A method for preparing a large ultra-long inconel flat material

Abstract

The application discloses a preparation method of large-size super-long invar alloy flat material, adopts four forging processes, and specifically comprises the following steps: first fire is used for head riser pretreatment, second fire is used for vertical ingot upsetting and octagonal shaping, third fire is used for secondary vertical ingot upsetting and multi-surface elongation, and fourth fire is used for finished product forging. Through segmented heating and forging cooperative control, the bottleneck problem existing in the forging process of the super-long specification is broken through, the large-size super-long invar alloy flat material with a weight of 25-30 t and a length of greater than or equal to 11 m is obtained, and the forging quality and production efficiency of the large-size super-long invar alloy flat material are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of Invar alloy forging, and more specifically, to a method for preparing large, ultra-long Invar alloy flats. Background Technology

[0002] Domestically produced ultra-large LNG storage tanks and other major equipment are developing towards large-scale and integrated designs. Their key structural components (such as tank walls and tank bottoms) rely on large Invar alloy materials, which have low expansion coefficients, high strength and excellent low-temperature stability.

[0003] Currently, the preparation of large Invar alloy materials typically employs a five-stage forging process: The first stage involves clamping the tail of the ingot and gently tapping and elongating the head, pressing down 10-80mm on one side. The head is then gently tapped and elongated twice to reduce the height difference between the ingot body and the riser step. The tail is tapped and elongated to maintain consistent diameters at both ends. The eight corners are then gently tapped and chamfered before being returned to the furnace for heat preservation. The second and third stages both involve using tongs to hold the ingot upright and performing disc upsetting, controlling the upsetting speed and pause time, while simultaneously elongating and chamfering, followed by heat preservation in the furnace. The fourth stage involves chamfering the ingot with tongs to prevent corner cracking, and then step-down deformation on one end, followed by heat preservation in the furnace. The fifth stage involves chamfering the unforged end and forging it to the finished thickness, then turning the ingot around and forging the other forged end to the finished thickness, completing the final shaping and dimensional adjustment. However, this process is only suitable for producing steel ingots of ≤14 tons (finished product length approximately 5.3 meters), which is insufficient to meet the demand for ultra-long Invar alloy flats of 25-30 tons. The main limiting factors include: (1) difficulty in quality control, ultra-long ingots are prone to head cracking and tail shrinkage cavities, resulting in a yield of less than 71%; (2) limited material properties, traditional processes lead to coarse grains and a thermal expansion coefficient deviation exceeding 0.3×10. -6 ℃, affecting equipment precision; (3) low production efficiency, lack of standardized processes, reliance on manual experience, and a single ingot forging cycle of up to 30 hours. If Invar alloy prepared by the five-fire forging process is used to build large LNG storage tanks (such as 160,000 cubic meters), only splicing can be used. This method has more welds, and the welds are easily affected by low temperature and high pressure to crack, significantly increasing the risk of LNG leakage.

[0004] In view of the above, there is an urgent need to study a method for preparing large-scale ultra-long Invar alloys, which can realize the preparation of large-scale ultra-long Invar alloys and meet the stringent requirements of major equipment such as ultra-large LNG storage tanks for the alloy material in terms of specifications and performance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for preparing large, ultra-long Invar alloy flats. This method employs a four-stage temperature-controlled forging process, with segmented heating and forging coordinated control, overcoming the bottleneck problems in the ultra-long specification forging process, and obtaining Invar alloy flats weighing 25-30 tons and with a length ≥11m. This significantly improves the forging quality and production efficiency of large, ultra-long Invar alloy flats.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The first aspect of this invention provides a method for preparing large, ultra-long Invar alloy flat bars, employing a four-stage forging process, specifically including the following steps:

[0008] S1, the first firing stage involves pre-treatment of the head riser.

[0009] A 25-30 ton Invar alloy steel ingot is hoisted onto the working platform of the double manipulator, clamping the head and tail of the ingot to ensure that the axis of the ingot coincides with the center line of the pressure head of either manipulator. The head of the ingot is then forged using a wide-face light tapping and lengthening process and chamfering. Immediately after forging, the ingot is sent to a heating furnace for heat treatment, with the heating temperature controlled at 900-1300℃.

[0010] S2, the second firing stage involves vertical ingot upsetting and octagonal shaping.

[0011] The steel ingot, after the first heat treatment, is vertically operated using a throwing tong, and a disc is placed at the bottom of the ingot for support. Then, upsetting is performed at a constant speed. When the upsetting height reaches the set amount, the upsetting is paused for at least 3 seconds before continuing. After upsetting is completed, the pressure head mode is quickly switched to perform octagonal shaping on the steel ingot. The eight sides of the steel ingot are gently tapped and lengthened in sequence. After octagonal shaping, the steel ingot is returned to the furnace for heat preservation treatment, and the heat preservation temperature is controlled at 900-1300℃.

[0012] S3, the third firing stage involves secondary vertical ingot upsetting and multi-faceted drawing.

[0013] After repeating the vertical ingot operation of the second forging, upsetting is performed, with the upsetting amount controlled at 1 / 3 to 2 / 3 of the height of the ingot on the current face. After upsetting, the process is quickly switched to drawing mode, with the thickness reduction per pass controlled at 10 to 100 mm, gradually pressing to the target thickness. During the drawing process, the wide face and sides of the ingot are forged alternately. After multi-face drawing, the ingot is returned to the furnace for heat treatment, with the heat treatment temperature controlled at 900 to 1300℃.

[0014] S4, the fourth firing stage for finished product forging.

[0015] The edges of the steel ingot are chamfered, and then one end of the steel ingot is clamped by a double manipulator while the other end is forged in a stepped pressing mode. The edge is finished according to the width of the finished product, and the position of the steel ingot is adjusted synchronously by the double manipulator during the pressing process. Finally, a large ultra-long Invar alloy flat bar with a weight of 25-30t and a length of ≥11m is obtained.

[0016] Preferably, in step S1:

[0017] The diameter of the Invar alloy steel ingot, weighing 25-30t, is ≥1350mm;

[0018] Before clamping the head and tail of the steel ingot, the dual manipulators are adjusted to control the clamping force of both manipulators to be 50-80N. At the same time, the infrared temperature measurement system is activated to monitor the preheating status of the work platform in real time, so as to accurately and timely grasp the temperature change of the steel ingot throughout the process and ensure the accuracy and timeliness of the temperature measurement data.

[0019] In the forging process of wide-face light tapping and lengthening and edge chamfering, the eight faces of the steel ingot head are alternately lightly tapped and lengthened, with the reduction amount controlled at 20-100mm. At the same time, the eight edges of the steel ingot are lightly tapped and chamfered, with the reduction amount controlled at 20-100mm.

[0020] The diameter of the steel ingot after forging is 1250-1300 mm;

[0021] The heat treatment is held at a temperature of 2 to 5 hours.

[0022] Preferably, in step S2:

[0023] Before the upsetting operation, the verticality deviation of the steel ingot shall not exceed 10°;

[0024] During the upsetting operation, the constant speed is 2-10 mm / s, the height upsetting amount is set to 20-100 mm, the pause time is 3-8 s, and the total height upsetting amount is 300-400 mm.

[0025] During the octagonal shaping process, each side of the steel ingot is patted back and forth 2 to 10 times, and the single-sided pressing amount is 10 to 100 mm.

[0026] The insulation temperature for the insulation treatment is 2 to 5 hours.

[0027] Preferably, in step S3:

[0028] During the multi-faceted drawing process, the steel ingot thickness is pressed to the target thickness in 2 to 7 passes.

[0029] During the alternating forging of the wide face and side of the steel ingot, after each wide face pressing forging in the first two passes, the side is forged once. After each two wide face pressing forgings in subsequent passes, the side is forged once.

[0030] The insulation temperature for the insulation treatment is 2 to 5 hours.

[0031] Preferably, in step S4:

[0032] The reduction amount for the chamfering process is 20-70 mm;

[0033] In the stepped forging process, the first pass reduces the thickness by 20-80 mm, and subsequent passes reduce it by 20-50 mm, with the thickness reduced to 260-270 mm in 4-7 passes.

[0034] Preferably, in step S4, the thickness of the large, ultra-long Invar alloy flat bar is 260–270 mm, and the width is 1150–1170 mm.

[0035] Preferably, in step S4, the grain size of the large, ultra-long Invar alloy flat material is grade 4 or higher, and the deviation of its coefficient of thermal expansion is ≤1.8×10⁻⁶. -6 ℃.

[0036] The present invention has the following beneficial effects:

[0037] 1. This invention adopts a four-stage precise temperature control forging system, which fully considers the poor plasticity of large Invar alloys at high temperatures. It creatively adopts the "segmented heating and forging synergistic control" method to optimize the traditional five-stage forging process (14-ton steel ingot production process) into four stages. By precisely controlling the heating temperature and forging operation of each stage, it effectively breaks through the bottleneck problem in the forging process of ultra-long specifications, and significantly improves the forging quality and efficiency.

[0038] 2. The preparation method of the present invention has outstanding economic benefits, which can significantly improve the yield of large ultra-long Invar alloy flats, shorten the forging cycle of a single ingot, thereby improving the overall forging efficiency and effectively reducing forging costs (cost reduction of at least 20%).

[0039] 3. The preparation method of this invention is the first in China to achieve large-scale mass production of 11-meter-class large ultra-long Invar alloy flat materials, which can fully meet the construction needs of large LNG storage tanks of 170,000 cubic meters and above, and effectively promote the technological upgrading and value enhancement of high-end industrial chains such as aerospace and energy equipment. Its market application prospects and industrial driving effect are significant.

[0040] 4. The preparation method of the present invention has significant social benefits. It not only ensures the independent production of major equipment and effectively reduces the risk of LNG storage tank leakage, but also contributes to national energy security. Attached Figure Description

[0041] Figure 1 This is a flowchart of the preparation method of the large ultra-long Invar alloy flat material of the present invention;

[0042] Figure 2 This is a dimensional diagram of the finished product of the large, ultra-long Invar alloy flat material prepared in Example 1 of this invention. Detailed Implementation

[0043] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0044] To address the challenges of forging large, ultra-long Invar alloy ingots, this invention provides a method for preparing large, ultra-long Invar alloy flats suitable for 25-30T ingots. It fully considers the poor plasticity of large Invar alloys at high temperatures and closely integrates with the equipment characteristics of a 25-30T large steel ingot high-speed forging machine. It innovatively adopts a "segmented heating and forging synergistic control" process system, employing a four-stage forging process and precisely controlling key aspects such as heating temperature and forging operation for each stage. This breaks through the limitation of domestic production of only 14-ton steel ingots (finished product length approximately 5.3 meters), achieving high-quality production of ultra-long Invar alloy flats with a length ≥11 meters, breaking the foreign monopoly, and promoting the localization of high-end equipment.

[0045] Combination Figure 1 As shown, this invention provides a method for preparing large, ultra-long Invar alloy flat bars, employing a four-stage forging process, specifically including the following steps:

[0046] S1, the first firing stage involves pre-treatment of the head riser.

[0047] Invar alloy steel ingots weighing 25-30t and with a diameter of 1300mm or more are hoisted onto the working platform of the double manipulator, clamping the head and tail of the ingot to ensure that the axis of the ingot coincides with the center line of the pressure head of the double manipulator; the head of the ingot is forged by a wide-face light tapping and lengthening and chamfering process; immediately after forging, the ingot is sent into a heating furnace for heat treatment, and the heating temperature is controlled at 900-1300℃;

[0048] The first firing process described above mainly involves the pretreatment operation of the riser at the head, as detailed below:

[0049] Equipment preparation: A comprehensive debugging process is conducted on the dual manipulators to ensure uniform clamping force (e.g., 50-80N) to guarantee balanced force on the steel ingot during forging and prevent displacement or uneven deformation. Simultaneously, an infrared temperature measurement system is activated to monitor the preheating status of the work platform in real time, accurately and promptly tracking the temperature changes of the steel ingot throughout the forging process, ensuring the accuracy and timeliness of the temperature data.

[0050] Ingot positioning: Using specialized hoisting equipment, Invar alloy steel ingots weighing 25-30 tons are smoothly hoisted onto the working platform of the high-speed forging machine. Subsequently, the two manipulators quickly clamp the head and tail of the ingot respectively. Through precise positioning adjustments, it is ensured that the axis of the ingot is completely aligned with the center line of the pressure head of either manipulator, providing a precise positional reference for subsequent forging operations.

[0051] Forging operation: A unique "wide-face light tapping and drawing + edge chamfering" process is employed. The single-sided pressing amount of the manipulator head at the head position is strictly controlled within an effective range. The eight faces of the ingot head are alternately and lightly tapped and drawn, controlling the diameter of the forged ingot within the range of 1250–1300 mm. In a specific embodiment, the pressing amount is controlled to 20–100 mm. This operation ensures a smooth and flat area near the riser line, effectively reducing the step height difference between the ingot body and the riser, and avoiding material damage caused by over-forging. Simultaneously, the eight edges of the ingot are lightly tapped and chamfered, with the pressing amount controlled to 20–100 mm. This operation eliminates stress concentration points at the edges, reducing the risk of cracks during subsequent forging.

[0052] Temperature control coordination: After the forging operation is completed, the steel ingot is immediately sent to the heating furnace for heating treatment. The heating furnace implements a temperature control strategy of "precise heat preservation of 900~1300℃" and the heat preservation time is controlled to be 2~5 hours.

[0053] S2, the second firing stage involves vertical ingot upsetting and octagonal shaping.

[0054] The steel ingot, after the first heat treatment, is vertically operated using a throwing tong, and a disc is placed at the bottom of the ingot for support. Then, upsetting is performed at a constant speed. When the upsetting amount reaches the set amount, it is paused for at least 3 seconds before continuing upsetting. After upsetting is completed, the pressure head mode is quickly switched to perform octagonal shaping on the steel ingot. The eight sides of the steel ingot are gently tapped and lengthened in sequence. After octagonal shaping, the steel ingot is returned to the furnace for heat preservation treatment, and the heat preservation temperature is controlled at 900-1300℃.

[0055] The second firing process mainly involves vertical upsetting and octagonal shaping, and the specific process is as follows:

[0056] Vertical ingot operation: Two manipulators work closely together to vertically raise the steel ingot. A throwing clamp is used to hold the ingot upright, and a disc is placed at the bottom to enhance its stability. Precise adjustments are made to ensure the verticality deviation of the ingot does not exceed 10° (e.g., 1–10°) to prevent the ingot from tilting during upsetting, which would affect forging quality.

[0057] Upsetting operation: The double manipulator slowly upsets the steel ingot at a constant speed of 2-10 mm / s. When the upsetting height reaches the set value (20-150 mm), pause for 3-8 seconds to allow the internal stress of the steel ingot to be fully released, and then continue upsetting. The total upsetting height is strictly controlled within 300-400 mm to ensure uniform internal structure of the steel ingot and avoid structural defects caused by excessive upsetting.

[0058] Octagonal Shaping: After upsetting, quickly switch to the pressure head mode of the dual-operation machine to perform a "light tapping and elongation + octagonal shaping" operation on the steel ingot. Each of the eight sides of the ingot is elongated sequentially, with each side tapped back and forth 2-10 times. The single-side reduction is set to 10-100mm. Through this precise operation, the steel ingot is shaped into a regular octagon (the width of the ingot is controlled between 1250-1300mm, and the length is 2±0.5 meters), effectively reducing the risk of warping during subsequent rolling and improving the dimensional accuracy and surface quality of the product.

[0059] Temperature control: After the octagonal shaping is completed, the steel ingot is returned to the furnace for heat preservation treatment. The heat preservation temperature is maintained at 900-1300℃ and the heat preservation time is 2-5 hours.

[0060] S3, the third firing stage involves secondary vertical ingot upsetting and multi-faceted drawing.

[0061] After repeating the vertical ingot operation of the second forging, upsetting is performed, with the upsetting amount controlled at 1 / 3 to 2 / 3 of the height of the ingot on the current face. After upsetting, the process is quickly switched to drawing mode, with the thickness reduction per pass controlled at 10 to 100 mm, gradually pressing to the target thickness. During the drawing process, the wide face and sides of the ingot are forged alternately. After multi-face drawing, the ingot is returned to the furnace for heat treatment, with the heat treatment temperature controlled at 900 to 1300℃.

[0062] The aforementioned third firing mainly involves secondary vertical ingot upsetting and multi-faceted drawing operations, the specific process of which is as follows:

[0063] Secondary vertical ingot: Repeat the vertical ingot operation in the second firing, and use throwing pliers to firmly fix the steel ingot to ensure the stability of the steel ingot during the vertical ingot process, so as to provide a reliable foundation for subsequent upsetting and drawing operations.

[0064] Upsetting operation: Use either of the two manipulators to perform the "throwing clamp vertical ingot upsetting" operation. The upsetting height should be strictly controlled to 1 / 3 to 2 / 3 of the height of the ingot to avoid uneven internal structure of the ingot due to excessive upsetting, which would affect the material properties.

[0065] Multi-face elongation: After completing the upsetting operation, quickly switch to elongation mode. The thickness reduction in each pass is controlled at 10-100mm, and the thickness of the steel ingot is gradually reduced to the target thickness in 2-7 passes. The first two passes complete one wide-face forging and one edge-reducing forging on the side. After alternating forging for two passes, in subsequent passes, after every two wide-face forgings, an edge-reducing forging is performed on the side (i.e., the reduction needs to be increased in the later stages) to ensure uniform internal structure of the material and improve the overall performance of the material.

[0066] Temperature control coordination: After the multi-faceted drawing is completed, the steel ingot is returned to the furnace for heat preservation treatment. The heat preservation temperature is set at 900-1300℃ and the heat preservation time is 2-5 hours to ensure the temperature uniformity of the steel ingot during the heating process.

[0067] S4, the fourth firing stage for finished product forging.

[0068] The edges of the steel ingot are chamfered, and then one end of the steel ingot is clamped by a double manipulator while the other end is forged in a stepped pressing mode. The edge is finished according to the width of the finished product, and the position of the steel ingot is adjusted synchronously by the double manipulator during the pressing process. Finally, a large ultra-long Invar alloy flat bar with a weight of 25-30t and a length of ≥11m is obtained.

[0069] The third firing process mentioned above is mainly for forging the finished product, and the specific process is as follows:

[0070] Angular pretreatment: The jaws of either of the two manipulators are used to chamfer the edges of the steel ingot, with the reduction controlled between 20 and 70 mm. This effectively prevents corner cracks from occurring at the edges of the steel ingot during forging, thereby improving product quality and reliability.

[0071] Stepped Forging: The ingot is firmly clamped at one end by two manipulators, while the other end is forged using a stepped forging pattern. The initial forging depth is controlled at 20-80mm, gradually decreasing to 20-50mm in subsequent passes, with the ingot's thickness precisely pressed to 260(0,+10)mm in 4-7 passes. Simultaneously, edge finishing is performed according to the finished product width requirements to ensure the ingot's width deviation meets the standard requirement (1150(0,+20)mm), guaranteeing the product's dimensional accuracy. The above process is repeated to forge the other end of the ingot using the stepped forging pattern.

[0072] Length and Surface Control: During the pressing process, the position of the steel ingot is adjusted synchronously and precisely using dual manipulators to ensure that the effective length of the ingot gradually extends to 11 meters or more. During the finished product forging process, the hammer mark residue is strictly controlled to ensure that there are no obvious indentations on the sides of the steel ingot, thereby improving the surface quality of the product.

[0073] The large, ultra-long Invar alloy flat material prepared by this invention has a thickness of 260–270 mm, a width of 1150–1170 mm, a length ≥11 m, and a weight of 25–30 t.

[0074] The aforementioned large, ultra-long Invar alloy flats have a grain size of grade 4 or higher and a thermal expansion coefficient deviation of ≤1.8×10⁻⁶. -6 / ℃.

[0075] The method for preparing large, ultra-long Invar alloy flat bars of this invention employs "segmented heating and forging synergistic control." The first heat stage involves pre-deformation treatment and precise adjustment of the ingot's height-to-diameter ratio to create favorable process conditions for subsequent upsetting. The second heat stage involves the initial upsetting and drawing operation to fully release residual stress within the ingot, while precisely controlling the upsetting height to lay the foundation for the subsequent two upsetting processes. The third heat stage completes the secondary upsetting and drawing operation, effectively breaking down the as-cast structure and significantly improving the slab's microstructure density and mechanical properties. The fourth heat stage leverages the advantages of dual-operator synergistic operation, employing a large reduction and rapid deformation process during stepped forging to directly form the billet, ensuring uniform and refined grain structure throughout the process. Through the synergistic effect of these four heat stages, precise plastic deformation and full-process microstructure control of the ingot from its as-cast state to the finished product are achieved.

[0076] Compared with the traditional five-stage forging process to produce 14-ton steel ingots, the application of the preparation method of the large-scale ultra-long Invar alloy flats of this invention increases the yield from 71% to over 83%, shortens the forging cycle of a single ingot from 30 hours to 15 hours (efficiency increased by 50%), reduces the cost of a single 11-meter flat by 20%, and can save more than 5 million yuan in costs with an annual production capacity of 10 pieces, thereby enhancing the competitiveness of enterprises.

[0077] The large-scale ultra-long Invar alloy flats prepared above have enabled the mass production of Invar alloy ingots of 11 meters and above, which can meet the needs of LNG storage tanks of more than 170,000 cubic meters. This avoids the phenomenon that large LNG storage tanks are built by splicing small-sized plates due to the lack of qualified ultra-long Invar alloys, which makes the welds susceptible to cracking due to low temperature and high pressure, and reduces the risk of LNG storage tank leakage.

[0078] Example

[0079] The preparation method of the large, ultra-long Invar alloy flat material in this embodiment was implemented in a steel company in Shanghai. The specific process is as follows:

[0080] First step: Pre-treatment of the head cap opening

[0081] Equipment preparation: Conduct a comprehensive debugging of the dual manipulators to ensure that the clamping force of the dual manipulators is uniform and consistent (the clamping force can be set to 80N) to ensure that the steel ingot is subjected to balanced forces during the forging process and to avoid displacement or uneven deformation. At the same time, preheat the infrared temperature measurement system to normal operating conditions to ensure accurate and timely monitoring of the temperature changes of the steel ingot.

[0082] Ingot Positioning: Using specialized hoisting equipment, Invar alloy steel ingots weighing 25-30 tons and with a diameter of 1300mm or more are smoothly hoisted onto the working platform of the dual manipulator. Subsequently, the dual manipulators quickly clamp the head and tail of the ingot respectively. Through precise positioning adjustments, the axis of the ingot is ensured to be completely aligned with the center line of the pressure head of one of the manipulators, providing a precise positional reference for subsequent forging operations.

[0083] Forging Operation: A unique "wide-face light tapping and drawing + edge chamfering" process is employed. The single-sided reduction of the high-speed forging mill is strictly controlled. The eight faces of the ingot head are alternately and lightly tapped and drawn, with a reduction controlled at 20-50mm. This operation ensures a smooth surface near the riser line, effectively reducing the step height difference between the ingot body and the riser, and avoids material damage caused by over-forging. Simultaneously, the eight edges of the ingot are lightly chamfered, with a reduction controlled at 20-50mm, keeping the ingot diameter within the range of 1250-1300mm to ensure proper breakage at the head and tail. This eliminates stress concentration points at the edges, reducing the risk of cracks during subsequent forging.

[0084] Temperature control: After forging, the steel ingot is immediately sent to the heating furnace for heating treatment. The heating furnace implements a temperature control strategy of "precise holding at 900-1300℃" for 2-5 hours.

[0085] Second stage: Vertical ingot upsetting and octagonal shaping

[0086] Vertical ingot clamping: Two manipulators work closely together to vertically hold the steel ingot. A throwing clamp is used to hold the ingot upright, and a disc is placed at the bottom of the ingot to enhance its stability. Precise adjustments ensure that the verticality deviation of the ingot does not exceed 10 degrees, preventing the ingot from tilting during upsetting and affecting forging quality.

[0087] Upsetting operation: The high-speed forging mill slowly upsets the steel ingot at a constant speed of 8-10 mm / s. When the upsetting height reaches the set value of 150 mm, pause for 6-8 seconds to allow the internal stress of the steel ingot to be fully released, and then continue upsetting. The total upsetting height is strictly controlled within 300-400 mm to ensure uniform internal structure of the steel ingot and avoid structural defects caused by excessive upsetting.

[0088] Octagonal Shaping: After the upsetting operation is completed, the pressure head mode of the high-speed forging machine is quickly switched to perform a "light tapping and elongation + octagonal shaping" operation on the steel ingot. Each of the eight sides of the ingot is elongated sequentially, with each side tapped back and forth 2-10 times. The single-side reduction is set to 80-100mm to facilitate the next upsetting. Through this precise operation, the steel ingot is shaped into a regular octagon (the width of the ingot is controlled between 1250-1300mm, and the length is approximately 2 meters), effectively reducing the risk of warping during subsequent rolling and improving the dimensional accuracy and surface quality of the product.

[0089] Temperature control: After the octagonal shaping is completed, the steel ingot is returned to the furnace for heat preservation treatment. The heat preservation temperature is maintained at 900-1300℃, and the heat preservation time is 2-5 hours.

[0090] Third firing: Second vertical ingot upsetting and multi-faceted drawing operation

[0091] Secondary vertical ingot: Repeat the vertical ingot operation in the second firing, and use throwing pliers to firmly fix the steel ingot to ensure the stability of the steel ingot during the vertical ingot process, so as to provide a reliable foundation for subsequent upsetting and drawing operations.

[0092] Quantitative upsetting: The dual-operator performs the "throwing clamp vertical ingot upsetting" operation, and the upsetting amount is strictly controlled to 1 / 3 to 2 / 3 of the current height of the steel ingot to avoid uneven internal structure of the steel ingot due to excessive upsetting, which would affect the material properties.

[0093] Multi-faceted drawing: After completing the upsetting operation, quickly switch to the drawing mode. The thickness reduction per pass is 80-100mm, and the thickness of the steel ingot is gradually reduced to the target thickness of 1000-1100mm in 2-7 passes. During the drawing process, the wide face and side of the steel ingot are alternately forged. In the first two passes, after each wide face reduction forging, the side is forged once. After two passes of alternating forging, in subsequent passes, after each two wide face reduction forgings, the side is forged once. This ensures the uniformity of the internal structure of the material and improves the overall performance of the material.

[0094] Temperature control: After multi-faceted drawing, the steel ingot is returned to the furnace for heat preservation treatment. The heat preservation temperature is set at 900-1300℃, and the heat preservation time is 2-5 hours to ensure the temperature uniformity of the steel ingot during the heating process.

[0095] Fourth step: Precision forging operation for finished product dimensions

[0096] Angular pretreatment: The edges of the steel ingot are chamfered using the jaws of a double manipulator, with the reduction controlled between 20 and 70 mm. This effectively prevents corner cracks from occurring at the edges of the steel ingot during forging, thereby improving product quality and reliability.

[0097] Stepped Forging Approximation: One end of the steel ingot is firmly clamped by two manipulators, while the other end is forged using a stepped forging pattern. The initial forging depth is controlled between 20 and 80 mm, gradually decreasing to 20-50 mm in subsequent passes, with the ingot's thickness precisely pressed to 260(0,+10) mm in 4-7 passes. Simultaneously, edge finishing is performed according to the finished product width requirement (1150(0,+20) mm) to ensure the width deviation of the ingot meets the standard requirements and guarantees the product's dimensional accuracy. This process is repeated to forge the other end of the ingot using the stepped forging pattern.

[0098] Length and Surface Control: During the pressing process, the position of the steel ingot is adjusted synchronously and precisely using dual manipulators to ensure that the effective length of the ingot gradually extends to 11 meters. During the forging process, the hammer mark residue is strictly controlled to ensure that there are no obvious indentations on the sides of the steel ingot, thereby improving the surface quality of the product.

[0099] Combination Figure 2 As shown, the large, ultra-long Invar alloy flat bar prepared in this embodiment has a thickness of 260 mm, a width of 1150 mm, a length of 11 m, and a weight of 25–30 t. The grain size of this large, ultra-long Invar alloy flat bar reaches 4 or higher, and the deviation of its coefficient of thermal expansion is ≤1.8 × 10⁻⁶. -6 / ℃.

[0100] The method for preparing large, ultra-long Invar alloy flats of this invention is the first technology in China to achieve mass production of Invar alloys exceeding 11 meters in length. It can meet the stringent requirements of major equipment such as LNG storage tanks with a capacity of 170,000 cubic meters or more for the specifications and performance of this alloy material, driving the upgrading of the aerospace and energy equipment industry chain; ensuring the localization of major equipment, reducing the risk of LNG storage tank leakage, and contributing to national energy security; promoting the transformation of domestic forging technology from "following" to "leading", cultivating high-end technical talents, and promoting the sustainable development of the industry.

[0101] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for preparing large, ultra-long Invar alloy flat bars, characterized in that: The four-stage forging process includes the following steps: S1, the first firing stage involves pre-treatment of the head riser. A 25-30 ton Invar alloy steel ingot is hoisted onto the working platform of the double manipulator, clamping the head and tail of the ingot to ensure that the axis of the ingot coincides with the center line of the pressure head of either manipulator. The head of the ingot is then forged using a wide-face light tapping and lengthening process and chamfering. Immediately after forging, the ingot is sent to a heating furnace for heat treatment, with the heating temperature controlled at 900-1300℃. S2, the second firing stage involves vertical ingot upsetting and octagonal shaping. The steel ingot, after the first heat treatment, is vertically operated using a throwing tong, and a disc is placed at the bottom of the ingot for support. Then, upsetting is performed at a constant speed. When the upsetting height reaches the set amount, the upsetting is paused for at least 3 seconds before continuing. After upsetting is completed, the pressure head mode is quickly switched to perform octagonal shaping on the steel ingot. The eight sides of the steel ingot are gently tapped and lengthened in sequence. After octagonal shaping, the steel ingot is returned to the furnace for heat preservation treatment, and the heat preservation temperature is controlled at 900-1300℃. S3, the third firing stage involves secondary vertical ingot upsetting and multi-faceted drawing. After repeating the vertical ingot operation of the second forging, upsetting is performed, with the upsetting amount controlled at 1 / 3 to 2 / 3 of the height of the ingot on the current face. After upsetting, the process is quickly switched to drawing mode, with the thickness reduction per pass controlled at 10 to 100 mm, gradually pressing to the target thickness. During the drawing process, the wide face and sides of the ingot are forged alternately. After multi-face drawing, the ingot is returned to the furnace for heat treatment, with the heat treatment temperature controlled at 900 to 1300℃. S4, the fourth firing stage for finished product forging. The edges of the steel ingot are chamfered, and then one end of the steel ingot is clamped by a double manipulator while the other end is forged in a stepped pressing mode. The edge is finished according to the width of the finished product, and the position of the steel ingot is adjusted synchronously by the double manipulator during the pressing process. Finally, a large ultra-long Invar alloy flat bar with a weight of 25-30t and a length of ≥11m is obtained.

2. The method for preparing large, ultra-long Invar alloy flats according to claim 1, characterized in that: In step S1: The diameter of the Invar alloy steel ingot, weighing 25-30t, is ≥1350mm; Before clamping the head and tail of the steel ingot, the double manipulator is adjusted to control the clamping force of both manipulators to be 50-80N. At the same time, the infrared temperature measurement system is activated to monitor the preheating status of the work platform in real time. In the forging process of wide-face light tapping and lengthening and edge chamfering, the eight faces of the steel ingot head are alternately lightly tapped and lengthened, with the reduction amount controlled at 20-100mm. At the same time, the eight edges of the steel ingot are lightly tapped and chamfered, with the reduction amount controlled at 20-100mm. The diameter of the steel ingot after forging is 1250-1300 mm; The heat treatment is held at a temperature of 2 to 5 hours.

3. The method for preparing large, ultra-long Invar alloy flats according to claim 1, characterized in that: In step S2: Before the upsetting operation, the verticality deviation of the steel ingot shall not exceed 10°; During the upsetting operation, the constant speed is 2-10 mm / s, the height upsetting amount is set to 20-100 mm, the pause time is 3-8 s, and the total height upsetting amount is 300-400 mm. During the octagonal shaping process, each side of the steel ingot is patted back and forth 2 to 10 times, and the single-sided pressing amount is 10 to 100 mm. The insulation temperature for the insulation treatment is 2 to 5 hours.

4. The method for preparing large, ultra-long Invar alloy flats according to claim 1, characterized in that: In step S3: During the multi-faceted drawing process, the steel ingot thickness is pressed to the target thickness in 2 to 7 passes. When alternating forging the wide face and side of the steel ingot, after each wide face pressing forging in the first two passes, the side is forged once; after each two wide face pressing forgings in subsequent passes, the side is forged once. The insulation temperature for the insulation treatment is 2 to 5 hours.

5. The method for preparing large, ultra-long Invar alloy flats according to claim 1, characterized in that: In step S4: The reduction amount for the chamfering process is 20–70 mm; In the stepped forging process, the first pass reduces the thickness by 20-80 mm, and subsequent passes reduce it by 20-50 mm, with the thickness reduced to 260-270 mm in 4-7 passes.

6. The method for preparing large, ultra-long Invar alloy flats according to claim 1, characterized in that: In step S4, the thickness of the large, ultra-long Invar alloy flat bar is 260-270 mm, and the width is 1150-1170 mm.

7. The method for preparing large, ultra-long Invar alloy flats according to claim 1, characterized in that: In step S4, the grain size of the large, ultra-long Invar alloy flat material reaches level 4 or above, and the deviation of the coefficient of thermal expansion is ≤1.8×10. -6 ℃.

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