A X-750 alloy large forging and its manufacturing method

Abstract

The present invention discloses a X-750 alloy large forging and a manufacturing method thereof, and belongs to the field of alloy forging. Aiming at the problem that the existing X-750 alloy forging is easy to crack and the size and performance of the forging cannot be achieved at the same time, the present invention provides a manufacturing method of a X-750 alloy large forging, comprising the following steps: steel ingot preparation: using vacuum induction smelting electrodes, and then using electroslag remelting to smelt the steel ingot; homogenization treatment; forging: forging includes two steps of blanking and forming, the forging temperature of the blanking step is 1100-1220°C, and the forging temperature of the forming step is 1000-1200°C; solution aging treatment. The present invention improves the dendrite segregation and crushes the primary carbonitride in the steel ingot through the reasonable setting of the manufacturing process and process parameters, and determines the appropriate forging temperature range, final forging temperature, solution heat treatment temperature, etc. by studying the precipitation and dissolution law of secondary carbonitrides. The forging has good formability and obtains a good organizational state, ensuring that the final forging meets the size and performance requirements, and is easy to operate.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy forging, and more specifically, relates to an X-750 alloy large forging and a manufacturing method thereof. Background Art

[0002] X-750 (corresponding to the domestic grade GH4145, implementation standard GB / T 38443-2019) is a precipitation-strengthened Ni-Cr-based high-temperature alloy. The main precipitation-strengthened phase is γ′. Its chemical composition is shown in Table 1 below:

[0003] Table 1 X-750 (GH4145) alloy chemical composition requirements (wt, %)

[0004] element C Si Mn Ni Cr Fe Cu Require ≤0.08 ≤0.50 ≤1.00 ≥70.00 14.00～17.00 5.00～9.00 ≤0.50 element Ti Nb Al P S Co -- Require 2.25～2.75 0.70～1.20 0.40～1.00 ≤0.015 ≤0.010 ≤1.00 --

[0005] Since X-750 parts have good anti-relaxation properties at high temperatures and still have good corrosion and oxidation resistance at temperatures as high as 700°C, they are commonly used materials for high-strength and high-plasticity springs and high-temperature fasteners such as bolts. They are widely used in gas turbines, rocket engines, aircraft structures, pressure vessels and reactors. At present, the research on X-750 materials at home and abroad mainly focuses on: (1) phase analysis based on phase diagram calculation software such as Thermo-Calc and laboratory observation; (2) determination of the thermal deformation and recrystallization characteristics of X-750 materials based on finite element simulation and Gleeble thermal simulation test; (3) based on the precipitation law of strengthening phase γ′, study the influence of heat treatment system (solid solution + aging) on ​​material properties. However, there is little research on the production and manufacturing technology of large forgings of X-750 materials using large ESR steel ingots. At present, the production and manufacturing technology of large forgings of X-750 materials still needs to be developed and further improved.

[0006] Corresponding improvements have also been made to the above problems, such as China's patent application number CN202111386023.7, published on February 11, 2022, which discloses a method for homogenizing high-alloy high-temperature alloy materials. The main core point of this patent invention is to pre-open the high-alloy high-temperature alloy ingots to improve the efficiency of homogenization treatment. Its shortcomings are: the applicable high-alloy high-temperature alloy ingot diameter size is limited, and forging larger ingots is still difficult; for large-sized high-alloy high-temperature alloy ingots, it is difficult to achieve pre-opening before homogenization treatment, and the forged ingot is prone to cracking during the opening process.

[0007] For the application of X-750 material forgings in nuclear power equipment, due to equipment upgrades, the required forging specifications are constantly increasing. For example, the X-750 material compression spring forgings for nuclear reactor internals have increased from 2000mm to 3000mm, and the ESR steel ingot has increased from 550mm to 700mm. In addition, the high-temperature alloy material itself has a high alloy degree and elements are easy to segregate. Under the circumstances that there are already great difficulties in producing X-750 material compression spring forgings for nuclear reactor internals from 550mm outer diameter ESR steel ingots (low forging yield, easy cracking, difficult to control grain size and inclusions, etc.), further developing the production technology of 700mm outer diameter ESR steel ingot large forgings has posed an unprecedented challenge to the hot processing technology level of forging suppliers. Summary of the invention

[0008] 1. Problems to be solved

[0009] Aiming at the problems that the blank is easy to crack and the size and performance of the forging cannot be achieved during the existing X-750 alloy forging process, the present invention provides an X-750 alloy large forging and a manufacturing method thereof. The manufacturing method of the present invention increases the uniformity of the components in the steel ingot by vacuum induction and electroslag remelting; the homogenization treatment improves the obvious dendrite segregation in the steel ingot, dissolves the secondary carbonitride into the matrix, so that the alloy elements participate in the diffusion, and improves the forgeability of the forging in the subsequent blanking step; the forming step adjusts the forging temperature range from 1100-1220°C in the blanking step to 1000-1200°C, expands the forgeable temperature range of the alloy blank, controls the final forging temperature to 1000°C, makes the forging have good formability, and obtains a good preparatory structure, ensures that the final forging meets the size and performance requirements, and is easy to operate. The outer diameter of the X-750 alloy forging of the present invention can reach 3000 mm, and the outer diameter of the steel ingot can be 700 mm; the X-750 alloy large forging prepared by the method of the present invention can be used in nuclear power equipment, such as X-750 material compression spring forgings for nuclear reactor internal components.

[0010] 2. Technical solution

[0011] To solve the above problems, the present invention adopts the following technical solutions.

[0012] A method for manufacturing a large X-750 alloy forging comprises the following steps:

[0013] S1: Ingot preparation: vacuum induction smelting electrodes followed by electroslag remelting to smelt ingots;

[0014] S2: Homogenization treatment: homogenization treatment of the steel ingot;

[0015] S3: Forging: Forging the steel ingot after homogenization treatment, including two steps of blanking and forming. The blanking step includes upsetting-drawing-upsetting. The forging temperature of the blanking step is 1100-1220°C, and the deformation of each fire is 40-60%; the forging temperature of the forming step is 1000-1200°C;

[0016] S4: Solid solution and aging treatment: The forged parts are subjected to solid solution and aging treatment to finally obtain X-750 alloy large forgings.

[0017] Furthermore, the homogenization treatment in step S2 includes heating the steel ingot to 600-650° C. and keeping it for 2-10 hours, then heating it to 1050-1100° C. and keeping it for 4-20 hours, and then heating it to 1200-1220° C. and keeping it for 40-70 hours.

[0018] Furthermore, the forming step in step S3 is not limited to be completed in one fire, and the deformation amount of each fire of the final forging hole expansion is 20-50%.

[0019] Furthermore, in step S4, the solution temperature is 1050-1100° C., and the insulation time is 3-10 hours; the aging insulation temperature is 650-710° C., and the insulation time is not less than 15 hours.

[0020] A large X-750 alloy forging produced by any of the above-mentioned methods for producing large X-750 alloy forgings, wherein the outer diameter of the large X-750 alloy forging is 3000 mm, and the outer diameter of the steel ingot is 700 mm.

[0021] A large X-750 alloy forging as described above, wherein the large X-750 alloy forging is used for nuclear reactor internals.

[0022] 3. Beneficial effects

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The production of X750 alloy large forgings is mainly difficult because of the obvious dendrite segregation in the ESR steel ingot, and the secondary carbides connect the primary carbonitrides in the steel ingot into a network, resulting in poor forging formability, difficult control of grain uniformity, and easy cracking of the alloy billet during forging. The present invention aims to homogenize the steel ingot to make the components in the steel ingot uniform and dissolve the secondary carbonitrides into the matrix, and then the billet opening stage is in a relatively high temperature range (i.e., 1100-1220°C: within this temperature range, the alloy billet has good plasticity, metallurgical pore defects are easy to close, inclusion defects are The high-temperature plasticity of the alloy billet is less affected, and the secondary carbonitrides are dissolved in the alloy matrix) A larger deformation amount is used to complete the upsetting process, break the primary carbonitrides, increase the forgeability of the forging billet, and prepare the organization for the forging of the forgings; in addition, due to the dislocations, grain boundaries, subgrain boundaries, etc. introduced by the billet forging, the secondary carbonitrides can be hindered from aggregating and growing at the original precipitation position to a certain extent, and the hereditary nature of the secondary carbonitrides that are easy to nucleate and grow at the original precipitation position is cut off, so that the forging temperature range of the subsequent forming steps is expanded, the final forging temperature can be reduced to 1000°C, and the forging formability is improved. With the reduction of the final forging temperature of the forming step, the forging billet can be deformed and recrystallized within a lower temperature range, and the alloy recrystallized grains are not easy to grow. In the temperature range of 1000-1100°C, the secondary carbonitrides in the alloy matrix are dispersed and small, providing more recrystallization nucleation points while pinning the grain boundaries, playing a role in hindering the growth of grains, so that the final forgings have fine and uniform grains;

[0025] (2) The hot working steps included in the present invention are: electroslag remelting (the electrode used is a vacuum induction smelting electrode), homogenization treatment, forging (including two steps of blanking and forming), solid solution and aging heat treatment; the entire manufacturing method is simple, and the final forging can obtain the ideal forging size, grain size, inclusion distribution and comprehensive performance;

[0026] The steel ingot used in the present invention is an electroslag remelting steel ingot, and a vacuum induction smelting electrode rod is used for smelting to initially increase the uniformity of the components in the steel ingot; then the steel ingot is homogenized to improve the obvious dendrite segregation in the steel ingot, and the homogenization treatment can dissolve part or all of the secondary carbonitrides connected in a network into the matrix, so that the alloy elements participate in the diffusion, and the forgeability of the subsequent forging blank is improved;

[0027] The forging process of the present invention is completed by two steps of blanking and forming. The blanking step of forging is effectively roughened and stretched. The forging temperature range is 1100-1220°C, and the final forging temperature of the roughening and stretching process is strictly controlled to be not less than 1100°C, so that the secondary (Ti, Nb) (C, N) is dissolved in the alloy matrix within the blanking forging temperature range, and the forging is performed within a relatively high temperature range. The high-temperature plasticity of the forging blank is relatively good, and the conditions for adopting a large deformation amount for forging are met to prevent the forging blank from cracking. The forging is fully upsetting and stretched. After that, the primary (Ti, Nb)(C, N) is fully crushed and dispersed, the secondary (Ti, Nb)(C, N) is dissolved in the matrix, the (Ti, Nb)(C, N) network structure is effectively improved, the forgeability of the forging blank is enhanced, and the subsequent forming forging can be carried out. The forging temperature range of the forming step is 1000-1200°C, and the final forging temperature of the forming step is controlled to be not less than 1000°C; by limiting the final forging temperature in the forming step, the alloy blank can ensure good toughness and good final formability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of dendrite segregation in X-750ESR steel ingot;

[0029] Figure 2 EDS analysis area selection diagram for X-750ESR steel ingot;

[0030] Figure 3 for Figure 2 EDS analysis image of area 1 in the middle;

[0031] Figure 4 Schematic diagram of homogenization process;

[0032] Figure 5 Schematic diagram of the distribution of inclusions and precipitates in X-750 alloy before and after homogenization treatment;

[0033] Figure 6 This is a metallographic photograph of the polished sample of X-750 alloy after solution annealing;

[0034] Figure 7 This is the microstructure photo of X-750 alloy forging sample after solution annealing;

[0035] Figure 8 This is the impact toughness curve of X-750 alloy forging sample after solution annealing;

[0036] Fig. 9 Schematic diagram of grain size and inclusions of X-750 alloy forgings after solution aging. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with specific embodiments and drawings.

[0038] Example 1

[0039] A method for manufacturing a large X-750 alloy forging comprises the following steps:

[0040] S1: Ingot preparation: The ingredients are prepared according to the X-750 alloy composition requirements, vacuum induction smelting electrodes are used, and then electroslag remelting is used to smelt the steel ingot; in this step, electroslag remelting steel ingots are selected as forging steel ingots, and vacuum induction smelting electrode rods are used for smelting to increase the composition uniformity of the steel ingot;

[0041] S2: Homogenization treatment: The steel ingot is subjected to homogenization treatment: the steel ingot is first heated to 600-650°C and kept at this temperature for 2-10 hours, then heated to 1050-1100°C and kept at this temperature for 4-20 hours, and then heated to 1200-1220°C and kept at this temperature for 40-70 hours. After the heat preservation is completed, the steel ingot is taken out of the furnace for forging;

[0042] Specifically, for the steel ingot prepared in step S1, the cast microstructure of the steel ingot after cooling is as follows: Figure 1 As shown in the figure, there is obvious dendrite segregation in the alloy steel ingot. In order to determine the difference in element content between dendrite rods and dendrites in the as-cast structure, EDS analysis was performed on the sample, as shown in the figure. Figure 2 As shown, Figure 2 Region 1 is located between dendrites, and a large amount of carbonitrides exist between dendrites; Region 2 is located in the dendrite rods. The EDS element analysis results of Region 1 and Region 2, W1 and W2, are shown in Table 2 and Figure 3 As shown:

[0043] Table 2 Element analysis results of Area 1 and Area 2 Analysis table of W1 and W2

[0044] element <![CDATA[W1(wt,%)]]> <![CDATA[W2(wt,%)]]> <![CDATA[W1 / W2]]> S K 0.72 0.32 2.3 Nb 0.81 0.40 2.0 TiK 3.19 1.71 1.9 KK 14.62 16.28 0.9 FeK 6.94 8.55 0.8 NiK 71.95 71.31 1.0

[0045] In addition to the high content of Nb and Ti in the interdendritic region, the content of Si in the interdendritic region is also relatively high, and its segregation index (concentration of solute elements in the interdendritic region / concentration of solute elements in the dendrite rod) is 2.3, the segregation index of Nb is 2.0, and the segregation index of Ti is 1.9; the segregation indexes of Cr and Fe are 0.9 and 0.8 respectively; Figure 2 The analysis results of regions 3, 4 and 5 are consistent with those of regions 1 and 2. Therefore, in view of the dendrite segregation in the X-750 alloy steel ingot, the ESR steel ingot before forging is homogenized. The homogenization process is as follows: Figure 4As shown in the figure, the cold ingot is heated. Considering that the ESR ingot used for X-750 large forgings for nuclear power is relatively large, two isothermal steps are set during the heating process of the ingot to reduce the temperature difference between the inside and outside of the ingot during the heating process. The isothermal temperatures of the two isothermal steps are set to 600-650°C and 1050-1100°C respectively. The holding temperature for homogenization treatment is 1200-1220°C, and the holding time is 40-70 hours. The setting of the above-mentioned 1050-1100°C holding step also takes into account that the holding in this temperature range can dissolve part or all of the secondary carbonitrides connected in a network into the matrix, so that the alloy elements participate in the diffusion. The polished metallographic photos of the X-750 alloy ingot before and after diffusion are shown in FIG. Figure 5 As shown in Figure 2, the primary carbonitrides in the steel ingot are connected into a network by the secondary carbonitrides, such as Figure 5 Figure a on the left shows the cast state (before homogenization treatment); after homogenization treatment, the secondary carbonitrides are dissolved into the alloy matrix, such as Figure 5 Figure b on the right shows the homogenization treatment. The dissolution of secondary carbonitrides can improve the forging performance of the forging blank. The primary and secondary carbonitrides in the X-750 alloy are mainly (Ti, Nb)(C, N).

[0046] S3: Forging: Forging the steel ingot after homogenization treatment; Specifically, forging includes two steps of blanking and forming in sequence, and the blanking step includes upsetting-drawing-upsetting; the forging temperature range of the blanking step is 1100-1220℃, and the deformation of each fire is 40-60%; the forging temperature range of the forming step is 1000-1200℃, and the forming step is not limited to one fire, and forging is allowed to be stopped. The intermediate forging process (if any) is water-cooled as required, and the subsequent forging blank is reheated for forging, and the heating process is set to keep warm. The insulation temperature of the first step is 600-650℃, and the insulation temperature of the second step is 1050-1100℃. Except for the isothermal process, the heating process is as fast as possible, which is controlled to be ≤140℃ / h. The insulation temperature range of the forging billet is 1160-1200℃, preferably 1170-1190℃. The forging billet is fully heated through. After the insulation is completed, it is taken out of the furnace for forging. The deformation of each fire of the forging hole expansion is 20-50%; the final forging temperature of the billet opening step is not less than 1100℃, and the final forging temperature of the forming step is not less than 1000℃.

[0047] In step S3, it is worth mentioning that: in order to determine the reasonable forging temperature range for the forging step and the forming step, the inventors conducted a large number of experimental studies and theoretical analyses, and carried out solution annealing treatment on a group of samples from ingots and another group of samples from forgings. The annealing temperature range is 900℃~1200℃, with intervals of 50℃, and a total of 7 annealing temperatures, namely 1200℃, 1150℃, 1100℃, 1050℃, 1000℃, 950℃, and 900℃. After annealing for 10 hours, the samples are water-cooled to determine the effect of annealing temperature on secondary (Ti, Nb) (C, N), which is called the first group of experiments; and the samples at 1100℃, 1150℃ and 1200℃ were not homogenized before solution annealing, while the samples at the other four temperatures were homogenized before solution annealing. The metallographic structure of the polished sample after solution annealing is as follows: Figure 6 (a-g) As shown. In the samples annealed at 1100℃, 1150℃ and 1200℃, the secondary (Ti, Nb) (C, N) dissolved in the alloy matrix, and the structure of the network carbonitride was weakened; in the sample annealed at 1050℃, a small amount of secondary (Ti, Nb) (C, N) precipitated, as shown in Figure 6 As shown in (d). The samples kept at 1000℃, 950℃ and 900℃ have more secondary (Ti, Nb) (C, N) precipitation, which has connected part of the primary (Ti, Nb) (C, N) into a network. However, since the holding temperature will also affect the diffusion rate of Ti, Nb, C, and N elements, the three samples at 1000℃, 950℃ and 900℃ do not show the trend of more severe precipitation as the holding temperature is lower. From the above analysis, it can be seen that the precipitation and dissolution of secondary (Ti, Nb) (C, N) carbonitrides are reversible in the temperature range of 900℃ to 1200℃, and due to heredity, when the holding temperature is lowered, the Ti, Nb, C, and N elements that have dissolved into the matrix are easy to re-aggregate and grow at the original precipitate position, which has an adverse effect on the forgeability of the forging blank. This heredity can be weakened after the forging blank is fully forged. Figure 6As shown in (h), the fully forged sample was annealed at 950℃ for 10h and then water-cooled. Except for the observation that the primary (Ti, Nb)(C, N) had been broken and dispersed, no aggregated and grown secondary (Ti, Nb)(C, N) was observed. The distribution of (Ti, Nb)(C, N) in the other five groups of forged samples annealed at 1000℃~1200℃ was the same as that of the sample annealed at 950℃. Through the above analysis of the precipitation and dissolution of secondary (Ti, Nb) (C, N), it can be known that the secondary (Ti, Nb) (C, N) of the alloy that has not been fully forged can be dissolved into the matrix when the temperature is greater than 1100°C, and when the temperature is 1050°C or below, the secondary carbonitrides of (Ti, Nb) (C, N) will re-precipitate. Therefore, the final forging temperature of the alloy billet that has not been fully forged is set at above 1100°C. In the production process, the final forging temperature of the forging blanking steps (upsetting-drawing-upsetting) is set to not less than 1100°C to ensure the forgeability of the forging blank.

[0048] After the forging blank is fully upset and drawn, the primary (Ti, Nb) (C, N) is fully crushed, and the secondary (Ti, Nb) (C, N) is dissolved into the matrix. The forgeability of the forging blank is enhanced, and the later forming forging can be carried out. In addition to considering the shape of the forging in the later forming forging, another thing that needs special attention is the grain size control of the forging. The samples taken from the forging blank (water-cooled after forging) are used to determine the effect of heating temperature on the grain size of the forging. This is called the second group of experiments. The heating system and cooling method are the same as those of the first group of experiments. The grain size of the second group of samples was observed after the corrosion was completed by water cooling. The results of the microscopic metallographic examination are as follows Figure 7 (a~g) As shown. At the three annealing temperatures of 1000℃, 1050℃ and 1100℃, the alloy underwent recrystallization, and a large number of annealing twins appeared in the samples. When the temperature rose to above 1150℃, the grains grew rapidly, while the two samples with solution annealing temperatures of 950℃ and 900℃ did not undergo effective recrystallization. In addition to grain size observation, the second group of samples was also subjected to room temperature KV impact tests. The KV impact value-solution annealing temperature curve drawn based on the test results is shown in Figure 8 As shown, Figure 8 The impact value corresponding to a certain temperature in is the weighted average of the impact values ​​of the three samples. Since it is difficult to directly measure the forgeability of the alloy billet at high temperature, the present invention attempts to use the impact value of the solution annealed sample to reflect the toughness and forgeability of the alloy at high temperature to a certain extent. Figure 8It can be seen that the impact value of the sample solution annealed at above 1000℃ is above 240J, and the impact value decreases slowly from 1200℃ to 1000℃. When the temperature drops to 950℃ and 900℃, the impact value of the sample drops sharply, and the impact value of the sample kept at 900℃ has dropped to about 130J. From the above experimental data, it can be seen that the billet still has good toughness above 1000℃ and its forgeability is good. Therefore, in the actual production process, the final forging temperature of the forming fire is set to be no less than 1000℃.

[0049] S4: Solution aging treatment: The forged parts are subjected to solution and aging treatment to obtain X-750 alloy large forgings. The solution temperature is 1050-1100℃, and the temperature is kept for 3-10 hours. The aging temperature is 650-710℃, and the temperature is kept for not less than 15 hours. The forgings have good final formability, and the grains are small and uniform. Fig. 9 As shown in the figure a on the left, Fig. 9 (a) shows the grain size of X-750 alloy forging after solution aging, and the inclusions are dispersed as shown in Fig. 9 As shown in the figure b on the right, Fig. 9 (b) Schematic diagram of inclusion distribution of X-750 alloy forgings after solution aging.

[0050] The preparation method of the present invention adopts electroslag remelting steel ingot as forging steel ingot through analysis of dendrite segregation in steel ingot of X-750 high temperature alloy, precipitation and dissolution of second phase in alloy, and adopts vacuum induction smelting electrode rod to increase the uniformity of components in steel ingot, and homogenization treatment improves obvious dendrite segregation in steel ingot, so that alloy elements participate in diffusion, improves the forgeability of subsequent forging blank, and creates favorable conditions for subsequent blank forging; the blank forging process further improves the forgeability of forgings, and enables it to ensure good toughness, expands the forging temperature range of forming step, reduces the terminal temperature, makes the final forging good, the forging grains are small and uniform, and finally successfully completes the forging of X-750 alloy forgings, and the size of forgings meets product requirements. At the same time, the above preparation method can be used to forge X-750 alloy large forgings with an outer diameter of 3000mm, and the outer diameter of the steel ingot used can be up to 700mm.

[0051] Example 2

[0052] A large X-750 alloy forging as described above, the large X-750 alloy forging is used for nuclear reactor internals. It is explained here that the X-750 material forgings used for nuclear reactor internals are not only large in size, but also have strict procurement technical conditions: the grain size is not coarser than grade 3; the fine system of precipitated phase (such as carbide, carbonitride, nitride, etc.) inclusions is not greater than grade 3, and the coarse system is not greater than grade 2; the room temperature KV impact is not less than 60J, and the yield strength Rp at 350℃0.2 Not less than 630MPa, tensile strength not less than 950Mpa; taking X-750 material compression spring forgings for nuclear reactor internals as an example, its dimensions are shown in Table 3 below:

[0053] Table 3 Dimensions of X-750 (GH4145) alloy compression spring forgings for nuclear reactor internals

[0054] Forging name Ingot equivalent cross-sectional dimensions (mm) Forging blank equivalent cross-sectional dimensions (mm) Forging outer diameter (mm) Forgings I ~θ550 ～110×270 ～2000 Forging II ~θ700 ～140×310 ～3000

[0055] For the application of X-750 material forgings in nuclear power equipment, due to equipment upgrades, the required forging specifications are constantly increasing. For example, the X-750 material compression spring forgings for nuclear reactor internals have increased from 2000mm to 3000mm, and the ESR steel ingot has increased from 550mm to 700mm. In addition, the high-temperature alloy material itself has a high alloy degree and elements are easy to segregate. Under the circumstances that there are already great difficulties in producing X-750 material compression spring forgings for nuclear reactor internals from 550mm outer diameter ESR steel ingots (low forging yield, easy cracking, difficult to control grain size and inclusions, etc.), further developing the production technology of 700mm outer diameter ESR steel ingot large forgings has posed an unprecedented challenge to the hot processing technology level of forging suppliers. Through the continuous efforts and exploration of the inventors, the X-750 alloy forgings prepared by the preparation method of the present invention, after aging and solution heat treatment, have a grain size of 3 to 4 levels, and the inclusions in the forgings are dispersed. The rating results meet the technical requirements of X-750 high-temperature alloy large forgings for nuclear power, and the comprehensive performance of the forgings is good. The mechanical properties test results of the forgings are shown in Table 4 below:

[0056] Table 4 Mechanical properties test results of X-750 (GH4145) alloy compression spring forgings for nuclear reactor internals

[0057]

[0058] The examples described in the present invention are merely descriptions of the preferred implementation modes of the present invention, and are not intended to limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various modifications and improvements made to the technical solutions of the present invention by engineers and technicians in this field should all fall within the protection scope of the present invention.

Claims

1. A method for manufacturing a large X-750 alloy forging, characterized in that: The following steps are involved: S1: Ingot preparation: vacuum induction smelting electrodes followed by electroslag remelting to smelt ingots; S2: Homogenization treatment: homogenization treatment of the steel ingot; S3: Forging: Forging the steel ingot after homogenization treatment. The forging includes two steps: blanking and forming. The blanking step includes upsetting-drawing-upsetting. The forging temperature of the blanking step is 1100~1220℃, and the deformation of each fire is 40~60%; the forging temperature of the forming step is 1000~1200℃; S4: Solid solution and aging treatment: The forged parts are subjected to solid solution and aging treatment to finally obtain X-750 alloy large forgings; The homogenization treatment in step S2 includes heating the steel ingot to 600-650° C. and keeping it for 2-10 hours, then heating it to 1050-1100° C. and keeping it for 4-20 hours, and then heating it to 1200-1220° C. and keeping it for 40-70 hours; In step S4, the solution temperature is 1050-1100° C., and the insulation time is 3-10 hours. The aging insulation temperature is 650-710° C., and the insulation time is not less than 15 hours.

2. The method for manufacturing a large X-750 alloy forging according to claim 1, characterized in that: The forming step in step S3 is not limited to being completed in one fire, and the deformation amount of each fire of the final forging hole expansion is 20-50%.

3. An X-750 alloy large forging manufactured by the manufacturing method of the X-750 alloy large forging according to any one of claims 1 to 2, characterized in that: The outer diameter of the X-750 alloy large forging is 3000 mm, and the outer diameter of the steel ingot is 700 mm.

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