A method for manufacturing an isostrength large-sized disc-shaped forging

Abstract

The present invention provides a method for manufacturing an isostrength large-sized disc-shaped forging, so as to reduce the strength difference between the core and the surface of the forging and help meet the requirements for manufacturing an isostrength forging, and relates to the technical field of forging. A method for manufacturing an isostrength large-sized disc-shaped forging for a disc-shaped forging made of NiCrMoV steel with the given external dimensions includes the following steps: obtaining a blanked cylinder; upsetting and spreading the blanked round bar to form an intermediate blank in the shape of a disc; heating the intermediate blank to 1150 - 1200 °C and fully insulating it; performing one-pass forging on the intermediate blank to form it, controlling the final forging temperature ≥ 850 °C, wherein during forging, first obtain a preliminary blank with cylindrical bosses respectively provided at the centers of both end faces, then apply pressure to the preliminary blank to flatten both end faces of the preliminary blank until the dimensions meet the requirements, thereby obtaining a disc-shaped forging with flat end faces; cooling the central region corresponding to the position of the bosses of the forging and the preliminary blank at a cooling rate of ≥ 180 °C / h but < 360 °C / h to 500 - 600 °C; performing heat treatment on the forging.

Description

Technical Field

[0001] The present invention relates to the technical field of forging, and particularly relates to a method for manufacturing an isostrength large-sized disk-shaped forging. Background Art

[0002] The steam temperature parameter of a nuclear power unit is lower than that of a thermal power generating unit. To ensure the unit efficiency, generally, the exhaust area (length) of the last-stage blade is increased to solve the problem. To reduce the stress borne by the last-stage blade during high-speed rotation, generally, a half-speed (1500 r / min) steam turbine design is adopted. In addition, since the exhaust area is increased by increasing the length of the last-stage blade, to ensure the stiffness of the rotor, the diameter of the rotor forging is significantly increased compared with that of a full-speed (3000 r / min) rotor forging, thereby significantly increasing the weight of the entire rotor forging and the mass of the ingot. Therefore, to reduce the manufacturing difficulty and risk, currently, the high-pressure rotor and low-pressure rotor forgings of nuclear power steam turbines mainly adopt a welded structure. The welded rotor is composed of two shaft-end forgings and several large-sized disk-shaped forgings welded together. Since the welded rotor forging has a large diameter and bears a large centrifugal force during rotation, higher requirements are imposed on the mechanical property uniformity of the surface and the core of the forging.

[0003] The diameter of the large-sized disk-shaped forging reaches more than 3000 mm, and the effective thickness exceeds 1000 mm. The material is generally NiCrMoV steel. To eliminate tissue heredity and ensure the strength and toughness of the forging, normalizing and tempering preparatory heat treatment and quenching and tempering property heat treatment are generally adopted. However, due to the large size of the forging, during the heat treatment process, due to the influence of cooling uniformity and the heat transfer rate of the forging, the cooling rates of the surface and the core of the large forging are different, and the grain size grade in the core area will be much smaller than that in the surrounding area. Coupled with the tissue heredity characteristics of the material, traditional process methods often lead to serious non-uniformity such as mixed grains, and it is difficult to achieve isostrength manufacturing of the mechanical properties of the core and the surface of the forging. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for manufacturing an isostrength large-sized disk-shaped forging, so as to reduce the strength difference between the core and the surface of the forging and help meet the requirements for isostrength manufacturing of the forging.

[0005] The technical solution adopted by the present invention to solve its technical problems is: a method for manufacturing an isostrength large-sized disk-shaped forging, which is used for a disk-shaped forging made of NiCrMoV steel, and includes the following steps:

[0006] Step 1: Upset and draw the ingot for multiple heats and then cut it to obtain a cut cylinder. Among them, each heat is heated to 1200 - 1260 °C and fully insulated to make the tissue temperature consistent;

[0007] Step 2: Heat the blanking cylinder to 1200 - 1260 °C and hold it for sufficient time to make the tissue temperature uniform, then upset and expand it to form an intermediate blank with flat ends at both ends, i.e., a disc-shaped intermediate blank;

[0008] Step 3: Heat the intermediate blank to 1150 - 1200 °C and hold it for sufficient time to make the tissue temperature uniform;

[0009] Step 4: After the intermediate blank finishes heat preservation, perform one-pass forging on the intermediate blank, control the final forging temperature ≥ 850 °C. Specifically, when forging, first obtain a preliminary blank with cylindrical bosses respectively provided at the centers of both end faces, then apply pressure to the preliminary blank to make both end faces of the preliminary blank flat until the dimensions meet the requirements, thereby obtaining a disc-shaped forging with flat end faces at both ends;

[0010] Step 5: Cool the central region corresponding to the position of the boss of the forging and the preliminary blank at a cooling rate of ≥ 180 °C / h but < 360 °C / h to 500 - 600 °C;

[0011] Step 6: Perform heat treatment on the forging.

[0012] Further, the diameter φ of the boss is (1.0 - 1.2)H, and the height h ≥ 10%H, where H is the height of the preliminary blank.

[0013] Further, the heat treatment includes the following steps:

[0014] Homogenization: Place the forging in a temperature range of 600 - 700 °C for homogenization;

[0015] First normalizing: After the forging finishes homogenization, cool the forging at a cooling rate of ≤ 30 °C / h to 200 - 300 °C, then hold it for sufficient time to make the tissue fully undergo phase transformation. After that, heat the forging at a heating rate of ≤ 60 °C / h to 650 - 720 °C, hold it, and the holding time is (0.8 - 1.2) h for every 100 mm of the forging thickness. Then heat the forging at a heating rate of ≤ 60 °C / h to 900 - 980 °C and hold it for sufficient time to make the tissue completely austenitized. Finally, take the forging out of the furnace and air-cool it to 150 - 300 °C;

[0016] Annealing: After the first normalizing is completed, heat the forging at a heating rate of ≤ 60 °C / h to 650 - 720 °C, hold it, and the holding time is (0.8 - 1.2) h for every 100 mm of the forging thickness. After that, heat the forging at a heating rate of ≤ 60 °C / h to 900 - 960 °C and hold it for sufficient time to make the tissue completely austenitized again. Then cool the forging at a cooling rate of < 35 °C / h to 610 - 680 °C and isothermally hold it in this temperature range for more than 300 h. Finally, cool the forging at a cooling rate of < 35 °C / h to below 100 °C;

[0017] Second normalizing: After annealing is completed, heat the forging to 650 - 720°C at a heating rate of ≤60°C / h, hold the temperature, and the holding time is (0.8 - 1.2) h for every 100 mm of forging thickness. Then, heat the forging to 820 - 900°C at a heating rate of ≤60°C / h and hold it fully to completely austenitize the structure again. Finally, cool the forging to below 150°C at a cooling rate of ≥180°C / h but ≤360°C / h;

[0018] First quenching: After the second normalizing is completed, heat the forging to 650 - 720°C at a heating rate of ≤60°C / h, hold the temperature, and the holding time is (0.8 - 1.2) h for every 100 mm of forging thickness. Then, heat the forging to 820 - 880°C at a heating rate of ≤60°C / h and hold it fully to completely austenitize the structure again. Finally, cool the forging to below 150°C at a cooling rate of ≥360°C / h;

[0019] Second quenching: After the first quenching is completed, heat the forging to 650 - 720°C at a heating rate of ≤60°C / h, hold the temperature, and the holding time is (0.8 - 1.2) h for every 100 mm of forging thickness. Then, heat the forging to 820 - 880°C at a heating rate of ≤60°C / h and hold it fully to completely austenitize the structure again. Finally, cool the forging to below 100°C at a cooling rate of ≥360°C / h;

[0020] Tempering: After the second quenching is completed, heat the forging to the range of 540 - 580°C at a rate of ≤30°C / h and hold for time t, then heat it to the range of 590 - 620°C for tempering and hold for time T to ensure that the quenched structure at the core and surface of the forging is fully decomposed. Finally, cool the forging to below 300°C at a cooling rate of ≤20°C / h and take it out of the furnace, where the value of t is 0.2T - 0.3T.

[0021] Further, in the second normalizing step, the first quenching step, and the second quenching step, a soaking step at a temperature range of 200 - 300°C is included before heating the forging.

[0022] Further, in the second normalizing, the cooling of the forging at a cooling rate of ≥180°C / h but ≤360°C is carried out by means of air blowing or water spraying.

[0023] Further, in the first quenching step and the second quenching step, the cooling of the forging at a cooling rate of ≥360°C / h is carried out by immersion water cooling, and when the forging is water cooled, the forging is placed vertically into the water, and it rotates horizontally and moves up and down when cooling in the water.

[0024] The beneficial effects of the present invention are as follows: The method for manufacturing an isostrength large-sized disc-shaped forging according to the present invention can refine and homogenize the grain sizes of the core and surface of the forging, and the difference in grain size levels between the core and the surface is less than 1.0 grade. There is no mixed grain in the internal structure, and the difference in yield strength between the core and the surface of the forging is only 5-10 MPa, meeting the requirements for high uniformity of mechanical properties and isostrength manufacturing of the core and surface of the large-sized disc-shaped forging. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic diagram of the forming of the forging;

[0026] Figure 2 is a schematic diagram of the structure of the initial blank;

[0027] Figure 3 is a half-sectional view of the forging;

[0028] Figure 4 is a heat treatment flow chart of the present invention;

[0029] Figure 5 is a metallographic diagram of the core test block of the forging in Example 1;

[0030] Figure 6 is a metallographic diagram of the edge surface layer test block of the forging in Example 1;

[0031] Figure 7 is a metallographic diagram of the core test block of the forging in Example 2;

[0032] Figure 8 is a metallographic diagram of the edge surface layer test block of the forging in Example 2;

[0033] Figure 9 is a metallographic diagram of the core test block of the forging in Example 3;

[0034] Figure 10 is a metallographic diagram of the edge surface layer test block of the forging in Example 3;

[0035] As shown in the figure, the blanking cylinder 1, the intermediate blank 2, the initial blank 3, the forging 4, the boss 31, the surface layer test block 41, and the core test block 42. DETAILED DESCRIPTION OF THE INVENTION

[0036] The present invention will be further described below in conjunction with the drawings and embodiments. It should be noted that the cooling rate and heating rate of the forging in the present invention are both in accordance with the existing conventional methods: obtained by measuring the surface temperature of the forging.

[0037] As Figures 1 to 3 shown, a method for manufacturing an isostrength large-sized disc-shaped forging according to the present invention is used for materials of NiCrMoV steel, For the disc-shaped forging 4, the following steps are included:

[0038] Step 1: The ingot is upset and drawn out in multiple heats and then cut to obtain a cut cylindrical blank 1. Among them, each heat is heated to 1200 - 1260 °C and fully insulated to make the tissue temperature uniform.

[0039] Step 2: The cut cylindrical blank 1 is heated to 1200 - 1260 °C and fully insulated to make the tissue temperature uniform, and then upset and rolled to form. The final forging temperature is ≥ 850 °C to obtain a disc-shaped intermediate blank 2 with both ends being flat surfaces.

[0040] Step 3: The intermediate blank 2 is heated to 1150 - 1200 °C and fully insulated to make the tissue temperature uniform, that is, to make the temperature of the core and the surface of the intermediate blank consistent.

[0041] Step 4: After the intermediate blank 2 finishes insulation, it is forged in one heat. Control the final forging temperature ≥ 850 °C. Among them, during forging, first set reserved deformation areas at the centers of both end faces of the intermediate blank 2, and then perform rotary rolling on the surrounding areas of the reserved deformation areas of the intermediate blank 2 to obtain a preliminary blank 3 with cylindrical bosses 31 respectively arranged at the centers of both end faces. Then, pressure is applied to the preliminary blank 3 to make both end faces of the preliminary blank 3 flat until the dimensions meet the requirements, thereby obtaining the disc-shaped forging 4 with both end faces being flat surfaces.

[0042] Step 5: The central area corresponding to the position of the boss 31 of the forging 4 and the preliminary blank is cooled to 500 - 600 °C at a cooling rate of ≥ 180 °C / h but < 360 °C / h.

[0043] Step 6: Heat treatment is performed on the forging.

[0044] Among them, the full insulation time in Step 1, Step 2, and Step 3 can be determined by experiments.

[0045] In Step 5, the central area corresponding to the position of the boss 31 of the forging 4 and the preliminary blank is cooled to 500 - 600 °C at a cooling rate of ≥ 180 °C / h but < 360 °C / h. Specifically, the cooling method of blowing, spraying, or water spraying can be adopted.

[0046] The method for manufacturing an isostrength large disc-shaped forging of the present invention forms a forging by means of one-step forming on the basis of an intermediate blank 2 of a disc shape. During forming, first, rotary rolling is performed on the peripheral area of the intermediate blank 2 except for the central area to form a preliminary blank 3 having cylindrical bosses 31 at both ends. Then, pressure is applied to the preliminary blank 3 to flatten both end faces of the preliminary blank 3, that is, the central area is forged. In this way, when the forging is formed, especially when the central area is forged, although the surface temperature and the core temperature of the central area have decreased to a certain extent and the plasticity is slightly lower, since the core of the central area is inside the forging, the temperature drop is less, the temperature is higher, and the plasticity is better than that of the surface. When pressure is applied to the preliminary blank, the core is more likely to deform, resulting in grain refinement. Finally, after forging is completed, the central areas of both end faces of the forging are blown and cooled to 500 - 600 °C to rapidly reduce the core temperature of the forging. In this way, the grain size grade of the central area of the obtained forging is not lower than that of the peripheral area, so that the grain size difference and strength difference between the central area and the peripheral area of the forging caused by the large difference in the heating and cooling rates between the central area and the peripheral area of the forging during subsequent heat treatment can be reduced, thereby improving the uniformity of the forging and helping to meet the requirements for isostrength manufacturing of the forging.

[0047] The boss can be changed. Preferably, the diameter φ of the boss is (1.0 - 1.2)H, and the height h ≥ 10%H, where H is the height of the preliminary blank 3.

[0048] In order to cooperate with the above manufacturing method and further improve the uniformity of the forging to meet the requirements for isostrength manufacturing, optimally, as Figure 4 shown, the heat treatment includes the following steps:

[0049] Homogenization: The forging is placed in a temperature range of 600 - 700 °C for homogenization;

[0050] First normalizing: After the forging is homogenized, the forging is cooled at a cooling rate of ≤ 30 °C / h to 200 - 300 °C, then fully insulated to allow its structure to fully undergo a phase change. After that, the forging is heated at a heating rate of ≤ 60 °C / h to 650 - 720 °C and insulated. The insulation time is (0.8 - 1.2) h for every 100 mm of the forging thickness. Then, the forging is heated at a heating rate of ≤ 60 °C / h to 900 - 980 °C and fully insulated to completely austenitize its structure. Finally, the forging is taken out of the furnace and air-cooled to 150 - 300 °C;

[0051] Annealing: After the first normalizing is completed, heat the forging at a heating rate of ≤60 °C / h to 650 - 720 °C, hold the temperature, and the holding time is (0.8 - 1.2) h for every 100 mm of forging thickness. Then heat the forging at a heating rate of ≤60 °C / h to 900 - 980 °C and hold the temperature sufficiently to fully austenitize the structure again. Then cool the forging at a cooling rate of <35 °C / h to 610 - 680 °C, and isothermally hold the temperature for more than 300 h in this temperature range. Finally, cool the forging at a cooling rate of <35 °C / h to below 100 °C;

[0052] Second normalizing: After annealing is completed, heat the forging at a heating rate of ≤60 °C / h to 650 - 720 °C, hold the temperature, and the holding time is (0.8 - 1.2) h for every 100 mm of forging thickness. Then heat the forging at a heating rate of ≤60 °C / h to 820 - 900 °C and hold the temperature sufficiently to fully austenitize the structure again. Finally, cool the forging at a cooling rate of ≥180 °C / h but ≤360 °C / h to below 150 °C;

[0053] First quenching: After the second normalizing is completed, heat the forging at a heating rate of ≤60 °C / h to 650 - 720 °C, hold the temperature, and the holding time is (0.8 - 1.2) h for every 100 mm of forging thickness. Then heat the forging at a heating rate of ≤60 °C / h to 820 - 880 °C and hold the temperature sufficiently to fully austenitize the structure again. Finally, cool the forging at a cooling rate of ≥360 °C / h to below 150 °C;

[0054] Second quenching: After the first quenching is completed, heat the forging at a heating rate of ≤60 °C / h to 650 - 720 °C, hold the temperature, and the holding time is (0.8 - 1.2) h for every 100 mm of forging thickness. Then heat the forging at a heating rate of ≤60 °C / h to 820 - 880 °C and hold the temperature sufficiently to fully austenitize the structure again. Finally, cool the forging at a cooling rate of ≥360 °C / h to below 100 °C;

[0055] Tempering: After the second quenching is completed, heat the forging at a rate of ≤30 °C / h to the range of 540 - 580 °C and hold the temperature for time t, then heat it at a rate of ≤30 °C / h to the range of 590 - 620 °C for tempering and hold the temperature for time T, ensuring that the quenched structure of the core and surface of the forging is fully decomposed. Finally, cool the forging at a cooling rate of ≤20 °C / h to below 300 °C and take it out of the furnace, where the value of t is 0.2T - 0.3T.

[0056] The sufficient holding time in the above first normalizing, annealing, second normalizing, first quenching, and second quenching steps, as well as the tempering holding time T in the tempering step, can all be obtained through experiments according to the corresponding holding purposes.

[0057] In the annealing step, the forging is cooled at a cooling rate of < 35 °C / h, and in the tempering step, the forging is cooled at a cooling rate of ≤ 20 °C / h. Specifically, furnace cooling can be adopted, and different furnace cooling rates can be achieved by controlling the opening and closing size of the flue valve of the heating furnace.

[0058] In the second normalizing step, the forging is taken out of the furnace and cooled at a cooling rate of ≥ 180 °C / h but ≤ 360 °C / h. Specifically, air blowing or water spraying can be adopted. Of course, other cooling methods that can meet the above requirements of the cooling rate can also be used.

[0059] Specifically, to achieve cooling the forging to below 100 °C at a cooling rate of ≥ 360 °C / h, immersion water cooling, oil cooling, etc. can be adopted; in the embodiments of the present invention, immersion water cooling is adopted for cooling the forging at a cooling rate of ≥ 360 °C / h in both the first quenching step and the second quenching step. When the forging is water-cooled, preferably, the forging is placed vertically into the water for cooling while rotating horizontally and moving up and down for large disc-shaped forgings, eliminating the steam film and quenching blind spots on the surface of the forging, which can make the forging cool more evenly and is beneficial to the homogenization and equal strength of the forging components.

[0060] If immersion water cooling is adopted for cooling the forging at a cooling rate of ≥ 360 °C / h in both the first quenching step and the second quenching step, it can be understood that in the second quenching step and the tempering step, the water remaining on the surface of the forging after water cooling needs to be removed before the forging is heated up. This water can be evaporated naturally or wiped dry, etc. Optimally, in both the second quenching step and the tempering step, there is a step of air-cooling the forging before heating up to evaporate the water on its surface. When a soaking step is set in the second quenching step and the tempering step, it can be understood that the step of air-cooling the forging to evaporate the water on its surface should be set before the soaking step.

[0061] When the forging is heated up, it is usually placed flat or vertically (the axis of the forging is horizontal). If the forging is placed flat for heating in the first normalizing, annealing, and second normalizing processes, it is preferably turned over for heating in the next process. For the convenience of subsequent quenching and cooling of the forging, preferably, the forging is placed vertically for heating during the first quenching and the second quenching, and the forging rotates 180° in the circumferential direction during the second quenching.

[0062] In order to further make the grains of the forging more uniform and create conditions for equal strength, the second normalizing step, the first quenching step, and the second quenching step all include a soaking step of soaking the forging in the temperature range of 200-300 °C before the forging is heated. This can ensure that the surface temperatures of all parts of the forging are the same before each heating and temperature rise, thereby reducing the temperature difference between the center and the surface of the forging during the heating process.

[0063] Example 1: Dimensions of the forging 4 The material is NiCrMoV steel;

[0064] Step 1: The steel ingot is upset and drawn multiple times and then blanked to obtain the blanked cylinder 1. Among them, each heating is to 1200-1260 °C and fully insulated to make the tissue temperature uniform;

[0065] Step 2: The blanked cylinder is heated to 1200-1260 °C and fully insulated to make the tissue temperature uniform, and then upset and expanded to form a disc-shaped intermediate blank with flat ends;

[0066] Step 3: The intermediate blank is heated to 1150-1200 °C and fully insulated to make the tissue temperature uniform;

[0067] Step 4: After the intermediate blank is insulated, it is forged in one heat to control the final forging temperature ≥850 °C. Among them, when forging, a preliminary blank with cylindrical bosses respectively provided at the centers of both end faces is first made. The height H of the preliminary blank is 1925 mm, the diameter φ of the boss is 1925 mm, and the height h of the boss is 220 mm. Then, the preliminary blank is pressed to make the end faces of the preliminary blank flat until the dimensions meet the requirements, thereby obtaining the disc-shaped forging 4 with flat end faces.

[0068] Step 5: The central area of the forging 4 corresponding to the position of the boss of the preliminary blank is cooled to 500-600 °C by means of air blowing cooling at a rate of about 180 °C / h;

[0069] Step 6: Heat treatment of the forging, specific steps:

[0070] 1. Soaking: The forging 4 is placed in the temperature range of 600-700 °C for soaking;

[0071] 2. First normalizing: After the forging is soaked, the forging is cooled to 200-300 °C at a cooling rate of 5 °C / h and insulated for 25 h to make its structure fully undergo a phase change. Then, the forging is heated to 650-720 °C at a heating rate of 5 °C / h and insulated for 12 h. Then, the forging is heated to 900-980 °C at a heating rate of 5 °C / h and insulated for another 25 h to make its structure completely austenitized. Finally, the forging is taken out of the furnace and air-cooled to 150-300 °C;

[0072] 3. Annealing: After the first normalizing is completed, heat the forging at a heating rate of 5 °C / h to 650 - 720 °C, hold for 12 h, then heat the forging at a heating rate of 5 °C / h to 900 - 960 °C and hold for 25 h to fully austenitize the structure again. Then cool the forging at a cooling rate of 5 °C / h to 610 - 680 °C and isothermally hold for more than 300 h in this temperature range. Finally, cool the forging at a cooling rate of 5 °C / h to below 100 °C;

[0073] 4. Second normalizing: After annealing is completed, heat the forging at a heating rate of 5 °C / h to 650 - 720 °C, hold for 12 h, then heat the forging at a heating rate of 5 °C / h to 820 - 900 °C and hold for another 25 h to fully austenitize the structure again. Finally, take the forging out of the furnace and blow air to cool it to below 150 °C at a cooling rate of about 180 °C / h;

[0074] 5. First quenching: After the second normalizing is completed, heat the forging at a heating rate of 5 °C / h to 650 - 720 °C, hold for 12 h, then heat the forging at a heating rate of 5 °C / h to 820 - 880 °C and hold for 25 h to fully austenitize the structure again. Finally, cool the forging to below 150 °C by immersion water cooling with a cooling rate of about 360 °C / h when taking it out of the furnace;

[0075] 6. Second quenching: After the first quenching is completed and the surface moisture of the forging naturally evaporates, then send it to an environment of 200 - 300 °C for temperature equalization. Then heat the forging at a heating rate of 5 °C / h to 650 - 720 °C, hold for 12 h, then heat the forging at a heating rate of 5 °C / h to 820 - 880 °C and hold for another 25 h to fully austenitize the structure again. Finally, cool the forging to below 100 °C by immersion water cooling with a cooling rate of about 360 °C / h when taking it out of the furnace;

[0076] 7. Tempering: After the second quenching is completed and the surface moisture of the forging naturally evaporates, then send it to an environment of 200 - 300 °C for temperature equalization. Then heat the forging at a rate of 5 °C / h to the range of 540 - 580 °C and hold for 6 h, then heat it at a rate of 5 °C / h to the range of 590 - 620 °C for tempering and hold for 30 h to ensure that the quenched structure in the core and surface layer of the forging is fully decomposed. Finally, cool the forging at a cooling rate of 5 °C / h to below 300 °C and take it out of the furnace.

[0077] Take a core test block 42 and a surface layer test block 41 at the edge on the forging 4. The metallographic diagram is shown in Figure 5 、 Figure 6 and the test parameters are shown in Table 1

[0078] Table 1:

[0079]

[0080]

[0081] Example 2: Dimensions of the forging 4 The material is NiCrMoV steel;

[0082] Step 1: The ingot is upset and drawn out in multiple heats and then cut to obtain a cut blank cylinder 1. Among them, each heat is heated to 1200 - 1260 °C and fully insulated to make the tissue temperature uniform;

[0083] Step 2: The cut blank cylinder is heated to 1200 - 1260 °C and fully insulated, and then upset and expanded to form a disc-shaped intermediate blank with flat ends;

[0084] Step 3: The intermediate blank is heated to 1150 - 1200 °C and fully insulated to make the tissue temperature uniform;

[0085] Step 4: After the intermediate blank is insulated, it is forged in one heat. Control the final forging temperature ≥ 850 °C. Among them, when forging, a preliminary blank with cylindrical bosses respectively provided at the centers of both end faces is first obtained. The height H of the preliminary blank is 1925 mm, the diameter φ of the boss is 2120 mm, and the height h of the boss is 205 mm. Then, the preliminary blank is pressed to make the end faces of the preliminary blank flat until the dimensions meet the requirements, thereby obtaining a disc-shaped forging 4 with flat end faces,

[0086] Step 5: The central area of the forging 4 corresponding to the position of the boss of the preliminary blank is cooled to 500 - 600 °C by means of air cooling at a rate of about 250 °C / h;

[0087] Step 6: Heat treatment of the forging. Specific steps:

[0088] 1. Temperature equalization: The forging is put into a temperature range of 600 - 700 °C for temperature equalization;

[0089] 2. First normalizing: After the forging is temperature equalized, the forging is cooled to 200 - 300 °C at a cooling rate of 15 °C / h and insulated for 25 h to make its tissue fully undergo phase transformation. Then, the forging is heated to 650 - 720 °C at a heating rate of 30 °C / h and insulated for 15 h. Then, the forging is heated to 900 - 980 °C at a heating rate of 30 °C / h and insulated for 25 h to make its tissue completely austenitized. Finally, the forging is taken out of the furnace and air cooled to 150 - 300 °C;

[0090] 3. Annealing: After the first normalizing is completed, heat the forging at a heating rate of 30 °C / h to 650 - 720 °C, hold for 15 h, then heat the forging at a heating rate of 30 °C / h to 900 - 960 °C and hold for 25 h to fully austenitize the structure again. Then cool the forging at a cooling rate of 15 °C / h to 610 - 680 °C and isothermally hold for more than 300 h in this temperature range. Finally, cool the forging at a cooling rate of 15 °C / h to below 100 °C;

[0091] 4. Second normalizing: After annealing is completed, heat the forging at a heating rate of 30 °C / h to 650 - 720 °C, hold for 15 h, then heat the forging at a heating rate of 30 °C / h to 820 - 900 °C and hold for another 25 h to fully austenitize the structure again. Finally, take the forging out of the furnace and blow air to cool it to below 150 °C at a cooling rate of about 300 °C / h;

[0092] 5. First quenching: After the second normalizing is completed, heat the forging at a heating rate of 30 °C / h to 650 - 720 °C, hold for 15 h, then heat the forging at a heating rate of 30 °C / h to 820 - 880 °C and hold for 25 h to fully austenitize the structure again. Finally, cool the forging to below 150 °C by immersion water cooling with a cooling rate of about 420 °C / h when taking it out of the furnace;

[0093] 6. Second quenching: After the first quenching is completed and the surface moisture of the forging naturally evaporates, then send it to an environment of 200 - 300 °C for temperature equalization. Then heat the forging at a heating rate of 30 °C / h to 650 - 720 °C, hold for 15 h, then heat the forging at a heating rate of 30 °C / h to 820 - 880 °C and hold for another 25 h to fully austenitize the structure again. Finally, cool the forging to below 100 °C by immersion water cooling with a cooling rate of about 420 °C / h when taking it out of the furnace;

[0094] 7. Tempering: After the second quenching is completed and the surface moisture of the forging naturally evaporates, then send it to an environment of 200 - 300 °C for temperature equalization. Then heat the forging at a rate of 15 °C / h to the range of 540 - 580 °C and hold for 8 h, then heat it at a rate of 15 °C / h to the range of 590 - 620 °C for tempering and hold for 30 h to ensure that the quenched structure of the core and surface layer of the forging is fully decomposed. Finally, cool the forging at a cooling rate of 15 °C / h to below 300 °C and take it out of the furnace.

[0095] Take a core test block 42 and a surface layer test block 41 at the edge on the forging. The metallographic diagram is shown in Figure 7 、 Figure 8 ,and the test parameters are shown in Table 2;

[0096] Table 2

[0097] Sampling location Rp0.2 / MPa Rm / MPa A / ％ Z / ％ Grain size Surface specimen 760 870 25 73 6.5 Core specimen 770 890 22 65 5.5

[0098] Step 1: After upsetting and drawing out the ingot in multiple heat treatments and then cutting it, a cut cylindrical blank 1 is obtained. Among them, it is heated to 1200 - 1260 °C in each heat treatment and fully insulated to make the tissue temperature uniform;

[0099] Step 2: The cut cylindrical blank is heated to 1200 - 1260 °C, fully insulated, and then upset and rolled to form a disc-shaped intermediate blank with flat ends at both ends;

[0100] Step 3: The intermediate blank is heated to 1150 - 1200 °C and fully insulated to make the tissue temperature uniform;

[0101] Step 4: After the intermediate blank finishes heat preservation, it is forged in one heat treatment, and the final forging temperature is controlled ≥ 850 °C. Among them, when forging, a preliminary blank with cylindrical bosses respectively provided at the centers of both end faces is first obtained. The height H of the preliminary blank is 1925 mm, the diameter φ of the boss is 2310 mm, and the height h of the boss is 192.5 mm. Then, the preliminary blank is pressed to make the end faces of the preliminary blank flat until the dimensions meet the requirements, thereby obtaining a disc-shaped forging 4 with flat end faces at both ends.

[0102] Step 5: The central area of the forging 4 corresponding to the position of the boss of the preliminary blank is cooled to 500 - 600 °C by means of air blowing cooling at a rate of about 350 °C / h;

[0103] Step 6: Heat treatment of the forging, specific steps:

[0104] 1. Temperature equalization: The forging is placed in a temperature range of 600 - 700 °C for temperature equalization;

[0105] 2. First normalizing: After the forging finishes temperature equalization, the forging is cooled to 200 - 300 °C at a cooling rate of 30 °C / h and held for 25 h to make the tissue fully undergo phase transformation. Then, the forging is heated to 650 - 720 °C at a heating rate of 60 °C / h and held for 18 h. Then, the forging is heated to 900 - 980 °C at a heating rate of 60 °C / h and held for another 25 h to make the tissue completely austenitized. Finally, the forging is taken out of the furnace and air-cooled to 150 - 300 °C;

[0106] 3. Annealing: After the first normalizing is completed, heat the forging at a heating rate of 60 °C / h to 650 - 720 °C, hold for 18 h, then heat the forging at a heating rate of 60 °C / h to 900 - 960 °C and hold for 25 h to fully austenitize the structure again. Then cool the forging at a cooling rate of 35 °C / h to 610 - 680 °C and isothermally hold for more than 300 h in this temperature range. Finally, cool the forging at a cooling rate of 35 °C / h to below 100 °C;

[0107] 4. Second normalizing: After annealing is completed, heat the forging at a heating rate of 60 °C / h to 650 - 720 °C, hold for 18 h, then heat the forging at a heating rate of 60 °C / h to 820 - 900 °C and hold for another 25 h to fully austenitize the structure again. Finally, take the forging out of the furnace and spray it to cool to below 150 °C at a cooling rate of about 360 °C / h;

[0108] 5. First quenching: After the second normalizing is completed, heat the forging at a heating rate of 30 °C / h to 650 - 720 °C, hold for 18 h, then heat the forging at a heating rate of 60 °C / h to 820 - 880 °C and hold for 25 h to fully austenitize the structure again. Finally, cool the forging to below 150 °C by immersion water cooling with a cooling rate of about 450 °C / h when taking it out of the furnace;

[0109] 6. Second quenching: After the first quenching is completed, wait for the surface moisture of the forging to naturally evaporate, then send it to an environment of 200 - 300 °C for temperature equalization. Then heat the forging at a heating rate of 60 °C / h to 650 - 720 °C, hold for 18 h, then heat the forging at a heating rate of 60 °C / h to 820 - 880 °C and hold for another 25 h to fully austenitize the structure again. Finally, cool the forging to below 150 °C by immersion water cooling with a cooling rate of about 450 °C / h when taking it out of the furnace;

[0110] 7. Tempering: After the second quenching is completed, wait for the surface moisture of the forging to naturally evaporate, then send it to an environment of 200 - 300 °C for temperature equalization. Then heat the forging at a rate of 30 °C / h to the range of 540 - 580 °C and hold for 9 h, then heat it at a rate of 30 °C / h to the range of 590 - 620 °C for tempering and hold for 30 h to ensure that the quenched structure of the core and surface layer of the forging is fully decomposed. Finally, cool the forging at a cooling rate of 20 °C / h to below 300 °C and take it out of the furnace.

[0111] Take a core test block 42 and a surface layer test block 41 at the edge on the forging. The metallographic diagram is shown in Figure 9 、 Figure 10 , and the test parameters are shown in Table 3;

[0112] Table 3:

[0113] Sampling location Rp0.2 / MPa Rm / MPa A / ％ Z / ％ Grain size Surface specimen 760 870 24 72 6.0 Core specimen 765 890 21 64 5.0

[0114] The above embodiments show that the manufacturing method of the present invention can refine and homogenize the grain sizes of the core and surface of the forging, and the difference in the grain size level between the core and the surface is less than 1.0 grade. There is no mixed grain in the internal structure, and the difference in the yield strength between the core and the surface of the forging is only 5-10 MPa, meeting the requirements for highly uniform mechanical properties and equal-strength manufacturing of the core and surface of large disc forgings.

Claims

1. A method for manufacturing an isostrength large-sized disk-shaped forging, which is used for a disk-shaped forging made of NiCrMoV steel, and It is characterized in that it includes the following steps: Step 1: Upset and draw out the ingot for multiple times and then cut it to obtain a cut cylindrical blank. Among them, each time it is heated to 1200 - 1260 °C and fully insulated to make the tissue temperature uniform; Step 2: Heat the cut cylindrical blank to 1200 - 1260 °C, fully insulate it to make the tissue temperature uniform, and then upset and expand it to form a cake-shaped intermediate blank with flat ends; Step 3: Heat the intermediate blank to within 1150 - 1200 °C and fully insulate it to make the tissue temperature uniform; Step 4: After the intermediate blank finishes insulation, perform one-time forging on the intermediate blank, control the final forging temperature ≥ 850 °C. Among them, when forging, first obtain a preliminary blank with cylindrical bosses respectively provided at the centers of the two end faces, and then apply pressure to the preliminary blank to make the two end faces of the preliminary blank flat until the dimensions meet the requirements, thereby obtaining a cake-shaped forging with flat end faces; Step 5: Cool the central area corresponding to the position of the boss of the forging and the preliminary blank at a cooling rate of ≥ 180 °C / h but < 360 °C / h to 500 - 600 °C; Step 6: Perform heat treatment on the forging; the heat treatment includes the following steps: Temperature equalization: Put the forging into a temperature range of 600 - 700 °C for temperature equalization; First normalizing: After the forging finishes temperature equalization, cool the forging at a cooling rate of ≤ 30 °C / h to 200 - 300 °C, then fully insulate it to make the tissue fully undergo phase transformation. After that, heat the forging at a heating rate of ≤ 60 °C / h to 650 - 720 °C, keep it warm, and the holding time is (0.8 - 1.2) h for every 100 mm thickness of the forging. Then heat the forging at a heating rate of ≤ 60 °C / h to 900 - 980 °C and fully insulate it to make the tissue completely austenitized. Finally, take the forging out of the furnace and air-cool it to 150 - 300 °C; Annealing: After the first normalizing is completed, heat the forging at a heating rate of ≤ 60 °C / h to 650 - 720 °C, keep it warm, and the holding time is (0.8 - 1.2) h for every 100 mm thickness of the forging. After that, heat the forging at a heating rate of ≤ 60 °C / h to 900 - 960 °C and fully insulate it to make the tissue completely austenitized again. Then cool the forging at a cooling rate of ≤ 35 °C / h to 610 - 680 °C, and isothermally keep it warm in this temperature range for more than 300 h. Finally, cool the forging at a cooling rate of ≤ 35 °C / h to below 100 °C; Second normalizing: After the annealing is completed, heat the forging at a heating rate of ≤ 60 °C / h to 650 - 720 °C, keep it warm, and the holding time is (0.8 - 1.2) h for every 100 mm thickness of the forging. After that, heat the forging at a heating rate of ≤ 60 °C / h to 820 - 900 °C and fully insulate it to make the tissue completely austenitized again. Finally, cool the forging at a cooling rate of ≥ 180 °C / h but ≤ 360 °C / h to below 150 °C; The first quenching: After the second normalizing is completed, heat the forging to 650 - 720°C at a heating rate of ≤60°C / h, hold the temperature, and the holding time is (0.8 - 1.2) h for every 100 mm of forging thickness. Then heat the forging to 820 - 880°C at a heating rate of ≤60°C / h and hold the temperature fully to completely austenitize the structure again. Finally, cool the forging to below 150°C at a cooling rate of ≥360°C / h; The second quenching: After the first quenching is completed, heat the forging to 650 - 720°C at a heating rate of ≤60°C / h, hold the temperature, and the holding time is (0.8 - 1.2) h for every 100 mm of forging thickness. Then heat the forging to 820 - 880°C at a heating rate of ≤60°C / h and hold the temperature fully to completely austenitize the structure again. Finally, cool the forging to below 100°C at a cooling rate of ≥360°C / h; Tempering: After the second quenching is completed, heat the forging to the range of 540 - 580°C at a speed of ≤30°C / h and hold the temperature for time t, then heat it to the range of 590 - 620°C for tempering and hold the temperature for time T to ensure that the quenched structure at the core and surface of the forging is fully decomposed. Finally, cool the forging to below 300°C at a cooling rate of ≤20°C / h and take it out of the furnace, where the value of t is 0.2T - 0.3T.

2. A method for manufacturing an isostrength large-sized disc-shaped forging as claimed in claim 1, characterized in that, the diameter φ of the boss is (1.0 - 1.2)H, and the height h ≥ 10%H, where H is the height of the intermediate billet.

3. A method for manufacturing an isostrength large-sized disc-shaped forging as claimed in claim 1, characterized in that, the second normalizing step, the first quenching step, and the second quenching step all include a step of equalizing the temperature of the forging in the temperature range of 200 - 300°C before heating the forging.

4. A method for manufacturing an isostrength large-sized disc-shaped forging as claimed in claim 1, characterized in that, in the second normalizing step, the forging is cooled at a cooling rate of ≥180°C / h but ≤360°C / h by means of air blowing or water spraying.

5. A method for manufacturing an isostrength large-sized disc-shaped forging as claimed in claim 1, characterized in that, in the first quenching step and the second quenching step, the forging is cooled at a cooling rate of ≥360°C / h by immersion water cooling, and when the forging is water cooled, the forging is placed vertically into the water, and the forging rotates horizontally and moves up and down when cooling in the water.

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