Preparation method of nuclear-grade hafnium plate and nuclear-grade hafnium plate

Abstract

The application provides a nuclear-grade hafnium plate preparation method and a nuclear-grade hafnium plate, and belongs to the technical field of nuclear fission reactor control rod neutron absorber material processing, and comprises the following steps: using nuclear-grade sponge hafnium as a raw material, controlling the oxygen content of hafnium ingot in a specific range through a smelting process, so that a more obvious strengthening effect is achieved, and the strength of the finished hafnium plate can meet the nuclear-grade requirement. At the same time, the deformation resistance of the material is increased, so that the optimization combination of the parameters of the following processes, i.e., forging, hot rolling, annealing, one-pass cold rolling-intermediate annealing-two-pass cold rolling and finished product heat treatment, not only solves the problem of difficult processing of the high-strength hafnium plate, but also prepares the nuclear-grade hafnium plate with all performances meeting the technical requirements, improves the tensile strength and welding strength of the hafnium plate, the process is stable, and the yield of finished products reaches more than 95%.

Description

Technical Field

[0001] This application belongs to the field of nuclear-grade hafnium plate processing technology for neutron absorber materials in control rods of nuclear fission reactors, specifically relating to a method for preparing nuclear-grade hafnium plates and nuclear-grade hafnium plates. Background Technology

[0002] Hafnium has a large thermal neutron absorption cross-section, and its fission reaction produces hafnium as a byproduct without generating secondary gamma rays. It is a safe and effective long-lived neutron absorbing material, used in the control rod neutron absorbers of nuclear reactors. Nuclear-grade hafnium plates are typically made from crystalline hafnium, but the manufacturing process for crystalline hafnium is complex and costly, resulting in expensive nuclear-grade hafnium plates. To reduce production costs, a technology has been developed that uses sponge hafnium as a raw material to prepare hafnium plates.

[0003] For example, patent CN117646154A discloses a method for improving the microstructure and properties of hafnium plates. This method uses sponge hafnium raw materials and prepares hafnium plates through melting, forging, hot rolling, annealing, a single cold rolling process, and final heat treatment. The key advantage is the absence of tempering during hot rolling to prevent grain growth and thus improve the microstructure strength of the hafnium plates. Matching the heat treatment process and parameters with the plate dimensions prevents a decrease in the mechanical strength and microstructure uniformity of the finished plate. However, there is still room for improvement in the final performance of the finished plate. Although a single cold rolling process with "multi-pass, small deformation" has produced qualified finished plates, if the oxygen content in the hafnium material fluctuates significantly during production, the forming performance of the hafnium plates prepared by this technology is unstable and the yield is low. Therefore, further improvements to the hafnium plate preparation process are needed to enhance performance and process stability. Summary of the Invention

[0004] To address the problems of unstable performance, low yield, and inability to meet the requirements of nuclear-grade hafnium plates in existing technologies, this application provides a method for preparing nuclear-grade hafnium plates and nuclear-grade hafnium plates. Using nuclear-grade sponge hafnium as raw material, the oxygen content of the hafnium ingot is controlled within a specific range through a smelting process, achieving a more significant strengthening effect and ensuring the strength of the finished hafnium plate meets nuclear-grade requirements. However, this also increases the material's deformation resistance, making it more difficult to process into plates of the target size. This application further optimizes the combination of parameters for forging upsetting, hot rolling (with one intermediate tempering), annealing, one-pass cold rolling-intermediate annealing-two-pass cold rolling, and finished product heat treatment. This not only solves the problem of difficult processing of high-strength hafnium plates but also produces nuclear-grade hafnium plates with properties meeting design requirements, improving the tensile strength and weld strength of the hafnium material, with stable processing and a yield exceeding 95%. The specific technical solution is as follows: Smelting nuclear-grade sponge hafnium to produce hafnium ingots; Forging hafnium ingots to produce hafnium slabs; Hot-rolled hafnium slab is annealed to produce hot-rolled slab. Multi-pass cold-rolled and hot-rolled slabs are subjected to intermediate annealing to produce cold-rolled hafnium sheets; The cold-rolled hafnium sheet undergoes finished product annealing treatment; Refining hafnium sheets into finished hafnium sheets.

[0005] In one feasible implementation, nuclear-grade sponge hafnium is smelted three times using a vacuum electron beam melting furnace to produce hafnium ingots.

[0006] In one feasible implementation, the oxygen content of the hafnium ingot is 100ppm to 400ppm.

[0007] In one feasible implementation, the step of forging hafnium ingots to produce hafnium slabs includes: The hafnium ingot is heated to 1100℃~1200℃ and held for 60min~120min; First, the hafnium ingot is roughed up, then the roughed hafnium ingot is drawn out and lengthened. Then the hafnium ingot is forged into a slab. During the forging process, it is selectively reheated in the furnace. The reheating temperature is 1100℃~1200℃, the reheating time is 20min~60min, and the final forging temperature is ≥750℃. The forged slab is air-cooled to room temperature; Remove the oxide layer from the surface of the forged slab and grind the defective areas to produce a hafnium slab.

[0008] In one feasible implementation, a hot-rolled hafnium slab is annealed to produce a hot-rolled slab, the steps of which include: Heat the hafnium slab to 800℃~850℃ and hold for 60min~120min; After the hafnium slab is hot-rolled to a certain thickness after being taken out of the furnace, it is returned to the furnace and heated to 800℃~850℃, and held for 20min~60min. The hafnium slab is then hot-rolled again to a thickness of 10mm~12mm, and the cumulative deformation during hot rolling is controlled to be 75%~85%. Remove the oxide layer from the surface of the hot-rolled slab and grind the defective areas. Vacuum annealing is performed to produce hot-rolled slabs.

[0009] In one feasible implementation, the cold-rolled sheet is subjected to intermediate annealing between two adjacent cold rolling passes.

[0010] In one feasible implementation, the cold-rolled sheet is subjected to intermediate annealing between two adjacent cold rolling passes, the steps of which include: The first cold rolling pass is performed, and the deformation amount of the first cold rolling pass is controlled at 20%~29%; Intermediate vacuum annealing is performed at a temperature of 740℃~810℃ for 60min~120min. A second cold rolling process is performed, with the deformation amount controlled at 25%~35%, to produce cold-rolled hafnium sheets.

[0011] In one feasible implementation, the step of performing finished product annealing on cold-rolled hafnium sheet includes: Install the cold-rolled hafnium sheet onto the leveling device; The leveling device and the cold-rolled hafnium sheet were placed together in a vacuum heat treatment furnace and subjected to a temperature of 720℃~800℃ and a temperature of 5×10⁻⁶. - 3 Annealing was performed under a vacuum of Pa for 60-120 minutes.

[0012] In one feasible implementation, the steps of finishing hafnium plates to produce finished hafnium plates include: Grind and polish hafnium plates to remove 0.2mm~0.5mm from one side; Remove scratches and defects from hafnium plates to obtain finished hafnium plates with a bright and scratch-free surface.

[0013] According to a second aspect of the embodiments of this application, a nuclear-grade hafnium plate is provided, which is prepared by the nuclear-grade hafnium plate preparation method of any of the above technical solutions.

[0014] The method for preparing nuclear-grade hafnium plate and the nuclear electrode hafnium plate disclosed in this application have the following advantages compared with the prior art: The method for preparing nuclear-grade hafnium plates provided in this application employs a forging-hot rolling-cold rolling-intermediate annealing-cold rolling-finished annealing process to prepare sponge hafnium into nuclear-grade hafnium plates. Intermediate annealing during the cold rolling process eliminates work hardening caused by cold rolling, prevents cold rolling cracking, improves process stability, and ensures crack-free multi-pass cold rolling, thus solving the manufacturing and processing challenges of high-strength hafnium plates. Furthermore, optimized matching of cold rolling deformation and annealing process parameters results in a uniform microstructure and reasonable texture in the hafnium plate, improving the creep resistance of the finished hafnium plate. The improved weldability and high-temperature performance of the hafnium plate result in higher room / high-temperature strength and elongation, ensuring that its properties meet the design requirements for nuclear electrode hafnium plates. By using nuclear electrode sponge hafnium as the raw material for hafnium plate preparation and redesigning and optimizing the process steps, high-strength hafnium plates that meet nuclear electrode requirements are produced, and the overall performance of the hafnium plate is significantly improved. In other words, this application further enhances the strength and overall performance of the hafnium plate, improves the stability of the hafnium plate preparation process, and achieves a high yield. Attached Figure Description

[0015] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 A schematic flowchart illustrating the steps of a method for preparing nuclear-grade hafnium plate according to an embodiment of this application; Figure 2 A schematic flowchart illustrating the forging process of a method for preparing nuclear-grade hafnium plate according to an embodiment of this application; Figure 3 A schematic flowchart illustrating the steps of a multi-pass hot rolling process for preparing nuclear-grade hafnium plate according to an embodiment of this application; Figure 4 A schematic flowchart illustrating the steps of a multi-pass cold rolling process for preparing nuclear-grade hafnium plate according to an embodiment of this application; Figure 5 A schematic flowchart illustrating the steps of a cold-rolling followed by annealing process in a method for preparing nuclear-grade hafnium plate according to an embodiment of this application; Figure 6 This is a schematic flowchart illustrating the finishing process of a method for preparing nuclear-grade hafnium plate according to an embodiment of this application. Detailed Implementation

[0016] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0017] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0018] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0019] The preferred embodiments of this application are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit this application.

[0020] like Figure 1 As shown, according to a first aspect of the embodiments of this application, a method for preparing nuclear-grade hafnium plate is proposed, comprising: Step 100: Melt nuclear-grade sponge hafnium to make hafnium ingots; using nuclear-grade sponge hafnium as the raw material for preparing nuclear-grade hafnium plates can reduce production costs, improve the economics of hafnium plate manufacturing, and make the prepared hafnium plates meet nuclear requirements; Step 200: Forging hafnium ingots to produce hafnium slabs; by forging the ingots into slabs, the plasticity and toughness of the hafnium ingots are improved, and the mechanical properties are enhanced. Step 300: Multi-pass hot rolling of hafnium slab, annealing the hafnium slab to produce hot-rolled slab; by reheating in the furnace at least once during the hot rolling process, the performance of the hot-rolled slab after hot rolling is ensured, the grains are broken, and rolling cracking is avoided; Step 400: Multi-pass cold-rolled hot-rolled slabs are subjected to intermediate annealing to produce cold-rolled hafnium sheets. By performing at least one intermediate annealing during the cold rolling process, work hardening is eliminated to ensure cold rolling formability. On the other hand, the intermediate annealing process is used to regulate the microstructure, making it more uniform and improving the overall performance. Step 500: Perform finished product annealing treatment on cold-rolled hafnium sheet; through annealing treatment after cold rolling, the residual stress generated during cold rolling is eliminated, and a uniform recovery and recrystallization structure is obtained, so that the cold-rolled hafnium sheet has better mechanical properties and processing properties; Step 600: Refine the hafnium plates to produce finished hafnium plates; through fine processing, the hafnium plates meet the standards for nuclear-grade hafnium plates.

[0021] The method for preparing nuclear-grade hafnium plates provided in this application employs a forging-hot rolling-cold rolling-intermediate annealing-cold rolling-finished annealing process to prepare sponge hafnium into nuclear-grade hafnium plates. By performing intermediate annealing during the cold rolling process, work hardening caused by cold rolling is eliminated, cold rolling cracking is prevented, process stability is improved, and multi-pass cold rolling without cracking is guaranteed. This solves the manufacturing and processing challenges of high-strength hafnium plates. Furthermore, by optimizing the matching of cold rolling deformation and annealing process parameters, the microstructure of the hafnium plate is made uniform and the texture is reasonable, improving the creep resistance of the finished hafnium plate. The improved performance and weldability of the hafnium plate give it higher room / high temperature strength and elongation, ensuring that its properties meet the design requirements of the nuclear electrode. By using nuclear electrode sponge hafnium as the raw material for hafnium plate preparation and redesigning and optimizing the process steps, a high-strength hafnium plate that meets the requirements of the nuclear electrode is produced, and the overall performance of the hafnium plate is significantly improved. In other words, this application further improves the strength of the hafnium plate, enhances its overall performance, improves the stability of the hafnium plate preparation process, and achieves a high yield.

[0022] In one feasible implementation, the nuclear electrode sponge hafnium is smelted three times using a vacuum electron beam melting furnace to produce hafnium ingots.

[0023] In this technical solution, vacuum electron beam melting is carried out in a high-vacuum environment, which can effectively remove gaseous elements, non-metallic inclusions, and metallic impurities from the sponge hafnium, ensuring the purity of the hafnium ingot. Through multiple meltings of the sponge hafnium, the sponge hafnium can be further purified, effectively reducing the oxygen content in the hafnium ingot. The small amount of oxygen element forms a non-metallic interstitial solid solution, which significantly improves the strength of the hafnium ingot, so that the strength of the final hafnium plate can meet the requirements of the nuclear electrode design. On the other hand, multiple meltings of sponge hafnium can also effectively control the content of interstitial impurity elements such as carbon, nitrogen, and hydrogen, thereby reducing the hardness of the hafnium ingot and reducing defects such as porosity, looseness, and shrinkage cavities, preparing for subsequent forging and rolling processes.

[0024] In one feasible implementation, the oxygen content of the hafnium ingot is 100ppm to 400ppm.

[0025] In this technical solution, the oxygen content of the hafnium ingot prepared from nuclear-grade sponge hafnium is controlled between 100ppm and 400ppm through three vacuum electron beam melting processes. A small amount of oxygen forms an interstitial solid solution in the hafnium ingot, which strengthens the ingot and consequently increases the strength of the finished hafnium plate. Furthermore, the hafnium lattice is distorted, inhibiting atomic dislocation movement and improving the tensile strength and corrosion resistance of the ingot. This ensures that the final hafnium plate meets the technical requirements for nuclear-grade hafnium plates in terms of tensile strength and corrosion resistance. Multiple vacuum electron beam melting processes control the oxygen content in the hafnium ingot, preventing brittleness caused by excessive oxygen levels and preventing cracking and brittle fracture of the slab during subsequent rolling.

[0026] Furthermore, by removing impurities from nuclear-grade sponge hafnium through three vacuum electron beam melting processes, other impurity elements in the hafnium ingot can also meet the technical requirements of nuclear-grade hafnium plates.

[0027] It should be noted that the oxygen content of nuclear-grade hafnium plates prepared using nuclear-grade sponge hafnium is significantly higher than that of hafnium plates prepared using crystal bar hafnium but lower than that of hafnium plates after grain refinement. This results in a significant interstitial solid solution strengthening effect of oxygen elements, which significantly improves the strength and recrystallization temperature of the hafnium plates. However, due to the increased strength of the hafnium plates, their resistance to processing deformation also increases significantly, making it difficult to process them into plates of the target size. Based on the significant increase in the strength and processing deformation resistance of the hafnium ingot, this application further improves the tensile strength and weld strength of the hafnium material by optimizing the combination of processing deformation and heat treatment parameters such as processing temperature, deformation amount, and annealing temperature. This reduces cracking during the subsequent preparation of hafnium plates, improves the tensile strength, weld strength, and creep performance of the hafnium plates, and achieves a yield of over 95% of hafnium plates that meet the design technical requirements, with significantly improved process stability.

[0028] like Figure 2 As shown, in one feasible embodiment, the step of forging hafnium ingots to form hafnium slabs includes: Step 210: Heat preservation of hafnium ingots; by heat preservation of ingots after melting, the metal plasticity of hafnium ingots is improved and the deformation resistance is reduced, thereby improving the forming ability of hafnium ingots in the forging process and reducing the forging difficulty of hafnium ingots. Step 220: First, rough the hafnium ingot, then draw the rough-upset hafnium ingot, and then forge the hafnium ingot into a slab. By first roughing the hafnium ingot, then drawing it, and then forging it to the required thickness, the microstructure is improved, the uniformity of the hafnium ingot is increased, the anisotropy of the mechanical properties of the slab is reduced, and the mechanical properties of the slab are improved. This prevents the high-strength slab from cracking during subsequent rolling, which is beneficial to improving the yield of nuclear-grade hafnium plates. Step 230: Air cool the forged slab to room temperature; forging improves the plasticity and toughness of the hafnium ingot, air cooling reduces forging stress, improves the comprehensive mechanical properties of the slab, avoids forging cracks caused by low temperature, and improves process stability. Step 240: Remove the oxide layer from the surface of the forged slab and grind the defective areas to form a hafnium slab; by performing surface treatment on the forged part to remove the oxide layer generated during forging, the surface quality of the forged slab is ensured, a clean surface is obtained, and surface defects are prevented from expanding in subsequent processing or affecting the performance of the final product.

[0029] In this technical solution, before multi-pass hot rolling, the hafnium ingot is forged into a plate shape and then air-cooled at room temperature to remove surface defects. The size and uniformity of the grains are controlled by plastic deformation during the forging process, thereby increasing the final hardness and strength of the plate, while improving plasticity and toughness. This makes the plate easier to hot-roll and form without cracking, which is beneficial to improving the yield of subsequent nuclear-grade hafnium plates. Forging before hot rolling can eliminate defects such as pores and inclusions inside the plate, further improving the mechanical properties of the plate, increasing its fatigue strength and service life, and ensuring that the final hafnium plate product meets the technical requirements of nuclear-grade hafnium plates.

[0030] As a preferred method, the ingot is first held at 1100℃~1200℃ for 60min~120min before being forged. During forging, the ingot is first uplifted to 2 / 3 of its original height, then elongated, and finally forged into a slab with a thickness of 50mm~60mm. The final forging temperature is controlled to be greater than or equal to 750℃, and the forging ratio is controlled to be 2~4. After forging, the slab is air-cooled to room temperature. Finally, the oxide layer on the surface of the forged slab is removed by machining, and defective areas are ground.

[0031] Furthermore, during the forging process, if the hardness of the ingot increases or the plasticity decreases, it can be reheated in the furnace to restore the plasticity of the material, facilitating the smooth progress of subsequent final forging.

[0032] In some examples, during the forging process, intermediate reheating to 1100°C~1200°C is permitted, with a holding time of 20min~60min.

[0033] like Figure 3 As shown, in one feasible embodiment, a hot-rolled hafnium slab is annealed to produce a hot-rolled slab, the steps of which include: Step 310: Heat the hafnium slab to 800℃~850℃ and hold for 60min~120min; Step 320: After the hafnium slab is hot-rolled to a certain thickness after being taken out of the furnace, it is returned to the furnace and heated to 800℃~850℃, and held for 20min~60min; Step 330: The hafnium slab is hot-rolled again to a thickness of 10mm~12mm, and the cumulative deformation during hot rolling is controlled to be 75~85%; Step 340: Remove the oxide layer from the surface of the hot-rolled slab and grind the defective areas; Step 350: Perform vacuum annealing to produce hot-rolled slabs.

[0034] In this technical solution, the solution-strengthened hafnium slab has a high work hardening rate and is prone to cracking. The hafnium slab is hot-rolled in two passes. After the first pass, it is reheated in the furnace. After the second pass, it is annealed. Each pass is heat-preserved before hot rolling to ensure hot rolling formability and ensure that the high-strength slab can be deformed smoothly. By controlling the cumulative deformation during hot rolling to 75%~85%, rolling cracking is avoided, and the yield of nuclear-grade hafnium plates is improved. The grains are broken by hot rolling with large deformation, making the microstructure of the hot-rolled slab more uniform. The oxide layer generated by hot rolling is removed and surface defects are eliminated before annealing treatment, which forms a clean and bright surface while homogenizing the internal microstructure, thus improving the surface finish of the hot-rolled slab.

[0035] It should be noted that the control of hot rolling temperature and holding time is a key factor affecting grain size. If the hot rolling temperature and holding time are not set properly, the design of hot rolling temperature and holding time in this application in conjunction with the large deformation of hot rolling is intended to break the grains through hot rolling with large deformation, thereby preventing rolling cracks, rather than to prevent grain growth.

[0036] In one feasible implementation, the cold-rolled sheet is subjected to intermediate annealing between two adjacent cold rolling passes.

[0037] In this technical solution, intermediate annealing is performed between two cold rolling passes. On the one hand, this is to eliminate work hardening, which is beneficial for the next cold rolling and ensures the cold rolling forming performance. On the other hand, it is to regulate the microstructure and further improve the uniformity of the microstructure, thereby improving the overall performance of the cold-rolled hafnium plate and making the finished hafnium plate meet the core electrode design requirements.

[0038] like Figure 4 As shown, in one feasible embodiment, the step of performing intermediate annealing on the cold-rolled sheet between two adjacent cold rolling passes to produce cold-rolled hafnium sheet includes: Step 410: Perform the first cold rolling pass, controlling the deformation amount of the first cold rolling pass to be 20%~29%; Step 420: Perform intermediate vacuum annealing at a temperature of 740℃~810℃ for 60min~120min; Step 430: Perform a second cold rolling pass, controlling the deformation amount of the second cold rolling pass to be 25%~35%, to produce cold-rolled hafnium sheet.

[0039] In this technical solution, hot-rolled hafnium sheet is cold-rolled in two passes, with an intermediate annealing performed between the two cold rolling passes. Since the sheet has high strength and cold work hardening after solid solution strengthening with oxygen, the cold rolling deformation amounts in the two passes are controlled at 20%~29% and 25%~35% respectively, and an intermediate annealing treatment is performed to avoid the situation where the slab does not move during cold rolling, ensuring smooth deformation of the slab, avoiding cold rolling cracks, and improving process stability and yield.

[0040] It should be noted that, based on the significant improvement in the strength of hafnium ingots, by redesigning the manufacturing process and adjusting the hot rolling temperature, hot rolling deformation, cold rolling passes, cold rolling deformation, and subsequent heat treatment temperature, it is possible to effectively reduce cracking or unrollable deformation during the subsequent processing of hafnium plates, thereby improving the yield of the final nuclear electrode hafnium plates.

[0041] like Figure 5 As shown, in one feasible embodiment, the step of performing finished product annealing on cold-rolled hafnium sheet includes: Step 510: Install the cold-rolled hafnium sheet onto the leveling device; Step 520: Place the leveling device and the cold-rolled hafnium sheet together into a vacuum heat treatment furnace, and heat at a temperature of 720℃~800℃ for 5×10 -3 Annealing was performed under a vacuum of Pa for 60-120 minutes.

[0042] In this technical solution, the cold-rolled hafnium sheet is further subjected to finished product annealing. The cold-rolled hafnium sheet is clamped by a leveling device and annealed to eliminate the stress and work hardening generated by cold rolling. This releases the stress within the hafnium sheet, and the hafnium sheet becomes flat under the pressure of the leveling device, obtaining a uniform recovery and recrystallization structure. This restores the sheet's plasticity and toughness, adjusts the grain structure and mechanical properties of the sheet, and makes the sheet surface flat and smooth, improving the surface quality and corrosion resistance of the sheet to meet the application requirements of nuclear electrode hafnium sheet.

[0043] like Figure 6 As shown, in one feasible implementation, the steps of finishing hafnium plates to produce finished hafnium plates include: Step 610: Grind and polish the hafnium plate to remove 0.2mm~0.5mm on one side; Step 620: Remove scratches and defects from the hafnium plate to obtain a finished hafnium plate with a bright surface and no scratches.

[0044] In this technical solution, after multiple cold rolling passes, the hafnium sheet is finished to ensure the standardization of the hafnium sheet, which facilitates subsequent uniform processing and forming.

[0045] Furthermore, before surface polishing, the hafnium plate needs to be leveled to ensure the flatness of the hafnium plate surface after polishing.

[0046] Furthermore, the final hafnium plates must undergo ultrasonic flaw detection and performance testing before they can be used to manufacture nuclear equipment such as neutron absorbers for control rod assemblies.

[0047] Example 1 Step 100': Ingot Preparation Nuclear-grade sponge hafnium was used as raw material, and hafnium was smelted three times in a vacuum electron beam melting furnace to produce finished nuclear-grade hafnium ingots. All impurity elements met the technical requirements, and the oxygen content was controlled at 260 ppm.

[0048] Step 200': Forging The hafnium ingot is heated to 1150℃ and held at that temperature for 90 minutes before being removed from the furnace. A 3t forging hammer is used to uplift and draw the ingot to form a slab with dimensions of approximately δ (thickness) 52mm × W (width) 200mm × L (length) (thickness 52mm, width 200mm, any length). The slab is reheated once during the forging process, with the reheating temperature controlled at 1150℃ and held at that temperature for 30 minutes. Then, the slab is forged at a temperature greater than or equal to 750℃. After the slab cools, the surface of the slab is ground to remove the oxide scale.

[0049] Step 300': Hot rolling and annealing The forged slab was heated to 820℃ in an electric resistance furnace and held for 90 minutes. It was then transferred to a 1300t four-roll hot rolling mill for hot rolling. Each pass underwent repeated hot rolling to a diameter of 18mm × W200mm × L. The slab was then reheated to 820℃ and held for 40 minutes. After exiting the furnace, it underwent another round of repeated hot rolling to a diameter of 10.4mm × W200mm × L, with the cumulative deformation controlled at 80%. The surface of the hot-rolled hafnium plate was then ground to remove the oxide scale, heated to 790℃, held for 120 minutes, and then vacuum annealed.

[0050] Step 400': Cold rolling and intermediate annealing After annealing, hot-rolled hafnium sheets undergo two cold rolling passes. The first pass involves repeated cold rolling to a thickness of δ7.4mm × W200mm × L, with the cumulative deformation controlled at 29%. The surface quality after the first cold rolling pass is good, with no cracking. After degreasing, cleaning, and vacuum annealing at 790℃ for 120 minutes, the finished product undergoes another round of cold rolling to the target thickness. The cumulative deformation in the second cold rolling pass is controlled at 26%, resulting in a finished cold-rolled sheet with good surface quality and no visible cracks or defects.

[0051] Step 500': Finished product annealing After degreasing and cleaning, the finished cold-rolled hafnium sheets are vacuum annealed at 780℃ for 120 minutes. This annealing process yields a uniform equiaxed grain structure. During the annealing process, a special fixture is used to hold the hafnium sheets to ensure their flatness after annealing.

[0052] Step 600': Finishing After annealing, the hafnium sheet undergoes surface polishing and leveling to obtain the finished hafnium sheet. The surface polishing removes approximately 0.25mm from one side, resulting in a bright surface free of scratches and other defects. The final finished hafnium sheet passes ultrasonic testing and performance evaluation.

[0053] Example 2 The difference between this embodiment and Embodiment 1 lies in the oxygen content and process parameters of each step in the preparation of the hafnium ingot in Embodiment 2, as detailed below: Step 100': Ingot Preparation Nuclear-grade sponge hafnium was used as raw material, and hafnium was smelted three times in a vacuum electron beam melting furnace to produce finished nuclear-grade hafnium ingots. All impurity elements met the technical requirements, and the oxygen content was controlled at 290 ppm.

[0054] Step 200': Forging The hafnium ingot is heated to 1200℃ and held for 60 minutes before being removed from the furnace. A 3t forging hammer is used to uplift and draw the ingot into a slab with dimensions of approximately δ60mm×W160mm×L. The slab is reheated once during the forging process, with the reheating temperature controlled at 1200℃ and held for 20 minutes. Then, the slab is forged at a temperature greater than or equal to 750℃. After the slab cools, the surface of the slab is ground to remove the oxide scale.

[0055] Step 300': Hot rolling and annealing The forged slab was heated to 850℃ in an electric resistance furnace and held for 60 minutes. It was then transferred to a 1300t four-roll hot rolling mill for hot rolling. Each pass underwent repeated hot rolling to a diameter of 22mm × W160mm × L. The slab was then reheated to 850℃ and held for 30 minutes. After exiting the furnace, it underwent another round of repeated hot rolling to a diameter of 11mm × W160mm × L, with the cumulative deformation controlled at 82%. The surface of the hot-rolled hafnium plate was then ground to remove the oxide scale, heated to 800℃, held for 60 minutes, and then vacuum annealed.

[0056] Step 400': Cold rolling and intermediate annealing After annealing, hot-rolled hafnium sheets undergo two passes of cold rolling. The first pass involves repeated cold rolling to a thickness of δ 8.05 mm × W 160 mm × L, with the cumulative deformation controlled at 27%. The surface quality after the first pass is good, with no cracking. After degreasing, cleaning, and vacuum annealing at 800℃ for 60 minutes, the finished product undergoes another round of cold rolling to the target thickness. The cumulative deformation in the second cold rolling is controlled at 27%, resulting in a finished cold-rolled sheet with good surface quality and no visible cracks or defects.

[0057] Step 500': Finished product annealing After degreasing and cleaning, the finished cold-rolled hafnium sheets are vacuum annealed at 790℃ for 60 minutes. This annealing process yields a uniform equiaxed grain structure. During the annealing process, a special fixture is used to hold the hafnium sheets to ensure their flatness after annealing.

[0058] Step 600': Finishing After annealing, the hafnium sheet undergoes surface polishing and leveling to obtain the finished hafnium sheet. The surface polishing removes approximately 0.25mm from one side, resulting in a bright surface free of scratches and other defects. The final finished hafnium sheet passes ultrasonic testing and performance evaluation.

[0059] Example 3 The difference between this embodiment and Embodiment 1 lies in the oxygen content and process parameters of each step in the preparation of the hafnium ingot in Embodiment 3, as detailed below: Step 100': Ingot Preparation Nuclear-grade sponge hafnium was used as raw material, and hafnium was smelted three times in a vacuum electron beam melting furnace to prepare finished nuclear-grade hafnium ingots. All impurity elements met the technical requirements, and the oxygen content was controlled at 220 ppm.

[0060] Step 200': Forging The hafnium ingot is heated to 1100℃ and held for 120 minutes before being removed from the furnace. A 3t forging hammer is used to uplift and draw the ingot into a slab with dimensions of approximately δ50mm×W200mm×L. The slab is reheated once during the forging process, with the reheating temperature controlled at 1100℃ and held for 60 minutes. Then, the slab is forged at a temperature greater than or equal to 750℃. After the slab cools, the surface of the slab is ground to remove the oxide scale.

[0061] Step 300': Hot rolling and annealing The forged slab was heated to 800℃ in an electric resistance furnace and held for 120 minutes. It was then transferred to a 1300t four-roll hot rolling mill for hot rolling. Each pass underwent repeated hot rolling to a diameter of 24mm × W200mm × L. The slab was then reheated to 800℃ and held for 60 minutes. After exiting the furnace, it underwent another round of repeated hot rolling to a diameter of 12mm × W160mm × L, with the cumulative deformation controlled at 76%. The surface of the hot-rolled hafnium plate was then ground to remove the oxide scale, heated to 780℃, held for 120 minutes, and then vacuum annealed.

[0062] Step 400': Cold rolling and intermediate annealing After annealing, hot-rolled hafnium sheets undergo two cold rolling passes. The first pass involves repeated cold rolling to a thickness of δ8.5mm × W200mm × L, with the cumulative deformation controlled at 29%. The surface quality after the first cold rolling pass is good, with no cracking. After degreasing, cleaning, and vacuum annealing at 780℃ for 120 minutes, the finished product undergoes another round of cold rolling to the target thickness. The cumulative deformation in the second cold rolling pass is controlled at 35%, resulting in a finished cold-rolled sheet with good surface quality and no visible cracks or defects.

[0063] Step 500': Finished product annealing After degreasing and cleaning, the finished cold-rolled hafnium sheets are vacuum annealed at 760℃ for 120 minutes. This annealing process yields a uniform equiaxed grain structure. During the annealing process, a special fixture is used to hold the hafnium sheets to ensure their flatness after annealing.

[0064] Step 600': Finishing After annealing, the hafnium sheet undergoes surface polishing and leveling to obtain the finished hafnium sheet. The surface polishing removes approximately 0.25mm from one side, resulting in a bright surface free of scratches and other defects. The final finished hafnium sheet passes ultrasonic testing and performance evaluation.

[0065] The finished hafnium plates produced in Example 1 were subjected to room / high temperature tensile property tests, weldability tests, and corrosion performance tests according to the production and use requirements of control rods. All properties met the technical requirements for nuclear electrode hafnium plates. Furthermore, multiple actual production runs showed very few cracking issues in the hafnium plates, with a yield rate as high as approximately 97%.

[0066] Comparative Example 1 Step 1: Ingot Preparation Nuclear-grade sponge hafnium was used as raw material, and hafnium was smelted three times in a vacuum electron beam melting furnace to produce finished nuclear-grade hafnium ingots. All impurity elements met the technical requirements, and the oxygen content was controlled at 340 ppm.

[0067] Step 2: Forging The hafnium ingot is heated to 1150℃ and held for 90 minutes before being removed from the furnace. A 3t forging hammer is used to uplift and draw the ingot to form a slab with a thickness of δ 52mm. The slab is reheated once during the forging process, with the reheating temperature controlled at 1150℃ and held for 30 minutes. Then, the slab is forged at a temperature greater than or equal to 750℃. After the slab cools, the surface of the slab is ground to remove the oxide scale.

[0068] Step 3: Hot rolling and annealing The forged slab was heated to 820℃ in an electric resistance furnace and held for 90 minutes. It was then transferred to a 1300t four-roll hot rolling mill for repeated hot rolling. During the hot rolling process, the slab was reheated and held at 820℃ for 40 minutes. The cumulative deformation during hot rolling was controlled to be within 80%. The surface of the hot-rolled hafnium plate was ground to remove the oxide scale. Vacuum annealing was then performed at 790℃ for 120 minutes.

[0069] Step 4: Cold rolling After annealing the hot-rolled hafnium sheet, it was cold-rolled. After multiple cold rolling passes without intermediate annealing, the cumulative deformation was 36%. After cold rolling, the hafnium sheet cracked from the long side, with the crack length being about 2 / 5 of the total length and the width being about 1 / 3 of the width. It could not be processed or tested further and was scrapped.

[0070] Comparative Example 2 Step 1: Ingot Preparation Nuclear-grade hafnium ingots were prepared by vacuum electron beam melting, with oxygen content controlled to be less than 100 ppm and other impurity elements meeting the technical requirements.

[0071] Step 2: Forging The hafnium ingot is heated to 1100℃, held for 60 minutes, and then forged to a thickness of 55mm. It is then air-cooled to room temperature, and the surface of the forged billet is ground to remove the oxide scale.

[0072] Step 3: Hot rolling and annealing The forged billet is heated to 800℃ and held for 90 minutes. Then, it is transferred to a four-roll hot rolling mill for repeated hot rolling in one pass. The hot rolling process does not involve reheating or holding in the furnace. The cumulative deformation during hot rolling is 85%. The surface of the hot-rolled hafnium plate is ground to remove the oxide scale. Vacuum annealing is then performed at 740℃ for 60 minutes.

[0073] Step 4: Cold rolling After annealing, hot-rolled hafnium plates are cold-rolled through multiple passes without intermediate annealing, resulting in a cumulative deformation of 37%. The surface quality after cold rolling is good, with no visible cracks or defects.

[0074] Step 5: Annealing of finished product After being degreased and cleaned, the finished cold-rolled hafnium sheets are vacuum annealed at 730℃ for 60 minutes.

[0075] Step 6: Finishing After annealing, the finished hafnium plates undergo surface polishing and leveling to obtain finished hafnium plates. The finished hafnium plates have a bright surface and are free of scratches and other defects. The finished hafnium plates are subjected to room / high temperature tensile property tests, weldability tests, and corrosion performance tests according to the production and usage requirements of the control rods. The results are shown in Tables 1-3.

[0076] Comparative Example 3 Step 1: Ingot Preparation Using sponge hafnium as raw material, the product is prepared by two melting processes in a vacuum electron beam melting furnace. The impurity elements all meet the technical requirements, and the oxygen content is not controlled.

[0077] Step 2: Forging The hafnium ingot is heated to 1080℃, held for 90 minutes, and then forged to a thickness of 45mm. It is then reheated once in the furnace at 1080℃ for 40 minutes. After forging, it is air-cooled to room temperature, and the surface of the forged billet is ground to remove the oxide scale.

[0078] Step 3: Hot rolling and annealing The forging billet is heated to 820℃ and held for 60 minutes. Then, it is transferred to a four-roll hot rolling mill for repeated hot rolling in one pass. The hot rolling process does not involve reheating in the furnace. The cumulative deformation during hot rolling is 60%. The surface of the hot-rolled hafnium plate is ground to remove the oxide scale. Vacuum annealing is then performed at 800℃ for 90 minutes.

[0079] Step 4: Cold rolling After annealing, hot-rolled hafnium plates are cold-rolled through multiple passes without intermediate annealing, resulting in a cumulative deformation of 40%. The surface quality after cold rolling is good, with no visible cracks or defects.

[0080] Step 5: Annealing of finished product After being degreased and cleaned, the finished cold-rolled hafnium sheets are vacuum annealed at 680℃ for 240 minutes.

[0081] Step 6: Finishing After annealing, the finished hafnium plates undergo surface polishing and leveling to obtain finished hafnium plates. The finished hafnium plates have a bright surface and are free of scratches and other defects. The finished hafnium plates are subjected to room / high temperature tensile property tests, weldability tests, and corrosion performance tests according to the production and usage requirements of the control rods. The results are shown in Tables 1-3.

[0082] Table 1. Tensile test results of sheet metal at room temperature and high temperature.

[0083] Table 2. Room temperature tensile test results of welds

[0084] Table 3 Corrosion performance test results

[0085] As can be seen from Comparative Example 1, the cumulative deformation of hafnium plates in a single cold rolling process is higher than 30% for the oxygen content range of this technology. Without intermediate annealing, obvious cracking will occur during cold rolling, making it impossible to continue producing finished nuclear electrode hafnium plates that meet the technical requirements.

[0086] The tensile properties of hafnium plates at room temperature and high temperature are shown in Table 1, the room temperature tensile properties of welds are shown in Table 2, and the corrosion properties are shown in Table 3. As can be seen from Table 1, the finished hafnium plates prepared using the nuclear-grade hafnium plate preparation method of this application maintain a tensile strength of approximately 570 MPa in both the transverse and longitudinal directions at room temperature, and approximately 370 MPa at 350°C, showing a significant improvement in strength compared to existing hafnium plates. The yield strength of the hafnium plates at room temperature exceeds 330 MPa in both the transverse and longitudinal directions, with the transverse yield strength approaching 500 MPa; the yield strength at 350°C exceeds 260 MPa. As can be seen from Table 2, the welds of the finished hafnium plates prepared using the nuclear-grade hafnium plate preparation method of this application can achieve a minimum tensile strength of 480 MPa at room temperature, and the yield strength at room temperature can be maintained at approximately 400 MPa, showing a significant improvement in the yield strength of the welds. As shown in Table 3, the corrosion weight gain of the finished hafnium plate prepared by the nuclear-grade hafnium plate preparation method of this application is only 50% of that prepared by existing hafnium plate preparation methods. The corrosion rate is slow, and the corrosion resistance is significantly improved. In addition to the significant improvement in tensile strength and yield strength, other properties of the finished hafnium plate are also improved, and all meet the design requirements for nuclear-grade hafnium plates.

[0087] According to a second aspect of this application, a nuclear-grade hafnium plate is proposed, which is prepared by any of the above-described methods for preparing nuclear-grade hafnium plates.

[0088] The nuclear-grade hafnium plate provided in this application embodiment is prepared by the nuclear-grade hafnium plate preparation method of any of the above technical solutions, and therefore the nuclear-grade hafnium plate has all the beneficial effects of the nuclear-grade hafnium plate preparation method of the above technical solutions.

[0089] The nuclear-grade hafnium plate provided in this application uses a forging-hot rolling-cold rolling-intermediate annealing-cold rolling-finished annealing process to prepare sponge hafnium into nuclear-grade hafnium plate. Intermediate annealing during the cold rolling process eliminates work hardening caused by cold rolling, prevents cold rolling cracking, improves process stability, and ensures crack-free multi-pass cold rolling. This solves the manufacturing and processing problems of high-strength hafnium plate, and also makes the microstructure of the hafnium plate uniform and the texture reasonable, improving the creep performance and weldability of the finished hafnium plate. The material has higher room / high temperature strength and elongation, enabling the various properties of the hafnium plate to meet the design requirements of the nuclear electrode. By using nuclear electrode sponge hafnium as the raw material for preparing hafnium plate and redesigning and optimizing the process steps of hafnium plate preparation, high-strength hafnium plate that meets the requirements of the nuclear electrode is prepared, and the comprehensive performance of hafnium plate is significantly improved. That is, this application further improves the strength of hafnium plate, enhances the comprehensive performance of hafnium plate, improves the stability of hafnium plate preparation process, and achieves high yield.

[0090] It will be readily understood by those skilled in the art that the aforementioned advantageous methods can be freely combined and superimposed without conflict.

[0091] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application. The above are merely preferred embodiments of this application. 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 this application, and these improvements and modifications should also be considered within the protection scope of this application.

Claims

1. A method for preparing nuclear-grade hafnium plate, characterized in that, The method for preparing the nuclear-grade hafnium plate includes: Nuclear-grade sponge hafnium is smelted to produce hafnium ingots; the nuclear-grade sponge hafnium is smelted three times using a vacuum electron beam melting furnace to produce the hafnium ingots; the oxygen content of the hafnium ingots is 100ppm~400ppm; The hafnium ingot is forged to form a hafnium slab. The ingot is first held at 1100℃~1200℃ for 60min~120min before being forged. During forging, the ingot is first uplifted to 2 / 3 of its original height, then drawn out, and finally forged into a slab with a thickness of 50mm~60mm. The final forging temperature is controlled to be greater than or equal to 750℃, and the forging ratio is controlled to be 2~4. After forging, the slab is air-cooled to room temperature. The surface oxide layer of the forged slab is removed, and defective areas are ground to produce the hafnium slab. The hafnium slab is hot-rolled and then annealed to produce a hot-rolled slab. The first cold rolling pass is performed, and the deformation amount of the first cold rolling pass is controlled at 20%~29%; Intermediate vacuum annealing is performed at a temperature of 740℃~810℃ for 60min~120min. A second cold rolling process is performed, with the deformation amount controlled at 25%~35% to produce cold-rolled hafnium sheets; The cold-rolled hafnium sheet is subjected to finished product annealing treatment; Refining hafnium sheets into finished hafnium sheets.

2. The method for preparing nuclear-grade hafnium plate according to claim 1, characterized in that, The step of forging the hafnium ingot to produce a hafnium slab includes: The hafnium ingot is heated to 1100℃~1200℃ and held for 60min~120min; First, the hafnium ingot is roughened, then the roughened hafnium ingot is drawn out, and then the hafnium ingot is forged into a slab. During the forging process, it is selectively reheated in the furnace. The reheating temperature is 1100℃~1200℃, the reheating time is 20min~60min, and the final forging temperature is ≥750℃. The forged slab is air-cooled to room temperature; The oxide layer on the surface of the forged slab is removed, and the defective areas are ground to produce the hafnium slab.

3. The method for preparing nuclear-grade hafnium plate according to claim 1, characterized in that, The hot-rolled hafnium slab is annealed to produce a hot-rolled slab, the steps of which include: The hafnium slab is heated to 800℃~850℃ and held at that temperature for 60min~120min; After the hafnium slab is hot-rolled to a certain thickness after being taken out of the furnace, it is reheated in the furnace to 800℃~850℃ and held for 20min~60min; The hafnium slab is then hot-rolled again to a thickness of 10mm~12mm, and the cumulative deformation during hot rolling is controlled to be 75%~85%. Remove the oxide layer from the surface of the hot-rolled slab and grind the defective areas. Vacuum annealing is performed to produce the hot-rolled slab.

4. The method for preparing nuclear-grade hafnium plate according to claim 1, characterized in that, The step of performing finished product annealing on the cold-rolled hafnium sheet includes: The cold-rolled hafnium sheet is mounted onto the leveling device; The leveling device and the cold-rolled hafnium sheet are placed together in a vacuum heat treatment furnace and subjected to a temperature of 720℃~800℃ and a temperature of 5×10⁻⁶. -3 Annealing was performed under a vacuum of Pa for 60-120 minutes.

5. The method for preparing nuclear-grade hafnium plate according to claim 1, characterized in that, The steps for preparing the refined hafnium sheet into finished hafnium sheet include: The hafnium plate is ground and polished to remove 0.2mm to 0.5mm from one side. Remove scratches and defects from the hafnium plate to obtain a finished hafnium plate with a bright and scratch-free surface.

6. A nuclear-grade hafnium plate, characterized in that, The nuclear-grade hafnium plate is prepared by the method for preparing nuclear-grade hafnium plate according to any one of claims 1 to 5.

Images