Shape control method for casing forge piece for large gas turbine

Abstract

The invention relates to a shape control method for a casing forge piece for a large gas turbine. The shape control method comprises the following steps that S1, blanking is conducted; step S2, chamfering is carried out; s3, upsetting and punching are carried out; s4, cooling after forging; s5, primary annealing is conducted, and heat preservation is conducted on the forged piece at the temperature of 690 + / -40 DEG C; s6, trestle chambering is conducted, and the forging temperature ranges from 900 DEG C to 1150 DEG C; s7, secondary annealing is conducted, specifically, the forged piece is annealed and subjected to heat preservation, and the annealing temperature is 690 DEG C + / -40 DEG C; step S8, normalizing: normalizing the forge piece and preserving heat at the normalizing temperature of 1130 + / -5 DEG C; s9, primary tempering is conducted, specifically, the forge piece is tempered and subjected to heat preservation, and the tempering temperature is 760 + / -5 DEG C; s10, quenching is conducted, specifically, the forge piece is quenched, and the quenching temperature is 1120 + / -5 DEG C; s11, secondary tempering is conducted, specifically, the forge piece is tempered, and the tempering temperature is 680 + / -5 DEG C; and S12, stress relief annealing is conducted, and the stress relief annealing temperature is 630 + / -5 DEG C. The method has the advantages that the performance stability is improved, and the cracking phenomenon of the product caused by stress concentration is avoided to the maximum extent.

Description

Technical Field

[0001] The invention relates to a large gas turbine component manufacturing technology, and in particular to a method for controlling the shape of a casing forging for a large gas turbine. Background Art

[0002] A gas turbine, also known as a gas turbine engine, is an internal combustion power machine that converts the energy of fuel into useful work. It is a rotary impeller heat engine. Its working principle is that the compressor inhales air from the external atmosphere and compresses it step by step through the axial flow compressor to increase the pressure. The compressed air is sent to the combustion chamber to mix with the injected fuel and burn to generate high-temperature and high-pressure gas. The high-temperature and high-pressure gas then enters the turbine to expand and do work, driving the turbine to drive the compressor and the external load rotor to rotate at high speed to achieve power output.

[0003] The casing forging refers to the outer shell that surrounds the internal parts of the gas turbine. It provides effective physical support and protection, prevents leakage of high-temperature and high-pressure gases, and helps to keep the components in the correct position. Therefore, the requirements for casing forgings are also higher. The casing needs to have higher dimensional accuracy, high strength and good high-temperature resistance.

[0004] At present, the casing is mainly made of martensitic stainless steel by segmented forming and then welding. However, cracks are very easy to occur during forging and cooling after forging. In severe cases, cracking will occur. After performance heat treatment, martensitic phase transformation will occur, which will cause stress concentration and thus induce product cracking. In order to eliminate stress, it is usually kept warm at 880℃, but the grain size of the structure at this temperature is very easy to grow, affecting the performance of the forging. And because multiple forgings undergo performance heat treatment processes, there will inevitably be process window errors. The accumulated errors of multiple forgings will also affect the overall uniformity of the casing.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention discloses a method for controlling the shape of a casing forging for a large gas turbine.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A method for controlling the shape of a casing forging for a large gas turbine, characterized in that it comprises the following steps:

[0009] Step S1, blanking, the forging material is martensitic stainless steel GX-8N;

[0010] Step S2, chamfering;

[0011] Step S3, upsetting and punching, the forging temperature range is 900~1150℃;

[0012] Step S4, cooling after forging, the forging is cooled in the furnace, and then air-cooled after being taken out of the furnace;

[0013] Step S5, primary annealing, the forging is kept at 690°C ± 40°C, and then taken out of the furnace and air-cooled;

[0014] Step S6, expanding the hole of the frame, the forging temperature range is 900-1150°C, and then cooling;

[0015] Step S7, secondary annealing, annealing and heat preservation of the forging, the annealing temperature range is 690℃±40℃;

[0016] Step S8, normalizing, normalizing the forging and keeping it warm, the normalizing temperature range is 1130±5℃;

[0017] Step S9, primary tempering, tempering and heat preservation of forgings, tempering temperature range 760±5℃;

[0018] Step S10, quenching, quenching and heat preservation of forgings, the quenching temperature range is 1120±5℃;

[0019] Step S11, secondary tempering, tempering and heat preservation of forgings, the tempering temperature range is 680±5℃;

[0020] Step S12, stress relief annealing, annealing and heat preservation of forgings, the stress relief annealing temperature range is 630±5℃.

[0021] Furthermore, in step S3, the deformation amount of the blank in the height direction during upsetting is 33-45%.

[0022] Furthermore, in step S5, the annealing holding time ranges from 12 to 16 hours.

[0023] Furthermore, in step S6, the forging is expanded four times. In the first expansion, the size ratio of the diameter of the inner hole of the forging before and after the change is 1:2.8-3.4; in the second expansion, the size ratio before and after the change is 1:1.1-1.30; in the third expansion, the size ratio before and after the change is 1:1.02-1.15; in the fourth expansion, the size ratio before and after the change is 1:1.03-1.08, and the angle of the tooling lever used for expansion is controlled to be 76° with the end face.

[0024] Furthermore, in step S7, the annealing holding time is 9 to 12 hours.

[0025] Furthermore, in step S8, the forging is put into the furnace at ≤750°C, the normalizing holding time ranges from 180 to 200 minutes, the forging is cooled in the furnace to ≤750°C, and then air-cooled to room temperature.

[0026] Furthermore, in step S9, the forging is put into the furnace at ≤500°C, the primary tempering holding time ranges from 360 to 380 minutes, and the forging is air-cooled to room temperature.

[0027] Furthermore, in step S10, the forging is put into the furnace at ≤750°C, the quenching and holding time ranges from 180 to 200 minutes, and the forging is oil-cooled to room temperature.

[0028] Furthermore, in step S11, the forging is put into the furnace at ≤500°C, the secondary tempering holding time ranges from 360 to 380 minutes, and the forging is air-cooled to room temperature.

[0029] Furthermore, in step S12, the forging is put into the furnace at ≤500°C, the stress relief annealing holding time ranges from 180 to 200 minutes, and the forging is air-cooled to room temperature.

[0030] The beneficial effects of the present invention are as follows:

[0031] 1. During the forging process, the deformation window of the special-shaped rack expansion hole should be reasonably controlled to avoid cracking caused by large deformation. During the deformation of the forging, the temperature of the forging should be monitored in real time to avoid the increase of product deformation resistance due to too low forging temperature, which may cause cracking of the forging.

[0032] 2. After the martensitic stainless steel is deformed, it is annealed. Since the martensitic stainless steel is very easy to grow grains during high-temperature heating, and the huge stress concentration caused by phase change will cause cracking of the forgings, the annealing temperature is controlled at around 690°C, which is lower than the austenitization temperature of GX-8N. It can effectively prevent the growth of grains. At the same time, by extending the holding time, the internal stress of the product can be homogenized, which greatly reduces the cracking caused by stress concentration.

[0033] 3. Martensitic stainless steel selects the appropriate process temperature window for normalizing. When heated to the specified temperature, carbon dissolves in the interstitial solid solution in γ-Fe, promoting austenite transformation, ensuring the holding time, and increasing the proportion of austenite. That is, at high temperatures, austenite is a stable phase. During the cooling process, austenite will transform into martensite, and the cooling rate is controlled to increase the degree of martensite transformation. Martensite itself is hard and brittle, which improves the hardness and strength of the forging.

[0034] 4. During the heat treatment process, during normalizing, martensite is transformed into austenite, so that the material obtains uniform and fine austenite grains. After that, tempering is performed once. The austenite formed by the previous normalizing will begin to decompose and partially transform into tempered martensite. At the same time, carbides begin to precipitate, generating internal stress and brittleness, which improves the toughness and plasticity of the material. Then, during the quenching process, the structure is transformed into austenite to ensure that most of the structure is austenite. Rapid cooling after quenching can inhibit the transformation of austenite to other structures, and obtain a large amount of high-hardness and high-strength martensitic structure. Then, secondary tempering is performed, and carbides will further precipitate and grow. At the same time, the dislocation density in martensite will be reduced, which will appropriately reduce the hardness and brittleness of the material and improve toughness and plasticity.

[0035] 5. Finally, the forgings are re-annealed for stress relief. The annealing temperature window is set at around 630°C. After the tempering temperature, phase change of the material is avoided. During the heating and insulation process, the residual stress inside the material will gradually relax through the relaxation process and be evenly distributed inside the material, avoiding cracking caused by stress concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the steps of the method for controlling the shape of casing forgings for large gas turbines.

[0037] Figure 2 Schematic diagram of the shape change of the forging in step S2.

[0038] Figure 3 Schematic diagram of the shape change of the forging in step S6.

[0039] Figure 4 is the temperature curve diagram in step S8.

[0040] Figure 5 is a temperature curve diagram in step S9.

[0041] Figure 6 is a temperature curve diagram in step S10.

[0042] Figure 7 is the temperature curve diagram in step S11.

[0043] Figure 8 is the temperature curve diagram in step S12.

[0044] Fig. 9 Schematic diagram of the sampling locations for forgings.

[0045] Fig.10 This is a 100-fold transverse metallographic image of sample 1.

[0046] Fig.11 This is a 200-fold metallographic image of sample 1 in the transverse direction.

[0047] Fig.12 This is a 100-fold metallographic image of sample 1 in the longitudinal direction. DETAILED DESCRIPTION

[0048] The specific implementation of the present invention will be described below in conjunction with the accompanying drawings.

[0049] Embodiment 1:

[0050] A method for controlling the shape of casing forgings for large gas turbines, such as Figure 1 As shown, the following steps are included:

[0051] Step S1, blanking, the forging material is martensitic stainless steel GX-8N, the initial blanking size is Φ600(+3 / -2)mm*1690(+5 / 0)mm, and the blanking weight is: 3750(+1 / 0)kg.

[0052] Step S2: chamfering, the chamfering size is R20mm.

[0053] Step S3, step S3, upsetting and punching, the forging temperature range is 900~1150℃. Figure 2 As shown, the initial size of the raw material is φ600mm*H1690mm. First, it is upset to H700m, and then the forging is spun. The forging size is: the big head of the forging is φ1020mm, the small head is φ950mm, and the height is H625mm. Then the small head is punched. The forging size is: the big head of the forging is φ1090mm, the small head is φ990mm, the height is H615mm, and the inner hole is φ380mm.

[0054] Step S4, cooling after forging, the forging is slowly cooled to ≤200°C and then taken out of the furnace (the furnace temperature of the forging is ≥900°C when it is put into the furnace).

[0055] Step S5, primary annealing, the forging is kept at 670°C for 12 to 16 hours, and then taken out of the furnace and air-cooled, and the annealing is carried out within 8 hours after the forging is taken out of the furnace and cooled.

[0056] Step S6, the frame is expanded, the forging temperature range is 900~1150℃, and then cooled. Figure 3As shown, the forging was expanded by four fires, and the tooling lever used was at an angle of 76° to the end face. In the first fire, the size ratio of the diameter of the inner hole of the forging before and after the change was 1:2.8~3.4, and the small end of the inner hole of the forging was φ924mm and the large end of the inner hole was φ120mm; in the second fire, the size ratio before and after the change was 1:1.1~1.30, and the small end of the inner hole of the forging was φ1224mm and the large end of the inner hole was φ1500mm; in the third fire, the size ratio before and after the change was 1:1.02~1.15, and the small end of the inner hole of the forging was φ1424mm and the large end of the inner hole was φ1700mm; in the fourth fire, the size ratio before and after the change was 1:1.03~1.08, and the small end of the inner hole of the forging was φ1540mm and the large end of the inner hole was φ1816mm. The deformation of each fire size is controlled at 14.7%-18% to avoid cracking caused by large deformation.

[0057] Step S7, secondary annealing, annealing and heat preservation of the forgings, annealing temperature 670°C, annealing heat preservation time 9-12h, then taking out of the furnace and air cooling.

[0058] Step S8, normalizing, such as Figure 4 As shown, the forgings are normalized and held at a normalizing temperature of 1125°C. The forgings are put into the furnace at ≤750°C, and the normalizing holding time ranges from 180 to 200 minutes. After that, the forgings are cooled in the furnace to ≤750°C, and then air-cooled to room temperature.

[0059] Step S9, primary tempering, such as Figure 5 As shown, the forgings are tempered and kept warm, the tempering temperature is 755°C, the forgings are put into the furnace at ≤500°C, the tempering and holding time ranges from 360 to 380 minutes, and the forgings are air-cooled to room temperature.

[0060] Step S10, quenching, such as Figure 6 As shown, the forgings are quenched and held, the quenching temperature is 1115°C, the forgings are put into the furnace at ≤750°C, the quenching and holding time ranges from 180 to 200 minutes, and the forgings are oil cooled to room temperature.

[0061] Step S11, secondary tempering, such as Figure 7 As shown, the forgings are tempered and kept warm, the tempering temperature range is 675°C, the forgings are put into the furnace at ≤500°C, the secondary tempering holding time range is 360 to 380 minutes, and the forgings are air-cooled to room temperature.

[0062] Sampling, the sampling position of the forging is as follows Fig. 9 shown.

[0063] The samples were subjected to physical and chemical tests, and the test items included: chemical composition, room temperature tensile strength, room temperature impact strength, low magnification, high magnification, and hardness.

[0064] After testing, if the performance of the sample meets the requirements, the forging is machined and the outer dimensions of the forging are adjusted to the design dimensions.

[0065] After machining, ultrasonic testing is carried out: 100% of forgings are subjected to ultrasonic testing, the method is in accordance with GB / T-6402, and the acceptance is in accordance with GB / T-4162-A grade.

[0066] Step S12, stress relief annealing, such as Figure 8 As shown, the forgings are annealed and held, the stress relief annealing temperature is 625°C, the forgings are put into the furnace at ≤500°C, the stress relief annealing holding time ranges from 180 to 200 minutes, and the forgings are air-cooled to room temperature.

[0067] Embodiment 2:

[0068] The steps different from Example 1 are:

[0069] Step S5, primary annealing, the forging is kept at 720°C for 12 to 16 hours, and then taken out of the furnace for air cooling, and the annealing is performed within 8 hours after the forging is taken out of the furnace and cooled.

[0070] Step S6, the frame is expanded, the forging temperature range is 900~1150℃, and then cooled. Figure 3 As shown, the forging was expanded by four fires, and the tooling lever used was at an angle of 76° to the end face. In the first fire, the size ratio of the diameter of the inner hole of the forging before and after the change was 1:2.8~3.4, and the small end of the inner hole of the forging was φ924mm and the large end of the inner hole was φ120mm; in the second fire, the size ratio before and after the change was 1:1.1~1.30, and the small end of the inner hole of the forging was φ1224mm and the large end of the inner hole was φ1500mm; in the third fire, the size ratio before and after the change was 1:1.02~1.15, and the small end of the inner hole of the forging was φ1424mm and the large end of the inner hole was φ1700mm; in the fourth fire, the size ratio before and after the change was 1:1.03~1.08, and the small end of the inner hole of the forging was φ1540mm and the large end of the inner hole was φ1816mm. The deformation of each fire size is controlled at 14.7%-18% to avoid cracking caused by large deformation.

[0071] Step S7, secondary annealing, annealing and heat preservation of the forgings, annealing temperature 720°C, annealing heat preservation time 9-12h, then taking out of the furnace and air cooling.

[0072] Step S8, normalizing, such as Figure 4 As shown, the forgings are normalized and held at a normalizing temperature of 1135°C. The forgings are put into the furnace at ≤750°C, and the normalizing holding time ranges from 180 to 200 minutes. After that, the forgings are cooled in the furnace to ≤750°C, and then air-cooled to room temperature.

[0073] Step S9, primary tempering, such as Figure 5As shown, the forgings are tempered and kept warm, the tempering temperature is 765°C, the forgings are put into the furnace at ≤500°C, the tempering and holding time ranges from 360 to 380 minutes, and the forgings are air-cooled to room temperature.

[0074] Step S10, quenching, such as Figure 6 As shown, the forgings are quenched and held, the quenching temperature is 1125°C, the forgings are put into the furnace at ≤750°C, the quenching and holding time ranges from 180 to 200 minutes, and the forgings are oil cooled to room temperature.

[0075] Step S11, secondary tempering, such as Figure 7 As shown, the forgings are tempered and kept warm, the tempering temperature is 685°C, the forgings are put into the furnace at ≤500°C, the secondary tempering and holding time ranges from 360 to 380 minutes, and the forgings are air-cooled to room temperature.

[0076] Sampling, the sampling position of the forging is as follows Fig. 9 shown.

[0077] The samples were subjected to physical and chemical tests, and the test items included: chemical composition, room temperature tensile strength, room temperature impact strength, low magnification, high magnification, and hardness.

[0078] After testing, if the performance of the sample meets the requirements, the forging is machined and the outer dimensions of the forging are adjusted to the design dimensions.

[0079] After machining, ultrasonic testing is carried out: 100% of forgings are subjected to ultrasonic testing, the method is in accordance with GB / T-6402, and the acceptance is in accordance with GB / T-4162-A grade.

[0080] Step S12, stress relief annealing, such as Figure 8 As shown, the forgings are annealed and held, the stress relief annealing temperature is 635°C, the forgings are put into the furnace at ≤500°C, the stress relief annealing holding time ranges from 180 to 200 minutes, and the forgings are air-cooled to room temperature.

[0081] Comprehensive performance testing:

[0082] The comprehensive physical and chemical properties of samples 1 and 2 are shown in Table 1.

[0083]

[0084] Test result analysis:

[0085] Tensile strength (σ b ): The forgings exceed the standard by nearly 30Mpa.

[0086] Yield strength (σ 0.2 ): The forgings exceed the standard by nearly 80Mpa.

[0087] Elongation after fracture (A%): Forgings exceed the standard by nearly 7%.

[0088] Sectional reduction (Z%): Forgings exceed the standard by nearly 13%

[0089] Impact energy (A k ): The forgings exceed the standard by nearly 20J.

[0090] Brinell hardness HB(d): standard.

[0091] In summary, the mechanical properties of forgings meet the requirements, the forgings have good strength and hardness, good plasticity and toughness, and the relevant indicators have a large margin.

[0092] Metallographic inspection of forgings:

[0093] Fig.10 This is a 100-fold transverse metallographic image of sample 1.

[0094] Fig.11 This is a 200-fold metallographic image of sample 1 in the transverse direction.

[0095] Fig.12 This is a 100-fold metallographic image of sample 1 in the longitudinal direction.

[0096] The grain size of the forging is level 5, the three types of inclusions A, B, and C are all level 0, and the type D inclusion is level 1, which meets the requirements and is qualified.

[0097] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0098] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for controlling the shape of a casing forging for a large gas turbine, characterized in that: The following steps are involved: Step S1, blanking, the forging material is martensitic stainless steel GX-8N; Step S2, chamfering; Step S3, upsetting and punching, the forging temperature range is 900~1150℃; Step S4, cooling after forging, the forging is cooled in the furnace, and then air-cooled after being taken out of the furnace; Step S5, primary annealing, the forging is kept at 690°C ± 40°C, and then taken out of the furnace and air-cooled; Step S6, expanding the hole of the frame, the forging temperature range is 900-1150°C, and then cooling; Step S7, secondary annealing, annealing and heat preservation of the forging, the annealing temperature range is 690℃±40℃; Step S8, normalizing, normalizing the forging and keeping it warm, the normalizing temperature range is 1130±5℃; Step S9, primary tempering, tempering and heat preservation of forgings, tempering temperature range 760±5℃; Step S10, quenching, quenching and heat preservation of forgings, the quenching temperature range is 1120±5℃; Step S11, secondary tempering, tempering and heat preservation of forgings, the tempering temperature range is 680±5℃; Step S12, stress relief annealing, annealing and heat preservation of forgings, the stress relief annealing temperature range is 630±5℃.

2. The method for controlling the shape of a casing forging for a large gas turbine according to claim 1, characterized in that: In step S3, the blank is upset so that the deformation amount in the height direction is 33-45%.

3. The method for controlling the shape of a casing forging for a large gas turbine according to claim 1, characterized in that: In step S5, the annealing holding time ranges from 12 to 16 hours.

4. The method for controlling the shape of a casing forging for a large gas turbine according to claim 1, characterized in that: In step S6, the forging is expanded by four fires. In the first fire, the size ratio of the diameter of the inner hole of the forging before and after the change is 1:2.8~3.4; in the second fire, the size ratio before and after the change is 1:1.1~1.30; in the third fire, the size ratio before and after the change is 1:1.02~1.15; in the fourth fire, the size ratio before and after the change is 1:1.03~1.08; the tooling lever used for controlling the expansion is at an angle of 76° to the end face.

5. The method for controlling the shape of a casing forging for a large gas turbine according to claim 1, characterized in that: In step S7, the annealing holding time is 9 to 12 hours.

6. The method for controlling the shape of a casing forging for a large gas turbine according to claim 1, characterized in that: In step S8, the forging is put into the furnace at ≤750°C, the normalizing holding time ranges from 180 to 200 minutes, the forging is cooled in the furnace to ≤750°C, and then air-cooled to room temperature.

7. The method for controlling the shape of a casing forging for a large gas turbine according to claim 1, characterized in that: In step S9, the forging is put into the furnace at ≤500°C, the primary tempering holding time ranges from 360 to 380 minutes, and the forging is air-cooled to room temperature.

8. The method for controlling the shape of a casing forging for a large gas turbine according to claim 1, characterized in that: In step S10, the forging is put into the furnace at ≤750°C, the quenching and holding time ranges from 180 to 200 minutes, and the forging is oil-cooled to room temperature.

9. The method for controlling the shape of a casing forging for a large gas turbine according to claim 1, characterized in that: In step S11, the forging is put into the furnace at ≤500°C, the secondary tempering holding time ranges from 360 to 380 minutes, and the forging is air-cooled to room temperature.

10. A method for controlling the shape of a casing forging for a large gas turbine according to claim 1, characterized in that: In step S12, the forging is put into the furnace at ≤500°C, the stress relief annealing holding time ranges from 180 to 200 minutes, and the forging is air-cooled to room temperature.

Images