Machining method for 100-ton-class generator shaft forgings made of Cr-Ni-Mo-V steel.

Abstract

This invention discloses a processing method for 100-ton-class Cr-Ni-Mo-V steel shaft forgings for generators, comprising: smelting and casting processes, using a process route of electric arc furnace primary smelting → refining furnace refining → vacuum treatment furnace degassing → vacuum carbon deoxidation two-stage casting for 100-ton-class double-vacuum steel ingots; a forging process, where the steel ingot is hot-forged after solidification and demolding, with the forging temperature controlled within the range of 1260~850℃, specifically including: first forging: pressing the steel ingot into jaws, chamfering, cutting the bottom, and rounding; second forging: upsetting, first WHF elongation and pressing into an octagon; third forging: upsetting, second WHF elongation and pressing into a flattened square; fourth forging: rounding, marking, forging steps, and finishing the finished product; and post-forging heat treatment processes, performance heat treatment processes, and stress-relieving heat treatment processes. This invention meets the requirements of high purity, high homogeneity, refined microstructure, and internal flaw detection for large forgings weighing hundreds of tons, improves the comprehensive mechanical properties of forgings, and achieves the comprehensive goals of low cost, high efficiency, and low energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of forging technology, and more specifically relates to a processing method for a 100-ton-class Cr-Ni-Mo-V steel forging shaft for generators. Background Technology

[0002] With the improvement of power generation efficiency, the weight and size of large generator shaft forgings are gradually increasing. As power generation capacity increases, the material performance requirements for shaft forgings also gradually rise. Under extreme operating conditions, shaft forgings are required to possess high strength, high ductility and toughness, high fracture toughness, and a low brittle-to-ductile transition temperature. This type of shaft is typically made of low-carbon Cr-Ni-Mo-V steel, generally 25Cr2Ni4MoV steel, which possesses good hardenability and strong toughness, among other comprehensive properties. Large-capacity generator shaft forgings are generally large shaft forgings weighing hundreds of tons. During hot-working manufacturing, large steel ingots weighing hundreds of tons are used. Because larger ingots result in more severe segregation and more internal metallurgical defects, and the manufacturing process requires prolonged heat treatment, severe mixed grains and coarse grains develop in the internal structure. If these defects cannot be completely avoided, they will seriously affect the serviceability of the shaft forgings.

[0003] For large forgings produced from steel ingots weighing hundreds of tons, the entire manufacturing process is extremely difficult. Conventional large shaft forgings have long manufacturing cycles. In order to eliminate mixed grains and coarse grains, repeated normalizing is required for a long time, resulting in cost waste. At the same time, the yield and pass rate are low, leading to low overall manufacturing efficiency. Summary of the Invention

[0004] To address some or all of the technical problems existing in the prior art, the present invention provides a method for processing 100-ton-class Cr-Ni-Mo-V steel forging shafts for generators, comprising the following steps:

[0005] (1) Smelting and casting processes

[0006] In the smelting and casting process, the following process route is adopted for the smelting and casting of 100-ton-level double-vacuum steel ingots: 80-ton electric arc furnace (EBT) primary smelting → 120-ton refining furnace (LF) refining → 120-ton vacuum treatment furnace (VD) degassing → 200-ton vacuum carbon deoxidation furnace (VCD) combined casting. The chemical composition of the steel ingot is controlled by mass percentage as follows: C≤0.25%, Mn: 0.15~0.35%, Si≤0.10%, P≤0. The gas content of steel ingots is controlled as follows: 0.15%, S≤0.018%, Cr: 1.50~2.00%, Ni: 3.25~4.00%, Mo: 0.20~0.50%, V: 0.05~0.13%, 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]≤1.0ppm;

[0007] (2) Forging process

[0008] After the steel ingot solidifies and is demolded, the surface temperature of the ingot is not lower than 700℃ before hot forging. The forging temperature range is controlled between 1260℃ and 850℃, and the total forging ratio is controlled to be greater than 6. 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] (3) Post-forging heat treatment process: After the forging is air-cooled to 300°C on the surface of the small shaft end, it is placed in a heat treatment furnace for post-forging heat treatment, which specifically includes:

[0014] a. Temperature equalization treatment: After holding the forging at 520-570℃ for 16 hours, slowly cool it down to 220-250℃ at a cooling rate of ≤15℃ / h and hold it for 25 hours.

[0015] b. For the first low-temperature normalizing treatment and high-temperature normalizing treatment, the forging is heated to 640~660℃ at a heating rate of ≤40℃ / h and held for 12h. Then the forging is heated to 900~950℃ according to the power of the heat treatment furnace and held for 20~22h. It is then air-cooled out of the furnace.

[0016] c. Second low-temperature normalizing treatment and high-temperature normalizing treatment: After air cooling the forging to 280-320℃, hold it for 22 hours, then heat it to 640-660℃ at a heating rate of ≤40℃ / h, hold it for 12 hours, and then heat the forging to 850-900℃ according to the power of the heat treatment furnace, hold it for 20-22 hours, and then air cool it out of the furnace.

[0017] d. Tempering treatment: After air cooling the forging to 180-210℃, hold it at that temperature for 26 hours. Then heat it to 640-660℃ at a heating rate of ≤40℃ / h, hold it at that temperature for 60 hours, and then furnace cool it to ≤150℃ before removing it from the furnace.

[0018] (4) 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:

[0019] a. Quenching treatment: Heat the forging to ≤200℃ and put it into the furnace. Heat it to 640~660℃ at a heating rate of ≤12℃ / h and hold it for 8h. Then heat the forging to 800~870℃ according to the power of the pit electric furnace and hold it for 32~36h. After air cooling for 10~20 minutes, spray water to cool it. Remove the forging from the water when the surface temperature of the shaft body is ≤100℃.

[0020] b. High-temperature tempering treatment: The forgings are held at 140-160℃ for 12-18 hours, then heated to 550-650℃ at a heating rate of ≤15℃ / h, held for 50-60 hours, and then furnace cooled to ≤150℃ at a cooling rate of ≤10℃ / h before being removed from the furnace.

[0021] Furthermore, in the above-mentioned processing method for 100-ton-class Cr-Ni-Mo-V steel shaft forgings for generators, a stress-relieving heat treatment process is also included after the performance heat treatment process: the semi-finished forgings are held at a temperature of 160-210℃ for 12-18 hours, then heated to 540-560℃ at a heating rate of ≤15℃ / h, held for 45-50 hours, and then furnace cooled to ≤150℃ at a cooling rate of ≤10℃ / h before being taken out of the furnace.

[0022] Furthermore, in the above-mentioned processing method for 100-ton-class Cr-Ni-Mo-V steel generator shaft forgings, in the smelting and casting processes:

[0023] During the initial refining of 80-ton electric arc furnace EBT, the process carbon content of the furnace charge is controlled at 0.60-0.80%, the tapping temperature is controlled at 1660-1690℃, and the C and P contents of the tapped steel are controlled at C≤0.10% and P≤0.002%, respectively.

[0024] When refining in a 120-ton refining furnace (LF) and degassing in a 120-ton vacuum treatment furnace (VD), electrode powder diffusion deoxidation is used, and argon gas is blown from the bottom of the ladle. VD treatment is carried out when the temperature reaches 1650-1660℃ and is maintained under a vacuum of ≤65Pa for at least 20 minutes.

[0025] When casting two vacuum carbon deoxidized VCDs together, the casting temperature of the intermediate ladle should be controlled at 1560~1580℃, and the vacuum degree at the start of casting should be controlled at ≤65Pa.

[0026] Furthermore, in the above-mentioned processing method for Cr-Ni-Mo-V steel 100-ton-class generator shaft forgings:

[0027] In the first forging stage of the forging process, after the hot-delivered double-vacuum steel ingot is loaded into the forging heating furnace, it is heated to 1250±10℃ at a heating rate of ≤70℃ / h and held at that temperature for 16 hours. 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 100-150mm on the upper part of the ingot body to perform jaw pressing operation. When pressing the jaws, it is ensured that the center line of the jaws is consistent with the center line of the steel ingot. After pressing the jaws, the excess riser material is cut off, the jaws are rolled round, the steel ingot is turned around, the bottom of the steel ingot is cut off, and then the steel ingot is chamfered and rounded.

[0028] In the second forging process, the billet is returned to the furnace and heated to 1250±10℃ according to the power of the forging furnace, and then held for 48 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 pressing 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.

[0029] In the third forging process, the billet is returned to the furnace and heated to 1250±10℃ according to the power of the forging furnace, and then held for 32 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.

[0030] 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 14 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 shaft body and the steps at both ends. 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.

[0031] Furthermore, in the above-mentioned processing method for 100-ton-class Cr-Ni-Mo-V steel shaft forgings for generators, 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 6 hours, and the small shaft end step is forged after being taken out of the furnace. Then, the rounded shape is corrected and rolled using a forming arc anvil, and the forging is finally formed.

[0032] As one specific implementation method, the above-mentioned machining method for Cr-Ni-Mo-V steel 100-ton-class generator shaft forgings is used to manufacture forgings with required outer diameters. The forging process for the shaft of a large generator set is as follows:

[0033] 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 part of the ingot body at a distance of 100-150mm. Light pressure is applied to the riser, pressing the riser root and the shoulder of the ingot body entirely onto the clamping material in the first pass. The pressure is increased starting 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. Using the pliers, after cutting off the bottom of the steel ingot with the lower chopping knife, the steel ingot is rolled into a round shape with a double-sided pressing amount of 100mm. After disembarking;

[0034] 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, 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 2210mm × 2110mm. Then, the edges are beveled to make the billet octagonal of 2400mm × 3600mm. The process parameters for the first WHF pressing are controlled according to the following table:

[0035]

[0036] 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 the double-sided reduction controlled at 20%. Through 11 passes of pressing, the billet is compacted to a flat square size of 1635mm × 1210mm. The process parameters for the second WHF pressing are controlled according to the table below:

[0037]

[0038] In the fourth forging process, a 125MN press is used. First, an 850mm flat anvil is used to press an octagonal 1370mm 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. 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 finally form the forging.

[0039] The processing method of the Cr-Ni-Mo-V steel generator shaft forging of the present invention has the following advantages and beneficial effects:

[0040] (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-piece casting is adopted. By effectively controlling the material composition and gas content, the high purity and high homogeneity requirements of 100-ton-class large shaft forgings for generators are met for 100-ton-class steel ingots.

[0041] (2) By adopting the key technology of multi-process forging through dense synergistic deformation, the forging fire and heating temperature are effectively controlled, and appropriate forging process methods are adopted to meet the requirements of compacting the core of large steel ingots and the requirements of large forgings for refined structure and internal flaw detection.

[0042] (3) After the forging is completed, effective post-forging heat treatment, performance heat treatment and stress relief heat treatment are carried out to adjust and improve the uneven structure and refine the austenite grains during the forging process, effectively cut off the structure inheritance and mixed crystal phenomenon, fully eliminate thermal stress, improve the subsequent machining cutting performance, so that the surface of the forging has martensite and lower bainite structure, the core has lower bainite structure or lower bainite plus a small amount of upper bainite structure, effectively improving the comprehensive mechanical properties of the large shaft forging of hundreds of tons for generators.

[0043] (4) For the first time, the 100-ton-class Cr-Ni-Mo-V steel forging shaft for generators was qualified in one go, achieving the comprehensive goal of low cost, high efficiency and low energy consumption. Attached Figure Description

[0044] 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:

[0045] Figure 1 This is a schematic flowchart illustrating the processing method of the Cr-Ni-Mo-V steel generator shaft forging for hundreds of tons according to the present invention.

[0046] Figure 2The following are schematic diagrams of the forging morphology in each step of the processing method of the 100-ton-class Cr-Ni-Mo-V steel generator shaft forging of the present invention: (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 it, and forging a step; and (f) is a schematic diagram of the finished forging.

[0047] Figure 3 This is a schematic diagram of the timing of the post-forging heat treatment process in the processing method of the 100-ton-class Cr-Ni-Mo-V steel generator shaft forging of the present invention.

[0048] Figure 4 This is a schematic diagram of the timing of the performance heat treatment process in the processing method of the 100-ton-class Cr-Ni-Mo-V steel generator shaft forging of the present invention.

[0049] Figure 5 This is a schematic diagram showing the timing of the stress-relieving heat treatment process in the processing method of the 100-ton-class Cr-Ni-Mo-V steel generator shaft forging of the present invention. Detailed Implementation

[0050] 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.

[0051] like Figure 1 As shown, the processing method of the Cr-Ni-Mo-V steel generator shaft forging of the present invention includes the following steps:

[0052] (1) Smelting and casting processes

[0053] Because the 100-ton-class large shaft forgings use 100-ton-class large steel ingots in the hot working manufacturing process, it is necessary to use two ladles of molten steel to be cast together through an intermediate ladle to produce double vacuum steel ingots. Therefore, in the smelting and casting process, the 100-ton-class large steel ingots used for the Cr-Ni-Mo-V steel large shaft forgings are smelted and cast using the following process route: 80-ton electric arc furnace (EBT) primary smelting → 120-ton refining furnace (LF) refining → 120-ton vacuum treatment furnace (VD) degassing → 200-ton vacuum carbon deoxidation furnace (VCD) two-ladle casting.

[0054] According to the technical requirements for 100-ton-class Cr-Ni-Mo-V steel forgings for generators, in order to meet the comprehensive performance indicators of the products, the chemical composition of the steel ingots is strictly controlled internally, especially the carbon content, which must be controlled within a reasonable range. At the same time, in order to improve the hardenability of the steel, the main alloying elements Cr, Ni, and Mo in the steel ingots must be controlled within the upper and middle ranges of the required range. Most importantly, harmful elements such as Si, P, S, As, Sn, Sb, H, O, and N, which affect the purity of the steel ingots, must be strictly controlled within the lower limit of the process requirements. Therefore, in the smelting and casting processes, the chemical composition of the steel ingot is controlled by mass percentage as follows: C≤0.25%, Mn: 0.15~0.35%, Si≤0.10%, P≤0.015%, S≤0.018%, Cr: 1.50~2.00%, Ni: 3.25~4.00%, Mo: 0.20~0.50%, V: 0.05~0.13%, 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]≤1.0ppm.

[0055] In addition, the following technical points need to be controlled in the smelting and ingot casting processes:

[0056] (1) During the primary refining of the 80-ton electric arc furnace EBT, the furnace charge is strictly selected and retested according to the process requirements. The charging process is strictly followed. The carbon content of the furnace charge is controlled at 0.60-0.80%. During the oxidation period, slag removal and new slag production are carried out and the amount of slag replacement is ensured. The primary refining requires reasonable oxygen blowing for melting and reasonable decarburization. Steel is tapped with steel and slag retention. Oxidized slag is strictly prohibited from entering the refining ladle. In addition, in order to meet the low P and low C process requirements of the primary refining steel, the tapping temperature is required to be controlled at 1660-1690℃, and the C and P contents of the tapped steel are controlled at C≤0.10% and P≤0.002%, respectively.

[0057] (2) When refining in a 120-ton refining furnace (LF) and degassing in a 120-ton vacuum treatment furnace (VD), electrode powder diffusion deoxidation is used, and argon is blown into the bottom of the ladle. The operation is strictly carried out in accordance with the process requirements to ensure that the inclusions in the steel float up fully and achieve the effect of purifying the molten steel. In addition, after adjusting the internal control chemical composition, VD treatment is carried out when the temperature reaches 1650~1660℃ and is maintained at a vacuum of ≤65Pa for at least 20 minutes.

[0058] (3) When casting two vacuum carbon deoxidation VCDs together, clean and dry the prepared steel ingot mold and other auxiliary tools in advance, and strictly follow the multi-ladle casting process to ensure the quality of vacuum steel ingot casting. Pay special attention to key aspects such as steel diversion, the alternating casting time of the two ladles, the control of casting temperature, and argon protection casting throughout the process. Among them, the casting temperature of the intermediate ladle is controlled at 1560~1580℃, the vacuum degree at the start of casting is controlled at ≤65Pa, and after the final casting is completed, add an appropriate amount of heating agent as soon as possible after breaking the vacuum.

[0059] Through the above measures in the smelting and casting processes, the [H] content in the finished double-vacuum steel ingot is 0.51 ppm, and the coarse and fine inclusions A, B, C, and D in the steel are all controlled at level 0 to 0.5, while DS is controlled at level ≤ 0.5.

[0060] (2) Forging process

[0061] 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, forging is carried out on a 125MN press through multiple heating cycles. The forging temperature range is controlled between 1260 and 850°C, and the total forging ratio is controlled to be greater than 6. Through an effective and reasonable forging process, inherent casting defects in steel ingots, such as segregation, gas, inclusions, shrinkage cavities, and porosity, can be improved, and the grain structure of the forging can be fully refined and uniform, effectively ensuring the compaction effect at the center of the forging. The specific process of the forging is as follows:

[0062] a. First Forging: Ingot clamping, chamfering, bottom trimming, and rounding. After being loaded into the forging furnace, the hot-delivered double-vacuum ingot is heated to 1250±10℃ at a rate of ≤70℃ / h and held for 16 hours. Using a 125MN press, an upper flat anvil and a lower V-shaped anvil are aligned along the ingot riser line at a point 100-150mm from the top of the ingot body to clamp the ingot. During clamping, ensure the center line of the clamping jaws is aligned 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, the bottom is cut off, and then chamfering 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 of the ingot clamping, chamfering, bottom trimming, and rounding process for the ingot. Figure 2 (b) in the middle.

[0063] 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 1250±10℃ according to the power of the forging furnace, and then held for 48 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, effectively compressing the internal pores of the steel ingot, breaking up the as-cast structure, improving segregation, improving the transverse properties of the shaft forging, and reducing the anisotropy of mechanical properties. After upsetting the steel ingot, the first WHF drawing is performed using wide and flat anvils on both sides. 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 anvil is staggered before another pass. Each pass of drawing 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 of drawing, 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.

[0064] c. Third Forging: Upsetting, Second WHF Drawing and Flattening. The billet is returned to the furnace and heated to 1250±10℃ according to the forging furnace power, then held for 32 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°, offset by half anvils, and then drawn again. Each pass begins 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.

[0065] d. Fourth forging: Rounding, marking, forging steps, and finishing. The billet is returned to the furnace and heated to 1220±10℃ according to the forging furnace power, then held for 14 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 cut the excess material at both ends according to the required dimensions to achieve the 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.

[0066] (3) Post-forging heat treatment process

[0067] After the shaft 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 refine the grains and solve the grain and mixed grain problems in the forging structure. Figure 3 As shown, the post-forging heat treatment process specifically includes:

[0068] 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 still higher than 700°C due to the large diameter of the forging cross section. In order to prevent the forging from cracking due to excessive internal and external temperature stress and structural stress, the forging needs to be homogenized. The forging is held at 520-570°C for 16 hours to homogenize the temperature difference between different parts of the forging. Then, it is slowly cooled to 220-250°C at a cooling rate of ≤15°C / h and held for 25 hours.

[0069] b. For the first low-temperature normalizing treatment and high-temperature normalizing treatment, the forging is heated to 640~660℃ at a heating rate of ≤40℃ / h and held for 12h. Then the forging is heated to 900~950℃ according to the power of the heat treatment furnace and held for 20~22h. It is then air-cooled out of the furnace.

[0070] c. Second low-temperature normalizing treatment and high-temperature normalizing treatment: After air cooling the forging to 280-320℃, hold it for 22 hours, then heat it to 640-660℃ at a heating rate of ≤40℃ / h, hold it for 12 hours, and then heat the forging to 850-900℃ according to the power of the heat treatment furnace, hold it for 20-22 hours, and then air cool it out of the furnace.

[0071] d. Tempering treatment: After air cooling the forging to 180-210℃, hold it at that temperature for 26 hours. Then heat it to 640-660℃ at a heating rate of ≤40℃ / h, hold it at that temperature for 60 hours, and then furnace cool it to ≤150℃ before removing it from the furnace.

[0072] (4) Performance heat treatment process

[0073] 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:

[0074] a. Quenching treatment: Heat the forging to ≤200℃ and put it into the furnace. Heat it to 640~660℃ at a heating rate of ≤12℃ / h and hold it for 8h. Then heat the forging to 800~870℃ according to the power of the pit electric furnace and hold it for 32~36h. After air cooling for 10~20 minutes, spray water to cool it. Remove the forging from the water when the surface temperature of the shaft body is ≤100℃.

[0075] b. High-temperature tempering treatment: The forgings are held at 140-160℃ for 12-18 hours, then heated to 550-650℃ at a heating rate of ≤15℃ / h, held for 50-60 hours, and then furnace cooled to ≤150℃ at a cooling rate of ≤10℃ / h before being removed from the furnace.

[0076] The aforementioned heat treatment, by controlling the quenching temperature and holding time, ensures that the forging has fine austenitic grains across its entire cross-section. The uniform cooling method achieves good hardenability, thereby homogenizing the overall microstructure and mechanical properties of the forging and meeting the comprehensive mechanical performance requirements of large generator shaft forgings in the hundreds-ton class. In particular, water spray cooling significantly improves the cooling rate of the shaft forging, especially the core, resulting in a martensitic and lower bainitic microstructure on the surface and a lower bainitic microstructure or a combination of lower bainitic and a small amount of upper bainitic microstructure in the core. This effectively enhances the comprehensive mechanical properties of the large generator shaft forgings in the hundreds-ton class.

[0077] Furthermore, in the forging process of the Cr-Ni-Mo-V steel 100-ton-class rotating shaft forging for generators 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 6 hours, and after being taken out of the furnace, the small shaft end step is forged, and then the rounding is corrected and rolled using a forming arc anvil to finally form the forging.

[0078] Furthermore, in the processing method of the Cr-Ni-Mo-V steel 100-ton-class generator shaft forging 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: stress-relieving heat treatment of the semi-finished forgings, holding the forgings at 160–210℃ for 12–18 hours, then heating to 540–560℃ at a heating rate of ≤15℃ / h, holding at that temperature for 45–50 hours, and then furnace cooling to ≤150℃ at a cooling rate of ≤10℃ / h before removing them from the furnace. This stress-relieving heat treatment plays a crucial role in stabilizing the dimensional accuracy during the subsequent finishing of the generator shaft forgings.

[0079] The following detailed description, with reference to specific embodiments, illustrates the processing method of the 100-ton-class Cr-Ni-Mo-V steel generator shaft forging of the present invention. The embodiments described below are for manufacturing and processing 100-ton-class large generator shaft forgings using a one-piece-per-ingot method. The required dimensions of the finished forging are: outer diameter... The length is 13062mm, and the grain size must be ≥5, with no more than 5% mixed grains of grade 4. Internal UT testing of the forging must meet the requirements of JB / T7178-2002 standard, and no equivalent diameter greater than or equal to... Continuous defect signals and wandering defect signals are not allowed in areas with high stress. dense defects and The defect is typical of large-section long-shaft forgings.

[0080] The processing method of the 100-ton-class Cr-Ni-Mo-V steel generator shaft forging of this 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-relieving heat treatment process, and the specific implementation process of the forging process is as follows:

[0081] 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 100-150mm from the ingot. 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. Using the pliers handle and the lower chopping knife to cut off the bottom of the steel ingot, the ingot is rounded by pressing down with both sides with a depth of 100mm. After removing it from the machine, use an oxygen lance to clean surface defects such as cracks and indentations.

[0082] 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, 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 between 18% and 22%, with an optimal reduction of 20%. Full anvil pressure is used, and the feed of each anvil should be greater than 90% of the anvil width. There should be a 100-200mm overlap between each anvil. Through 6 passes of drawing, the billet is compacted to a flat square of 2210mm × 2110mm. Then, the edges are chamfered to make the billet octagonal of 2400mm × 3600mm. 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 in a hot state. The process parameters for the first WHF drawing are controlled according to Table 1 below:

[0083] Table 1. Process parameters for the first WHF pressing down.

[0084]

[0085] 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 11 passes of reduction, the billet is compacted to a flat square size of 1635mm × 1210mm. 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:

[0086] Table 2. Second WHF pressing process parameters

[0087]

[0088]

[0089] In the fourth forging stage of the forging process, a 125MN press is used. First, an 850mm flat anvil is used to press an octagonal 1370mm anvil. The dimensions for the step portion are measured, and the steps are marked using a marking anvil. The shaft body and the steps at both ends are then forged separately. A forming arc anvil is then used to correct and round the edges. The remaining material at both ends is then gas-cut to the required dimensions for final forging. If the small shaft end step cannot be formed in the fourth forging stage, a fifth forging stage is performed after the fourth. The billet is returned to the furnace and heated to 1050±10℃, held for 6 hours, and then the small shaft end step is forged after removing it from the furnace. A forming arc anvil is then used to correct and round the edges for final forging.

[0090] 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 this embodiment of the invention are described above and will not be repeated here.

[0091] According to the above embodiments of the present invention, two generator shaft forgings, No. 1 and No. 2, made of Cr-Ni-Mo-V steel with a capacity of 100 tons, were processed and produced. All inspection results met the technical requirements. Specifically:

[0092] (1) Chemical composition detection

[0093] Chemical composition analysis was performed on samples taken from the shaft bodies of forgings #1 and #2. The results are shown in Table 3 below:

[0094] Table 3. Results of Chemical Composition Analysis (mass percentage, %)

[0095]

[0096] (2) Mechanical performance testing

[0097] Samples were taken from the tangential direction of the shaft head, the tangential direction of the shaft body, the radial direction of the shaft body, and the center of the No. 1 and No. 2 shaft forgings, respectively, for mechanical property testing. The test results are shown in Table 4 below:

[0098] Table 4 Results of Mechanical Performance Tests

[0099]

[0100] In the table above, A1 indicates the radial test specimen position of the shaft body in the direction of the sprue; A2 indicates the radial test specimen position of the shaft body in the direction of the riser; A3 indicates the tangential test specimen position of the shaft body in the direction of the sprue; A4 indicates the tangential test specimen position of the shaft body in the direction of the riser; A5 indicates the tangential test specimen position of the shaft head in the direction of the sprue; and A6 indicates the tangential test specimen position of the shaft head in the direction of the riser. For details, please refer to [reference needed]. Figure 2 (f) in the middle.

[0101] (3) Furthermore, testing revealed that the grain sizes of the Cr-Ni-Mo-V steel large-scale rotating shaft forgings for generators manufactured using the embodiments of this invention at positions A1, A2, A3, and A4 were 5.0, 5.5, 5.5, and 6.0, respectively, meeting the technical requirement of grain size ≥ 5 and mixed grains not exceeding 5% at position 4. Moreover, the ultrasonic testing results of the entire rotating shaft forging met the requirements of the JB / T7178-2002 standard.

[0102] In summary, the processing method for 100-ton-class Cr-Ni-Mo-V steel generator shaft forgings 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 in the large steel ingots, effective compaction of the center of the large forgings, and uniform heat treatment performance. Ultimately, it meets the excellent comprehensive performance requirements of 100-ton-class large generator shaft forgings, filling a technological gap. Compared with existing technologies, it has the following advantages and beneficial effects:

[0103] (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-piece casting is adopted. By effectively controlling the material composition and gas content, the high purity and high homogeneity requirements of 100-ton-class large shaft forgings for generators are met for 100-ton-class steel ingots.

[0104] (2) By adopting the key technology of multi-process forging through dense synergistic deformation, the forging fire and heating temperature are effectively controlled, and appropriate forging process methods are adopted to meet the requirements of compacting the core of large steel ingots and the requirements of large forgings for refined structure and internal flaw detection.

[0105] (3) After the forging is completed, effective post-forging heat treatment, performance heat treatment and stress relief heat treatment are carried out to adjust and improve the uneven structure and refine the austenite grains during the forging process, effectively cut off the structure inheritance and mixed crystal phenomenon, fully eliminate thermal stress, improve the subsequent machining cutting performance, so that the surface of the forging has martensite and lower bainite structure, the core has lower bainite structure or lower bainite plus a small amount of upper bainite structure, effectively improving the comprehensive mechanical properties of the large shaft forging of hundreds of tons for generators.

[0106] (4) For the first time, the 100-ton-class Cr-Ni-Mo-V steel forging shaft for generators was qualified in one go, achieving the comprehensive goal of low cost, high efficiency and low energy consumption.

[0107] 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.

[0108] 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 processing a hundred-ton class rotor shaft forging of a Cr-Ni-Mo-V steel for a generator, characterized by, Comprise the following procedures: (1) smelting and ingot casting process In the smelting and ingot casting process, the process route of 80 tons of EBT initial smelting→120 tons of LF refining→120 tons of VD degassing→200 tons of VCD two ladle pouring is adopted for the smelting and ingot casting of the hundred-ton double vacuum steel ingot, the chemical composition of the steel ingot is controlled as follows in percentage by mass: C≤0.25%, Mn: 0.15~0.35%, Si≤0.10%, P≤0.015%, S≤0.018%, Cr: 1.50~2.00%, Ni: 3.25~4.00%, Mo: 0.20~0.50%, V: 0.05~0.13%, 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]≤1.0ppm; In the smelting and ingot casting process: In the 80 tons of EBT initial smelting, the process carbon content of the charging material is controlled as 0.60~0.80%, the tapping temperature is controlled at 1660~1690℃, and the C, P content in the tapping molten steel is controlled as C≤0.10%, P≤0.002% respectively; In the 120 tons of LF refining and 120 tons of VD degassing treatment, the electrode powder diffusion deoxidation is adopted, and at the same time, the argon is bottom-blown in the ladle, when the temperature reaches 1650~1660℃, the VD treatment is carried out, and the vacuum is maintained at ≤65Pa for at least 20min or more; In the VCD two ladle pouring, the pouring temperature of the tundish is controlled at 1560~1580℃, and the vacuum degree at the beginning of pouring is controlled as ≤65Pa; Through the smelting and ingot casting process, in the double vacuum steel ingot finished product, [H]: 0.51ppm, the steel inclusions A, B, C, D coarse and fine systems are controlled at 0~0.5 level, and the DS is controlled at ≤0.5 level; (2) forging process After the solidification demoulding of the steel ingot, the steel ingot is hot sent for forging when the surface temperature is not lower than 700℃, the forging temperature range is controlled at 1260~850℃, the total forging ratio is controlled as greater than 6, and the specific process of the forging process is as follows: a, first fire forging: steel ingot pressure jaw, chamfer, cut bottom, pressure circle; b, second fire forging: roughing, first WHF lengthening and pressure octagonal; c, third fire forging: roughing, second WHF lengthening and pressure flat square; d, fourth fire forging: pressure circle, number stamping, forging out step, finishing out finished product; (3) post-forging heat treatment process, after the forged part is air cooled to 300℃ on the surface of the small shaft end shaft body, the forged part is loaded into a heat treatment heating furnace for post-forging heat treatment, which specifically includes: a, uniform temperature treatment, the forged part is kept at 520~570℃ for 16h, then slowly cooled to 220~250℃ at a cooling rate of ≤15℃ / h, and kept at 220~250℃ for 25h; b, first low-temperature normalizing treatment and high-temperature normalizing treatment, the forged part is heated to 640~660℃ at a heating rate of ≤40℃ / h, kept at 640~660℃ for 12h, then heated to 900~950℃ according to the power of the heat treatment heating furnace, kept at 900~950℃ for 20~22h, and air cooled out of the furnace; c. second low temperature normalizing treatment and high temperature normalizing treatment, after air cooling the forged piece to 280-320℃, holding for 22h, then heating to 640-660℃ at a heating rate of ≤40℃ / h, holding for 12h, then heating the forged piece to 850-900℃ according to the heating power of the heating furnace, holding for 20-22h, air cooling to get out of the furnace; d. tempering treatment, after air cooling the forged piece to 180-210℃, holding for 26h, then heating to 640-660℃ at a heating rate of ≤40℃ / h, holding for 60h, furnace cooling to ≤150℃ to get out of the furnace; (4) performance heat treatment process, after the forging heat treatment process, using an electric pit furnace to perform performance heat treatment on the forged piece, specifically including: a. quenching treatment, heating the forged piece to ≤200℃ into the furnace, heating to 640-660℃ at a heating rate of ≤12℃ / h, holding for 8h, then heating the forged piece to 800-870℃ according to the power of the electric pit furnace, holding for 32-36h, air cooling for 10-20min, then water cooling, and getting out of the water when the surface temperature of the shaft of the forged piece is ≤100℃; b. high temperature tempering treatment, holding the forged piece at 140-160℃ for 12-18h, then heating to 550-650℃ at a heating rate of ≤15℃ / h, holding for 50-60h, then furnace cooling to ≤150℃ at a cooling rate of ≤10℃ / h to get out of the furnace; By controlling the quenching heating temperature and holding time, fine austenite grains are obtained in the whole cross section of the forged piece, and by using a uniform cooling method, good hardenability is obtained, thereby realizing the homogenization of the overall microstructure and mechanical properties of the forged piece, meeting the comprehensive mechanical property requirements of the hundred-ton large-scale shaft forged piece for the generator, and by using water cooling, the cooling speed of the shaft forged piece can be improved, so that the surface of the forged piece obtains martensite and lower bainite microstructure, the core obtains lower bainite microstructure or lower bainite microstructure plus a small amount of upper bainite microstructure, and the comprehensive mechanical properties of the hundred-ton large-scale shaft forged piece for the generator are effectively improved; After the performance heat treatment process, a stress relief heat treatment process is further included: holding the semi-finished forged piece at 160-210℃ for 12-18h, then heating to 540-560℃ at a heating rate of ≤15℃ / h, holding for 45-50h, then furnace cooling to ≤150℃ at a cooling rate of ≤10℃ / h to get out of the furnace.

2. The processing method of the Cr-Ni-Mo-V steel hundred-ton shaft forged piece for the generator according to claim 1, characterized in that: in the first fire forging of the forging process, after the hot charging of the double vacuum ingot, the ingot is heated to 1250±10℃ at a heating rate of ≤70℃ / h, and held for 16h; using a 125MN press, the upper anvil and the lower V-shaped anvil are aligned along the ingot head line at 100-150mm of the upper ingot body to perform the press mouth operation, and the center line of the mouth is ensured to be consistent with the center line of the ingot during the press mouth operation; after the press mouth operation, the excess head material is cut off, the ingot is rolled, the ingot is turned over, the bottom of the ingot is cut off, and then the ingot is subjected to the chamfering and rounding operations; In the second fire forging of the forging process, the blank is re-melted, heated to 1250±10℃ according to the power of the forging heating furnace, and kept for 48h; the blank is roughed by using a 125MN press, a leakage disc and a spherical top pier head; after the ingot is upset, the first WHF lengthening is performed by using upper and lower wide flat anvil, full anvil strong pressure, and the deformation amount of double-side pressing is controlled to be 18~22%, the blank is pressed to a flat square after each pass is completed, and then the blank is chamfered to achieve an eight square; In the third fire forging of the forging process, the blank is re-melted, heated to 1250±10℃ according to the power of the forging heating furnace, and kept for 32h; the blank is roughed by using a 125MN press, a leakage disc and a spherical top pier head; after the ingot is upset, the second WHF lengthening is performed by using upper and lower flat anvil, and the deformation amount of double-side pressing is controlled to be 18~22%, the blank is pressed to a flat square after each pass is completed, and then the blank is chamfered to achieve an eight square; In the fourth fire forging of the forging process, the blank is re-melted, heated to 1220±10℃ according to the power of the forging heating furnace, and kept for 14h; the blank is pressed to an eight square by using a 125MN press, then the blank is stamped according to the size of the stepped material by using a number stamping anvil, and then the shaft body and two end steps are forged, and the roundness is corrected by using a forming arc anvil, the excess material at the two ends is cut by using gas cutting, and the final forming of the forging is performed.

3. The processing method for the 100-ton-class Cr-Ni-Mo-V steel generator shaft forging according to claim 2, characterized in that, If the small shaft end step of the forging cannot be formed in the fourth fire forging, the forging process further includes a fifth fire forging: the blank is re-melted, heated to 1050±10℃ according to the power of the forging heating furnace, and kept for 6h, the small shaft end step is forged after being taken out of the furnace, the roundness is corrected by using a forming arc anvil, and the final forming of the forging is performed.

4. A method for machining Cr-Ni-Mo-V steel generator shaft forgings of 100-ton class according to any one of claims 2 to 3, used for manufacturing large generator shaft forgings with an outer diameter requirement of Ø1232mm, characterized in that, The specific implementation process of the forging process is as follows: In the first fire forging of the forging process, the 125MN press is used, the upper 850mm flat anvil and the lower 850mm V-shaped anvil are aligned along the ingot riser line at the upper ingot body 100~150mm, the riser is lightly pressed, the riser root and the ingot shoulder are pressed to the handle material in the first circle, and the pressing amount is increased in the second circle; After the size of the handle is pressed to Ø1400mm×1500mm, the excess riser material is cut by using a lower chopping knife, and the handle is rounded; after the ingot is turned over, the Ø1400mm handle that has been pressed is clamped, the lower chopping knife is used to cut the bottom of the ingot, and then the ingot is rounded to Ø2400mm×3800mm with a 100mm double-side pressing amount, and then the ingot is taken out of the machine; In the second fire forging of the forging process, the blank is upset to Ø3300mm×2000mm by using a 125MN press, a Ø1400mm die disc and a spherical top upsetting cap, then the first WHF elongation is performed by using an upper and lower 1700mm wide flat anvil, the flat anvil arc angle R is 170mm, the double-sided reduction is controlled to be 20%, full-anvil heavy pressing is adopted, the feeding amount of each anvil is greater than 90% of the anvil width, there is 100~200mm of anvil joint amount between each anvil, the blank is compacted to a flat square 2210mm×2110mm by 6 passes of pressing, then chamfering is performed to make the blank reach an octagon 2400mm×3600mm, wherein the first WHF pressing process parameters are controlled according to the following table: ； In the third fire forging of the forging process, the blank is upset to Ø3200mm×2000mm by using a 125MN press, a Ø1400mm die disc and a spherical top upsetting cap, then the second WHF elongation is performed by using an upper and lower 1700mm flat anvil, the double-sided reduction is controlled to be 20%, the blank is compacted to a flat square 1635mm×1210mm by 11 passes of pressing, and the second WHF pressing process parameters are controlled according to the following table: ； In the fourth fire forging of the forging process, a 125MN press is used to press an octagon 1370mm by using an upper and lower 850mm flat anvil, the stepped distribution size is measured, the anvil number is marked after marking, then the shaft body and two ends are forged respectively, a forming arc anvil is used to correct the rounding, the excess material at the two ends is gas cut according to the required size, and the final forming of the forgings is performed.

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