Steel for a container for a high-level waste glassified body and a forming method

Abstract

The application relates to a steel for a container for a high-level waste glass solidification body and a forming method, and belongs to the technical field of part manufacturing. The steel solves the problem that the existing material cannot meet the use requirement in the high-level waste solidification, storage and transportation and geological disposal links. The components of the steel include C 0.02%-0.05%, Si 1.0%-1.75%, Mn 1.25%-1.75%, Cr 23.0%-25.0%, Ni 13.0%-15.0%, Mo 0.75%-1.0%, N 0.2%-0.25%, Nb 0.15%-0.25%, S<=0.01, P<=0.012, and the balance of Fe and inevitable impurities.

Description

Technical Field

[0001] This invention relates to the field of component manufacturing technology, and in particular to a steel for a container used in high-level radioactive waste vitrified bodies and a forming method thereof. Background Technology

[0002] High-level radioactive waste (HRFW) is crucial for the sustainable development of nuclear power, and its safe and rational disposal is of paramount importance. To date, the widely accepted method for radioactive waste disposal worldwide involves vitrifying the waste, packaging it in vitrified containers, and then subjecting it to geological disposal. Therefore, vitrified containers play a vital role in the safe disposal of HRFW throughout the entire process, from solidification and storage to transportation and geological disposal.

[0003] Because the glass temperature reaches above 1100℃ during the casting process, which lasts for several hours, the tank needs to undergo temporary cooling for decades after casting. Therefore, the vitrified container needs to remain undeformed when subjected to the 1100℃ high-temperature glass, while also exhibiting good creep resistance at medium and low temperatures. After casting and temporary cooling, the tank needs to undergo long-distance and complex transportation and placement, during which it may be subject to drops or collisions. Therefore, it is also necessary to ensure that the tank material retains good plasticity and toughness after high-temperature casting and long-term medium and low-temperature temporary storage. Currently, there is only one type of material used for high-level radioactive waste vitrified storage tanks in China: improved 310S austenitic heat-resistant steel. While this steel has acceptable high-temperature strength, impact toughness after high-temperature service, and creep performance below 800℃, it cannot withstand temperatures up to 1000℃. The material's oxidation resistance and thermal shock resistance at 1000℃ are crucial to the safety and service life of high-level radioactive waste vitrified containers. Summary of the Invention

[0004] In view of the above analysis, the present invention aims to provide a steel for a container for high-level radioactive waste vitrification and a forming method thereof, in order to solve the problem that existing materials cannot meet the usage requirements in the solidification, storage, transportation and geological disposal of high-level radioactive waste.

[0005] The objective of this invention is mainly achieved through the following technical solutions: In a first aspect, the present invention provides a steel for containers used in high-level radioactive waste vitrification, wherein the steel comprises, by mass percentage: C 0.02%-0.05%, Si 1.0%-1.75%, Mn 1.25%-1.75%, Cr 23.0%-25.0%, Ni 13.0%-15.0%, Mo 0.75%-1.0%, N 0.2%-0.25%, Nb 0.15%-0.25%, S≤0.01%, P≤0.012%, with the balance being Fe and unavoidable impurities.

[0006] Optionally, the steel composition includes: C 0.042%, Si 1.25%, Mn 1.32%, Cr 23.48%, Ni 14.3%, Mo 0.84%, N 0.24%, Nb 0.23%, S≤0.002%, P≤0.006%, with the balance being Fe and unavoidable impurities.

[0007] Optionally, the microstructure of the steel is a single-phase austenitic structure.

[0008] In a second aspect, the present invention provides a method for molding a container for high-level radioactive waste vitrified body, comprising: Step 1: Prepare raw materials: Form the aforementioned steel into plates and pipes; Step 2: Component Forming: The formed sheet metal is then shaped into top and bottom caps, and pipes are formed. It is a cylindrical body; Step 3: Heat treatment: The formed upper head, cylinder and bottom are subjected to solution treatment; Step 4: Assembly welding: The top head, cylinder and bottom end after solution treatment are sequentially welded circumferentially to obtain a container for high-level radioactive waste vitrified body.

[0009] Optionally, in step 1, the sheet material is rolled.

[0010] Optionally, in step 1, the pipe is formed by extrusion or die forging.

[0011] Optionally, in step 2, the upper end cap is formed using the first mold assembly.

[0012] Optionally, in step 2, the cylinder is formed using a second mold assembly.

[0013] Optionally, in step 2, a third mold assembly is used to form the bottom seal.

[0014] Optionally, in step 4, the welding current is 140~220A and the arc voltage is 12~14V.

[0015] Optionally, the bottom seal is formed using a spinning process.

[0016] Optionally, in step 3, the solution treatment includes: heating the upper end cap, cylinder, and bottom end cap to 1000~1150℃, holding at that temperature for 20~50 minutes, and then cooling.

[0017] Thirdly, the present invention provides a mold system for forming a container for high-level radioactive waste vitrified bodies, the mold system comprising a first mold assembly, a second mold assembly, and a third mold assembly; the first mold assembly is used to form the upper end cap of the container, the second mold assembly is used to form the cylindrical body of the container, and the third mold assembly is used to form the bottom cap of the container; the second mold assembly includes a mandrel, the mandrel being cylindrical and having a flange at one end.

[0018] Optionally, the first mold assembly includes a first core mold, a second core mold, a third core mold, and a fourth core mold; the second core mold includes a first column, a second column protruding outward from one end face of the first column, and a square protrusion protruding outward from one end face of the second column, wherein the diameter of the first column is larger than the diameter of the second column.

[0019] Optionally, the third mold assembly includes a lower mold, an upper mold, and an inner mold; the lower mold is cylindrical and has a first through hole, the first through hole being arranged along the axial direction of the cylinder, and the axis of the cylinder coinciding with the axis of the first through hole.

[0020] Optionally, the third mold assembly further includes a pressure ring, which is sleeved on one end of the lower mold for fixing the workpiece blank.

[0021] Optionally, the pressure ring is cylindrical with a second through hole. The second through hole is arranged along the axial direction of the cylinder, and the axis of the cylinder coincides with the axis of the through hole.

[0022] Optionally, the upper mold is cylindrical, with an outwardly protruding arc-shaped protrusion on one end face, and the upper mold can extend into the first through hole of the lower mold.

[0023] Optionally, the inner mold is cylindrical, with an inwardly recessed portion on one end face. The arc-shaped protrusion of the upper mold cooperates with the recess of the inner mold to form the arc-shaped end face of the container bottom.

[0024] Fourthly, the present invention provides a container for high-level radioactive waste vitrified body, comprising an upper end cap, a cylindrical body, and a bottom end cap, wherein the upper end cap, the cylindrical body, and the bottom end cap are formed using the above-described mold system; the upper end cap and the bottom end cap are respectively welded to the cylindrical body, and the weld at the weld is a circumferential weld.

[0025] Optionally, the second through hole is a stepped hole, including a first stepped hole, a second stepped hole, and a third stepped hole that are interconnected; the first stepped hole is used for the upper die to pass through, the second stepped hole is used to accommodate the workpiece blank, and the third stepped hole is used to accommodate the lower die. The diameter of the first stepped hole is smaller than the diameter of the second stepped hole, the diameter of the second stepped hole is smaller than the diameter of the third stepped hole, and the diameter of the third stepped hole is smaller than the outer diameter of the lower die.

[0026] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. Existing steels used in high-level radioactive waste vitrification storage tanks exhibit acceptable high-temperature strength, post-service impact toughness, and creep performance below 800℃. However, when used for high-level radioactive waste, the growth of brittle phases into δ-ferrite during service (after thermal shock cycling) leads to a sharp decline in material plasticity and toughness, as well as insufficient high-temperature strength, failing to meet the technical requirements for high-level radioactive waste solidification, storage, transportation, and geological disposal. This invention improves the steel's toughness, high-temperature strength, and high-temperature oxidation resistance through a combination of alloy composition design and process adjustments, thereby extending the container's service life.

[0027] Specifically, based on the results of thermal shock cycling tests, this invention adjusts the material composition by controlling the C and N content and using a solution treatment process to form a single-phase austenitic structure, thereby improving the high-temperature strength, high-temperature oxidation resistance, and room-temperature toughness of the steel. Adding Mo and optimizing the N and Nb content further enhances the high-temperature strength, thus extending the service life of the container. Furthermore, compared to SUS310S, this invention has approximately 7% lower nickel content, offering a cost advantage in raw materials.

[0028] 2. Existing molds used to form the upper head, cylinder, and bottom end have numerous longitudinal welds after welding. These longitudinal welds significantly impact the material's high-temperature strength and impact toughness, reducing the container's service life. This invention designs specific first, second, and third mold components (which respectively form the upper head, cylinder, and bottom end), ensuring that the formed upper head, cylinder, and bottom end themselves are free of longitudinal welds. The upper head, cylinder, and bottom end are then welded together to form a high-temperature protected vessel. The welding process only forms circumferential welds, eliminating the influence of longitudinal welds and increasing the service life of the high-temperature protected vessel by more than 40%.

[0029] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages will become apparent from the description or may be learned by practicing the invention. Attached Figure Description

[0030] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0031] Figure 1 This is a schematic diagram illustrating one step of forming the upper end cap according to the present invention; Figure 2 This is a schematic diagram illustrating one step of forming the upper end cap according to the present invention; Figure 3 This is a schematic diagram illustrating one step of forming the upper end cap according to the present invention; Figure 4 This is a schematic diagram illustrating one step of forming the upper end cap according to the present invention; Figure 5 This is a schematic diagram illustrating one step of forming the upper end cap according to the present invention; Figure 6 This is a schematic diagram of one step in the molding of the cylindrical body according to the present invention; Figure 7 This is a schematic diagram of one step in the molding of the cylindrical body according to the present invention; Figure 8 This is a schematic diagram of the structure of the cylindrical body formed according to the present invention; Figure 9 This is a schematic diagram of one step in the molding and sealing process of the bottom of the present invention; Figure 10 This is a schematic diagram of one step in the molding and sealing process of the bottom of the present invention; Figure 11 This is a schematic diagram of one step in the molding and sealing process of the bottom of the present invention; Figure 12 This is a schematic diagram of one step in the molding and sealing process of the bottom of the present invention; Figure 13 The image shows the metallographic structure of the steel container for the high-level radioactive waste obtained in this embodiment of the invention after solution treatment. Figure 14 This is a schematic diagram of the upper end cap structure formed according to an embodiment of the present invention; Figure 15 This is a schematic diagram of the bottom sealing structure formed according to an embodiment of the present invention.

[0032] Figure label: A - Workpiece; 0 - Steel plate; 1 - First core mold; 11 - Square protrusion; 2 - Second core mold; 21 - First column; 22 - Second column; 3 - Third core mold; 31 - Third column; 32 - Chamfer; 4 - Fourth core mold; 41 - Shoulder structure; 42 - Flanged structure; 5 - Forged tube blank; 6 - Mandrel; 61 - Flange; 7 - Upper mold; 8 - Lower mold; 9 - Pressure ring; 10 - Inner mold; 12 - Workpiece blank. Detailed Implementation

[0033] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0034] In a first aspect, the present invention provides a steel for containers used in high-level radioactive waste vitrification, wherein the steel composition, by mass percentage, comprises: C 0.02%-0.05%, Si 1.0%-1.75%, Mn 1.25%-1.75%, Cr 23.0%-25.0%, Ni 13.0%-15.0%, Mo 0.75%-1.0%, N 0.2%-0.25%, Nb 0.15%-0.25%, S≤0.01%, P≤0.012%, with the balance being Fe and unavoidable impurities.

[0035] In one embodiment, the steel composition includes: C 0.042%, Si 1.25%, Mn 1.32%, Cr 23.48%, Ni 14.3%, Mo 0.84%, N 0.24%, Nb 0.23%, S≤0.002%, P≤0.006%, with the balance being Fe and unavoidable impurities.

[0036] The following details the function and dosage selection of the components contained in this invention: C: Carbon has high solubility in steel and is an austenite-forming and stabilizing element, expanding the austenite region. Carbon is also a solid solution strengthening element in steel, significantly increasing the strength of austenitic stainless steel. Generally, the strength of austenitic stainless steel is positively correlated with carbon content. In austenitic heat-resistant steel, carbon primarily affects M... 23 The precipitation of C6-type carbides is due to the fact that carbon in steel readily combines with chromium at high temperatures to form chromium-rich M... 23 C6 type carbides cause intergranular corrosion and reduce the corrosion resistance of the steel. Therefore, the carbon content in austenitic heat-resistant steels is relatively low; in this invention, the carbon content is controlled at 0.02~0.05%.

[0037] Nitrogen (N) is an austenite-forming element. Besides stabilizing austenite, nitrogen can also precipitate dispersed nitrides in nickel-chromium austenitic heat-resistant steel, improving the steel's hot strength while having almost no effect on brittleness. The nitrogen content in the composition of this invention is controlled at 0.2%~0.25%.

[0038] Ni: Ni is an austenitic element. A major reason for adding nickel to austenitic stainless steel is to form an austenitic crystal structure, thereby improving the steel's corrosion resistance, plasticity, weldability, and toughness. However, excessive nickel reduces nitrogen solubility. Therefore, the nickel content in this invention is 13-15%.

[0039] Mn: Mn is an austenite-forming element. Manganese has a lower austenite-forming ability compared to nickel, nitrogen, and carbon. Therefore, excessive manganese will reduce the material's resistance to high-temperature oxidation and corrosion. However, manganese can make more nitrogen dissolve into stainless steel. The manganese content in the composition of this invention is 1.25%~1.75%.

[0040] Mo: Molybdenum is an important alloying element in austenitic heat-resistant steel, enhancing the corrosion resistance of chromium in the steel. Its main function is to improve the corrosion resistance of steel in reducing media and to enhance its resistance to pitting and crevice corrosion. Both molybdenum and chromium are elements that form and stabilize ferrite and expand the ferrite phase region. Molybdenum can also promote the precipitation of intermetallic phases such as δ-phase and Laves phase in austenitic stainless steel, which can adversely affect the mechanical properties of the steel, especially leading to a decrease in plasticity and toughness. Therefore, the molybdenum content in this invention is controlled at 0.75%~1.0%.

[0041] Si: Silicon is a beneficial element in heat-resistant steel for resisting high-temperature corrosion. At high temperatures, a protective and dense SiO2 film forms on the surface of silicon-containing heat-resistant steel. A significant anti-oxidation effect is observed when the silicon content in the steel reaches 1.0% or higher. Therefore, this invention selects a Si content of 1.0% to 1.75%.

[0042] Nb: Nb carbides and nitrides have high melting points. Adding an appropriate amount of Nb can prevent austenite grain growth and reduce the dislocation reaction rate, which can help improve high-temperature strength. However, when the amount added is large, it will significantly reduce impact toughness. Therefore, the Nb content in this invention is 0.15%~0.25%.

[0043] Cr: The addition of 23%-25% chromium in this invention ensures that the material of this invention has good antioxidant and corrosion resistance and provides strength guarantee when working in high-temperature environments, without affecting the stability of the material structure. The chromium content in the composition of this invention can meet the high temperature resistance and corrosion resistance requirements of this type of material.

[0044] S and P: S and P are harmful elements, and the content of both S and P must be below 0.03%.

[0045] This invention relates to the composition design of heat-resistant steel for high-level radioactive waste containers. It addresses the technical problem that existing materials suffer from a sharp decline in plasticity and toughness due to the growth of brittle δ-ferrite phases during service (after thermal shock cycling), resulting in insufficient high-temperature strength and failing to meet the requirements for high-level radioactive waste solidification, storage, transportation, and geological disposal. Based on thermal shock cycling test results, this invention adjusts the material composition by controlling the C and N content to form a single-phase austenitic structure, thereby improving the steel's high-temperature strength and high-temperature oxidation resistance. Adding Mo and optimizing the Nb content further enhances the steel's high-temperature strength, thus extending the container's service life. Furthermore, compared to SUS310S, this invention has approximately 7% lower nickel content, offering a raw material cost advantage.

[0046] Secondly, the present invention also provides a method for molding the container for the above-mentioned high-level radioactive waste vitrified body: including... Step 1: Prepare raw materials: Roll the above-mentioned steel into plates using conventional processes, or extrude or forge it into pipes; Step 2: Component forming: The formed sheet metal is formed into the top end cap and bottom end cap, and the pipe is formed into the cylinder; Step 3: Heat treatment: The formed upper head, cylinder and bottom are subjected to solution treatment; Step 4: Assembly welding: The top head, cylinder and bottom of the solution-treated container are sequentially welded circumferentially to obtain a container for high-level radioactive waste vitrified.

[0047] Specifically, in step 3 above, the solution treatment includes heating, heat preservation, and cooling the upper end cap, cylinder, and bottom end cap.

[0048] The heating temperature is 1000~1150℃, for example, 1000℃, 1030℃, 1050℃, 1080℃, 1100℃, 1120℃, 1150℃.

[0049] The heat preservation time is 20~50 minutes, for example, 20 minutes, 30 minutes, 40 minutes, and 50 minutes.

[0050] Water cooling is used for cooling.

[0051] Specifically, in step 2 above, the upper end cap is formed using the first mold assembly.

[0052] Specifically, in step 2 above, the cylinder is formed using the second mold assembly.

[0053] Specifically, in step 2 above, the bottom is formed using a third mold assembly.

[0054] Specifically, in step 4 above, the welding parameters used are: welding current 140~220A, arc voltage 12~14V, wire feed speed 900~1200mm / min, welding speed 80~110mm / min, current polarity DCSP, and arc protection using 99.99% high-purity argon gas.

[0055] Specifically, in step 4, the upper end cap of the formed container includes: Step i: As Figure 1 As shown, a steel plate 0 containing the above-mentioned components is fixed on a first mandrel 1, and the steel plate 0 is heated to 1000°C with a flame. The steel plate 0 is a circular steel plate with a thickness of 12mm and a diameter of 520mm. A square through hole is provided on the steel plate 0 along its thickness direction for the square protrusion of the first mandrel 1 to pass through. The size of the square through hole is 45mm × 45mm.

[0056] Step ii: As Figure 2 As shown, steel plate 0 is spun to form the neck cylinder of the upper head, resulting in workpiece A.

[0057] The specific process parameters are as follows: Spinning direction: positive spinning; Maximum wall thickness reduction rate: 35%; Spinning linear speed is 160-240 m / min, for example, 160 m / min, 170 m / min, 180 m / min, 190 m / min, 200 m / min, 210 m / min, 220 m / min, 230 m / min, 240 m / min; Feed ratio: 1.5-2 mm / revolution, for example, 1.5 mm / revolution, 1.6 mm / revolution, 1.7 mm / revolution, 1.8 mm / revolution, 2 mm / revolution; Spinning passes: 6-10, double-wheel spinning with no wheel misalignment; Spinning temperature: 900-1100℃, for example, 900℃, 920℃, 950℃, 970℃, 1000℃, 1050℃, 1100℃.

[0058] Step iii: As Figure 3 As shown, the second core mold 2 is used, and the second column 22 of the second core mold 2 is inserted into the neck cylinder of the upper end cap to spin the workpiece A until the bottom is flat.

[0059] The specific process parameters are as follows: Spinning direction: positive spinning; Maximum wall thickness reduction rate: 35%; Spinning linear speed is 160-240 m / min, for example, 160 m / min, 170 m / min, 180 m / min, 190 m / min, 200 m / min, 210 m / min, 220 m / min, 230 m / min, 240 m / min; Feed ratio: 1.5-1.8 mm / revolution, for example, 1.5 mm / revolution, 1.6 mm / revolution, 1.7 mm / revolution, 1.8 mm / revolution; Spinning passes: 6, double-wheel spinning, wheel offset 0; Spinning temperature: 900-1000℃, for example, 900℃, 920℃, 950℃, 970℃, 1000℃.

[0060] Step iv: as Figure 4 As shown, remove the part with square hole at the top of the straight section of the workpiece neck, and use the third core mold 3 to spin the bottom of the upper end cap. The spinning process parameters are the same as in step ii.

[0061] Step v: as Figure 5 As shown, the third core mold 3 and the fourth core mold 4 are used to spin-form the top of the upper end cap by flanging. The spinning process parameters are the same as in step ii.

[0062] This completes the forming of the upper head of the container. The formed upper head structure is shown in the image. Figure 14 .

[0063] Specifically, the cylindrical body of the molded container includes: Step a: As Figure 6 As shown, a forged tube blank with ID426mm×25mm, L=400mm and the above composition is placed on a mandrel and heated by flame to 350-400℃, for example, 350℃, 360℃, 370℃, 380℃, 390℃, or 400℃.

[0064] Step b: As Figure 7 As shown, pressure is applied through the rotation of the wheel, resulting in plastic deformation.

[0065] The specific process parameters are as follows: Spinning direction: counter-spinning; Wall thickness reduction rate: 70%; Spinning linear speed is 180-200 m / min, for example, 180 m / min, 185 m / min, 190 m / min, 195 m / min, 200 m / min; Feed ratio: 1.5-2 mm / revolution, for example, 1.5 mm / revolution, 1.6 mm / revolution, 1.7 mm / revolution, 1.8 mm / revolution, 2 mm / revolution; Spinning passes: 5-6; double-wheel spinning with no wheel misalignment.

[0066] Because the circumferential flow resistance of the metal is relatively large, it flows along the axis with less resistance, accumulating to form a thin-walled long cylindrical part. During spinning, the billet temperature is maintained at 350-400℃, for example, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃.

[0067] Step c: Remove excess material from both ends of the workpiece to complete the container's cylindrical body forming. See the diagram for the formed cylindrical body structure. Figure 8 .

[0068] Specifically, the bottom sealing of the molded container includes: Step A: As Figure 9 As shown, the workpiece blank 12 with the above composition is placed on the lower mold 8, centered, and the pressure ring 9 and the upper mold 7 are installed.

[0069] The workpiece blank has a thickness of 12mm and a diameter of 680mm.

[0070] Step B: As Figure 10 As shown, the upper die 7 is pressed down until the edge of the workpiece blank enters the gap between the upper die 7 and the lower die 8, forming the side of the workpiece, and the workpiece is U-shaped.

[0071] It should be noted that in step B, the U-shaped workpiece can be formed by cold forming or by thermoforming.

[0072] Step C: As Figure 11 As shown, the U-shaped workpiece is inverted, with the spherical crown on top and the opening facing down, and the side of the workpiece is placed in the gap between the lower mold 8 and the inner mold 10.

[0073] Step D: As Figure 12 As shown, the upper mold 7 is pressed down, and the spherical crown of the U-shaped workpiece is pressed into the U-shaped recess of the inner mold, completing the bottom sealing of the container. The resulting bottom sealing structure is shown below. Figure 15 .

[0074] Thirdly, the present invention also provides a mold forming system for forming the aforementioned container. The mold forming system includes a first mold assembly, a second mold assembly, and a third mold assembly. The first mold assembly is used to form the upper end cap of the container, the second mold assembly is used to form the cylindrical body of the container, and the third mold assembly is used to form the bottom cap of the container.

[0075] See Figures 1-5 The first mold assembly includes a first core mold 1, a second core mold 2, a third core mold 3, and a fourth core mold 4.

[0076] like Figure 1 and Figure 2 As shown, the first core mold 1 is cylindrical, and a square protrusion 11 is provided on one end face to cooperate with the square through hole of the steel plate.

[0077] like Figure 3 As shown, the second core mold 2 includes a first column 21, a second column 22 protruding outward from one end face of the first column 21, and a square protrusion 11 protruding outward from one end face of the second column 22. The diameter of the first column 21 is larger than the diameter of the second column 22, and the second column 22 extends into the neck cylinder of the upper end cap.

[0078] like Figure 4 As shown, the third core mold 3 includes a third column 31, and a chamfer 32 is provided at the connection between one end face and the side of the third column 31 to form the shoulder structure of the third core mold 3.

[0079] like Figure 5 As shown, the fourth core mold 4 includes a shoulder structure 41 that mates with the end face, side face and chamfer 33 of the third core mold 3 and a flanging structure 42 for forming the workpiece flanging.

[0080] The second mold assembly includes a mandrel 6.

[0081] like Figure 6 As shown, the core rod 6 is cylindrical, with a flange 61 at one end, which serves as a limiting element.

[0082] The third mold assembly includes a lower mold 8, an upper mold 7, an inner mold 10, and a pressure ring 9.

[0083] like Figure 9 As shown, the lower mold 8 is cylindrical with a through hole. The through hole is arranged along the axial direction of the cylinder, and the axis of the cylinder coincides with the axis of the through hole, so that the lower mold 8 is a hollow cylinder.

[0084] Continue to refer to Figure 9 The upper mold 7 is cylindrical, with an outwardly protruding arc-shaped protrusion on one end face, allowing the upper mold 7 to extend into the through hole of the lower mold 8.

[0085] like Figure 9 As shown, the inner mold 10 is cylindrical, with an inwardly recessed part on one end face. The arc-shaped protrusion of the upper mold 7 cooperates with the recess of the inner mold 10 to form the arc-shaped end face of the bottom.

[0086] The pressure ring 9 is fitted onto one end of the lower die 8 to fix the workpiece blank 12. The pressure ring 9 is cylindrical with a through hole. The through hole is arranged along the axial direction of the cylinder, and the axis of the cylinder coincides with the axis of the through hole, so that the pressure ring 9 is a hollow cylinder.

[0087] Specifically, the through hole is a stepped hole, which includes a first stepped hole, a second stepped hole, and a third stepped hole that are interconnected.

[0088] The first stepped hole is used for the upper mold 7 to pass through, and the second stepped hole is used to accommodate the workpiece blank 12 and to fix and limit it. Specifically, the workpiece blank 12 is fixed in the second stepped hole to prevent the workpiece blank 12 from moving during the forming process.

[0089] The third stepped hole is used to accommodate the lower mold 8 and serves as a fixing and limiting function. Specifically, it fixes the lower mold 8 in the third stepped hole to prevent it from moving during the molding process.

[0090] In one embodiment, the diameter of the first stepped hole is smaller than the diameter of the second stepped hole, the diameter of the second stepped hole is smaller than the diameter of the third stepped hole, and the diameter of the third stepped hole is smaller than the outer diameter of the lower mold 8.

[0091] Examples 1-4 The advantages of precise control of the composition and process parameters of the steel of the present invention will be demonstrated below with specific embodiments and comparative examples.

[0092] Examples 1-4 of the present invention provide a steel for a container for high-level radioactive waste vitrified body and a forming method thereof. The chemical composition of the steel in Examples 1-4 is shown in Table 1.

[0093] The specific process parameters of Examples 1-4 are shown in Table 2; the room temperature tensile properties, high temperature tensile properties, room temperature impact properties, and room temperature impact properties after thermal cycling of the steel used for containers of high-level radioactive waste are shown in Table 3-6.

[0094] It should be noted that, because tensile testing can damage the workpiece, in order not to damage the formed upper head, cylinder and bottom, in Examples 1-4, the upper head, cylinder and bottom were not formed. Instead, the high-level radioactive waste glass solidified body was directly subjected to tensile testing after solution treatment with container steel.

[0095] Table 1 Chemical composition, wt%

[0096] Table 2 Production Process Parameters

[0097] Table 3 Results of room temperature tensile properties test

[0098] Table 4. Results of High-Temperature Tensile Properties Test

[0099] Note: The steels in Comparative Examples 1 and 2 cannot withstand temperatures of 1000℃, therefore, it is impossible to measure the yield strength and tensile strength at 1000℃.

[0100] Table 5. Results of Room Temperature Impact Performance Test

[0101] Table 6. Results of room temperature shock performance after thermal cycling

[0102] Figure 13 This is a metallographic image of the steel used as a container for the high-level radioactive waste vitrified body obtained in Example 1 after solution treatment. Figure 13 It is known that the steel used in the container for the high-level radioactive waste vitrified body of the present invention has a single-phase austenitic structure with a grain size of 7-8. The grains are fine and the structure is uniform, with a large number of elongated black precipitates and a small number of twins.

[0103] The inventors conducted extensive experimental research during the research process, and some poorly performing solutions are now presented as comparative examples.

[0104] Comparative Example 1 This comparative example provides a steel whose composition is shown in Table 1. The solution treatment is the same as that in Example 1, and will not be repeated here.

[0105] Comparative Example 2 This comparative example provides another steel, the composition of which is shown in Table 1. The solution treatment is the same as that in Example 1, and will not be repeated here.

[0106] Comparative Example 3 This comparative example provides another steel with the same composition as Example 1, except that it is not subjected to solution treatment.

[0107] The main performance test results of the comparative steel are shown in Table 3-6.

[0108] As can be seen from the performance test results of Examples 1-4 and Comparative Examples 1-2 in Tables 3-6, when the chemical composition does not contain Mo and Nb (Comparative Example 1), the thermal tensile properties, high-temperature tensile properties, room temperature impact properties, and room temperature impact properties after thermal cycling of the steel are all lower than those of the steel containing Mo and Nb of the present invention.

[0109] When the chemical composition does not contain Mo, Nb, and N (Comparative Example 2), the room temperature tensile properties, high temperature tensile properties, room temperature impact properties, and room temperature impact properties after thermal cycling of the steel are all lower than those of the steel containing Mo and Nb of this invention.

[0110] As can be seen from the performance test results of Examples 1-4 and Comparative Example 3 in Tables 3-6, the steel without solution treatment has lower room temperature tensile properties, high temperature tensile properties, room temperature impact properties, and room temperature impact properties after thermal cycling than the steel of the present invention that has undergone solution treatment.

[0111] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for molding a container for high-level radioactive waste vitrified body, characterized in that, include: Step 1: Prepare raw materials: Form steel into plates and pipes; The steel composition, by mass percentage, includes: C 0.02%-0.05%, Si 1.0%-1.75%, Mn 1.25%-1.75%, Cr 23.0%-25.0%, Ni 13.0%-15.0%, Mo 0.75%-1.0%, N 0.2%-0.25%, Nb 0.15%-0.25%, S≤0.01%, P≤0.012%, with the balance being Fe and unavoidable impurities; Step 2: Component forming: The formed sheet metal is formed into the top end cap and bottom end cap, and the pipe is formed into the cylinder; Step 3: Heat treatment: The formed upper head, cylinder and bottom are subjected to solution treatment; The solution treatment includes: heating, holding, and cooling the upper end cap, cylinder, and bottom end cap; the heating temperature is 1000-1150℃, and the holding time is 20-50 minutes; Step 4: Assembly welding: The top head, cylinder and bottom end after solution treatment are sequentially welded circumferentially to obtain a container for high-level radioactive waste vitrified body; The welding parameters used are: welding current 140-220A, arc voltage 12-14V, wire feed speed 900-1200mm / min, welding speed 80-110mm / min, current polarity DCSP, and arc protection using 99.99% high-purity argon gas.

2. The molding method according to claim 1, characterized in that, In step 1, the sheet material is rolled.

3. The molding method according to claim 1, characterized in that, In step 1, the pipe is formed by extrusion or die forging.

4. The molding method according to claim 1, characterized in that, In step 2, the upper end cap is formed using the first mold assembly.

5. The molding method according to claim 1, characterized in that, In step 2, the cylinder is formed using the second mold assembly.

6. The molding method according to claim 1, characterized in that, In step 2, the bottom is formed using the third mold assembly.

7. The molding method according to claim 1, characterized in that, The bottom seal is formed using a spinning process.

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