Integrated forging forming method for pump shell of nuclear power main pump

Abstract

The invention relates to the technical field of nuclear power equipment manufacturing, in particular to a nuclear power main pump shell integrated forging forming method which comprises the following steps that a blank is heated and subjected to heat preservation treatment; the heated blank is subjected to preforming forging, and a cylindrical blank with a boss on one side is formed through forging; punching and chambering the cylindrical blank to form a boss cylindrical blank; a step core rod is inserted into the inner hole of the boss cylindrical blank, radial spinning is conducted on the blank on one side of the small opening end of the step core rod, and a small-end-opening forge piece is formed; and punching and chambering the boss of the small-port forge piece to form the forge piece which is in near-net forming with the pump shell. According to the integrated forging forming method for the pump shell of the nuclear power main pump, near-net forming of multiple ports and internal flow channels can be achieved, continuity of metal flow lines is guaranteed, the material utilization rate is increased, machining procedures are reduced, and therefore the production period is shortened, and the production cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear power equipment manufacturing, and in particular to a nuclear power main pump shell integrated forging forming method. BACKGROUND

[0002] The nuclear reactor main pump (referred to as "nuclear main pump") as the core equipment of the nuclear island primary system of a nuclear power plant undertakes the key task of transporting high-temperature and high-pressure coolant, and its performance is directly related to the safe operation of the entire nuclear power plant. As the core pressure-bearing component of the main pump, the pump shell needs to meet multiple stringent performance requirements: it must be able to withstand high pressure, high temperature, corrosive medium and long-term vibration load; it needs to have excellent high-temperature creep resistance, corrosion resistance (especially resistance to boric acid solution) and radiation damage resistance; and in terms of structural design, it also needs to take into account complex flow channel design and stress distribution optimization to ensure good fluid mechanics performance and avoid cracks caused by stress concentration.

[0003] The traditional pump shell manufacturing process faces many technical bottlenecks. Due to the complex structural characteristics of the pump shell, which is "hollow thick wall + multiple openings", it is difficult to achieve near-net forming in free forging. Although the existing technology proposes a scheme of using a near-net forming die, this process is only suitable for small forgings. For medium and large shell forgings, due to size constraints, near-net forming dies are difficult to apply in actual production. Currently, the manufacturing of medium and large pump shells still generally uses the process route of first forging into an approximate cylinder and then forming through a large amount of mechanical machining. This method has significant technical defects.

[0004] In terms of material performance, during integral forging, it is difficult to ensure the continuity and uniformity of the metal flow lines due to the large difference in cross-sectional dimensions of the forgings. The thick-walled area often has coarse grains due to insufficient forging ratio, making it difficult to meet the mechanical performance (including strength and toughness) standards; while the thin-walled area is prone to work hardening or micro-cracks due to excessive deformation. In the subsequent mechanical machining process, a large amount of material needs to be cut to form complex internal cavities and multiple opening structures, which not only destroys the original metal flow line continuity, but also forms stress concentration points on the machined surface, seriously affecting the fatigue life and safety of the pump shell under high pressure and vibration conditions.

[0005] From the perspective of economy, the material utilization rate of the traditional manufacturing process is extremely low, usually requiring the removal of 60% to 80% of the original material, resulting in a serious waste of high-value alloy materials. At the same time, the multi-process machining leads to long production cycles, high energy consumption and low efficiency, further increasing the manufacturing cost. In view of the above problems, the existing technology needs to be improved. SUMMARY

[0006] In view of the above-mentioned defects existing in the pump shell forming at present, the application provides a nuclear power main pump shell integrated forging forming method, which can realize near-net forming of multi-port and internal flow channel, ensure the continuity of metal flow line, improve the material utilization rate, reduce the machining process, thereby shortening the production cycle and reducing the production cost.

[0007] To achieve the above-mentioned purpose, the embodiments of the application adopt the following technical solutions: A nuclear power main pump shell integrated forging forming method, comprising the following steps: Heating and heat preservation treatment are performed on the blank; Preforming forging is performed on the heated blank, and a cylindrical blank with a boss on one side is formed by forging; Punching and hole expanding are performed on the cylindrical blank to form a boss cylindrical blank; A stepped mandrel is inserted into the inner hole of the boss cylindrical blank, and the blank on the small end side of the stepped mandrel is radially spun to form a small-port forged piece; Punching and hole expanding are performed on the boss of the small-port forged piece to form a forged piece near-net formed with the pump shell.

[0008] According to one aspect of the application, the preforming forging on the heated blank is to perform upsetting, elongating and upsetting operations on the blank in sequence by using an upper anvil at a certain speed to break the grains in the blank.

[0009] According to one aspect of the application, the certain speed is 2 to 5 mm / s, and the forging ratio of the upsetting, elongating and upsetting is 1.3 to 2.0.

[0010] According to one aspect of the application, after the blank is subjected to the upsetting, elongating and upsetting operations in sequence, elongating and number stamping are performed to form the boss cylindrical blank. According to one aspect of the application, the punching and hole expanding on the cylindrical blank to form the boss cylindrical blank is to punch by using a punch, then set the punch on a mandrel and place it on a jig, and perform radial spinning on the boss cylindrical blank until it meets the preset requirements.

[0011] According to one aspect of the application, the punching and hole expanding on the boss of the small-port forged piece to form the forged piece near-net formed with the pump shell is to punch the side boss by using a punch, then perform radial spinning by using a hole expanding tool until it meets the preset requirements.

[0012] According to one aspect of the application, it further includes trimming the forged piece after the punching and hole expanding on the boss of the small-port forged piece, and the trimming is to insert the stepped mandrel into the inner hole of the small-port forged piece, and form the forged piece near-net formed with the pump shell by pressure processing the outer surface.

[0013] According to one aspect of the present application, the heating of the blank is heating the blank to a temperature of 1100-1220°C at a rate of 50 to 80°C / h.

[0014] According to one aspect of the present application, the blank is made of low-alloy steel or stainless steel ingot.

[0015] According to one aspect of the present application, the weight of the ingot is determined according to the size of the pump shell and the forging ratio, which is > 3.5.

[0016] According to one aspect of the present application, the blank is subjected to a peeling treatment before the heating and soaking treatment.

[0017] The advantages of the embodiment of the present application are as follows: by heating the blank to 1100-1220 DEG C to make it in the metal recrystallization temperature interval, the deformation resistance can be reduced, and overheating or overburning can be avoided; by heating at a heating speed of 50-80 DEG C / h, the thermal stress cracking caused by the large temperature difference between the inside and outside of the blank can be effectively prevented, and the uniform internal temperature is ensured by the heat preservation treatment, thereby providing a uniformity basis for subsequent forging. By means of upsetting, elongating and upsetting, the original coarse grains of the ingot can be broken, the uniform distribution of the forging ratio can eliminate internal porosity and segregation, a dense and uniform forging structure can be formed, and the overall strength and toughness of the blank can be improved. After the stamping, a reference is provided for suppressing the cylinder shape of the boss, the coaxiality error between the boss and the shell is ensured to be small, and the position deviation during subsequent port forming is avoided. By expanding the hole, the metal flows uniformly in the circumferential direction, the continuity of the forging streamline is preserved, the fatigue strength of the cylinder wall is improved compared with the traditional machining cutting streamline, and the cracking under high pressure working condition is avoided. By radial spinning, the metal is plastic flow, the metal deformation amount in the spinning process is controllable, the work hardening phenomenon caused by local excessive deformation is avoided, the uniformity of the hardness distribution in the small port area is ensured, and the anti creep performance of the material is improved. By punching and expanding the boss, a shape close to the shape of the connecting pipe hole is formed, the subsequent machining amount is reduced, the forging streamline is preserved along the flow channel, and the anti-erosion ability is improved. The nuclear reactor pump shell integrated whole forging forming manufacturing method has obvious advantages. In terms of structural integrity, the welding and connection defects caused by traditional split manufacturing splicing are avoided, the welding defects such as pores, cracks and heat affected zone performance hidden dangers are eliminated, a continuous and complete whole is formed, the structural sealing and integrity are greatly enhanced, and the high temperature and high pressure and other harsh working conditions are adapted. In terms of performance improvement, the metal streamline is accurately controlled in the forging process, and is reasonably distributed along the pump shell structure, the strength, toughness, fatigue resistance and anti creep performance are significantly improved compared with the traditional machining cutting streamline; meanwhile, the forging ratio, temperature and other parameters are accurately regulated, the grain structure is refined, and the performance degradation risk under harsh service environment is reduced. In terms of size precision control, the shell and port near net forming is realized by relying on the precise design of the step mandrel and other molds and the accurate control of the forging size, the size cumulative error is reduced, and the size stability and precision are improved. The production efficiency is significantly improved, the multiple processes are integrated, the clamping, transfer and intermediate processing links are reduced, the production cycle is shortened, and the workpiece transfer quality risk is reduced; the near net forming greatly reduces the machining allowance and time, and improves the overall efficiency. The cost control effect is good, the material utilization rate is greatly improved, and the consumption of high value alloy materials is reduced; the production efficiency is improved and the material is saved, the waste product repair cost is reduced, and the comprehensive production cost is reduced in multiple dimensions. In addition, the pump shell manufactured by the method has reliable quality, meets the strict requirements of nuclear safety regulations on pump shell anti radiation and anti corrosion, reduces the operation accident risk, and provides a solid guarantee for the safe and stable operation of the nuclear power station. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only represent some of the embodiments of the present application, and all other drawings obtained by those of ordinary skill in the art without any creative effort based on these drawings also belong to the protection scope of the present application.

[0019] Figure 1 A forming step schematic diagram of the nuclear power main pump shell integrated forging forming method; Figure 2 A boss cylindrical blank structure schematic diagram of the nuclear power main pump shell integrated forging forming method; Figure 3 A cylindrical blank hole expanding schematic diagram in the nuclear power main pump shell integrated forging forming method; Figure 4 A radial spinning schematic diagram in the nuclear power main pump shell integrated forging forming method; Figure 5 A small port punching and hole expanding schematic diagram in the nuclear power main pump shell integrated forging forming method; Figure 6 A nuclear power main pump shell structure size schematic diagram after forming in the embodiment 3 of the present application.

[0020] Marked numbers in the drawings: 1, core rod; 2, mandrel; 3, stepped core rod; 4, punch. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments only represent some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without any creative effort belong to the protection scope of the present application.

[0022] Embodiment one

[0023] As shown in Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 , a nuclear power main pump shell integrated forging forming method, the forming method comprises the following steps: S01: heating and holding treatment to the blank: First, a low-alloy steel or stainless steel ingot that meets nuclear-grade standards is selected. The ingot material is not restricted, but is based on the design requirements of the nuclear power main pump casing. The weight of the ingot is determined by the pump casing size and the required forging ratio, which is generally ≥3.5. The ingot is peeled to remove surface defects and ensure the surface quality of the ingot. The ingot is then heated to 1100-1220°C at a heating rate of 50-80°C / h. The holding time is calculated based on the ingot size, generally 1-2 hours / 100mm, to ensure a uniform internal temperature. Heating and holding treatments are performed to bring the material to a uniform plastic deformation temperature, ensuring that the temperature difference between the core and surface of the ingot is within a reasonable range, providing a uniform microstructure foundation for subsequent forging.

[0024] S02: The heated blank is subjected to pre-forming forging to form a cylindrical blank with a boss on one side: The heated billet is lifted onto the lower anvil of the forging press, and the press is started. The upper anvil is pressed down at a speed of 2 to 5 mm / s, and the billet is subjected to preliminary upsetting, drawing, and upsetting in sequence. The forging ratio of each step is controlled at 1.3 to 2.0, so that the billet can initially break the grains and optimize the structure. Then, after drawing and stamping, it is pressed into a cylindrical billet with a boss to form the approximate shape of the blank for the pump casing. The stamping can mark key positions on the surface of the billet to facilitate pressing and positioning. The upper anvil refers to a forging tool with a flat contact surface. Its planar structure can ensure that the deformation force is evenly distributed on the surface of the billet, avoiding local stress concentration and cracks. By pressing down at a speed of 2 to 5 mm on the upper anvil, the contradiction between dynamic recrystallization and abnormal grain growth can be balanced, which can not only promote grain boundary migration to achieve grain refinement, but also avoid structural coarsening caused by overheating.

[0025] Specifically, during the preforming forging process, the billet is first upset using the upper flat anvil to break the as-cast coarse-grained structure using triaxial compressive stress; this is followed by a drawing operation to form a fibrous structure through axial extension; and finally, upsetting again to eliminate anisotropy through multi-directional compression. This process alternates the stress state, causing the grains to slip and dynamically recrystallize in multiple directions, forming a uniform and fine equiaxed structure. The forging speed is controlled within a specific range, which can not only ensure that the metal fully recrystallizes, but also prevent secondary grain growth at high temperatures. The selection of the forging ratio takes into account both the grain refinement requirements and the plastic limit of the material, avoiding internal defects caused by excessive deformation.

[0026] S03: Punch and expand the cylindrical blank to form a boss cylindrical blank: After the pre-forming forging is completed, a punch is used to punch the cylindrical blank, and then the cylindrical blank is sleeved on the core rod, and the core rod is placed on a horse frame, which is a supporting tool. The hole diameter of the blank is gradually expanded by rotating the blank and applying radial pressure, i.e., radial spinning. In this process, the blank is uniformly subjected to pressure in the circumferential direction, and the metal continuously flows outward, thereby increasing the hole diameter, so that the blank forms a cylindrical blank with a boss under the action of pressure. The radial spinning can be implemented by a hydraulic spinning machine or a wire wheel in cooperation with the core rod. Through radial spinning, the material is uniformly migrated from the thick-walled area to the thin-walled area, and this controlled plastic deformation mode can maintain the continuity distribution of metal fibers.

[0027] S04: Forging one side of the boss cylindrical blank to form a small port forging; A specially designed stepped core rod is inserted into the inner hole of the boss cylindrical blank, and the stepped core rod is designed to match the shape of the inner hole of the blank and to support and guide the metal flow in subsequent processing. During the insertion of the stepped core rod, the coaxiality of the stepped core rod and the inner hole of the blank needs to be ensured to ensure the uniformity of subsequent processing.

[0028] Radial spinning is performed on one side of the small port end of the stepped core rod, and the spinning operation is performed on one side of the small port end (T end) by using a spinning process. During spinning, the blank is rotated at the same time, and a specific spinning tool, such as a spinning wheel, is used to apply radial pressure to the blank to make the metal of the blank flow plastically. Under the action of pressure, the metal of the T end side of the cylinder gradually shrinks inward to achieve the effect of hole shrinking. Radial spinning is generally performed in multiple times, i.e., rough forging is performed first and then fine forging is performed. During the spinning process, the processing parameters such as spinning pressure, rotation speed, rotation angle, and feed amount are strictly controlled. Preferably, the single rotation angle is 30 to 60 degrees, the rough forging feed amount (downward pressure amount) is 50-100mm, and the fine forging feed amount (downward pressure amount) is 20-50mm, until the hole on one side of the cylinder is shrunk to the target outer diameter size. Through real-time monitoring and adjustment, the size accuracy and surface quality are ensured, so that the formed forging meets the design requirements.

[0029] S05: Punching and reaming the boss of the small port forging to form a near-net-shaped forging with the pump shell: A punch is used to punch the boss of the blank to form the initial shape of the side pipe hole. The punch applies concentrated pressure to the blank under the action of the press to make the metal of the blank separate or flow plastically, thereby punching out the side pipe hole. The pressure, stroke, and punching position of the punch need to be accurately controlled to ensure that the position accuracy and initial size of the side pipe hole meet the design requirements.

[0030] After the side nozzle hole punching is completed, the hole is expanded to the design size by the hole expansion process. During the hole expansion process, appropriate hole expansion tools such as hole expansion drills, mandrels, etc. are selected, and the hole wall metal is gradually expanded outward by rotation and the application of radial force, so as to reach the design required hole diameter size.

[0031] The beneficial effects of the embodiment: by heating the blank to 1100-1220℃ to make it in the metal recrystallization temperature interval, the deformation resistance can be reduced, and overheating or overburning can be avoided; the heating speed of 50-80℃ / h can effectively prevent the thermal stress cracking caused by the too large temperature difference between the inside and outside of the blank, and the internal temperature uniformity is ensured by the heat preservation treatment, which provides the basis for the uniformity of the organization for subsequent forging. By upsetting, elongating and upsetting, the original coarse grains of the ingot can be broken, the uniform distribution of the forging ratio can eliminate internal porosity and segregation, form a dense and uniform forging structure, and improve the overall strength and toughness of the blank. After the stamping, a reference is provided for the suppression of the boss cylinder, the coaxiality error between the boss and the shell is ensured to be small, and the position deviation during the subsequent port forming is avoided. By expanding the hole, the metal flows uniformly in the circumferential direction, the continuity of the forging streamline is preserved, the fatigue strength of the cylinder wall is improved compared to the traditional machining cutting of the streamline, and cracks are avoided under high pressure working conditions. By radial spinning, the metal is plastically flowed, the metal deformation amount in the spinning process is controllable, the work hardening phenomenon caused by local excessive deformation is avoided, the uniformity of the hardness distribution in the small port area is ensured, and the anti-creep performance of the material is improved. By punching and expanding the boss to form a shape close to the nozzle hole, the subsequent machining amount is reduced, the forging streamline is preserved along the flow passage, and the anti-erosion capability is improved.

[0032] Example Two

[0033] As shown in Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 , a nuclear power pump shell integrated forging forming method, the forming method comprises the following steps: S01: peeling treatment is performed on the ingot; Firstly, a low alloy steel or stainless steel ingot meeting the nuclear level standard is selected, the material of the ingot is not limited, and the design requirements of the nuclear power pump shell are used as the reference, the weight of the ingot is determined according to the size of the pump shell and the forging ratio requirement, and the forging ratio is generally ≥3.5. The ingot is subjected to peeling treatment to remove the surface defect layer and ensure the surface quality of the blank.

[0034] S02: heating and heat preservation treatment is performed on the blank: The billet after skinning treatment is heated to 1100-1220℃, the heating speed is controlled at 50-80℃ / h, the holding time is calculated according to the size of the billet, generally 1-2H / 100mm, to ensure the uniformity of the internal temperature of the billet. The heating and holding treatment refers to making the material reach the uniform plastic deformation temperature, ensuring that the core-surface temperature difference of the billet is controlled within a reasonable range, and providing a uniform structure basis for subsequent forging.

[0035] S03: preforming the heated billet to form a cylindrical billet with a boss on one side: The heated billet is hoisted to the lower anvil of the forging press, the press is started, and the upper anvil is pressed down at a speed of 2-5mm / s, the billet is sequentially subjected to preliminary upsetting, elongation, and upsetting, the forging ratio of each step is controlled at 1.3-2.0, the billet is preliminarily broken into grains, and the structure is optimized. Then, after elongation and number marking, a cylindrical billet with a boss is pressed to form the approximate shape of the billet for the pump shell housing. The upper anvil refers to a forging tool with a planar contact surface, and the planar structure can ensure that the deformation force is uniformly distributed on the surface of the billet, avoiding local stress concentration leading to cracks. By pressing the upper anvil at a speed of 2-5mm, the contradiction between dynamic recrystallization and abnormal grain growth can be balanced, which can promote grain boundary migration to achieve grain refinement, and can also avoid organization coarsening caused by overheating.

[0036] Specifically, in the preforming process, first, the billet is subjected to upsetting operation by the upper anvil, and the three-dimensional compressive stress is used to break the as-cast coarse grain structure; then elongation operation is performed, and fiber-like structure is formed by axial extension; finally, the billet is upset again, and anisotropy is eliminated by multi-directional compression. The process changes the stress state alternately, so that the grains slip and dynamically recrystallize in multiple directions, forming uniform and fine equiaxed grain structure. The forging speed is controlled within a certain range, which can ensure that the metal fully recrystallizes, and can also prevent the secondary growth of grains at high temperature. The selection of forging ratio takes into account the grain refinement requirement and the plastic limit of the material, avoiding internal defects caused by excessive deformation.

[0037] S04: punching and expanding the cylindrical billet to form a boss cylinder billet: After the pre-forming forging is completed, a punch is used to punch the cylindrical blank, and then the cylindrical blank is sleeved on the core rod, and the core rod is placed on a horse frame, which is a supporting tool. The hole diameter of the blank is gradually expanded by rotating the blank and applying radial pressure, i.e., radial spinning. In this process, the blank is uniformly subjected to pressure in the circumferential direction, and the metal continuously flows outward, thereby increasing the hole diameter, so that the blank forms a cylindrical blank with a boss under the action of pressure. The radial spinning can be implemented by a hydraulic spinning machine or a wire wheel in cooperation with the core rod. Through radial spinning, the material is uniformly migrated from the thick-walled area to the thin-walled area, and this controlled plastic deformation mode can maintain the continuity distribution of metal fibers.

[0038] S05: Forging one side of the boss cylindrical blank to form a small port forging; A specially designed stepped core rod is inserted into the inner hole of the boss cylindrical blank, and the stepped core rod is designed to match the shape of the inner hole of the blank and to support and guide the metal flow in subsequent processing. During the insertion of the stepped core rod, the coaxiality of the stepped core rod and the inner hole of the blank needs to be ensured to ensure the uniformity of subsequent processing.

[0039] Radial spinning is performed on one side of the small port end of the stepped core rod, and the spinning operation is performed on one side of the small port end (T end) by using a spinning process. During spinning, the blank is rotated at the same time, and a specific spinning tool, such as a spinning wheel, is used to apply radial pressure to the blank to make the metal of the blank flow plastically. Under the action of pressure, the metal of the cylinder on one side of the T end gradually shrinks inward to achieve the effect of hole shrinking. Radial spinning is generally performed in multiple times, i.e., rough forging is performed first and then fine forging is performed. During the spinning process, the processing parameters such as spinning pressure, rotation speed, rotation angle, and feed amount are strictly controlled. Preferably, the single rotation angle is 30 to 60 degrees, the rough forging feed amount (downward pressure amount) is 50-100mm, and the fine forging feed amount (downward pressure amount) is 20-50mm, until the cylinder on one side is shrunk to the target outer diameter size. Through real-time monitoring and adjustment, the size accuracy and surface quality are ensured, so that the formed forging meets the design requirements.

[0040] S06: Punching and hole expanding of the boss of the small port forging: A punch is used to punch the boss on the side of the blank to form the initial shape of the side pipe hole. The punch applies concentrated pressure to the blank under the action of the press, so that the metal of the blank separates or flows plastically, thereby punching out the side pipe hole. The pressure, stroke, and punching position of the punch need to be accurately controlled to ensure that the position accuracy and initial size of the side pipe hole meet the design requirements.

[0041] After the side pipe hole is punched, the hole is expanded to the design size by using a hole expansion process. During the hole expansion process, a suitable hole expansion tool such as a hole expansion drill, a core rod, etc. is selected, and the hole wall metal is gradually expanded outward by rotating and applying a radial force, so as to reach the design required hole diameter size.

[0042] S07: The forged piece after punching and hole expansion of the boss of the small port forged piece is trimmed to form a near net shape forged piece with the pump shell: The billet is trimmed as a whole by using a stepped core rod to form a near net shape forged piece with the pump shell of the nuclear main pump. The stepped core rod is inserted into the inner hole of the billet, and the outer surface of the forged piece is forged by pressure processing (such as light forging, upsetting, etc. on the forging equipment) to further accurately size the forged piece. In this process, the stepped core rod plays a supporting and positioning role, guides the uniform flow of the billet metal, eliminates the size deviation, shape error, etc. that may be generated in the previous processing, and ensures that the overall size accuracy, shape and position tolerance, etc. of the billet meet the final forging size requirements.

[0043] The beneficial effects of the embodiment are: The manufacturing method of the integrated whole forging of the pump shell of the nuclear reactor main pump in the embodiment avoids the welding and connection defect problems caused by traditional split manufacturing and splicing, eliminates the defects such as pores, cracks, incomplete fusion, etc. caused by welding, and the hidden dangers of performance degradation in the welding heat affected zone, so that the pump shell becomes a continuous and complete whole, greatly improves the structural integrity and sealing, and better withstands harsh working conditions such as high temperature, high pressure, strong radiation and vibration.

[0044] During the forging process, the metal flow lines can be reasonably distributed along the pump shell structure to ensure the continuity and uniformity of the metal flow lines. Compared with the traditional metal flow line cutting method, the strength, toughness, fatigue resistance and creep resistance of the pump shell are significantly improved. At the same time, by accurately controlling the forging ratio, temperature, deformation amount and other parameters, the grain structure is refined, and the comprehensive mechanical properties of the material are further improved, and the risk of performance degradation in harsh service environment is reduced.

[0045] Through the precise design of the mold such as the stepped core rod and the accurate control of the size during the forging process, the near net shape of the shell and the multiple ports can be realized, the size cumulative error caused by multi-process processing is reduced, the size accuracy of the pump shell is higher. And the whole forging reduces the deformation problem caused by the generation and release of residual stress in the processing process, improves the size stability, ensures the size accuracy of the pump shell in long-term operation, and improves the assembly accuracy and operation stability with other components.

[0046] Production efficiency is improved: multiple independent forging, forming, machining processes are integrated into one overall forging process, reducing the multiple clamping, transportation and intermediate heat treatment of workpieces, effectively shortening the production cycle and improving the production efficiency. At the same time, the reduction of the process also reduces the quality risk of the workpiece in the transportation process, such as knocking and scratching. Machining allowance is reduced: near-net-shape process makes the pump shell close to the final size after overall forging, greatly reducing the subsequent machining allowance, shortening the machining time, reducing tool wear and equipment occupation time, and further improving the overall production efficiency.

[0047] Material utilization is improved: compared with the traditional forging and re-machining method, the integrated overall forging near-net-shape process greatly reduces the material removal amount, and the material utilization rate can be greatly improved, effectively reducing the consumption of high-value alloy materials (such as nuclear-grade stainless steel, low-alloy steel, etc.), and reducing the cost of raw materials. Comprehensive production cost is reduced: the improvement of production efficiency means that the cost of equipment use time and labor hours is reduced; the improvement of material utilization rate reduces material cost; and the reduction of waste loss, repair cost and subsequent maintenance cost due to quality problems, etc., reduces the comprehensive production cost from multiple aspects.

[0048] Safety and reliability are improved: the nuclear reactor main pump shell is a key equipment component of the nuclear island, and its quality and safety are crucial. The pump shell manufactured by the integrated overall forging forming method has excellent structural integrity and mechanical properties, better meeting the stringent requirements of nuclear safety regulations and standards for pump shells in terms of radiation resistance, corrosion resistance, structural reliability, etc., providing a solid guarantee for the safe and stable operation of nuclear power plants. Reducing the risk of operation: high-quality pump shells reduce the risk of accidents caused by structural defects (such as cracks, leaks, etc.) during operation, improve the reliability of the nuclear reactor main pump, reduce the probability of unplanned shutdown, and reduce economic losses and safety hazards caused by equipment failure.

[0049] Example Three

[0050] As shown in Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 6 , an integrated forging forming method for a nuclear power main pump shell is used in this embodiment, using a SA-508M steel ingot with a weight of 65T and a forging ratio of the steel ingot ≥3.5 to form a pump shell as shown in Figure 6 , the forming method includes the following steps: S01: Skin treatment is performed on the steel ingot; The above steel ingot is subjected to skin treatment to remove the surface defect layer and ensure the surface quality of the blank.

[0051] S02: The blank is heated and subjected to heat preservation treatment: The billet after skinning treatment is heated to 1100-1220°C, the heating speed is controlled at 50-80°C / h, the holding time is calculated according to the size of the billet, and generally, the holding time is 1-2H / 100mm to ensure the uniform temperature of the billet. The heating and holding treatment means that the material reaches the uniform plastic deformation temperature, and ensures that the temperature difference between the core and the surface of the billet is controlled within a reasonable range, providing a uniform structure basis for subsequent forging.

[0052] S03: Preforming forging is performed on the heated billet to form a cylindrical billet with a boss on one side: The heated billet is hoisted to the lower anvil of the forging press, the press is started, and the upper anvil is pressed down at a speed of 2-5mm / s. The billet is sequentially subjected to preliminary upsetting, elongation, and upsetting, and the forging ratio of each step is controlled at 1.3-2.0 to preliminarily break the grains of the billet and optimize the structure. Then, after elongation and marking, a cylindrical billet with a boss is pressed to form the approximate shape of the billet for the pump shell housing. In this embodiment, a boss cylindrical billet with a diameter of φ1600mm, a boss diameter of 800mm, and a boss height of 300mm is pressed.

[0053] The upper anvil refers to a forging tool with a planar contact surface, and the planar structure can ensure that the deformation force is uniformly distributed on the surface of the billet, avoiding local stress concentration leading to cracks. By pressing the upper anvil at a speed of 2-5mm, the contradiction between dynamic recrystallization and abnormal grain growth can be balanced, which can promote grain boundary migration to achieve grain refinement, and can also avoid organization coarsening caused by overheating.

[0054] Specifically, in the preforming forging process, first, the billet is subjected to upsetting operation by the upper anvil to break the as-cast coarse grain structure by using three-dimensional compressive stress; then elongation operation is performed to form fibrous structure by axial extension; finally, upsetting is performed again to eliminate anisotropy by multi-directional compression. This process changes the stress state alternately, so that the grains slip and dynamically recrystallize in multiple directions to form uniform and fine equiaxed grain structure. The forging speed is controlled within a certain range, which can ensure that the metal recrystallizes sufficiently and can prevent the secondary growth of grains at high temperature. The selection of forging ratio takes into account the grain refinement requirement and the plastic limit of the material, avoiding internal defects caused by excessive deformation.

[0055] S04: Punching and expanding the cylindrical billet to form a boss cylindrical billet: After the pre-forming forging is completed, the cylindrical blank is punched with a punch and then sleeved on a mandrel, which is placed on a horse frame, which is a supporting tool. By rotating the blank and applying radial pressure to it, i.e., radial spinning, the aperture of the blank is gradually expanded. In this process, the blank is uniformly subjected to pressure in the circumferential direction, and the metal continuously flows outward, thereby increasing the aperture and forming a cylindrical blank with a boss under the action of pressure. In this embodiment, a boss cylindrical blank with an outer diameter of 2100mm, an inner diameter of 1250mm, and a height of 2100mm is formed by radial spinning. The radial spinning can be implemented using a hydraulic spinning machine or a wire wheel in conjunction with a mandrel. Through radial spinning, the material is promoted to migrate evenly from the thick-walled area to the thin-walled area. This controlled plastic deformation mode can maintain the continuous distribution of the metal fibers.

[0056] S05: Forging one side of the boss cylindrical blank to form a small port forging; A specially designed stepped mandrel is inserted into the inner bore of the cylindrical blank. Designed to fit the shape of the blank, the stepped mandrel supports and guides metal flow during subsequent processing. During insertion, the mandrel must be aligned with the blank to ensure uniformity in subsequent processing.

[0057] The billet on the narrow end of the stepped mandrel undergoes radial spinning. This spinning process forges the narrow end (T-end) using a spinning process. During spinning, while the billet rotates, radial pressure is applied to the billet by a specific spinning tool, such as a spinning wheel, causing the metal to plastically flow. Under this pressure, the metal of the cylinder on the T-end gradually contracts inward, achieving a hole-closing effect. Radial spinning is typically performed in multiple steps, beginning with multiple rough forgings followed by multiple fine forgings. During the spinning process, processing parameters such as spinning pressure, rotation speed, rotation angle, and feed rate are strictly controlled. Preferably, a single rotation angle of 30 to 60 degrees, a rough forging feed (pressing force) of 50-100 mm, and a fine forging feed (pressing force) of 20-50 mm are used until the hole on the cylinder is closed to the target outer diameter of 1100 mm. Real-time monitoring and adjustment ensure dimensional accuracy and surface quality, ensuring that the final forging meets design requirements.

[0058] S06: Punching and expanding the boss of the small port forging: A punch is used to punch the side boss of the blank to form the initial shape of the side pipe hole. Under the action of the press, the punch applies concentrated pressure to the blank locally, causing the blank metal to separate or plastically flow, thus punching out the side pipe hole. This process requires precise control of the punch pressure, stroke, and punching position to ensure that the positional accuracy and initial dimensions of the side pipe hole meet the design requirements.

[0059] After the side pipe hole punching is completed, the hole is expanded to the design size by the hole expansion process. During the hole expansion process, appropriate hole expansion tools such as hole expansion drills, mandrels, etc. are selected, and the hole wall metal is gradually expanded outward by rotating and applying radial force, so as to reach the design required hole diameter size.

[0060] S07: The forged piece after punching and hole expansion of the small port forged piece is trimmed to form a forged piece that is near net shape with the pump shell: The billet is trimmed as a whole by using a stepped mandrel to form a forged piece that is near net shape with the pump shell of the nuclear main pump. The stepped mandrel is inserted into the inner hole of the billet, and the outer surface of the forged piece is processed by pressure processing (such as light forging, upsetting, etc. on the forging equipment) to further accurately the size of each part of the forged piece. In this process, the stepped mandrel plays a supporting and positioning role, guides the uniform flow of the forged piece metal, eliminates the size deviation, shape error, etc. that may be generated in the previous processing, and ensures that the overall size accuracy, shape and position tolerance, etc. of the billet meet the final forging size requirements.

[0061] The advantages of the embodiment of the present application are as follows: by heating the blank to 1100-1220 DEG C to make it in the metal recrystallization temperature interval, the deformation resistance can be reduced, and overheating or overburning can be avoided; by heating at a heating speed of 50-80 DEG C / h, the thermal stress cracking caused by the large temperature difference between the inside and outside of the blank can be effectively prevented, and the uniform internal temperature is ensured by the heat preservation treatment, thereby providing a uniform structure basis for subsequent forging. By means of upsetting, elongating and upsetting, the original coarse grains of the ingot can be broken, the uniform distribution of the forging ratio can eliminate internal porosity and segregation, a dense and uniform forging structure can be formed, and the overall strength and toughness of the blank can be improved. After the stamping, a reference is provided for suppressing the cylinder into a convex cylindrical shape, the coaxiality error between the convex and the shell is ensured to be small, and the position deviation during subsequent port forming is avoided. By expanding the hole, the metal flows uniformly in the circumferential direction, the continuity of the forging streamline is preserved, the fatigue strength of the cylinder wall is improved compared with the traditional machining cutting streamline, and cracks are avoided under high pressure working conditions. By radial spinning, the metal is plastic flow, the metal deformation amount in the spinning process is controllable, the work hardening phenomenon caused by local excessive deformation is avoided, the uniformity of the hardness distribution in the small port area is ensured, and the anti creep performance of the material is improved. By punching and expanding the convex, a shape close to the shape of the connecting pipe hole is formed, the subsequent machining amount is reduced, the forging streamline is preserved along the flow passage, and the anti-erosion capability is improved. The nuclear reactor pump shell integrated whole forging forming manufacturing method has obvious advantages. In terms of structural integrity, the welding and connection defects caused by traditional split manufacturing splicing are avoided, the welding defects such as pores, cracks and heat affected zone performance risks are eliminated, a continuous and complete whole is formed, the structural sealing and integrity are greatly enhanced, and the high temperature and high pressure and other harsh working conditions are adapted. In terms of performance improvement, the metal streamline is accurately controlled during forging, and is reasonably distributed along the pump shell structure, the strength, toughness, fatigue resistance and anti creep performance are significantly improved compared with the traditional machining cutting streamline; meanwhile, the forging ratio, temperature and other parameters are accurately regulated, the grain structure is refined, and the performance degradation risk under harsh service environment is reduced. In terms of size precision control, the shell and the port are realized near net forming by relying on the precise design of the step mandrel and other molds and the accurate control of the forging size, the size cumulative error is reduced, and the size stability and precision are improved. The production efficiency is significantly improved, the multiple processes are integrated, the clamping, transportation and intermediate processing links are reduced, the production cycle is shortened, and the workpiece transportation quality risk is reduced; the near net forming greatly reduces the machining allowance and time, and improves the overall efficiency. The cost control effect is good, the material utilization rate is greatly improved, and the consumption of high-value alloy materials is reduced; the production efficiency is improved and the material is saved, the waste product repair cost is reduced, and the comprehensive production cost is reduced in multiple dimensions. In addition, the pump shell manufactured by the method has reliable quality, meets the strict requirements of nuclear safety regulations on pump shell anti radiation and anti corrosion, reduces the operation accident risk, and provides a solid guarantee for the safe and stable operation of the nuclear power station.

[0062] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of the changes or replacements within the technical scope disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for integrally forging a nuclear power main pump casing, characterized in that: The following steps are involved: Heating and keeping the blank warm; The heated blank is subjected to preforming forging to form a cylindrical blank having a boss on one side; Punching and expanding the cylindrical blank to form a boss cylindrical blank; Inserting a stepped core rod into the inner hole of the boss cylindrical blank, and radially spinning the blank on the small-end end of the stepped core rod to form a small-end forging; The boss of the small port forging is punched and expanded to form a forging that is nearly net-shape with the pump casing.

2. The method for integrally forging a nuclear power main pump casing according to claim 1, characterized in that: The preforming forging of the heated blank is to use an upper flat anvil to perform upsetting, drawing and upsetting operations on the blank in sequence at a certain speed to break the grains in the blank.

3. The method for integrally forging a nuclear power main pump casing according to claim 2, characterized in that: The certain speed is 2 to 5 mm / s, and the forging ratio of upsetting, drawing and upsetting is 1.3 to 2.

0.

4. The method for integrally forging a nuclear power main pump casing according to claim 2, characterized in that: The steps sequentially perform upsetting, stretching, and upsetting operations on the blank, and then stretching and stamping the blank to form a boss cylindrical blank.

5. The method for integrally forging a nuclear power main pump casing according to claim 1, characterized in that: The steps are to punch and expand the cylindrical blank to form a boss cylindrical blank. After punching the cylindrical blank with a punch, it is sleeved on a core rod and placed on a horse frame, and radial spinning is performed on the cylindrical blank until it meets the preset requirements.

6. The method for integrally forging a nuclear power main pump casing according to claim 1, characterized in that: The steps of punching and expanding the boss of the small port forging to form a forging that is nearly net-shape with the pump casing are to use a punch to punch the side boss and then use an expanding tool to perform radial spinning until it meets the preset requirements.

7. The method for integrally forging a nuclear power main pump casing according to claim 1, characterized in that: The method also includes trimming the forging after punching and expanding the boss of the small-port forging. The trimming is to insert a stepped core rod into the inner hole of the small-port forging and press-process the outer surface to form a forging that is nearly net-shaped with the pump casing.

8. The method for integrally forging a nuclear power main pump casing according to claim 1, characterized in that: The blank is heated to 1100-1220° C. at a heating rate of 50 to 80° C. / h.

9. The method for integrally forging a nuclear power main pump casing according to claim 1, characterized in that: The blank is made of low alloy steel or stainless steel ingot, and the forging ratio of the ingot is ≥3.

5.

10. The method for integrally forging a nuclear power main pump casing according to any one of claims 1 to 9, characterized in that: Before the steps of heating and heat-insulating the blank, the blank is subjected to a peeling treatment.

Images