Forging process and evaluation method for spherical forge piece of reactor pressure vessel

Abstract

The invention provides a forging process and an evaluation method for a spherical forge piece of a reactor pressure vessel, and relates to the technical field of manufacturing and production of spherical forge pieces of reactor pressure vessels. The forging process comprises the following steps: (1) smelting; (2) forging; (3) heat treatment after forging; (4) rough machining; and (5) performance heat treatment. By evaluating the whole process flow of the forging process of the spherical forge piece of the reactor pressure vessel, various technical indexes of the process evaluation stage of the spherical forge piece of the reactor pressure vessel can be comprehensively and effectively evaluated, and a set of complete and normative comprehensive technical evaluation method is formed; clear thoughts and directions are provided for technical evaluation and process curing of the spherical forgings of the reactor pressure vessel.

Description

Technical Field

[0001] The invention relates to the technical field of manufacturing and producing spherical forgings for reactor pressure vessels, and in particular to a forging process and an evaluation method for spherical forgings for reactor pressure vessels. Background Art

[0002] The spherical forgings of reactor pressure vessels have the following difficulties in forging due to their special geometric shape and application scenarios: the material flow path is more complicated, and the material flow needs to be precisely controlled to avoid internal defects; the mold design and manufacturing are relatively complex, and it is necessary to ensure the synchronous movement of various parts of the mold during the forging process to avoid local overpressure or underpressure; since the surface area to volume ratio of the sphere is different from that of flat or linear forgings, the heating and cooling processes need to be controlled more accurately to avoid cracks caused by thermal stress; it is necessary to ensure uniform deformation of the material to avoid defects caused by local stress concentration; it is more difficult to detect internal defects of spherical forgings because the application of non-destructive detection technology is limited by the shape; it is necessary to ensure the uniformity of heat treatment of the entire forging to avoid problems such as uneven hardness or residual stress.

[0003] Due to the above-mentioned forging difficulties of spherical forgings, it is difficult to ensure the consistency of the performance of various parts of the forgings, and local parts are prone to damage. Therefore, the forging process of spherical forgings is very important for the overall quality of spherical forgings. The current forging process is prone to excessive defects, carbon segregation, excessive impurity elements and other risks during the forging process.

[0004] By evaluating the forging process, the rationality and feasibility of the forging process of spherical forgings can be verified. Due to the special structure of spherical forgings, the sampling positions in the evaluation samples need to meet the requirements of representativeness and uniformity. In order to ensure the representativeness of the samples, samples should be taken from different positions of the spherical forgings, including the central area, the thickest area, the area with wall thickness changes, and the near-surface area; the sampling points should be distributed as evenly as possible in different directions of the spherical forgings to reflect the overall properties of the forgings. However, the diversity of sampling points will increase the complexity and cost of sampling work. At the same time, too many sampling points will increase the cost and workload, while too few sampling points may not be able to fully reflect the quality status of the spherical forgings. Summary of the invention

[0005] The object of the present invention is to provide a forging process for a spherical forging of a reactor pressure vessel, which can improve the forging quality of the spherical forging.

[0006] Another object of the present invention is to provide a method for evaluating the forging process of a spherical forging of a reactor pressure vessel, which can fully inspect the overall quality of the spherical forging and verify the rationality and feasibility of the forging process of the spherical forging.

[0007] On the one hand, the present invention provides a forging process for a spherical forging of a reactor pressure vessel, comprising the following steps:

[0008] (1) Smelting: Three packages of molten steel are cast together using a vacuum casting process to obtain a steel ingot;

[0009] (2) Forging: gas cutting of nozzles, risers and ingot body discards, upsetting, processing, punching, and obtaining prefabricated forgings. The total forging ratio of the prefabricated forgings is greater than 3;

[0010] (3) Post-forging heat treatment: heat the prefabricated forging to the austenitizing temperature range and keep it warm. After sufficient austenitization, air cool it and temper it.

[0011] (4) Rough machining;

[0012] (5) Performance heat treatment: The prefabricated forging is heated in an electric furnace to the austenitizing temperature range and kept warm to homogenize the austenite structure, and then quenched; then the prefabricated forging is reheated to the critical temperature range, partially austenitized, and quenched again. After quenching, it is tempered at 635℃~665℃ to obtain a finished forging;

[0013] In the heat treatment process of steps (3) and (5), the maximum deviation between the actual treatment temperature and the standard heat treatment temperature is ±10°C.

[0014] On the other hand, the present invention provides a method for evaluating the forging process of a spherical forging of a reactor pressure vessel, wherein the spherical forging includes an upper head and a lower head, and comprises the following steps:

[0015] S1. Cut samples at the 1 / 4 wall thickness position, 1 / 2 wall thickness position, and 3 / 4 wall thickness position from the nozzle end of the forging to the inner surface for performance testing. Cut samples at the 1 / 4 wall thickness position, 1 / 2 wall thickness position, and 3 / 4 wall thickness position that are 90° away from the performance sample position. The sampling direction of the samples is circumferential and radial;

[0016] S2, cutting the sample from the opening at the top of the upper head to obtain a cylindrical sample;

[0017] S3. Cut the forging along the center line and take multiple test pieces along the chord direction on the cross section;

[0018] S4. Carry out performance tests on the cut samples and compare the fluctuation ranges of performance tests of different samples.

[0019] The technical solution of the present invention has at least the following advantages and beneficial effects:

[0020] 1. Limit the sequence and conditions of the forging process to make the forging process more standardized and improve the quality of spherical forgings after forging;

[0021] 2. Sampling points are determined at the wall thickness position, opening position and section position. The sampling amount can be reduced while ensuring the representativeness of the sampling points. Combined with the limitation of sampling direction and sampling size, the samples cut from spherical forgings can meet the requirements of representativeness and uniformity. They are located in the key areas of forgings and can fully reflect the overall quality of forgings. This can effectively improve the accuracy and reliability of quality assessment of spherical forgings and comprehensively test the overall quality of spherical forgings.

[0022] 3. Sampling and testing in the chord direction of the spherical forging section can effectively evaluate key indicators such as the microstructure and mechanical properties of the spherical forging to ensure that the quality of the forging meets the design requirements and usage standards.

[0023] 4. The assessment of the forging process of reactor pressure vessel spherical forgings covers the entire process flow of forging manufacturing, and can comprehensively and effectively evaluate the various technical indicators of the process assessment stage of reactor pressure vessel spherical forgings, forming a complete and standardized comprehensive technical assessment method, providing clear ideas and directions for the technical assessment and process consolidation of reactor pressure vessel spherical forgings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a cross-sectional view of the upper head of the reactor pressure vessel;

[0025] Figure 2 It is a top view of the upper head of the reactor pressure vessel;

[0026] Figure 3 It is a cross-sectional view of the lower head of the reactor pressure vessel;

[0027] Figure 4 This is a top view of the lower head of the reactor pressure vessel. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0029] Taking the head forging as an example, a forging process of a spherical forging of a reactor pressure vessel includes the following steps:

[0030] (1) Smelting stage

[0031] The smelting of steel should adopt electric furnace (EF) to smelt molten steel, and then vacuum refining in refining furnace. The steel ingot is cast by 3 bags of molten steel by vacuum pouring process, and the total weight of the steel ingot is 114 tons. Among them, the method of rough refining in electric furnace (EF) + vacuum refining and vacuum pouring process are key processes for evaluation; the number of 3 bags of molten steel for co-casting is the key parameter for evaluation, and the weight of the steel ingot is 114 tons (allowable deviation ±7%). At the same time, the impurity elements of the raw materials for forgings should be strictly controlled, and samples should be taken for smelting chemical composition analysis. The chemical composition needs to detect the content of C, Si, Mn, P, S, Cr, Ni, Mo, V, Cu, Al, Co, As, Sn, Sb, B, N, H, and O elements.

[0032] (2) Forging stage

[0033] The forging process and forging sequence of the upper head forging are as follows:

[0034] The gas cutting nozzle, riser and ingot body discarded materials are upsetting, processing and punching out the finished products.

[0035] The forging process and forging sequence of forgings are key processes for evaluation. During forging, sufficient pressure should be ensured to deform the steel ingot deeply and complete plastic deformation under reasonable stress state to make the structure dense. The amount of steel ingot removed should be sufficient, and the weight of the steel ingot and the percentage of removed weight should be recorded and archived. The amount of head and tail removed from the forging is a key parameter for evaluation. The total forging ratio of the forging should be greater than 3, which is a key parameter for evaluation.

[0036] (3) Post-forging heat treatment stage

[0037] The normalizing + tempering process is adopted. The forgings are heated to the austenitizing temperature range and kept warm. After full austenitization, they are air-cooled to obtain a uniform and refined structure, and then tempered. The post-forging heat treatment process is the key process for evaluation. The number of heat treatments, normalizing temperature, tempering temperature, and holding time are the key parameters for evaluation. Thermocouples should be placed at the nozzle end and riser end of the forging to ensure that the positions of the expected maximum and minimum temperatures of the forging are covered. The maximum allowable deviation between the actual temperature of different parts of the forging being treated and the specified heat treatment temperature is ±10°C.

[0038] (4) Rough processing stage

[0039] The outer dimensions of the processed forgings should be as close as possible to those of the final product, but sufficient size should be left at the nozzle and riser ends of the forgings to cut test rings for performance testing. At the same time, sufficient margins should be left on the inner and outer walls of the forgings for subsequent defect removal (if any) and finishing processes.

[0040] (5) Performance heat treatment stage

[0041] The forging is heated in an electric furnace to the austenitizing temperature range (850℃~925℃) and kept warm to homogenize the austenite structure, and then quenched to fully transform the structure. Here, a multi-stage austenitizing heat treatment process can be selectively adopted according to the performance requirements of the forging (the forging is heated in an electric furnace to the austenitizing temperature range and kept warm to homogenize the austenite structure, and then quenched; then the forging is reheated to the critical temperature range, partially austenitized, and quenched again).

[0042] After completing the austenitization-quenching cycle, the forging is tempered at 635℃~665℃ to obtain a stable tempered bainite structure. The performance heat treatment process is the key process for evaluation, and the number of heat treatments, quenching temperature, tempering temperature, holding time, heating rate, and cooling rate are the key parameters for evaluation; thermocouples should be placed at the nozzle end and riser end of the forging to ensure that the positions of the expected maximum and minimum temperatures of the forging are covered. The maximum allowable deviation between the actual temperature of different parts of the forging being treated and the specified heat treatment temperature is ±10℃.

[0043] In the heat treatment process of steps (3) and (5), the maximum deviation between the actual treatment temperature and the standard heat treatment temperature is ±10°C.

[0044] In this embodiment, in step (1), the weight of the steel ingot is 114 tons, and the maximum deviation is ±7%.

[0045] In this embodiment, in the finished forging, the P element is ≤0.008%, the S element is ≤0.005%, and the Cu element is ≤0.08%.

[0046] A method for evaluating the forging process of a spherical forging of a reactor pressure vessel, wherein the spherical forging comprises an upper end cap and a lower end cap, comprising the following steps:

[0047] S1. Cut samples at the 1 / 4 wall thickness position, 1 / 2 wall thickness position, and 3 / 4 wall thickness position from the nozzle end of the forging to the inner surface for performance testing. Cut samples at the 1 / 4 wall thickness position, 1 / 2 wall thickness position, and 3 / 4 wall thickness position that are 90° away from the performance sample position. The sampling direction of the samples is circumferential and radial;

[0048] S2, cutting the sample from the opening at the top of the upper head to obtain a cylindrical sample;

[0049] S3. Cut the forging along the center line and take multiple test pieces along the chord direction on the cross section;

[0050] S4. Carry out performance tests on the cut samples and compare the fluctuation ranges of performance tests of different samples.

[0051] In this embodiment, when cutting samples at the opening position on the top of the upper head, at least three cylindrical samples are cut at the top and bottom of the opening position respectively, and the three cylindrical samples located at the top or bottom are evenly distributed around the hole in a ring shape, and the distance between the cylindrical sample and the hole is 40 mm.

[0052] After the hole is opened, the bearing area on the upper head is reduced, resulting in uneven stress distribution at the edge of the hole, generating local film stress, bending stress and peak stress. If these stresses exceed the allowable stress of the material and reach the yield point of the material, the material will deform greatly. Due to the unevenness of stress distribution, a single sampling position cannot reflect the quality of the forgings around the hole. Therefore, the present invention assesses the quality of the forgings by cutting three samples evenly distributed around the hole at the top and bottom of the hole respectively, which can cover the key areas around the hole, fully reflect the quality of the forgings, and ensure the safety and reliability of the forgings.

[0053] In this embodiment, among the multiple samples of the upper head, at least one sample is located at the center of the dome, and at least two samples are located at the two ends of the lower part; among the multiple samples of the lower head, at least one sample is located at the center of the bottom, and at least two samples are located at the two ends of the upper part.

[0054] In the performance test, the tensile specimen size is φ10mm×50mm, the impact specimen size is 10mm×10mm×55mm, and the drop weight specimen size is 80mm×10mm×4mm.

[0055] Sampling points are determined at the wall thickness position, opening position and section position. The sampling amount can be reduced while ensuring the representativeness of the sampling points. Combined with the limitation of sampling direction and sampling size, the samples cut from spherical forgings can meet the requirements of representativeness and uniformity. They are located in the key area of ​​the forgings, which can fully and completely reflect the overall quality of the forgings. This can effectively improve the accuracy and reliability of the quality assessment of spherical forgings and can comprehensively test the overall quality of spherical forgings.

[0056] When a spherical forging is subjected to external force, the stress distribution in the chord direction of its cross section is uneven, which is mainly due to the combined effect of multiple factors such as the material properties, geometric shape and stress conditions of the forging. Specifically, when a spherical forging is subjected to pressure or tension, the stress distribution on its surface and inside will be affected by the elastic modulus, Poisson's ratio, geometric dimensions and force direction of the material, resulting in uneven stress distribution in the chord direction of the cross section, which may lead to stress concentration, especially at the edges, corners and center of the forging. Therefore, the present invention performs sampling and inspection in the chord direction of the cross section of the spherical forging, which can effectively evaluate key indicators such as the microstructure and mechanical properties of the spherical forging, and ensure that the quality of the forging meets the design requirements and usage standards. Among them, the chord direction is the bending direction of the spherical forging.

[0057] Therefore, the key processes and key parameters for evaluation formulated in this evaluation method are summarized as follows:

[0058] Smelting: smelting process, number of ladles, weight of ingots.

[0059] Forging: forging process, forging sequence, head / tail removal, total forging ratio.

[0060] Post-forging heat treatment: post-forging heat treatment process, number of heat treatments, normalizing temperature, tempering temperature, and holding time.

[0061] Performance heat treatment: performance heat treatment process, number of heat treatments, quenching temperature, tempering temperature, holding time, heating rate, cooling rate.

[0062] Sampling inspection: sample status, sampling location, and sampling quantity.

[0063] Non-destructive testing: acceptance criteria.

[0064] When evaluating key processes, the process method shall not be changed without authorization, otherwise the original forging evaluation results will be invalid. The key parameters of the evaluation are valid within the evaluation approval range, and exceeding the evaluation approval range will cause the original evaluation results to be invalid.

[0065] Forging samples are taken for performance testing, including chemical composition analysis, metallographic inspection and mechanical properties testing:

[0066] 1) The chemical composition needs to detect the content of C, Si, Mn, P, S, Cr, Ni, Mo, V, Cu, Al, Co, As, Sn, Sb, B, N, H, and O elements, and calculate the welding reheat crack sensitivity coefficient and carbon equivalent. Special attention should be paid to the control of impurity elements. For the upper and lower head forgings, the P element content needs to be controlled below 0.008%, the S element content needs to be controlled below 0.005%, and the Cu element content needs to be controlled below 0.08%;

[0067] The chemical composition shall be determined in accordance with the relevant provisions of GB / T 223. Other testing standards and methods with a testing accuracy not less than that of GB / T223 may also be used. If there is a dispute over the test results of a certain element, the test results of GB / T223 shall prevail;

[0068] 2) The metallographic structure should measure the grain size of the material, evaluate the non-metallic inclusions, and provide metallographic photos;

[0069] 3) Mechanical property tests include tensile test, impact test, KV-T curve test and drop hammer test. The tensile test sampling is circumferential, the sample state includes HTMP state and HTMP+SSRHT state, the test temperature includes room temperature and 350℃, and the tensile strength, yield strength, elongation after fracture and cross-sectional shrinkage of the material should be obtained respectively; the impact test sampling includes circumferential and radial directions, the sample state includes HTMP state and HTMP+SSRHT state, the test temperature includes -20℃, 0℃ and 20℃, and the impact absorption energy and lateral expansion value should be obtained respectively; the KV-T curve test sampling is circumferential, the sample state includes HTMP state and HTMP+SSRHT state, at least 8 test temperatures should be taken, and a complete KV-T curve and upper platform energy should be obtained; the drop hammer test sampling is circumferential, the sample state is HTMP+SSRHT state, and the reference non-plastic transition temperature should be obtained.

[0070] In this embodiment, the evaluation method also includes selecting three generatrixes parallel to the axis of the forging and spaced 120° apart from each other on the circumferential direction of the inner surface of the spherical forging for sampling, and evenly cutting multiple samples on the generatrix for chemical composition analysis. The inner surface sampling inspection can directly detect the chemical composition, organizational structure and mechanical properties inside the forging, ensure the quality and reliability of the forging, and avoid potential problems caused by internal defects or insufficient performance. The spacing between multiple samples on the generatrix is ​​200mm. The sampling distance is limited to ensure the representativeness and accuracy of the forging sampling, and to avoid the influence of the sampling results on the unevenness of the heat treatment of the forging and the changes in the chemical composition and mechanical properties during the forging process.

[0071] In this embodiment, the evaluation method also includes selecting three other generatrixes parallel to the axis of the forging and spaced 120 degrees apart from each other on the circumferential direction of the inner surface of the spherical forging to polish sulfur print inspection strips, the width of the sulfur print inspection strips being 100-150 mm, and performing sulfur print inspection.

[0072] Sulfur exists in steel mainly in the form of iron sulfide or manganese sulfide. Iron sulfide forms a eutectic with iron and is often distributed in a network along the grain boundaries. This distribution significantly increases the brittleness of steel and may lead to hot brittleness. Manganese sulfide has a high melting point, and adding a certain amount of manganese can reduce the hot brittleness of steel. Through the sulfur print test, the segregation or distribution of sulfur in steel can be directly tested, and the distribution of other elements in steel can be indirectly judged, thereby providing an important basis for the quality control and improvement of steel, which is crucial for controlling steel quality, avoiding hot brittleness, and improving the performance of forgings. Limiting the width of the sulfur print inspection band can ensure accurate measurement of sulfur distribution and avoid inspection errors caused by too wide or too narrow an inspection area. Such a limitation helps to improve the accuracy and reliability of the inspection, thereby ensuring that the quality of forgings meets standards and requirements.

[0073] Among them, busbar sampling inspection and sulfur print inspection are the preliminary inspection stage. Preliminary inspection is an additional requirement for forging assessment. The inspection at this stage can identify in advance the risks of excessive defects, carbon segregation, excessive impurity elements and other non-conformities in the forging process, which is predictive and necessary in the early stage of manufacturing.

[0074] After sampling and inspection, non-destructive inspection of forgings is also included, specifically: (a) 100% ultrasonic inspection of the processed reactor pressure vessel spherical forgings. Ultrasonic inspection includes straight probe inspection and oblique probe inspection. The straight probe inspection results should meet the requirements of quality level II in Table 12 of NB / T 20003.2-2021. During oblique probe inspection, there should be no defect display with echo amplitude exceeding 100% of the DAC curve; (b) Magnetic particle inspection is performed on the non-surfacing surface of the processed reactor pressure vessel spherical forgings. The surface that needs to be surfacing can be selectively subjected to magnetic particle inspection or liquid penetration inspection.

[0075] Through the above multi-dimensional comprehensive evaluation, a complete and standardized comprehensive technical assessment method is formed.

[0076] Example 1

[0077] A forging process for a spherical forging of a reactor pressure vessel, taking the upper head of the Hualong One reactor pressure vessel as an example, comprises the following steps:

[0078] (1) Smelting: Three packages of molten steel are cast together using a vacuum casting process to obtain a steel ingot;

[0079] (2) Forging: gas cutting of nozzles, risers and ingot body discards, upsetting, processing, punching, and obtaining prefabricated forgings. The total forging ratio of the prefabricated forgings is greater than 3;

[0080] (3) Post-forging heat treatment: heat the prefabricated forging to the austenitizing temperature range and keep it warm. After sufficient austenitization, air cool it and temper it.

[0081] (4) Rough machining;

[0082] (5) Performance heat treatment: The prefabricated forging is heated in an electric furnace to the austenitizing temperature range and kept warm to homogenize the austenite structure, and then quenched; then the prefabricated forging is reheated to the critical temperature range, partially austenitized, and quenched again. After quenching, it is tempered at 650°C to obtain the finished forging.

[0083] Example 2

[0084] A method for evaluating the forging process of a spherical forging of a reactor pressure vessel comprises the following steps:

[0085] S1. Cut samples at the 1 / 4 wall thickness position, 1 / 2 wall thickness position, and 3 / 4 wall thickness position from the nozzle end of the forging to the inner surface for performance testing. Cut samples at the 1 / 4 wall thickness position, 1 / 2 wall thickness position, and 3 / 4 wall thickness position that are 90° away from the performance sample position. The sampling direction of the samples is circumferential and radial;

[0086] S2, cutting the sample from the opening at the top of the upper head to obtain a cylindrical sample;

[0087] Specifically, at least three cylindrical samples are cut from the top and bottom of the opening, and the three cylindrical samples at the top or bottom are evenly distributed around the hole in a ring shape, with the distance between the cylindrical sample and the hole being 40 mm;

[0088] S3. Cut the forging along the center line, and cut multiple samples along the chord direction on the cross section. Among the multiple samples of the upper head, at least one sample is located at the center of the dome, and at least two samples are located at the two ends of the lower part respectively;

[0089] S4. Perform performance tests on the cut specimens and compare the fluctuation ranges of performance tests of different specimens. In the performance tests, the size of the tensile specimen is φ10mm×50mm, the size of the impact specimen is 10mm×10mm×55mm, and the size of the drop hammer specimen is 80mm×10mm×4mm.

[0090] Test results

[0091] The forging process of the upper head forging of Example 1 is evaluated based on the sample test results of Example 2. The evaluated process and parameters include the number of ladles and the weight of the ingot in the smelting process, the forging sequence, the head / tail resection amount, and the total forging ratio in the forging process, the number of heat treatments, the normalizing temperature, the tempering temperature, and the holding time in the post-forging heat treatment, and the number of heat treatments, the quenching temperature, the tempering temperature, the holding time, the heating rate, and the cooling rate in the performance heat treatment.

[0092] Table 1 Upper head tensile properties test results

[0093]

[0094]

[0095] Among them, the sample states include HTMP state and HTMP+SSRHT state. The data in the table are for the former state and for the latter state.

[0096] According to the data in Table 1, the strength value fluctuation among various parts of the upper head forging is small and the strength distribution is uniform.

[0097] Table 2 Upper head impact performance test results

[0098]

[0099]

[0100] According to Table 2, the impact toughness values ​​of various parts of the upper head forging fluctuate slightly and are relatively uniform.

[0101] In addition, the chemical composition of each part of the upper head forging was tested according to GB / T 223. The results show that it meets the requirements of GB / T 223. In addition, the KV-T curve test, drop hammer test, non-metallic inclusions, and grain size of the upper head forging all meet the relevant requirements of the spherical forgings of the reactor pressure vessel. Therefore, the performance test results of the upper head spherical forgings are qualified, and the forging process of the upper head spherical forgings meets the requirements. The evaluation method of the present invention can verify the rationality and feasibility of the forging process of the spherical forgings.

[0102] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A forging process for a spherical forging of a reactor pressure vessel, characterized in that: The following steps are involved: (1) Smelting: Three packages of molten steel are cast together using a vacuum casting process to obtain a steel ingot; (2) Forging: gas cutting of nozzles, risers and ingot body discards, upsetting, processing, punching, and obtaining prefabricated forgings. The total forging ratio of the prefabricated forgings is greater than 3; (3) Post-forging heat treatment: heat the prefabricated forging to the austenitizing temperature range and keep it warm. After sufficient austenitization, air cool it and temper it. (4) Rough machining; (5) Performance heat treatment: The prefabricated forging is heated in an electric furnace to the austenitizing temperature range and kept warm to homogenize the austenite structure, and then quenched; then the prefabricated forging is reheated to the critical temperature range, partially austenitized, and quenched again. After quenching, it is tempered at 635℃~665℃ to obtain the finished forging.

2. The method for technical evaluation of a spherical forging for a reactor pressure vessel according to claim 1, characterized in that: In step (1), the weight of the steel ingot is 114 tons and the maximum allowable deviation is ±7%.

3. The method for technical evaluation of a spherical forging for a reactor pressure vessel according to claim 1, characterized in that: In the finished forging, the P element is ≤0.008%, the S element is ≤0.005%, and the Cu element is ≤0.08%.

4. A method for evaluating the forging process of a spherical forging for a reactor pressure vessel according to any one of claims 1 to 3, characterized in that: The spherical forging comprises an upper head and a lower head, and comprises the following steps: S1. Cut the samples at the 1 / 4 wall thickness position, 1 / 2 wall thickness position, and 3 / 4 wall thickness position from the inner surface of the forging nozzle end, and cut the samples at the 1 / 4 wall thickness position, 1 / 2 wall thickness position, and 3 / 4 wall thickness position which are 90° away from the performance sample position. The sampling direction of the samples is circumferential and radial; S2, cutting the sample from the opening at the top of the upper head to obtain a cylindrical sample; S3. Cut the forging along the center line and take multiple test pieces along the chord direction on the cross section; S4. Carry out performance tests on the cut samples and compare the fluctuation ranges of performance tests of different samples.

5. The evaluation method according to claim 4, characterized in that: In S2, when cutting samples at the opening position at the top of the upper head, at least three cylindrical samples are cut at the top and bottom of the opening position respectively, and the three cylindrical samples located at the top or bottom are evenly distributed around the hole in a ring shape.

6. The evaluation method according to claim 5, characterized in that: The distance between the cylindrical sample and the hole is 40 mm.

7. The evaluation method according to claim 4, characterized in that: In S3, when sampling in the chord direction, among the multiple samples of the upper head, at least one sample is located at the center of the dome, and at least two samples are located at the two ends of the lower part; among the multiple samples of the lower head, at least one sample is located at the center of the bottom, and at least two samples are located at the two ends of the upper part.

8. The evaluation method according to claim 4, characterized in that: In the performance test, the tensile specimen size is φ10mm×50mm, the impact specimen size is 10mm×10mm×55mm, and the drop weight specimen size is 80mm×10mm×4mm.

Images