Large rotor and preparation method thereof

Abstract

The invention discloses a large rotor and a preparation method thereof, belongs to the technical field of rotor preparation, and solves the problems of long production period, high energy consumption and easy cracking of forge pieces in the existing preparation method of the large rotor. The preparation method comprises the steps of first-time two-phase region normalizing, second-time two-phase region normalizing, third-time complete austenitizing normalizing, tempering and thermal refining which are sequentially carried out. According to the method, the forge piece can be prevented from cracking, grain refinement can be achieved, and the rotor with excellent performance is provided.

Description

Technical Field

[0001] The present invention relates to the technical field of rotor preparation, and particularly relates to a large rotor and a preparation method thereof. Background Art

[0002] As a key core component of a steam turbine generator set, with the inevitable development trend of increasing parameters and capacity of the steam turbine unit, the size of the rotor forging, which is the core component, is also continuously increasing. Currently, the shaft body cross-sections of forgings such as large flywheel rotors, low-pressure rotors, generator rotors, and welded rotors have all increased to Among them. Due to the increase in the shaft body size of the forging, the heat treatment cycle for making the forging structure uniform and refined through post-forging heat treatment of the forging to ensure the UT flaw detection sensitivity before quenching and tempering is relatively long, and there are problems such as high energy consumption and easy cracking of the forging, bringing great pressure to production and unable to ensure obtaining a large rotor that meets the requirements. Summary of the Invention

[0003] In view of the above situation, the present invention aims to provide a large rotor and a preparation method thereof, which can at least solve one of the following technical problems: the existing preparation method of large rotors has a long production cycle, high energy consumption, easy cracking of forgings, poor performance of large rotors, and cannot meet the technical requirements.

[0004] The object of the present invention is mainly achieved through the following technical solutions:

[0005] The present invention provides a preparation method of a large rotor, and the preparation method includes normalizing in the first two-phase region, normalizing in the second two-phase region, normalizing with complete austenitization for the third time, tempering, and quenching and tempering treatments carried out in sequence.

[0006] Further, the preparation method includes the following steps:

[0007] S1. Heat the heat treatment furnace to Ar1±20°C, and quickly load the large rotor forging blank after forging into the heat treatment furnace and keep it warm;

[0008] S2. Heat it to T1 at a speed of v1 and keep it warm;

[0009] S3. Air-cool the forging blank;

[0010] S4. Load the forging blank into the heat treatment furnace and carry out low-temperature heat preservation in the range of 100-150°C below the Ms point;

[0011] S5. Heat it to AC1-20°C to AC1 at a speed of v2;

[0012] S6. Then heat it to T2 at a speed of v3, keep it warm, and then air-cool it, where v3>v2;

[0013] S7. Load the forging blank into the heat treatment furnace and carry out low-temperature heat preservation in the range of 100-150°C below the Ms point;

[0014] S8 is the same as S5;

[0015] S9: Heat up to T3 at a relatively fast speed v4, hold the temperature, and then air cool;

[0016] S10 is the same as S7;

[0017] S11: Heat up to AC1 - (50 - 80°C), hold the temperature;

[0018] S12: Cool down at a cooling rate of 10°C / h or less to 250°C, then air cool to room temperature; then perform quenching and tempering treatment.

[0019] Furthermore, the quenching and tempering treatment includes:

[0020] S13: Machining the forging blank obtained in S12;

[0021] S14: Heat up to AC1 - 20°C to AC1 at a speed of v5;

[0022] S15: Then heat up to AC3 + (30 - 50°C) at a speed of v6, hold the temperature, and then water cool;

[0023] S16: Load the forging blank into the heat treatment furnace and perform low-temperature holding within the range of 150 - 200°C below the Ms point;

[0024] S17: Heat up to AC1 - 200°C to AC1 - 50°C at the same heating rate as S11, hold the temperature;

[0025] S18 is the same as S12.

[0026] Furthermore, v5 > v2.

[0027] Furthermore, v6 > v4.

[0028] Furthermore, the holding temperature in S16 is lower than the holding temperature in S10.

[0029] Furthermore, in S3, when air cooling to 500 - 550°C of the journal, cover the journal of the forging blank with a slow cooling cover and continue air cooling until the shaft body is 120 - 150°C below the Ms point.

[0030] Furthermore, in S14, the temperature of AC1 - 20°C to AC1 is 670 - 700°C.

[0031] Furthermore, the component of the large rotor is low-carbon C-Cr-Ni-Mo-V steel.

[0032] The present invention also provides a large rotor prepared by the above method.

[0033] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0034] a) In the method for preparing a large rotor of the present invention, two two-phase region normalizations are adopted, so that the large-section forging is kept at a temperature as high as possible in the two-phase region (the temperature is above AC3 - 20°C and less than AC3, hereinafter abbreviated as AC3 - 20°C to <AC3), so that most of the forging structure inside and outside (volume percentage 70% - 90%) is transformed into a uniform and fine austenite structure, and a small part remains the bainite high-temperature tempered structure; it should be noted that the bainite high-temperature tempered structure is segmented by the transformed austenite structure, and the two phases are interpenetrated and mixed together, and then air-cooled. After two consecutive two-phase region normalizations close to the AC3 temperature, the crystal orientation of the original coarse austenite structure is completely disrupted, and the original coarse austenite grains have been broken by the two-phase structure of incomplete austenitization twice, forming uniform and fine grain boundaries, phase boundaries and carbide dispersed distributions. At this time, after the third full austenitization normalization, the structure is completely formed into equiaxed austenite grains, and the structure after normalization and tempering forms a uniform bainite tempered structure, effectively refining the forging structure and grains, and fully preparing the structure for the subsequent quenching and tempering treatment. After the quenching and tempering treatment of the method of the present invention, the grains are fine and uniform, and the flaw detection sensitivity reaches the acceptance level that meets the standard.

[0035] b) In the preparation method of the present invention, by precisely controlling the cooling method after forging, process parameters such as the normalizing temperature at different steps, the heating rate, holding temperature, holding time, and cooling rate at different stages; the forging cracking is avoided, and grain refinement is achieved, and the structure can be fully prepared for the subsequent quenching and tempering treatment.

[0036] c) In the preparation method of the present invention, the temperature of the first two normalizations is relatively low. By precisely controlling each process step and the control of key process parameters, it can ensure that the forging structure meets the requirements, greatly reducing the time, reducing the energy consumption cost, and improving the production efficiency.

[0037] d) The structure of the large rotor before quenching and tempering of the present invention is a bainite tempered structure, with fine and uniform grains. For example, the grain size is 3.5 - 5 grades, and the flaw detection sensitivity reaches a good level. For example, the central limit sensitivity is Φ2.0 - 2.5mm, providing good structural preparation for quenching and tempering. After quenching and tempering heat treatment, a uniform and fine bainite tempered structure is obtained, and the grain size reaches 4.5 - 6.5 grades. The flaw detection sensitivity of the above large rotor reaches a good level. For example, the central limit sensitivity is Φ1.0 - 1.6mm. The performance is excellent.

[0038] Other features and advantages of the present invention will be set forth in the following description, and in part will be obvious from the description, or may be learned by practice of the present invention. The objectives and other advantages of the present invention may be realized and attained by the content particularly pointed out in the written description and the drawings. Description of the Drawings

[0039] The drawings are only for the purpose of illustrating specific embodiments and are not considered as a limitation to the present invention. Throughout the drawings, the same reference signs denote the same components.

[0040] Figure 1 Schematic diagram of the large rotor of the present invention;

[0041] Figure 2 Schematic diagram of the slow cooling cover of the present invention;

[0042] Figure 3 Schematic diagram of the air cooling of the slow cooling cover forging;

[0043] Figure 4 Grain diagram of the forging billet after the S3 step of Example 1;

[0044] Figure 5 Grain diagram of the forging billet after the S6 step of Example 1;

[0045] Figure 6 Grain diagram of the forging billet after the S9 step of Example 1;

[0046] Figure 7 Grain diagram of the rotor after the S18 step of Example 1.

[0047] Reference Signs

[0048] 1 - Shaft body, 2 - Journal, 3 - Flange, 4 - Slow cooling cover, 41 - Inner lining, 42 - Outer skin, 43 - Support frame. Detailed Description of the Preferred Embodiments

[0049] The following will specifically describe the preferred embodiments of the present invention in conjunction with the drawings, wherein the drawings form a part of the present invention and are used together with the embodiments of the present invention to explain the principles of the present invention.

[0050] As shown in the attached Figure 1As shown in the figure, the present invention provides a large rotor, which includes a shaft body 1 and shaft necks 2 connected to both sides of the shaft body 1. The diameter D1 of the shaft body 1 and the diameter D2 of the shaft necks 2 satisfy the following relationship: D1 > D2, and the difference between D1 and D2 is more than 1000 mm. For example, the difference between D1 and D2 is 1100 - 2000 mm, such as 1200 mm, 1300 mm, 1400 mm, 1500 mm, 1600 mm, 1700 mm, 1800 mm, 1900 mm. The cross-section difference at the connection position between the shaft body 1 and the shaft necks 2 of the large rotor is relatively large, resulting in a larger temperature difference between the inside and outside during the heat treatment of the forging, a larger structure stress and thermal stress. Coupled with the large crystal grain size and coarse structure in the as-forged state after forging, and insufficient strength and toughness reserve, the phenomenon of forging cracking is likely to occur during the post-forging heat treatment after forging.

[0051] Specifically, the large rotor may further include a flange 3 connected to the outside of the shaft neck 2. The diameter D2 of the shaft neck 2 and the diameter D3 of the flange 3 satisfy the following relationship: D3 > D2, and the difference between D3 and D2 is 100 - 700 mm, such as 100 mm, 200 mm, 300 mm, 400 mm, 500 mm, 600 mm.

[0052] Specifically, the diameter D1 of the shaft body 1 is 1700 mm or more, such as 1700 - 3000 mm, such as 1800 mm, 2000 mm, 2200 mm, 2400 mm, 2600 mm, 2800 mm.

[0053] Specifically, the diameter D2 of the shaft neck 2 is 600 mm or more, such as 600 - 900 mm, such as 650 mm, 700 mm, 750 mm, 800 mm, 850 mm.

[0054] Specifically, the diameter D3 of the flange 3 is 700 mm or more, such as 700 - 1600 mm, such as 800 mm, 900 mm, 1000 mm, 1100 mm, 1200 mm, 1300 mm, 1400 mm, 1500 mm.

[0055] Specifically, the large rotor of the present invention is made of C-Cr-Ni-Mo-V steel with low carbon and tissue heredity characteristics, such as 30Cr2Ni4MoV steel, 35Cr2Ni4MoV steel, 25Cr2Ni4MoV steel, and 22Cr2Ni3MoV steel.

[0056] For example, the components of the large rotor of the present invention include, by mass percentage: C: 0.2% - 0.35%, Si: 0.04% - 0.1%, Mn: 0.2% - 0.6%, Cr: 1.7% - 4.0%, Mo: 0.3% - 0.5%, Ni: 3.0% - 4.0%, V: 0.05% - 0.15%, Al: 0.003% - 0.01%, S: ≤0.004%, P: ≤0.004%, and the balance is Fe and inevitable impurities.

[0057] The present invention provides a method for preparing a large rotor, which includes normalizing in the first two-phase region, normalizing in the second two-phase region, full austenitizing normalizing, tempering, and quenching and tempering treatments carried out in sequence.

[0058] Specifically, the holding temperature of the first two-phase region normalizing is T1, where AC3 - 20°C ≤ T1 < AC3; the holding temperature of the second two-phase region normalizing is T2, where AC3 - 20°C ≤ T2 < AC3, and the holding temperature of the third full austenitizing normalizing is T3, where T3 = AC3 + (50 - 80°C).

[0059] Specifically, the method for preparing the above-mentioned large rotor includes the following steps:

[0060] S1. Heat the heat treatment furnace to Ar1 ± 20°C, and quickly load the forged blank of the large rotor after forging into the heat treatment furnace for heat preservation.

[0061] S2. Raise the temperature at a speed v1 of more than 15°C / h to AC3 - 20°C to < AC3 and hold for heat preservation.

[0062] S3. Air-cool the forged blank.

[0063] S4. After removing the slow-cooling cover, load the forged blank into the heat treatment furnace and carry out low-temperature heat preservation in the range of 100 - 150°C below the Ms point.

[0064] S5. Raise the temperature at a slow speed v2 to AC1 - 20°C to AC1.

[0065] S6. Then raise the temperature at a faster speed v3 to AC3 - 20°C to < AC3, hold for heat preservation, and then air-cool; v3 > v1.

[0066] S7. After removing the slow-cooling cover, load the forged blank into the heat treatment furnace and carry out low-temperature heat preservation in the range of 100 - 150°C below the Ms point.

[0067] S8. The same as S5.

[0068] S9. Then raise the temperature at a faster speed v4 to AC3 + (50 - 80°C), hold for heat preservation, and then air-cool; v4 > v3.

[0069] S10. The same as S7.

[0070] S11. Heat up to AC1 - (50 - 80°C) and hold for heat preservation.

[0071] S12. Cool down at a cooling rate of below 10°C / h to 250°C, and then air cool to room temperature.

[0072] S13. Machine the forging blank obtained in S12 into a smooth surface with a full surface Ra of 3.2.

[0073] S14. Heat up to AC1 - 20°C to AC1 at a speed of v5, where v5 > v2.

[0074] S15. Then heat up to AC3 + (30 - 50°C) at a speed of v6, hold for heat preservation, and then spray water for cooling; v6 > v4.

[0075] S16. Load the forging blank into a heat treatment furnace and conduct low - temperature heat preservation within the range of 150 - 200°C below the Ms point.

[0076] S17. Heat up to AC1 - 200°C to AC1 - 50°C at the same heating rate as S11 and hold for heat preservation.

[0077] S18. The same as S12.

[0078] Specifically, the above S1 - S3 are the first two - phase region normalizing, S4 - S6 are the second two - phase region normalizing, S7 - S9 are the third complete austenitizing normalizing, S10 - S12 are tempering, and S13 - S18 are quenching and tempering treatment (quenching + high - temperature tempering).

[0079] Specifically, before the above S1, it includes the forging of a large - scale rotor forging blank. The forging of the large - scale rotor forging blank includes: first forging out the journal region with a small cross - section (if there is a flange, the journal region here includes the journal and the flange), and then forging and deforming the shaft body with a large forging ratio. Specifically, the range of the large forging ratio is 1.2 - 1.3; by making the shaft body have a large deformation, a large austenite nucleation driving force is formed, which is beneficial to subsequent static recrystallization and is beneficial to the refinement of the grains and structure of the forging.

[0080] Specifically, in the above S1, after the forging of the large - scale rotor forging blank, it is not air - cooled to room temperature. After the forging is completed, it is loaded into the heat treatment furnace as quickly as possible for heat preservation, and partial pearlite transformation from grain boundary to grain interior distribution (volume percentage 20% - 35%) can occur. At this time, the structure of the forging blank is a mixed structure of pearlite isothermal structure + untransformed austenite, which can prevent the forging blank from cracking.

[0081] Specifically, in the above-mentioned S1, considering that when the temperature is too high or too low, the incubation period of pearlite transformation is too long, which will reduce the pearlite content and the refinement effect. Therefore, the holding temperature of S1 is controlled at Ar1±20°C, such as 600-630°C, such as 610°C, 620°C, 630°C.

[0082] Specifically, in the above-mentioned S1, the function of holding is to ensure that the internal and external temperatures of the forging billet are consistent, reduce the temperature difference during the heating process of the forging billet, and reduce the thermal stress. Considering that too long holding time will increase the heat treatment cycle; too short holding time will result in the core and surface temperatures not being uniform and the pearlite structure content being less. Therefore, the holding time of S1 is controlled to be not less than D1 / 100, where D1 is the diameter of the shaft body, the unit of D1 is mm, and the unit of the holding time is h. Preferably, the holding time is (1.5-2)D1 / 100.

[0083] Specifically, in the above-mentioned S2, in the plastic deformation stage, when ensuring that the instantaneous internal stress is controllable, it reaches close to AC3 relatively quickly (such as AC3-20°C to <AC3, such as 780-800°C, such as 785°C, 790°C, 795°C), there are many nucleation points, and the original austenite grains are fully disrupted, achieving the effect of grain refinement. Therefore, the heating rate v1 is above 15°C / h. Preferably, v1 is 15-20°C / h, such as 16°C / h, 17°C / h, 18°C / h, 19°C / h.

[0084] Specifically, in the above-mentioned S2, in order to make the core of the forging billet fully burn through, the internal and external temperatures are consistent, and full nucleation occurs in the two-phase region of the core. The holding time is controlled to be (2-4)D1 / 100, where D1 is the diameter of the shaft body, the unit of D1 is mm, and the unit of the holding time is h. Preferably, the holding time is (2.3-3.5)D1 / 100h, such as the holding time is 2.5D1 / 100, 2.7D1 / 100, 3D1 / 100, 3.2D1 / 100, 3.5D1 / 100.

[0085] Specifically, in the above-mentioned S3, the forging billet is lifted onto a pad iron 1000 mm high for air cooling.

[0086] Specifically, in the above-mentioned S3, when air-cooling to a range of 500 - 550 °C for the journal (if there is a flange, here it is the journal and the flange), put a slow-cooling cover 4 on the journal (if there is a flange, here it is the journal and the flange) of the forging blank, and air-cool until the shaft body is 120 - 150 °C below the Ms point, such as 220 - 250 °C. It should be noted that the slow-cooling cover can reduce the cooling rate of the journal and the flange (for example, the cooling rate reaches 5 - 10 °C / h), so as to reduce the thermal stress and tissue stress at the transition of the large cross-section between the journal and the shaft body, and reduce the risk of forging cracking. At the same time, it can ensure that the forging blank is air-cooled to a lower temperature, making the core temperature of the forging blank lower, enabling more sufficient tissue transformation, and achieving the effect of refining the tissue and grains.

[0087] Specifically, in the above-mentioned S3, the structure of the slow-cooling cover 4 is as Figure 2 shown. The inner diameter of the slow-cooling cover 4 is equivalent to the diameter of the shaft body. The slow-cooling cover 4 includes a lining 41 and an outer skin 42. The lining 41 is an asbestos felt with good heat insulation effect, and the outer skin 42 is an iron sheet for support; the slow-cooling cover 4 also includes a support frame 43 with adjustable height, and the support frame 43 is connected to the outer skin 42 and can adjust the position of the slow-cooling cover 4.

[0088] Specifically, as Figure 3 shown is a schematic diagram of air-cooling the forging blank with the slow-cooling cover sleeved.

[0089] Specifically, in the above-mentioned S4, keep the temperature constant for a long time below the Ms point to make the core of the forging blank fully undergo tissue transformation as much as possible, which is beneficial to adjusting and refining the grain structure of the steel through subsequent phase transformation recrystallization. Therefore, control the holding time to be (1.2 - 1.6)D1 / 100, where D1 is the diameter of the shaft body, the unit of D1 is mm, and the unit of the holding time is h. Preferably, for example, 1.3D1 / 100, 1.4D1 / 100, 1.5D1 / 100, 1.6D1 / 100.

[0090] Specifically, in the above-mentioned S5, this stage belongs to speed-limited heating, minimizing the internal and external temperature difference and instantaneous internal stress in the large rotor in the elastic deformation zone of the forging, reducing the cracking risk, and at the same time preparing for the tissue transformation in the two-phase zone; therefore, control v2 < v1, for example, v2 is below 10 °C / h, preferably, v2 is 5 - 10 °C / h, for example, 6 °C / h, 7 °C / h, 8 °C / h, 9 °C / h.

[0091] Specifically, in the above-mentioned S5, the temperature of AC1 - 20 °C to AC1 is preferably 670 - 700 °C, for example, 680 °C, 690 °C, 700 °C.

[0092] Specifically, in the above-mentioned S6, during the plastic deformation stage, while ensuring controllable instantaneous internal stress, it reaches close to AC3 relatively quickly, with numerous nucleation sites, fully disrupting the original austenite grains and achieving the effect of grain refinement. This stage is a speed-limiting heating process. In the plastic deformation zone of the forging and after the forging has undergone a normalizing treatment, the structure is relatively fine and the plastic and toughness reserves have increased. Therefore, control v3 > v1. For example, v3 is below 30 °C / h, preferably, v3 is 20 - 30 °C / h, such as 22 °C / h, 24 °C / h, 26 °C / h, 28 °C / h.

[0093] Specifically, in the above-mentioned S6, considering the large cross-section of the large forging and the certain temperature difference inside and outside the forging during the heating process, therefore, control the holding time to be (2 - 4)D1 / 100, where D1 is the diameter of the shaft body, the unit of D1 is mm, and the unit of the holding time is h. The holding time is the same as that in the holding stage of S2.

[0094] Specifically, in the above-mentioned S6, the operating steps of air cooling are the same as those in S3, except that this time the air cooling is carried out until the surface temperature of the shaft body is 30 - 50 °C lower than the final temperature of S3.

[0095] Specifically, in the above-mentioned S7, considering that in S6, the air cooling is carried out until the temperature of the shaft body is lower than that of S3, and the core of the forging will also decrease accordingly. Therefore, the holding time in the low-temperature holding stage is controlled to be relatively shortened. For example, control the holding time to be 1 - 1.5D1 / 100mm, where D1 is the diameter of the shaft body, the unit of D1 is mm, and the unit of the holding time is h, such as 1.1D1 / 100mm, 1.2D1 / 100mm, 1.2D1 / 100mm, 1.4D1 / 100mm.

[0096] Specifically, in the above-mentioned S9, v4 > v3. Compared with the previous two normalizing processes, the forging has more sufficient plastic and toughness reserves and stronger crack resistance. Further increasing the heating rate in the two-phase region can effectively refine the grains and the structure. Preferably, v4 is 30 - 40 °C / h, such as 32 °C / h, 34 °C / h, 36 °C / h, 38 °C / h.

[0097] Specifically, in the above-mentioned S9, hold at AC3 + (50 - 80 °C) (such as 850 - 890 °C) to make the structure fully form equiaxed austenite grains. Since two normalizing processes have been carried out before, the structure and grain size are already very fine, and the time required for austenitization to make the grains uniform is shorter than that of the previous two times. Therefore, the holding time required during the process is (1.8 - 3.5)D1 / 100, preferably, the holding time is 2 - 3D1 / 100mm, such as 2.2D1 / 100mm, 2.4D1 / 100mm, 2.6D1 / 100mm, 2.8D1 / 100mm, where D1 is the diameter of the shaft body, the unit of D1 is mm, and the unit of the holding time is h.

[0098] Specifically, in the above S9, the operation of air cooling is the same as that in S6 and will not be elaborated here.

[0099] Specifically, in S11, the heating rate is 10 - 25 °C / h, such as 13 °C / h, 15 °C / h, 18 °C / h, 20 °C / h, 23 °C / h.

[0100] Specifically, in S11, the holding time is (2.5 - 4)D1 / 100, such as 2.6D1 / 100mm, 2.8D1 / 100mm, 3D1 / 100mm, 3.2D1 / 100mm, 3.4D1 / 100mm, 3.6D1 / 100mm, 3.8D1 / 100mm. Here, D1 is the diameter of the shaft body, with the unit of mm, and the unit of the holding time is h. This step forms a uniform bainite tempered structure through sufficient tempering, effectively refining the structure and grains of the forging, and fully preparing the structure for subsequent processes.

[0101] Specifically, in S12, considering that too high a cooling rate will cause excessive thermal stress at different cross-sections, resulting in forging deformation, and in addition, too high a cooling rate will make the hardness of the forging with forging black skin too high, causing the risk of difficult machining. Therefore, the cooling rate is controlled below 10 °C / h. For example, 5 - 10 °C / h, such as 6 °C / h, 7 °C / h, 8 °C / h, 9 °C / h.

[0102] Specifically, in the above S13, the forging blank is machined to a forging with a surface finish of Ra3.2, which is convenient for flaw detection before quenching and tempering, and can avoid micro-cracks in the forging and prevent cracking during the quenching process. In addition, removing the forging black skin can improve the quenching and cooling effect.

[0103] Specifically, in the above S14, this stage is a speed-limited heating stage. In the elastic deformation zone of the forging, the internal and external temperature difference and instantaneous internal stress in the large rotor are minimized as much as possible to reduce the cracking risk, and at the same time, it prepares for the phase transformation of the two-phase zone structure; however, after the forging in this stage has undergone three normalizations + temperings, it already has sufficient strength and toughness reserves. Therefore, v5 > v2 is controlled. For example, v5 is below 15 °C / h, and preferably, v5 is 8 - 13 °C / h, such as 9 °C / h, 10 °C / h, 11 °C / h, 12 °C / h.

[0104] Specifically, in the above S14, the temperature of AC1 - 20 °C to AC1 is preferably 670 - 700 °C, such as 680 °C, 690 °C, 700 °C.

[0105] Specifically, in the above-mentioned S15, during the plastic deformation stage, while ensuring controllable instantaneous internal stress, it reaches AC3 + 30°C to AC3 + 50°C relatively quickly. There are many nucleation points, which fully disrupt the original austenite grains and achieve the effect of grain refinement. This stage is a speed-limiting heating. In the plastic deformation zone of the forging and after the forging has undergone three normalizations + temperings, the structure is relatively fine and the plastic and toughness reserves have increased. Therefore, control v6 > v4. For example, v6 is below 65°C / h. Preferably, v6 is 45 - 55°C / h, such as 46°C / h, 48°C / h, 50°C / h, 52°C / h, 54°C / h.

[0106] Specifically, in the above-mentioned S15, considering the large cross-section of the large forging, there is a certain temperature difference between the inside and outside of the forging during the heating process. Therefore, control the holding time to be (2 - 3.5)D1 / 100, and the preferred holding time is (2.5 - 3.0)D1 / 100, where D1 is the diameter of the shaft body, the unit of D1 is mm, and the unit of the holding time is h.

[0107] Specifically, in the above-mentioned S15, the quenching operation steps are that the forging rotates vertically and is sprayed with water for cooling, and at the same time, water circulation cooling is carried out until the surface temperature of the forging shaft body ≤ 100°C. During this stage, the forging is sprayed with water for cooling while ensuring that the forging rotates. The distance between the water spray nozzle and the forging surface is 300 - 500 mm, and the nozzle water pressure is 0.3 - 0.4 MPa. The powerful water flow can break through the water film formed when the water contacts the hot forging, improving the hardening effect.

[0108] It should be noted that during the entire quenching and tempering process, the forging needs to be kept in a vertical state to avoid forging deformation.

[0109] Specifically, the holding temperature in the above-mentioned S16 is lower than the holding temperature in S10, and the holding temperature is Ms - (150°C - 200°C) to ensure that the core of the forging can reach a lower temperature, making the tissue transformation more complete and reducing the retained austenite in the tissue.

[0110] Specifically, in the above-mentioned S16, control the holding time to be 1 - 1.5D1 / 100mm, where D1 is the diameter of the shaft body, the unit of D1 is mm, and the unit of the holding time is h, such as 1.1D1 / 100mm, 1.2D1 / 100mm, 1.2D1 / 100mm, 1.4D1 / 100mm.

[0111] Specifically, the heat preservation time in S17 is (2 - 4)D1 / 100, and the preferred heat preservation time is (3 - 3.5)D1 / 100. For example, 3.1D1 / 100mm, 3.2D1 / 100mm, 3.3D1 / 100mm, 3.4D1 / 100mm, where D1 is the diameter of the shaft body, the unit of D1 is mm, and the unit of the heat preservation time is h. This step forms a uniform bainite tempered structure through sufficient tempering to fully ensure that the mechanical properties of the forging can meet the standard requirements both inside and outside.

[0112] Specifically, in S17, the heating rate is 10 - 25°C / h, for example, 13°C / h, 15°C / h, 18°C / h, 20°C / h, 23°C / h.

[0113] Specifically, in S18, considering that too large a cooling rate will cause excessive thermal stress at different cross-sections, resulting in deformation of the forging. In addition, too high a cooling rate will cause too high residual stress, posing a risk of non-compliance of residual stress performance. Therefore, the cooling rate is controlled below 10°C / h. For example, 5 - 10°C / h, such as 6°C / h, 7°C / h, 8°C / h, 9°C / h.

[0114] The present invention also provides a large rotor prepared by the above preparation method.

[0115] Specifically, the structure of the above large rotor before quenching and tempering is a bainite tempered structure, with fine and uniform grains. For example, the grain size is 3.5 - 5 levels, and the flaw detection sensitivity reaches a good level. For example, the central limit sensitivity is Φ2.0 - 2.5mm, providing good tissue preparation for quenching and tempering. After quenching and tempering heat treatment, a uniform and fine bainite tempered structure is obtained, and the grain size reaches 4.5 - 6.5 levels. The flaw detection sensitivity of the above large rotor reaches a good level. For example, the central limit sensitivity is Φ1.0 - 1.6mm. And the performance is excellent.

[0116] Compared with the prior art, in the preparation method of the large rotor of the present invention, two two-phase region normalizations are adopted, and the large-section forging is insulated at a temperature as high as possible in the two-phase region (AC3 - 20°C to <AC3), so that most (volume percentage 70% - 90%) of the internal and external structures of the forging are transformed into uniform and fine austenite structures, and a small part remains the bainite high-temperature tempered structure; it should be noted that the bainite high-temperature tempered structure is segmented by the transformed austenite structure, and the two phases are interpenetrated and mixed together, and then air-cooled. After two consecutive two-phase region normalizations close to the AC3 temperature, the crystal orientation of the original coarse austenite structure is completely disrupted, and the original coarse austenite grains have been broken by the two-phase structures that are incompletely austenitized twice, forming uniform and fine grain boundaries, phase boundaries, and carbide distributed dispersedly. At this time, after a third complete austenitizing normalization, the structure is completely formed into equiaxed austenite grains, and the structure after normalization and tempering forms a uniform bainite tempered structure, effectively refining the forging structure and grains, and fully preparing the structure for the subsequent quenching and tempering treatment.

[0117] In the preparation method of the present invention, during the forging process of the large rotor forging blank, first forge the journal area with a small cross-section (if there is a flange, this is the journal and the flange here), and then deform the shaft body by large forging ratio. There is a large deformation in the shaft body, forming a large austenite nucleation driving force, which is beneficial to subsequent static recrystallization and beneficial to the refinement of the grains and structure of the forging.

[0118] In the preparation method of the present invention, by precisely controlling the cooling method after forging, process parameters such as the normalizing temperature in different steps, the heating rate, holding temperature, holding time, and cooling rate in different stages; the cracking of the forging is avoided, and the grain refinement is achieved, and the structure can be fully prepared for the subsequent quenching and tempering treatment.

[0119] In the preparation method of the present invention, the temperature of the first two normalizations is relatively low. Combining the precise control of each process step and the control of key process parameters, it can ensure that the forging structure meets the requirements, greatly reduces the time, reduces the energy consumption cost, and improves the production efficiency.

[0120] Example 1

[0121] This example provides a large motor rotor forging and its preparation method. The large rotor in this example includes a shaft body 1 and journals 2 connected to both sides of the shaft body 1. The cross-sectional diameter of the shaft body is The cross-sectional diameter of the journal 2 is 700 mm; the material of the rotor is 25Cr2Ni4MoV steel, and the composition is C: 0.24%, Si: 0.05%, Mn: 0.25%, Cr: 1.75%, Mo: 0.38%, Ni: 3.35%, V: 0.1%, Al: 0.005%, S: 0.002%, P: 0.002%, and the balance is Fe and unavoidable impurities.

[0122] The preparation method of the large rotor in this embodiment includes the following steps:

[0123] S0. First, forge a journal with a small cross-section, and then deform the shaft body by forging with a large forging ratio. The value of the large forging ratio is 1.25;

[0124] S1. Heat the heat treatment furnace to 610 °C, and quickly load the forged blank of the large rotor after forging into the heat treatment furnace, and keep it warm for 30 h;

[0125] S2. Raise the temperature to 795 °C at a speed of 15 °C / h, and keep it warm for 50 h;

[0126] S3. Air-cool the forged blank. After the journal is air-cooled to 500 - 550 °C, add a slow-cooling cover to the journal and air-cool it until the surface temperature of the shaft body is 250 °C;

[0127] S4. After removing the slow-cooling cover, load the forging into the heat treatment furnace and keep it warm at 200 °C for 25 h;

[0128] S5. Raise the temperature to 680 °C at a slow speed of 8 °C / h;

[0129] S6. Then raise the temperature to 795 °C at a faster speed of 25 °C / h, keep it warm for 50 h, and then air-cool. The journal is air-cooled to 500 - 550 °C, and the journal is air-cooled with a slow-cooling cover until the surface temperature of the shaft body is 200 °C;

[0130] S7. After removing the slow-cooling cover, load the forging into the heat treatment furnace and keep it warm at 180 °C for 22 h;

[0131] S8. The same as S5;

[0132] S9. Then raise the temperature to 860 °C at a faster speed of 34 °C / h, keep it warm for 45 h, and then air-cool. The journal is air-cooled to 500 - 550 °C, and the journal is air-cooled with a slow-cooling cover until the surface temperature of the shaft body is 200 °C;

[0133] S10. The same as S7;

[0134] S11. Raise the temperature to 640 °C at a speed of 25 °C / h and keep it warm for 55 h;

[0135] S12: Cool down at a cooling rate of 10 °C / h to 250 °C, and then air-cool to room temperature.

[0136] S13. Rough machine to a surface finish of Ra 3.2 for the entire surface;

[0137] S14. Raise the temperature to 680 °C at a speed of 13 °C / h;

[0138] S15. Then raise the temperature to 840 °C at 50 °C / h, keep it warm for 50 h, and then spray water to cool until the surface temperature of the shaft body is 70 °C;

[0139] S16. Load the forging blank into the heat treatment furnace and keep it at 130 °C for 22 h;

[0140] S17. Heat it up to 598 °C at a rate of 25 °C / h and keep it at this temperature for 55 h;

[0141] S18. Cool it down to 250 °C at a rate of 10 °C / h and then air-cool it to room temperature.

[0142] The grain size of the forging blank after the S3 step of this embodiment is as Figure 4 shown, the grain size of the forging blank after the S6 step is as Figure 5 shown, the grain size of the forging blank after the S9 step is as Figure 6 shown. The flaw detection sensitivity and grain size of the forgings in this embodiment have reached a good level. The central limit sensitivity is Φ2.0 mm and the grain size is grade 5. And during the preparation process of this embodiment, the forgings did not crack. After quenching and tempering, the grain size is grade 6, as Figure 7 shown, and the performance meets the standard requirements as shown in Table 1. For example, the performance of this embodiment is as follows: Rp 0.2 reaches above 728 MPa, Rm reaches above 830 MPa, A reaches above 19%, Z reaches above 68%, AKv reaches above 175 J, FATT reaches below -90 °C, and the residual stress reaches below 37 MPa, with excellent performance.

[0143] Table 1 Performance results of the quenching and tempering of Example 1

[0144]

[0145]

[0146] Example 2

[0147] This embodiment provides a large low-pressure rotor forging and its preparation method. The shape of the large rotor in this embodiment is basically the same as that in Example 1, except that the shaft body cross-section of the rotor forging is the journal size is 800 mm; the material of the rotor is 30Cr2Ni4MoV steel, and its chemical composition includes C: 0.26%, Si: 0.06%, Mn: 0.26%, Cr: 3.65%, Mo: 0.39%, Ni: 3.75%, V: 0.087%, Al: 0.003%, S: 0.0021%, P: 0.004%, and the balance is Fe and inevitable impurities.

[0148] The preparation method of the large rotor in this embodiment is roughly the same as that in Example 1, including:

[0149] S0. First forge the journal with a small cross-section and then deform the shaft body by large reduction forging. The value of the large reduction ratio is 1.26;

[0150] S1. Heat the heat treatment furnace to 620 °C, and quickly load the large rotor forging blank after forging into the heat treatment furnace, and keep it warm for 32 h;

[0151] S2. Heat it up to 790 °C at a speed of 15 °C / h, and keep it warm for 55 h;

[0152] S3. The same as in Example 1;

[0153] S4. After removing the slow cooling cover, load the forging into the heat treatment furnace, and keep it warm at 210 °C for 28 h;

[0154] S5. Heat it up to 700 °C at a slow speed of 8 °C / h;

[0155] S6. Then heat it up to 790 °C at a faster speed of 23 °C / h, keep it warm for 55 h, and then air cool. Air cool the journal to 500 - 550 °C, and add a slow cooling cover to the journal and air cool it until the surface temperature of the shaft body is 200 °C;

[0156] S7. After removing the slow cooling cover, load the forging into the heat treatment furnace, and keep it warm at 180 °C for 25 h;

[0157] S8. The same as S5;

[0158] S9. Then heat it up to 870 °C at a faster speed of 31 °C / h, keep it warm for 50 h, and then air cool. Air cool the journal to 500 - 550 °C, and add a slow cooling cover to the journal and air cool it until the surface temperature of the shaft body is 200 °C;

[0159] S10. The same as S7;

[0160] S11. Heat it up to 640 °C and keep it warm for 60 h;

[0161] S12: The same as in Example 1.

[0162] S13. Rough machine it until the surface finish of the whole surface reaches Ra3.2;

[0163] S14. Heat it up to 700 at a speed of 12 °C / h;

[0164] S15. Then heat it up to 842 °C at a speed of 50 °C / h, keep it warm for 50 h, and then spray water to cool it until the surface temperature of the shaft body is 60 °C;

[0165] S16. Load the forging blank into the heat treatment furnace, and keep it warm at 130 °C for 25 h;

[0166] S17. Heat it up to 592 °C at a speed of 23 °C / h and keep it warm for 60 h;

[0167] S18. After cooling it down to 250 °C at a cooling rate of 10 °C / h, air cool it to room temperature.

[0168] The flaw detection sensitivity and grain size of the forged parts after tempering in this embodiment have reached a good level. The central limit sensitivity is Φ2.5mm, and the grain size is grade 4.5. And during the preparation process of this embodiment, the forged parts did not crack. After quenching and tempering, the grain size is grade 5.5, and the performance meets the standard requirements, as shown in Table 2. For example, the performance of this embodiment is as follows: Rp 0.2 reaches above 805MPa, Rm reaches above 910MPa, A reaches above 19%, Z reaches above 67%, AKv reaches above 165J, FATT reaches below -105°C, and the residual stress reaches below 47MPa, with excellent performance.

[0169] Table 2 Performance results of Example 2 after quenching and tempering

[0170]

[0171] Example 3

[0172] This embodiment provides a large flywheel rotor forged part and its preparation method. The shape of the large rotor in this embodiment is basically the same as that in Example 1, except that the shaft body cross-section of the rotor forged part is the journal size is 800mm; the material of the rotor is 35Cr2Ni4MoV steel, and the chemical composition includes C: 0.33%, Si: 0.1%, Mn: 0.28%, Cr: 1.8%, Mo: 0.42%, Ni: 3.75%, V: 0.09%, Al: 0.003%, S: 0.002%, P: 0.003%, and the balance is Fe and unavoidable impurities.

[0173] The preparation method of the large rotor in this embodiment is basically the same as that in Example 1, including:

[0174] S0. First, forge the journal with a small cross-section and then deform the shaft body by forging with a large forging ratio. The value of the large forging ratio is 1.28;

[0175] S1. Heat in a heat treatment furnace to 630°C, and quickly load the large rotor forging blank after forging into the heat treatment furnace and keep it warm for 45h;

[0176] S2. Heat up to 800°C at a speed of 16°C / h and keep it warm for 65h;

[0177] S3. The same as in Example 1;

[0178] S4. After removing the slow cooling cover, load the forged part into the heat treatment furnace and keep it warm at 250°C for 38h;

[0179] S5. Heat up to 700°C at a slow speed of 6°C / h;

[0180] S6. Then, heat it up to 800°C at a relatively fast rate of 25°C / h, hold for 65 h, and then air cool. Air cool the journal to 500 - 550°C, and then add a slow cooling cover to the journal and air cool until the surface temperature of the shaft body is 200°C;

[0181] S7. After removing the slow cooling cover, load the forging into the heat treatment furnace and hold at 200°C for 35 h;

[0182] S8. The same as S5;

[0183] S9. Then, heat it up to 880°C at a relatively fast rate of 33°C / h, hold for 60 h, and then air cool. Air cool the journal to 500 - 550°C, and then add a slow cooling cover to the journal and air cool until the surface temperature of the shaft body is 200°C;

[0184] S10. The same as S7;

[0185] S11. Heat it up to 660°C and hold for 80 h;

[0186] S12: Cool it down to 250°C at a cooling rate of 8°C / h, and then air cool to room temperature.

[0187] S13. Rough machine it until the surface finish of the whole surface reaches Ra3.2;

[0188] S14. Heat it up to 700°C at a rate of 9°C / h;

[0189] S15. Then, heat it up to 852°C at a relatively fast rate of 48°C / h, hold for 75 h, and then spray water to cool until the surface temperature of the shaft body is 50°C;

[0190] S16. Load the forging blank into the heat treatment furnace and hold at 120°C for 35 h;

[0191] S17. Heat it up to 554°C at a rate of 23°C / h and hold for 80 h;

[0192] S18. Cool it down to 250°C at a cooling rate of 10°C / h, and then air cool to room temperature.

[0193] The flaw detection sensitivity and grain size of the forging after tempering in this embodiment have reached good levels. The center limit sensitivity is Φ2.5 mm and the grain size is grade 4. And during the preparation process of this embodiment, the forging did not crack. After quenching and tempering, the grain size is 5.0 grade, and the performance meets the standard requirements as shown in Table 3. For example, the performance of this embodiment is as follows: Rp 0.2 Reaches above 965 MPa, Rm reaches above 1020 MPa, A reaches above 17.5%, Z reaches above 56%, AKv reaches above 115 J, FATT reaches below -45°C, and the residual stress reaches below 47 MPa, with excellent performance.

[0194] Table 3 Performance Results after Quenching and Tempering of Example 3

[0195]

[0196] Example 4

[0197] This example provides a large welded rotor forging and its preparation method. The shape of the large rotor in this example is basically the same as that in Example 1, except that the shaft body cross-section of the rotor forging is The journal size is 700 mm; the material of the rotor is 22Cr2Ni3MoV steel, and the chemical composition includes C: 0.22%, Si: 0.04%, Mn: 0.58%, Cr: 1.7%, Mo: 0.45%, Ni: 3.15%, V: 0.095%, Al: 0.003%, S: 0.002%, P: 0.003%, and the balance is Fe and unavoidable impurities.

[0198] The preparation method of the large rotor in this example is generally the same as that in Example 1, including:

[0199] S0. First, forge the journal with a small cross-section and then deform the shaft body by forging with a large forging ratio. The value of the large forging ratio is 1.27;

[0200] S1. Heat the heat treatment furnace to 600 °C, and quickly load the forged large rotor forging blank into the heat treatment furnace and keep it warm for 43 h;

[0201] S2. Raise the temperature to 780 °C at a rate of 16 °C / h and keep it warm for 63 h;

[0202] S3. The same as in Example 1;

[0203] S4. After removing the slow cooling cover, load the forging into the heat treatment furnace and keep it warm at 230 °C for 35 h;

[0204] S5. Raise the temperature to 670 °C at a slow rate of 7 °C / h;

[0205] S6. Then raise the temperature to 780 °C at a faster rate of 22 °C / h, keep it warm for 63 h, and then air cool. The journal is air cooled to 500 - 550 °C, and the journal is air cooled with a slow cooling cover until the surface temperature of the shaft body is 200 °C;

[0206] S7. After removing the slow cooling cover, load the forging into the heat treatment furnace and keep it warm at 180 °C for 32 h;

[0207] S8. The same as S5;

[0208] S9. Then raise the temperature to 850 °C at a faster rate of 33 °C / h, keep it warm for 60 h, and then air cool. The journal is air cooled to 500 - 550 °C, and the journal is air cooled with a slow cooling cover until the surface temperature of the shaft body is 200 °C;

[0209] S10: The same as S7;

[0210] S11: Heat up to 640 °C and hold for 75 h;

[0211] S12: The same as in Example 3.

[0212] S13: Rough machine to a surface finish of Ra 3.2 over the entire surface;

[0213] S14: Heat up to 670 °C at a rate of 10 °C / h;

[0214] S15: Then heat up to 845 °C at a faster rate of 50 °C / h, hold for 60 h, and then spray water to cool until the surface temperature of the shaft body is 60 °C;

[0215] S16: Load the forging blank into a heat treatment furnace and hold at 130 °C for 32 h;

[0216] S17: Heat up to 600 °C at a rate of 24 °C / h and hold for 75 h;

[0217] S18: Cool down to 250 °C at a cooling rate of 10 °C / h and then air cool to room temperature.

[0218] The flaw detection sensitivity and grain size of the forging after tempering in this example both reached a good level. The center limit sensitivity was Φ2.2 mm and the grain size was grade 3.5. And during the preparation process of this example, the forging did not crack. After quenching and tempering, the grain size was grade 4.5 and the performance met the standard requirements as shown in Table 4. For example, the performance of this example was as follows: Rp 0.2 Reached above 745 MPa, Rm reached above 830 MPa, A reached above 18%, Z reached above 66%, AKv reached above 125 J, FATT reached below -48 °C, and the residual stress reached below 32 MPa, with excellent performance.

[0219] Table 4 Performance results of Example 4 after quenching and tempering

[0220]

[0221]

[0222] During the research process, the inventor conducted a large amount of research. Now, some solutions with poor performance are taken as comparative examples.

[0223] Comparative Example 1

[0224] This comparative example provides a large rotor and its manufacturing method. The components and shape of the large rotor forging in this comparative example are the same as those in Example 1, which will not be elaborated here.

[0225] The preparation method of this comparative example is substantially the same as that of Example 1, except that:

[0226] In S3, no slow cooling cover was added. When air-cooled to 250 °C of the shaft body, it was found that the entire longitudinal cracking occurred in the shaft body and shaft neck of the forging, resulting in the scrapping of the forging and making it impossible to carry out subsequent heat treatment.

[0227] Comparative Example 2

[0228] This comparative example provides a large rotor and its preparation method. The components and shape of the large rotor forging in this comparative example are the same as those in Example 2, which will not be elaborated here.

[0229] The preparation method of this comparative example is substantially the same as that of Example 2, except that:

[0230] The holding temperature heated in S2 and S6 is 760 °C.

[0231] After the post-forging heat treatment of the large rotor forging in this comparative example, severe mixed crystal grains occurred, with 25% of grade 1.0, 30% of grade 2.5, and 45% of grade 4. And the flaw detection sensitivity reached Φ4.5mm, showing grass-like waves, making it impossible to carry out the next sequence of quenching and tempering.

[0232] Comparative Example 3

[0233] This comparative example provides a large rotor and its preparation method. The components and shape of the large rotor forging in this comparative example are the same as those in Example 3, which will not be elaborated here.

[0234] The preparation method of this comparative example is substantially the same as that of Example 3, except that:

[0235] The high-temperature holding times of S2, S6 and S9 are all 35h.

[0236] After the post-forging heat treatment of the large rotor forging in this comparative example, severe mixed crystal grains occurred, with 35% of grade 1.0, 30% of grade 2.0, and 35% of grade 3.0. And the flaw detection sensitivity reached Φ5.5mm, showing grass-like waves, making it impossible to carry out the next sequence of quenching and tempering.

[0237] Comparative Example 4

[0238] This comparative example provides a large rotor and its preparation method. The components and shape of the large rotor forging in this comparative example are the same as those in Example 1, which will not be elaborated here.

[0239] In the preparation method of this comparative example, in S0, after forging the shaft body with a forging ratio of 1.25, the shaft neck has not been forged yet, and the temperature of the forging has dropped below the process range and cannot be forged. The forging is returned to the heating furnace for forging heating. After the heating is completed, the shaft neck is forged, and the shaft body is not deformed, and the finished product is obtained. The remaining steps are substantially the same as those in Example 1.

[0240] After the post-forging heat treatment of the large rotor forging in this comparative example, the grain size shows coarse grains of grade 2.0 - 2.5, and the flaw detection sensitivity reaches Φ4mm, showing a grass-like wave, making it impossible to carry out the subsequent quenching and tempering.

[0241] Comparative Example 5

[0242] This comparative example provides a large rotor and its preparation method. The components and shape of the large rotor in this comparative example are the same as those in Example 2, and will not be elaborated here.

[0243] The preparation method of the large rotor in this comparative example is generally the same as that in Example 2, except that:

[0244] S18: After cooling at a rate of 30°C / h to 250°C, it is air-cooled to room temperature.

[0245] This results in the absolute value of the residual stress exceeding the standard requirements. The performance is shown in Table 5 below.

[0246] Table 5 Performance Results of Comparative Example 5 after Quenching and Tempering

[0247]

[0248]

[0249] Comparative Example 6

[0250] This comparative example provides a large rotor and its preparation method. The components and shape of the large rotor in this comparative example are the same as those in Example 3, and will not be elaborated here.

[0251] The preparation method of the large rotor in this comparative example is generally the same as that in Example 3, except that:

[0252] S15: After the heat preservation ends, it is sprayed with water and cooled to the surface temperature of the shaft body being 300°C;

[0253] S16: The forging blank is loaded into the heat treatment furnace and kept at 350°C for 35h;

[0254] This results in a low yield strength and a significant reduction in toughness after quenching and tempering, as shown in Table 6.

[0255] Table 6 Performance Results of Comparative Example 6 after Quenching and Tempering

[0256]

[0257] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a large rotor, characterized in that: The preparation method comprises the following steps: first two-phase normalizing, second two-phase normalizing, third complete austenitizing normalizing, tempering and quenching and tempering treatments are performed in sequence.

2. The preparation method according to claim 1, characterized in that: The preparation method comprises the following steps: S1. Heat the heat treatment furnace to Ar1±20℃, load the large rotor forging blank after forging into the heat treatment furnace as soon as possible and keep it warm; S2, heating to T1 at speed v1, keeping warm; S3, air cooling of forging blank; S4, loading the forging billet into a heat treatment furnace and performing low temperature insulation in the range of 100 to 150°C below the Ms point; S5, heating at speed v2 to AC1-20℃~AC1; S6, then heat up to T2 at speed v3, keep warm, and then air cool, v3>v2; S7, loading the forging billet into a heat treatment furnace, and performing low temperature insulation in the range of 100 to 150°C below the Ms point; S8, same as S5; S9, heat up to T3 at a faster speed v4, keep warm, and then air cool; S10, same as S7; S11, heat up to AC1- (50~80℃), keep warm; S12, cool the temperature to 250°C at a cooling rate of less than 10°C / h, and then air cool to room temperature; then perform tempering treatment.

3. The preparation method according to claim 2, characterized in that: The quenching and tempering treatment comprises: S13, machining the forging blank obtained in S12; S14, heating at speed v5 to AC1-20℃~AC1; S15, then heat up to AC3+ (30-50°C) at speed v6, keep warm, and then water cool; S16, loading the forging billet into a heat treatment furnace, and performing low temperature insulation in the range of 150 to 200° C. below the Ms point; S17, heating to AC1-200℃~AC1-50℃ at the same heating rate as S11, and keeping warm; S18. Same as S12.

4. The preparation method according to claim 3, characterized in that: v5>v2.

5. The preparation method according to claim 3, characterized in that: v6>v4.

6. The preparation method according to claim 3, characterized in that: The insulation temperature in S16 is lower than the insulation temperature in S10.

7. The preparation method according to any one of claims 2 to 6, characterized in that: In the above S3, when the journal temperature is cooled to 500-550°C by air, the journal of the forging blank is slowly cooled by a cover, and air cooling is continued until the shaft body temperature is 120-150°C lower than the Ms point.

8. The preparation method according to claim 3, characterized in that: In the above S14, the temperature of AC1-20°C to AC1 is 670°C to 700°C.

9. The preparation method according to claim 1, characterized in that: The large rotor is made of low-carbon C-Cr-Ni-Mo-V steel.

10. A large rotor, characterized in that: The large rotor is prepared by the method according to any one of claims 1 to 9.

Images