Processing method of 25crni1mov steel rotating shaft forging

Abstract

The application discloses a 25CrNi1MoV steel rotating shaft forging machining method, which comprises the following steps: smelting and ingot casting process, adopting the process route of electric furnace initial smelting, LF furnace refining, VD furnace degassing, LF furnace refining and down pouring casting to prepare 25CrNi1MoV down pouring single vacuum steel ingot; forging process, hot sending forging heating after steel ingot solidification demolding, and the forging temperature range is controlled to be 1260-850 DEG C; the forging process comprises the following steps: first fire forging, steel ingot pressure jaw, chamfering and bottom cutting; second fire forging, upsetting, lengthening and eight square pressing by adopting WHF method; third fire forging, upsetting and flat pressing; fourth fire forging, circle pressing, number printing, step forging and product finishing; and heat treatment process, comprising post-forging heat treatment and performance heat treatment. The machining method can meet the requirements of rotating shaft on material high purity homogeneity, meet the requirements of rotating shaft flaw detection, meet the requirements of rotating shaft comprehensive mechanical properties, and can save cost and improve machining efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of forging, and more particularly to a 25CrNi1MoV steel rotating shaft forging processing method. BACKGROUND

[0002] The rotating shaft of a generator is a key large-sized part in a generator set device, and its manufacturing process involves key working procedures such as smelting ingot, forging and heat treatment, etc. In order to improve product competitiveness and reduce manufacturing cost, the material selection of the rotating shaft is changed from traditional 30(25)Cr2Ni4MoV, Ni3.5CrMoV, Ni3.5MoV, Ni2.8CrMoV and Ni2CrMoV to relatively low-alloy 25CrNi1MoV steel.

[0003] When the generator is running at high speed, the rotating shaft of the generator has to bear huge centrifugal force, and at the same time, has to bear the bending moment caused by the transmission torque and the dead weight, the comprehensive working condition is complex, and the rotating shaft forging of the generator is required to have high strength and plasticity, superior toughness, low brittle transition temperature, good magnetic conductivity, therefore, the 25CrNi1MoV steel rotating shaft forging is required to have uniform chemical composition, dense forging body and good comprehensive mechanical properties.

[0004] However, in order to achieve the goal of uniform chemical composition of the 25CrNi1MoV steel rotating shaft forging, dense forging body and good comprehensive mechanical properties of the forging, the conventional forging processing method of the prior art is difficult to meet the design technical target, meet the manufacturing economic requirement and achieve the carbon reduction and emission reduction target. Therefore, it is necessary to develop a 25CrNi1MoV steel rotating shaft forging processing method to ensure the internal organization and performance requirements of the rotating shaft forging, and at the same time, save cost and improve processing efficiency. SUMMARY

[0005] In order to solve part or all of the technical problems existing in the prior art, the application provides a 25CrNi1MoV steel rotating shaft forging processing method, which comprises the following working procedures:

[0006] (1) Smelting and ingot casting working procedure

[0007] In the smelting and ingot casting process, the process route of electric furnace primary smelting-LF furnace refining-VD furnace degassing-LF furnace refining- pouring casting is adopted to prepare 25CrNi1MoV pouring single vacuum steel ingot, and the chemical composition of the steel ingot is controlled as follows in percentage by mass: C: 0.22-0.28%, Mn: 0.40-0.70%, Si: 0.15-0.30%, S: ≤0.018%, P: ≤0.015%, Cr: 1.00-1.50%, Ni: 1.00-1.50%, Mo: 0.25-0.40%, V: 0.05-0.15%, Cu: ≤0.20%, Al: ≤0.025%, Sn: ≤0.025%, Sb: ≤0.0015;

[0008] (2)Forging process

[0009] After the steel ingot is solidified and demoulded, the surface temperature of the steel ingot is controlled to be not lower than 700℃ for hot forging heating, the forging temperature range is controlled to be 1260-850℃, the total forging ratio is controlled to be greater than 6, the forging ratio during upsetting and elongating is controlled to be greater than 2, and the specific process of the forging process is as follows:

[0010] a. First fire forging: steel ingot pressure jaw, chamfering, cutting bottom;

[0011] b. Second fire forging: upsetting, elongating and eight-side pressing by WHF method;

[0012] c. Third fire forging: upsetting and flat pressing;

[0013] d. Fourth fire forging: round pressing, marking, forging out steps and finishing products;

[0014] (3) Heat treatment process

[0015] The heat treatment process includes post-forging heat treatment and performance heat treatment, the post-forging heat treatment includes: after the shaft is air-cooled, first low-temperature normalizing treatment and high-temperature normalizing treatment are performed, then after the shaft is air-cooled again, second low-temperature normalizing treatment and high-temperature normalizing treatment are performed, and then after the shaft is air-cooled again, tempering treatment is performed; the performance heat treatment is performed in a quenching and high-temperature tempering manner, including quenching treatment and high-temperature tempering treatment.

[0016] Further, in the above-mentioned 25CrNi1MoV steel shaft forging processing method:

[0017] In the smelting and ingot casting process, the process carbon content is controlled to be ≥0.60% during the electric furnace primary smelting, the decarburization amount of the primary smelted molten steel is controlled to be ≥0.30%, and the tapping temperature is controlled to be ≥1660℃; during pouring casting, the argon curtain is used to protect the whole process at a pressure of 0.15-0.30 MPa, and after the pouring is completed, the heating agent and the covering agent are added at the same time to strengthen the riser heat preservation;

[0018] In the first fire forging of the forging process, the ingot is heated to 1250±10℃ in a heating furnace and kept for 10h, when the ingot is discharged and the tongs are pressed, the ingot surface defects such as heavy skin and slag inclusion are pressed to the tongs along the ingot head line about 50mm of the ingot body, the forging defects at the root of the tongs are removed after the tongs are pressed, and the center axis of the tongs is consistent with the center of the ingot when the tongs are pressed; after the tongs are pressed and the bottom of the ingot is cut, the height-diameter ratio is controlled to be 2-2.2 according to the size of the ingot;

[0019] In the second fire forging of the forging process, the blank is reheated to 1250±10℃ and kept for 24h; the blank is roughened by using a press, a leakage disc and a spherical top pier head; WHF elongation is performed by using upper and lower wide flat anvil, the deformation amount of double-side pressing is controlled to be 18-22%, the blank is pressed to flat square after one pass, and then the blank is chamfered to reach eight square;

[0020] In the third fire forging of the forging process, the blank is reheated to 1250±10℃ and kept for 19h; the blank is roughened by using a press, a leakage disc and a spherical top pier head, and elongation and flat square are performed by using upper and lower flat anvil, the deformation amount of double-side pressing is controlled to be 18-22%;

[0021] In the fourth fire forging of the forging process, the blank is reheated to 1220±10℃ and kept for 8h; the blank is pressed to round by using upper and lower flat anvil, the blank is marked, the shaft body and two end steps are forged, the roundness is corrected, and the final forming of the shaft forging is performed.

[0022] As a specific embodiment, the above-mentioned 25CrNi1MoV steel shaft forging machining method is used to manufacture a shaft forging for a 100MW generator set, the outer diameter specification of the shaft forging is Wherein:

[0023] In the first fire forging of the forging process, the ingot is pressed to tongs, chamfered, and cut to bottom, and finally the ingot is pressed to round

[0024] In the second fire forging of the forging process, the blank is roughened to by using a 125MN press, a leakage disc and a spherical top pier head, WHF elongation is performed by using upper and lower 1700mm wide flat anvil, the deformation amount of double-side pressing is controlled to be 20%, the feeding amount is greater than 90% of the anvil width during strong pressing, the anvil feeding amount is 100-200mm each time, the blank is pressed to flat square 1550mm×1680mm by 6 passes, and then the blank is chamfered to reach eight square 1500mm×3095mm, the WHF pressing process parameters are controlled according to the following table:

[0025] ​

[0026] In the third fire forging of the forging process, the blank is upset to In the third fire forging of the forging process, the blank is upset to The blank is elongated and flattened to 1275mm*945mm by using the upper and lower 850mm flat anvil, and the deformation amount of double-side reduction is controlled to be 20%;

[0027] In the fourth fire forging of the forging process, the blank is upset to

[0028] The post-forging heat treatment of the heat treatment process comprises: (1) the first low-temperature normalizing treatment and high-temperature normalizing treatment, the shaft is air-cooled to 300-350 DEG C, and then heated to 660-680 DEG C at a heating rate of less than or equal to 40 DEG C / h, and then heated to 900-950 DEG C, and then air-cooled to be discharged from the furnace; (2) the second low-temperature normalizing treatment and high-temperature normalizing treatment, the shaft is air-cooled to 280-320 DEG C, and then heated to 660-680 DEG C at a heating rate of less than or equal to 40 DEG C / h, and then heated to 870-900 DEG C, and then air-cooled to be discharged from the furnace; (3) the tempering treatment, the shaft is air-cooled to 280-320 DEG C, and then heated to 640-660 DEG C at a heating rate of less than or equal to 40 DEG C / h, and then air-cooled to be discharged from the furnace;

[0029] The performance heat treatment of the heat treatment process comprises: (1) the quenching treatment, the shaft is heated to less than or equal to 300 DEG C, and then heated to 640-660 DEG C at a heating rate of less than or equal to 60 DEG C / h, and then heated to 860-900 DEG C, and then air-cooled for 2 minutes and then water-cooled for 3-4 h, and then discharged from the water when the surface temperature of the shaft body is less than or equal to 200 DEG C; (2) the high-temperature tempering treatment, the shaft is kept at 290-310 DEG C for 6 h, and then heated to 600-650 DEG C at a heating rate of less than or equal to 50 DEG C / h, and then kept for 28-30 h, and then air-cooled to less than or equal to 200 DEG C at a cooling rate of less than or equal to 50 DEG C / h, and then discharged from the furnace.

[0030] The 25CrNi1MoV steel shaft forging processing method of the present application innovatively solves the problems of high-purity homogeneous steel ingot manufacturing, forging forming and flaw detection, and product organization and mechanical property of the shaft forgings, fills the technical gap, and specifically has the following advantages and beneficial effects:

[0031] (1) The process route of short-flow electric furnace initial refining-LF furnace refining-VD furnace degassing-LF furnace refining-bottom pouring is adopted, the material composition and gas content are controlled, the high-purity homogeneous requirement of the shaft forgings for the material is met, and then the strict requirement of the shaft flaw detection is met;

[0032] (2) The forging process adopts the forging penetration compaction method under the multi-process path of axisymmetric loading, the forging heating times are four, the WHF method is used to make the blank, and the cast state organization is effectively broken, and the internal defects of the steel ingot are compacted;

[0033] (3) The heat treatment process includes post-forging heat treatment and performance heat treatment, the post-forging heat treatment adopts twice high-low temperature normalizing and tempering treatment, the performance heat treatment adopts quenching plus high-temperature tempering and water cooling, the grain is refined, the internal organization is improved, the comprehensive mechanical property requirements of the rotating shaft are met, and the flaw detection requirements are further met;

[0034] (4) The rotating shaft forgings are batch manufactured in the one ingot one piece manufacturing mode, one-time qualified, and the purposes of saving cost and improving processing efficiency are achieved. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings. In the drawings:

[0036] Figure 1 It is a flowchart of the 25CrNi1MoV steel rotating shaft forging processing method of the present application;

[0037] Figure 2 It is a schematic diagram of the deformation form of the forging in each process step of the 25CrNi1MoV steel rotating shaft forging processing method of the present application, wherein (a) is a schematic diagram of a steel ingot, (b) is a schematic diagram of a blank with pressed jaws, chamfered and bottomed, (c) is a schematic diagram of a blank with roughed steel ingot, WHF lengthened and eight-sided pressed, (d) is a schematic diagram of a blank with roughed steel ingot and flattened square, (e) is a schematic diagram of a blank with round pressed, numbered and stepped forged, and (f) is a schematic diagram of a finished forging;

[0038] Figure 3 It is a timing diagram of post-forging heat treatment in the 25CrNi1MoV steel rotating shaft forging processing method of the present application;

[0039] Figure 4 It is a timing diagram of performance heat treatment in the 25CrNi1MoV steel rotating shaft forging processing method of the present application. DETAILED DESCRIPTION

[0040] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in combination with specific embodiments of the present application and corresponding drawings. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0041] As shown in the figure, the 25CrNi1MoV steel rotating shaft forging processing method of the present application comprises the following steps: Figure 1

[0042] (1) Smelting and ingot casting process

[0043] In the smelting and ingot casting process, the process route of electric furnace primary smelting→LF furnace refining→VD furnace degassing→LF furnace refining→down pouring casting is adopted, and the content of O, S and P is reduced by optimizing the composition of molten steel, the number of non-metallic inclusions is reduced, the morphology and distribution of inclusions are controlled, and the purity of the ingot is improved, so as to prepare a high-purity homogeneous low-segregation 25CrNi1MoV down-pouring single vacuum ingot;

[0044] In the smelting and ingot casting process, the chemical composition of the ingot is controlled as follows in terms of mass percentage: C: 0.22-0.28%, Mn: 0.40-0.70%, Si: 0.15-0.30%, S≤0.018%, P≤0.015%, Cr: 1.00-1.50%, Ni: 1.00-1.50%, Mo: 0.25-0.40%, V: 0.05-0.15%, Cu≤0.20%, Al≤0.025%, Sn≤0.025%, Sb≤0.0015;

[0045] In the smelting and ingot casting process, during the electric furnace primary smelting, the process carbon content is controlled to be≥0.60%, the P removal operation is strengthened during the oxidation period to prevent the over-oxidation of the molten steel, the decarburization amount of the primary smelted molten steel is ensured to be≥0.30%, the slag sticking operation during tapping is controlled to avoid the introduction of oxidized slag, and the tapping temperature is controlled to be≥1660℃;

[0046] In the smelting and ingot casting process, during the LF furnace refining, the LF furnace is used for front and middle period smelting, all the added alloys and auxiliary materials are strictly roasted to reduce the hydrogen content, the diffusion deoxidation is performed by using carbon powder and ferrosilicon powder, the reducing agent is scattered on the surface of the slag layer in batches to prevent the carbon pick-up of the molten steel, so as to control the composition of the molten steel, and when the slag color becomes white, the [O] in the molten steel is≤8ppm, and the temperature is≥1640℃, the VD furnace degassing treatment is performed;

[0047] ​In the smelting and ingot casting process, the cleanliness and dryness of the flow steel pouring system and the pouring speed are controlled well during the pouring process, a special base is used to reduce the turbulence of molten steel during the pouring process, to prevent molten steel from rolling slag, and the ingot mold and refractory materials used are carefully blown to ensure cleanliness. The pouring process uses an argon curtain to protect the whole process at 0.15-0.30 MPa, reducing the secondary oxidation of molten steel, and finally adding a heating agent after the pouring is completed to add a covering agent to strengthen the riser insulation.

[0048] Through the above measures in the smelting and ingot casting process, the [H] in the molten steel is ≤1.0 ppm, T.O is ≤15 ppm, [N] is ≤70 ppm, the inclusion A, B, C, D coarse and fine system is controlled at ≤0.5 level, and the DS is controlled at ≤1.0 level, thereby ensuring the UT flaw detection equivalent requirement of the finished forging.

[0049] (2) Forging process

[0050] After the ingot is solidified and demoulded, the surface temperature of the ingot is controlled to be not lower than 700℃ for hot forging heating, and the ingot schematic diagram is shown in (a) of Figure 2 The forging temperature range is controlled to be 1260-850℃, and the total forging ratio is controlled to be greater than 6, wherein the forging ratio during the upsetting and elongation is controlled to be greater than 2; the relatively low thermal deformation resistance and good plasticity of the 25CrNi1MoV steel are fully utilized, the axisymmetric loading, multi-process path, dense forging and organization refinement method are adopted for the shaft forging, the ingot is deformed and recrystallized after forging, the original coarse dendrite and columnar grain of the ingot are transformed into uniform and fine recrystallized structure, and the original segregation, pores, looseness and slag inclusion in the ingot are compacted and welded through high-temperature deformation, so that a more dense structure is obtained, thereby improving the flaw detection qualification rate and comprehensive mechanical properties of the forging. The specific process of the forging process is as follows:

[0051] a. First fire forging: ingot pressing jaw, chamfering and bottom cutting. After the ingot is heated to 1250±10℃ in the heating furnace, it is kept for 10h; when the ingot is pressed out of the jaw, the ingot surface defects such as heavy skin and slag inclusion are pressed onto the jaw along the ingot riser line about 50mm above the ingot body, so as to avoid being brought into the forging, and the forging defects at the root of the jaw are removed after the jaw is pressed, and the center axis of the jaw is made consistent with the center of the ingot during the pressing of the jaw, so as to prepare for the subsequent forging process; after the ingot is pressed, the bottom is cut, and according to the size of the ingot, the height-diameter ratio is controlled to be 2-2.2, and finally the ingot is pressed round. The blank schematic diagram of ingot pressing jaw, chamfering and bottom cutting is shown in (b) of Figure 2 .

[0052] b. Second fire forging: roughing, lengthening and octagonalizing by WHF (Wide Anvil Heavy Forging) method. After the billet is reheated to 1250±10℃ and kept for 24h, the billet is roughed by using the press, the leakage disc and the spherical top roughing cap. The dendritic casting structure of the ingot is broken by the roughing deformation, the transverse performance of the shaft is improved and the mechanical property anisotropy is reduced. The lengthening is performed by using the upper and lower wide flat anvil, the deformation of the double-sided reduction is controlled to be 18-22%, the workpiece is turned over by 90° after one pass, the half anvil is staggered, and one pass is pressed to ensure that each region of the billet can be subjected to heavy deformation and the deformation uniformity of the billet is ensured to obtain the forging effect of overall compaction, fine and uniform grains and consistent performance. The billet is compacted to a flat square by multiple passes, and then is chamfered to achieve an octagonal shape. The surface defects such as surface cracks and indentation are cleaned by using the oxygen lance. The schematic diagram of the billet roughed, lengthened and octagonalized by the ingot is shown in (c) of FIG. 1. Figure 2

[0053] c. Third fire forging: roughing and flat square forging. After the billet is reheated to 1250±10℃ and kept for 19h, the billet is roughed by using the press, the leakage disc and the spherical top roughing cap. The lengthening and flat square forging are performed by using the upper and lower flat anvil, the deformation of the double-sided reduction is controlled to be 18-22%, and the purpose of realizing the densification of the metal structure inside the billet, completely eliminating the porosity defects and segregation, and improving the coarse grain structure is ensured. The surface defects such as surface cracks and indentation are cleaned by using the oxygen lance. The schematic diagram of the billet roughed and flat square forged by the ingot is shown in (d) of FIG. 1. Figure 2

[0054] d. Fourth fire forging: round, marking, forging steps and finishing. After the billet is reheated to 1220±10℃ and kept for 8h, the round, marking, shaft body and two end steps are forged by using the upper and lower flat anvil, and the round is corrected to perform the final forming of the shaft forging. The schematic diagram of the billet round, marked and forged with steps by the ingot is shown in (e) of FIG. 1, and the schematic diagram of the finished forging is shown in (f) of FIG. 1. Figure 2 Figure 2

[0055] (3) Heat treatment process

[0056] The heat treatment process includes post-forging heat treatment and performance heat treatment. After the shaft forging is formed, the excess material at both ends is cut by using the air cutting according to the required size of the finished shaft, and the post-forging heat treatment is performed, including: after the shaft is air cooled, the first low-temperature normalizing treatment and high-temperature normalizing treatment are performed, then after the shaft is air cooled again, the second low-temperature normalizing treatment and high-temperature normalizing treatment are performed, and then after the shaft is air cooled again, the tempering treatment is performed, so as to meet the requirements of adjusting the structure and refining the grains by three times of undercooling and two times of austenitizing; after the post-forging heat treatment, the performance heat treatment is performed on the shaft, the performance heat treatment is performed by using the quenching and high-temperature tempering and water cooling, including quenching and high-temperature tempering, so as to meet the comprehensive mechanical properties of the shaft.

[0057] ​​​​The 25CrNi1MoV steel rotating shaft forging processing method of the embodiment of the present application is used to manufacture the rotating shaft forging for 100MW generator set in one ingot per piece manufacturing forming mode, and the outer diameter specification of the rotating shaft forging is The internal UT flaw detection requirement is strict, and no dense defects with equivalent diameter greater than or equal to No single defect with equivalent diameter greater than The rotating shaft forging belongs to a typical long shaft forging with large cross-section transmission end flange and special shape.

[0058] The 25CrNi1MoV steel rotating shaft forging processing method of the embodiment of the present application is performed according to the above smelting and ingot casting process, forging process and heat treatment process, and specifically:

[0059] In the first fire forging of the forging process, the steel ingot is pressed, the edge is chamfered, the bottom is cut, and finally the steel ingot is pressed to

[0060] In the second fire forging of the forging process, the blank is roughened to by using the 125MN press, WHF elongation is performed by using the upper and lower 1700mm wide flat anvil, the deformation amount of double-sided pressing is controlled to be 20%, the feeding amount is greater than 90% of the anvil width during strong pressing, the anvil amount is 100-200mm each time, the blank is pressed to flat square 1550mmx1680mm through 6 passes of pressing, the blank is chamfered to achieve eight square 1500mmx3095mm, and the WHF pressing process parameters are controlled according to the following table 1:

[0061] Table 1 WHF pressing process parameters

[0062]

[0063] In the third fire forging of the forging process, the blank is roughened to by using the 125MN press, Elongation and flat square pressing are performed by using the upper and lower 850mm flat anvil, the deformation amount of double-sided pressing is controlled to be 20%, and the blank is elongated and pressed to flat square 1275mmx945mm;

[0064] In the fourth fire forging of the forging process, the blank is pressed to by using the upper and lower 850mm flat anvil, and then the finished product rotating shaft forging with the outer diameter specification of can be finally formed by machining;

[0065] In the heat treatment process, the blank is heated to Figure 3The time sequence diagram shown is for post-forging heat treatment, and the performance heat treatment is carried out according to Figure 4 The time sequence diagram shown is for performance heat treatment. The post-forging heat treatment specifically comprises: (1) first low-temperature normalizing treatment and high-temperature normalizing treatment, air cooling the shaft to 300-350℃, heating to 660-680℃ at a heating rate of ≤40℃ / h, holding for 10h, then heating the shaft to 900-950℃, holding for 18-20h, and air cooling to leave the furnace; (2) second low-temperature normalizing treatment and high-temperature normalizing treatment, air cooling the shaft to 280-320℃, holding for 20h, then heating to 660-680℃ at a heating rate of ≤40℃ / h, holding for 10h, then heating the shaft to 870-900℃, holding for 18-20h, and air cooling to leave the furnace; (3) tempering treatment, air cooling the shaft to 280-320℃, holding for 20h, then heating to 640-660℃ at a heating rate of ≤40℃ / h, holding for 40h, and furnace cooling to ≤150℃ before leaving the furnace. The performance heat treatment specifically comprises: (1) quenching treatment, heating the shaft to ≤300℃ to enter the furnace, heating to 640-660℃ at a heating rate of ≤60℃ / h, holding for 6h, then heating the shaft to 860-900℃, holding for 15-17h, air cooling for 2min, then water cooling for 3-4h, and leaving the water after the shaft body surface temperature is ≤200℃; (2) high-temperature tempering treatment, holding the shaft at 290-310℃ for 6h, then heating to 600-650℃ at a heating rate of ≤50℃ / h, holding for 28-30h, then air cooling to ≤200℃ at a cooling rate of ≤50℃ / h, and leaving the furnace.

[0066] Two 25CrNi1MoV steel shafts, i.e. a 1# shaft and a 2# shaft, manufactured by using the embodiment of the present application, are taken, and samples are taken from the shaft bodies of the shafts, and chemical composition detection is carried out, and the results are shown in Table 2:

[0067] Table 2: Results of chemical composition detection of shafts (% by mass)

[0068] Element Required Value Measured Value 1 # Spindle Measured Value 2 # Spindle C 0.22～0.28 0.24 0.25 Mn 0.40～0.70 0.57 0.57 Si 0.15～0.30 0.23 0.20 S ≤0.018 0.001 0.001 P ≤0.015 0.005 0.005 Cr 1.00～1.50 1.39 1.47 Ni 1.00～1.50 1.38 1.40 Mo 0.25～0.40 0.31 0.33 V 0.05～0.15 0.093 0.092 Cu ≤0.20 0.056 0.03 Al ≤0.025 0.010 0.010 Sn ≤0.025 ＜0.005 ＜0.005 Sb ≤0.0015 ＜0.0015 ＜0.0015 [H] ≤ 1 ppm 0.78 ppm 0.51 ppm

[0069] Two 25CrNi1MoV steel shafts, i.e. a 1# shaft and a 2# shaft, manufactured by using the embodiment of the present application, are taken, and samples are taken from the tangential, radial and / or core parts of the shafts, respectively, and mechanical property detection is carried out, and the results are shown in Table 3:

[0070] Table 3: Results of mechanical property detection of shafts

[0071]

[0072] In the above table, T1 refers to sampling at the small shaft end part of the shaft, and T3 refers to sampling at the shaft body part of the shaft.

[0073] As can be seen, the 25CrNi1MoV steel shaft forgings manufactured using the processing method of the present invention have uniform chemical composition, dense body, and good comprehensive mechanical properties.

[0074] In summary, compared with the prior art, the processing method for 25CrNi1MoV steel shaft forgings of the present invention innovatively solves the problems of manufacturing high-purity homogeneous steel ingots, forging forming and flaw detection, and product microstructure and mechanical properties of this type of shaft forging, filling a technological gap, and specifically has the following advantages and beneficial effects:

[0075] (1) The process route of short-process electric furnace primary refining → LF furnace refining → VD furnace degassing → LF furnace refining → casting is adopted. By controlling the material composition and gas content, the high purity and homogeneity requirements of the shaft forging are met, thereby meeting the strict requirements of shaft flaw detection.

[0076] (2) The forging process adopts the forging through compaction method under axisymmetric loading and multi-process path, and the forging fire is determined to be four fires. The WHF method is used to make billets, effectively breaking the as-cast structure and compacting the internal defects of the steel ingot.

[0077] (3) The heat treatment process includes post-forging heat treatment and performance heat treatment. Post-forging heat treatment adopts two high and low temperature normalizing and tempering treatments. Performance heat treatment adopts quenching and tempering treatment with high temperature tempering and water cooling to refine grains, improve internal structure, meet the comprehensive mechanical performance requirements of the shaft, and further meet the flaw detection requirements.

[0078] (4) The shaft forgings are manufactured in batches using a one-ingot-one-piece manufacturing and forming method, and are qualified in one go, so as to save costs and improve processing efficiency.

[0079] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Additionally, the terms "front," "back," "left," "right," "upper," and "lower" in this document refer to the placement shown in the accompanying drawings.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for machining 25CrNi1MoV steel shaft forgings, characterized in that, The process includes the following steps: (1) Smelting and casting processes In the smelting and ingot casting process, the following process route is adopted: electric furnace primary smelting → LF furnace refining → VD furnace degassing → LF furnace refining → casting. 25CrNi1MoV casting single-vacuum steel ingots are prepared. The chemical composition of the ingots is controlled by mass percentage as follows: C: 0.22~0.28%, Mn: 0.40~0.70%, Si: 0.15~0.30%, S≤0.018%, P≤0.015%, Cr: 1.00~1.50%, Ni: 1.00~1.50%, Mo: 0.25~0. 0.40%, V: 0.05~0.15%, Cu≤0.20%, Al≤0.025%, Sn≤0.025%, Sb≤0.0015%. Among them, during the electric furnace primary smelting, the process carbon content is controlled at ≥0.60%, the decarburization of the primary smelting steel is controlled at ≥0.30%, and the tapping temperature is controlled at ≥1660℃. During the casting process, an argon curtain ring with 0.15~0.30MPa is used to protect the casting process. After the casting is completed, a heating agent is added and a covering agent is added at the same time to strengthen the riser insulation. (2) Forging process After the steel ingot solidifies and is demolded, the surface temperature of the steel ingot is controlled to be no less than 700℃ before hot forging. The forging temperature range is controlled to be 1260~850℃, and the total forging ratio is controlled to be greater than 6, of which the forging ratio during upsetting and drawing is controlled to be greater than 2. The specific process of forging is as follows: a. First forging: pressing the steel ingot into jaws, chamfering, and cutting the bottom. The steel ingot is heated to 1250±10℃ in the heating furnace and held for 10 hours. When pressing the jaws after exiting the furnace, the steel ingot with surface defects such as heavy scale and slag inclusions at the root of the riser is pressed onto the jaws along the riser line about 50mm from the ingot body. After pressing the jaws, the forging defects at the root of the jaws are removed by heat treatment. During the pressing process, the center axis of the jaws is aligned with the center of the steel ingot. After pressing the jaws and cutting off the bottom of the steel ingot, the height-to-diameter ratio is controlled to be 2~2.2 according to the size of the steel ingot. b. Second forging: Upsetting and drawing into an octagon using the WHF method. The billet is heated to 1250±10℃ in the furnace and held for 24 hours. The billet is upset using a press, a slotted pan and a spherical top upsetting cap. The billet is then drawn into an octagon using a wide and flat anvil. The deformation is controlled to be 18~22% after each pressing. After each pressing, the billet is rotated 90° and the anvil is staggered for another pressing. Through multiple pressings, the billet is compacted into a flat square shape. Then, the edges are beveled to make the billet octagonal. c. Third forging: upsetting and flattening. The billet is heated to 1250±10℃ in the furnace and held for 19 hours. The billet is upsetting using a press, a slotted pan and a spherical top upsetting cap. The billet is then elongated and flattened using upper and lower flat anvils. The deformation on both sides is controlled to be 18~22%. d. Fourth forging: pressing, marking, forging steps, and finishing the finished product. The billet is returned to the furnace and heated to 1220±10℃ and held for 8 hours. It is then pressed, marked, and the shaft body and the steps at both ends are forged using upper and lower flat anvils. The rounding is then corrected and the shaft forging is finally formed. (3) Heat treatment process The heat treatment process includes post-forging heat treatment and performance heat treatment. Post-forging heat treatment includes: air cooling the shaft and then performing a first low-temperature normalizing treatment and a high-temperature normalizing treatment, followed by air cooling again and then performing a second low-temperature normalizing treatment and a high-temperature normalizing treatment, followed by air cooling again and then tempering treatment. Performance heat treatment is carried out by quenching and tempering and water cooling, including quenching treatment plus high-temperature tempering treatment.

2. The method for processing 25CrNi1MoV steel shaft forgings according to claim 1, used to manufacture shaft forgings for 100MW generator sets, wherein the outer diameter of the shaft forging is Ø1008mm, characterized in that: In the first forging process, the steel ingot is pressed with jaws, chamfered, and cut at the bottom, and finally rounded to Ø1500mm×3080mm. In the second forging stage of the forging process, a 125MN press, an Ø900 slotted die, and a spherical top upsetting cap are used to upset the billet to Ø2290mm×1380mm. A wide flat anvil of 1700mm is used for WHF (Wafer-Held-Flat) drawing, with the double-sided deformation controlled at 20%. During high-pressure drawing, the feed rate is greater than 90% of the anvil width, with each anvil insertion being 100-200mm. Through six passes, the billet is compacted to a flat square of 1550mm×1680mm. Then, chamfering is applied to make the billet octagonal at 1500mm×3095mm. The WHF drawing process parameters are controlled according to the table below: ； In the third forging process, a 125MN press, an Ø900 slotted plate and a spherical top uphead are used to roughen the billet to Ø2240mm×1350mm; then, a flat anvil with an upper and lower 850mm is used to draw and flatten the billet into a square shape, with the deformation on both sides controlled at 20%, and the billet is drawn and flattened into a square shape of 1275mm×945mm. In the fourth forging process, the billet is rounded to Ø1080mm using a flat anvil with an upper and lower diameter of 850mm. The post-forging heat treatment process includes: (1) a first low-temperature normalizing treatment and a high-temperature normalizing treatment, where the shaft is air-cooled to 300~350℃ for material preparation, heated to 660~680℃ at a heating rate of ≤40℃ / h, held for 10h, and then heated to 900~950℃, held for 18~20h, and air-cooled out of the furnace; (2) a second low-temperature normalizing treatment and a high-temperature normalizing treatment, where the shaft is air-cooled to 280~32℃. After 0℃, keep it at 20h, then heat it to 660~680℃ at a heating rate of ≤40℃ / h, keep it at 10h, then heat the shaft to 870~900℃, keep it at 18~20h, and air cool it out of the furnace; (3) Tempering treatment: air cool the shaft to 280~320℃ and keep it at 20h, then heat it to 640~660℃ at a heating rate of ≤40℃ / h, keep it at 40h, and then furnace cool it to ≤150℃ before taking it out of the furnace; The heat treatment process includes: (1) Quenching treatment: the shaft is heated to ≤300℃ and put into the furnace. It is heated to 640~660℃ at a heating rate of ≤60℃ / h and held for 6h. Then the shaft is heated to 860~900℃ and held for 15~17h. After air cooling for 2 minutes, it is water cooled for 3~4h. The shaft body surface temperature is ≤200℃ before it is taken out of the water. (2) High temperature tempering treatment: the shaft is held at 290~310℃ for 6h. Then it is heated to 600~650℃ at a heating rate of ≤50℃ / h and held for 28~30h. Then it is air cooled to ≤200℃ at a cooling rate of ≤50℃ / h before it is taken out of the furnace.

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