JP6171762B2 - Method of forging Ni-base heat-resistant alloy - Google Patents

Description

  The present invention relates to a Ni-base heat-resistant alloy forging method, and more particularly to a forging method for obtaining a thick cylindrical forged product having a diameter of more than 200 mm.

As a method of processing a material to be processed made of a Ni-base heat-resistant alloy into a cylindrical shape, a processing method by four-side forging has been conventionally known.
In this four-side forging process, as shown in FIG. 7, tools 102 arranged on four sides every 90 ° around the outer periphery of the workpiece 100 are simultaneously pushed into the workpiece 100 from four directions perpendicular to the axis. The impact is applied, and the movement is repeated while rotating the workpiece 100 little by little and further while feeding the workpiece 100 little by little in the axial direction to apply a reduction to the workpiece 100 and process it into a circular cross section.

The four-side forging process has an advantage that the material to be processed can be processed at a high speed, and therefore, even a difficult-to-process material can be processed.
If the processing speed is slow, the material to be processed cools in the middle of processing, and in this case, if the material to be processed is difficult to process, it becomes impossible to process. In other words, since it is possible to finish the processing before the material to be processed is cooled and hard and the deformation resistance becomes large, even a difficult-to-process material can be processed.

On the other hand, in this four-side forging process, the reduction ratio of the process cannot be taken large, and the strain can be imparted by the process is limited to the range from the surface to the near position.
In general, in this four-side forging process, when the diameter is close to 200 mm, it becomes difficult to sufficiently impart distortion to the central portion of the cross section of the material to be processed, and the shape that can be processed is limited to a small diameter of less than 200 mm. There is a problem.
This is because sufficient strain is not applied to the central portion of the cross section, and it is difficult to sufficiently refine the crystal grains in the central portion by recrystallization.

Mechanical properties such as high-temperature tensile strength, impact properties, and fatigue properties of Ni-base heat-resistant alloys depend on the grain size of the Ni-base heat-resistant alloys.
Ni-based heat-resistant alloy is an austenite single-phase material, so it is impossible to refine crystal grains using phase transformation, and by recrystallizing the crystal by hot working (hot forging) at a temperature higher than the recrystallization temperature. Although crystal grains are refined, in the case of a four-side forging process, when it becomes a large cylindrical member having a diameter exceeding 200 mm, it is difficult to sufficiently exert the effect of crystal refinement by recrystallization on the center of the cross section. Therefore, the application is limited to a small diameter of less than 200 mm.

As a method for processing a large-diameter columnar member made of a Ni-base heat-resistant alloy having a diameter exceeding 200 mm, there is another processing method by rolling, but also in the case of processing by rolling, a large-diameter columnar member On the other hand, it is difficult to give sufficient distortion until it reaches the center.
Accordingly, even in the case of rolling, it is difficult to refine the crystal grains by recrystallization while giving sufficient strain to the center.

In addition, as prior art to the present invention, in Patent Document 1 below, as a method for processing a Ni-based heat-resistant alloy, first, forging is performed on a material to be processed, and then corner reduction is applied to the material to be processed after forging. It is disclosed that a shaping process is performed to make this polygonal, and then a four-side forging process is performed.
However, in the one disclosed in Patent Document 1, the forging process corresponding to the rough forging process does not repeat upsetting and forging process, but is merely a forging process. And different.

As another prior art to the present invention, the following Patent Document 2 discloses an invention relating to “a method for producing a Ni-base heat-resistant alloy”, in which a reduction rate per impact is obtained at a forging temperature of 940 ° C. or more and 1000 ° C. or less. It is disclosed that the crystal grain size can be made uniform and fine by performing processing at 7% or more at the same location at least twice.
However, even in this Patent Document 2, although the point of forging is disclosed, there is no disclosure of the point for rough forging by combining upsetting and forging, and a columnar material having a large diameter of more than 200 mm is used. There is no disclosure of points obtained by forging, which is different from the present invention.

  Further, as another prior art, the following Patent Document 3 discloses an invention about a “forging method of a Ni-base superalloy”, in which a Ni-base superalloy ingot is heated at 1050 ° C. and forged by a high-speed four-side forging machine. Then, after forming a φ200 mm primary forging product, a secondary forging is performed using a high-speed four-side forging machine at a lower temperature of 960 ° C., and a φ118 mm secondary forging product is formed. Yes.

In the technique disclosed in Patent Document 3, the temperature of secondary forging is lowered and the deformation resistance is increased so that strain is applied to the inside, thereby reducing the crystal grains.
However, even the one disclosed in Patent Document 3 only discloses the point for forging, the point for rough forging by combining upsetting and forging, and forging prior to high-speed four-side forging. There is no disclosure about the point of rough forging combined with stretching and upsetting, which is different from the present invention.

JP-A-11-342443 Japanese Patent Laid-Open No. 2008-200320 Japanese Patent Laid-Open No. 3-64435

  The present invention is based on the above circumstances, and can process and form a cylindrical forged product having a diameter of more than 200 mm made of a Ni-base heat-resistant alloy and refines the crystal until it reaches the center. It is made for the purpose of providing the forging method which can be used.

  Thus, the content of claim 1 is by mass: Cr: 17.0 to 21.0%, Co: 11.0 to 13.0%, Mo: 8.0 to 12.0%, Al: 1.0 to 2.0%, Ti: 2.5 to 4.0%, Fe: ≦ 6.0%, B: 0.001 to 0.020%, C: ≦ 0.15%, a rough forging process as a pre-processing for a workpiece made of a Ni-based heat-resistant alloy having a composition of the balance Ni and inevitable impurities, The forging process is performed by processing and forming the treated material into a cylindrical forged product having a cross-sectional diameter exceeding 200 mm in diameter, and in the rough forging process, after soaking at 1180 to 1280 ° C. in advance, The upsetting with a reduction ratio of 20% or more and the forging with a reduction ratio of 20% or more are repeated twice or more for the treated material after the soaking, and the final upsetting and forging in the rough forging process are performed. The final stage process including stretching is defined as a grain size adjusting process of crystal grains, and upsetting and forging before the grain size adjusting process are 1030 to 115. In the final stage particle size adjustment step, upsetting and forging are performed at a low temperature of 1030 to 1080 ° C., and the forging is performed until the core reaches the center of the processed material after rough forging. The forged product having a fine grain structure equal to or larger than the set crystal grain size required for a product, and having the target material in the target shape while ensuring the set crystal grain size at a temperature of 1080 ° C. or lower and 1030 ° C. or higher in the finish forging process. It is characterized in that it is molded.

  According to a second aspect of the present invention, in the first aspect, the upsetting and forging before the grain size adjusting step in the rough forging process are performed at a temperature of 1100 to 1150 ° C.

  According to a third aspect of the present invention, in any one of the first and second aspects, as the finish forging process, a cross-section of the material to be processed is performed by performing corner reduction on the material to be processed having a quadrangular cross section after the rough forging process. A four-side forging process is performed, in which the shape is shaped into a polygonal shape with more than four corners by forging, as a preparatory process, and the workpiece is simultaneously hit from four directions perpendicular to the axis. It is characterized by that.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the set crystal grain size is ASTM crystal grain size No. 4 or more.

Effects and effects of the invention

  The Ni-base heat-resistant alloy in the present invention is a high-strength Ni-base alloy with a high tensile strength at high temperatures, containing 17.0-21.0% Cr, 11.0-13.0% Co, and 8.0-12.0% Mo. It is a difficult-to-machine material that has a large deformation resistance during inter-machining.

In the present invention, such a hard-to-process Ni-base heat-resistant alloy is forged into a thick cylindrical member having a diameter of more than 200 mm as follows.
Specifically, in the present invention, the forging process is divided into a rough forging process as a pre-process and a finish forging process, and is finally processed into a forged product, that is, a large-diameter column having a diameter exceeding 200 mm.

In the present invention, roles are assigned to the rough forging process and the finish forging process as follows.
In the present invention, four-face forging is performed in finish forging.
As described above, this four-side forging process can be completed at a high speed and in a short time, and therefore, even a difficult-to-process material can be completed satisfactorily.
In the four-side forging process, the workpiece can be evenly processed in the circumferential direction, and the strain can be evenly applied to the surface layer and the area close to it, thus equalizing the structure in the circumferential direction. can do.

However, in this four-sided forging, sufficient strain is applied to the cylindrical member having a diameter of more than 200 mm until reaching the center portion, that is, the crystal grains are sufficiently formed by the sufficient strain applied to the center portion. It is difficult to miniaturize.
Therefore, in the present invention, the formation of the structure up to the center portion required for the final forged product, that is, the cylindrical member after finish forging is performed by the first rough forging. In other words, the role of the fine forging process is assigned to the rough forging process until reaching the center.

  For this reason, in the present invention, in the rough forging process, first, soaking at 1180 to 1280 ° C. is performed, and then the material to be treated after the soaking is set up at a reduction rate of 20% or more at a temperature of 1030 to 1150 ° C. And forging with a reduction rate of 20% or more at a temperature of 1030 to 1150 ° C. are repeated twice or more.

In this rough forging soaking, the MC crystallized product is dissolved in the matrix. The MC-type crystallized material that has been dissolved dissolves M6C-type carbides finely during the aging treatment after completion of forging, thereby strengthening the grain boundaries.
Here, the reason why the soaking temperature is set to 1180 ° C. or more is that the MC type crystallized product cannot be sufficiently dissolved at a temperature lower than this.
On the other hand, if it exceeds 1280 ° C., the Ni-base heat-resistant alloy will cause local melting.

In the present invention, by performing a combination of upsetting and forging under the above conditions, sufficient strain is imparted to the entire material to be processed until reaching the center by rough forging. As a result, immediately after the upsetting and forging processes, the crystal grains of the material to be processed are sufficiently refined until reaching the center.
That is, a fine grain structure having a grain size larger than the set crystal grain size required for the final forged product until reaching the center.
In the final finish forging process, the material to be processed is formed into a forged product having the target shape by four-face forging while ensuring the set crystal grain size at a temperature of 1080 ° C. or lower.

In the present invention, upsetting at a rolling reduction rate of 20% or more is performed by rough forging, and sufficient strain is applied to the central portion of the material to be processed (strain amount is 0.22 or more). By being able to give.
Similarly, forging at a reduction rate of 20% or more is because sufficient strain (a strain amount of 0.22 or more) can be imparted to the central portion of the material to be processed by processing at such a reduction rate.
In other words, in the present invention, upsetting and forging are performed at a rolling reduction of 20% or more so that a sufficient strain amount of 0.22 or more can be imparted to the central portion in rough forging.
In addition, the processing of 20% or more of rolling reduction said here means the total rolling reduction of the process performed between reheats.

In this rough forging process, upsetting and forging are performed at a temperature of 1030 ° C. to 1150 ° C., respectively. If the temperature is less than 1030 ° C., recrystallization does not occur in the material to be processed regardless of the forging ratio. This is because crystal refinement cannot be expected.
On the other hand, when the temperature is higher than 1150 ° C., the temperature is too high, and the grain growth rate immediately after the upsetting and forging processes becomes too high, leading to the coarsening of the crystal grains.

In this rough forging process, if processing is performed at a high temperature close to 1150 ° C. even in the final process including final upsetting and forging, the grain growth of the crystal grains becomes faster at high temperatures, resulting in coarse crystals. Thus, the set crystal grain size required for the final forged product cannot be secured in the rough forging process.
Therefore, in the present invention, the final process including final upsetting and forging is set as the grain size adjustment process of the crystal grains, and in the grain size adjustment process, the upsetting and forging processes are performed at a low temperature of 1080 ° C. or less. Do.

  According to the present invention as described above, the structure of the forged product is set to a fine grain structure having a grain size equal to or larger than the set grain size, for example, the grain size of ASTM grain size No. 4 or more (Claim 4). While having a fine-grained structure, it can be satisfactorily processed into a large-diameter cylindrical forged product having a diameter of more than 200 mm.

The Ni-base heat-resistant alloy of the present invention is a difficult-to-process material, and before the particle size adjustment step in the rough forging process, the upsetting and forging processes can be performed at a high temperature of 1100 to 1150 ° C. that can relatively reduce deformation resistance. (Claim 2).
By performing upsetting and forging at such a temperature, it is possible to satisfactorily process them.
However, under such a high temperature, the crystal grains generated by recrystallization tend to grow rapidly and become coarse, but in the present invention, the grain size adjustment process at the end of the rough forging process has a low temperature of 1080 ° C. or lower. Since the upsetting and forging processes are performed at a temperature, the growth of crystal grains after processing can be suppressed, and the structure of the material to be processed can be retained in the fine structure until it reaches the center.

In this invention, the cross-sectional shape of the to-be-processed material after rough forging can be made into a square shape.
On the other hand, in the above-mentioned four-side forging process in the finish forging process, the final shape is a circular cross section. In this four-face forging process, a cross-sectional shape whose initial shape is close to a circle is basically made into a circular cross-section, and the diameter is gradually reduced by repeating this.
In this case, it is difficult to directly perform a four-side forging process on the workpiece having a quadrangular cross section after the rough forging process.

  Therefore, according to claim 3, as a preparatory process prior to four-side forging in finish forging, corner reduction is performed on the material to be processed after rough forging, so that the cross-sectional shape of the material to be processed is less than four by forging. It is desirable to perform a shaping process to shape the polygonal shape having a large number of corners.

  This shaping process basically adjusts the cross-sectional shape of the material to be processed to a shape close to a circle by reducing the corners, and, due to the nature of the processing, applies sufficient strain until it reaches the center of the material to be processed. Although it is difficult, in the present invention, the rough forging process adds the necessary strain to the material to be refined, and the final forging process only holds the fine structure. And even when performing a four-face forging process, the microstructure of the forged product can be made a fine structure until it reaches the center.

Here, in the finish forging process, it is possible to apply a strain greater than a certain level due to processing to the central portion of the material to be processed, specifically, the strain necessary for making the crystal grains further finer than the crystal grains after the rough forging process. What is necessary is just to perform the process for performing the final shape required for a forged product.
That is, in the finish forging process, the material to be processed may be formed into a final cross-sectional shape. In the present invention, finish forging plays a role for shaping.

Next, the reason for adding each component and the reason for limiting the amount added in the Ni-base heat-resistant alloy of the present invention will be described.
Cr: 17.0-21.0%
If Cr is less than 17.0%, heat resistance is insufficient, and if over 21.0% is contained, a large amount of carbides such as M ₂₃ C ₆ are generated and ductility is lowered, so the content is made 17.0-21.0%.

Co: 11.0-13.0%
If Co is less than 11.0%, heat resistance is insufficient, and if it exceeds 13.0% and excessively contained, a compound with Al and Ti that does not intend to precipitate is formed, resulting in insufficient hot strength, so the content is made 11.0-13.0% .

Mo: 8.0-12.0%
If Mo is less than 8.0%, heat resistance is insufficient, and if it exceeds 12.0% and excessively contained, excessive carbides such as M ₂ C and ductility are lowered, so the content is set to 8.0 to 12.0%.

Al: 1.0-2.0%
Al is less than 1.0%, causing insufficient strength due to Ni ₃ (Al, Ti) deficiency. If it exceeds 2.0% and excessively contained, ductility decreases due to excessive Ni ₃ Al precipitation, so the content is 1.0 to 2.0%. And

Ti: 2.5-4.0%
When Ti is less than 2.5%, Ni ₃ (Al, Ti) lacks strength, and when it exceeds 4.0%, Ni ₃ (Al, Ti) becomes excessive and TiC becomes excessive, resulting in ductility. In order to decrease, the content is set to 2.5 to 4.0%.

Fe: ≤6.0%
Fe is restricted to 6.0% or less in order to prevent unintended changes in components due to the formation of various compounds.

B: 0.001 to 0.020%
When B is less than 0.001%, the grain boundary strength is insufficient, and the target creep characteristics cannot be achieved. If it exceeds 0.020%, the grain boundary strength due to BN crystallization decreases, so the content is 0.001 to 0.020%.

C: ≤ 0.15%
If C is contained excessively exceeding 0.15%, TiC, CrC, MoC is excessive and ductility is lowered, so the content is made 0.15% or less.

It is the figure which showed the process of the rough forging process in the Example of this invention. It is the figure which showed the crystal grain size of each processed goods at the time of performing the rough forging process. It is the figure which showed the distortion amount of each processed goods at the time of performing the rough forging process. It is the figure which showed the process of the shaping process after the rough forging process. It is the figure which showed the process of the 4 face forging process following a shaping process with the distortion amount of a workpiece. It is the figure which showed the crystal grain size of each processed goods at the time of performing the rough forging process of a comparative example. It is explanatory drawing of the processing method by a conventionally well-known four surface forging.

Next, examples of the present invention will be described below.
The Ni-base heat-resistant alloy having the chemical composition shown in Table 1 was melted in a vacuum induction furnace, and further electroslag remelting (ESR) was performed to obtain a 2.5-ton Ni-base heat-resistant alloy ingot.
The processed material (material to be processed) obtained from the ingot is then subjected to rough forging as described in detail below, followed by shaping by forging and four-sided forging as final forging, and the final forged product A cylindrical forged product having a diameter of more than 200 mm and a diameter of 374 mm was obtained.
The details of the process will be described below.

Table 2 and FIG. 1 specifically show the contents of the first rough forging process.
As shown in Table 2 and FIG. 1, in the rough forging process, first, a soaking process (soaking process) is performed on a processed material (processed material) 10 (φ530 mm × 1245 mm) at 1200 ° C. × 30 hr. went. By this soaking treatment, the workpiece 10 was uniformly heated to 1200 ° C. until it reached the center, and the MC type crystallized product was dissolved in the matrix.
The numerical value in the column of forging temperature in Table 2 indicates the temperature (material surface temperature) at the start of processing (except for forging (4)) in the leftmost column of Table 2.

Next, upsetting (1) was performed in a state where the temperature of the workpiece 10 was lowered to 1150 ° C. to obtain a workpiece (processed material; the same applies hereinafter) 12-1 having a diameter of 750 mm and a length of 625 mm. The number of hits at this time was 1.
Thereafter, rework (1) is performed on the processed product 12-1 under the conditions of 1150 ° C. × 3 hr, and forging (1) is performed. A cross section 4 having a cross section of 500 × 550 mm and a length of 1000 mm is obtained. A square shaped workpiece 12-2 was obtained.

Subsequently, rework (2) is performed on the processed product 12-2 under the condition of 1150 ° C. × 3 hr, and then forging (2) is performed, so that the cross section has a cross section of 500 × 500 mm and a length of 1100 mm. A shaped processed product 12-3 was obtained. The number of hits in this forge (2) was 8.
At this time, the processing rate in forging (2) is small, and the rolling reduction is less than 20%.
After that, reheat (3) is further performed under the conditions of 1150 ° C. × 3 hr, and then the workpiece 12-3 is placed (2) at 1150 ° C. to obtain a cross section of 797 × 797 mm and a length of 550 mm. A processed product 12-4 having a square cross section was obtained.

Next, forging (3) was performed at a temperature of 1080 ° C. to obtain a processed product 12-5 having a square cross section of 500 × 500 mm and a length of 1100 mm.
Subsequently, after reheating (4) under conditions of 1080 ° C. × 3 hr, upsetting (3) is performed, and a processed product 12-6 having a cross-sectional square shape having a cross section of 797 × 797 mm and a length of 550 mm is obtained. Obtained.

Subsequently, forging (4) was performed to obtain a processed product 12-7 having a square cross section of 500 × 500 mm in cross section and 1100 mm in length.
In Table 2, forging (4) is carried out after heating (3) after reheating (4) and without subsequent heating, and the surface temperature of the material is the amount of time elapsed. It is lower than 1080 ° C. Therefore, in Table 2, the temperature corresponding to forge (4) is shown in parentheses.

Center part (longitudinal and radial center part), D / 4 part (longitudinal center) of each process (that is, each processed product 12-1 to 12-7) when rough forging as described above is performed 2 shows the crystal grain size (ASTM grain size number) immediately after processing of each part of the surface layer (the middle part between the radial center part and the surface layer) and the surface layer (surface layer at the longitudinal center part), and the amount of distortion is shown in FIG. Respectively.
As shown in these figures, in this rough forging process, in any process except forging (2), the amount of strain in each part of the processed material 10 and each processed product is reduced by recrystallization. Exceeds 0.22, which is necessary in particular, in this case, 0.25.

Further, in the final stage of the rough forging process (here, forging (3) and subsequent processes), since the processing temperature is set to a low temperature of 1080 ° C. or less, the grain growth of the crystal grains during and after the processing is effective. The material to be processed after rough forging, that is, the structure of the processed product 12-7, has a fine grain structure with a grain size of ASTM grain size No. 4 or more until it reaches the center.
This fine-grained structure is a fine structure that satisfies the set grain size number required for the final forged product, that is, a φ374 mm cylindrical member.

After performing the rough forging as described above, finish forging was performed. In the finish forging process, first, before the final four-side forging process, a shaping process by forging, which is a preparation process, was performed.
In this shaping process, as shown in FIG. 4, first, relative to the processed product 12-7 having a square shape of 500 × 500 in the cross-sectional shape finally obtained by the rough forging process, the diagonal direction is relatively set. The cross-sectional shape is reduced to a hexagonal shape by performing a reduction (corner reduction) on a pair of facing corners, and then a cross-sectional shape is obtained by performing a reduction (corner reduction) on a pair of corners facing in the opposite diagonal direction. An octagonal processed product 14-2 was obtained. The width dimension of the cross section of the processed product 14-2 is 440 mm.
In this shaping process by forging, a process for eliminating the swelling of the flat portion between the corners caused by the corner pressure is also performed, and reheating is performed during that time.

In the shaping process by forging shown in FIG. 4, a strain amount of 0.22 or more required for refining the crystal by recrystallization is not applied to the central portion, and here 0.25 or more is not applied.
That is, the shaping process by forging here is a process with a small process amount that does not give such a strain amount to the central part. This is because the finish forging process is mainly intended to shape the cross-sectional shape of the material to be processed into a target cross-sectional shape.

After finishing the shaping process as described above, a four-side forging process was performed as a final forging process.
In this four-side forging process, tools placed on four sides at positions separated by 90 ° around the outer periphery are simultaneously driven into the final workpiece 14-2 having an octagonal cross section shown in FIG. As shown in FIG. 5, the workpiece 16-1 having a circular cross section of φ420 mm is first formed, and then the workpiece 16-2 having a cross section of φ400 mm and a workpiece 16-3 having a diameter of φ380 mm are formed by gradually reducing the diameter. Finally, a forged product 18 having a diameter of 374 mm was obtained.

The amount of distortion of each part in each process, that is, each processed product 16-1, 16-2, 16-3, and forged product 18, was as shown in FIG.
Incidentally, the crystal grain size in the final forged product 18 after the four-surface forging was ASTM grain size No. 4, D / 4 part was No. 5, and the surface layer was No. 5 in the center.

As described above, in this embodiment, although it was a cylindrical forged product having a diameter of 374 mm, a product having a fine grain structure of ASTM grain size No. 4 or more was obtained well until it reached the center. .
This is a processed product having a crystal grain size equal to or larger than the ASTM crystal grain size required for the central part of the final forged product 18 by rough forging before the final forging process in which a strain amount of 0.25 cannot be applied to the central part. This is because 12-7 is processed and formed.

Incidentally, FIG. 6 shows a comparative example. In FIG. 6, up to forging (2), the same processing as that up to forging (2) in the rough forging step of the embodiment of the present invention is performed. . Therefore, the ASTM grain size of the processed product at each processing stage is the same as that in the example.
However, in this comparative example, forging (3) is the final processing, and the processing is performed at a high temperature of 1150 ° C. As a result, the crystal grain size at the center of the final processed product in the rough forging process is ASTM crystal grain size No. 2.5, which is smaller in grain size number than ASTM crystal grain size No. 4, that is, the crystal grains are coarse and coarse. there were.

  Although the embodiment of the present invention has been described in detail above, this is merely an example, and the present invention can be implemented in variously modified forms without departing from the spirit of the present invention.

10 Processed material (treated material)
12-1, 12-2, 12-3, 12-4, 12-5, 12-6, 12-7, 14-1, 14-2, 16-1, 16-2, 16-3 Material to be treated)
18 Forged products

Claims (4)

In mass%
Cr: 17.0-21.0%
Co: 11.0-13.0%
Mo: 8.0-12.0%
Al: 1.0-2.0%
Ti: 2.5-4.0%
Fe: ≤6.0%
B: 0.001 to 0.020%
C: ≤ 0.15%
A rough forging process as a pre-process for a material to be processed made of a Ni-base heat-resistant alloy having a composition of the balance Ni and inevitable impurities, and a cylindrical forging with a large diameter with a cross-sectional shape exceeding 200 mm in diameter. In the rough forging process, after soaking at 1180 to 1280 ° C. in advance, the reduction ratio is 20% or more with respect to the treated material after the soaking. The upsetting and forging with a reduction ratio of 20% or more are repeated twice or more, and the final stage including the upsetting and forging in the rough forging process is used as the grain size adjusting step for the grain size. The previous upsetting and forging are performed at a temperature of 1030 to 1150 ° C., and in the final stage particle size adjustment process, the upsetting and forging are performed at a low temperature of 1030 to 1080 ° C. The organization up to the center The fine forged product has a fine grain structure that is equal to or greater than the set crystal grain size. In the finish forging process, the forging of the target material is the target shape while securing the set crystal grain size at a temperature of 1080 ° C. or lower and 1030 ° C. or higher A forging method of a Ni-base heat-resistant alloy characterized by forming into a product.   The forging method for a Ni-base heat-resistant alloy according to claim 1, wherein upsetting and forging before the grain size adjusting step in the rough forging process are performed at a temperature of 1100 to 1150 ° C.   3. The finish forging process according to claim 1, wherein corner finishing is performed on the material to be processed having a quadrangular cross section after the rough forging process so that the cross sectional shape of the material to be processed is more than square. Ni-base, characterized by performing four-side forging that simultaneously strikes the material to be treated from four directions perpendicular to the axis after shaping as a preparatory process for shaping into a large number of polygonal shapes by forging Forging method of heat-resistant alloy.   4. The forging method for a Ni-base heat-resistant alloy according to claim 1, wherein the set crystal grain size is ASTM crystal grain size No. 4 or more.

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