A heat treatment method for reducing the near-surface flaw detection sensitivity of a rotor forging and a rotor forging

Abstract

The application relates to a heat treatment method for reducing flaw detection sensitivity of a rotor forging near a surface and a rotor forging, and belongs to the technical field of heat treatment. The heat treatment method comprises post-forging heat treatment and quenching and tempering heat treatment. The secondary normalizing in the post-forging heat treatment comprises the following steps: carrying out low-temperature heat preservation on the rotor forging after primary normalizing at 150-250 DEG C for 10-25 h; adopting a temperature rising speed of 6-15 DEG C / h to rise to 650-700 DEG C; then adopting a temperature rising speed of 15-40 DEG C / h to rise to 970-1000 DEG C; heat preserving at 970-1000 DEG C for 6-15 h; after heat preserving, adopting a temperature falling speed of 6-15 DEG C / h to fall to 940-970 DEG C and heat preserving for 5-15 h, and then air cooling. The method provided by the application can coarsen the grain size of the rotor forging near the surface, reduce flaw detection sensitivity, and ensure the performance of the rotor forging.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat treatment, in particular to a heat treatment method for effectively reducing the near-surface flaw detection sensitivity of a rotor forging. BACKGROUND

[0002] The whole-forging nuclear power conventional island high-pressure rotor and low-pressure rotor is one of the core components of power generation in a nuclear power plant, and has an irreplaceable position in the nuclear power plant. Therefore, the performance of the whole-forging nuclear power conventional island high-pressure rotor and low-pressure rotor directly affects the service life of the nuclear power plant.

[0003] For more than ten years, the heat treatment process of the whole-forging nuclear power conventional island rotor forging still follows the traditional heat treatment process mode: "multiple normal tempering" post-forging heat treatment and "quenching + tempering" quenching and tempering heat treatment. However, due to the large cross section of the rotor forging, when the traditional heat treatment is adopted, the heating and cooling speeds of the surface and the core of the rotor forging are seriously inconsistent, which leads to the difference in grain size between the near-surface and the core of the rotor forging, and finally causes the large difference in the flaw detection limit sensitivity between the surface and the core of the rotor forging shaft, which cannot meet the acceptance of the nuclear power standard without the lower limit requirement of the ultrasonic flaw detection defect display.

[0004] Therefore, there is an urgent need for a heat treatment method to coarsen the near-surface grains of the rotor forging, keep the grain size of the surface and the core consistent, solve the problem of unqualified products caused by the display of micro-defects after traditional heat treatment, reduce the flaw detection sensitivity of the forging surface, and meet the acceptance of the nuclear power standard without the lower limit requirement of the ultrasonic flaw detection defect display. SUMMARY

[0005] In view of the above analysis, the present application aims to provide a heat treatment method for effectively reducing the near-surface flaw detection sensitivity of a rotor forging, to solve the problem of high surface flaw detection sensitivity caused by the fine surface grain size of the rotor forging using traditional heat treatment.

[0006] In one aspect, the present application provides a heat treatment method for effectively reducing the near-surface flaw detection sensitivity of a rotor forging, which comprises post-forging heat treatment and quenching and tempering heat treatment, and the post-forging heat treatment comprises primary normalizing and secondary normalizing.

[0007] The secondary normalizing comprises the following steps:

[0008] S1: the rotor forging after primary normalizing is subjected to low-temperature holding at 150-250℃ for 10-25h;

[0009] S2: slowly heating at a heating speed of 6-15℃ / h to 650-700℃, and then rapidly heating at a heating speed of 15-40℃ / h to 970-1000℃;

[0010] S3: holding at 970-1000℃ for 6-15h;

[0011] S4: after holding, cooling down to 940-970℃ at a cooling rate of 6-15℃ / h;

[0012] S5: holding at 940-970℃ for 5-15h, and then air cooling.

[0013] Further, in step S1, the holding time is 15-20h.

[0014] Further, in the slow heating stage, the heating rate is 8-12℃ / h.

[0015] Further, in the fast heating stage, the heating rate is 25-35℃ / h.

[0016] Further, the holding at 970-1000℃ is for 6-10h.

[0017] Further, the primary normalizing comprises the following steps:

[0018] S1: holding the forging at 170-270℃ for 10-25h;

[0019] S2: slowly heating to 650-700℃ at a heating rate of 6-15℃ / h, and then heating to 860-910℃ at a heating rate of 5-10℃ / h;

[0020] S3: holding at 860-910℃ for 30-50h;

[0021] S4: after holding, air cooling to 170-270℃.

[0022] Further, the rotor forging is made of 30Cr2Ni4MoV steel, and the chemical components include C: ≤0.37%, Si: ≤0.12%, Mn: 0.17-0.43%, Cr: 1.45-2.05%, Mo: 0.22-0.62%, Ni: 3.18-3.82%, V: 0.06-0.16%, Al: ≤0.012%, S: ≤0.015%, P: ≤0.015%.

[0023] Further, the rotor forging has a diameter of Φ1300-2000mm.

[0024] In another aspect, the present application provides a rotor forging prepared by the heat treatment method.

[0025] Further, the surface grain size is 3.5-4.5 levels.

[0026] Compared with the prior art, the present application can achieve at least one of the following beneficial effects:

[0027] 1、 the rotor forging in the present application is subjected to forging heat treatment and quenching and tempering heat treatment, wherein the forging heat treatment comprises primary normalizing and secondary normalizing; the secondary normalizing is performed by low-temperature heat preservation at 150-250 DEG C, then by slow heating and rapid heating in combination to heat to 970-1000 DEG C, heat preservation at 970-1000 DEG C, furnace cooling to 940-970 DEG C after heat preservation, and air cooling to room temperature after heat preservation for a period of time. The rotor forging is subjected to the above heat treatment, so that the grain size near the surface of the rotor forging is coarsened, the flaw detection sensitivity is reduced, the grain size near the surface of the rotor forging is closer to the grain size inside, and the mechanical properties of the rotor forging meet the standard requirements.

[0028] 2、 the forging heat treatment and quenching and tempering heat treatment provided by the present application can coarsen the grain size near the surface of the rotor forging by controlling the secondary normalizing in the forging heat treatment, and is suitable for rotor forgings with a diameter of 1300 mm or more, so that the grain size of the core and the surface is consistent, the grain size reaches 3.5-4.5 levels, meets the flaw detection standard requirements, and does not affect the overall mechanical properties of the rotor forging.

[0029] 3、 the rotor forging is subjected to ultrasonic flaw detection by using the heat treatment process of the present application, the surface equivalent ≤Φ0.4 small defects are effectively shielded, and the center limit sensitivity ≤Φ1.6 meets the standard requirements.

[0030] In the present application, the above technical solutions can be combined with each other to realize more preferred combination solutions. Other features and advantages of the present application will be described in the subsequent specification, and some advantages will become apparent from the specification, or will be understood by implementing the present application. The purpose and other advantages of the present application can be realized and obtained by the contents specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings are included to provide a further understanding of the present application and are incorporated herein and constitute a part of the specification. The drawings illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application.

[0032] Figure 1 It is a schematic diagram of secondary normalizing process;

[0033] Figure 2 It is a surface metallographic photograph of example 1;

[0034] Figure 3 It is an internal metallographic photograph of example 1;

[0035] Figure 4 The surface metallographic photo of Comparative Example 1;

[0036] Figure 5 The internal metallographic photo of Comparative Example 1. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present application will be described in detail below with reference to the drawings, which constitute a part of this application, and are used to explain the principles of the application together with the embodiments of the application, but are not used to limit the scope of the application.

[0038] At present, for the rotor forging with the material of 30Cr2Ni4MoV, the traditional heat treatment is adopted to adjust the size of grain degree and performance. The traditional heat treatment includes post-forging heat treatment and quenching and tempering heat treatment, and the post-forging heat treatment includes twice normalizing and once tempering, wherein the twice normalizing has the same process. However, after the traditional heat treatment is adopted, the grains in the near-surface area of the rotor forging are relatively fine, and the grains in the core part are relatively coarse, which cannot meet the acceptance of the nuclear power standard without the lower limit requirement of the ultrasonic flaw detection defect display.

[0039] Therefore, the present application provides a heat treatment method for effectively reducing the flaw detection sensitivity of the near-surface area of the rotor forging, which comprises post-forging heat treatment and quenching and tempering heat treatment; the post-forging heat treatment comprises once normalizing and twice normalizing, and the grains in the near-surface area of the rotor forging are coarsened by controlling the twice normalizing, so that the flaw detection standard is met, and the mechanical performance of the rotor forging is not affected.

[0040] The twice normalizing comprises the following steps:

[0041] S1: the rotor forging after once normalizing is kept at 150-250 DEG C for 10-25 h;

[0042] S2: slowly heating to 650-700 DEG C at the heating speed of 6-15 DEG C / h, and then rapidly heating to 970-1000 DEG C at the heating speed of 15-40 DEG C / h;

[0043] S3: keeping at 970-1000 DEG C for 6-15 h;

[0044] S4: after keeping, cooling to 940-970 DEG C at the cooling speed of 6-15 DEG C / h;

[0045] S5: keeping at 940-970 DEG C for 5-15 h, and then air cooling.

[0046] Compared with the prior art, the application is based on traditional heat treatment, and the secondary normalizing is first performed at a lower temperature and then heated by combining slow heating with rapid heating; after a period of holding, the temperature is decreased, first decreased to a certain temperature by furnace cooling, then held for a period of time, and then decreased to room temperature by air cooling. By controlling the secondary normalizing process, the grains near the surface of the rotor forging can be gradually coarsened, the grain size is 3.5-4.5 after quenching and tempering heat treatment, the flaw detection sensitivity is reduced, the nuclear power standard of no lower limit requirement for ultrasonic flaw detection defect display acceptance is met, and the mechanical properties of the rotor forging meet the use requirements.

[0047] In the application, the overall preparation of the rotor forging includes smelting, forging, post-forging heat treatment and quenching and tempering heat treatment. The post-forging heat treatment includes primary normalizing and secondary normalizing, and the secondary normalizing is roughly divided into a low-temperature holding stage, a heating stage, a high-temperature holding stage and a cooling stage.

[0048] In the low-temperature holding stage, the holding is performed at 150-250℃, and the main role is to ensure that the structure after the first normalizing is fully converted into bainite structure in the low-temperature holding stage, and the content of residual austenite is reduced as much as possible. The fully converted structure has obvious effect on cutting off the genetic structure and refining the grains, and also tries to fully convert the structure of the core of the forging.

[0049] For example, the temperature of the low-temperature holding can be 150℃, 170℃, 190℃, 200℃, 210℃, 230℃ or 250℃.

[0050] For example, the time of the low-temperature holding can be 10h, 12h, 13h, 15h, 18h, 20h, 22h, 23h or 25h.

[0051] Preferably, in step S1, the low-temperature holding time is 15-20h.

[0052] In the heating stage, the heating is performed by combining slow heating with rapid heating. In the slow heating stage, to avoid the existence of black skin and rough large section on the surface after forging, when the temperature is below 700℃, it is the elastic deformation stage of the forging, and slow heating will not increase the thermal stress, so as to reduce the risk of cracking of the rotor forging.

[0053] After the forging is slowly heated to 650-700℃, the forging is in a plastic deformation stage, and there is no risk of cracking when it is rapidly heated. Rapid heating can ensure that there is a temperature difference between the inside and outside of the same cross section of the forging at a high temperature stage, the surface is quickly heated to a higher temperature for heat preservation, and the core reaches above Ac3 and below the coarsening temperature, so as to realize that the surface grain size is not refined on the basis of primary normalizing, and ensure that the grain is relatively coarse, while the core only reaches a lower temperature recrystallization above Ac3, so as to realize the effect of refinement on the basis of primary normalizing. Further, after the rotor forging is subjected to primary normalizing and secondary normalizing, there is no grain size deviation phenomenon of coarse inside and fine outside, and after subsequent quenching and tempering heat treatment, the rotor forging has a small grain size gradient inside and outside, and effectively controls the flaw detection sensitivity of the surface of the forging.

[0054] Exemplarily, in the slow heating stage, the heating rate can be 15℃ / h, 14℃ / h, 13℃ / h, 12℃ / h, 11℃ / h, 10℃ / h, 9℃ / h, 8℃ / h or 6℃ / h.

[0055] Preferably, in the slow heating stage, the heating rate is 8-12℃ / h.

[0056] Exemplarily, in the rapid heating stage, the heating rate can be 16℃ / h, 18℃ / h, 20℃ / h, 22℃ / h, 25℃ / h, 28℃ / h, 30℃ / h, 33℃ / h, 35℃ / h, 38℃ / h or 40℃ / h.

[0057] Preferably, in the rapid heating stage, the heating rate is 25-35℃ / h.

[0058] In the high-temperature heat preservation stage, heat preservation is carried out at 970-1000℃ for 6-15h. Because there is a temperature difference between the furnace temperature and the temperature of the rotor forging, when the forging surface is rapidly heated to 940-960℃, the furnace temperature gradually cools to 940-970℃ and is kept at this temperature for 5-15h, so as to ensure that the temperature of the forging within 150mm of the surface reaches 940-960℃, and the temperature of the core of the rotor forging is in the range of 830-880℃. The surface grain size of the rotor forging is not refined on the basis of primary normalizing, and the grain is relatively coarse, while the core only reaches a lower temperature recrystallization above Ac3, so as to realize the effect of refinement on the basis of primary normalizing.

[0059] Exemplarily, heat preservation is carried out at 970-990℃, and the heat preservation time can be 6h, 8h, 10h, 12h or 15h.

[0060] Preferably, heat preservation is carried out at 970-1000℃, and the heat preservation time is 6-10h.

[0061] Short-time holding and then cooling in the range of 970-1000℃ is mainly to ensure that the surface temperature of the forging is raised to below the roughening temperature and then slowly cooled, so that the surface of the forging does not obviously roughen, and the center of the forging is in the heating stage during the slow cooling process and the subsequent lower temperature 940-970℃ holding. When the center temperature rises to the range of 830-880℃, the furnace is discharged for air cooling, so as to realize the effect that the surface grain size is not refined, and the center is refined.

[0062] Specifically, the primary normalizing comprises the following steps:

[0063] S1: holding the forging at 170-270℃ for 10-25h;

[0064] S2: slowly heating to 650-700℃ at a heating rate of 6-15℃ / h, and then heating to 860-910℃ at a heating rate of 5-10℃ / h;

[0065] S3: holding at 860-910℃ for 30-50h;

[0066] S4: discharging the furnace after holding for air cooling to 170-270℃.

[0067] The purpose of the primary normalizing is to refine the coarse structure and grain after forging; and the purpose of the secondary normalizing is to refine the relatively coarse grain size and structure after the primary normalizing, so that the center is refined and the surface is not further refined, thereby reducing the grain size gradient of the center and the surface of the forging.

[0068] Specifically, the material of the rotor forging is 30Cr2Ni4MoV steel, and the chemical components include C: ≤0.37%, Si: ≤0.12%, Mn: 0.17-0.43%, Cr: 1.45-2.05%, Mo: 0.22-0.62%, Ni: 3.18-3.82%, V: 0.06-0.16%, Al: ≤0.012%, S: ≤0.015%, and P: ≤0.015%.

[0069] Specifically, the diameter of the rotor forging is Φ1300-2000mm.

[0070] The preparation of the rotor forging comprises the following steps:

[0071] S1: smelting: obtaining the ingot after smelting the alloy raw materials;

[0072] S2: forging: obtaining the forging after forging the ingot;

[0073] S3: post-forging heat treatment: including primary normalizing, the secondary normalizing provided by the application, and post-forging tempering;

[0074] S4: quenching and tempering treatment: including primary quenching and quenching and tempering.

[0075] Specifically, in the smelting process, the basic electric furnace is used to refine the molten steel, and appropriate slagging system and ladle refining and vacuum carbon deoxidization (LVCD+VCD) are used. The vacuum treatment is carried out before pouring and during the process of pouring the ingot, the vacuum degree is ≤266 Pa, the tapping temperature is 1620-1640℃, the pouring temperature is 1575-1595℃, and the ingot is prepared.

[0076] Specifically, in the forging process, the ingot is forged to obtain the forged piece by adopting the process form of "pressing the mouth + first upsetting + second upsetting + elongating out of the finished product", the initial forging temperature is 1250℃, the final forging temperature is 750℃, the process fire times is four fires, and the total deformation is ≥3.5%.

[0077] Specifically, the primary normalizing includes the following steps:

[0078] S1: heating the 30Cr2Ni4MoV steel rotor forging, and low-temperature holding for 10-25h at 170-270℃;

[0079] S2: slowly heating to 650-700℃ at a heating rate of 6-15℃ / h; and then heating to 860-910℃ at a heating rate of 5-10℃ / h;

[0080] S3: holding at 860-910℃, and the holding time is 30-50h;

[0081] S4: after holding, air cooling to 170-270℃.

[0082] Further, the post-forging tempering includes the following steps:

[0083] S1: heating the rotor forging after the secondary normalizing, and low-temperature holding for 10-20h at 170-210℃;

[0084] S2: slowly heating to 640-660℃ at a heating rate of 10-25℃ / h;

[0085] S3: holding at 640-660℃, and the holding time is 40-70h;

[0086] S4: after holding, slowly cooling to 250℃ at a cooling rate of ≤10℃ / h, and then air cooling to room temperature.

[0087] Further, the quenching and tempering treatment is quenching and tempering.

[0088] Preferably, the quenching heat treatment includes the following steps:

[0089] S1: heating the rotor forge piece after the post-forging heat treatment, slowly heating to 650-700℃ at a heating rate of 10-25℃ / h, and then rapidly heating to 830-850℃ at a heating rate of 25-50℃ / h;

[0090] S2: holding at 830-850℃ for 30-50h;

[0091] S4: after holding, spraying water or immersing in water to ≤50℃.

[0092] Preferably, the quenching and tempering process is as follows:

[0093] S1: heating the rotor forge piece after quenching, holding at 170-210℃ for 10-20h;

[0094] S2: slowly heating to 640-660℃ at a heating rate of 10-25℃ / h;

[0095] S3: holding at 590-630℃ for 40-60h;

[0096] S4: after holding, slowly cooling to 250℃ at a cooling rate of ≤10℃ / h, and then air cooling to room temperature.

[0097] In order to more clearly understand the present application, the following examples and comparative examples are used for illustration.

[0098] The rotor forge piece is prepared from 30Cr2Ni4MoV steel through smelting and forging, and has a diameter of φ1500mm. Then, the rotor forge piece is subjected to post-forging heat treatment and quenching and tempering treatment, wherein the post-forging heat treatment comprises primary normalizing, secondary normalizing and post-forging tempering, and the quenching and tempering treatment comprises quenching and quenching and tempering.

[0099] Reference Figure 1 is made to the examples and comparative examples, which differ in the secondary normalizing, and the specific preparation process is as follows:

[0100] Smelting: smelting the alloy raw materials, with a vacuum degree of 266Pa, a tapping temperature of 1630℃ and a pouring temperature of 1585℃, to obtain a steel ingot;

[0101] Forging: forging the steel ingot, with a starting forging temperature of 1250℃, a final forging temperature of 750℃, four forging passes and a total deformation of 5%;

[0102] The primary normalizing process is as follows:

[0103] S1: heating the forge piece, and holding at 270℃ for 15h;

[0104] S2: slow heating to 700°C at a heating rate of 8°C / h, and then heating to 900°C at a heating rate of 7°C / h;

[0105] S3: holding at 900°C for 35h;

[0106] S4: after holding, air cooling to 200°C.

[0107] The tempering process after forging is as follows:

[0108] S1: heating the forged piece air-cooled to room temperature, and holding at 200°C for 10h;

[0109] S2: heating to 650°C at a heating rate of 15°C / h;

[0110] S3: holding at 650°C for 50h;

[0111] S4: after holding, slow cooling to 250°C at a cooling rate of 10°C / h, and then air cooling to room temperature.

[0112] The quenching process is as follows:

[0113] S1: heating the forged piece after the heat treatment after forging, slow heating to 650°C at a heating rate of 15°C / h, and then rapid heating to 840°C at a heating rate of 35°C / h;

[0114] S2: holding at 840°C for 40h;

[0115] S4: after holding, water quenching to ≤50°C.

[0116] The quenching and tempering process is as follows:

[0117] S1: heating the forged piece air-cooled to room temperature, and holding at 190°C for 15h;

[0118] S2: heating to 650°C at a heating rate of 20°C / h;

[0119] S3: holding at 600°C for 40h;

[0120] S4: after holding, slow cooling to 250°C at a cooling rate of 10°C / h, and then air cooling to room temperature to obtain the rotor forged piece.

[0121] Example 1

[0122] The secondary normalizing includes the following steps:

[0123] S1: the rotor forge piece after primary normalizing is kept at low temperature in the range of 200℃ for 20h;

[0124] S2: slow heating to 680℃ with heating rate of 12℃ / h, then fast heating to 980℃ with heating rate of 25℃ / h;

[0125] S3: keeping at 980℃ for 8h;

[0126] S4: cooling to 950℃ with cooling rate of 10℃ / h;

[0127] S5: keeping at 950℃ for 8h, then air cooling to 200℃.

[0128] Example 2

[0129] Example 2 is substantially the same as Example 1 except that the low temperature keeping time of Example 2 is 15h;

[0130] In step S2, the slow heating rate is 8℃ / h, and the fast heating rate is 35℃ / h;

[0131] In step S4, the cooling rate is 8℃ / h;

[0132] In step S5, the keeping time is 12h.

[0133] Example 3

[0134] Example 3 is substantially the same as Example 1 except that the rotor forge piece of Example 3 is Φ1800mm in diameter, and the keeping time in S1 is 25h.

[0135] Example 4

[0136] Example 4 is substantially the same as Example 3 except that the keeping temperature in S3 of Example 4 is 990℃.

[0137] Comparative Example 1

[0138] The secondary normalizing in Comparative Example 1 is the same as the primary normalizing.

[0139] Comparative Example 2

[0140] Comparative Example 2 is substantially the same as Example 1 except that in the secondary normalizing step S2 of Comparative Example 2, slow and fast heating is adopted to reach 870℃; and in step S3, keeping is performed at 870℃.

[0141] Performance detection

[0142] The rotor forgings obtained after heat treatment of examples 1-4 and comparative examples 1-2 are subjected to grain size and performance detection, and the specific detection results are shown in Table 1, and the metallographic structure is shown in Figures 2-5

[0143] Table 1 detection results

[0144]

[0145] It can be seen from examples 1-4 and comparative examples 1-2 in combination with Table 1 that, referring to Figures 2-5 , the grain size of the rotor forging near the surface is coarsened from 6.5 to about 3.5-4.5, which can effectively reduce the UT flaw detection sensitivity and achieve the effect of effectively shielding the UT tiny defect display, and in the range of the grain size coarsening, the performance of the rotor forging is still met.

[0146] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.​

Claims

1. A heat treatment method for effectively reducing near-surface flaw detection sensitivity of a rotor forging, the heat treatment method including post-forging heat treatment and quenching and tempering heat treatment, characterized by, The post-forging heat treatment comprises primary normalizing and secondary normalizing; The secondary normalizing comprises the following steps: S1: the rotor forging after primary normalizing is kept at 150-250 DEG C for 10-25h; S2: slowly heating to 650-700 DEG C at a heating rate of 6-15 DEG C / h, and then rapidly heating to 970-1000 DEG C at a heating rate of 15-40 DEG C / h; S3: keeping at 970-1000 DEG C for 6-15h; S4: after keeping, cooling to 940-970 DEG C at a cooling rate of 6-15 DEG C / h; S5: keeping at 940-970 DEG C for 5-15h, and then air cooling; The rotor forging has a diameter of 1300-2000mm; the grain size of the core and the surface is kept consistent, and the grain size reaches 3.5-4.5 grade.

2. The heat treatment method according to claim 1, wherein In step S1, the keeping time is 15-20h.

3. The heat treatment method according to claim 1, wherein In the slow heating stage, the heating rate is 8-12 DEG C / h.

4. The heat treatment method according to claim 1, wherein In the rapid heating stage, the heating rate is 25-35 DEG C / h.

5. The heat treatment method according to claim 1, wherein Keeping at 970-1000 DEG C for 6-10h.

6. The heat treatment method according to claim 1, wherein The primary normalizing comprises the following steps: S1: keeping the forging at 170-270 DEG C for 10-25h; S2: slowly heating to 650-700 DEG C at a heating rate of 6-15 DEG C / h, and then heating to 860-910 DEG C at a heating rate of 5-10 DEG C / h; S3: keeping at 860-910 DEG C for 30-50h; S4: after keeping, air cooling to 170-270 DEG C.

7. The heat treatment method according to claim 1, wherein The rotor forging is made of 30Cr2Ni4MoV steel, and the chemical components include C: <=0.37%, Si: <=0.12%, Mn: 0.17-0.43%, Cr: 1.45-2.05%, Mo: 0.22-0.62%, Ni: 3.18-3.82%, V: 0.06-0.16%, Al: <=0.012%, S: <=0.015%, P: <=0.015%.

8. A rotor forging characterized by, Prepared by the heat treatment method of any one of claims 1-7.

9. The rotor forging of claim 8 wherein, The grain size of the surface is 3.5-4.5 grade.

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