Thick-walled SA350Gr.LF3 large forgings for transfer containers used in spent fuel dry storage systems and their manufacturing process

Abstract

The application discloses a thick-wall SA350Gr.LF3 large forging for a transfer container of a spent fuel dry storage system, which comprises a SA350Gr.LF3 large forging body, and the components contained in the large forging body and the mass percentage content (wt.%) thereof are as follows: C: 0.05%-0.15%; Cr: 0.10-0.20%; Mo: 0.04-0.06%; V: 0.01-0.03%; Nb: 0.01-0.02%; Al: 0.013-0.017%; N: 80-120ppm; Si: 0.20-0.30%; Mn: 0.70-0.80%; Ni: 3.5-3.7%; P≤0.006%; S≤0.003%; and the balance is Fe. The application further discloses a manufacturing process of the large forging, and the low-temperature toughness of the SA350Gr.LF3 large forging can be improved.

Description

Technical Field

[0001] This invention belongs to the field of forging manufacturing and relates to a forging and its manufacturing process. Specifically, it relates to a thick-walled SA350 Gr.LF3 large forging for a transfer container for a spent fuel dry storage system and its manufacturing process. Background Technology

[0002] The safe storage of spent fuel is a crucial aspect of nuclear power plant safety management. Spent fuel transfer containers are one of the main pieces of equipment in dry storage projects. During dry storage operations, these containers are used to transfer sealed storage tanks containing spent fuel assemblies to concrete storage modules. The transfer containers provide radiation shielding, structural protection, and heat dissipation for the spent fuel during transfer operations. The forged cylinder is the main forging in the transfer container; to ensure safety during spent fuel transportation, the material must possess excellent strength, toughness, and impact resistance.

[0003] SA350 Gr.LF3 is a commonly used carbon steel material for cryogenic pressure vessels internationally, and its main manufacturing standard is ASME SA-350. SA350 Gr.LF3 material used in large forgings for spent fuel dry storage systems, in addition to meeting the standard ASME SA-350 requirements, also has additional requirements for cryogenic drop hammer toughness and high-temperature strength, as detailed in Table 1.

[0004] Table 1 Performance Requirements for SA350 Gr.LF3 Large Forgings for Spent Fuel Containers

[0005]

[0006] Furthermore, this material is typically used domestically for manufacturing thick steel plates, with a thickness generally not exceeding 150mm. Testing usually only includes room temperature tensile testing and low-temperature impact testing, without drop weight transformation temperature testing. Heat treatment generally employs conventional quenching and tempering processes. Overseas, spent fuel-related containers and equipment manufactured using this material typically have a wall thickness of around 50mm.

[0007] The SA350 Gr.LF3 large forgings in this project require a tempered wall thickness exceeding 300mm. This material has a limited alloy content and poor hardenability. As the wall thickness increases to over 200mm, conventional composition control and heat treatment methods are insufficient to meet the performance requirements of spent fuel transfer container forgings. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a manufacturing process for SA350 Gr.LF3 forgings with a wall thickness exceeding 200 mm, suitable for spent fuel transfer containers. Therefore, the first objective of this invention is to provide a large, thick-walled SA350 Gr.LF3 forging for transfer containers used in spent fuel dry storage systems. The second objective of this invention is to provide a manufacturing process for such large forgings.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] As a first aspect of the present invention, a thick-walled SA350 Gr.LF3 forging for a transfer container for a spent fuel dry storage system is provided, comprising an SA350 Gr.LF3 forging body, wherein the components contained in the SA350 Gr.LF3 forging body and their mass percentage content (wt.%) are as follows:

[0011] C: 0.05%-0.15%; Cr: 0.10-0.20%; Mo: 0.04-0.06%; V: 0.01-0.03%; Nb: 0.01-0.02%; Al: 0.012-0.017%; N: 0.008-0.012%; Si: 0.20-0.30%; Mn: 0.70-0.80%; Ni: 3.5-3.7%; P≤0.006%; S≤0.003%; balance Fe.

[0012] Preferably, the composition and its mass percentage (wt.%) of the SA350 Gr.LF3 large forging body are as follows:

[0013] C: 0.06%-0.08%; Cr: 0.12-0.15%; V: 0.02-0.03%; Nb: 0.01-0.02%; Al: 0.012-0.017%; N: 0.009-0.011%; Mo: 0.04-0.06%; Si: 0.20-0.30%; Mn: 0.70-0.80%; Ni: 3.5-3.7%; P≤0.006%; S≤0.003%; balance Fe.

[0014] According to the present invention, in the SA350 Gr.LF3 large forging body, N(wt.%) / Al(wt.%)≥0.5.

[0015] As a second aspect of the present invention, a manufacturing process for a thick-walled SA350Gr.LF3 large forging for a transfer container for a spent fuel dry storage system includes the following steps:

[0016] S1. Preparation of steel ingots: Smelting scrap steel and casting the resulting smelting liquid to obtain steel ingots, wherein the steel ingots contain the components and their mass percentage content contained in the SA350 Gr.LF3 large forging body as described above.

[0017] S2, Forging: The steel ingot obtained in S1 is heated in a furnace and forged to obtain a forging;

[0018] S3. Post-forging heat treatment: The forgings obtained in S2 are subjected to post-forging heat treatment by normalizing and tempering.

[0019] S4. Performance heat treatment: The forgings after the post-forging heat treatment in S3 are subjected to performance heat treatment by quenching + sub-temperature quenching + tempering to obtain SA350 Gr.LF3 large forgings.

[0020] Specifically, in S2, the forging temperature for forging the steel ingot is 1100℃-1240℃, and the final forging temperature is ≥850℃.

[0021] Preferably, the forging temperature for forging the steel ingot in step S2 is 1150℃-1240℃, and the final forging temperature is ≥850℃.

[0022] Specifically, the step of performing post-forging heat treatment on the forging in S3 includes: S31, normalizing: the forging obtained by forging is placed in a waiting furnace for heat preservation, cooled to 230±20℃ and kept at that temperature; then heated to 860-880℃ and kept at that temperature.

[0023] S32. Tempering: After the forging is taken out of the furnace, it is air-cooled to 250-300℃, then put into the furnace and held at 230±20℃; then the temperature is raised to 600-630℃ and held.

[0024] S33. Cool in the furnace to <150℃ before unloading.

[0025] Furthermore, the step of normalizing the forging in S31 includes:

[0026] After forging, the forgings obtained are first air-cooled to about 500-600℃ and then placed in the furnace to wait for material, and then held at 600-650℃.

[0027] Then, cool the temperature at a rate of ≤50℃ / h, and hold it at 230±20℃.

[0028] Then, heat the temperature at a rate of ≤50℃ / h and hold it at 650-700℃.

[0029] Then quickly raise the temperature to 860-880℃ and keep it warm.

[0030] Preferably, in step S31, the holding time for the forging after it has been placed in the furnace and held at 600-650°C is 8 hours.

[0031] After cooling to 230±20℃, the holding time is 15 hours.

[0032] After heating to 650-700℃, the holding time is 8 hours.

[0033] After rapidly raising the temperature to 860-880℃, maintain the temperature for 15 hours.

[0034] Furthermore, the step of tempering the forging in S32 includes:

[0035] After the normalizing treatment, the forgings are first taken out of the furnace and air-cooled until the surface temperature of the forgings is 250-300℃, and then put into the furnace and held at 230±20℃.

[0036] The forgings are then heated at a rate of ≤50℃ / h and held at 600-630℃.

[0037] Preferably, in step S32, the forging after normalizing is air-cooled to a surface temperature of 250-300℃, and then held in the furnace at 230±20℃ for 15 hours.

[0038] After heating to 600-630℃, the holding time is 30 hours.

[0039] Specifically, the step of performing performance heat treatment on the forging in S4 includes:

[0040] S41. Quenching: The forging is placed in the furnace at room temperature, heated to 830-860℃ and held at that temperature, and then water-cooled until the surface temperature of the forging is ≤80℃.

[0041] S42, Sub-temperature quenching: The forgings are transferred to the furnace for sub-temperature quenching, heated to 710-740℃ and held at that temperature, and then water-cooled after being taken out of the furnace until the surface temperature of the forgings is ≤80℃.

[0042] S43, Tempering: The forging is transferred to the furnace for tempering, heated to 600-630℃ and held at that temperature, then air-cooled after being taken out of the furnace to obtain SA350Gr.LF3 large forgings.

[0043] Furthermore, the step of quenching the forging after the post-forging heat treatment in S41 includes:

[0044] First, place the forgings into the furnace at room temperature and heat them to 400-450℃ at a rate of ≤40℃ / h, and hold them at that temperature.

[0045] Then raise the temperature to 600-650℃ at a rate of ≤50℃ / h and hold.

[0046] Then raise the temperature to 830-860℃ at a rate of ≤140℃ / h and hold.

[0047] After being removed from the furnace, the forgings are water-cooled until the surface temperature is ≤80℃.

[0048] Preferably, in step S41, the holding time after heating the forging to 400-450°C is 3 hours.

[0049] After heating to 600-650℃, the holding time is 4 hours.

[0050] After heating to 830-860℃, the holding time is 6 hours.

[0051] Furthermore, the step of performing sub-temperature quenching on the quenched forging in S42 includes:

[0052] First, heat the forgings into the furnace at a rate of ≤40℃ / h to 400-450℃ and hold them there.

[0053] Then raise the temperature to 600-650℃ at a rate of ≤50℃ / h and hold.

[0054] Then raise the temperature to 710-740℃ at a rate of ≤140℃ / h and hold.

[0055] After being removed from the furnace, the forgings are water-cooled until the surface temperature is ≤80℃.

[0056] Preferably, in step S42, the holding time after heating the forging to 400-450°C is 3 hours.

[0057] After heating to 600-650℃, the holding time is 4 hours.

[0058] After heating to 710-740℃, the holding time is 6 hours.

[0059] Furthermore, the step of tempering the forging in S43 includes:

[0060] First, put the forging into the furnace and heat it to 300-350℃ at a rate of ≤40℃ / h and hold it thereafter.

[0061] Then raise the temperature to 600-630℃ at a rate of ≤80℃ / h and hold.

[0062] After being removed from the furnace and air-cooled, SA350 Gr.LF3 large forgings were obtained.

[0063] Preferably, in step S43, the holding time after heating the forging to 300-350°C is 3 hours.

[0064] After heating to 600-630℃, the holding time is 6 hours.

[0065] The beneficial effects of this invention are:

[0066] The mechanical properties of the thick-walled SA350 Gr.LF3 forging for the dry storage system of spent fuel described in this invention have been significantly improved, and the manufacturing process can overcome the phenomenon of unstable low-temperature toughness caused by the limited hardenability of the material and the thick wall. Attached Figure Description

[0067] Figure 1 This is a schematic diagram of the post-forging heat treatment process of the forging in an embodiment of the present invention.

[0068] Figure 2 This is a schematic diagram of the performance heat treatment process of the forgings according to an embodiment of the present invention. Detailed Implementation

[0069] The present invention will be further explained and illustrated below with reference to specific embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the materials used in the following embodiments are commercially available. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0070] I. Finished product requirements for forgings:

[0071] Forging heat treatment dimensions are The heat-treated wall thickness is 305mm. Forgings require sampling at position T×T / 4 for mechanical property testing. Performance requirements include room temperature tensile strength Rp0.2 ≥ 260MPa, Rm 485~655MPa, and 240℃ tensile strength Rp... 0.2 ≥214MPa, Rm≥439MPa, average KV at -101℃≥27J, drop hammer temperature≤-88℃. In other words, the forgings must meet the performance requirements in Table 1.

[0072] II. Components and their content in forgings:

[0073] The thick-walled SA350 Gr.LF3 forging for a transfer container for a spent fuel dry storage system according to the present invention includes an SA350 Gr.LF3 forging body. The components and their mass percentage (wt.%) contained in the SA350 Gr.LF3 forging body are as follows:

[0074] C: 0.05%-0.15%; Cr: 0.10-0.20%; Mo: 0.04-0.06%; V: 0.01-0.03%; Nb: 0.01-0.02%; Al: 0.012-0.017%; N: 0.008-0.012%; Si: 0.20-0.30%; Mn: 0.70-0.80%; Ni: 3.5-3.7%; P≤0.006%; S≤0.003%; balance Fe.

[0075] Through experimentation, it was found that controlling the content of each component and its mass percentage as follows yielded SA350Gr.LF3 large forgings with superior performance:

[0076] C: 0.06%-0.08%; Cr: 0.12-0.15%; V: 0.02-0.03%; Nb: 0.01-0.02%; Al: 0.012-0.017%; N: 0.009-0.011%; Mo: 0.04-0.06%; Si: 0.20-0.30%; Mn: 0.70-0.80%; Ni: 3.5-3.7%; P≤0.006%; S≤0.003%; balance Fe.

[0077] (1) Through experiments, it was found that controlling the C content within the range of 0.05%-0.15% (wt%) can greatly improve the low-temperature toughness of the material. If the C content is higher than this range, the low-temperature toughness of the material will be greatly reduced and the ductile-brittle transition temperature will be greatly increased if the material wall thickness is thick and a good quenching rate cannot be obtained. If the C content is higher than this temperature range, the material strength will be at a certain risk.

[0078] (2) Through experiments, it was found that for forgings with a wall thickness of more than 200 mm, the hardenability of the material is limited. Adding trace elements such as Cr, Mo, V and Nb to the raw materials and controlling the trace element content of the material can increase the hardenability of the material and thus improve the material performance.

[0079] (3) Through experiments, it was found that when the wall thickness of the material increases to a certain extent, the matrix structure is ferrite. Under this structure condition, in order to obtain good strength and low temperature toughness, the structure needs to be uniform and fine. Adding appropriate amounts of Al and N and controlling the N / Al ratio can form AlN, which can uniformly refine the structure, hinder grain growth, and thus improve the overall performance of the material.

[0080] III. Manufacturing process of forgings:

[0081] The manufacturing process of the thick-walled SA350 Gr.LF3 large forging for the transfer container of the spent fuel dry storage system described in this invention is as follows:

[0082] S1. Preparation of steel ingots:

[0083] The scrap steel is smelted using an electric furnace roughing-vacuum refining-vacuum casting process. The resulting smelting liquid is then cast to obtain steel ingots. The components and their mass percentage (wt.%) of the steel ingots are as follows:

[0084] C: 0.05%-0.15%; Cr: 0.10-0.20%; Mo: 0.04-0.06%; V: 0.01-0.03%; Nb: 0.01-0.02%; Al: 0.012-0.017%; N: 0.008-0.012%; Si: 0.20-0.30%; Mn: 0.70-0.80%; Ni: 3.5-3.7%; P≤0.006%; S≤0.003%; balance Fe.

[0085] Preferably, the components contained in the steel ingot and their mass percentage (wt.%) are as follows:

[0086] C: 0.06%-0.08%; Cr: 0.12-0.15%; V: 0.02-0.03%; Nb: 0.01-0.02%; Al: 0.012-0.017%; N: 0.009-0.011%; Mo: 0.04-0.06%; Si: 0.20-0.30%; Mn: 0.70-0.80%; Ni: 3.5-3.7%; P≤0.006%; S≤0.003%; balance Fe.

[0087] And at the same time, N / Al > 0.5.

[0088] S2, Forging:

[0089] S1 steel ingots are heated in a furnace to 1100℃-1240℃ and held forged to obtain forgings. The forging process involves operations such as drawing, billet preparation, upsetting, punching, reaming, and drawing again to forge forgings that meet the dimensional and shape requirements. The final forging temperature is ≥850℃.

[0090] S3. Post-forging heat treatment:

[0091] To reduce residual stress after forging, refine the microstructure, and prepare the forgings for subsequent performance heat treatment, the forgings undergo post-forging heat treatment using a normalizing and tempering process. The specific steps include:

[0092] S31, Right Fire:

[0093] After forging, the forgings are air-cooled to about 500-600℃ and then placed in the furnace to wait for material. They are then held at 600-650℃ for about 8 hours.

[0094] Cool the sample at a rate of ≤50℃ / h, then subcool it to 230±20℃ and hold it for 15 hours.

[0095] Heat the sample at a rate of ≤50℃ / h and hold it at 650-700℃ for 8 hours.

[0096] Heat the temperature to 860-880℃ as soon as possible and keep it warm for 15 hours.

[0097] S32, Tempering:

[0098] After being taken out of the furnace and air-cooled until the surface temperature of the forging is 250-300℃, it is then put back into the furnace and held at 230±20℃ for 15 hours.

[0099] Heat the sample at a rate of ≤50℃ / h and hold it at 600-630℃ for 30h.

[0100] Remove from the furnace when cooled to <150℃.

[0101] S4. Performance heat treatment:

[0102] Compared to small SA350 Gr.LF3 forgings, the challenge in performance control of large SA350 Gr.LF3 forgings lies in their thicker walls and limited hardenability. The conventional quenching and tempering methods commonly used for small forgings are insufficient to achieve a fine microstructure, thus failing to meet the excellent high-temperature strength and low-temperature toughness requirements of spent fuel. Therefore, the heat-treated forgings undergo performance heat treatment using a process of quenching + sub-temperature quenching + tempering. The specific steps include:

[0103] S41, Quenching:

[0104] The forgings are placed in a furnace at room temperature and heated to 400-450℃ at a rate of ≤40℃ / h, and held for 3 hours.

[0105] Heat to 600-650℃ at a rate of ≤50℃ / h and hold for 4 hours;

[0106] Heat to 830-860℃ at a rate of ≤140℃ / h and hold for 6 hours;

[0107] After being removed from the furnace, the forgings are water-cooled until the surface temperature is ≤80℃.

[0108] S42, Sub-temperature quenching:

[0109] The forgings are placed in the furnace and heated to 400-450℃ at a rate of ≤40℃ / h, and held for 3 hours.

[0110] Heat to 600-650℃ at a rate of ≤50℃ / h and hold for 4 hours;

[0111] Heat to 710-740℃ at a rate of ≤140℃ / h and hold for 6 hours;

[0112] After being removed from the furnace, the forgings are water-cooled until the surface temperature is ≤80℃.

[0113] S43, Tempering:

[0114] The forging is placed in the furnace and heated to 300-350℃ at a rate of ≤40℃ / h, and held for 3 hours.

[0115] Heat to 600-630℃ at a rate of ≤80℃ / h and hold for 6 hours;

[0116] Air cool after baking.

[0117] IV. Examples and Comparative Examples

[0118] Example

[0119] 1. The preparation process is as follows:

[0120] S1. Preparation of steel ingots:

[0121] The scrap steel is smelted using an electric furnace roughing-vacuum refining-vacuum casting process. The resulting smelting liquid is then cast to obtain steel ingots. The components and their mass percentage content of the steel ingots are as follows: C: 0.06%-0.08%;

[0122] Cr: 0.12-0.15%; V: 0.02-0.03%; Nb: 0.01-0.02%; Al: 0.012-0.017%; N: 0.009-0.011%; Mo: 0.04-0.06%; Si: 0.20-0.30%; Mn: 0.70-0.80%; Ni: 3.5-3.7%; P≤0.006%; S≤0.003%; balance Fe.

[0123] The above-mentioned components and their mass percentage content were obtained by sampling and testing at different locations on the steel ingot. Since there were many sampling sites and a large amount of data, range values ​​were used to summarize them.

[0124] S2, Forging:

[0125] The steel ingot is heated to 1150-1240℃ and held for forging. The forging process involves drawing, billet preparation, upsetting, punching, reaming, and drawing again to produce forgings that meet the size and shape requirements. The final forging temperature is ≥850℃.

[0126] S3. Post-forging heat treatment:

[0127] Forgings that have completed forging are processed according to Figure 1 The process shown involves post-forging heat treatment of the forging. It includes the following steps:

[0128] S31, Right Fire:

[0129] After forging, the forgings are air-cooled to about 500-600℃ and then placed in the furnace to wait for material. They are then held at 600-650℃ for about 8 hours.

[0130] Cool the sample at a rate of ≤50℃ / h, then subcool it to 230±20℃ and hold it for 15 hours.

[0131] Heat the sample at a rate of ≤50℃ / h and hold it at 650-700℃ for 8 hours.

[0132] Heat the temperature to 860-880℃ as quickly as possible and keep it at that temperature for 15 hours.

[0133] S32, Tempering:

[0134] After being taken out of the furnace and air-cooled until the surface temperature of the forging is 250-300℃, it is then put back into the furnace and held at 230±20℃ for 15 hours.

[0135] Heat the sample at a rate of ≤50℃ / h and hold it at 600-630℃ for 30h.

[0136] Remove from the furnace when cooled to ≤150℃.

[0137] S4. Performance heat treatment:

[0138] according to Figure 2 The process shown is for heat treatment of forgings to improve their performance:

[0139] S41. Quenching: Place the forging in a furnace at room temperature and heat it to 400-450℃ at a rate of ≤40℃ / h, then hold it for 3 hours.

[0140] Heat to 600-650℃ at a rate of ≤50℃ / h and hold for 4 hours;

[0141] Heat to 830-860℃ at a rate of ≤140℃ / h and hold for 6 hours;

[0142] After being removed from the furnace, the forgings are water-cooled until the surface temperature is ≤80℃.

[0143] S42, Sub-temperature quenching: The forging is placed in the furnace and heated to 400-450℃ at a rate of ≤40℃ / h and held for 3h.

[0144] Heat to 600-650℃ at a rate of ≤50℃ / h and hold for 4 hours;

[0145] Heat to 710-740℃ at a rate of ≤140℃ / h and hold for 6 hours;

[0146] After being removed from the furnace, the forgings are water-cooled until the surface temperature is ≤80℃.

[0147] S43. Tempering: Place the forging into the furnace and heat it to 300-350℃ at a rate of ≤40℃ / h, then hold it for 3 hours.

[0148] Heat to 600-630℃ at a rate of ≤80℃ / h and hold for 6 hours;

[0149] Air cool after baking.

[0150] 2. Samples were taken from different sites of the SA350 Gr.LF3 large forgings prepared in the examples, and their chemical composition was tested. The component content at each site was slightly different. Therefore, the specific component content of the SA350 Gr.LF3 large forgings obtained by the test is a range value.

[0151] The components and their mass percentage (wt.%) contained in the SA350 Gr.LF3 large forging body of Example are as follows:

[0152] (1)C: 0.06%-0.08%; Cr: 0.12-0.15%; V: 0.02-0.03%; Nb: 0.01-0.02%; Al: 0.012-0.017%; N: 0.009-0.011%;

[0153] (2) Mo: 0.04-0.06%; Si: 0.20-0.30%; Mn: 0.70-0.80%; Ni: 3.5-3.7%; P≤0.006%; S≤0.003%; balance Fe.

[0154] 3. The mechanical properties of the SA350 Gr.LF3 large forgings obtained in the example were tested, and the test results are shown in Table 2.

[0155] Table 2. Test results of mechanical properties of forgings at different locations.

[0156]

[0157]

[0158] As shown in Table 2, the mechanical properties of the forgings were tested, and all parameters met the requirements for use of large forgings for spent fuel storage containers, demonstrating good overall mechanical properties.

[0159] Comparative Example 1

[0160] Except for the chemical composition of the steel ingot, the forging process of Comparative Example 1 was identical to that in the examples. Samples were taken from different locations at the steel ingot obtained during the forging process of Comparative Example 1 and the SA350 Gr.LF3 large forging obtained after forging for testing. The components contained therein and their mass percentage content are as follows:

[0161] (1)C: 0.10%-0.14%; Cr: 0.12%-0.15%; V: 0.02%-0.03%; Nb: 0.01%-0.02%; Al: 0.012%-0.017%; N: 0.009%-0.011%;

[0162] (2) Mo: 0.04-0.06%; Si: 0.20-0.30%; Mn: 0.70-0.80%; Ni: 3.5-3.7%; P≤0.006%; S≤0.003%; balance Fe.

[0163] Comparative Example 2

[0164] Except for the chemical composition of the steel ingot, the forging process of Comparative Example 2 was identical to that in the examples. Samples were taken from different locations at the steel ingot obtained during the forging process of Comparative Example 2 and the SA350 Gr.LF3 large forging obtained after forging for testing. The components contained therein and their mass percentage content are as follows:

[0165] (1)C: 0.06%-0.08%; Cr: <0.10%; V: <0.01%; Nb: <0.01%; Al: 0.025%-0.035%; N: 0.006%-0.007%;

[0166] (2) Mo: 0.04-0.06%; Si: 0.20-0.30%; Mn: 0.70-0.80%; Ni: 3.5-3.7%; P≤0.006%; S≤0.003%; balance Fe.

[0167] The chemical components with different contents in the Examples and Comparative Examples 1 and 2 are compared, as shown in Table 3. The values ​​in Table 3 are all mass percentages (wt.%) of each component.

[0168] Table 3. Chemical composition of different contents in Examples 1 and 2.

[0169] Element C Cr V Nb Al N Example 0.06-0.08 0.12-0.15 0.02-0.03 0.01-0.02 0.012-0.017 0.0090-0.011 Comparative Example 1 0.10-0.14 0.12-0.15 0.02-0.03 0.01-0.02 0.012-0.017 0.0090-0.011 Comparative Example 2 0.06-0.08 ＜0.10 ＜0.01 ＜0.01 0.025-0.035 0.0060-0.0070

[0170] Note: The chemical composition was adjusted in the examples and comparative examples. After forging, samples were taken from multiple sites to test the components and their contents. The component contents at each site in each example group had slight differences. Therefore, the contents of each component in the above chemical composition table are specifically expressed as range values.

[0171] Comparative Example 3

[0172] Compared to the forging process in the embodiment, the forging process in Comparative Example 3 is the same as the steps in the embodiment, except that the sub-temperature quenching step in the performance heat treatment step S4 is missing.

[0173] After forging and post-forging heat treatment, the forgings of Comparative Example 3 were subjected to performance heat treatment according to the following steps:

[0174] (1) Quenching:

[0175] The forgings are placed in a furnace at room temperature and heated to 400-450℃ at a rate of ≤40℃ / h, and held for 3 hours.

[0176] Heat to 600-650℃ at a rate of ≤50℃ / h and hold for 4 hours;

[0177] Heat to 830-860℃ at a rate of ≤140℃ / h and hold for 6 hours;

[0178] Water-cooled until the surface temperature of the forging is ≤80℃.

[0179] (2) Tempering:

[0180] Heat the forging to 300-350℃ at a rate of ≤40℃ / h and hold for 3 hours;

[0181] Heat to 600-630℃ at a rate of ≤80℃ / h and hold for 6 hours;

[0182] Air cool after baking.

[0183] Comparative Example 4

[0184] Compared to the forging process in the embodiments, the forging process in Comparative Example 4, including the preparation of steel ingots in S1, forging in S2, and post-forging heat treatment in S3, is consistent with the steps in the embodiments. The only difference is that in the performance heat treatment step S4, the tempering temperature in S43 is different from that in the embodiments.

[0185] After forging and post-forging heat treatment, the forgings of Comparative Example 4 underwent performance heat treatment according to the following steps:

[0186] (1) Quenching:

[0187] The forgings are placed in a furnace at room temperature and heated to 400-450℃ at a rate of ≤40℃ / h, and held for 3 hours.

[0188] Heat to 600-650℃ at a rate of ≤50℃ / h and hold for 4 hours;

[0189] Heat to 830-860℃ at a rate of ≤140℃ / h and hold for 6 hours;

[0190] Water-cooled until the surface temperature of the forging is ≤80℃.

[0191] (2) Sub-temperature quenching:

[0192] Heat the forgings to 400-450℃ at a rate of ≤40℃ / h and hold for 3 hours;

[0193] Heat to 600-650℃ at a rate of ≤50℃ / h and hold for 4 hours;

[0194] Heat to 710-740℃ at a rate of ≤140℃ / h and hold for 6 hours;

[0195] Water-cooled until the surface temperature of the forging is ≤80℃.

[0196] (3) Tempering:

[0197] Heat the forging to 300-350℃ at a rate of ≤40℃ / h and hold for 3 hours;

[0198] Heat to 630-650℃ at a rate of ≤80℃ / h and hold for 6 hours;

[0199] Air cool after baking.

[0200] Comparative Example 5

[0201] Compared to the forging process in the embodiments, the forging process in Comparative Example 5 is the same as that in the embodiments in S1 (preparing steel ingots), S2 (forging), and S3 (post-forging heat treatment), except that the S41 (quenching) step is missing in the S4 performance heat treatment step.

[0202] After forging and post-forging heat treatment, the forgings of Comparative Example 5 were subjected to performance heat treatment according to the following steps:

[0203] (1) Sub-temperature quenching:

[0204] Heat the forgings to 400-450℃ at a rate of ≤40℃ / h and hold for 3 hours;

[0205] Heat to 600-650℃ at a rate of ≤50℃ / h and hold for 4 hours;

[0206] Heat to 710-740℃ at a rate of ≤140℃ / h and hold for 6 hours;

[0207] Water-cooled until the surface temperature of the forging is ≤80℃.

[0208] (2) Tempering:

[0209] Heat the forging to 300-350℃ at a rate of ≤40℃ / h and hold for 3 hours;

[0210] Heat to 600-630℃ at a rate of ≤80℃ / h and hold for 6 hours;

[0211] Air cool after baking.

[0212] VI. Implementation Examples

[0213] Various physical properties of the SA350 Gr.LF3 large forgings prepared in the above embodiments and comparative examples 1-5 were tested, and the test results are shown in Table 4.

[0214] Table 4 Performance Test Tables for Examples and Comparative Examples

[0215]

[0216]

[0217] As shown in Table 4, the performance of the forgings in the embodiments is significantly better than that of the comparative examples. Therefore, the SA350 Gr.LF3 large forgings described in this invention can achieve better performance in terms of both chemical composition and forging process.

[0218] The above description is merely an example of the embodiments of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A thick-walled SA350 Gr.LF3 forging for a transfer container in a spent fuel dry storage system, comprising an SA350 Gr.LF3 forging body, characterized in that, The composition and its mass percentage (wt.%) of the SA350 Gr.LF3 large forging body are as follows: C: 0.06%-0.08%; Cr: 0.12-0.15%; V: 0.02-0.03%; Nb: 0.01-0.02%; Al: 0.012-0.017%; N：0.009-0.011％； Mo: 0.04-0.06%; Si: 0.20-0.30%; Mn: 0.70-0.80%; Ni: 3.5-3.7%; P≤0.006%; S≤0.003%; balance Fe; The manufacturing process of the SA350 Gr.LF3 large forging includes post-forging heat treatment and performance heat treatment of the forging. The post-forging heat treatment steps include: S31. Normalizing: After forging, the forging obtained is air-cooled to 500-600℃ and put into the furnace to wait for material. It is then cooled to 230±20℃ and held at that temperature. Then it is heated to 860-880℃ and held at that temperature. S32. Tempering: After the forging is taken out of the furnace, it is air-cooled to 250-300℃, then put into the furnace and held at 230±20℃; then the temperature is raised to 600-630℃ and held. S33. Cool the furnace to <150℃ before unloading; The performance heat treatment steps include: S41. Quenching: The forging is placed in the furnace at room temperature, heated to 830-860℃ and held at that temperature, and then water-cooled until the surface temperature of the forging is ≤80℃. S42, Sub-temperature quenching: The forgings are transferred to the furnace for sub-temperature quenching, heated to 710-740℃ and held at that temperature, and then water-cooled after being taken out of the furnace until the surface temperature of the forgings is ≤80℃. S43, Tempering: The forging is transferred to the furnace for tempering, heated to 600-630℃ and held at that temperature, then air-cooled after being taken out of the furnace to obtain SA350Gr.LF3 large forgings.

2. The SA350 Gr.LF3 large forging as described in claim 1, characterized in that, The composition of the SA350 Gr.LF3 large forging body has N (wt.%) / Al (wt.%) ≥ 0.

5.

3. The SA350 Gr.LF3 large forging as described in any one of claims 1 or 2, characterized in that, Its manufacturing process includes the following steps: S1. Preparation of steel ingots: Smelting scrap steel and casting the resulting smelting liquid to obtain steel ingots, wherein the steel ingots contain the components and their mass percentage content contained in the SA350 Gr.LF3 large forging body as described in any one of claims 1 or 2. S2, Forging: The steel ingot obtained in S1 is heated in a furnace and forged to obtain a forging; S3. Post-forging heat treatment: The forgings obtained in S2 are subjected to post-forging heat treatment by normalizing and tempering. S4. Performance heat treatment: The forgings after the post-forging heat treatment in S3 are subjected to performance heat treatment by quenching + sub-temperature quenching + tempering to obtain SA350 Gr.LF3 large forgings.

4. The SA350 Gr.LF3 large forging as described in claim 3, characterized in that, The forging temperature of the steel ingot in S2 is 1100℃-1240℃, and the final forging temperature is ≥850℃.

5. The SA350 Gr.LF3 large forging as described in claim 4, characterized in that, The forging temperature of the steel ingot in S2 is 1150℃-1240℃, and the final forging temperature is ≥850℃.

6. The SA350 Gr.LF3 large forging as described in claim 1, characterized in that, The step of normalizing the forging obtained by forging in S31 includes: After forging, the forgings are air-cooled to 500-600℃ and then placed in the furnace to wait for material. They are then held at 600-650℃ for about 8 hours. Cool the sample at a rate of ≤50℃ / h, then subcool it to 230±20℃ and hold it for 15 hours. Heat the sample at a rate of ≤50℃ / h and hold it at 650-700℃ for 8 hours. Heat the temperature to 860-880℃ as quickly as possible and keep it at that temperature for 15 hours. The step of tempering the forging in S32 includes: After the normalizing treatment, the forgings are taken out of the furnace and air-cooled until the surface temperature of the forgings is 250-300℃, and then put into the furnace at 230±20℃ for 15 hours. Heat the sample at a rate of ≤50℃ / h and hold it at 600-630℃ for 30h.

7. The SA350 Gr.LF3 large forging as described in claim 1, characterized in that, The step of quenching the forging after the post-forging heat treatment in S41 includes: The forgings are placed in a furnace at room temperature and heated to 400-450℃ at a rate of ≤40℃ / h, and held for 3 hours. Heat to 600-650℃ at a rate of ≤50℃ / h and hold for 4 hours; Heat to 830-860℃ at a rate of ≤140℃ / h and hold for 6 hours; After being removed from the furnace, the forgings are water-cooled until the surface temperature of the forgings is ≤80℃. The step of performing sub-temperature quenching on the quenched forging in S42 includes: The forgings are placed in the furnace and heated to 400-450℃ at a rate of ≤40℃ / h, and held for 3 hours. Heat to 600-650℃ at a rate of ≤50℃ / h and hold for 4 hours; Heat to 710-740℃ at a rate of ≤140℃ / h and hold for 6 hours; After being removed from the furnace, the forgings are water-cooled until the surface temperature of the forgings is ≤80℃. The step of tempering the forging in S43 includes: The forging is placed in the furnace and heated to 300-350℃ at a rate of ≤40℃ / h, and held for 3 hours. Heat to 600-630℃ at a rate of ≤80℃ / h and hold for 6 hours; After being removed from the furnace and air-cooled, SA350 Gr.LF3 large forgings were obtained.

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