Method for improving mechanical property of large section of low alloy steel A182F22

Abstract

The invention relates to the technical field of low alloy steel, in particular to a method for improving the large-section mechanical property of low alloy steel A182F22, which comprises the following steps: S1, raw material selection: selecting proper raw materials according to smelting requirements, and treating the raw materials; s2, raw material smelting, wherein the selected raw materials are poured into a smelting furnace to be smelted; the forging cogging and forging forming mode is adopted, so that the structure of the forge piece is more compact, anvil block preheating and temperature control in each step in the forging process are achieved, the internal and external temperature difference of the forge piece is delayed, the cracking tendency of the forge piece is reduced, and no obvious forging crack is generated on the surface; in the forging forming stage, the last-fire forging ratio is larger than 2, grains are refined, and no defect exists in UT detection; the forge piece is subjected to normalizing twice, oxide skin is removed before quenching, the structure is more uniform, saline water is used as quenching liquid, and the whole forge piece can be rapidly and thoroughly quenched; the dissection performance of the 700mm large-section forge piece produced by the process is far superior to that of a conventional forging and heat treatment forge piece after heat treatment.

Description

Technical Field

[0001] The invention relates to the technical field of low alloy steel, and in particular to a method for improving large-section mechanical properties of low alloy steel A182F22. Background Art

[0002] A182F22 alloy steel is well-known for its excellent corrosion resistance. It can work stably for a long time in low temperature, high pressure and corrosive media environment without obvious corrosion or performance degradation. This material is often used to manufacture key components of oil production equipment, such as valve bodies and casings. In deep-sea environments, these components need to withstand low temperature, high pressure and corrosive oil and gas erosion. Its excellent corrosion resistance and comprehensive mechanical properties make it an ideal material choice.

[0003] For example, the heat treatment process method for improving the mechanical properties of ZG25CrNiMo cast low alloy steel with the authorization announcement number CN202010704083.8 and the publication date 20201023 belongs to the field of metal heat treatment technology. The ZG25CrNiMo cast low alloy steel is first kept at 940-950℃ for 2 hours and air-cooled; the second time is kept at 890-900℃ for 2 hours and high temperature normalizing and air-cooling; 650-670℃ annealing for 5-6 hours, furnace cooling to 500℃, air-cooling out of the furnace; then kept at 870-880℃ for 4 hours, quenched in 18-23℃ water, air-cooled out of water at less than 100℃; finally kept at 590-620℃ for 8h for high temperature tempering. The beneficial effects of the present invention are as follows: the microstructure of the test steel under the process of twice high-temperature normalizing + annealing + quenching and tempering is a mixed structure of troostite + a very small amount of proeutectoid ferrite; through comparison of mechanical property test results, it can be seen that ZG25CrNiMo cast low alloy steel has the best low-temperature impact performance.

[0004] The wall thickness of conventional F22 forgings exceeds 500 mm, and the core strength is low, resulting in unqualified performance of large-section forgings, which often cannot meet the requirements of deep-sea construction. Therefore, it is urgent to design a method to improve the mechanical properties of large-section low-alloy steel A182F22 to solve the above problems. Summary of the invention

[0005] The object of the present invention is to provide a method for improving the large-section mechanical properties of low alloy steel A182F22 to solve the above-mentioned deficiencies in the prior art.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for improving the large-section mechanical properties of low alloy steel A182F22 comprises the following steps:

[0008] S1. Raw material selection: Select appropriate raw materials according to smelting requirements and process the raw materials;

[0009] S2. Raw material smelting: pouring the selected raw materials into a smelting furnace for smelting, adding a catalyst during smelting, and preparing the raw materials into steel ingots;

[0010] S3. Open forging: Place the steel ingot in a heating furnace for heating and forging, and ensure the temperature during forging;

[0011] S4. Sawing: Put the blank into the sawing equipment, operate the sawing equipment, and the sawing equipment will saw the blank;

[0012] S5. Forging: The sawn forgings are put back into the heating furnace, and the temperature is raised for forging. After forging, they are buried in sand for slow cooling.

[0013] S6. Preliminary heat treatment: The forged forgings are subjected to the first normalizing and tempering treatment, and then buried in sand for cooling;

[0014] S7. Rough machining: Place the cooled forging into the machining equipment, use a turning tool to machine the forging surface to remove the oxide scale, and use MT to inspect the surface defects after machining;

[0015] S8. Heat treatment: Place the forgings back into the heating furnace for normalizing, quenching and tempering to obtain high-strength forgings.

[0016] Furthermore, the raw material composition in step S1 is as follows: C: 0.14-0.15%, Mn: 0.50-0.60%, P: ≤0.010%, S: ≤0.005%, Si: ≤0.50%, Cr: 2.40-2.50%, Ni: 0.45-0.50%, Mo: 1.10-1.13%, Cu: ≤0.25%, As: ≤0.010%, Sn: ≤0.010%, Sb: ≤0.010%, V: ≤0.03%, gas elements [H] ≤2PPm, [O] ≤25PPm, [N] ≤0.012, and the remaining elements are Fe and impurity elements.

[0017] Furthermore, in step S2, the catalyst is iron oxide, and the mass of the steel ingot prepared in step S2 is 6 tons.

[0018] Furthermore, in the step S3, during the blanking manufacturing process, the furnace loading temperature is ≤300°C, the heating rate is ≤100°C / h, and the subsequent temperature is averaged at 650°C for 2 hours, and then heated to 1240°C after two hours, and the final forging temperature is >850°C. Before forging in the step S3, the anvil and other tooling need to be preheated, and the forging ratio of each fire during blanking is controlled to be >1.5, and the blank is drawn to 700 square meters. After forging, the furnace needs to be cooled to room temperature.

[0019] Further, the step S3 of blank forging is described as follows, and specifically includes the following steps:

[0020] First fire: After heating the billet for 6 hours, transfer it to a 2000-ton hydraulic press, roughen it axially to a height of 800mm, draw it to a square of 700mm, chamfer it slightly, forge the billet at a temperature of 850-1230℃, forge ratio>1.5, and reheat for no less than 3 hours;

[0021] Second fire: Roughen to a height of 800mm, draw to 700mm square, control the forging temperature at 850-1230℃, forging ratio>1.5, trim and shape, then cool to room temperature.

[0022] Furthermore, the sawing length in step S4 is 800-1000 mm.

[0023] Furthermore, the forging process of step S5 is as follows:

[0024] Place a 800mm long forging in a heating furnace with a charging temperature of ≤300℃, a heating rate of ≤100℃ / h, a heating temperature of 1200℃, a final forging temperature of>850℃, and a large deformation in the range of 850℃-1000℃. After forging, bury the forging in sand and cool it slowly.

[0025] Furthermore, in the forging process of step S5, the last fire has a large deformation at a temperature of 850-1000°C, and the forging ratio of this process needs to be greater than 2.

[0026] Furthermore, the normalizing + tempering step in step S6 is specifically as follows:

[0027] First normalizing: heating to 950℃ at ≤150℃ / h, keeping at this temperature for ≥14h, then air cooling to room temperature;

[0028] First tempering: heat to 650-670℃ at ≤100℃ / h, keep warm for >28h, then air cool.

[0029] Furthermore, the processing process of step S7 is as follows:

[0030] Secondary normalizing, the temperature is lower than the first normalizing. During normalizing, the temperature is raised to 945℃ at ≤150℃ / h, kept at this temperature for ≥14h, then air-cooled to room temperature, shot blasted to remove the oxide scale, and subsequently cooled with brine. After cooling, the surface of the forging is cleaned;

[0031] During quenching, the temperature is raised to 650℃ at a rate of ≤120℃ / h and kept at that temperature for 5h, and then the temperature is continued to be raised to 935℃ at the same rate and kept at that temperature for more than 14 hours. The brine is cooled to room temperature, the product is stirred, and the cooling rate is increased. The water temperature of the quenching pool does not exceed 20℃ throughout the process. After the forgings are cooled to room temperature, they are cleaned and tempered in time;

[0032] During tempering, the temperature is raised to 660℃ at ≤100℃ / h and kept for >28h, then water-cooled. When the forging cools to room temperature, repeat the above-mentioned tempering process once more. After tempering twice, water cooling is used.

[0033] In the above technical solution, the present invention provides a method for improving the large-section mechanical properties of low alloy steel A182F22, and the beneficial effects are:

[0034] (1) The present invention makes the forging structure more compact by forging blanking and forging forming, preheats the anvil and controls the temperature at each step in the forging process, delays the temperature difference between the inside and outside of the forging, reduces the cracking tendency of the forging, and no obvious forging cracks are generated on the surface; in the forging forming stage, the forging ratio of the last fire is greater than 2, the grains are refined, and no defects are found in UT detection; the forging is normalized twice, and the oxide scale is removed before quenching to ensure a more uniform structure, and salt water is used as the quenching liquid so that the entire forging can be quickly quenched; the 700mm large-section forging produced by this process, after heat treatment, has a performance far superior to that of conventional forging + heat treatment forgings.

[0035] (2) The present invention can effectively improve the performance of forgings with a wall thickness of more than 700 mm, increase the yield strength by 15%, increase the tensile strength by 10%, increase the elongation by 15%, increase the end shrinkage by 20%, and increase the -46°C impact performance by 20%, effectively solving the problem of unqualified performance of large-section forgings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0037] Figure 1 A method flow chart provided for an embodiment of the present invention for improving the large-section mechanical properties of low alloy steel A182F22;

[0038] Figure 2 A forging process diagram provided for an embodiment of a method for improving the large-section mechanical properties of low alloy steel A182F22 of the present invention;

[0039] Figure 3 A heat treatment process diagram is provided for an embodiment of a method for improving the large-section mechanical properties of low alloy steel A182F22 of the present invention. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0041] like Figure 1 As shown, a method for improving the large-section mechanical properties of low alloy steel A182F22 provided by an embodiment of the present invention comprises the following steps:

[0042] S1. Raw material selection: According to the smelting requirements, select appropriate raw materials. The raw material composition is as follows: C: 0.14-0.15%, Mn: 0.50-0.60%, P: ≤0.010%, S: ≤0.005%, Si: ≤0.50%, Cr: 2.40-2.50%, Ni: 0.45-0.50%, Mo: 1.10-1.13%, Cu: ≤0.25%, As: ≤0.010%, Sn: ≤0.010%, Sb: ≤0.010%, V: ≤0.03%, gas elements [H] ≤2PPm, [O] ≤25PPm, [N] ≤0.012 and the remaining elements are Fe and impurity elements, and the raw materials are processed by crushing, grinding and grading;

[0043] S2. Raw material smelting: pour the selected raw materials into a smelting furnace for smelting, and add a catalyst during smelting. The catalyst is iron oxide, and the raw materials are prepared into steel ingots. The mass of the prepared steel ingots is 6 tons;

[0044] S3. Open forging: The steel ingot is placed in a heating furnace for heating and forging. The temperature is maintained during forging. The furnace temperature during the open manufacturing process is ≤300°C, the heating rate is ≤100°C / h, and then the temperature is averaged at 650°C for 2 hours, and then heated to 1240°C after two hours. The final forging temperature is>850°C. Before forging in step S3, the anvil and other tooling need to be preheated, and the forging ratio of each fire during the open process is controlled to be>1.5, and the blank is drawn to 700 square meters. After forging, the furnace needs to be cooled to room temperature. The open forging is described as follows, and specifically includes the following processes:

[0045] First fire: After heating the billet for 6 hours, transfer it to a 2000-ton hydraulic press, roughen it axially to a height of 800mm, draw it to a square of 700mm, chamfer it slightly, forge the billet at a temperature of 850-1230℃, forge ratio>1.5, and reheat for no less than 3 hours;

[0046] Second fire: roughing to a height of 800mm, drawing to 700mm square, forging temperature controlled at 850-1230℃, forging ratio>1.5, trimming and shaping, then furnace cooling to room temperature;

[0047] S4. Sawing: Put the blank into the sawing equipment and operate the sawing equipment. The sawing equipment will saw the blank, and the sawing length is 800mm;

[0048] S5. Forging: The sawn forgings are put back into the heating furnace, and the temperature is raised for forging. After forging, they are buried in sand and slowly cooled. The forging process is as follows:

[0049] Place the 800mm long forging in a heating furnace, with a charging temperature of ≤300℃, a heating rate of ≤100℃ / h, a heating temperature of 1200℃, a final forging temperature of>850℃, a large deformation in the range of 850℃-1000℃, and a slow cooling after sand burying. The last fire in the forging process has a large deformation at a temperature of 850-1000℃, and the forging ratio of this process needs to be greater than 2;

[0050] S6. Preliminary heat treatment: The forged forgings are subjected to the first normalizing + tempering treatment, and then buried in sand for cooling. The normalizing + tempering steps are as follows:

[0051] First normalizing: heating to 950℃ at ≤150℃ / h, keeping at this temperature for ≥14h, then air cooling to room temperature;

[0052] First tempering: ≤100℃ / h, heating to 650-670℃, keep warm for more than 28h, then air cool;

[0053] (1) S7. Rough machining: Place the cooled forging into a machining device and use a turning tool to machine the forging surface to remove the oxide scale. After machining, use MT to inspect surface defects.

[0054] S8. Heat treatment: Put the forgings back into the heating furnace for normalizing, quenching and tempering to obtain high-strength forgings. The processing process is as follows:

[0055] (1) Secondary normalizing, the temperature is lower than the first normalizing. During normalizing, the temperature is raised to 945℃ at ≤150℃ / h, kept at this temperature for ≥14h, then air-cooled to room temperature, shot blasted to remove the oxide scale, and subsequently cooled with brine. After cooling, the surface of the forging is cleaned;

[0056] (2) During quenching, the temperature is raised to 650℃ at a rate of ≤120℃ / h and kept at that temperature for 5h, and then the temperature is continued to be raised to 935℃ at this rate and kept at that temperature for more than 14 hours. The brine is cooled to room temperature, the product is stirred, and the cooling rate is increased. The water temperature of the quenching pool does not exceed 20℃ throughout the process. After the forgings are cooled to room temperature, they are cleaned and tempered in time;

[0057] (3) During tempering, heat to 660℃ at ≤100℃ / h and keep at this temperature for more than 28h, then water cool. When the forging cools to room temperature, repeat the above tempering process once more. After tempering twice, water cool.

[0058] Embodiment 1

[0059] A method for improving the large-section mechanical properties of low alloy steel A182F22 comprises the following steps:

[0060] S1. Raw material selection: According to the smelting requirements, select appropriate raw materials. The raw material composition is as follows: C: 0.15%, Mn: 0.57%, P: 0.004%, S: 0.002%, Si: 0.27%, Cr: 2.46%, Ni: 0.47%, Mo: 1.12%, Cu: 0.04%, As: 0.006%, Sn: 0.002%, Sb: 0.003%, gas elements [H]: 0.7PPm, [O]: 6PPm, [N] ≤ 0.011PPm, and the remaining elements are Fe and impurity elements. The raw materials are processed by crushing, grinding and grading;

[0061] S2. Raw material smelting: pour the selected raw materials into a smelting furnace for smelting, and add a catalyst during smelting. The catalyst is iron oxide, and the raw materials are prepared into steel ingots. The mass of the prepared steel ingots is 6 tons;

[0062] S3. Open forging: Before forging, the anvil and other tooling need to be preheated to avoid too fast temperature dissipation, which will increase the number of forging fires and cause serious decarburization; the steel ingot is heated in a heating furnace and forged. The temperature is guaranteed during forging. The furnace temperature during the open manufacturing process is ≤300℃, the heating rate is ≤100℃ / h, and then the temperature is averaged at 650℃ for 2 hours, and then heated to 1240℃ after two hours. The final forging temperature is>850℃, and the forging ratio of each fire during the open process is controlled to be>1.5, and the steel is pulled to 700 square meters. After forging, the steel needs to be cooled to room temperature in the furnace. The open forging is described as follows, and specifically includes the following processes:

[0063] First fire: After heating the billet for 6 hours, transfer it to a 2000-ton hydraulic press, roughen it axially to a height of 800mm, draw it to a square of 700mm, chamfer it slightly, forge the billet at a temperature of 850-1230℃, forge ratio>1.5, and reheat for no less than 3 hours;

[0064] Second fire: roughing to a height of 800mm, drawing to 700mm square, forging temperature controlled at 850-1230℃, forging ratio>1.5, trimming and shaping, then furnace cooling to room temperature;

[0065] S4. Sawing: Put the blank into the sawing equipment and operate the sawing equipment. The sawing equipment will saw the blank, and the sawing length is 800mm;

[0066] S5. Forging: The sawn forgings are put back into the heating furnace, and the temperature is raised for forging. After forging, they are buried in sand and slowly cooled. The forging process is as follows:

[0067] Place the 800mm long forging in a heating furnace, with the furnace temperature ≤300℃, the heating rate ≤100℃ / h, the heating temperature 1200℃, the final forging temperature>850℃, and large deformation in the range of 850℃-1000℃. After forging, bury in sand and cool slowly. The last fire in the forging process has large deformation at a temperature of 850-1000℃, and the forging ratio of this process needs to be greater than 2. Then reduce the heating temperature to 1200℃, keep warm for 6h, transfer the open billet to a 2000-ton hydraulic press, axially roughen to 600 high, draw to 700 square, axially roughen to 500 high, draw to 700 square, trim and shape, ensure that the forging ratio is greater than 2 in the temperature range of 850℃-1000℃, and then bury in sand and cool to room temperature;

[0068] S6. Preliminary heat treatment: The forged forgings are subjected to the first normalizing + tempering treatment, and then buried in sand for cooling. The normalizing + tempering steps are as follows:

[0069] First normalizing: heating to 950℃ at ≤150℃ / h, keeping at this temperature for ≥14h, then air cooling to room temperature;

[0070] First tempering: ≤100℃ / h, heating to 650-670℃, keep warm for more than 28h, then air cool;

[0071] (1) S7. Rough machining: Place the cooled forging into a machining device and use a turning tool to machine the forging surface to remove the oxide scale. After machining, use MT to inspect surface defects.

[0072] S8. Heat treatment: Put the forgings back into the heating furnace for normalizing, quenching and tempering to obtain high-strength forgings. The processing process is as follows:

[0073] (1) Secondary normalizing, the temperature is lower than the first normalizing. During normalizing, the temperature is raised to 945℃ at ≤150℃ / h, kept at this temperature for ≥14h, then air-cooled to room temperature, shot blasted to remove the oxide scale, and subsequently cooled with brine. After cooling, the surface of the forging is cleaned;

[0074] (2) During quenching, the temperature is raised to 650℃ at a rate of ≤120℃ / h and kept at that temperature for 5h, and then the temperature is continued to be raised to 935℃ at this rate and kept at that temperature for more than 14 hours. The brine is cooled to room temperature, the product is stirred, and the cooling rate is increased. The water temperature of the quenching pool does not exceed 20℃ throughout the process. After the forgings are cooled to room temperature, they are cleaned and tempered in time;

[0075] (3) During tempering, heat to 660℃ at ≤100℃ / h and keep at this temperature for more than 28h, then water cool. When the forging cools to room temperature, repeat the above tempering process once more. After tempering twice, water cool.

[0076] Embodiment 2

[0077] A method for improving the large-section mechanical properties of low alloy steel A182F22 comprises the following steps:

[0078] S1. Raw material selection: According to the smelting requirements, select appropriate raw materials. The raw material composition is as follows: C: 0.15%, Mn: 0.57%, P: 0.004%, S: 0.002%, Si: 0.27%, Cr: 2.46%, Ni: 0.47%, Mo: 1.12%, Cu: 0.04%, As: 0.006%, Sn: 0.002%, Sb: 0.003%, gas elements [H]: 0.7PPm, [O]: 6PPm, [N] ≤ 0.011PPm, and the remaining elements are Fe and impurity elements. The raw materials are processed by crushing, grinding and grading.

[0079] S2. Raw material smelting: pour the selected raw materials into a smelting furnace for smelting, and add a catalyst during smelting. The catalyst is iron oxide, and the raw materials are prepared into steel ingots. The mass of the prepared steel ingots is 6 tons;

[0080] S3. Open forging: Before forging, the anvil and other tooling need to be preheated to avoid too fast temperature dissipation, which will increase the number of forging fires and cause serious decarburization; the steel ingot is placed in a heating furnace for heating and forging, and the temperature is guaranteed during forging. During the open forging process, the furnace temperature is ≤300℃, the heating rate is ≤100℃ / h, and then the temperature is averaged at 650℃ for 2 hours, and then heated to 1240℃ after two hours. The final forging temperature is>850℃, and the forging ratio of each fire is controlled to be>1.5 during the open forging, and two piers and two pulls are made to 700 square meters. After forging, the furnace needs to be cooled to room temperature. The open forging is described as follows, and specifically includes the following processes:

[0081] First fire: After heating the billet for 6 hours, transfer it to a 2000-ton hydraulic press, roughen it axially to a height of 800mm, draw it to a square of 700mm, chamfer it slightly, forge the billet at a temperature of 850-1230℃, forge ratio>1.5, and reheat for no less than 3 hours;

[0082] Second fire: roughing to a height of 800mm, drawing to 700mm square, forging temperature controlled at 850-1230℃, forging ratio>1.5, trimming and shaping, then furnace cooling to room temperature;

[0083] S4. Sawing: Put the blank into the sawing equipment and operate the sawing equipment. The sawing equipment will saw the blank, and the sawing length is 800mm;

[0084] S5. Forging: The sawn forgings are put back into the heating furnace, and the temperature is raised for forging. After forging, they are buried in sand and slowly cooled. The forging process is as follows:

[0085] Place the 800mm long forging in a heating furnace, with a charging temperature of ≤300℃, a heating rate of ≤100℃ / h, a heating temperature of 1240℃, a final forging temperature of>850℃, and draw it to 700 square meters, shape it, and bury it in sand to cool it to room temperature;

[0086] S6. Preliminary heat treatment: The forged forgings are subjected to the first normalizing + tempering treatment, and then buried in sand for cooling. The normalizing + tempering steps are as follows:

[0087] First normalizing: heating to 950℃ at ≤150℃ / h, keeping at this temperature for ≥14h, then air cooling to room temperature;

[0088] S7. Rough machining: Place the cooled forging into the machining equipment, use a turning tool to machine the forging surface to remove the oxide scale, and use MT to inspect the surface defects after machining;

[0089] S8. Heat treatment: Put the forgings back into the heating furnace for normalizing, quenching and tempering to obtain high-strength forgings. The processing process is as follows:

[0090] (1) Quenching: Raise the temperature to 650℃ at a rate of ≤120℃ / h and keep at that temperature for 5h, then continue to raise the temperature to 935℃ at the same rate and keep at that temperature for more than 14 hours, then cool to room temperature with water.

[0091] (2) Tempering: Raise the temperature to 660℃ at a rate of ≤100℃ / h, keep at this temperature for more than 28h, then cool in air.

[0092] The core position performance test is as follows:

[0093]

[0094] It can be seen from the above table that the grain size of the center of Example 1 reaches above level 8, and the grain size of the center of Example 2 is level 6. The four types of non-metallic inclusions all meet the requirements. The mechanical properties of the products of the two processes are shown in the above table. The large-section forgings produced by the method of this Example 1 have reached the domestic leading level in various indicators and have been used in actual production and delivered to domestic and foreign customers.

[0095] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for improving the mechanical properties of low alloy steel A182F22 large cross section, characterized in that: The following steps are involved: S1. Raw material selection: Select appropriate raw materials according to smelting requirements and process the raw materials; S2. Raw material smelting: pouring the selected raw materials into a smelting furnace for smelting, adding a catalyst during smelting, and preparing the raw materials into steel ingots; S3. Open forging: Place the steel ingot in a heating furnace for heating and forging, and ensure the temperature during forging; S4. Sawing: Put the blank into the sawing equipment, operate the sawing equipment, and the sawing equipment will saw the blank; S5. Forging: The sawn forgings are put back into the heating furnace, and the temperature is raised for forging. After forging, they are buried in sand for slow cooling. S6. Preliminary heat treatment: The forged forgings are subjected to the first normalizing and tempering treatment, and then buried in sand for cooling; S7. Rough machining: Place the cooled forging into the machining equipment, use a turning tool to machine the forging surface to remove the oxide scale, and use MT to inspect the surface defects after machining; S8. Heat treatment: Place the forgings back into the heating furnace for normalizing, quenching and tempering to obtain high-strength forgings.

2. A method for improving the large-section mechanical properties of low alloy steel A182F22 according to claim 1, characterized in that: The raw material composition in step S1 is as follows: C: 0.14-0.15%, Mn: 0.50-0.60%, P: ≤0.010%, S: ≤0.005%, Si: ≤0.50%, Cr: 2.40-2.50%, Ni: 0.45-0.50%, Mo: 1.10-1.13%, Cu: ≤0.25%, As: ≤0.010%, Sn: ≤0.010%, Sb: ≤0.010%, V: ≤0.03%, gas elements [H] ≤2PPm, [O] ≤25PPm, [N] ≤0.012, and the remaining elements are Fe and impurity elements.

3. A method for improving the large-section mechanical properties of low alloy steel A182F22 according to claim 1, characterized in that: In the step S2, the catalyst is iron oxide, and the mass of the steel ingot prepared in the step S2 is 6 tons.

4. A method for improving the large-section mechanical properties of low alloy steel A182F22 according to claim 1, characterized in that: In the step S3, during the blanking manufacturing process, the furnace loading temperature is ≤300°C, the heating rate is ≤100°C / h, and then the temperature is averaged at 650°C for 2 hours, and then heated to 1240°C after two hours, and the final forging temperature is >850°C. Before forging in the step S3, the anvil and other tooling need to be preheated, and the forging ratio of each fire during blanking is controlled to be >1.5, and the blank is drawn to 700 square meters. After forging, the furnace needs to be cooled to room temperature.

5. A method for improving the large-section mechanical properties of low alloy steel A182F22 according to claim 1, characterized in that: The step S3 of blank forging is described as follows, and specifically includes the following steps: First fire: After heating the billet for 6 hours, transfer it to a 2000-ton hydraulic press, roughen it axially to a height of 800mm, draw it to a square of 700mm, chamfer it slightly, forge the billet at a temperature of 850-1230℃, forge ratio>1.5, and reheat for no less than 3 hours; Second fire: Roughen to a height of 800mm, draw to 700mm square, control the forging temperature at 850-1230℃, forging ratio>1.5, trim and shape, then cool to room temperature.

6. A method for improving the large-section mechanical properties of low alloy steel A182F22 according to claim 1, characterized in that: The sawing length in step S4 is 800-1000 mm.

7. A method for improving the large-section mechanical properties of low alloy steel A182F22 according to claim 1, characterized in that: The forging process of step S5 is as follows: Place a 800mm long forging in a heating furnace with a charging temperature of ≤300℃, a heating rate of ≤100℃ / h, a heating temperature of 1200℃, a final forging temperature of>850℃, and a large deformation in the range of 850℃-1000℃. After forging, bury the forging in sand and cool it slowly.

8. The method for improving the large-section mechanical properties of low alloy steel A182F22 according to claim 1, characterized in that: In the forging process of step S5, the last fire at a temperature of 850-1000°C has a large deformation, and the forging ratio of this process needs to be greater than 2.

9. A method for improving the large-section mechanical properties of low alloy steel A182F22 according to claim 1, characterized in that: The normalizing + tempering step in step S6 is specifically as follows: (1) First normalizing: heat to 950℃ at ≤150℃ / h, keep at this temperature for ≥14h, then cool to room temperature by air; (2) First tempering: heat to 650-670℃ at ≤100℃ / h, keep at this temperature for more than 28h, then air cool.

10. A method for improving the large-section mechanical properties of low alloy steel A182F22 according to claim 1, characterized in that: The processing process of step S7 is as follows: (1) Secondary normalizing, the temperature is lower than the first normalizing. During normalizing, the temperature is raised to 945℃ at ≤150℃ / h, kept at this temperature for ≥14h, then air-cooled to room temperature, shot blasted to remove the oxide scale, and subsequently cooled with brine. After cooling, the surface of the forging is cleaned; (2) During quenching, the temperature is raised to 650℃ at a rate of ≤120℃ / h and kept at that temperature for 5h, and then the temperature is continued to be raised to 935℃ at this rate and kept at that temperature for more than 14 hours. The brine is cooled to room temperature, the product is stirred, and the cooling rate is increased. The water temperature of the quenching pool does not exceed 20℃ throughout the process. After the forgings are cooled to room temperature, they are cleaned and tempered in time; (3) During tempering, heat to 660℃ at ≤100℃ / h and keep at this temperature for more than 28h, then water cool. When the forging cools to room temperature, repeat the above process for tempering. After tempering twice, water cool.

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