replacing cold with heat" in the field of high-end products, and effectively improve the shortcomings and problems of the original thin strip continuous casting technology in producing low-carbon steel with an ultra-short process and fully continuous near-net-shape production method. It has the advantages of high production efficiency, energy saving and environmental protection, low CO2 emissions, and cost reduction. In addition, the product has high elongation, good forming performance, and high surface quality.

[0013] To achieve the above object, the technical solution of the present invention is:

[0014] A method for continuously producing hot-dip galvanized aluminum-magnesium alloy strips without pickling, comprising the following steps:

[0015] 1) Smelting

[0016] The chemical composition of the molten steel is as follows: 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;

[0017] 2) Induction heating of tundish

[0018] The qualified molten steel is poured into the tundish through the ladle, and the tundish is equipped with an electromagnetic induction heating device;

[0019] 3) Thin strip continuous casting

[0020] Molten steel is poured from the tundish into a distributor and evenly distributed into the molten pool formed by two crystallization rollers for continuous casting. Twin-roller thin strip casting is used, with a 1.5-3mm thick cast strip formed at the smallest gap between the two crystallization rollers. The diameter of the crystallization rollers ranges from 500 to 1500mm. The crystallization rollers are internally cooled by water, and the casting speed of the casting machine is 50-150m / min.

[0021] 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.

[0022] 4) Rolling

[0023] After the cast strip passes through the pinch rollers in the lower closed chamber, it enters the online six-high rolling mill for rolling in a closed environment. The starting rolling temperature is 1000-1250℃, 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℃.

[0024] 5) Cutting

[0025] The rolled strip is conveyed to the No. 1 flying shear device via a conveyor roller to cut off the poor quality head, which falls into the flying shear pit along the flying shear guide plate.

[0026] 6) Reduction annealing

[0027] After rolling, the strip steel is subjected to reduction annealing at 800-1100°C using the residual heat of the strip steel to remove the iron oxide scale on the strip steel surface. The reducing gas in the reduction annealing furnace is carbon monoxide (CO), hydrogen (H2), or a mixture of CO and H2. When the reducing gas is a mixture of CO and H2, CO:H2 = 5%:95% to 95%:5%. The reduction time is 30-120 seconds.

[0028] An inert gas cooling device is installed at the outlet of the reduction annealing furnace to control the outlet temperature of the strip steel at 450-470°C.

[0029] 7) Hot dip coating

[0030] After reduction annealing, the strip passes through a holding section at 450-470°C and directly enters a pot equipped with zinc-aluminum-magnesium alloy liquid for hot-dip zinc-aluminum-magnesium alloy coating. The immersion time is 1-5 seconds.

[0031] 8) Volume

[0032] After the hot-dip zinc-aluminum-magnesium alloy strip is cooled, it passes through the 2# flying shear device, which is set in front of the coiler to realize coiling during the continuous production process of the strip;

[0033] 9) Strip coiling

[0034] The hot-dip galvanized aluminum-magnesium alloy sheet and strip coil is obtained by the coiler.

[0035] Preferably, in step 1), the molten steel is smelted in an electric furnace or a converter, or further refined in an LF furnace, a VD / VOD furnace or a RH furnace.

[0036] Preferably, in step 2), the tundish is equipped with an electromagnetic induction heating device with a heating power of 1200 to 1600 kW.

[0037] Preferably, in step 3), the non-oxidizing gas in the lower sealed chamber is N2, Ar or CO2 obtained by sublimation of dry ice.

[0038] Preferably, in step 4), lubrication rolling is used for rolling, and the iron oxide scale of the strip steel after rolling is evenly distributed and relatively thin. By controlling the oxygen concentration in the lower closed chamber, the thickness of the iron oxide scale can be controlled to 3 to 10 μm, preferably 3 to 6 μm.

[0039] Preferably, the hot-dip galvanized aluminum-magnesium alloy plate has a yield strength of 250-280 MPa, a tensile strength of 290-330 MPa, and an elongation of ≥35%.

[0040] In the chemical composition design of the low carbon steel of the present invention:

[0041] 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%.

[0042] 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 is controlled to ≤ 0.15%.

[0043] 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%.

[0044] 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 that used in traditional production processes is employed, while the P content is appropriately relaxed. Dephosphorization is eliminated from the steelmaking process. In actual operation, no dephosphorization process is required, nor is additional phosphorus addition. The P content is limited to ≤0.02%.

[0045] 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%.

[0046] 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 to be less than 0.001%.

[0047] 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%.

[0048] In the production method of the present invention:

[0049] The tundish is equipped with an electromagnetic induction heating device. The induction heating of the tundish 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 is kept within a constant range, thereby ensuring the stability of the thin strip continuous casting process from the start of pouring to the replacement of the ladle to the final pouring; it can also make inclusions float, thereby effectively removing high-melting-point deoxidation products.

[0050] Twin-roller thin strip casting is used. After exiting the crystallization rolls, the strip, at a temperature of 1400-1480°C, enters the lower sealed chamber, where a non-oxidizing cooling gas is passed. This not only protects the strip from oxidation but also cools it. The oxygen concentration in the lower sealed chamber is controlled to <5%.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] After rolling, the strip does not need to be cooled. Instead, it undergoes reduction annealing at 800-1100°C using the strip's own residual heat to remove the surface oxide scale. Because the strip's residual heat reaches 800-1100°C and the oxide scale is very thin, the reducing atmosphere allows for rapid reduction and effective removal of the surface oxide scale, significantly shortening the reduction time to 30-120 seconds.

[0055] After reduction annealing, the strip passes through a holding section with a temperature range of 450-470°C, and directly enters a pot equipped with zinc-aluminum-magnesium alloy liquid for hot-dip galvanizing. The immersion time is 1-5s, and finally it is coiled after cooling to obtain a hot-dip galvanized aluminum-magnesium alloy strip.

[0056] As an option, in addition to the hot-dip galvanized aluminum-magnesium alloy described above, the present invention can also perform hot-dip galvanizing, hot-dip aluminum-zinc alloy, hot-dip aluminum-silicon alloy, etc., so as to obtain alloy plates and strips with different coating types.

[0057] After the above manufacturing process, the final product has mechanical properties of a yield strength of 250-280 MPa, a tensile strength of 290-330 MPa, and an elongation of 35% or more. The product has high elongation, good formability, high surface quality, and excellent corrosion resistance, truly achieving the "heat-in-cold" approach in the high-end product sector and representing a green, low-carbon product. This ultra-short process, fully continuous, near-net-shape production method effectively addresses the shortcomings and problems 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.

[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 reduction annealing. 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] 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, the present invention uses a six-high mill for the first time. This mill has the characteristics of a cold rolling mill, allowing for a smaller work roll diameter. Since the cast strip obtained 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 a thinner and better-shaped strip product.

[0061] 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.

[0062] In order to reduce the damage to the environment caused by traditional chemical pickling methods, Chinese patent CN103537640B proposes a method for producing hot-rolled pickling-free plates by combining thin strip continuous casting with reduction annealing. This method eliminates the cold rolling pickling process, but the thin strip cast and rolled coils need to be re-unrolled and separated into separate lines, which lacks continuity.

[0063] Chinese patent CN1387467A discloses a method for producing thin steel strips. The steel strips cast by twin rollers are hot-rolled online, forcibly cooled to about 750°C by a water jet, and then enter a descaling machine for descaling. This method uses a high-pressure water jet nozzle to spray for descaling, which makes it difficult to remove the scales completely. The present invention uses an online reduction annealing process to achieve better descaling effects.

[0064] 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 present invention. The present invention also does not involve technical means such as tundish induction heating, six-roll online hot rolling, or online reduction.

[0065] 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 reduction annealing, to continuously produce "heat instead of cold" products in the field of high-performance, high-end products with low carbon emissions, and is technologically innovative and advanced.

[0066] Beneficial effects of the present invention:

[0067] The present invention proposes to effectively ensure that the temperature of the molten steel in the tundish is maintained within a constant range through electromagnetic induction heating of the tundish, thereby ensuring the stability of the thin strip continuous casting process during the entire process of start-pouring, replacement of the ladle, and final pouring; the cast strip cast by twin-roll casting is subjected to online hot rolling on an online six-roll rolling mill to obtain ultra-thin hot-rolled strip steel; the product produced by the present invention has 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 is a green and low-carbon product.

[0068] (1) 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.

[0069] (2) 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 reduction rate (>50%) in a single pass 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 0.3mm.

[0070] (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.

[0071] (4) The present invention utilizes the residual heat of the steel strip after online rolling, without the need for cooling, and performs reduction annealing on the steel strip at its own residual heat of 800-1100°C, thereby removing the iron oxide scale on the surface of the steel strip, making the surface of the steel strip bright and achieving the surface quality of cold-rolled plate, while also greatly improving the metal yield. This method replaces the traditional pickling process, avoiding the serious pollution and damage to the environment caused by the waste acid generated by pickling; the traditional pickling process also greatly reduces the metal yield. At the same time, because the residual heat of the steel strip is very high and the iron oxide scale is very thin, rapid reduction can be achieved in the reducing atmosphere of this working condition, removing the surface iron oxide scale, and significantly shortening the reduction time.

[0072] (5) The ultra-short process, fully continuous, near-net-shape production method of the present invention eliminates many complex intermediate steps in traditional process production. The production line has the advantages of small footprint, simplicity and high 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

[0073] Figure 1 This is a typical process flow diagram of the existing twin-roll thin strip continuous casting and rolling technology;

[0074] Figure 2 This is a schematic diagram of the process layout of the pickling-free continuous production method of hot-dip galvanized aluminum-magnesium alloy strips described in the present invention. DETAILED DESCRIPTION

[0075] 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.

[0076] See also Figure 2 The present invention is a schematic diagram of the process layout of the method for continuous production of hot-dip galvanized aluminum-magnesium alloy plates and strips without pickling, in which molten steel conforming to 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 immersed nozzle 4 and a distributor 5. The molten steel solidifies on the rotating circumferential surfaces of the crystallizing rollers 8a, 8b, and then forms a solidified shell which gradually grows to form a 1.5-3 mm thick cast strip 11 at the minimum gap between the two crystallizing rollers (nip point); the crystallization diameter of the present invention is between 500 and 1500 mm, and the interior is cooled by water; the casting speed of the casting machine ranges from 50 to 150 m / min depending on the thickness of the cast strip.

[0077] After the casting strip 11 leaves the crystallization rollers 8a and 8b, the casting strip temperature is 1400-1480°C and 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. On the one hand, it can realize the anti-oxidation protection of the casting strip 11, and also play a cooling role on the casting strip 11. The anti-oxidation protection atmosphere can be N2, Ar, or other non-oxidizing gases, such as CO2 gas obtained by sublimation of dry ice, etc. The oxygen concentration in the lower closed chamber 10 is controlled at <5%. The lower closed chamber 10 has a great impact on the casting strip 11. The cast strip 11 is heated to 1100-1250°C at the exit of the lower sealed chamber 10, after being protected from oxidation. The cast strip 11 is then fed into the inline six-high mill 13' via the swinging guide plate 9 and pinch rollers 12 for rolling. The starting rolling temperature is 1000-1250°C, the rolling reduction range is 15-80%, and the thickness of the rolled strip is 0.3-2.5 mm. The outlet temperature is 850-1100°C. Lubricated rolling improves the strip's surface quality and reduces roll wear. The strip's oxide scale is evenly distributed, with a thickness of 3-10 μm.

[0078] The rolled strip is conveyed via a conveyor roller 15 to a No. 1 flying shear device 16, where the poor-quality head is removed. The cut head falls into a flying shear pit 18 along a flying shear guide 17. The strip does not need to be cooled, but instead utilizes its own waste heat to enter a reduction annealing furnace 20 at 800-1100°C for reduction annealing to remove iron oxide scale from the strip surface. The reducing gas in the reduction annealing furnace 20 is carbon monoxide (CO), hydrogen (H2), or a mixture of CO and H2 (CO:H2 = 5%:95% to 95%:5%). The reduction time is 30-120 seconds. An inert gas cooling device 21 is provided at the outlet of the reduction annealing furnace 20 to control the outlet temperature of the strip in the reduction annealing furnace 20 to be 450-470°C; the strip after reduction annealing passes through the insulation section 22 with a temperature of 450-470°C and directly enters the zinc pot 23 equipped with zinc-aluminum-magnesium alloy liquid to be hot-dip galvanized aluminum-magnesium alloy for a immersion time of 1-5s; the hot-dip zinc-aluminum-magnesium alloy strip is cooled by the cooling device 24 and passes through the 2# flying shear device 25. The 2# flying shear device 25 is provided in front of the coiler 19 to realize coiling in the continuous production process of the strip; finally, the hot-dip galvanized aluminum-magnesium alloy strip coil is obtained by the coiler 19.

[0079] The chemical compositions of Examples 1 to 10 of the present invention are shown in Table 1, with the remainder being Fe and other unavoidable impurities. The manufacturing method of the present invention is carried out with process parameters shown in Table 2, and the properties of the final product are shown in Table 3.

[0080] After the above manufacturing process, the final product has mechanical properties of a yield strength of 250-280 MPa, a tensile strength of 290-330 MPa, and an elongation of 35% or greater. This product has high elongation, good formability, high surface quality, and excellent corrosion resistance, truly replacing cold with hot in the high-end product market and is a green, low-carbon product. This ultra-short, fully continuous, near-net-shape production method effectively overcomes the shortcomings and problems 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.

[0081]

[0082]

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Claims

1. A method for continuous production of hot-dip galvanized aluminum-magnesium alloy strip without pickling, characterized in that: The steps include: 1) Smelting According to the following composition, the chemical composition of molten steel is as follows: 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; 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 Molten steel is poured from the tundish into a distributor and evenly distributed into the molten pool formed by two crystallization rollers for continuous casting. Twin-roller thin strip casting is used, with a 1.5-3mm thick cast strip formed at the smallest gap between the two crystallization rollers. The diameter of the crystallization rollers ranges from 500 to 1500mm. The crystallization rollers are internally cooled by water, and the casting speed of the casting machine is 50-150m / 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 After the cast strip passes through the pinch rollers in the lower closed chamber, it enters the online six-high rolling mill for rolling in a closed environment. The starting rolling temperature is 1000-1250℃, 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℃. 5) Cutting The rolled strip is conveyed to the No. 1 flying shear device via a conveyor roller to cut off the poor quality head, which falls into the flying shear pit along the flying shear guide plate. 6) Reduction annealing After rolling, the strip steel is subjected to reduction annealing at 800-1100°C using the residual heat of the strip steel to remove the iron oxide scale on the strip steel surface. The reducing gas in the reduction annealing furnace is carbon monoxide (CO), hydrogen (H2), or a mixture of CO and H2. When the reducing gas is a mixture of CO and H2, CO:H2 = 5%:95% to 95%:5%. The reduction time is 30-120 seconds. An inert gas cooling device is installed at the outlet of the reduction annealing furnace to control the outlet temperature of the strip steel at 450-470°C. 7) Hot dip coating After reduction annealing, the strip passes through a holding section at 450-470°C and directly enters a zinc pot equipped with zinc-aluminum-magnesium alloy liquid for hot-dip zinc-aluminum-magnesium alloy coating. The immersion time is 1-5 seconds. 8) Volume After cooling, the hot-dip zinc-aluminum-magnesium alloy strip passes through the 2# flying shear device, which is set in front of the coiler to realize coiling during the continuous production process of the strip; 9) Coiling The hot-dip galvanized aluminum-magnesium alloy sheet and strip coil is obtained by the coiler.

2. The method for continuously producing hot-dip galvanized aluminum-magnesium alloy strip without pickling according to claim 1, characterized in that: In step 1), the molten steel is smelted in an electric furnace or a converter, or further refined in an LF furnace, a VD / VOD furnace or a RH furnace.

3. The method for continuously producing hot-dip galvanized aluminum-magnesium alloy strip without pickling according to claim 1, wherein: In step 2), the tundish is equipped with an electromagnetic induction heating device with a heating power of 1200 to 1600 kW.

4. The method for continuously producing hot-dip galvanized aluminum-magnesium alloy strip without pickling according to claim 1, wherein: In step 3), the non-oxidizing gas in the lower sealed chamber is N2, Ar or CO2 obtained by sublimation of dry ice.

5. The method for continuously producing hot-dip galvanized aluminum-magnesium alloy strip without pickling according to claim 1, wherein: In step 4), lubrication rolling is used for rolling, and the thickness of the iron oxide scale is controlled to be 3 to 10 μm.

6. The method for continuously producing hot-dip galvanized aluminum-magnesium alloy strip without pickling according to claim 5, characterized in that: In step 4), the thickness of the iron oxide scale is controlled to be 3 to 6 μm.

7. The method for continuously producing hot-dip galvanized aluminum-magnesium alloy strip without pickling according to claim 1, wherein: The hot-dip galvanized aluminum-magnesium alloy plate has a yield strength of 250-280 MPa, a tensile strength of 290-330 MPa, and an elongation of ≥35%.

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