Processing method of Cr-Ni-Mo-V steel solid whole rotor body forging for large thermal power steam turbine

Abstract

The application discloses a processing method of a Cr-Ni-Mo-V steel solid whole rotor body forging for a large thermal power steam turbine, which comprises the following steps: a smelting and ingot casting process, wherein the steel ingot is smelted and cast by adopting the process route of arc furnace initial smelting, refining furnace refining, vacuum treatment furnace degassing and vacuum carbon deoxidization two-packing pouring; a forging process, wherein the steel ingot is hot sent for forging after solidification demolding, and the forging process specifically comprises the following steps: first fire forging, steel ingot pressure jaw, chamfering, bottom cutting and round pressing; second fire forging, roughening, first WHF lengthening and eight side pressing; third fire forging, roughening, second WHF lengthening and flat side pressing; fourth fire forging, round pressing, number stamping, step forging and product finishing; and a post-forging heat treatment process, a performance heat treatment process and a stress relief heat treatment process. The application meets the comprehensive performance requirements of the solid whole rotor body forging for the large thermal power steam turbine, realizes one-time qualification of the solid whole rotor forging for the large thermal power steam turbine unit, and realizes the comprehensive goals of short cycle, low cost and high efficiency.

Description

Technical Field

[0001] This invention belongs to the field of forging technology, and more specifically relates to a processing method for a solid integral rotor body forging of Cr-Ni-Mo-V steel for large thermal power turbines. Background Technology

[0002] The rotor body is a core component of large thermal power steam turbines, operating under harsh conditions of high temperature, high pressure, and high speed. Therefore, rotor body forgings require excellent comprehensive mechanical properties. In my country, 30Cr2Ni4MoV steel from the Cr-Ni-Mo-V series is widely used as raw material for low-pressure rotors of supercritical and ultra-supercritical steam turbine units. This type of steel possesses good hardenability and mechanical properties. For large steam turbine low-pressure integral rotor body forgings, the rotor shaft blank diameter reaches approximately... Throughout the entire hot processing and manufacturing process, the focus is on smelting large steel ingots with high purity and low segregation. Through effective forging, the casting structure is thoroughly broken, internal void defects are forged together, and the generation of mixed crystals is controlled, thereby achieving the goal of meeting the requirements for ultrasonic flaw detection and mechanical properties of the rotor body.

[0003] For large thermal power turbine rotor body forgings, the conventional manufacturing process involves multiple upsetting and various compaction methods, which results in long manufacturing cycles, high manufacturing costs, and large fluctuations in product qualification rates. This leads to low overall manufacturing efficiency and may even fail to meet the comprehensive performance requirements of large thermal power turbine rotor body forgings. Summary of the Invention

[0004] To address some or all of the technical problems existing in the prior art, this invention provides a method for manufacturing a solid integral rotor forging of Cr-Ni-Mo-V steel for large thermal power turbines. The method utilizes a 100-ton-level vacuum carbon deoxidation double-vacuum steel ingot to manufacture the large solid integral rotor forging of Cr-Ni-Mo-V steel for large thermal power turbines, producing one piece from each ingot. The method includes the following steps:

[0005] I. Smelting and casting processes

[0006] In the smelting and casting processes, the process route of 80-ton electric arc furnace (EBT) primary smelting → 120-ton refining furnace (LF) refining → vacuum treatment furnace (VD) degassing → vacuum carbon deoxidation furnace (VCD) combined casting is adopted for the smelting and casting of steel ingots for large thermal power turbine solid integral rotor forgings made of Cr-Ni-Mo-V steel. The chemical composition of the steel ingots is controlled by mass percentage as follows: C≤0.35%, Mn: 0.20~0.40%, Si≤0.10%, P≤0.01%. 0%, S≤0.010%, Cr: 1.50~2.00%, Ni: 3.25~3.75%, Mo: 0.25~0.60%, V: 0.07~0.15%, Cu≤0.15%, Al≤0.010%, As≤0.020%, Sn≤0.015%, Sb≤0.0015%, and the gas content of steel ingots is controlled as [H]≤1.5ppm, [O]≤35ppm, and [N]≤70ppm;

[0007] II. Forging Process

[0008] After the steel ingot solidifies and is demolded, it is removed from the mold. The surface temperature of the ingot is not lower than 700℃. It is then loaded into a heat-insulating car for hot forging. The forging temperature range is controlled between 1270℃ and 850℃. The forging ratio of the rotor shaft is controlled to be greater than 3.5. The specific process of forging is as follows:

[0009] a. First forging: pressing the steel ingot into jaws, chamfering, cutting the bottom, and rounding;

[0010] b. Second forging: roughing, first WHF drawing and pressing in all directions;

[0011] c. Third forging: upsetting, second WHF drawing and flattening;

[0012] d. Fourth forging: pressing into a round shape, marking, forging steps, and finishing the product;

[0013] III. Post-forging heat treatment process

[0014] After the rotor body forging is forged, it is air-cooled until the surface temperature of the shaft body at the small shaft end reaches 300℃, and then placed in a heat treatment furnace for post-forging heat treatment, which specifically includes:

[0015] a. Temperature equalization treatment: After holding the forging at 520-570℃ for 20 hours, the temperature is reduced to 220-270℃ at a rate of ≤10℃ / h and held for 36 hours.

[0016] b. The first austenitizing low-temperature normalizing treatment and high-temperature normalizing treatment: the forging is heated to 640~660℃ at a heating rate of ≤35℃ / h and held for 16h. Then the forging is heated to 890~950℃ according to the power of the heat treatment furnace and held for 18~22h. It is then air-cooled out of the furnace.

[0017] c. Second austenitizing low-temperature normalizing and high-temperature normalizing treatment: After air cooling the forging to 200-250℃, hold it for 36 hours, then heat it to 640-660℃ at a heating rate of ≤35℃ / h, hold it for 16 hours, and then heat the forging to 860-900℃ according to the power of the heat treatment furnace, hold it for 18-22 hours, and then air cool it out of the furnace.

[0018] d. Tempering treatment: After air cooling the forging to 200-250℃, hold it at that temperature for 40 hours. Then heat it to 640-660℃ at a heating rate of ≤30℃ / h, hold it at that temperature for 70 hours, and then furnace cool it to ≤150℃ before removing it from the furnace.

[0019] IV. Performance Heat Treatment Process

[0020] After the post-forging heat treatment process, the forgings are subjected to performance heat treatment using a pit furnace, specifically including:

[0021] a. Quenching treatment: The forging is held at 140-160℃ for 10 hours, then heated to 640-660℃ at a heating rate of ≤40℃ / h and held for 15 hours. Then the forging is heated to 830-880℃ according to the power of the pit furnace and held for 38-45 hours. It is then cooled by water spray for 12-16 hours. After the surface temperature of the forging shaft is ≤100℃, it is removed from the water.

[0022] b. High-temperature tempering treatment: The forgings are held at 140-160℃ for 18-25 hours, then heated to 570-650℃ at a heating rate of ≤30℃ / h, held for 50-60 hours, and then furnace cooled to ≤150℃ at a cooling rate of ≤10℃ / h before being taken out of the furnace.

[0023] Furthermore, in the above-mentioned processing method for solid integral rotor forgings of Cr-Ni-Mo-V steel for large thermal power turbines, a stress-relieving heat treatment process is also included after the performance heat treatment process: for rotor forgings after semi-finished impeller grooves, the temperature is held at 160-210℃ for 12-18h, then heated to 540-560℃ at a heating rate of ≤15℃ / h, held for 40-45h, and then furnace cooled to ≤150℃ at a cooling rate of ≤10℃ / h before being taken out of the furnace.

[0024] Furthermore, in the aforementioned processing method for solid integral rotor forgings of Cr-Ni-Mo-V steel for large thermal power turbines, during the smelting and casting processes:

[0025] The process carbon content of the furnace charge is controlled at 0.60-0.80%;

[0026] The initial smelting temperature is controlled at 1660–1690℃, and the C and P contents in the molten steel are controlled at C≤0.10% and P≤0.002%, respectively.

[0027] During refining, electrode powder diffusion deoxidation is used, and argon gas is blown from the bottom of the ladle. The temperature is adjusted to 1650-1660℃ for VD degassing, and the process is maintained under a vacuum of ≤65Pa for at least 20 minutes.

[0028] When using a two-stage tundish casting method, the tundish casting temperature should be controlled at 1560–1580℃, and the initial vacuum degree should be controlled at ≤65Pa.

[0029] Furthermore, in the aforementioned processing method for the solid integral rotor body forging of Cr-Ni-Mo-V steel for large thermal power turbines:

[0030] In the first forging stage of the forging process, after the hot-delivered steel ingot is loaded into the forging heating furnace, it is heated to 1260±10℃ at a heating rate of ≤70℃ / h and held at that temperature for 18h. Using a 125MN press, the upper flat anvil and lower V-shaped anvil are aligned along the riser line of the steel ingot at a position of 150-200mm on the upper part of the ingot body to perform jaw pressing operation. When pressing the jaw, it is ensured that the center line of the jaw is consistent with the center line of the steel ingot. After pressing the jaw, the excess riser material is cut off, the jaw is rolled round, the steel ingot is turned around, and the steel ingot is chamfered, the bottom is cut off, and the ingot is rounded.

[0031] In the second forging process, the billet is returned to the furnace and heated to 1260±10℃ according to the power of the forging furnace, and then held for 51 hours. The billet is then upsetting using a 125MN press, a slotted plate, and a spherical top upsetting cap. After the ingot is upset, the first WHF elongation is performed using a wide and flat anvil. Full anvil pressure is used, and the deformation on both sides is controlled to be 18-22%. After each pass, the billet is rotated 90°, the anvil is staggered by half, and then the billet is pressed down again. Each pass of pressing starts from the riser end. Through multiple passes of pressing, the billet is compacted into a flat square shape, and then the edges are chamfered to make the billet octagonal.

[0032] In the third forging process, the billet is returned to the furnace and heated to 1260±10℃ according to the power of the forging furnace, and then held for 34 hours. The billet is upsetting using a 125MN press, a slotted plate and a spherical top cap. After the ingot is upset, it is drawn using upper and lower flat anvils for the second WHF drawing. The deformation on both sides is controlled to be 18-22%. After each pass, the billet is rotated 90° and the anvil is staggered by half. Each pass of drawing starts from the riser end. Through multiple passes of drawing, the billet is compacted into a flat square.

[0033] In the fourth forging process, the billet is returned to the furnace and heated to 1220±10℃ according to the power of the forging furnace, and then held for 18 hours. Using a 125MN press, the upper and lower flat anvils are used to press the eight sides first. Then, according to the step material size, the marking anvil is used to mark the shape, and the shaft body and the steps at both ends are forged. Then, the forming arc anvil is used to correct and round the shape. The remaining material at both ends is cut according to the required size to form the final forging.

[0034] Furthermore, in the above-mentioned processing method for solid integral rotor forgings of Cr-Ni-Mo-V steel for large thermal power turbines, if the small shaft end step of the forging cannot be formed in the fourth forging, the forging process includes a fifth forging after the fourth forging: the billet is returned to the furnace, heated to 1050±10℃ according to the power of the forging heating furnace, held for 10h, and the small shaft end step is forged after exiting the furnace. Then, the forming arc anvil is used to correct and round the forging, and the forging is finally formed.

[0035] As one specific implementation method, the above-mentioned machining method for large thermal power steam turbine solid integral rotor body forgings made of Cr-Ni-Mo-V steel is used to manufacture forgings with a machining dimension of outer diameter. The forging process for a large 7890mm thick solid integral rotor body made of Cr-Ni-Mo-V steel for thermal power turbines is as follows:

[0036] In the first forging stage of the forging process, a 125MN press is used. An 850mm upper flat anvil and a 850mm lower V-shaped anvil are aligned along the riser line on the upper ingot body at a point 150-200mm from the top. Initially, the riser is lightly pressed, pressing the riser root and the ingot shoulder completely onto the clamping material in the first pass. The pressing amount increases in the second pass. Once the clamping size is reached... Use a chopping knife to cut off excess riser material, then use rolling pincers to round the ingot; after turning the ingot around, clamp the already pressed piece. The clamp handle, with a double-sided pressing amount of 100mm, rounds the steel ingot to... Then, the bottom of the steel ingot is cut off at 700mm from the top of the ingot body using the lower chopping blade before it is removed from the machine;

[0037] In the second forging stage of the forging process, a 125MN press is used. The upsetting plate and spherical top upsetting cap, upsetting to Then, a 1700mm wide flat anvil is used for the first WHF drawing. The anvil radius R is 170mm, and the double-sided reduction is controlled at 20%. Full anvil pressure is used, and the feed amount of each anvil is greater than 90% of the anvil width. There is a 100-200mm joint between each anvil. Through 6 passes of pressing, the billet is compacted to a flat square of 2290mm × 2180mm. Then, the edges are chamfered to make the billet octagonal of 2200mm × 4500mm. The process parameters for the first WHF pressing are controlled according to the following table:

[0038]

[0039] In the third forging stage of the forging process, a 125MN press is used. The upsetting plate and spherical top upsetting cap, upsetting to Then, a second WHF drawing is performed using a 1700mm flat anvil, with the double-sided reduction controlled at 20%. Through 9 passes of pressing, the billet is compacted to a flat square size of 2125mm × 1575mm. The process parameters for the second WHF pressing are controlled according to the table below:

[0040]

[0041]

[0042] In the fourth forging process, a 125MN press is used. First, an 850mm flat anvil is used to press an 1860mm square anvil. The dimensions of the step are measured and marked with a marking anvil. The shaft body and the steps at both ends are forged separately. Then, a forming arc anvil is used to correct and round the shape. The remaining material at both ends is cut with gas according to the required dimensions to form the final forging.

[0043] The processing method for large solid integral rotor forgings made of Cr-Ni-Mo-V steel for large thermal power turbines of this invention adopts a low-cost, high-efficiency, and low-energy-consumption process. Effective control is exercised at each stage, from smelting large steel ingots to forging and heat treatment, achieving high purity and low segregation of large steel ingots, effective compaction of the center of large forgings, and uniform heat treatment performance. Ultimately, it meets the excellent comprehensive performance requirements of Cr-Ni-Mo-V steel solid integral rotor forgings for large thermal power turbines. This method achieves, for the first time, one-time qualified production of low-pressure solid integral rotor forgings for large thermal power turbine units, filling a technological gap and achieving the comprehensive goals of short cycle time, low cost, and high efficiency. Compared with existing technologies, it has the following advantages and beneficial effects:

[0044] (1) The process route of electric arc furnace EBT primary refining → refining furnace LF refining → vacuum treatment furnace VD degassing → vacuum carbon deoxidation VCD two-ladle casting is adopted to formulate a pure smelting technology scheme for Cr-Ni-Mo-V steel. By effectively controlling the material composition and gas content, using composite deoxidizer to enhance deoxidation, reducing the oxygen content in the steel, allowing inclusions to float fully, purifying the molten steel, controlling the process with fine operation and protecting the casting, reducing the risk of secondary oxidation of molten steel and the introduction of foreign inclusions, and meeting the high purity and high homogeneity requirements of large steel ingots for the solid integral rotor of Cr-Ni-Mo-V steel for large thermal power turbines.

[0045] (2) Adopt a multi-fire forging process, formulate low internal tensile stress forging deformation process measures of two upsetting and three drawing to meet the requirements of compaction and forging through the rotor body and forging internal metallurgical defects. At the same time, control the forging temperature and deformation amount of each fire to avoid internal cracks in the forging and obtain the original structure with controllable grains, obtain a solid integral rotor body forging with excellent internal quality, and ensure the final flaw detection requirements of the rotor body.

[0046] (3) After the forging is completed, effective post-forging heat treatment, performance heat treatment and stress relief heat treatment are carried out. Quenching and cooling are carried out by using a large vertical spray quenching system. The large amount of water sprayed is used to meet the requirements of the rotor body for rapid cooling and deep cooling. By controlling the reasonable tempering temperature, the surface and core performance and microstructure requirements are taken into account at the same time, so that the rotor body can obtain excellent comprehensive mechanical properties. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings:

[0048] Figure 1 This is a schematic flowchart illustrating the processing method of the solid integral rotor body forging of Cr-Ni-Mo-V steel for large thermal power turbines according to the present invention.

[0049] Figure 2 The following are schematic diagrams of the forging morphology in each process step of the processing method of the solid integral rotor body forging of Cr-Ni-Mo-V steel for large thermal power turbines of the present invention. Among them, (a) is a schematic diagram of the steel ingot, (b) is a schematic diagram of the billet after pressing the steel ingot jaws, chamfering, cutting the bottom and pressing it into a round shape, (c) is a schematic diagram of the billet after the steel ingot is upsetting, first WHF drawing and pressing into an octagon, (d) is a schematic diagram of the billet after the steel ingot is upsetting, second WHF drawing and pressing into a flat square shape, (e) is a schematic diagram of the billet after pressing the steel ingot into a round shape, marking and forging into steps, and (f) is a schematic diagram of the finished forging.

[0050] Figure 3 This is a schematic diagram of the timing of the post-forging heat treatment process in the processing method of the large Cr-Ni-Mo-V steel solid integral rotor forging for thermal power turbines of the present invention.

[0051] Figure 4 This is a schematic diagram of the timing of the performance heat treatment process in the processing method of the large Cr-Ni-Mo-V steel solid integral rotor forging for thermal power turbines of the present invention.

[0052] Figure 5 This is a schematic diagram of the timing of the stress-relieving heat treatment process in the processing method of the solid integral rotor body forging of Cr-Ni-Mo-V steel for large thermal power turbines of the present invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0054] The present invention discloses a method for manufacturing large solid integral rotor forgings of Cr-Ni-Mo-V steel for thermal power turbines. This method employs a 100-ton-level vacuum carbon deoxidation double-vacuum steel ingot, producing one forging from each ingot. Figure 1 As shown, the process includes the following steps:

[0055] I. Smelting and casting processes

[0056] In the smelting and casting process, the steel ingots used for the Cr-Ni-Mo-V steel solid integral rotor body forgings for large thermal power turbines are smelted and cast using the following process route: 80-ton electric arc furnace EBT primary smelting → 120-ton refining furnace LF refining → vacuum treatment furnace VD degassing → vacuum carbon deoxidation VCD two-ladle combined casting.

[0057] Based on the technical requirements for flaw detection and comprehensive mechanical properties of solid integral rotor forgings made of Cr-Ni-Mo-V steel for large thermal power turbines, strict internal control is implemented on the chemical composition of the steel ingots, especially the content of harmful impurity elements and gases. For example, impurity elements such as P, As, Sn, and Sb, which cause temper embrittlement, elements that promote embrittlement such as Si and Mn, and elements that reduce toughness such as S are controlled. Furthermore, Cr-Ni-Mo-V steel is a hypoeutectoid steel, and its phase transformation during cooling is complex. In particular, the H content in the molten steel must be strictly controlled. If the H content is high, significant internal stress will be generated during solidification, causing white spots in the hydrogen-rich areas of the forging and resulting in a severe tendency for longitudinal cracking.

[0058] Therefore, in the smelting and casting processes, the chemical composition of the steel ingot is controlled by mass percentage as follows: C≤0.35%, Mn: 0.20~0.40%, Si≤0.10%, P≤0.010%, S≤0.010%, Cr: 1.50~2.00%, Ni: 3.25~3.75%, Mo: 0.25~0.60%, V: 0.07~0.15%, Cu≤0.15%, Al≤0.010%, As≤0.020%, Sn≤0.015%, Sb≤0.0015%, and the gas content of the steel ingot is controlled as follows: [H]≤1.5ppm, [O]≤35ppm, [N]≤70ppm.

[0059] In addition, the following technical points need to be controlled in the smelting and ingot casting processes:

[0060] (1) Charge control: Scrap steel and pig iron are preferred for batching, and the elements As, Sn, Sb, P, and S are tested batch by batch to ensure they meet process requirements. All steel, ferroalloy, and auxiliary materials entering the furnace are strictly baked and dried according to process specifications. The carbon content of the furnace charge is strictly controlled within the process range of 0.60–0.80%.

[0061] (2) 80-ton electric arc furnace (EBT) primary refining: Primary refining requires reasonable oxygen blowing for melting and reasonable decarburization. Strong oxidizing properties, high basicity, large slag volume, and strong oxygen supply are employed. Low-temperature dephosphorization is performed in the initial melting stage, with multiple slag discharges and excessive oxygen blowing. Sulphurization is carried out under high-temperature, high-basicity conditions before tapping. During the oxidation period, slag flow and new slag generation are carried out to ensure sufficient slag replacement. Tapping is performed with both steel and slag retained; oxidized slag is strictly prohibited from entering the refining ladle. The tapping temperature of the primary refining is controlled at 1660–1690℃, and the C and P contents in the tapped steel are controlled to C≤0.10% and P≤0.002%, respectively.

[0062] (3) LF refining in a 120-ton refining furnace: Electrode powder diffusion deoxidation is used, along with bottom blowing of argon gas into the ladle. Adding deoxidizing materials containing Si and Al is strictly prohibited. During the refining process, it is crucial to prevent an increase in Si and P content, to quickly generate reducing slag for deoxidation and desulfurization, and to maximize the flotation of non-metallic inclusions in the molten steel. Maintain appropriate slag basicity, slag quantity, and molten steel temperature. Add alloying materials according to process requirements and adjust the chemical composition. Adjust the temperature to 1650–1660℃ for vacuum degassing in a VD furnace.

[0063] (4) Vacuum Degassing in a Vacuum Furnace: After high-vacuum treatment, oxygen in the molten steel is removed by the carbon-oxygen reaction. The generated CO bubbles diffuse and float H, O, N, and other gases and inclusions in the molten steel, thus purifying it. This process is maintained at a vacuum of ≤65 Pa for at least 20 minutes. After vacuum treatment, the molten steel is allowed to stand and then gently stirred with argon gas for at least 15 minutes to further ensure that inclusions float to the surface.

[0064] (5) Vacuum Carbon Deoxidation VCD Two-Ladle Combined Casting: Two-ladle casting is used. During vacuum casting, the prepared steel ingot mold and other auxiliary tools are cleaned and dried in advance. The operation is strictly carried out in accordance with the multi-ladle combined casting process to ensure the quality of vacuum steel ingot casting. Special attention is paid to key aspects such as steel diversion, control of the alternating casting time between the two ladles, casting temperature, casting speed, and argon protection throughout the casting process. The tundish casting temperature is controlled at 1560~1580℃, and the vacuum degree at the start of casting is controlled at ≤65Pa. After the final casting is completed, an appropriate amount of exothermic agent is added as soon as possible after the vacuum is broken.

[0065] Through the above measures in the smelting and casting processes, the chemical composition of the finished double-vacuum steel ingot meets the standard requirements. In the finished double-vacuum steel ingot, [H]: 0.8ppm, [O]: 15ppm, [N]: 50ppm, and the coarse and fine inclusions A, B, C, and D in the steel are all controlled at level 0 to 0.5, and DS is controlled at level ≤ 0.5.

[0066] II. Forging Process

[0067] According to the requirements of the steel ingot solidification and cooling process, after the steel ingot solidifies and is demolded, it is removed from the mold. The surface temperature of the steel ingot should not be lower than 700℃. It is then loaded into a heat-insulating car for hot forging. See the schematic diagram of the steel ingot. Figure 2 (a) In the forging process, a 125MN press is used for multi-pass forging, and the forging temperature range is controlled between 1270 and 850°C. The rotor shaft forging ratio is controlled to be greater than 3.5, so that the forging is fully deformed, the grain structure is fully and uniformly refined, and the core of the steel ingot is compacted, thereby forging together the loose and dispersed inclusions in the core, and obtaining a solid integral rotor forging with excellent internal quality, which meets the requirements of ultrasonic flaw detection.

[0068] The specific process of forging is as follows:

[0069] a. First Forging: Ingot clamping, chamfering, undercutting, and rounding. After being loaded into the forging furnace, the hot-delivered double-vacuum ingot is heated to 1260±10℃ at a rate of ≤70℃ / h and held for 18 hours. Using a 125MN press, with an upper flat anvil and a lower V-shaped anvil aligned along the ingot riser line at a point 150-200mm from the top of the ingot, clamping is performed, ensuring the center line of the clamping jaws aligns with the center line of the ingot. After clamping, excess riser material is cut off, the clamping jaws are rounded, the ingot is turned around, and chamfering, undercutting, and rounding are performed. After the first forging, surface defects such as cracks and indentations are cleaned using an oxygen lance. See the schematic diagram for the ingot clamping, chamfering, undercutting, and rounding process. Figure 2 (b) in the middle.

[0070] b. Second forging: roughing, first WHF (wide anvil high-pressure forging method) drawing and pressing in eight directions. The billet is returned to the furnace and heated to 1260±10℃ according to the power of the forging furnace, and then held for 51 hours. The billet is then upsetting using a 125MN press, a spool, and a spherical top cap. This upsetting increases the cross-sectional area of ​​the steel ingot billet through axisymmetric deformation, increasing the forging ratio for subsequent drawing. It effectively closes the internal pores of the steel ingot, breaks up the as-cast structure, improves segregation, enhances the lateral properties of the rotor body forging, and reduces the anisotropy of mechanical properties. After upsetting, the steel ingot is first drawn using a wide and flat anvil. Full anvil pressure is used, and the deformation on both sides is controlled at 18-22%. After each pass, the anvil is rotated 90° and half-staggered before another pass. Each pass begins from the riser end to ensure effective coverage of the overall deformation of the forging and to ensure the uniformity of the billet deformation. Through multiple passes, the billet is compacted into a flat square shape, and then chamfered to make the billet octagonal. After the second forging process, surface defects such as cracks, pits, and folds in the billet are cleaned using an oxygen lance. See the schematic diagram of the billet undergoing the initial WHF drawing and octagonal pressing. Figure 2 (c) in the middle.

[0071] c. Third Forging: Upsetting, Second WHF Drawing and Flattening. The billet is returned to the furnace and heated to 1260±10℃ according to the forging furnace power, then held for 34 hours. The billet is upset using a 125MN press, a spool, and a spherical top upsetting cap. After upsetting, a second WHF drawing is performed using upper and lower flat anvils. The double-sided deformation is controlled at 18-22%. After each pass, the billet is rotated 90°, with the anvils offset by half, and then drawn again. Each pass begins with drawing from the riser end. Through multiple passes, the billet is compacted into a flat shape. After the third forging is completed, surface defects such as cracks, pits, and folds are cleaned using an oxygen lance. See the schematic diagram of the billet for the ingot upsetting, second WHF drawing, and flattening process. Figure 2 (d) in the middle.

[0072] d. Fourth Forging: Rounding, Marking, Forging Steps, and Finishing. The billet is returned to the furnace and heated to 1200±10℃ according to the forging furnace power, then held for 18 hours. Using a 125MN press, first use upper and lower flat anvils to press the octagon, then mark the dimensions of the step section using a marking anvil, forging the shaft body and the steps at both ends. Then, use a forming arc anvil to correct and round the billet, and gas-cut the remaining material at both ends to the required dimensions for final forging. See the schematic diagram of the billet rounding, marking, and forging steps for steel ingots. Figure 2 (e) In the diagram, see the schematic diagram of the finished forging after finishing. Figure 2 (f) in the middle.

[0073] III. Post-forging heat treatment process

[0074] After the rotor body forging is formed, it is air-cooled until the surface temperature of the small shaft end reaches 300℃. Then, it is placed in a heat treatment furnace for post-forging heat treatment. The main purpose is to eliminate thermal stress, adjust and improve the uneven microstructure during forging, refine the austenite grains, effectively cut off the microstructure inheritance, improve the detectability of ultrasonic testing, and improve the subsequent machining performance. Figure 3 As shown, the post-forging heat treatment process specifically includes:

[0075] a. Temperature homogenization treatment: After the forging is air-cooled to 300°C on the surface of the small shaft end, the core temperature of the forging is high due to its large cross-sectional diameter. Therefore, temperature homogenization treatment is required. The forging is held at 520-570°C for 20 hours to homogenize the temperature difference between different parts of the forging. Then, it is cooled to 220-270°C at a cooling rate of ≤10°C / h and held for 36 hours to ensure that the core of the rotor body forging is also cooled below the lower bainite transformation temperature to complete the microstructure transformation.

[0076] b. The first austenitizing low-temperature normalizing treatment and high-temperature normalizing treatment: the forging is heated to 640~660℃ at a heating rate of ≤35℃ / h and held for 16h. Then the forging is heated to 890~950℃ according to the power of the heat treatment furnace and held for 18~22h. It is then air-cooled out of the furnace.

[0077] c. Second austenitizing low-temperature normalizing and high-temperature normalizing treatment: After air cooling the forging to 200-250℃, hold it for 36 hours, then heat it to 640-660℃ at a heating rate of ≤35℃ / h, hold it for 16 hours, and then heat the forging to 860-900℃ according to the power of the heat treatment furnace, hold it for 18-22 hours, and then air cool it out of the furnace.

[0078] d. Tempering treatment: After air cooling the forging to 200-250℃, hold it at that temperature for 40 hours. Then heat it to 640-660℃ at a heating rate of ≤30℃ / h, hold it at that temperature for 70 hours, and then furnace cool it to ≤150℃ before removing it from the furnace.

[0079] IV. Performance Heat Treatment Process

[0080] After the post-forging heat treatment process, the forgings are subjected to performance heat treatment using a pit-type electric furnace. For example... Figure 4 As shown, the performance heat treatment process specifically includes:

[0081] a. Quenching treatment: The forging is held at 140-160℃ for 10 hours, then heated to 640-660℃ at a heating rate of ≤40℃ / h and held for 15 hours. Then the forging is heated to 830-880℃ according to the power of the pit furnace and held for 38-45 hours. It is then cooled by water spray for 12-16 hours. After the surface temperature of the forging shaft is ≤100℃, it is removed from the water.

[0082] b. High-temperature tempering treatment: The forgings are held at 140-160℃ for 18-25 hours, then heated to 570-650℃ at a heating rate of ≤30℃ / h, held for 50-60 hours, and then furnace cooled to ≤150℃ at a cooling rate of ≤10℃ / h before being taken out of the furnace.

[0083] The above-mentioned heat treatment, by controlling the quenching heating temperature and holding time and cooling by water spraying, quenches the entire cross section of the rotor body forging, so as to obtain martensite or martensite plus lower bainite structure, thereby achieving uniformity of the overall microstructure and mechanical properties of the rotor forging.

[0084] Furthermore, in the forging process of the processing method of the solid integral rotor body forging of Cr-Ni-Mo-V steel for large thermal power turbines of the present invention, if the small shaft end step of the forging cannot be formed in the fourth forging, the forging process also includes a fifth forging: the billet is returned to the furnace, heated to 1050±10℃ according to the power of the forging heating furnace, held for 10h, the small shaft end step is forged after taking it out of the furnace, and then the rounding is corrected and rolled using a forming arc anvil to finally form the forging.

[0085] Furthermore, in the processing method of the large Cr-Ni-Mo-V steel solid integral rotor forging for thermal power turbines of the present invention, a stress-relieving heat treatment process may be included after the performance heat treatment process, such as... Figure 5 As shown, the stress-relieving heat treatment process specifically includes: for the rotor body forging after semi-finishing the impeller grooves, holding at 160–210℃ for 12–18 hours, then heating to 540–560℃ at a heating rate of ≤15℃ / h, holding at that temperature for 40–45 hours, and then furnace cooling to ≤150℃ at a cooling rate of ≤10℃ / h before removal from the furnace. This stress-relieving heat treatment plays a crucial role in stabilizing dimensional accuracy during subsequent finishing processes.

[0086] The following detailed description, with reference to specific embodiments, illustrates the processing method of the large solid integral rotor body forging of Cr-Ni-Mo-V steel for thermal power turbines according to the present invention. The embodiments described below utilize a 100-ton-level vacuum carbon deoxidation double-vacuum steel ingot to manufacture the large solid integral rotor body forging of Cr-Ni-Mo-V steel for thermal power turbines, producing one piece from each ingot. The required dimensions of the finished forging are: outer diameter... The grain size must be ≥4, and ultrasonic testing requires that no equivalent defects be present within 150mm of the rotor forging impeller surface. Non-metallic inclusion dense areas are not allowed to have an equivalent diameter greater than 1. A single defect, the rest of the area is allowed to have There are 3 densely populated areas, but the spacing between them must be greater than 120mm, and some are allowed. Individual defects are permitted, but the total number must not exceed 20; more than 20 defects are not allowed. dense defects and The single defect. This rotor body forging is a typical large-section, short and thick shaft forging with extremely high flaw detection requirements and extremely difficult manufacturing. The weight of the forging blank reaches hundreds of tons, and the minimum forging ratio of the rotor body shaft is 3.5.

[0087] The processing method of the solid integral rotor body forging of Cr-Ni-Mo-V steel for large thermal power turbines according to the present invention is carried out in accordance with the aforementioned smelting and casting process, forging process, post-forging heat treatment process, performance heat treatment process, and stress relief heat treatment process, and the specific implementation process of the forging process is as follows:

[0088] In the first forging stage of the forging process, a 125MN press is used. An 850mm upper flat anvil and a 850mm lower V-shaped anvil are aligned along the riser line on the upper ingot body at a point 150-200mm from the top. Initially, the riser is lightly pressed, pressing the riser root and the ingot shoulder completely onto the clamping material in the first pass. In the second pass, the pressing amount is increased, carefully controlling the uniform rotation angle of the clamping jaws and the pressing amount per hammer blow to ensure the clamping jaw centerline is aligned with the ingot centerline. Once the clamping jaws have pressed to the required size... Use the lower chopping knife to cut off excess riser material, and round the handle of the clamps to ensure that it can be placed into the upsetting tray in the next firing; after the steel ingot is turned around, the manipulator clamps the already pressed ingot. The clamp handle, with a double-sided pressing amount of 100mm, rounds the steel ingot to... Then, the bottom of the steel ingot is cut off at 700mm (including the cutting edge) on the upper ingot body using a downward chopping knife, and then removed from the machine. Finally, surface defects such as cracks and indentations are cleaned using an oxygen lance.

[0089] In the second forging stage of the forging process, a 125MN press is used. The upsetting plate and spherical top upsetting cap, upsetting roughness to approximately Then, the first WHF drawing is performed using a 1700mm wide flat anvil. The anvil radius R is 170mm, and the double-sided reduction is controlled at 20%. Full anvil pressure is used, and the feed amount of each anvil is greater than 90% of the anvil width. There is a 100-200mm gap between each anvil. After each pass, the anvil is rotated 90° and offset by half before the next pass. Each pass begins with pressure from the riser end. Through 6 passes, the billet is compacted to a flat square of 2290mm × 2180mm. Then, the edges are chamfered to make the billet approximately octagonal, 2200mm × 4500mm. After the billet exits the machine, any cracks, pits, folds, or other defects that appear on the surface of the billet during the drawing process are completely cleaned with an oxygen lance. The process parameters for the first WHF reduction are controlled according to Table 1 below:

[0090] Table 1. Process parameters for the first WHF pressing down.

[0091]

[0092] In the third forging stage of the forging process, a 125MN press is used. The upsetting plate and spherical top upsetting cap, upsetting roughness to approximately Then, a second WHF drawing is performed using a 1700mm flat anvil, with a double-sided reduction controlled at 20%. The specific parameters and precautions for the second WHF drawing are the same as for the first WHF drawing. Through nine passes of reduction, the billet is compacted to a flat square size of 2125mm × 1575mm. After the billet exits the machine, any defects such as cracks, pits, and folds that occurred during the drawing process are completely removed using an oxygen lance in a hot state. The process parameters for the second WHF reduction are controlled according to Table 2 below:

[0093] Table 2. Second WHF pressing process parameters

[0094]

[0095] In the fourth forging stage of the forging process, a 125MN press is used. First, an 850mm flat anvil is used to press an 1860mm square anvil. The dimensions of the step are measured and marked with a marking anvil. Then, the shaft body and the steps at both ends are forged separately. Next, a forming arc anvil is used to correct and round the shape. The remaining material at both ends is cut with gas according to the required dimensions to achieve the final shape of the forging. If the small shaft end step of the forging cannot be formed in the fourth forging stage, a fifth forging stage is performed after the fourth forging stage. The billet is returned to the furnace and heated to 1050±10℃. After holding at this temperature for 10 hours, the small shaft end step is forged after being taken out of the furnace. Then, a forming arc anvil is used to correct and round the shape to achieve the final shape of the forging.

[0096] The specific implementation process of the smelting and casting process, the post-forging heat treatment process, the performance heat treatment process, and the stress-relieving heat treatment process in the above embodiments of the present invention are described above and will not be repeated here.

[0097] According to the above embodiment of the present invention, a large solid integral rotor body forging of Cr-Ni-Mo-V steel for thermal power turbine was manufactured. All inspection results met the technical requirements. Specifically:

[0098] (1) Chemical composition detection

[0099] Chemical composition analysis was performed on samples taken from both ends of the rotor body forging. The results are shown in Table 3 below:

[0100] Table 3. Results of Chemical Composition Analysis (mass percentage, %)

[0101]

[0102] In the table above, X1 indicates the radial sampling position of the rotor shaft in the direction of the rotor nozzle, and X3 indicates the radial sampling position of the rotor shaft in the direction of the rotor riser. For details, please refer to [reference needed]. Figure 2 (f) in the middle.

[0103] (2) Mechanical performance testing

[0104] Mechanical properties were tested by taking samples from the axial direction of the shaft head and the radial direction of the shaft body of the rotor body forging. The test results are shown in Table 4 below:

[0105] Table 4 Results of Mechanical Performance Tests

[0106]

[0107]

[0108] In the table above, L1 refers to the axial sampling position of the rotor head in the direction of the rotor nozzle, L2 refers to the axial sampling position of the rotor head in the direction of the rotor riser, X1 refers to the radial sampling position of the rotor shaft in the direction of the rotor nozzle, X2 refers to the radial sampling position of the middle part of the rotor shaft, and X3 refers to the radial sampling position of the rotor shaft in the direction of the rotor riser. For details, please refer to [the table / reference needed]. Figure 2 (f) in the middle.

[0109] (3) Furthermore, testing revealed that the grain size of the large Cr-Ni-Mo-V steel solid integral rotor forging for thermal power turbines manufactured using the embodiments of the present invention was 6.0 and 6.0 at positions X2 and X3, respectively, meeting the technical requirement of grain size ≥ 4. Moreover, ultrasonic testing of the entire rotor forging revealed no recorded or excessive defects.

[0110] In summary, the processing method for the large solid integral rotor forging of Cr-Ni-Mo-V steel for thermal power turbines of the present invention adopts a low-cost, high-efficiency, and low-energy-consumption process. Effective control is exercised at each stage, from smelting large steel ingots to forging and heat treatment, achieving high purity and low segregation of large steel ingots, effective compaction of the center of large forgings, and uniform heat treatment performance. Ultimately, it meets the excellent comprehensive performance requirements of the Cr-Ni-Mo-V steel solid integral rotor forging for large thermal power turbines. This method achieves, for the first time, one-time qualification in the production of low-pressure solid integral rotor forgings for large thermal power turbine units, filling a technological gap and achieving the comprehensive goals of short cycle time, low cost, and high efficiency. Compared with existing technologies, it has the following advantages and beneficial effects:

[0111] (1) The process route of electric arc furnace EBT primary refining → refining furnace LF refining → vacuum treatment furnace VD degassing → vacuum carbon deoxidation VCD two-ladle casting is adopted to formulate a pure smelting technology scheme for Cr-Ni-Mo-V steel. By effectively controlling the material composition and gas content, using composite deoxidizer to enhance deoxidation, reducing the oxygen content in the steel, allowing inclusions to float fully, purifying the molten steel, controlling the process with fine operation and protecting the casting, reducing the risk of secondary oxidation of molten steel and the introduction of foreign inclusions, and meeting the high purity and high homogeneity requirements of large steel ingots for the solid integral rotor of Cr-Ni-Mo-V steel for large thermal power turbines.

[0112] (2) Adopt a multi-fire forging process, formulate low internal tensile stress forging deformation process measures of two upsetting and three drawing to meet the requirements of compaction and forging through the rotor body and forging internal metallurgical defects. At the same time, control the forging temperature and deformation amount of each fire to avoid internal cracks in the forging and obtain the original structure with controllable grains, obtain a solid integral rotor body forging with excellent internal quality, and ensure the final flaw detection requirements of the rotor body.

[0113] (3) After the forging is completed, effective post-forging heat treatment, performance heat treatment and stress relief heat treatment are carried out. Quenching and cooling are carried out by using a large vertical spray quenching system. The large amount of water sprayed is used to meet the requirements of the rotor body for rapid cooling and deep cooling. By controlling the reasonable tempering temperature, the surface and core performance and microstructure requirements are taken into account at the same time, so that the rotor body can obtain excellent comprehensive mechanical properties.

[0114] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Additionally, the terms "front," "back," "left," "right," "upper," and "lower" in this document refer to the placement shown in the accompanying drawings.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for machining a solid integral rotor body forging of Cr-Ni-Mo-V steel for large thermal power turbines, comprising manufacturing the forging of a solid integral rotor body for large thermal power turbines using a 100-ton-level vacuum carbon deoxidation double-vacuum steel ingot in a one-ingot-one-piece manner, characterized in that... The process includes the following steps: I. Smelting and casting processes In the smelting and casting processes, an 80-ton electric arc furnace (EBT) for initial smelting → a 120-ton refining furnace (LF) for refining → a vacuum treatment furnace (VD) for degassing → a vacuum carbon deoxidation furnace (VCD) for combined casting is adopted for the smelting and casting of steel ingots for large thermal power turbine solid integral rotor forgings made of Cr-Ni-Mo-V steel. The chemical composition of the steel ingots is controlled by mass percentage as follows: C≤0.35%, Mn: 0.20~0.40%, Si≤0.10%, P≤0.010%, S≤0.010%, Cr: 1.50~2.0%. 0%, Ni: 3.25~3.75%, Mo: 0.25~0.60%, V: 0.07~0.15%, Cu≤0.15%, Al≤0.010%, As≤0.020%, Sn≤0.015%, Sb≤0.0015%, and the gas content of the steel ingot is controlled as [H]≤1.5ppm, [O]≤35ppm, and [N]≤70ppm; when using two tundishes for casting, the tundish casting temperature is controlled at 1560~1580℃, and the opening vacuum degree is controlled at ≤65Pa; II. Forging Process After the steel ingot solidifies and is demolded, it is removed from the mold. The surface temperature of the ingot is not lower than 700℃. It is then loaded into a heat-insulating car for hot forging. The forging temperature range is controlled between 1270 and 850℃. The forging ratio of the rotor shaft is controlled to be greater than 3.

5. The specific process of forging is as follows: a. First forging: pressing the steel ingot into jaws, chamfering, cutting the bottom, and rounding; b. Second forging: roughing, first WHF drawing and pressing in all directions; c. Third forging: upsetting, second WHF drawing and flattening; d. Fourth forging: pressing into a round shape, marking, forging steps, and finishing the product; III. Post-forging heat treatment process After the rotor body forging is forged, it is air-cooled until the surface temperature of the shaft body at the small shaft end reaches 300℃, and then placed in a heat treatment furnace for post-forging heat treatment, which specifically includes: a. Temperature equalization treatment: After holding the forging at 520~570℃ for 20h, cool it down to 220~270℃ at a cooling rate of ≤10℃ / h and hold it for 36h. b. The first austenitizing low-temperature normalizing treatment and high-temperature normalizing treatment: the forging is heated to 640~660℃ at a heating rate of ≤35℃ / h and held for 16h. Then the forging is heated to 890~950℃ according to the power of the heat treatment furnace and held for 18~22h. It is then air-cooled out of the furnace. c. Second austenitizing low-temperature normalizing and high-temperature normalizing treatment: After air cooling the forging to 200~250℃, hold it for 36h, then heat it to 640~660℃ at a heating rate of ≤35℃ / h, hold it for 16h, and then heat the forging to 860~900℃ according to the power of the heat treatment furnace, hold it for 18~22h, and then air cool it out of the furnace. d. Tempering treatment: After air cooling the forging to 200~250℃, hold it at that temperature for 40h, then heat it to 640~660℃ at a heating rate of ≤30℃ / h, hold it at that temperature for 70h, and then furnace cool it to ≤150℃ before removing it from the furnace. IV. Performance Heat Treatment Process After the post-forging heat treatment process, the forgings are subjected to performance heat treatment using a pit furnace, specifically including: a. Quenching treatment: The forging is held at 140~160℃ for 10h, then heated to 640~660℃ at a heating rate of ≤40℃ / h, held for 15h, and then heated to 830~880℃ according to the power of the pit furnace, held for 38~45h, and cooled by water spraying for 12~16h. The forging is removed from the water when the surface temperature of the shaft body is ≤100℃. b. High-temperature tempering treatment: The forgings are held at 140~160℃ for 18~25h, then heated to 570~650℃ at a heating rate of ≤30℃ / h, held for 50~60h, and then furnace cooled to ≤150℃ at a cooling rate of ≤10℃ / h before being taken out of the furnace. V. Stress-relieving heat treatment process For rotor body forgings after semi-finished impeller grooves, the temperature is held at 160~210℃ for 12~18h, then heated to 540~560℃ at a heating rate of ≤15℃ / h, held for 40~45h, and then furnace cooled to ≤150℃ at a cooling rate of ≤10℃ / h before being taken out of the furnace.

2. The processing method of the solid integral rotor body forging of Cr-Ni-Mo-V steel for large thermal power turbines according to claim 1, characterized in that, In the smelting and casting processes: The process carbon content of the furnace charge is controlled between 0.60% and 0.80%. The initial smelting temperature is controlled at 1660~1690℃, and the C and P contents in the molten steel are controlled at C≤0.10% and P≤0.002%, respectively. During refining, electrode powder diffusion deoxidation is used, and argon gas is blown into the bottom of the ladle. The temperature is adjusted to 1650~1660℃ for VD degassing, and the process is maintained under a vacuum of ≤65Pa for at least 20 minutes.

3. The processing method of the solid integral rotor body forging of Cr-Ni-Mo-V steel for large thermal power turbines according to claim 1, characterized in that: In the first forging stage of the forging process, after the hot-delivered steel ingot is loaded into the forging heating furnace, it is heated to 1260±10℃ at a heating rate of ≤70℃ / h and held at that temperature for 18 hours. Using a 125MN press, the upper flat anvil and the lower V-shaped anvil are aligned along the riser line of the steel ingot at a position of 150~200mm on the upper part of the ingot body to perform jaw pressing operation. When pressing the jaw, it is ensured that the center line of the jaw is consistent with the center line of the steel ingot. After pressing the jaw, the excess riser material is cut off, the jaw is rolled round, the steel ingot is turned around, and the steel ingot is chamfered, the bottom is cut off, and the ingot is pressed round. In the second forging process, the billet is returned to the furnace and heated to 1260±10℃ according to the power of the forging furnace, and then held for 51 hours. The billet is upsetting using a 125MN press, a slotted plate and a spherical top cap. After the ingot is upset, the first WHF elongation is carried out using a wide and flat anvil. Full anvil strong pressure is used, and the deformation on both sides is controlled to be 18~22%. After each pressing, the billet is rotated 90°, the anvil is staggered by half, and then pressed down again. Each pressing starts from the riser end. Through multiple pressings, the billet is compacted into a flat square shape, and then the edges are chamfered to make the billet octagonal. In the third forging process, the billet is returned to the furnace and heated to 1260±10℃ according to the power of the forging furnace, and then held for 34 hours. The billet is upsetting using a 125MN press, a slotted plate and a spherical top cap. After the ingot is upset, it is drawn using upper and lower flat anvils for the second WHF drawing. The deformation on both sides is controlled to be 18~22%. After each pass, the billet is rotated 90° and the anvil is staggered by half. Each pass of drawing starts from the riser end. Through multiple passes of drawing, the billet is compacted into a flat square. In the fourth forging process, the billet is returned to the furnace and heated to 1220±10℃ according to the power of the forging furnace, and then held for 18 hours. Using a 125MN press, the upper and lower flat anvils are used to press the eight sides first. Then, according to the step material size, the marking anvil is used to mark the shape, and the shaft body and the steps at both ends are forged. Then, the forming arc anvil is used to correct and round the shape. The remaining material at both ends is cut according to the required size to form the final forging.

4. The processing method of the solid integral rotor body forging of Cr-Ni-Mo-V steel for large thermal power turbines according to claim 3, characterized in that, If the small shaft end step of the forging cannot be formed in the fourth forging, the forging process includes a fifth forging after the fourth forging: the billet is returned to the furnace, heated to 1050±10℃ according to the power of the forging heating furnace, held for 10 hours, and the small shaft end step is forged after taking it out of the furnace. Then, the forming arc anvil is used to correct and round it, and the forging is finally formed.

5. A method for machining a large solid integral rotor body forging of Cr-Ni-Mo-V steel for thermal power turbines according to any one of claims 1 to 4, characterized in that, it is used to manufacture a large solid integral rotor body forging of Cr-Ni-Mo-V steel for thermal power turbines with an outer diameter of Ø1640mm × a length of 7890mm, and is characterized in that, The specific implementation process of the forging process is as follows: In the first forging process of the forging process, a 125MN press is used. An upper 850mm flat anvil and a lower 850mm V-shaped anvil are aligned along the riser line of the steel ingot at a position of 150~200mm on the upper ingot body. The riser is lightly pressed, and the root of the riser and the shoulder of the ingot body are pressed onto the clamp material in the first round. The pressing amount is increased in the second round. Once the jaw size is pressed to Ø1400mm×1500mm, use the lower chopping knife to cut off the excess riser material and roll the jaws into a round shape. After turning the steel ingot around, clamp the pressed Ø1400mm jaws and roll the steel ingot into a round shape to Ø2300mm×4800mm with a double-sided pressing amount of 100mm. Then, use the lower chopping knife to cut off the bottom of the steel ingot at 700mm from the top of the ingot body before removing it from the machine. In the second forging stage of the forging process, a 125MN press, a Ø1400mm upsetting plate, and a spherical upsetting cap are used to upset the billet to Ø3400mm×2000mm. Then, a first WHF (whole-face high-low) drawing is performed using a 1700mm wide flat anvil with an anvil radius R of 170mm. The double-sided reduction is controlled at 20%, and full-anvil high-pressure is used. The feed of each anvil is greater than 90% of the anvil width, and there is a 100-200mm joint between each anvil. Through 6 passes of pressing, the billet is compacted to a flat square of 2290mm×2180mm. Then, the edges are chamfered to make the billet octagonal of 2200mm×4500mm. The process parameters for the first WHF pressing are controlled according to the following table: ； In the third forging stage of the forging process, a 125MN press, a Ø1400mm upsetting plate, and a spherical upsetting cap are used to upset the billet to Ø3300mm×2000mm. Then, a second WHF (whole-face high-pressure) drawing is performed using 1700mm flat anvils on both sides, with the double-sided reduction controlled at 20%. Through 9 passes of pressing, the billet is compacted to a flat square of 2125mm×1575mm. The process parameters for the second WHF pressing are controlled according to the table below: ； In the fourth forging process, a 125MN press is used. First, an 850mm flat anvil is used to press an 1860mm square anvil. The dimensions of the step are measured and marked with a marking anvil. The shaft body and the steps at both ends are forged separately. Then, a forming arc anvil is used to correct and round the shape. The remaining material at both ends is cut with gas according to the required dimensions to form the final forging.

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