Large rotor forge piece and heat treatment method thereof

Abstract

The invention discloses a large rotor forge piece and a heat treatment 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 the forge piece in the existing heat treatment method of the large rotor forge piece. The heat treatment method comprises the steps of first-time two-phase region normalizing, second-time two-phase region normalizing and third-time complete austenitizing normalizing. By means of the method, the forge piece can be prevented from cracking, grain refinement can be achieved, and tissue preparation can be fully made for subsequent thermal refining.

Description

Technical Field

[0001] The invention relates to the technical field of rotor preparation, and in particular to a large rotor forging and a heat treatment method thereof. Background Art

[0002] As the key core component of the steam turbine generator set, the size of the core component rotor forging is also increasing with the inevitable development trend of increasing parameters and capacity of the steam turbine set. At present, the shaft section of forgings such as large flywheel rotors, low-pressure rotors, generator rotors and welded rotors has increased to between φ1600mm-φ3000mm. Due to the increase in the shaft size of the forgings, the heat treatment cycle is long to make the forgings finer and more uniform through post-forging heat treatment to ensure the sensitivity of UT flaw detection before quenching and tempering, and there are problems such as high energy consumption and easy cracking of forgings, which brings great pressure to production. Summary of the invention

[0003] In view of the above situation, the present invention aims to provide a large rotor forging and a heat treatment method thereof, which can at least solve one of the following technical problems: the existing heat treatment method for large rotor forgings has a long production cycle, high energy consumption, and the forgings are prone to cracking.

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

[0005] The invention provides a heat treatment method for a large rotor forging. The heat treatment method comprises: a first two-phase zone normalizing, a second two-phase zone normalizing and a third complete austenitizing normalizing.

[0006] Furthermore, the insulation temperature of the first two-phase zone normalizing is T1, AC3-20℃≤T1<AC3; the insulation temperature of the second two-phase zone normalizing is T2, AC3-20℃≤T2<AC3, and the insulation temperature of the third complete austenitizing normalizing is T3, T3 is AC3+(50~80℃).

[0007] Furthermore, the heat treatment method comprises the following steps:

[0008] 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;

[0009] S2, heating to T1 at speed v1, keeping warm;

[0010] S3, air cooling of forging blank;

[0011] S4. After removing the slow cooling cover, the forging billet is placed into the heat treatment furnace and kept warm at a temperature of 100 to 150°C below the Ms point;

[0012] S5, slowly raise the temperature to AC1-20℃~AC1 at a speed v2;

[0013] S6, then heat up to T2 at a faster speed v3, keep warm, and then air cool;

[0014] S7. After removing the slow cooling cover, the forging blank is placed into the heat treatment furnace and kept at a low temperature within the range of 100 to 150°C below the Ms point;

[0015] S8, same as S5;

[0016] S9, heat up to T3 at a faster speed v4, keep warm, and then air cool.

[0017] Furthermore, v3>v1.

[0018] Furthermore, in S3, when the journal temperature is air-cooled to 500-550°C, the journal sleeve of the forging blank is slowly cooled, and air cooling is continued until the shaft body temperature is 120-150°C lower than the Ms point.

[0019] Furthermore, the holding time of S1 is not less than D1 / 100, D1 is the diameter of the shaft body, the unit of D1 is mm, and the unit of the holding time is h.

[0020] Furthermore, in S2, v1 is 15 to 20°C / h.

[0021] Furthermore, in S2, the holding time is (2-4)D1 / 100, D1 is the diameter of the shaft body, the unit of D1 is mm, and the unit of the holding time is h.

[0022] Furthermore, in S5, v2<v1.

[0023] The present invention also provides a large rotor forging, which is prepared by the above method.

[0024] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0025] a) In the heat treatment method of large rotor forgings of the present invention, two-phase normalizing is adopted to keep the large cross-section forgings at the highest possible temperature in the two-phase region (temperature is above AC3-20°C and less than AC3, hereinafter referred to as AC3-20°C~<AC3), so that most of the forging structure (70% to 90% by volume) is transformed into a uniform and fine austenite structure, and a small part retains a bainite high temperature tempering structure; it is worth noting that the bainite high temperature tempering structure is divided by the transformed austenite structure, and the two phases are interspersed and mixed together, and then air-cooled. After two consecutive two-phase normalizings close to the AC3 temperature, the crystallographic degree phase of the original austenite coarse structure is completely disrupted, and the original coarse austenite grains have been broken by the two-phase structure that has been incompletely austenitized twice, forming uniform and fine grain boundaries, phase boundaries and dispersed carbides. At this time, it undergoes a third complete austenitizing and normalizing to make the structure completely form equiaxed austenite grains. After normalizing, it is tempered to form a uniform bainite tempered structure, which effectively refines the forging structure and grains and can fully prepare the structure for subsequent quenching and tempering treatment.

[0026] b) In the preparation method of the present invention, by accurately controlling the cooling method after forging, the normalizing temperature in different steps, the heating rate in different stages, the holding temperature, the holding time, the cooling rate and other process parameters; the cracking of the forging is avoided, and the grain refinement is achieved, which can fully prepare the organization for the subsequent tempering treatment.

[0027] c) In the preparation method of the present invention, the temperature of the first two normalizing is relatively low, and combined with 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 reduce time, reduce energy consumption costs, and improve production efficiency.

[0028] d) The structure of the large rotor forging of the present invention is a bainite tempered structure with fine and uniform grains, for example, the grain size is 3.5 to 5. The flaw detection sensitivity of the large rotor forging reaches a good level, for example, the center limit sensitivity is Φ2.0 to 2.5 mm.

[0029] Other features and advantages of the present invention will be described in the following description, and part of them will become obvious from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the contents particularly pointed out in the written description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0031] Figure 1 is a schematic diagram of a large rotor forging of the present invention;

[0032] Figure 2 It is a schematic diagram of the slow cooling cover of the present invention;

[0033] Figure 3 It is a schematic diagram of air cooling of slow cooling hood forgings;

[0034] Figure 4 The grain map of the forging blank after the S3 step of Example 1;

[0035] Figure 5 The grain map of the forging blank after the S6 step of Example 1;

[0036] Figure 6 This is the grain diagram of the forging blank after processing in step S9 of Example 1.

[0037] Reference numerals

[0038] 1-shaft body, 2-shaft neck, 3-flange, 4-slow cooling cover, 41-lining, 42-outer skin, 43-support frame. DETAILED DESCRIPTION

[0039] Preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used to explain the principles of the present invention together with the embodiments of the present invention.

[0040] As attached Figure 1 As shown, the present invention provides a large rotor forging, which includes an axle body 1 and a journal 2 connected to both sides of the axle body 1. The diameter D1 of the axle body 1 and the diameter D2 of the journal 2 meet the following relationship: D1>D2. The difference between D1 and D2 is more than 1000mm, for example, the difference between D1 and D2 is 1100-2000mm, for example, 1200mm, 1300mm, 1400mm, 1500mm, 1600mm, 1700mm, 1800mm, 1900mm. The cross-sectional difference at the connecting position of the axle body 1 and the journal 2 of the large rotor forging is large, resulting in a large internal and external temperature difference of the forging during the heat treatment process, and increasing the structural stress and thermal stress. In addition, the forged grain size and structure after forging are coarse, and the toughness reserve is insufficient. The forging is prone to cracking during the post-forging heat treatment process after forging.

[0041] Specifically, the large rotor forging may further include a flange 3 connected to the outer side of the journal 2. The diameter D2 of the journal 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, for example, 100 mm, 200 mm, 300 mm, 400 mm, 500 mm, 600 mm.

[0042] Specifically, the diameter D1 of the shaft body 1 is greater than 1700 mm, for example, 1700-3000 mm, such as 1800 mm, 2000 mm, 2200 mm, 2400 mm, 2600 mm, or 2800 mm.

[0043] Specifically, the diameter D2 of the journal 2 is greater than 600 mm, for example, 600 to 900 mm, such as 650 mm, 700 mm, 750 mm, 800 mm, or 850 mm.

[0044] Specifically, the diameter D3 of the flange 3 is greater than 700 mm, for example, 700-1600 mm, such as 800 mm, 900 mm, 1000 mm, 1100 mm, 1200 mm, 1300 mm, 1400 mm, or 1500 mm.

[0045] Specifically, the large rotor forging of the present invention is composed of low-carbon C-Cr-Ni-Mo-V steel with structural genetic characteristics, such as 30Cr2Ni4MoV steel, 35Cr2Ni4MoV steel, 25Cr2Ni4MoV steel and 22Cr2Ni3MoV steel.

[0046] For example, the components of the large rotor forging 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 unavoidable impurities.

[0047] The invention provides a heat treatment method for a large rotor forging, which comprises a first two-phase region normalizing, a second two-phase region normalizing and a third complete austenitizing normalizing.

[0048] Specifically, the holding temperature of the first two-phase zone normalizing is T1, AC3-20℃≤T1<AC3; the holding temperature of the second two-phase zone normalizing is T2, AC3-20℃≤T2<AC3, and the holding temperature of the third complete austenitizing normalizing is T3, T3 is AC3+(50~80℃).

[0049] Compared with the prior art, the heat treatment method of the large rotor forging of the present invention adopts two-phase normalizing to keep the large cross-section forging at the highest temperature (AC3-20℃~<AC3) in the two-phase region, so that most of the forging structure (70% to 90% by volume) inside and outside the forging is transformed into a uniform and fine austenite structure, and a small part retains a bainite high-temperature tempered structure; it is worth noting that the bainite high-temperature tempered structure is divided by the transformed austenite structure, and the two phases are interspersed and mixed together, and then air-cooled. After two consecutive two-phase normalizings close to the AC3 temperature, the crystallographic degree phase of the original austenite coarse structure is completely disrupted, and the original coarse austenite grains have been broken by the two-phase structure that has been incompletely austenitized twice, forming uniform and fine grain boundaries, phase boundaries and dispersed carbides. At this time, it undergoes a third complete austenitizing and normalizing to make the structure completely form equiaxed austenite grains. After normalizing, it is tempered to form a uniform bainite tempered structure, which effectively refines the forging structure and grains and can fully prepare the structure for subsequent quenching and tempering treatment.

[0050] Specifically, the heat treatment method of the large rotor forging comprises the following steps:

[0051] 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;

[0052] S2, raise the temperature to AC3-20℃~<AC3 at a speed v1 of more than 15℃ / h, and keep warm;

[0053] S3, air cooling of forging blank;

[0054] S4. After removing the slow cooling cover, the forging billet is placed into the heat treatment furnace and kept warm at a temperature of 100 to 150°C below the Ms point;

[0055] S5, slowly raise the temperature to AC1-20℃~AC1 at a speed v2;

[0056] S6, then raise the temperature to AC3-20℃~<AC3 at a faster speed v3, keep warm, and then air cool; v3>v1;

[0057] S7. After removing the slow cooling cover, the forging blank is placed into the heat treatment furnace and kept at a low temperature within the range of 100 to 150°C below the Ms point;

[0058] S8, same as S5;

[0059] S9, then raise the temperature to AC3+ (50-80°C) at a faster speed v4, keep warm, and then air cool; v4>v3.

[0060] Specifically, the forging of large rotor forgings includes the forging of large rotor forgings before S1, which includes: first forging a small-section journal area (if there is a flange, the journal area includes the journal and the flange), and then forging the shaft body with a large forging ratio. Specifically, the range of the large forging ratio is 1.2 to 1.3; by making the shaft body deformed greatly, a larger austenite nucleation driving force is formed, which is beneficial to the subsequent static recrystallization and the refinement of the grain and structure of the forging.

[0061] Specifically, in the above S1, the large rotor forging blank after forging is not air-cooled to room temperature, but is loaded into a heat treatment furnace as quickly as possible for insulation after forging, so that partial pearlite transformation from grain boundaries to intracrystalline distribution can occur (volume percentage 20% to 35%). 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.

[0062] Specifically, in the above S1, considering that the temperature is too high or too low, the incubation period of pearlite transformation is too long, which will reduce the pearlite content and reduce the refinement effect. Therefore, the holding temperature of S1 is controlled to be Ar1±20℃, such as 600~630℃, such as 610℃, 620℃, 630℃.

[0063] Specifically, in the above S1, the role of insulation is to ensure the consistency of the temperature inside and outside the forging blank, reduce the temperature difference during the heating process of the forging blank, and reduce thermal stress. Considering that the insulation time is too long, the heat treatment cycle will be increased; if the insulation time is too short, the core and surface temperatures cannot be uniform and the pearlite content is less. Therefore, the insulation time of S1 is controlled to be not less than D1 / 100, D1 is the diameter of the shaft, the unit of D1 is mm, and the unit of insulation time is h. Preferably, the insulation time is (1.5~2)D1 / 100.

[0064] Specifically, in the above S2, the plastic deformation stage reaches close to AC3 (e.g., AC3-20°C~<AC3, e.g., 780~800°C, e.g., 785°C, 790°C, 795°C) relatively quickly while ensuring that the instantaneous internal stress is controllable, with many nucleation points, which fully disrupts the original austenite grains and achieves the effect of grain refinement. Therefore, the temperature is increased at a speed v1 of more than 15°C / h. Preferably, v1 is 15~20°C / h, e.g., 16°C / h, 17°C / h, 18°C / h, 19°C / h.

[0065] Specifically, in the above S2, in order to make the core of the forging blank burn through, the internal and external temperatures are consistent, and the core has two-phase region fully nucleated. The holding time is controlled to be (2-4)D1 / 100, D1 is the diameter of the shaft, 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, for example, the holding time is 2.5D1 / 100, 2.7D1 / 100, 3D1 / 100, 3.2D1 / 100, 3.5D1 / 100.

[0066] Specifically, in the above S3, the forging blank is hung on a pad iron with a height of 1000 mm for air cooling.

[0067] Specifically, in the above S3, when the shaft neck (if there is a flange, here the shaft neck and flange) is air-cooled to within the range of 500-550°C, the shaft neck (if there is a flange, here the shaft neck and flange) of the forging blank is covered with a slow cooling cover 4, and air-cooled to 120-150°C below the Ms point of the shaft body, for example, 220-250°C. It should be noted that the slow cooling cover can reduce the cooling rate of the shaft neck and flange (for example, the cooling rate reaches 5-10°C / h), thereby achieving the effect of reducing the thermal stress and structural stress at the transition between the large cross-section of the shaft neck and the shaft body, and reducing the risk of cracking of the forging. At the same time, it can ensure that the forging blank is air-cooled to a lower temperature, so that the temperature of the core of the forging blank is lower, and the structural transformation can be more sufficient, achieving the effect of refining the structure and grain.

[0068] Specifically, in the above S3, the structure of the slow cooling cover 4 is as follows: Figure 2 As shown, the inner diameter of the slow cooling hood 4 is equivalent to the diameter of the shaft body. The slow cooling hood 4 includes an inner lining 41 and an outer skin 42. The inner lining 41 is asbestos felt with good thermal insulation effect, and the outer skin 42 is an iron sheet for supporting. The slow cooling hood 4 also includes a height-adjustable support frame 43, which is connected to the outer skin 42 and can adjust the position of the slow cooling hood 4.

[0069] Specifically, Figure 3 Shown is a schematic diagram of air cooling of slow cooling hood forgings.

[0070] Specifically, in the above S4, the temperature is kept below the Ms point for a long time to make the core of the forging blank fully transform, which is conducive to adjusting and refining the grain structure of the steel through subsequent phase transformation and recrystallization. Therefore, the holding time is controlled to be (1.2-1.6)D1 / 100, D1 is the diameter of the shaft, 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.

[0071] Specifically, in the above S5, this stage belongs to speed-limited heating, which minimizes the internal and external temperature difference and instantaneous internal stress in the large rotor forging in the elastic deformation zone of the forging, reduces the risk of cracking, and prepares for the transformation of the two-phase zone structure; therefore, v2 is controlled to be less than 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.

[0072] Specifically, in the above S5, the temperature of AC1-20°C to AC1 is preferably 670°C to 700°C, for example, 680°C, 690°C, or 700°C.

[0073] Specifically, in the above S6, in the plastic deformation stage, while ensuring that the instantaneous internal stress is controllable, it reaches close to AC3 relatively quickly, with many nucleation points, fully disrupting the original austenite grains, and achieving the effect of grain refinement. This stage belongs to rate-limited heating. In the plastic deformation zone of the forging and the forging has undergone a normalizing treatment, the structure is relatively fine and the plastic toughness reserve is increased, so v3>v1 is controlled, for example, v3 is below 30℃ / h, preferably, v3 is 20-30℃ / h, for example, 22℃ / h, 24℃ / h, 26℃ / h, 28℃ / h.

[0074] Specifically, in the above S6, considering that the large cross-section of the large forging is large, there is a certain temperature difference between the inside and outside of the forging during the heating process. Therefore, the holding time is controlled to be (2~4)D1 / 100, D1 is the diameter of the shaft body, the unit of D1 is mm, the unit of the holding time is h, and the holding time is the same as the holding stage in S2.

[0075] Specifically, in the above S6, the air cooling operation steps are the same as S3, except that the temperature of the shaft surface is cooled by air this time by 30-50° C. lower than the final temperature of S3.

[0076] Specifically, in the above S7, considering that in S6, the temperature of the shaft body is lower than that of S3 due to air cooling, the core of the forging will also be lowered accordingly, so the holding time in the low temperature holding stage is relatively shortened. For example, the holding time is controlled to be 1 to 1.5D1 / 100mm, 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.

[0077] Specifically, in the above S9, v4>v3, compared with the first two normalizing, the forging has more sufficient plastic toughness reserves and stronger crack resistance, and further increasing the heating rate of the two-phase region can effectively refine the grains and structure. Preferably, v4 is 30-40°C / h, such as 32°C / h, 34°C / h, 36°C / h, 38°C / h.

[0078] Specifically, in the above S9, the temperature is kept at AC3+(50-80°C) (e.g., 850-890°C) to completely form equiaxed austenite grains. Since normalizing has been performed twice before, the structure and grain size are very fine, and the time required for austenitization to uniform grains is shorter than the previous two times, so the required holding time in 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, D1 is the diameter of the shaft, the unit of D1 is mm, and the unit of holding time is h.

[0079] Specifically, in the above S9, the air cooling operation is the same as the air cooling in S6, and will not be repeated here.

[0080] Specifically, the heat treatment method of the large rotor forging further includes a tempering process, and the tempering process includes the following steps:

[0081] S10, same as S7;

[0082] S11, heat up to AC1- (50~80℃), keep warm;

[0083] S12, cool the temperature to 250°C at a cooling rate of less than 10°C / h, and then air cool to room temperature.

[0084] Specifically, in S11, the heating rate is 10 to 25°C / h, for example, 13°C / h, 15°C / h, 18°C / h, 20°C / h, and 23°C / h.

[0085] 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, D1 is the diameter of the shaft, the unit of D1 is mm, and the unit of the holding time is h. This step forms a uniform bainite tempering structure through sufficient tempering, effectively refines the forging structure and grains, and can fully prepare the structure for subsequent processes.

[0086] Specifically, in S12, considering that too high a cooling rate may cause excessive thermal stress at different cross sections, causing deformation of the forgings, and too high a cooling rate may cause the hardness of the forgings with forged black skin to be too high, resulting in the risk of being difficult to process. Therefore, the cooling rate is controlled to be below 10°C / h. For example, 5 to 10°C / h, such as 6°C / h, 7°C / h, 8°C / h, and 9°C / h.

[0087] The present invention also provides a large rotor forging, which is prepared by the above-mentioned heat treatment method.

[0088] Specifically, the structure of the large rotor forging is a tempered bainite structure with fine and uniform grains, for example, the grain size is 3.5 to 5. The flaw detection sensitivity of the large rotor forging reaches a good level, for example, the center limit sensitivity is Φ2.0 to 2.5 mm.

[0089] Compared with the prior art, the heat treatment method of the large rotor forging of the present invention adopts two-phase normalizing to keep the large cross-section forging at the highest temperature (AC3-20℃~<AC3) in the two-phase region, so that most of the forging structure (70% to 90% by volume) inside and outside the forging is transformed into a uniform and fine austenite structure, and a small part retains a bainite high-temperature tempered structure; it is worth noting that the bainite high-temperature tempered structure is divided by the transformed austenite structure, and the two phases are interspersed and mixed together, and then air-cooled. After two consecutive two-phase normalizings close to the AC3 temperature, the crystallographic degree phase of the original austenite coarse structure is completely disrupted, and the original coarse austenite grains have been broken by the two-phase structure that has been incompletely austenitized twice, forming uniform and fine grain boundaries, phase boundaries and dispersed carbides. At this time, it undergoes a third complete austenitizing and normalizing to make the structure completely form equiaxed austenite grains. After normalizing, it is tempered to form a uniform bainite tempered structure, which effectively refines the forging structure and grains and can fully prepare the structure for subsequent quenching and tempering treatment.

[0090] In the preparation method of the present invention, during the forging process of the large rotor forging blank, the journal area with a small cross-section is forged first (if there is a flange, this is the journal and the flange), and then the shaft body is deformed by a large forging ratio. The shaft body is greatly deformed, forming a larger austenite nucleation driving force, which is beneficial to the subsequent static recrystallization and the refinement of the grain and structure of the forging.

[0091] In the preparation method of the present invention, by accurately controlling the cooling method after forging, the normalizing temperature in different steps, the heating rate in different stages, the holding temperature, the holding time, the cooling rate and other process parameters; the cracking of the forging is avoided, and the grain refinement is achieved, which can fully prepare the organization for the subsequent tempering treatment.

[0092] In the preparation method of the present invention, the temperature of the first two normalizing processes is relatively low, and combined with 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 reduce time, reduce energy consumption costs, and improve production efficiency.

[0093] The advantages of precise control of process parameters of the present invention are demonstrated below with specific examples and comparative examples.

[0094] Example 1

[0095] The present embodiment provides a large motor rotor forging and a heat treatment method thereof. The large rotor forging of the present embodiment includes an axle body 1 and a shaft neck 2 connected on both sides of the axle body 1. The cross-sectional diameter of the axle body is φ1800 mm, and the cross-sectional diameter of the shaft neck 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 remainder is Fe and unavoidable impurities.

[0096] The heat treatment method of the large rotor forging of this embodiment comprises the following steps:

[0097] S0, first forge a small-section journal and then forge the shaft body with a large forging ratio, the value of the large forging ratio is 1.25;

[0098] S1. Heat the heat treatment furnace to 610°C, load the large rotor forging blank after forging into the heat treatment furnace as soon as possible, and keep it warm for 30 hours;

[0099] S2, heat up to 795℃ at a rate of 15℃ / h and keep warm for 50h;

[0100] S3, air-cool the forging billet, air-cool the journal to 500-550℃, then add a slow cooling cover to air-cool the journal until the shaft surface temperature reaches 250℃;

[0101] S4. After removing the slow cooling cover, place the forging into the heat treatment furnace and keep it at 200℃ for 25h;

[0102] S5, slowly raise the temperature to 680°C at a rate of 8°C / h;

[0103] S6. Then heat up to 795℃ at a faster speed of 25℃ / h, keep warm for 50h, and then air cool the shaft neck to 500-550℃, and add a slow cooling cover to air cool the shaft neck to 200℃ on the shaft surface;

[0104] S7. After removing the slow cooling cover, place the forging into the heat treatment furnace and keep it at 180℃ for 22h;

[0105] S8, same as S5;

[0106] S9, then heat up to 860℃ at a faster speed of 34℃ / h, keep warm for 45h, then air cool the shaft neck to 500~550℃, add a slow cooling cover to air cool the shaft neck to the shaft body surface temperature of 200℃;

[0107] S10, same as S7;

[0108] S11, heating to 640℃, keeping warm for 55h;

[0109] S12: Cool down to 250°C at a cooling rate of 10°C / h, and then air cool to room temperature.

[0110] The grain size of the forging blank after the S3 step of this embodiment is as follows: Figure 4 As shown in FIG. 1 , the grain size of the forging blank after step S6 is as follows: Figure 5 As shown in FIG. 1 , the grain size of the forging blank after step S9 is as follows: Figure 6 As shown, the flaw detection sensitivity and grain size of the forging of this embodiment have reached a good level, the center limit sensitivity is Φ2.0mm, and the grain size is level 5. In addition, the forging of this embodiment did not crack during the preparation process.

[0111] Example 2

[0112] The present embodiment provides a large low-pressure rotor forging and a heat treatment method thereof. The shape of the large rotor forging of the present embodiment is basically the same as that of Embodiment 1, except that the shaft section of the rotor forging is φ2000mm and the journal size is 800mm; the material of the rotor is 30Cr2Ni4MoV steel, and the 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 remainder is Fe and unavoidable impurities.

[0113] The heat treatment method of the large rotor forging in this embodiment is substantially the same as that in Embodiment 1, including:

[0114] S0, first forge a small-section journal and then forge the shaft body with a large forging ratio, the value of the large forging ratio is 1.26;

[0115] S1. Heat the heat treatment furnace to 620°C, load the forged large rotor forging into the heat treatment furnace as soon as possible, and keep it warm for 32 hours;

[0116] S2, heat up to 790℃ at a rate of 15℃ / h and keep warm for 55h;

[0117] S3, same as in Example 1;

[0118] S4. After removing the slow cooling cover, place the forging into the heat treatment furnace and keep it at 210℃ for 28h;

[0119] S5, slowly raise the temperature to 700°C at a rate of 8°C / h;

[0120] S6. Then heat up to 790℃ at a faster speed of 23℃ / h, keep warm for 55h, then air cool the journal to 500-550℃, add a slow cooling cover to air cool the journal to the shaft surface temperature of 200℃;

[0121] S7. After removing the slow cooling cover, place the forging into the heat treatment furnace and keep it at 180℃ for 25h;

[0122] S8, same as S5;

[0123] S9, then heat up to 870℃ at a faster speed of 31℃ / h, keep warm for 50h, then air cool the shaft neck to 500-550℃, add a slow cooling cover to air cool the shaft neck to 200℃ on the shaft surface;

[0124] S10, same as S7;

[0125] S11, heating to 640℃, keeping warm for 60h;

[0126] S12: Same as Example 1.

[0127] The flaw detection sensitivity and grain size of the forging of this embodiment have reached a relatively good level, with the center limit sensitivity being Φ2.5 mm and the grain size being level 4.5. In addition, the forging of this embodiment did not crack during the preparation process.

[0128] Example 3

[0129] The present embodiment provides a large flywheel rotor forging and a heat treatment method thereof. The shape of the large rotor forging of the present embodiment is basically the same as that of Embodiment 1, except that the shaft section of the rotor forging is φ2800 mm and the journal size is 800 mm; 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 remainder is Fe and unavoidable impurities.

[0130] The heat treatment method of the large rotor forging in this embodiment is substantially the same as that in Embodiment 1, including:

[0131] S0, first forge a small-section journal and then forge the shaft body with a large forging ratio, the value of the large forging ratio is 1.28;

[0132] S1. Heat the heat treatment furnace to 630°C, load the large rotor forging blank after forging into the heat treatment furnace as soon as possible, and keep it warm for 45 hours;

[0133] S2, raise the temperature to 800℃ at a rate of 16℃ / h and keep it at this temperature for 65h;

[0134] S3, same as in Example 1;

[0135] S4. After removing the slow cooling cover, place the forging into the heat treatment furnace and keep it at 250℃ for 38h;

[0136] S5, slowly raise the temperature to 700°C at a rate of 6°C / h;

[0137] S6. Then heat up to 800℃ at a faster speed of 25℃ / h, keep warm for 65h, then air cool the journal to 500-550℃, add a slow cooling cover to air cool the journal to the shaft surface temperature of 200℃;

[0138] S7. After removing the slow cooling cover, place the forging into the heat treatment furnace and keep it at 200℃ for 35h;

[0139] S8, same as S5;

[0140] S9, then heat up to 880℃ at a faster speed of 33℃ / h, keep warm for 60h, then air cool the shaft neck to 500~550℃, add a slow cooling cover to air cool the shaft neck to 200℃ on the shaft surface;

[0141] S10, same as S7;

[0142] S11, heating to 660℃, keeping warm for 80h;

[0143] S12: Cool down to 250°C at a cooling rate of 8°C / h, and then air cool to room temperature.

[0144] The flaw detection sensitivity and grain size of the forging of this embodiment have reached a relatively good level, the center limit sensitivity is Φ2.5mm, and the grain size is level 4. In addition, the forging of this embodiment does not crack during the preparation process.

[0145] Example 4

[0146] The present embodiment provides a large welded rotor forging and a heat treatment method thereof. The shape of the large rotor forging of the present embodiment is basically the same as that of Embodiment 1, except that the shaft section of the rotor forging is φ2500 mm and 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 remainder is Fe and unavoidable impurities.

[0147] The heat treatment method of the large rotor forging in this embodiment is substantially the same as that in Embodiment 1, including:

[0148] S0, first forge a small-section journal and then forge the shaft body with a large forging ratio, the value of the large forging ratio is 1.27;

[0149] S1. Heat the heat treatment furnace to 600°C, load the forged large rotor forging billet into the heat treatment furnace as soon as possible, and keep it warm for 43 hours;

[0150] S2, heat up to 780℃ at a rate of 16℃ / h and keep warm for 63h;

[0151] S3, same as in Example 1;

[0152] S4. After removing the slow cooling cover, place the forging into the heat treatment furnace and keep it at 230℃ for 35h;

[0153] S5, slowly raise the temperature to 670°C at a rate of 7°C / h;

[0154] S6. Then heat up to 780℃ at a faster speed of 22℃ / h, keep warm for 63h, then air cool the journal to 500-550℃, add a slow cooling cover to air cool the journal to the shaft surface temperature of 200℃;

[0155] S7. After removing the slow cooling cover, place the forging into the heat treatment furnace and keep it at 180℃ for 32h;

[0156] S8, same as S5;

[0157] S9, then heat up to 850℃ at a faster speed of 33℃ / h, keep warm for 60h, then air cool the shaft neck to 500~550℃, add a slow cooling cover to air cool the shaft neck to the shaft body surface temperature of 200℃;

[0158] S10, same as S7;

[0159] S11, heating to 640℃, keeping warm for 75h;

[0160] S12: Same as Example 3.

[0161] The flaw detection sensitivity and grain size of the forging of this embodiment have reached a relatively good level, with the center limit sensitivity being Φ2.2 mm and the grain size being level 3.5. In addition, the forging of this embodiment did not crack during the preparation process.

[0162] The inventor has conducted a lot of research during the research process, and now uses some solutions with poor performance as comparative examples.

[0163] Comparative Example 1

[0164] This comparative example provides a large rotor forging and a heat treatment method thereof. The components and shapes of the large rotor forging in this comparative example are the same as those in Example 1, and will not be described in detail herein.

[0165] The preparation method of the large rotor forging of this comparative example is substantially the same as that of Example 1, except that:

[0166] S3 was not equipped with a slow cooling cover. When the shaft was air-cooled to 250°C, it was found that the shaft and journal of the forging had overall longitudinal cracks, which resulted in the forging being scrapped and unable to undergo subsequent heat treatment.

[0167] Comparative Example 2

[0168] This comparative example provides a large rotor forging and a heat treatment method thereof. The components and shape of the large rotor forging of this comparative example are the same as those of Example 2, and will not be described in detail here.

[0169] The preparation method of the large rotor forging of this comparative example is substantially the same as that of Example 2, except that:

[0170] The holding temperature to which S2 and S6 are heated is 760°C.

[0171] After heat treatment, the large rotor forgings in this comparative example have serious mixed grain size of 25% for level 1.0, 30% for level 2.5, and 45% for level 4. The flaw detection sensitivity reaches Φ4.5mm, and grass-like waves appear, making it impossible to carry out the next order tempering.

[0172] Comparative Example 3

[0173] This comparative example provides a large rotor forging and a heat treatment method thereof. The components and shape of the large rotor forging of this comparative example are the same as those of Example 3, and will not be repeated here.

[0174] The preparation method of the large rotor forging of this comparative example is substantially the same as that of Example 3, except that:

[0175] The high temperature holding time of S2, S6 and S9 is 35h.

[0176] After heat treatment, the large rotor forgings in this comparative example had serious mixed grain size of 35% for level 1.0, 30% for level 2.0, and 35% for level 3.0, and the flaw detection sensitivity reached Φ5.5mm, with grass-like waves, making it impossible to carry out the next order quenching and tempering.

[0177] Comparative Example 4

[0178] This comparative example provides a large rotor forging and a heat treatment method thereof. The components and shapes of the large rotor forging in this comparative example are the same as those in Example 1, and will not be described in detail herein.

[0179] In the preparation method of this comparative example, in S0, the shaft body is forged at a forging ratio of 1.25, but the shaft neck has not yet been forged. The forging temperature 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 to obtain a finished product.

[0180] The remaining steps are substantially the same as those in Example 1.

[0181] After the large rotor forgings of this comparative example were heat treated after forging, the grain size was coarse 2.0-2.5, and the flaw detection sensitivity reached Φ4mm, with grass-like waves, making it impossible to carry out the next-order quenching and tempering.

[0182] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A heat treatment method for a large rotor forging, characterized in that: The heat treatment method comprises: a first two-phase region normalizing, a second two-phase region normalizing and a third complete austenitizing normalizing.

2. The heat treatment method according to claim 1, characterized in that The insulation temperature of the first two-phase normalizing is T1, AC3-20℃≤T1<AC3; the insulation temperature of the second two-phase normalizing is T2, AC3-20℃≤T2<AC3, and the insulation temperature of the third complete austenitizing normalizing is T3, T3 is AC3+(50~80℃).

3. The heat treatment method according to claim 2, characterized in that: The heat treatment 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, slowly raise the temperature to AC1-20℃~AC1 at a speed v2; S6, then heat up to T2 at a faster speed v3, keep warm, and then air cool; 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.

4. The heat treatment method according to claim 3, characterized in that: v3>v1.

5. The heat treatment method according to claim 3, 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.

6. The heat treatment method according to claim 3, characterized in that: The insulation time of S1 is not less than D1 / 100, D1 is the diameter of the shaft body, the unit of D1 is mm, and the unit of insulation time is h.

7. The heat treatment method according to claim 3, characterized in that: In the S2, v1 is 15 to 20°C / h.

8. The heat treatment method according to claim 3, characterized in that: In S2, the holding time is (2-4)D1 / 100, D1 is the diameter of the shaft body, the unit of D1 is mm, and the unit of the holding time is h.

9. The heat treatment method according to any one of claims 3 to 8, characterized in that: The heat treatment method further includes a tempering process, and the tempering process includes the following steps: S10, same as S7; S11, heat up to AC1- (50~80℃), keep warm; S12. After cooling to 250°C, air cool to room temperature.

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

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