Manufacturing method of ultra-thin and ultra-wide 06Ni9DR medium plate for LNG storage tank

Abstract

This invention discloses a method for manufacturing ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks. The method includes billet design, sub-bill surface treatment, beveling, preparation of protective separating agent, non-vacuum welding assembly, drilling vent holes, spraying anti-oxidation coating, heating, rolling, cutting and separation, heat treatment, and inspection. The chemical composition of the 06Ni9DR plates is controlled by mass percentage as follows: C≤0.05%, Si≤0.35%, Mn: 0.30%~0.80%, P≤0.005%, S≤0.002%, Ni: 8.50%~10.00%, with the remainder being iron and unavoidable impurities. This invention effectively reduces production costs, improves assembly efficiency, and can be used for mass production. The produced thin and wide 06Ni9DR steel plates fully meet the technical requirements for ultra-large LNG storage tanks in China.

Description

Technical Field

[0001] This invention belongs to the field of rolling technology, and in particular relates to a method for manufacturing ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks. Background Technology

[0002] 06Ni9DR is a key material for manufacturing large LNG storage tanks. Due to its low service temperature, high design strength, excellent ability to prevent crack propagation under ultra-low temperature conditions, and "zero defects" on the surface, it is recognized by the metallurgical industry as one of the most technologically advanced steel grades. As LNG storage tank designs become increasingly larger, the demand for steel plates is shifting towards ultra-thin and ultra-wide specifications, requiring "zero defects" on the surface and a flatness of ≤5mm / m, which greatly increases the manufacturing difficulty for medium and heavy plate manufacturers.

[0003] Invention patent CN 109365553 A, published on February 22, 2019, discloses a protective separating agent and a rolling method for high-nickel wide and thin plates. Its separating agent binder is composed of silica and deionized water, and the protective separating agent powder is composed of nano-silica, silicon nitride, zirconium dioxide, and aluminum silicate. Its disadvantages include complex component ratios and high cost; low efficiency of gas-shielded welding for billet assembly; a billet firing temperature of 1200–1250℃ and a total furnace time exceeding 7 hours, resulting in a rough surface on the finished product; in the example, 6*3050mm thin and wide high-nickel steel was only tested in small batches and not mass-produced. Invention patent CN 113564467 A, published on October 29, 2021, discloses a protective separating agent of silica with a thickness of 1–2 mm. This ratio results in poor isolation effect and a certain degree of resource waste. Invention patent CN 110369501 A, published on October 25, 2019, and invention patent CN111482457 A, published on October 26, 2010, respectively disclose a method for quality control of the stacking and rolling of ultra-thin and ultra-wide steel plates and a method for thin-film rolling of high-carbon steel stacked billets. The methods are applicable to the production of ultra-thin and ultra-wide ship plates and high-carbon steel, but not applicable to the production control of 06Ni9DR steel ultra-thin and ultra-wide plates.

[0004] Therefore, there is a need in the art for a method for manufacturing ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks, which can eliminate or at least alleviate all or part of the defects in the prior art. Summary of the Invention

[0005] To address some or all of the technical problems existing in the prior art, the present invention provides a method for manufacturing ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks.

[0006] The manufacturing method of ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks of the present invention includes: billet design - sub-bill surface treatment - beveling - preparation of protective separating agent - non-vacuum welding assembly - drilling vent holes - spraying anti-oxidation coating - heating - rolling - cutting and separation - heat treatment - inspection. The chemical composition of 06Ni9DR is controlled by mass percentage as follows: C≤0.05%, Si≤0.35%, Mn: 0.30%~0.80%, P≤0.005%, S≤0.002%, Ni: 8.50%~10.00%, with the remainder being iron and unavoidable impurities.

[0007] Billet design: Prepare sub-bills according to the production plan, and select two sub-bills of the same specification to form a stacked master billet according to the billet assembly principle;

[0008] Sub-billet surface treatment: The sub-billet is rough-ground to remove the iron oxide scale on the upper and lower surfaces, and then the separated surfaces are fine-ground to remove the rough grinding texture of the raw material. The roughness requirement is <3μm.

[0009] Beveling: A single-sided V-shaped bevel is formed around the separation surface of one of the blanks using plasma machining.

[0010] Preparation of protective separating agent: The main components of the protective separating agent are nano-sized silica and polyvinyl alcohol glue. Water and glue are mixed in a ratio of 40:1, heated to 100°C and then mixed evenly. After cooling to below 40°C, nano-sized silica powder is added. The ratio of protective separating agent powder to glue is 1:3. After stirring evenly, it is brushed onto the separation surface of the sub-form. After the protective separating agent is dried, it is assembled and sent into a press. The drying temperature does not exceed 400°C.

[0011] Non-vacuum welding of billet assembly: Welding of the sub-billets, first using gas shielded welding for spot welding and positioning, and then using submerged arc welding for full welding;

[0012] Drill vent holes: Drill holes for non-vacuum welded billets. According to the thickness of the stacked billet, adjust the center of the drill bit to the center of the separation surface. The holes are located on the diagonal sides of the rolling direction, 200mm away from the corner, with a hole diameter of 10mm and a depth to the joint surface.

[0013] Spraying anti-oxidation coating: Spray a special anti-oxidation coating on the outer surface of the stacked billet, and then package it according to the process requirements before sending it into the steel rolling process;

[0014] Heating: Heat the stacked billet to 1200℃~1240℃ for no more than 4 hours, with a temperature difference of less than 40℃ between the upper and lower surfaces, to ensure that the billet is heated evenly and thoroughly.

[0015] Rolling: The heated stacked billets are rolled to remove scale using a roll crown of -0.20mm to -0.35mm, with a final rolling temperature ≥700℃;

[0016] Cutting and Separation: The rolled slabs are cut and separated, and the separated slabs are then subjected to thickness measurement, surface inspection, marking, and heat treatment.

[0017] Heat treatment: The quenching heat treatment temperature is 820℃~840℃, the tempering temperature is 540℃~600℃, and the tempering treatment is combined with a heated straightening process to ensure the flatness of the plate after heat treatment.

[0018] Inspection: Each piece is inspected for its shape, surface, and mechanical properties.

[0019] Furthermore, in the above-mentioned manufacturing method of ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks, in the billet design step, the design principle of the sub-bill is that the thickness of the sub-bill is 60mm to 120mm, the width is the original width of the billet, the length is the finished width plus the trimming allowance, and the billet is rolled laterally into a plate after assembly.

[0020] Furthermore, in the above-mentioned manufacturing method of ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks, in the surface treatment step of the sub-blank, a slab grinding machine is used for rough grinding, and a flap wheel is used for fine grinding.

[0021] Furthermore, in the above-mentioned manufacturing method of ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks, in the beveling step, the beveling angle is 25° to 35° and the depth is 30mm to 40mm.

[0022] Furthermore, in the above-mentioned manufacturing method for ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks, the welding material used in the non-vacuum welding assembly step is as follows: and Ordinary welding wire;

[0023] During spot welding, the press applies 200-400 tons of pressure and presses it tightly before using gas shielded welding for spot welding positioning. The weld spot is 50mm-100mm long and spaced 200mm apart.

[0024] For full welding, the first pass is a manual or gas-shielded welding for the root pass. After welding, the slag is cleaned and the weld joints are free of cracks and pinholes. The welding billet machine is then hoisted, and a submerged arc welding machine is used to perform the second pass on all four sides in a specific sequence. Starting from the third pass, each weld should overlap half of the previous weld, until both the upper and lower surfaces are completely filled with weld seams. Preheating and interpass temperatures (T ≤ 100℃) must be strictly controlled to ensure the steel billet does not crack during prolonged high-temperature heating and rolling.

[0025] The welding process parameters are shown in the table below:

[0026]

[0027] Furthermore, in the aforementioned manufacturing method for ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks, during the rolling process, the roll period design includes loading a furnace of carbon steel after roll changing and arranging approximately 20 wide plates for transition hot rolling. Initial descaling requires two passes to remove 90% of the surface coating. If the coating is not completely removed, an additional small reduction pass is added during the initial rolling to break up the coating, ensuring complete removal of the coating in the first three passes. The initial rolling temperature is 980℃~1030℃, and the process strictly employs two-speed constant rolling to fully utilize the favorable conditions of high temperature, concentrating the reduction as much as possible in the first few passes. Simultaneously, the first pass before the mill descaling ensures the surface quality of the steel plate. The intermediate billet thickness is 3-4 times the finished product thickness. The second rolling pass uses four-speed high-speed rolling, prioritizing plate shape. Descaling begins in the first pass, with subsequent passes handled according to the plate shape. After rolling, hot straightening is performed without controlled cooling, with 1-3 passes to ensure a flat plate shape.

[0028] Furthermore, in the above-mentioned manufacturing method of ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks, during the cutting and separation process, the upper steel plate is lifted by a vacuum suction cup, and the upper and lower plates are separated by the weight of the steel plate itself. The corners are assisted by pry bars, the width is determined according to the planned dimensions, and the length is kept to the maximum.

[0029] The manufacturing method of ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks of the present invention has the following advantages and

[0030] Beneficial effects:

[0031] (1) The present invention uses nano-sized silica as the protective separating agent and special glue as the ingredient. The protective separating agent has a simple ratio, low cost, high temperature resistance and strong adhesion, which effectively ensures the surface quality of the separation surface after steel plate stacking.

[0032] (2) The blanking is filled by submerged arc welding through non-vacuum welding and ordinary welding wire is used as the welding material, which effectively reduces the blanking cost and improves the blanking efficiency. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0034] This invention provides a method for manufacturing ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks. By using a non-vacuum welding and stacking method, combined with a proprietary fine descaling method and stacking plate shape control technology, it breaks through the design limits of medium-thick plate production lines and achieves low-cost, high-efficiency mass production of 3-10*2000-3500*L(mm) ultra-thin and ultra-wide 06Ni9DR plates, bringing significant economic and social benefits to enterprises.

[0035] Due to the characteristics of 06Ni9DR steel, the two major challenges in producing wide and thin steel plates are surface and shape control. These two challenges are often contradictory in the production process. To maintain a low surface quality requirement, the heating temperature should be lower and more descaling water should be added. To maintain a high shape requirement, the rolling temperature should be lower and less descaling should be used to reduce the temperature drop during the process. The rolling difficulty can be reduced to some extent by using the stack rolling method, but to achieve mass production, the optimal rolling process window still needs to be found.

[0036] The manufacturing method of ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks of the present invention includes: billet design - sub-bill surface treatment - beveling - preparation of protective separating agent - non-vacuum welding assembly - drilling vent holes - spraying anti-oxidation coating - heating - rolling - cutting and separation - heat treatment - inspection. The chemical composition of 06Ni9DR is controlled by mass percentage as follows: C≤0.05%, Si≤0.35%, Mn: 0.30%~0.80%, P≤0.005%, S≤0.002%, Ni: 8.50%~10.00%, with the remainder being iron and unavoidable impurities.

[0037] Billet design: Prepare sub-bills according to the production plan, and select two sub-bills of the same specification to form a stacked master billet according to the billet assembly principle;

[0038] Sub-billet surface treatment: The sub-billet is rough-ground to remove the iron oxide scale on the upper and lower surfaces, and then the separated surfaces are fine-ground to remove the rough grinding texture of the raw material. The roughness requirement is <3μm.

[0039] Beveling: A single-sided V-shaped bevel is formed around the separation surface of one of the blanks using plasma machining.

[0040] Preparation of protective separating agent: The main components of the protective separating agent are nano-sized silica and polyvinyl alcohol glue. Water and glue are mixed in a ratio of 40:1, heated to 100℃ and then mixed evenly. After cooling to below 40℃, nano-sized silica powder is added. The ratio of protective separating agent powder to glue is 1:3. After stirring evenly, it is brushed onto the separation surface of the sub-bill. After the protective separating agent is dried, it is assembled and sent into the press. The drying temperature does not exceed 400℃. During the transportation process, the separation surface is protected to prevent the protective separating agent from falling off and to ensure normal separation after rolling.

[0041] Non-vacuum welding of the preform assembly: The preform assembly is welded by first using gas shielded welding for spot welding and then using submerged arc welding for full welding; welding materials: and Ordinary welding wire;

[0042] Spot welding: After applying 200-400 tons of pressure with a press and pressing it tightly, spot welding is performed using gas shielded welding for positioning. The length of the weld spot is 50mm-100mm and the interval is 200mm.

[0043] Full welding: The first pass is a manual or gas-shielded welding for the root pass. After welding, the slag is cleaned and the weld joint is free of cracks, pinholes, and other defects. The welding billet machine is then hoisted, and a submerged arc welding machine is used to perform the second pass on all four sides in a specific sequence. From the third pass onwards, each weld should overlap half of the previous weld, until both the upper and lower surfaces are completely filled with weld seams. Preheating and interpass temperature T must be strictly controlled to ≤100℃. This ensures that the steel billet will not crack during prolonged high-temperature heating and rolling.

[0044] The welding process parameters are shown in the table below:

[0045]

[0046] Drilling vent holes: Drill holes for non-vacuum welded billets. According to the thickness of the stacked billets, adjust the center of the drill bit to the center of the separation surface. The holes are located on the diagonal sides of the rolling direction, 200mm away from the corner, with a diameter of 10mm and a depth to the joint surface, so as to ensure that the gas can be discharged during heating and rolling.

[0047] Spraying anti-oxidation coating: Spray a special anti-oxidation coating on the outer surface of the stacked billet, and then package it according to the process requirements before sending it into the steel rolling process;

[0048] Heating: The slab is heated to 1200℃~1240℃ for no more than 4 hours, with a temperature difference of less than 40℃ between the upper and lower surfaces to ensure uniform and thorough heating. If the heating temperature is too low or the time is too short, the temperature drop in the rolled thin section will be large, resulting in a heavy load and uneven thickness. If the heating temperature is too high or the time is too long, the grains will become excessively coarse, which is detrimental to low-temperature toughness, and incomplete descaling will lead to a rough surface of the finished product. Therefore, the heating process is set at a heating temperature of 1200~1240℃ and a heating time of 9~12 min / 10mm.

[0049] Rolling: The heated stacked billets are rolled to remove scale using a roll crown of -0.20mm to -0.35mm, with a final rolling temperature ≥700℃;

[0050] Cutting and Separation: The rolled slabs are cut and separated, and the separated slabs are then subjected to thickness measurement, surface inspection, marking, and heat treatment.

[0051] Heat treatment: The quenching heat treatment temperature is 820℃~840℃, the tempering temperature is 540℃~600℃, and the tempering treatment is combined with a heated straightening process to ensure the flatness of the plate after heat treatment.

[0052] Inspection: Each piece is inspected for its shape, surface, and mechanical properties.

[0053] Furthermore, in the manufacturing method of ultra-thin and ultra-wide 06Ni9DR medium-thick plate for LNG storage tanks of the present invention, in the billet design step, the design principle of the sub-bill is that the thickness of the sub-bill is 60mm to 120mm, the width is the original width of the billet, the length is the finished width plus the trimming allowance, and the billet is rolled laterally into a plate after assembly.

[0054] Furthermore, in the manufacturing method of ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks of the present invention, in the surface treatment step of the sub-blank, a slab grinding machine is used for rough grinding, and a flap wheel is used for fine grinding.

[0055] Furthermore, in the manufacturing method of ultra-thin and ultra-wide 06Ni9DR medium-thick plate for LNG storage tanks of the present invention, in the beveling step, the beveling angle is 25° to 35° and the depth is 30mm to 40mm.

[0056] Furthermore, in the manufacturing method of ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks of the present invention, in the non-vacuum welding assembly step, welding materials are used: ordinary welding wire with a diameter of 1.2 mm and a diameter of 4.0 mm.

[0057] During spot welding, the press applies 200-400 tons of pressure and presses it tightly before using gas shielded welding for spot welding positioning. The weld spot is 50mm-100mm long and spaced 200mm apart.

[0058] For full welding, the first pass is a manual or gas-shielded welding for the root pass. After welding, the slag is cleaned and the weld joints are free of cracks and pinholes. The welding billet machine is then hoisted, and a submerged arc welding machine is used to perform the second pass on all four sides in a specific sequence. Starting from the third pass, each weld should overlap half of the previous weld, until both the upper and lower surfaces are completely filled with weld seams. Preheating and interpass temperatures (T ≤ 100℃) must be strictly controlled to ensure the steel billet does not crack during prolonged high-temperature heating and rolling.

[0059] The welding process parameters are shown in the table below:

[0060]

[0061] Furthermore, in the manufacturing method of ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks of the present invention, during the rolling process, the roll period design includes loading a furnace of carbon steel after the roll change and arranging about 20 wide plates for transition hot rolling. Initial descaling requires double-pass descaling to remove 90% of the surface coating. If the coating is not completely removed, an additional small reduction pass is added in the initial rolling to break up the coating, ensuring complete removal of the coating in the first three passes of the initial rolling. The initial rolling temperature is 980℃~1030℃, and the process strictly adopts two-speed constant rolling to fully utilize the favorable conditions of high temperature, concentrating the reduction as much as possible in the first few passes. Simultaneously, the first pass before the mill descaling ensures the surface quality of the steel plate. The intermediate billet thickness is 3-4 times the finished product thickness. The second rolling pass uses four-speed high-speed rolling, focusing on maintaining the plate shape. Descaling begins in the first pass, and subsequent passes are handled according to the plate shape. After rolling, hot straightening is performed without controlled cooling, with 1-3 passes to ensure a flat plate shape.

[0062] Furthermore, in the manufacturing method of ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks of the present invention, during the cutting and separation process, the upper steel plate is lifted by a vacuum suction cup, and the upper and lower plates are separated by the weight of the steel plate itself. The corners are separated with the assistance of pry bars. The width is determined according to the planned dimensions, and the length is kept to the maximum.

[0063] Through non-vacuum welding and stacking, proprietary fine descaling methods, and stacking shape control technology, coupled with reasonable separation and heat treatment processes, the flatness of the steel plate is ≤5mm / m, the surface quality of the upper and lower surfaces is good, the thickness difference between the same plate is less than 0.03mm, and the thickness difference between the upper and lower plates is 0.02-0.08mm; the average tensile strength is 715MPa, the average yield strength is 637MPa, the average elongation is 24.5%, the average impact energy of 6mm specification at -196℃ is 84.6J, and the average lateral expansion coefficient is 1.64mm. The physical quality and performance indicators fully meet the technical requirements of the LNG storage tank technical specifications, realizing the mass production of wide and thin 06Ni9DR on the medium and heavy plate production line.

[0064] Example 1:

[0065] The 06Ni9DR steel is 5mm thick and 3000mm wide. The steel plate has a tensile strength of 725MPa, an average yield strength of 625MPa, an elongation of 24.5%, a flatness of 5mm / m, and a difference of 0.03mm between plates.

[0066] Billet design: The billet design principle is that the thickness of the sub-bills is 60mm to 120mm, the width is the original width of the billet, and the length is the finished width plus the trimming allowance. After the billets are assembled, they are rolled into plates in the transverse direction. Sub-bills are prepared according to the production plan. Two sub-bills of the same specification are selected according to the billet assembly principle to form a stacked rolling master billet. The external dimensions of the stacked rolling billet are 180×1750×3100 (mm). The target size of the rolled steel plate is 10×3100×26000 (mm), and the finished product size is 5×3100×12000 (mm).

[0067] Surface treatment of billet: Use a slab grinding machine to perform rough grinding to remove iron oxide scale from the upper and lower surfaces of the billet, and then use a flap wheel to perform fine grinding on the separated surface to remove the rough grinding texture of the raw material. The roughness requirement is <3μm.

[0068] Beveling: A single-sided V-shaped bevel is formed around the separation surface of one of the blanks using plasma machining, with a bevel angle of 30° and a depth of 35mm.

[0069] Preparation of protective separating agent: The main components of the protective separating agent are nano-sized silica and polyvinyl alcohol glue. Water and glue are mixed in a ratio of 40:1, heated to 100℃ and then mixed evenly. After cooling to below 40℃, nano-sized silica powder is added. The ratio of protective separating agent powder to glue is 1:3. After stirring evenly, it is brushed onto the separation surface of the sub-bill. After the protective separating agent is dried, it is assembled and sent into the press. The drying temperature does not exceed 400℃. During the transportation process, the separation surface is protected to prevent the protective separating agent from falling off and to ensure normal separation after rolling.

[0070] Non-vacuum welding of the preform assembly: The preform assembly is welded by first spot welding with gas shielded welding for positioning, and then full welding with submerged arc welding. The welding materials used are: and Ordinary welding wire;

[0071] During spot welding, the press applies 200-400 tons of pressure and presses it tightly before using gas shielded welding for spot welding positioning. The weld spot is 50mm-100mm long and spaced 200mm apart.

[0072] For full welding, the first pass is a manual or gas-shielded welding for the root pass. After welding, the slag is cleaned and the weld joints are free of cracks and pinholes. The welding billet machine is then hoisted, and a submerged arc welding machine is used to perform the second pass on all four sides in a specific sequence. Starting from the third pass, each weld should overlap half of the previous weld, until both the upper and lower surfaces are completely filled with weld seams. Preheating and interpass temperatures (T ≤ 100℃) must be strictly controlled to ensure the steel billet does not crack during prolonged high-temperature heating and rolling.

[0073] The welding process parameters are shown in the table below:

[0074]

[0075] Drill vent holes: Drill holes for non-vacuum welded billets. According to the thickness of the stacked billet, adjust the center of the drill bit to the center of the separation surface. The holes are located on the diagonal sides of the rolling direction, 200mm away from the corner, with a hole diameter of 10mm and a depth to the joint surface.

[0076] Spraying anti-oxidation coating: Spray a special anti-oxidation coating on the outer surface of the stacked billet, and then package it according to the process requirements before sending it into the steel rolling process;

[0077] Heating: Heat the stacked billet to 1200℃~1240℃ for 3 hours, with the temperature difference between the upper and lower surfaces less than 40℃, to ensure that the billet is heated evenly and thoroughly.

[0078] Rolling: The heated stacked billets are descaled using a roll crown of -0.30mm. Initial descaling requires two passes at an initial rolling temperature of 1030℃. The process strictly employs two-speed constant rolling, with descaling in each pass before the mill to ensure the surface quality of the steel plate. The intermediate billet thickness is 30mm. The second rolling pass uses four-speed high-speed rolling, with descaling initiated in the first pass, followed by six passes to form the plate, with a final rolling temperature of 702℃. After rolling, hot straightening is performed without controlled cooling, in three passes. The straightened plate has a flat shape and is then cooled before being cut into sections online, marked, and collected.

[0079] Cutting and Separation: The rolled slab is plasma cut on all four sides with a fixed width of 3000mm and a maximum length. It is then separated using a vacuum chuck. After separation, the slab is measured for thickness, inspected for surface, marked, and then sent for heat treatment.

[0080] Heat treatment: The quenching heat treatment temperature is 820℃~840℃, the tempering temperature is 540℃~600℃, and the tempering treatment is combined with a heated straightening process to ensure the flatness of the plate after heat treatment.

[0081] Inspection: Each piece was inspected for its shape, surface, and mechanical properties. The inspection results showed that the physical quality and performance indicators fully met the technical requirements of the 270,000 cubic meter LNG storage tank technical specifications.

[0082] Example 2:

[0083] The 06Ni9DR steel is 6mm thick and 2920mm wide. The steel plate has a tensile strength of 720MPa, an average yield strength of 615MPa, an elongation of 25.0%, a flatness of 5mm / m, and a difference of 0.03mm between plates.

[0084] Billet design: The billet design principle is that the thickness of the sub-bills is 60mm to 120mm, the width is the original width of the billet, and the length is the finished width plus the trimming allowance. After the billets are assembled, they are rolled into plates laterally. Sub-bills are prepared according to the production plan. Two sub-bills of the same specification are selected according to the billet assembly principle to form a stacked rolling master billet. The external dimensions of the stacked rolling billet are 200×1750×1200 (mm). The target size of the rolled steel plate is 6×2600×24000 (mm), and the finished product specification is 3×2600×12000 (mm).

[0085] Surface treatment of billet: Use a slab grinding machine to perform rough grinding to remove iron oxide scale from the upper and lower surfaces of the billet, and then use a flap wheel to perform fine grinding on the separated surface to remove the rough grinding texture of the raw material. The roughness requirement is <3μm.

[0086] Beveling: A single-sided V-shaped bevel is formed around the separation surface of one of the blanks using plasma machining, with a bevel angle of 25° and a depth of 30mm.

[0087] Preparation of protective separating agent: The main components of the protective separating agent are nano-sized silica and polyvinyl alcohol glue. Water and glue are mixed in a ratio of 40:1, heated to 100℃ and then mixed evenly. After cooling to below 40℃, nano-sized silica powder is added. The ratio of protective separating agent powder to glue is 1:3. After stirring evenly, it is brushed onto the separation surface of the sub-bill. After the protective separating agent is dried, it is assembled and sent into the press. The drying temperature does not exceed 400℃. During the transportation process, the separation surface is protected to prevent the protective separating agent from falling off and to ensure normal separation after rolling.

[0088] Non-vacuum welding of the preform assembly: The preform assembly is welded by first spot welding with gas shielded welding for positioning, and then full welding with submerged arc welding. The welding materials used are: and Ordinary welding wire;

[0089] During spot welding, the press applies 200-400 tons of pressure and presses it tightly before using gas shielded welding for spot welding positioning. The weld spot is 50mm-100mm long and spaced 200mm apart.

[0090] For full welding, the first pass is a manual or gas-shielded welding for the root pass. After welding, the slag is cleaned and the weld joints are free of cracks and pinholes. The welding billet machine is then hoisted, and a submerged arc welding machine is used to perform the second pass on all four sides in a specific sequence. Starting from the third pass, each weld should overlap half of the previous weld, until both the upper and lower surfaces are completely filled with weld seams. Preheating and interpass temperatures (T ≤ 100℃) must be strictly controlled to ensure the steel billet does not crack during prolonged high-temperature heating and rolling.

[0091] The welding process parameters are shown in the table below:

[0092]

[0093] Drill vent holes: Drill holes for non-vacuum welded billets. According to the thickness of the stacked billet, adjust the center of the drill bit to the center of the separation surface. The holes are located on the diagonal sides of the rolling direction, 200mm away from the corner, with a hole diameter of 10mm and a depth to the joint surface.

[0094] Spraying anti-oxidation coating: Spray a special anti-oxidation coating on the outer surface of the stacked billet, and then package it according to the process requirements before sending it into the steel rolling process;

[0095] Heating: Heat the stacked billet to 1200℃~1240℃ for 2.5 hours, with the temperature difference between the upper and lower surfaces less than 40℃, to ensure that the billet is heated evenly and thoroughly.

[0096] Rolling: The heated stacked billets are descaled using a roll crown of -0.22mm. Initial descaling requires two passes at an initial rolling temperature of 1030℃. The process strictly employs two-speed constant rolling, with descaling in each pass before the mill to ensure the surface quality of the steel plate. The intermediate billet thickness is 36mm. The second rolling pass uses four-speed high-speed rolling, with descaling initiated in the first pass, followed by six passes to form the plate, with a final rolling temperature of 718℃. After rolling, hot straightening is performed without controlled cooling, in three passes. The straightened plate has a flat shape and is then cooled before being cut into sections online, marked, and collected.

[0097] Cutting and Separation: The four sides of the rolled billet are cut by plasma cutting, with a fixed width of 2600mm and a maximum length. Vacuum chucks are used to separate the billet. After separation, the thickness is measured, the surface is inspected, and the billet is marked and then sent for heat treatment.

[0098] Heat treatment: The quenching heat treatment temperature is 820℃~840℃, the tempering temperature is 540℃~600℃, and the tempering treatment is combined with a heated straightening process to ensure the flatness of the plate after heat treatment.

[0099] Inspection: Each piece is inspected for its shape, surface, and mechanical properties. The inspection results show that the physical quality and performance indicators fully meet the technical requirements of the LNG storage tank technical specifications.

[0100] In summary, compared with the prior art, the manufacturing method of ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks of the present invention has the following advantages and beneficial effects:

[0101] (1) The present invention uses nano-sized silica as the protective separating agent and special glue as the ingredient. The protective separating agent has a simple ratio, low cost, high temperature resistance and strong adhesion, which effectively ensures the surface quality of the separation surface after steel plate stacking.

[0102] (2) The blanking is filled by submerged arc welding through non-vacuum welding and ordinary welding wire is used as the welding material, which effectively reduces the blanking cost and improves the blanking efficiency.

[0103] (3) By adjusting the heating process, roll design and rolling process, the surface, plate shape and thickness accuracy control was achieved.

[0104] It should be noted that, unless otherwise expressly specified and limited, the term "connection" or its synonyms should be interpreted broadly in this document. For example, "connection" can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal communication of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances. Furthermore, expressions such as "first" and "second" are merely used to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. At the same time, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for manufacturing ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks, characterized in that, The manufacturing method of the ultra-thin and ultra-wide 06Ni9DR medium-thick plate for LNG storage tanks includes: billet design - sub-bill surface treatment - beveling - preparation of protective separating agent - non-vacuum welding assembly - drilling vent holes - spraying anti-oxidation coating - heating - rolling - cutting and separation - heat treatment - inspection. The chemical composition of 06Ni9DR is controlled by mass percentage as follows: C≤0.05%, Si≤0.35%, Mn: 0.30%~0.80%, P≤0.005%, S≤0.002%, Ni: 8.50%~10.00%, with the remainder being iron and unavoidable impurities. Billet design: Prepare sub-bills according to the production plan, and select two sub-bills of the same specification to form a stacked master billet according to the billet assembly principle; Sub-billet surface treatment: The sub-billet is rough-ground to remove the iron oxide scale on the upper and lower surfaces, and then the separated surfaces are fine-ground to remove the rough grinding texture of the raw material. The roughness requirement is <3µm. Beveling: A single-sided V-shaped bevel is formed around the separation surface of one of the blanks using plasma machining. Preparation of protective separating agent: The protective separating agent consists of nano-sized silica and polyvinyl alcohol glue. Water and glue are mixed in a 40:1 ratio, heated to 100°C and then mixed evenly. After cooling to below 40°C, nano-sized silica powder is added. The ratio of protective separating agent powder to glue is 1:

3. After stirring evenly, it is brushed onto the separation surface of the sub-form. After the protective separating agent is dried, it is assembled and sent into a press. The drying temperature does not exceed 400°C. Non-vacuum welding of billet assembly: Welding of the sub-billets, first using gas shielded welding for spot welding and positioning, and then using submerged arc welding for full welding; Drill vent holes: Drill holes for non-vacuum welded billets. According to the thickness of the stacked billet, adjust the center of the drill bit to the center of the separation surface. The holes are located on the diagonal sides of the rolling direction, 200mm away from the corner, with a hole diameter of 10mm and a depth to the joint surface. Spraying anti-oxidation coating: Spray a special anti-oxidation coating on the outer surface of the stacked billet, and then package it according to the process requirements before sending it into the steel rolling process; Heating: Heat the stacked billet to 1200℃~1240℃ for no more than 4 hours, with a temperature difference of less than 40℃ between the upper and lower surfaces, to ensure that the billet is heated evenly and thoroughly. Rolling: The heated stacked billet is rolled to remove scale using a roll crown of -0.20mm to -0.35mm, with a final rolling temperature ≥700℃; Cutting and Separation: The rolled slabs are cut and separated, and the separated slabs are then subjected to thickness measurement, surface inspection, marking, and heat treatment. Heat treatment: The quenching heat treatment temperature is 820℃~840℃, the tempering temperature is 540℃~600℃, and the tempering treatment is combined with a heated straightening process to ensure that the plate shape is flat after heat treatment. Inspection: Each piece is inspected for its shape, surface, and mechanical properties.

2. The method for manufacturing ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks as described in claim 1, characterized in that, In the billet design process, the design principle for the sub-bills is that the thickness of the sub-bills is 60mm~120mm, the width is the original width of the billet, and the length is the finished width plus the trimming allowance. After the billets are assembled, they are rolled laterally into plates.

3. The method for manufacturing ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks as described in claim 1, characterized in that, In the surface treatment step of the sub-blank, a slab grinding machine is used for rough grinding, and a flap wheel is used for fine grinding.

4. The method for manufacturing ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks as described in claim 1, characterized in that, In the beveling step, the beveling angle is 25°~35° and the depth is 30mm~40mm.

5. The method for manufacturing ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks as described in claim 1, characterized in that, In the non-vacuum welding assembly step, the welding materials used are: ¢1.2mm and ¢4.0mm ordinary welding wire; During spot welding, the press applies 200-400 tons of pressure and presses it tightly before using gas shielded welding for spot welding positioning. The weld spot is 50mm-100mm long and spaced 200mm apart. For full welding, the first pass is done by manual welding or gas shielded welding to lay the foundation. After welding, the slag is cleaned and it is ensured that there are no defects such as cracks and pinholes at the weld joint. The welding billet machine is hoisted and the submerged arc welding machine is used to weld the four weld joints in a certain order for the second pass. Starting from the third pass, each weld is required to overlap half of the upper weld, until the upper and lower welds are completely filled. The preheating and interpass temperature T≤100℃ are strictly controlled to ensure that the steel billet will not crack during the long-term high-temperature heating and rolling process. The welding process parameters are shown in the table below: 。 6. The method for manufacturing ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks as described in claim 1, characterized in that, During the rolling process, the roll period design includes loading a furnace of carbon steel after the roll change and arranging about 20 wide plates for transition hot rolling. Initial descaling requires double descaling to remove 90% of the surface coating. If the coating is not completely removed, an additional small reduction pass is added to the initial rolling to break up the coating, ensuring that the coating is completely removed in the first three passes of the initial rolling. The initial rolling temperature is 980~1030℃, and the process strictly adopts two-speed constant rolling to make full use of the favorable conditions of high temperature and concentrate the reduction as much as possible in the first few passes. At the same time, the first pass before the mill is descaled to maintain the surface quality of the steel plate. The thickness of the intermediate billet is 3~4 times the thickness of the finished product. The second rolling pass adopts four-speed high-speed rolling. The rolling process focuses on maintaining the plate shape. Descaling is initiated in the first pass, and subsequent passes are handled according to the plate shape. After rolling, hot straightening is performed without controlled cooling for 1-3 passes to ensure the plate shape is flat.

7. The method for manufacturing ultra-thin and ultra-wide 06Ni9DR medium-thick plates for LNG storage tanks as described in claim 1, characterized in that, During the cutting and separation process, the upper steel plate is lifted by a vacuum suction cup, and the upper and lower plates are separated by the weight of the steel plate itself. Pry bars are used to assist in the separation at the corners. The width is determined according to the planned dimensions, and the length is kept to the maximum.

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