A method for producing a thin-gauge low-density steel sheet by a pack rolling method

Abstract

This invention relates to a method for producing thin-gauge low-density steel sheets using a lap-rolling process. The chemical composition of the steel sheet, by mass percentage, is: C: 0.70–1.20%, Si: 0.10–0.50%, Mn: 16.00–24.00%, P: ≤0.015%, S: ≤0.003%, Al: 7.00–10.00%, Ni: 4.00–8.00%, Nb+Ti: 0.02–0.20%, with the balance being iron and unavoidable impurities. The method includes the following steps: billet preparation, billet compositing, billet welding, compositing billet heating, compositing billet rolling, steel sheet separation, and compositing billet straightening. A low-density steel intermediate billet of a certain thickness and identical length and width is selected as the lap-rolling billet. After welding, thin-gauge low-density steel sheets with a thickness of 3–6 mm and a width of 2000–3500 mm are produced on a medium-thick plate mill. The steel plate has an Fe-Mn-Al-C series composition and a density of 6.90-7.10 g / cm³. 3 The finished steel plate has a yield strength ≥1000MPa, tensile strength ≥1100MPa, elongation ≥20%, and Charpy V impact energy ≥20J at -40℃. The rolled steel plate has good uniformity in shape, thickness tolerance ≤±0.25mm, and flatness ≤4mm / m.

Description

Technical Field

[0001] This invention belongs to the field of special steel smelting technology, specifically relating to a method for producing thin-gauge low-density steel plates by a stacking rolling process. Background Technology

[0002] With the increasing trend and requirements for low-carbon, energy-saving, and environmentally friendly industrial development, equipment manufacturing, automobiles, and other industries have continuously put forward lightweight development goals. Low-density steel is a new type of material that has emerged in response to this need. Compared with non-ferrous metals such as titanium alloys, aluminum alloys, and magnesium alloys, low-density steel has obvious advantages in terms of economy, low-carbon manufacturing, and machinability.

[0003] Among different types of low-density steel, Fe-Mn-Al-C series low-density steel has become a hot topic both domestically and internationally due to its low density, high toughness, high strength-ductility product, and good ductility. Through reasonable compositional design, the density of Fe-Mn-Al-C series low-density steel can be reduced by more than 10% compared to traditional steel grades. By preparing a multiphase microstructure with austenite as the matrix and rationally controlling the stability of austenite, mechanisms such as TRIP, TWIP, and MBIP effects are generated during impact, giving it excellent strength, toughness, weldability, and processing properties such as cold bending and stamping. These characteristics have significant application potential in fields such as automotive crash protection and bulletproof armor.

[0004] Our company has successfully achieved large-scale industrial production of Fe-Mn-Al-C series low-density steel, mastering production technologies such as large ingot casting, heating, rolling, and heat treatment. Due to limitations in production equipment and steel characteristics, the minimum thickness specification for directly rolled low-density steel is currently 6mm, and this specification is produced using a hot-rolling mill. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for producing thin-gauge low-density steel plates by a stacking rolling process, which can use a medium-thick plate rolling mill to produce 3-6mm thick, 2000-3500mm low-density steel plates, realize the industrial production of thinner low-density steel, and achieve higher thickness precision control, which is of great significance for the lightweight development of special vehicles, weapons and equipment, ships and other fields.

[0006] The technical solution adopted by the present invention to solve the above problems is as follows: a method for producing thin-gauge low-density steel plates by a roll-rolling process, wherein the metallographic structure at room temperature is austenitic, and the chemical composition of the steel plate by weight percentage is: C: 0.70-1.20%, Si: 0.10-0.50%, Mn: 16.00-24.00%, P: ≤0.015%, S: ≤0.003%, Al: 7.00-10.00%, Ni: 4.00-8.00%, Nb+Ti: 0.02-0.20%, with the balance being iron and unavoidable impurity elements.

[0007] The main functions and design basis of each chemical element in the steel of this invention are as follows:

[0008] C: C is an austenite-stabilizing element that can prevent the martensitic transformation of austenite during deformation and promote the formation of single-phase austenite. Simultaneously, C can dissolve into the steel matrix, improving the steel's strength through solid solution strengthening. In this invention, the C content is 0.70–1.20%.

[0009] Si: Si can improve the strength of steel and the mechanical stability of retained austenite, but it is also a solid solution strengthening element. However, excessive silicon content can reduce the solubility of carbon in austenite, increase the number of κ carbides, and reduce the ductility and toughness of the steel. Therefore, the Si content in this invention is controlled at 0.10–0.50%.

[0010] Mn: Mn can expand the austenite region and inhibit the transformation of austenite to martensite, thus stabilizing the austenite. In austenitic structures, Mn can utilize the TRIP and TWIP effects to maintain a high work hardening rate in steel, improving plasticity. Adding Mn is beneficial for obtaining a good strength-plasticity balance. However, with increasing Mn content, the tendency of the billet to crack during rapid heating and cooling increases, and excessively high Mn content is detrimental to weldability. Therefore, the Mn content in this invention is 16.00–24.00%.

[0011] Al: As a lightweight element, adding 3% Al can reduce the density of steel to 7.4 g / cm³. 3 Al is the main element used to reduce the density of steel in this invention. Furthermore, Al can increase stacking fault energy, which not only inhibits the transformation of austenite to martensite but also promotes the formation of deformation twins. Al can delay the dynamic recrystallization of high-manganese steel, thereby refining the austenite grains, and can also increase the strain hardening rate and low-temperature toughness. However, excessive Al can promote the formation of large amounts of κ carbides, thus deteriorating the plasticity of the steel. Therefore, the Al content in this invention is 7.00–10.00%.

[0012] Ni: Adding a certain amount of Ni to steel can effectively improve its strength and ensure its low-temperature impact toughness. Ni is also an austenite-forming element, which can stabilize the austenite matrix. Furthermore, Ni combines with Al to form the brittle intermetallic compound B2 phase (NiAl), which can improve the material's strength. However, excessive Ni content can lead to an increase in the number and size of NiAl precipitates, which is detrimental to the steel's plasticity. Therefore, in this invention, the Ni content is controlled between 4.00% and 8.00%.

[0013] Nb: Nb can form carbonitrides, which refines the grain size. It also increases the temperature of the non-recrystallization zone, making it easier to control the flattening of austenite during rolling, thus improving the strength and toughness of the steel. However, the effect is not significant above 0.10%. In this invention, the Nb content is 0.02–0.10%.

[0014] Ti: Ti is a strong carbide-forming element, capable of forming TiC carbides, which provide grain refinement and precipitation strengthening, effectively improving the strength of steel. However, excessively high Ti content can reduce the carbon content in austenite, leading to decreased matrix stability. Therefore, the Ti content in this invention is 0.02–0.10%.

[0015] The specific manufacturing process steps of the steel plate described in this invention are as follows:

[0016] 1. Billet Preparation. Molten steel is smelted and cast into steel ingots or continuously cast billets. The steel ingots or continuously cast billets are rolled into low-density steel intermediate billets with a thickness of 40-80mm and a width of 2000mm-3200mm, which are used as stacked billets. The number of stacked billets is 2-3 pieces depending on the selection. The billet thickness tolerance is controlled within (0, ±0.5mm), and the length and width tolerances are controlled within (0, ±5mm).

[0017] 2. Billet Composite. The upper and lower surfaces of the stacked billets are shot-blasted. After shot blasting, the contact surfaces of the billets are selected according to the design requirements for two- or three-bill stacking. The contact surfaces of the low-density steel slabs are then ground using a milling or grinding machine to a thickness of 1-2 mm. Compressed air is then used to clean the contact surfaces. After grinding, a 0.5-1.5 mm thick release agent is evenly sprayed onto the contact surfaces and allowed to air dry. The release agent consists of 30%-50% by weight of binder and 50%-70% by weight of release powder, with the total weight percentage of both raw materials being 100%. The release powder consists of magnesium oxide powder (40%-70%) and silica powder (30%-60%); the binder is a nano-silica aqueous solution, in which nano-sized silica particles account for 30%-40% by weight.

[0018] 3. Billet Welding. Laser welding is used to weld the upper and lower billets together around the contact surface. First, two billets of the same size are aligned and stacked together, ensuring the gap between them is as small as possible (≤0.2mm). To minimize this gap, special clamps are used to clamp the two billets along the edge of the steel plate, with the clamps distributed as densely as possible (recommended spacing ≤200mm). Laser welding parameters: defocusing amount -3mm; laser tilt angle 5°; laser power 10-30KW; welding speed 1.0±2m / min. The final laser weld penetration depth is ≥10mm. A 10-15mm long vent hole is reserved on each side of the weld seam of the billets to be stacked, with 4-10 holes recommended to prevent bulging due to trapped gas during heating and rolling, which would affect rolling quality.

[0019] 4. Billet Heating. A walking beam furnace is used to heat the prepared low-density steel slab billets. The cold billets are fed into the furnace. The preheating zone temperature range is 600–900℃, and the preheating time is approximately 1.0–2.0 hours. The first heating zone temperature range is 900–1100℃, and the heating time is approximately 1.0–2.0 hours. The second heating zone temperature range is 1100–1240℃, and the soaking zone temperature range is 1180–1200℃. The total time for the second heating zone and the soaking zone is approximately 1.0–2.0 hours. The total heating time is approximately 4.0–6.0 hours. The core temperature of the billet at tapping is ≥1170℃. After tapping, it undergoes high-pressure water descaling, with a descaling water pressure >20MPa. The staged heating process ensures sufficient dissolution of alloying elements, and specifying the core temperature at tapping ensures uniform heating of the slab billet, which is beneficial for the uniformity of the dimensions and properties of the finished steel plate.

[0020] 5. Steel Plate Stacking. Due to the high content of this steel grade, the deformation resistance during rolling is large, and the finished steel plate is relatively thin. The rapid cooling during rolling increases the rolling difficulty; therefore, a high-temperature fast rolling method is adopted. The initial rolling temperature is 1080-1150℃, and the final rolling temperature is controlled at ≥880℃. The rolling speed for the first four passes is 1.5-2.5 m / s, and the rolling speed from the fifth to the last pass is 3.0-5.0 m / s. The steel plate is rolled using either full longitudinal rolling or transverse-longitudinal rolling. Billets that do not require widening are rolled directly longitudinally; billets requiring widening are widened in 2-3 passes during roughing. A total of 12-16 rolling passes are performed, with a cumulative reduction rate of ≥45% for the first four passes. After rolling, the steel plate is straightened 1-2 times by a pre-straightening machine.

[0021] 6. Steel Plate Separation. The four sides of the stacked steel plate are removed using a flame cutting machine at a speed of 400-600 mm / min. The removal amount at the beginning and end of the steel plate is 200-400 mm, and the removal amount on both sides is 150-200 mm.

[0022] After cutting, vacuum suction cups are used to lift and separate the upper and lower steel plates.

[0023] 7. Steel plate shearing. Steel plates are sheared to length using plasma cutting or sawing methods.

[0024] 8. Steel plate straightening. The separated steel plates are subjected to intensive straightening using a nine-roll straightener to ensure that the flatness of the finished steel plate is ≤4mm / m.

[0025] The density of the finished steel plate of this invention is 6.90-7.10 g / cm³. 3 Thickness 3-6mm, width 2000-3500mm, surface unevenness ≤4mm / m, thickness accuracy controllable within ±0.25mm. Steel plate yield strength ≥1000MPa, tensile strength ≥1100MPa, elongation ≥15%, impact absorption energy at -40℃ ≥20J.

[0026] Compared with the prior art, the advantages of the present invention are as follows:

[0027] The thin-gauge, low-density steel (less than 6mm) described in this invention has high deformation resistance, a large rolling compression ratio, many rolling passes, and rapid temperature drop during the process, making direct rolling extremely difficult and prone to warping. This invention employs a stacked rolling process design to increase the overall thickness of the rolled steel plate, while using high-temperature, high-speed rolling to reduce temperature drop during the rolling process and lower the rolling difficulty. Pre-straightening is performed after rolling, and the steel plate undergoes strong straightening after shearing, further improving the plate shape and flatness.

[0028] This invention uses a medium-thick plate rolling mill to roll stacked billets. The rolling process controls the thickness accuracy of the stacked steel plates. After the steel plates are trimmed and separated, the thickness tolerance of a single sheet can be controlled within ±0.25mm, which is higher than the thickness accuracy of directly rolling a single steel plate.

[0029] This invention enables the production of ultra-thin and ultra-wide low-density steel plates with a thickness of 3-6mm and a width of 2000-3500mm, achieving strict control over plate shape and precision, and allowing for industrial-scale mass production. Attached Figure Description

[0030] Figure 1 This is a 500x metallographic image of the 5mm low-density steel in an embodiment of the present invention. Detailed Implementation

[0031] The technical solution of the present invention will be described in more detail with reference to preferred embodiments. However, these embodiments are merely descriptions of preferred implementations of the present invention and should not be construed as limiting the scope of the invention.

[0032] Example 1: Production of 4mm thick, 2800mm wide low-density steel plates using a two-slab stacking rolling process

[0033] The chemical composition of the steel plate, by mass percentage, is as follows: C: 0.85%, Si: 0.20%, Mn: 19.0%, P: 0.012%, S: 0.003%, Al: 8.50%, Ni: 6.00%, Nb+Ti: 0.10%, with the balance being iron and unavoidable impurity elements.

[0034] The specific manufacturing process steps of the steel plate described in this invention are as follows:

[0035] 1. Billet Production: Molten steel is smelted and cast into a 150mm thick and 2600mm wide continuous casting billet. The continuous casting billet is rolled into a low-density steel intermediate billet with a thickness of 50mm and a width of 3000mm, which serves as the lap-rolled billet. The number of lap-rolled billets is 2, and the billet thickness tolerance is controlled within (0, ±0.5mm), and the length and width tolerances are controlled within (0, ±5mm).

[0036] 2. Billet bonding: The upper and lower surfaces of the stacked billets are shot blasted, and the surfaces to be bonded are selected after shot blasting. The bonding surfaces of the billets are then ground using a milling or grinding machine to a thickness of 1.0 mm. The bonding surfaces are then cleaned with compressed air. After grinding, a 0.5-1.0 mm thick release agent is evenly sprayed onto the bonding surfaces, and then allowed to air dry naturally.

[0037] 3. Billet Welding. Laser welding is used to weld the upper and lower billets together around the contact surface. For laser welding, two billets of the same size are first aligned and stacked together. It is essential to ensure the gap between the two billets to be stacked is as small as possible; this invention requires a gap ≤ 0.2mm. To ensure the gap is as small as possible, special clamps are used to clamp the two billets along their edges. The clamps are distributed as densely as possible, with a recommended spacing of ≤ 200mm. Laser welding parameters: defocusing amount -3mm; laser tilt angle 5°; laser power 150KW; welding speed 1.0m / min. The final laser weld penetration depth is guaranteed to be 18mm. A 15mm long vent hole is reserved on each side of the weld seam of the billets to be stacked, with four vent holes on each side, to prevent bulging due to gas trapped in the gap during heating and rolling, which would affect the rolling quality.

[0038] 4. Billet Heating: A walking beam furnace is used to heat the prepared low-density steel slab billets. The cold billets are fed into the furnace. The preheating section temperature range is 600–950℃, and the preheating time is approximately 1.5 hours. The first heating section temperature range is 900–1100℃, and the heating time is approximately 1 hour. The second heating section temperature range is 1100–1240℃, and the soaking section temperature range is 1160–1200℃. The total time for the second heating section and the soaking section is approximately 1.5 hours. The total heating time is approximately 4 hours, and the core temperature of the billet at tapping is 1180℃. After tapping, the billets undergo high-pressure water descaling, with a descaling water pressure >20MPa. The staged heating process ensures sufficient dissolution of alloying elements, and specifying the core temperature at tapping ensures uniform heating of the slab billets, which is beneficial for the uniformity of the dimensions and properties of the finished steel plates.

[0039] 5. Steel Plate Stacking. The initial rolling temperature is 1100℃, and the final rolling temperature is 900℃. The rolling speed for the first four passes is 1.5–2.5 m / s, and the rolling speed from the fifth to the last pass is 3.0–5.0 m / s. The steel plate is rolled using either full longitudinal rolling or transverse-longitudinal rolling. Billets that do not require widening are rolled directly longitudinally; billets requiring widening are widened in 2–3 passes during the roughing stage. The total number of rolling passes is 12–16, with a cumulative reduction rate of ≥45% for the first four passes. The rolled steel plate is straightened once by a pre-straightening machine.

[0040] 6. Steel Plate Separation. The four sides of the stacked steel plates are removed using a flame cutting machine at a speed of 450 mm / min. 300 mm is removed from the beginning and end of the steel plate, and 200 mm is removed from both sides. After cutting, a vacuum suction cup is used to lift and separate the upper and lower layers of steel plates.

[0041] 7. Steel plate shearing. Steel plates are sheared to length using plasma cutting or sawing methods.

[0042] 8. Steel plate straightening. The separated steel plates are subjected to intensive straightening using a nine-roll straightener, and the flatness of the finished steel plate is 3mm / m.

[0043] The density of the finished steel plate of this invention is 6.90-7.10 g / cm³. 3 The steel plate has a thickness of 4mm, a width of 2800mm, a surface roughness of 3mm / m, and a thickness accuracy controlled within ±0.25mm. Its yield strength is 1026MPa, tensile strength is 1130MPa, elongation is 21.5%, and impact absorption energy at -40℃ is 23J.

[0044] Example 2: Production of 3mm thick, 2400mm wide low-density steel plates using a three-slab stacking process

[0045] The chemical composition of the steel plate, by mass percentage, is as follows: C: 0.82%, Si: 0.25%, Mn: 18.5%, P: 0.012%, S: 0.003%, Al: 8.80%, Ni: 6.00%, Nb+Ti: 0.10%, with the balance being iron and unavoidable impurity elements.

[0046] The specific manufacturing process steps of the steel plate described in this invention are as follows:

[0047] 1. Billet Production: Molten steel is smelted and cast into 150mm thick, 2550mm continuous casting billets. The steel ingots are then rolled into low-density steel intermediate billets with a thickness of 40mm and a width of 2550mm, which serve as the lap-rolled billets. The number of lap-rolled billets is 2, with the billet thickness tolerance controlled within (0, ±0.3mm) and the length and width tolerance controlled within (0, ±5mm).

[0048] 2. Billet bonding: The upper and lower surfaces of the stacked billets are shot blasted, and the surfaces to be bonded are selected after shot blasting. The bonding surfaces of the billets are then ground using a milling or grinding machine to a thickness of 1.0 mm. The bonding surfaces are then cleaned with compressed air. After grinding, a 0.5-1.0 mm thick release agent is evenly sprayed onto the bonding surfaces, and then allowed to air dry naturally.

[0049] 3. Billet Welding. Laser welding is used to weld the upper and lower billets together around the contact surface. Using laser welding technology, two billets of the same size are first aligned and stacked together. It is essential to ensure that the gap between the two billets to be stacked is as small as possible; this invention requires a gap ≤ 0.2mm. To ensure the gap is as small as possible, special clamps are used to clamp the two billets along their edges. The clamps are distributed as densely as possible, with a recommended spacing of ≤ 200mm. Laser welding parameters: defocusing amount -3mm; laser tilt angle 5°; laser power 16KW; welding speed 1.1m / min. The final laser weld penetration depth is guaranteed to be 15mm. A 12mm long vent hole is reserved on each side of the weld seam of the billets to be stacked, with 9 vent holes on each side, to prevent bulging due to gas trapped in the gap during heating and rolling, which would affect the rolling quality.

[0050] 4. Billet Heating: A walking beam furnace is used to heat the prepared low-density steel slab billets. The cold billets are fed into the furnace. The preheating section temperature range is 600–950℃, and the preheating time is approximately 1.5 hours. The first heating section temperature range is 900–1100℃, and the heating time is approximately 1.5 hours. The second heating section temperature range is 1100–1240℃, and the soaking section temperature range is 1160–1200℃. The total time for the second heating section and the soaking section is approximately 1.5 hours. The total heating time is approximately 4.5 hours, and the core temperature of the billet at tapping is 1185℃. This staged heating process allows for complete dissolution of alloying elements, and specifying the core temperature at tapping ensures uniform heating of the slab billet, which is beneficial for the uniformity of the dimensions and properties of the finished steel plate.

[0051] 5. Steel plate stacking. The rolling stage adopts high-temperature fast rolling, directly rolling the entire longitudinal direction without widening the billet. The initial rolling temperature is 1130℃, the final rolling temperature is 875℃, and there are a total of 14 rolling passes. The reduction rate of the first pass is 20%. After rolling, the steel plate is straightened twice by a pre-straightening machine.

[0052] 6. Steel Plate Separation. The stacked steel plates are flame-cut on all four sides, with 300mm removed from the beginning and end and 150mm removed from both sides. After cutting, vacuum suction cups are used to lift and separate the three layers of steel plates.

[0053] 7. Steel plate shearing. Steel plates are sheared to length using plasma cutting or sawing methods.

[0054] 8. Steel plate straightening. The separated steel plates are subjected to intensive straightening using a nine-roll straightener, and the flatness of the finished steel plate is 3mm / m.

[0055] The density of the finished steel plate of this invention is 6.90-7.10 g / cm³. 3 The steel plate has a thickness of 4mm, a width of 2400mm, a surface unevenness of 5mm / 2m, and a thickness accuracy controlled within ±0.25mm. Its yield strength is 1075MPa, tensile strength is 1180MPa, elongation is 21%, and impact absorption energy at -40℃ is 21J.

[0056] Example 3: Production of 5mm thick, 3000mm wide low-density steel plates using a two-slab stacking rolling process

[0057] The chemical composition of the steel plate, by mass percentage, is as follows: C: 0.84%, Si: 0.20%, Mn: 19.0%, P: 0.010%, S: 0.003%, Al: 9.10%, Ni: 5.50%, Nb+Ti: 0.12%, with the balance being iron and unavoidable impurity elements.

[0058] The specific manufacturing process steps of the steel plate described in this invention are as follows:

[0059] 1. Billet Production: Molten steel is smelted and cast into 35-ton steel ingots. The ingot blanking process adopts a horizontal and vertical rolling method to roll the steel ingot into a low-density steel intermediate billet with a thickness of 60mm and a width of 2600mm, which serves as the lap-rolled billet. The number of lap-rolled billets is 2, and the billet thickness tolerance is controlled within (0, ±0.3mm), and the length and width tolerances are controlled within (0, ±5mm).

[0060] 2. Billet bonding: The upper and lower surfaces of the stacked billets are shot blasted, and the surfaces to be bonded are selected after shot blasting. The bonding surfaces of the billets are then ground using a grinding machine to a thickness of 1.5 mm, and then the bonding surfaces are cleaned with compressed air. After grinding, a 0.5-1.0 mm thick release agent is evenly sprayed onto the bonding surfaces, and then allowed to air dry naturally.

[0061] 3. Billet Welding. Laser welding is used to weld the upper and lower billets together around the contact surface. For laser welding, two billets of the same size are first aligned and stacked together. It is essential to ensure that the gap between the two billets to be stacked is as small as possible; this invention requires a gap ≤ 0.2mm. To ensure the gap is as small as possible, special clamps are used to clamp the two billets along their edges. The clamps are distributed as densely as possible, with a recommended spacing of ≤ 200mm. Laser welding parameters: defocusing amount -3mm; laser tilt angle 5°; laser power 20KW; welding speed 1.2m / min. The final laser weld penetration depth is guaranteed to be 18mm. A 13mm long vent hole is reserved on each side of the weld seam of the billets to be stacked, with 6 vent holes on each side, to prevent bulging due to gas trapped in the gap during heating and rolling, which would affect the rolling quality.

[0062] 4. Billet Heating: A walking beam furnace is used to heat the prepared low-density steel slab billets. The cold billets are fed into the furnace. The preheating section temperature range is 600–950℃, and the preheating time is approximately 1.5 hours. The first heating section temperature range is 900–1100℃, and the heating time is approximately 1.5 hours. The second heating section temperature range is 1100–1240℃, and the soaking section temperature range is 1160–1200℃. The total time for the second heating section and the soaking section is approximately 2 hours. The total heating time is approximately 4.5 hours, and the core temperature of the billet at tapping is 1185℃. This staged heating process allows for complete dissolution of alloying elements, and specifying the core temperature at tapping ensures uniform heating of the slab billet, which is beneficial for the dimensional and performance uniformity of the finished steel plate.

[0063] 5. Steel Plate Rolling. The rolling process employs high-temperature, high-speed rolling. In the roughing stage, the billet is widened by rolling at an initial temperature of 1130℃. The first three passes are transverse rolling, widening the billet to a predetermined width of 3200mm. Afterward, the billet is transferred to longitudinal rolling at a final temperature of 857℃. A total of 12 rolling passes are performed. The cumulative reduction rate of the first four passes is ≥49%. The rolled steel plate is then straightened once by a pre-straightening machine.

[0064] 6. Steel Plate Separation. The four sides of the stacked steel plates are removed using a flame cutting machine at a speed of 500 mm / min. 300 mm is removed from the beginning and end of the steel plate, and 200 mm is removed from both sides. After cutting, a vacuum suction cup is used to lift and separate the upper and lower layers of steel plates.

[0065] 7. Steel plate shearing. Steel plates are sheared to length using plasma cutting or sawing methods.

[0066] 8. Steel plate straightening. The separated steel plates are subjected to strong straightening using a nine-roll straightener, and the flatness of the finished steel plate is 2.5mm / m.

[0067] The density of the finished steel plate of this invention is 6.90-7.10 g / cm³. 3 The steel plate has a thickness of 4mm, a width of 3000mm, a surface roughness of 2.5mm / m, and a thickness accuracy controlled within ±0.25mm. The steel plate has a yield strength of 1043MPa, a tensile strength of 1150MPa, an elongation of 22.5%, and an impact absorption energy of 25J at -40℃.

[0068] Although preferred embodiments of the present invention have been described in detail above, it should be clearly understood that various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing thin-gauge low-density steel sheets by a stacking rolling process, characterized in that... The chemical composition of the steel plate, by mass percentage, is as follows: C: 0.70–1.20%, Si: 0.10–0.50%, Mn: 16.00–24.00%, P: ≤0.015%, S: ≤0.003%, Al: 7.00–10.00%, Ni: 4.00–8.00%, Nb+Ti: 0.02–0.20%, with the balance being iron and unavoidable impurities. The gas content is: [O] ≤12 ppm; [N] ≤50 ppm; [H] ≤2.0 ppm. The steel plate composition is designed as an Fe-Mn-Al-C series, with a density of 6.90–7.10 g / cm³. 3 The method includes the following steps: 1) Billet preparation: Low-density steel intermediate billets with a thickness of 40-80mm and a width of 2000mm-3200mm are selected as the billet for lap rolling. The thickness tolerance of the lap rolling billet is controlled within ±0.2mm, and the length and width tolerance is controlled within ±5mm. 2) Billet composite: The upper and lower surfaces of the stacked billet are shot blasted. After shot blasting, according to the design requirements of two-bill stacking or three-bill stacking, the contact surface of the billet is selected and the contact surface is ground. After the billet is ground, a 0.5-1.5mm thick release agent is evenly sprayed on the contact surface. After spraying, it is naturally dried. Then, the upper and lower billets are welded together around the contact surface of the billet using laser welding. 3) Billet heating: The preheating section temperature range is 600-900℃, and the preheating time is 1.0-2.0h; the first heating section temperature range is 1000-1100℃, and the heating time is 1.0-2.0h; the second heating section temperature range is 1100-1180℃, and the soaking section temperature range is 1180-1230℃; the total time for the second heating section and the soaking section is 1.5-2.0h, and the total heating time is 4.0-6.0h. The billet core temperature at the exit of the furnace is ≥1170℃. After exiting the furnace, the billet is descaled by high-pressure water with a descaling water pressure >20MPa. 4) Steel plate stacking: The rolling stage adopts high temperature fast rolling method, with an initial rolling temperature of 1080-1150℃ and a final rolling temperature of ≥880℃. The rolling speed of the first four passes is 1.5~2.5m / s, and the rolling speed from the fifth pass to the last pass is 3.0~5.0m / s. There are a total of 12-16 rolling passes. The cumulative reduction rate of the first four passes is ≥45%. After rolling, the steel plate is straightened by a pre-straightening machine 1-2 times. 5) Steel plate separation: The four sides of the rolled steel plate are cut with a flame cutting machine at a speed of 400-600 min / mm. After cutting, the upper and lower steel plates are separated by vacuum suction cups. 6) Steel plate shearing: Use plasma cutting or sawing to cut steel plates to length. The head and tail removal of the stacked steel plate is 200-400mm, and the double-sided removal is 150-200mm. 7) Steel plate straightening: The separated steel plates are subjected to strong straightening by a nine-roll straightener. The flatness of the finished steel plate after straightening is ≤4mm / m.

2. The method for producing thin-gauge low-density steel plates by a stacking rolling process according to claim 1, characterized in that... The steel plate has a thickness of 3-6 mm and a width of 2000-3500 mm.

3. The method for producing thin-gauge low-density steel sheets by a stacking rolling process according to claim 1, characterized in that... The steel plate has a yield strength ≥1000MPa, tensile strength ≥1100MPa, elongation ≥20%, Charpy V impact energy ≥20J at -40℃, and the rolled steel plate has good uniformity in shape, thickness tolerance ≤±0.25mm, and flatness ≤4mm / m.

4. The method for producing thin-gauge low-density steel plates by a stacking rolling process according to claim 1, characterized in that: In step 1), the number of stacked billets is 2-3 pieces. The billet preparation uses steel ingots or continuously cast billets as raw materials, and intermediate billets with the same thickness, width and length are made by rolling.

5. The method for producing thin-gauge low-density steel plates by a stacking rolling process according to claim 1, characterized in that: The method for grinding the surface to be contacted in step 2) is as follows: the low-density steel slab to be contacted is ground by milling or grinding machine, the grinding thickness is 1~2mm, and then the surface to be contacted is cleaned by compressed air.

6. The method for producing thin-gauge low-density steel plates by a stacking rolling process according to claim 1, characterized in that: In step 2), after welding, air holes are opened on each side of the weld seam of the billet to prevent the steel plate from bulging during rolling. The number of air holes opened on each side of the weld seam of the stacked billet is 4-10.

7. The method for producing thin-gauge low-density steel plates by a stacking rolling process according to claim 1, characterized in that: In step 2), the laser welding parameters are as follows: defocusing amount -3mm; laser tilt angle 5°, laser power 10-30KW, welding speed 1.0±2m / min; ultimately ensuring that the laser weld penetration depth is ≥10mm.

8. The method for producing thin-gauge low-density steel plates by a stacking rolling process according to claim 1, characterized in that: The separating agent in step 2) is composed of 30% to 50% by weight of binder and 50% to 70% by weight of separating powder, with the sum of the weight percentages of the two raw materials being 100%. The separating powder consists of 40% to 70% magnesium oxide powder and 30% to 60% silica powder. The binder is an aqueous solution of nano-silica, wherein the weight percentage of nano-sized silica particles is 30% to 40%.

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