A method for forging large L-shaped stainless steel main pump pipe with coordinated control of shape

Abstract

This invention provides a method for shape and property coordinated control for forging of large L-shaped stainless steel main pump pipe forgings. The method comprises: preparing a tooling auxiliary tool, comprising a flat-bottom upper die, a profiling lower die, a profiling upper die and a core rod, wherein the profiling lower die has a V-shaped die cavity and the profiling upper die is V-shaped; obtaining a square blank 1 under forging conditions in which the deformation of the steel ingot during upsetting is ≥50%, the deformation of each anvil during drawing is ≥15%, the forging temperature per fire is 1150° C. to 1240° C., and the forging time does not exceed 20 minutes; flattening and thickening the blank 1 by using the profiling lower die and the flat-bottom upper die to obtain a blank 2 with a flat side and right angles between two sides of the other side; stamping the blank 2 by using the profiling upper die and the profiling lower die to obtain a blank 3, wherein the blank 3 is used to provide a transition area of ​​two branch pipes and a main body of the branch pipe; maintaining the mold closing state of the profiling upper die and the profiling lower die, and limiting the movement of the blank 3 by using the core rod, so as to respectively flatten the ends of the two branch pipes, thereby obtaining an L-shaped stainless steel main pump pipe large forging. According to the present invention, the problem of contour forming and the problem of grain uniformity of the existing L-shaped stainless steel main pump pipe large forging can be solved.

Description

Technical Field

[0001] This invention belongs to the field of metal material forming, and more specifically, relates to a method for shape and property coordinated control for forging of large L-shaped stainless steel main pump pipe forgings. Background Technology

[0002] The main pump nozzle is the connecting link between the nuclear reactor pressure vessel and the main pump, thus forming a complete loop within the reactor. Its primary function is to transport fluids and heat. The connection between the main pump nozzle and the pressure vessel shell is the weakest link in the reactor pressure vessel and a key area for evaluating its safety; therefore, the main pump nozzle must possess reliable safety features.

[0003] The main pump connector is a complex, irregularly shaped forging. Two branch pipes intersect to form a right-angle transition area, with one branch pipe having a diameter exceeding 500mm and a length reaching 1000mm. Given the structural characteristics of the L-shaped main pump connector, previous forging methods often employed drawing and segmentation forming, only shaping the right-angle transition area formed by the intersection of the two branch pipes, without forming the branch pipes themselves. Figure 10 As shown, the forging after drawing and shaping weighs 8.0t, while the weight of the rough-machined product accounts for only 31% of the forging weight, resulting in low material utilization and a significant increase in machining workload and processing cycle. With increasingly fierce market competition, the original forming scheme can no longer meet the market's requirements for production cost and cycle control of main pump nozzle products. Achieving near-net-shape forming of main pump nozzles using die forging will become a production trend. However, for large main pump nozzles with single-sided branch pipe lengths reaching 1000mm and branch pipe diameters D≥Φ500mm, the resistance during plastic deformation is high in the right-angle transition area and when flowing towards the ends of the two branch pipes, easily leading to forging defects such as insufficient material, requiring additional rework processes to ensure forging formation. Therefore, there is an urgent need to develop a near-dimensional contour forging forming process based on integrated irregular forgings for main pump nozzle forgings to achieve near-net-shape forming and solve the technical difficulties in forging main pump nozzle forgings.

[0004] Furthermore, the main pump pipe forging is made of ultra-low carbon austenitic stainless steel. Due to its material properties, it does not undergo phase transformation, making it difficult to effectively improve the grain size through heat treatment processes such as solution treatment. Grain size is one of the main factors affecting material properties; coarse grains can drastically deteriorate material properties, leading to premature product failure and potentially causing major safety accidents. Therefore, for the main pump pipe forging, to ensure product quality and performance and improve its safety and reliability, it is essential to effectively control the grain size during the forging process. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of imitation forming and grain uniformity of existing L-shaped stainless steel main pump pipe large forgings (branch pipe diameter D≥Φ500mm, single-side branch pipe length≥1000mm).

[0006] To achieve the above objectives, the present invention provides a method for shape and property coordinated control forging of large L-shaped stainless steel main pump pipe forgings, the method comprising the following steps:

[0007] Prepare tooling and fixtures, which include a flat-bottomed upper mold, a contouring lower mold, a contouring upper mold, and a mandrel. The contouring lower mold has a V-shaped cavity, and the contouring upper mold is V-shaped.

[0008] A square billet 1 is obtained under the following forging conditions: the upsetting deformation of the steel ingot is ≥50%, the deformation per anvil during drawing is ≥15%, the forging temperature per forging is 1150℃~1240℃, and the forging time does not exceed 20min.

[0009] The blank 1 is flattened and thickened using the lower mold and the upper flat mold to obtain a blank 2 with one side being a plane and the other side having a right angle between the two sides;

[0010] The blank 2 is stamped and formed using the upper and lower molds to obtain the blank 3, which is used to provide the transition area between the two branch pipes and the main body of the branch pipes.

[0011] By keeping the upper and lower molds in the closed state, and using the mandrel to restrict the movement of the blank 3, the ends of the two pipes are flattened to obtain the L-shaped stainless steel main pump pipe forging.

[0012] Alternatively, the dimensions of the blank 1 are determined based on the following formula:

[0013]

[0014] t1=a-(40~60) (2)

[0015]

[0016] In the above formula, L1 is the length of billet 1, V 坯料1 t1 is the volume of billet 1, t1 is the thickness of billet 1, a is the diameter of the large forging branch pipe section of the L-shaped stainless steel main pump connector, and V is the volume of billet 1. 锻件 The volume of the large forging for the L-shaped stainless steel main pump pipe.

[0017] Optionally, the step of flattening and thickening the blank 1 using the contouring lower die and the flat-bottomed upper die to obtain a blank 2 with one side being a plane and the other side having a right angle between the two sides further includes the following steps:

[0018] The blank 1 is rotated 45° clockwise and then placed in the mold cavity of the lower mold. The thickness of the mold cavity is the same as the diameter of the forging branch pipe, and the inner arc radius of the lower mold is the same as the arc radius of the forging.

[0019] After aligning the flat-bottomed upper die covering the horizontal length direction of the blank 1 with the lower die, press down with a pressing amount of H1 / 3 to form a blank 2 with a length of L2, a height of H2, and a thickness of t2, where H1 is the length of the diagonal of the blank 1 and t2 = a.

[0020] Optionally, the process of stamping the blank 2 using the upper and lower molds to obtain the blank 3 specifically involves:

[0021] The blank 2 is held in the cavity of the lower mold, the upper mold is replaced, and the upper mold is aligned with the lower mold before the blank 2 is stamped. The reduction is H2-a-(60~70), so that the transition area of ​​the two branches and the main body of the L-shaped stainless steel main pump pipe forging are formed.

[0022] Optionally, the forging method for the L-shaped stainless steel main pump pipe large forging with shape and property coordinated control further includes the following steps:

[0023] After the ends of the two branches of the billet 3 are flattened to obtain the L-shaped stainless steel main pump pipe forging, the L-shaped stainless steel main pump pipe forging is immersed in water for cooling, and the immersion time is ≤5min.

[0024] The beneficial effects of this invention are as follows:

[0025] This invention provides a forging method for controlling the shape and properties of large L-shaped stainless steel main pump pipe forgings. Through corresponding forming schemes and tooling design schemes, using a 10,000-ton press and assembling corresponding tooling and auxiliary tools, and by means of free forging and die forging, the method solves the problems of grain uniformity and imitation forming of large L-shaped stainless steel main pump pipe forgings. While meeting the dimensional requirements of the forgings, the method achieves a grain size of ≥3 on the entire cross section of the forgings, thus meeting the requirements for controlling the shape and properties of large L-shaped stainless steel main pump pipe forgings.

[0026] This invention first utilizes high-temperature and large-deformation forging technology to break up columnar crystals, improve macroscopic segregation, and refine the as-cast structure, resulting in a uniform forged microstructure. It also solves the forging problem of the right-angle transition region formed by the intersection of the two branch pipes in the L-shaped main pump connector forging, and the difficulty in forming the branch pipe through contour forging. The forging weight is only 6.9t, a 14% reduction compared to previous methods, improving product utilization and indirectly reducing machining workload and cycle time, thus lowering overall manufacturing costs. Pre-fabricated square billets effectively reduce the forming difficulty of the right-angle transition region formed by the intersection of the two branch pipes in the L-shaped main pump connector forging. Flattening and thickening prepares for subsequent branch pipe pressing and provides conditions for contour forming of the branch pipe body. Through contour forming with upper and lower dies, the metal flow of the branch pipe body exhibits a streamlined curve, resulting in superior mechanical properties. Finally, by using a mandrel to flatten the ends when the upper and lower dies are closed, the allowance in the length direction of the branch pipe can be effectively reduced, thereby reducing the forging weight and improving the contour forming accuracy of the forging.

[0027] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0028] The present invention can be better understood by referring to the following description taken in conjunction with the accompanying drawings, in which the same or similar reference numerals are used throughout the drawings to denote the same or similar parts.

[0029] Figure 1 A flowchart illustrating the implementation of a forging method for large L-shaped stainless steel main pump nozzles with form-property coordinated control according to an embodiment of the present invention is shown.

[0030] Figure 2 A schematic diagram of the structure of the large forging of the L-shaped stainless steel main pump nozzle according to an embodiment of the present invention is shown;

[0031] Figure 3 A schematic diagram showing the dimensions of the blank 1 according to an embodiment of the present invention is shown;

[0032] Figure 4 A schematic diagram of the structure of a flat-bottomed upper mold according to an embodiment of the present invention is shown;

[0033] Figure 5 A schematic diagram of a contour mold according to an embodiment of the present invention is shown;

[0034] Figure 6 An assembly schematic diagram of the contouring lower mold according to an embodiment of the present invention is shown;

[0035] Figure 7 A schematic diagram showing the dimensions of the blank 2 according to an embodiment of the present invention is shown;

[0036] Figure 8 A schematic diagram of the structure of the contour-following upper mold according to an embodiment of the present invention is shown;

[0037] Figure 9 A schematic diagram showing the dimensions of the blank 3 according to an embodiment of the present invention is shown;

[0038] Figure 10 A schematic diagram of the L-shaped stainless steel main pump nozzle forging and forming scheme according to the background technology of the present invention is shown.

[0039] Figure 11 A metallographic image of the grain size of the finished L-shaped stainless steel main pump nozzle forging according to an embodiment of the present invention is shown. Detailed Implementation

[0040] To enable those skilled in the art to more fully understand the technical solutions of the present invention, exemplary embodiments of the present invention will be described more comprehensively and in detail below with reference to the accompanying drawings. Obviously, the one or more embodiments of the present invention described below are merely one or more specific ways to implement the technical solutions of the present invention, and are not exhaustive. It should be understood that other ways belonging to a general inventive concept can be used to implement the technical solutions of the present invention, and should not be limited to the embodiments described exemplary. Based on one or more embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0041] Example: Figure 1 The flowchart illustrates the implementation of the L-shaped stainless steel main pump pipe large forging shape and property coordinated control forging method according to an embodiment of the present invention. Figure 2 A schematic diagram of the structure of the large forging of the L-shaped stainless steel main pump pipe according to an embodiment of the present invention is shown.

[0042] Reference Figure 1 and Figure 2 The forging method for the L-shaped stainless steel main pump pipe large forging with shape and property coordinated control according to an embodiment of the present invention includes the following steps:

[0043] Step S100: Prepare tooling and fixtures, which include a flat-bottomed upper mold, a lower mold for contouring, an upper mold for contouring, and a mandrel. The lower mold for contouring has a V-shaped cavity, and the upper mold for contouring is V-shaped.

[0044] Step S200: Obtain a square billet 1 under the forging conditions of steel ingot upsetting deformation ≥50%, anvil deformation ≥15% during drawing, forging temperature of 1150℃~1240℃ per forging pass and forging time not exceeding 20 minutes.

[0045] Step S300: Use the lower mold and the upper mold to flatten and thicken the blank 1 to obtain blank 2 with one side being a plane and the other side having a right angle between the two sides;

[0046] Step S400: The blank 2 is stamped and formed using the upper and lower molds to obtain the blank 3. The blank 3 is used to provide the transition area between the two branches and the main body of the branch.

[0047] Step S500: Keep the upper and lower molds closed, and use the mandrel to restrict the movement of the blank 3 so as to flatten the ends of the two branches respectively, and obtain the L-shaped stainless steel main pump pipe forging.

[0048] Specifically, in this embodiment of the invention, the tooling and auxiliary equipment prepared includes, but is not limited to, the following:

[0049] A flat-bottomed upper die, which works in conjunction with a contour-following lower die to flatten and thicken a square blank 1, such as... Figure 4 As shown.

[0050] The combined contouring die, also known as the lower die, is used to contour the L-shaped stainless steel main pump pipe forging. The lower die consists of two mirror-symmetrical parts, assembled together with bolts, nuts, and other fasteners. Figure 5 and Figure 6 As shown.

[0051] A contouring die, also known as a contouring die, is an upper die used to contour the L-shaped stainless steel main pump pipe forging. Figure 8 As shown.

[0052] The mandrel is a columnar mandrel that has been flattened at the end of the blank 3.

[0053] In this embodiment of the invention, a square billet 1 is forged in step S200. Specifically, a square billet with a uniform and dense structure is pre-formed using conventional forging methods such as upsetting and drawing, for example... Figure 3 As shown. The requirements are: upsetting deformation ≥ 50% for the steel ingot, deformation per anvil ≥ 15% during drawing, forging temperature per forging pass of 1150℃~1240℃, and forging time (from the start of forging to the end of forging and remelting) not exceeding 20 minutes. Through upsetting and drawing processes, the billet achieves a sufficient forging ratio to ensure overall compaction. High temperature and large deformation effectively compact and break down the cast dendrites inside the steel ingot, achieving overall grain refinement within the billet.

[0054] The dimensions of billet 1 can be calculated using formulas (1)(2)(3):

[0055]

[0056] t1=a-(40~60) (2)

[0057]

[0058] In the above formula, L1 is the length of billet 1, V 坯料1 t1 is the volume of billet 1, t1 is the thickness of billet 1, a is the diameter of the large forging branch pipe section of the L-shaped stainless steel main pump connector, and V is the volume of billet 1. 锻件 The volume of the large forging for the L-shaped stainless steel main pump pipe.

[0059] In this embodiment of the invention, the blank 1 is flattened and thickened through step S300. Specifically, the blank 1 is rotated 45° clockwise and placed in the cavity of the assembled lower mold. The thickness of the lower mold cavity is the same as the diameter of the forging branch pipe, and the inner radius of the lower mold is the same as the radius of the forging arc. The flat upper mold covering the horizontal length of the blank 1 is aligned with the lower mold and then pressed down. The pressing amount is approximately H1 / 3, meaning the absolute value of the difference between the pressing amount and H1 / 3 does not exceed a set value, where H1 is the length of the diagonal of the blank 1. The pressing down of the flat upper mold increases the overall thickness of the blank 1, resulting in a blank 2 with one side being a plane and the other side having a right angle between the two sides, as shown below. Figure 7 As shown. The length of billet 2 is L2, the height is H2, and the thickness is t2, where t2 = a.

[0060] In this embodiment of the invention, material separation and shaping are achieved through step S400. Specifically, after the flat-bottomed upper die has pressed down to meet the requirements, the blank 2 is kept within the cavity of the shaping lower die, and the V-shaped shaping upper die is replaced. Utilizing... Figure 8 The upper and lower molds, as shown, are aligned and then used to stamp the blank 2. The reduction is H2 - a - (60~70), which forms the transition area between the two branches and the main body of the L-shaped stainless steel main pump pipe forging. The forming result is as follows. Figure 9 The blank shown is 3.

[0061] In this embodiment of the invention, the branch pipe end forming is achieved through step S500. After material separation and shaping, the upper and lower shaping molds are kept in the closed state. The movement of the billet 3 is restricted by the mandrel. The ends of the two branch pipes of the L-shaped stainless steel main pump pipe forging are flattened and completed. After completion, the forging is immediately immersed in water for cooling. The water immersion time is ≤5min to allow the forging to cool down quickly and avoid grain coarsening or mixed crystals due to high residual heat.

[0062] The L-shaped stainless steel main pump pipe forging method of the present invention, which controls the shape and properties of the large forging, adopts a grain control method of "high temperature + large deformation" and a forming method of "prefabricated square billet + flattening and thickening + material separation and shaping + branch pipe end forming", which has the following beneficial effects:

[0063] 1. For example Figure 3As shown, the prefabricated square blank 1 can reduce the forming difficulty of the right-angle transition area formed by the intersection of the two branches of the L-shaped stainless steel main pump pipe forging.

[0064] 2. Flattening and thickening the blank 1 can prepare for the subsequent pressing and forming of the branch pipe. Flattening and thickening the blank as a whole facilitates the next step of separating the two branch pipes and forming the main body.

[0065] 3. After the upper mold and the combined lower mold are closed, the right-angle transition part of the L-shaped stainless steel main pump pipe forging and the main body of the branch pipe are formed. By using the mandrel to flatten the end when the upper and lower molds are closed, the allowance in the length direction of the branch pipe can be effectively reduced, thereby reducing the weight of the forging and improving the degree of conformity of the forging.

[0066] 4. During the forging process, high temperature and large deformation are guaranteed, which effectively breaks up columnar grains, breaks up the as-cast structure, improves macroscopic segregation, refines grains and obtains a uniform forged structure.

[0067] 5. For example Figure 8 The upper mold shown is used to make a contouring allowance based on the right-angle transition area of ​​the large forging of the L-shaped stainless steel main pump pipe and the diameter of the branch pipe. Combined with the combined lower mold, it can effectively contour the L-shaped main pump pipe forging.

[0068] 6. For example Figure 5 and Figure 6 The drawing and assembly diagram of the contouring lower die shown indicate that the combined contouring lower die consists of two parts that are mirror-symmetrical and assembled together with fasteners such as bolts and nuts. By allowing for contouring with a margin, it can effectively contour the L-shaped main pump pipe forging. Furthermore, after the end is flattened, the combined contouring lower die can be quickly and easily demolded by disassembling the lower die fasteners.

[0069] The following is a specific example, for a forging schematic diagram with a length L0≈1800mm and a branch pipe diameter... The forging process of the large L-shaped ultra-low carbon austenitic stainless steel main pump pipe with two branches having a 90° included angle is as follows:

[0070] Step 1: Pre-fabrication of square billets. Using conventional forging methods such as upsetting and drawing, pre-fabricate square billets with uniform and dense structure, a length L1≈1350mm, a thickness t1≈550mm, and rounded corners. This is billet 1, with a corner radius R≈50mm. The requirements are: upsetting deformation ≥50%, drawing deformation per anvil ≥15%, and forging time per heat (from the start of forging to the end of forging and remelting) not exceeding 20 minutes.

[0071] Step 2: Flattening and Thickening. Rotate blank 1 45° clockwise and place it into the assembled lower mold cavity. Cavity diameter... Using a flat-bottomed upper die that is 2600mm long and 595mm wide, and aligned with the lower die, press down with a pressing amount of ≈650mm to form a blank 2 with an upper length of L2≈2000mm, a height of H2≈1350mm, and a thickness of t2≈600mm.

[0072] Step 3: Material shaping. After the flat-bottomed upper die is pressed down, keeping the blank 2 inside the shaping lower mold cavity, replace it with a V-shaped shaping upper die. The diameter of the upper mold cavity is... After aligning the V-shaped upper and lower molds, the blank 2 is stamped with a reduction of approximately 800mm, forming the transition area between the two branch pipes and the main body of the branch pipes. 3. The blank.

[0073] Step 4: Forming the branch pipe ends. After material separation and shaping, keep the upper and lower molds in the closed state. Use a mandrel with a diameter of approximately 600mm to restrict the movement of the billet. Flatten the ends of the two branch pipes of the L-shaped main pump pipe forging until the branch pipe length is approximately 1800mm. After the forging is completed, immediately immerse it in water for 2 minutes to allow for rapid cooling and prevent coarsening or mixed crystal formation caused by preheating.

[0074] After forging according to the above steps, the dimensions of the L-shaped ultra-low carbon austenitic stainless steel main pump pipe forgings were measured and samples were taken for grain size testing. The L-shaped main pump pipe forgings with a branch pipe diameter of Φ600mm and a branch pipe length of 1800mm met the dimensional requirements, and the grain size of all forgings reached level 3 or above. Figure 11 As shown, the grain morphology distribution is generally uniform.

[0075] While one or more embodiments of the present invention have been described above, those skilled in the art will recognize that the present invention can be implemented in any other form without departing from its spirit and scope. Therefore, the embodiments described above are illustrative and not restrictive, and many modifications and substitutions will be apparent to those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method for forging large L-shaped stainless steel main pump pipe pipe with shape and property coordinated control, characterized in that, include: Prepare tooling and fixtures, which include a flat-bottomed upper mold, a contouring lower mold, a contouring upper mold, and a mandrel. The contouring lower mold has a V-shaped cavity, and the contouring upper mold is V-shaped. A square billet 1 is obtained under the following forging conditions: the upsetting deformation of the steel ingot is ≥50%, the deformation per anvil during drawing is ≥15%, the forging temperature per forging is 1150℃~1240℃, and the forging time is no more than 20 minutes. The blank 1 is flattened and thickened using the lower mold and the upper flat mold to obtain a blank 2 with one side being a plane and the other side having a right angle between the two sides; The blank 2 is stamped and formed using the upper and lower molds to obtain the blank 3, which is used to provide the transition area between the two branch pipes and the main body of the branch pipes. By keeping the upper and lower molds closed, and using the mandrel to restrict the movement of the blank 3, the ends of the two pipes are flattened to obtain the L-shaped stainless steel main pump pipe forging. The dimensions of the blank 1 are determined based on the following formula: In the above formula, L1 is the length of billet 1, V 坯料1 t1 is the volume of billet 1, t1 is the thickness of billet 1, a is the diameter of the large forging branch pipe section of the L-shaped stainless steel main pump connector, and V is the volume of billet 1. 锻件 The volume of the large forging for the L-shaped stainless steel main pump connecting pipe; The step of using the lower mold and the upper flat mold to flatten and thicken the blank 1 to obtain a blank 2 with one side being a plane and the other side having a right angle between the two sides includes: The blank 1 is rotated 45° clockwise and then placed in the mold cavity of the lower mold. The thickness of the mold cavity is the same as the diameter of the forging branch pipe, and the inner arc radius of the lower mold is the same as the arc radius of the forging. After aligning the flat-bottomed upper die covering the horizontal length direction of the blank 1 with the lower die, press down with a pressing amount of H1 / 3 to form a blank 2 with a length of L2, a height of H2, and a thickness of t2, where H1 is the length of the diagonal of the blank 1 and t2 = a. The specific steps of using the upper and lower contouring dies to stamp the blank 2 to obtain the blank 3 are as follows: The blank 2 is held in the cavity of the lower mold, the upper mold is replaced, and the upper mold is aligned with the lower mold before the blank 2 is stamped. The reduction is H2-a-(60~70), so that the transition area of ​​the two branches and the main body of the L-shaped stainless steel main pump pipe forging are formed.

2. The forging method for large forgings with synergistic shape and properties control of L-shaped stainless steel main pump pipe according to claim 1, characterized in that, Also includes: After the ends of the two branches of the billet 3 are flattened to obtain the L-shaped stainless steel main pump pipe forging, the L-shaped stainless steel main pump pipe forging is immersed in water for cooling, and the immersion time is ≤5min.

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