Method for forming an ultra-large size integral rotor retaining ring forging

Abstract

The application discloses a forming method for a super-large integral rotor guard ring forge piece, and technical solution points comprise the following steps: step S1, blanking, manufacturing a blank; step S2, modifying forging, the blank is elongated, blank feeding amount W1=0.3-0.6W, and the downward pressing amount H1=0.1-0.2H, then the blank is turned over by 180 degrees to repeat the elongation process, then the blank is turned over by 90 degrees to repeat the elongation process, one elongation cycle is completed, and the elongation cycle is repeated until the target size; step S3, upsetting, vertical blank upsetting, upsetting deformation amount is greater than or equal to 40%; step S4, blank punching; step S5, blank horse frame hole expansion; step S6, blank ring rolling; step S7, blank solid solution: the blank is heated to 960-980 DEG C, then air-cooled to 900-910 DEG C, and finally water-cooled to room temperature; and step S8, aging treatment: the blank is heated to 700 DEG C-720 DEG C, and then air-cooled after furnace discharge, and the method has the advantages that the uniformity of the structure is improved, the quality of the forge piece is improved, and the strict indexes of manufacturing super-large parts are met.

Description

Technical Field

[0001] This invention relates to the field of large rotor manufacturing, and more particularly to a method for forming ultra-large integral rotor retaining ring forgings. Background Technology

[0002] The hydropower industry plays a vital role in global energy supply. With the growth of global energy demand, the development and utilization of hydropower are receiving increasing attention. Currently, more and more variable-speed pumped-storage generators are changing the operating speed of the unit by adjusting the operating frequency of the rotor current, thus expanding the range of head-to-head ratio for the pump-turbine and achieving optimal performance. Research, design, and manufacturing of AC-excited generators for variable-speed pumped-storage power stations are attracting increasing attention.

[0003] The generator retaining ring is a crucial component of the generator rotor in a power plant. It is a high-strength, non-magnetic, metallic ring-shaped structure primarily used to prevent deformation, displacement, and eccentricity of the rotor components and excitation winding ends under electromagnetic forces and high-speed centrifugal forces. When the generator rotates at high speed, the rotor ends are subjected to significant centrifugal forces; the retaining ring is used to fix the position of the winding ends, preventing them from moving during rotor operation. With advancements in large-scale variable-speed pumped-storage generator technology, the size of these units is also increasing.

[0004] Existing retaining rings with a diameter of approximately 2m are made of 1Mn18Cr18N alloy. They are produced through a process of expansion molding, solution treatment, and cold deformation, requiring cold deformation after heat treatment to achieve the desired performance characteristics. 1Mn18Cr18N is an austenitic stainless steel, its microstructure mainly consisting of an austenitic matrix and carbonitride precipitates. The carbonitride precipitates are compounds formed by the interaction of nitrogen and carbon in the alloy, typically distributed in a dispersed granular form within the austenitic matrix.

[0005] However, there is currently a need for ultra-large integral retaining ring forgings (5m diameter class). These forgings have large diameters, thin walls, and high heights. Manufacturing ultra-large integral retaining rings using processes typically used for 2m diameters presents the following problems: The austenite in the alloy contains a large number of carbonitride precipitates, resulting in high hardness and making it difficult to break down the original microstructure. This leads to uneven microstructure after forging and high residual stress within the microstructure, all of which negatively impact the quality of the forging. More importantly, to achieve high strength, cold expansion forming after heat treatment is necessary to improve performance. The cold expansion force required for 5m-class stainless steel needs to reach over 20,000 tons, and currently, there is no equipment large enough to perform this expansion process. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for forming ultra-large integral rotor retaining ring forgings, which has the advantages of improving the uniformity of the structure, improving the quality of the forgings, and meeting the strict requirements for manufacturing ultra-large parts.

[0007] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0008] A method for forming an ultra-large integral rotor retaining ring forging includes the following steps:

[0009] Step S1: Blanking and manufacturing the billet;

[0010] Step S2, reforging, the billet is drawn out, the billet feed amount W1 = 0.3~0.6W, the downward pressure H1 = 0.1~0.2H, then the billet is flipped 180° to repeat the drawing process, then the billet is flipped 90° to repeat the drawing process, completing one drawing cycle, repeating the drawing cycle until the target size is reached;

[0011] Step S3, upsetting, vertical upsetting, upsetting deformation ≥40%;

[0012] Step S4: Punching holes in the blank;

[0013] Step S5: Expand the hole in the billet using a frame;

[0014] Step S6, ring rolling of the billet;

[0015] Step S7, billet solution treatment: The billet is heated to 960-980°C, then air-cooled to 900-910°C, and finally water-cooled to room temperature;

[0016] Step S8, aging treatment: The billet is heated to 700℃~720℃, and then removed from the furnace and air-cooled.

[0017] Further, in step S1, the billet comprises, by mass percentage: C ≤ 0.05%, Cr 13.50-16.00%, Ni 24.44-27.00%, Mo 1.00-1.50%; Al ≤ 0.40%; Ti 2.00-2.50%; V 0.001-0.010%; B 0.001-0.010%; Si ≤ 1.00%; Mn 1.00-2.00%, P ≤ 0.030%; S ≤ 0.020%; with the balance being Fe.

[0018] Furthermore, the Ti content is 7 to 9 times the Al content.

[0019] Furthermore, in step S1, the difference in Al content between the head and tail of the billet is Δ≤0.3%; the difference in Ti content between the head and tail of the billet is Δ≤0.3%.

[0020] Furthermore, in step S2, the billet is heated before drawing, with the core temperature of the billet ≥1000℃ or the surface temperature greater than 900℃.

[0021] Furthermore, in step S2, the lengthening is performed using a method of narrow anvil at the top and frustum at the bottom.

[0022] Furthermore, in step S7, the billet is charged into the furnace at ≤450°C.

[0023] Furthermore, in step S7, the billet is held at 960–980°C for 120 minutes.

[0024] Furthermore, in step S8, the billet is charged into the furnace at ≤450°C.

[0025] Furthermore, in step S8, the billet is kept at 700-720°C for 14-18 hours.

[0026] In summary, the present invention has the following beneficial effects:

[0027] 1. In iron-based high-temperature alloys, the γ' phase plays a major strengthening role. Al and Ti are the main elements forming the γ' phase. Increasing the Ti content can significantly improve the strength after heat treatment. However, the Ti content is strictly controlled to be 7 to 9 times that of Al. The formation of TiC increases, and TiC will significantly reduce the impact toughness of the material. In order to ensure that the mechanical properties of the forgings reach a stable high level.

[0028] 2. Controlling the difference in Ti and Al content between the head and tail of the billet ingot can significantly improve the mechanical properties of the alloy and make the mechanical properties of the upper and lower parts of the forging consistent, thus suppressing uneven stress distribution.

[0029] 3. Solution cooling at a high temperature of 960–980℃ prevents stress deformation caused by excessively rapid and uneven cooling of large forgings. Rapid water cooling from air cooling to 900–910℃ allows the γ' phase reinforcing phase to fully integrate into the material matrix, resulting in coherent distortion between them. This distortion hinders dislocation movement, thus producing a significant strengthening effect.

[0030] 4. This allows the alloy to fully absorb the second phases γ', γ" and carbides precipitated from the supersaturated solid solution during subsequent aging processes, thereby strengthening the alloy. These second phases can hinder dislocation movement, thus improving the strength and hardness of the material and ensuring the high performance of the forging.

[0031] 5. During repeated stretching cycles, iron-based superalloys undergo a series of compression and tensile deformations. This repeated strain and strain rate promote the diffusion and uniform distribution of alloying elements, while making the precipitates in the alloy finer, more dispersed, and more uniformly distributed, resulting in more γ' strengthening phases. These precipitates can effectively hinder dislocation movement and improve the alloy's hardness, fatigue resistance, and high-temperature strength.

[0032] 6. During the cyclic elongation process, defects such as cracks and shrinkage at grain boundaries and dislocations in the alloy will be gradually repaired and filled. At the same time, the dislocation density inside the grains will also increase, and the structure will become more compact and uniform.

[0033] 7. The amount of pressure applied each time is H1 = 0.1~0.2H, to prevent defects such as folding at the step in the middle of each pressure.

[0034] 8. After drawing, the billet is fed into the furnace with a square interface formed by chamfering the edges. At the chamfer, the concentration gradient increases, and the concentration difference of the diffusing substance becomes more obvious, thus increasing the diffusion rate. Furthermore, the increased surface area at the edges further enhances the diffusion rate of the diffusing substance. Simultaneously, the chamfer structure also increases the diffusion path of the diffusing substance, making the diffusion process more uniform and ultimately enhancing the high-temperature diffusion effect. Attached Figure Description

[0035] Figure 1 This is a schematic diagram illustrating the steps of forming an ultra-large integral rotor retaining ring forging.

[0036] Figure 2 This is a schematic diagram of step S2.

[0037] Figure 3 This is an ultrasonic testing image of the forging obtained in Example 1.

[0038] Figure 4 This is an ultrasonic testing image of the forging obtained in Example 1. Detailed Implementation

[0039] Example 1:

[0040] A method for forming an ultra-large integral rotor retaining ring forging, such as Figure 1 As shown, it includes the following steps:

[0041] Step S1: Blanking and billet preparation. The resulting billet ingot comprises, by mass percentage: C≤0.05%, Cr13.50-16.00%, Ni24.44-27.00%, Mo1.00-1.50%; Al≤0.40%; Ti2.00-2.50%; V0.001-0.010%; B0.001-0.010%; Si≤1.00%; Mn1.00-2.00%, P≤0.030%; S≤0.020%; with the balance being Fe.

[0042] The carbon content is controlled to be ≤0.05% in order to suppress the formation of excessive metal carbides.

[0043] The Ti content should be 7 to 9 times that of the Al content. While aluminum (Al) possesses good oxidation resistance, it readily reacts with oxygen at high temperatures to form oxides. Excessive Ti content leads to the formation of a surface oxide film on the alloy, while excessive Al content results in the formation of oxides with lower melting points, both of which negatively impact the alloy's performance. A suitable Ti-to-Al ratio promotes the formation of appropriate precipitates, such as the Ti(Al,Cr)2 phase, which can improve the alloy's hardness and high-temperature strength.

[0044] The difference in Al content between the beginning and end of the billet is Δ≤0.3%; the difference in Ti content between the beginning and end of the billet is Δ≤0.3%.

[0045] Step S2, reforging, such as Figure 2 As shown, the billet is drawn, with a feed rate W1 = 0.3~0.6W and a pressing rate H1 = 0.1~0.2H. The billet is then rotated 180° to repeat the drawing process, followed by a 90° rotation to complete one drawing cycle. This cycle is repeated until the target size is reached. Specific deformation parameters are shown in Table 1.

[0046] During the billet drawing process, the core temperature of the billet is ≥1000℃, or the surface temperature is greater than 900℃.

[0047]

[0048] Table 1

[0049] Step S3, upsetting, vertical upsetting, upsetting deformation ≥40%. In this embodiment, the billet height before upsetting is 2400mm, the size after upsetting is 1200mm, and the upsetting deformation is 50%. Repeat the drawing process once, with the same dimensions as above.

[0050] Step S4: Punching the blank. The blank is punched with a punch with a diameter of φ530mm. After punching, the inner diameter of the blank is 530mm±20mm, and the blank size is Ф1660×Ф530±30×940±20(mm).

[0051] Step S5, billet frame enlargement hole leveling height, forging dimensions: Ф2950±30×Ф2500±30×920(mm).

[0052] Step S6: Ring rolling of the billet to: Ф5032±8×Ф4780±8×900±8 (mm). Control the speed change: 2-5mm / s in the initial rolling stage, 8-12mm / s in the main rolling stage, and 4-8mm / s in the deceleration stage. When the distance reaches the final diameter of 100-200mm, lift it onto the conical roll for the rounding stage.

[0053] Step S7, billet solution treatment: The billet is charged into the furnace at 400°C, heated to 960°C, held for 120 minutes, then air-cooled to 900°C, and finally water-cooled to room temperature. The billet temperature is based on the temperature displayed by the load thermocouple for temperature control.

[0054] Step S8, Aging Treatment: The billet is charged into the furnace at 400℃, heated to 700℃, held for 14 hours, and then air-cooled after being removed from the furnace. A retaining ring is obtained.

[0055] Step S9: Sampling of the retaining ring.

[0056] Step S10: Physical and chemical testing of the protective ring.

[0057] Step S11, machining of the retaining ring.

[0058] Step S12: Ultrasonic flaw detection of the retaining ring.

[0059] Example 2:

[0060] The steps differ from those in Example 1 in that:

[0061] Step S7, billet solution treatment: The billet is charged into the furnace at 400°C, heated to 970°C, held for 120 minutes, then air-cooled to 900°C, and finally water-cooled to room temperature. The billet temperature is based on the temperature displayed by the load thermocouple for temperature control.

[0062] Step S8, Aging treatment: The billet is charged into the furnace at 400°C, heated to 710°C, held for 15 hours, and then removed from the furnace and air-cooled.

[0063] Example 3:

[0064] The steps differ from those in Example 1 in that:

[0065] Step S7, billet solution treatment: The billet is charged into the furnace at 400°C, heated to 980°C, held for 120 minutes, then air-cooled to 900°C, and finally water-cooled to room temperature. The billet temperature is based on the temperature displayed by the load thermocouple for temperature control.

[0066] Step S8, Aging treatment: The billet is charged into the furnace at 400°C, heated to 720°C, held for 18 hours, and then removed from the furnace and air-cooled.

[0067] Comparative Example 1:

[0068] The steps differ from those in Example 1 in that:

[0069] First, the blank is enlarged using a frame, and the inner diameter of the blank after enlargement is 530mm.

[0070] The billet is then heated to 980℃ and held for 120 minutes, followed by air cooling to 900℃.

[0071] The final forging dimensions are: Ф2950±30×Ф2500±30×920 (mm).

[0072] Microcracks appeared in the forging.

[0073] Comparative Example 2:

[0074] The steps differ from those in Example 1 in that:

[0075] Step S7, billet solution treatment: The billet is heated to 980℃ and held for 120 minutes, then the billet is water cooled to room temperature.

[0076] Finally, ultrasonic nondestructive testing was performed on the forging, and the test results are shown in the figure. Figure 4 .

[0077] Results analysis: The presence of obvious noise signals indicates that during the propagation of ultrasonic waves inside the forging, they encountered defects such as cracks, inclusions, and pores, resulting in reflection, scattering, or attenuation.

[0078] Comprehensive performance testing of forgings:

[0079] The performance requirements for the ring components are detailed in Table 2.

[0080]

[0081] Table 2

[0082] Actual results of room temperature tensile testing of forgings:

[0083] Two samples were taken from each of the four quadrants: one at room temperature, one at 100°C for high-temperature tensile testing, and one at room temperature for impact testing. The test results are as follows: the results of the room temperature test are shown in Table 3, and the results of the 100°C test are shown in Table 4.

[0084]

[0085]

[0086] Table 3

[0087]

[0088]

[0089]

[0090] Table 4

[0091] Impact results: See Table 5 for details.

[0092]

[0093] Table 5

[0094] Ultrasonic testing of forgings:

[0095] Testing criteria: The retaining ring forgings shall be subjected to 100% ultrasonic testing in accordance with the method specified in JB / T4010.

[0096] Inspection methods: The outer circle is inspected using transverse and longitudinal waves, while the two end faces are inspected using longitudinal waves.

[0097] Longitudinal wave testing must meet the following requirements:

[0098] a) During end-face scanning, no display exceeding 10% is permitted; displays less than 10% must not exceed 10%.

[0099] No more than one per 100 mm² area;

[0100] b) During radial scanning, reflected signals with an equivalent diameter equal to or greater than 2 mm are not allowed.

[0101] c) All displays with an equivalent diameter exceeding 1.6 mm shall be recorded and reported to the ordering party.

[0102] Whether internal defects exceeding the above provisions are permissible shall be handled through negotiation between the two parties, except for hazardous defects such as cracks and shrinkage cavities.

[0103] Shear wave testing must meet the following requirements:

[0104] Within any 100mm wide full circumference, there should be no more than 4 defect signals between the 1 / 2 reference line and the 1 / 4 reference line, and the distance between any two adjacent defects should not be less than 50mm.

[0105] in conclusion:

[0106] like Figure 3 As shown, there is no obvious noise signal, indicating that during the propagation of the ultrasonic waves inside the forging, they encounter internal defects such as cracks, inclusions, and pores, resulting in reflection, scattering, or attenuation. This indirectly proves that the internal structure of the forging is uniform and dense.

[0107] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0108] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for forming an ultra-large integral rotor retaining ring forging, characterized in that, Includes the following steps: Step S1: Blanking and manufacturing the billet; Step S2, reforging, the billet is drawn out, the billet feed amount W1=0.3~0.6W, the downward pressure H1=0.1~0.2H, then the billet is flipped 180° to repeat the drawing process, then the billet is flipped 90° to repeat the drawing process, completing one drawing cycle, repeating the drawing cycle until the target size is reached; Step S3, upsetting, vertical upsetting, upsetting deformation ≥40%; Step S4: Punching holes in the blank; Step S5: Expand the hole in the billet using a frame; Step S6, ring rolling of the billet; Step S7, billet solution treatment: The billet is heated to 960~980℃, then air-cooled to 900~910℃, and finally water-cooled to room temperature; Step S8, aging treatment: The billet is heated to 700℃~720℃, and then removed from the furnace and air-cooled; In step S1, the billet comprises, by mass percentage: C≤0.05%, Cr13.50-16.00%, Ni24.44-27.00%, Mo1.00-1.50%; Al≤0.40%; Ti2.00-2.50%; V0.001-0.010%; B0.001-0.010%; Si≤1.00%; Mn1.00-2.00%, P≤0.030%; S≤0.020%; the balance being Fe; The Ti content is 7 to 9 times the Al content; In step S1, the difference in Al content between the beginning and end of the billet is Δ≤0.3%; the difference in Ti content between the beginning and end of the billet is Δ≤0.3%. In step S2, the billet is heated before drawing, and the core temperature of the billet is ≥1000℃ or the surface temperature is greater than 900℃. In step S7, the billet is held at 960–980°C for 120 min; In step S8, the billet is kept at 700-720℃ for 14-18 hours.

2. The method for forming an ultra-large integral rotor retaining ring forging according to claim 1, characterized in that: In step S2, the lengthening process is performed using a narrow anvil at the top and a frustum at the bottom.

3. The method for forming an ultra-large integral rotor retaining ring forging according to claim 1, characterized in that: In step S7, the billet is charged into the furnace at ≤450°C.

4. The method for forming an ultra-large integral rotor retaining ring forging according to claim 1, characterized in that: In step S8, the billet is charged into the furnace at ≤450°C.

Images