JP2014161861A5 - - Google Patents

Description

Free forging method of Ni-base heat-resistant alloy member

  The present invention relates to a free forging method for a Ni-base heat-resistant alloy member.

  Ni-base heat-resistant alloys are widely used in aircraft engines, turbine turbines for power generation, and the like that require high tensile strength and fatigue strength at high temperatures. Inconel (registered trademark) 718 is a typical example, and has a composition of 0.04C-19.0Cr-52.5Ni-3.05Mo-5.13Nb-0.90Ti-0.50Al-18.5Fe.

The mechanical properties of Ni-base heat-resistant alloys such as high-temperature tensile strength, impact properties, and fatigue properties depend on the crystal grain size of the Ni-base heat-resistant alloys. Get higher.
Since Ni-base heat-resistant alloys are austenite single-phase materials, crystal grains cannot be refined using phase transformation, and crystals are recrystallized by hot forging at a temperature higher than the recrystallization temperature and subsequent heating and holding. A technique for refining crystal grains by suppressing the growth of recrystallized grains at the time is used.

As one of them, after precipitating the intermetallic compound Ni ₃ Nb called δ phase, the forging (hot forging) process is carried out below the δ phase solid solution temperature, and the pinning effect (pinning effect) by the precipitated δ phase The method of refining the recrystallized crystal grains is conventionally known.
Patent Document 1 listed below discloses a technique for refining crystal grains of a Ni-base heat-resistant alloy by this method.

  The pinning effect by the δ phase is also disclosed in Patent Document 2 below. That is, Patent Document 2 discloses that in the forging process of a Ni-base heat-resistant alloy, fine particles of an intermetallic compound (δ phase) having a function of pinning grain boundaries when the heating temperature is too high are dissolved in the matrix. There is a description that grain growth of crystal grains occurs.

In Patent Document 1, when a method of refining crystal grains by precipitation of a δ phase is applied to a manufacturing method in which a large forging ratio is applied at a high strain rate such as stamping forging, a part of the member is δ during forging. As the temperature rises above the solid solution temperature of the phase, there is a problem that it is difficult to obtain fine particles throughout, so that the temperature of the forged product does not exceed the δ phase solid solution temperature during forging Once forging is interrupted and heated again to forge, and when forging is divided into several times, the driving force for crystal grain refinement becomes smaller than when it is performed once. . It discloses the use of a finer product of 6 or more.
However, there is no disclosure of how much δ phase is precipitated as the initial δ phase in relation to the final target grain size before the final forging step.

  As mentioned in Patent Document 1, there is a problem of the crystal grain size of the material to be forged before the start of forging as a problem when miniaturizing crystal grains by forging (finish forging).

FIG. 9 schematically shows how recrystallization occurs and grows by forging and subsequent heating.
As shown in the figure, the crystal grains are deformed by forging, and recrystallized grains are generated along the grain boundaries of the deformed crystal grains.
The generated recrystallized grains then grow and gradually increase. However, if the initial crystal grains are coarse, the core does not reach the core and crystal growth due to recrystallization does not reach, and the core is not recrystallized ( It is easy to remain as a hatched part).
In particular, such a problem is likely to occur in the case of die forging that generally requires only one forging.

In contrast, in free forging, in which the same portion is usually hit several times and strain is applied, recrystallization is repeated from the grain boundaries of the recrystallized grains. It is easy to make it finer more effectively, and it is easy to lose unrecrystallized parts.
In this sense, free forging is a desirable forging method for making the crystal grains fine and uniform.

As described above, the technology for refining crystal grains using the pinning effect of the δ phase is a conventionally known technology, but the amount of precipitation of the δ phase and the degree of crystal grain refinement before the final forging process. The technology for controlling the grain size of the finally obtained crystal by controlling the amount of precipitation of the δ phase is not conventionally proposed.
That is, even if the δ phase precipitation treatment is performed to refine the crystal grains, it is considered difficult to sufficiently refine the crystal grains if the amount of precipitation of the δ phase is too small.
However, if the amount of precipitation of the δ phase is excessive, the crystal grains may be excessively refined.
Although the mechanical properties such as tensile strength, impact strength, and fatigue strength improve as the crystal grains become finer, it is known that the high temperature creep strength deteriorates when the crystal grains are excessively fine. .
In addition, the initial δ phase generated by the δ phase precipitation treatment has a needle-like form, and if this needle-like δ phase remains until the end, there arises a problem that mechanical characteristics are lost.
However, there has been no report on control of crystal grain refinement based on such a viewpoint.

As another prior art to the present invention, the following Patent Document 3 discloses an invention about a “Ni-base alloy forging / stretching method”, in which a processing material is used as a method for producing a billet from a Ni-base alloy ingot. The amount of compression caused by one stroke in the direction perpendicular to the feed direction is made small and cumulative deformation is applied, and the first strike position and the next strike position are shifted, and the cross section of the forge and stretch feed direction It is disclosed that the crystal grain size is made uniform.
However, the one described in Patent Document 3 is not different from the present invention in that there is no disclosure of the point that the crystal grains are refined by the pinning effect by the δ phase.

JP-A-6-293946 Japanese Patent Laid-Open No. 2008-200320 JP 2003-251429 A

  The present invention is based on the above circumstances, and when the crystal grains are refined by the pinning effect by the δ phase, the Ni-base heat-resistant alloy member can easily control the crystal grains to the desired crystal grains. It is made for the purpose of providing the free forging method of a heat-resistant alloy member.

  Thus, in the first aspect, Ni: 50 to 55%, Cr: 17 to 21%, Al: 0.2 to 0.8%, Ti: 0.6 to 1.2%, Nb: 4.7 to 5.6%, Mo: 2.8-3.3%, Co: ≤1.0%, C + Si + Mn + P + S + Cu + B: ≤1.1%, δ phase precipitation treatment for depositing δ phase in a needle shape for Ni-base heat-resistant alloy having the remaining Fe composition Thereafter, the forged material subjected to the δ phase precipitation treatment is heated at 920 to less than 1025 ° C. for 1 to 36 hours to partially dissolve the precipitated needle-like δ phase with separation, thereby precipitating the δ phase. A final forging process in which an initial amount adjusting process of the δ phase for adjusting the amount is performed, and thereafter, the free forging and reheating at which the striking is performed at a recrystallization temperature or more and a total reduction ratio of 33% or more is repeated at least once. It is carried out to obtain a Ni-based heat-resistant alloy member with refined crystal grains.

A second aspect of the present invention is characterized in that, in the first aspect, the δ phase precipitation treatment is performed in a temperature range of 800 to 1020 ° C. and a time range of 0.1 to 36 hr.

According to a third aspect of the present invention, in any one of the first and second aspects, the reheating is performed in a temperature range of 920 to 980 ° C.

Effects and effects of the invention

  As described above, the present invention includes Ni: 50 to 55%, Cr: 17 to 21%, Al: 0.2 to 0.8%, Ti: 0.6 to 1.2%, Nb: 4.7 to 5.6%, Mo: 2.8 to 3.3%, The present invention relates to a forging method for obtaining a Ni-base heat-resistant alloy member made of an Inconel 718 equivalent material having a composition of Co: ≦ 1.0%, C + Si + Mn + P + S + Cu + B: ≦ 1.1%, and the balance Fe.

According to the present invention, the final crystal grain size of the Ni-base heat-resistant alloy member can be easily set to a desired grain size.
In particular, according to the present invention, the final crystal grain size of the entire Ni-base heat-resistant alloy member can be set to ASTM No. 8 or more.

(Solution heat treatment of forged materials)
In the present invention, ST treatment (solution heat treatment) is performed in advance on the material to be forged (forged material). The ST treatment can be performed together with the processing for obtaining the material to be forged.
The processing is desirably performed at 1050 ° C to 1120 ° C.
If the temperature is lower than 1050 ° C., solid solution cannot be performed satisfactorily. In addition, cracking or the like occurs during processing, and processing cannot be performed satisfactorily.
On the other hand, the material melts at a high temperature exceeding 1200 ° C.

In the present invention, the crystal grain size of the material to be forged is previously adjusted to a predetermined grain size. The adjustment of the crystal grain size can be performed together with the above-described processing for obtaining the forged material. Specifically, the crystal grain size can be adjusted by appropriately adjusting conditions such as the heating temperature and heating time during processing and the processing amount.
The crystal grain size of the material to be forged (forging material) is ASTM No. In case of 8 or more, ASTM No. It is desirable to set it to 4 or more.

(Δ phase precipitation treatment)
In the present invention, the δ phase is deposited before the finish forging step.
The δ phase precipitation treatment mentioned here is a treatment for precipitating the δ phase intermetallic compound Ni ₃ Nb from a solid solution state, and this δ phase precipitation treatment causes the needle-like δ phase to enter the grain boundaries and grain boundaries. Precipitate.
Here, the δ phase precipitation treatment can be performed in a temperature range of 800 to 1020 ° C. and a time range of 0.1 to 36 hr.
If the temperature is too high, the amount of precipitation of the δ phase will be insufficient, while if it is too low, the amount of precipitation of the δ phase will be excessive.
In the present invention, it is desirable that the δ phase is precipitated in a total of 2% (volume%) or more and 13% or less in the grain boundaries and grains.
Preferably, the δ phase is precipitated under the condition of 915 ° C. × 36 hr.

(Δ phase initial amount adjustment processing)
In the present invention, the initial amount adjustment process of the δ phase is performed after the δ phase precipitation process.
Specifically, the needle-like δ phase precipitated by the previous δ phase precipitation treatment is partly solid-solved by heating and divided, and the amount of δ phase is adjusted to decrease. That is, the initial amount of the δ phase before the finish forging process is adjusted to an appropriate amount.
This initial amount adjustment process of the δ phase is a characteristic process in the present invention.
This treatment has a close causal relationship between the fineness of the crystal grain of the finally obtained Ni-base heat-resistant alloy member and the initial amount of the δ phase before the finish forging step, and the initial amount of the δ phase is the final amount. It is carried out in the present invention under the knowledge that it is a major factor that determines the fineness of the crystal grains that are obtained.

The δ phase, a part of which is partly dissolved by the initial amount adjustment processing of the δ phase, remains in the alloy while still maintaining the needle-like form.
As will be described later, the remaining needle-like δ phase is further divided by forging and reheating in the subsequent finishing forging process, and then solid-dissolved to form a fine spheroid, and the refined spherical δ phase has a pinning effect. To suppress grain growth of recrystallization during forging and reheating.
At that time, if the amount of the fine and spherical δ phase is large, the inhibitory effect on the grain growth of the recrystallized grains becomes large, and conversely if the amount is small, the inhibitory effect becomes small.

Even in this finish forging process, the δ phase gradually dissolves, so the δ phase in the alloy is less than the initial amount, but the amount of decrease is due to the processing conditions of the finish forging process, and further to the subsequent solution heat treatment, etc. Therefore, the reduction amount can be known in advance from the conditions such as processing.
Therefore, according to this, the amount of δ phase to be left in the initial amount adjustment processing of δ phase, that is, the initial amount of δ amount appropriate for the grain size of the crystal grain of the Ni-base heat-resistant alloy member to be finally targeted You can also know.
In other words, the final crystal grain size required for the Ni-base heat-resistant alloy member can be easily obtained by setting the δ-phase existing amount (initial amount) to an appropriate amount in the δ-phase initial amount adjustment process.
The appropriate initial amount of the δ phase differs depending on the subsequent processing, processing conditions, etc. Including this, the initial amount of the δ phase is 1.5% (volume%) or more in the present invention. , 10% or less is desirable.

As described above, the finer the final crystal grains of the Ni-based heat-resistant alloy member, the better. However, if the crystal grains become too fine, the high-temperature creep characteristics that are important mechanical characteristics deteriorate.
Conversely, if the crystal grains are coarse, other mechanical properties such as high-temperature tensile strength, fatigue strength, and impact properties deteriorate.
Therefore, the grain size of the crystal grain of the Ni-base heat-resistant alloy member also has an appropriate grain size.
In the present invention, the final appropriate crystal grain size can be easily obtained by adjusting the amount of the initial δ phase by the initial amount adjustment process of the δ phase.

In the present invention, for the adjustment of the initial amount of the δ phase, the δ phase is divided and partially dissolved by heating under a time condition of 920 to less than 1025 ° C. for 1 to 36 hours.
By controlling the heating temperature and heating time, the initial amount of the δ phase can be adjusted to the required amount.
Here, the heating temperature is set to 920 ° C. or more. If the temperature is lower than this, partial dissolution of the δ phase is difficult to proceed, and it takes an extremely long time to obtain the initial amount to be obtained, or the δ phase Partial solid solution cannot be performed well.
On the other hand, when the temperature is higher than 1025 ° C., the solid solution temperature of the δ phase is exceeded, and the entire δ phase is dissolved in the matrix.
Also, if the time condition is less than 1 hour, it is difficult to perform partial solid solution with acicular δ phase separation, and if it exceeds 36 hours, the treatment time becomes too long and the productivity deteriorates. End up.

In the initial amount adjustment process of the δ phase of the present invention, prior to the above-described decomposition and partial solution treatment of the δ phase by heating, forging (preliminary treatment) is performed as a pretreatment for promoting the fragmentation and partial solution of the acicular δ phase. Forging) can be performed.
That is, the initial amount adjustment process of the δ phase can include a preliminary forging process and a δ phase division / partial solution process by heating.

By performing such a preliminary forging process in advance, it is possible to promote the splitting / partial solution of the needle-like δ phase during subsequent splitting / partial solution treatment of the δ phase by heating. The δ phase is easily refined and spheroidized in the forging process.
Here, various processing methods can be applied as preliminary forging. The forward extrusion process is a preferable processing method as the pre-forging processing method.
A processing temperature of 800 to 980 ° C. and a processing rate (area reduction rate) of 15 to 60% can be suitably employed.

The pre-forging process prior to the δ phase splitting and partial solid solution treatment by this heating is not limited to the above-mentioned acicular δ phase splitting and partial solid solution processing, but also the crystal of the forged material before the final forging process. It has the significance that the grains can be refined in advance.
And this makes it easy to obtain fine crystal grains in the finish forging process, and by controlling the grain size of the crystal grains before the finish forging process in advance by setting the processing conditions during the preliminary forging process, It becomes easy to control the grain size of the final crystal grains after the forging process.

(Finish forging process)
In the present invention, after the above-described initial amount adjustment processing of the δ phase, a finishing forging step is performed in which forging (free forging) in which the material to be forged is squeezed by striking (free forging) and reheating are repeated at least once.
The initial δ phase in the form of needles remaining in the alloy is divided, dissolved, and spheroidized in this final forging process.
The δ phase, which has become spheroidized and fine, suppresses the grain growth of recrystallized grains that occurs during forging and reheating due to the pinning effect.
That is, under such a state where there is no pinning effect of the δ phase, the recrystallization generated by forging and reheating grows greatly, but the graining due to the pinning effect by the fine spheroidized δ phase Growth is effectively suppressed.

In this finish forging step, it is preferable to perform the reduction by striking with a processing amount of a total reduction ratio of 33% or more.
If the rolling reduction is less than 33%, it is difficult to obtain a sufficient driving force for recrystallization, and it is difficult to sufficiently refine crystal grains by recrystallization.
The reduction ratio of 33% means the total reduction ratio by a plurality of hits when a plurality of hits are applied before reheating is performed.

In this final forging step, it is desirable to perform reheating under conditions of 920 to 980 ° C. and 3 hours or more.
If the temperature is lower than 920 ° C., the δ phase is not sufficiently divided or spheroidized by solid solution, and conversely, at a high temperature exceeding 980 ° C., the amount of solid solution in the δ phase becomes excessive and the recrystallized crystal grains are coarse. Easy to convert.

In the present invention, generally, after each of the above treatments, a solution heat treatment for precipitating the intermetallic compound γ ″ (gamma double prime, Ni ₃ Nb) is performed, and thereafter an aging treatment is performed to obtain γ ″. The Ni-base heat-resistant alloy member is strengthened by precipitation and precipitation hardening.
This solution heat treatment can be performed also for final particle size adjustment.
The solution heat treatment here can be suitably performed under conditions of, for example, 975 ° C. for 2 hours.
The aging treatment can be performed, for example, under the conditions of 718 to 760 ° C. and 8 to 20 hours, and the second aging treatment can be performed under the conditions of 621 to 648 ° C. and 8 to 36 hours.

It is the figure which showed the microstructure of the sample which carried out the solution heat treatment. FIG. 2 is a diagram showing the precipitation behavior of a δ phase when a δ phase precipitation treatment is performed on the microstructure sample shown in FIG. 1. It is the figure which showed the solid solution behavior when the partial solid solution process of (delta) phase was performed after precipitation process. FIG. 6 is a diagram showing a relationship between a holding time, a δ phase precipitation amount, and a crystal grain size when forward extrusion is performed after the δ phase precipitation treatment and then heated and held. FIG. 5 is a diagram showing a microstructure and a δ phase precipitation state after holding times of 15 min and 360 min in FIG. 4. It is the figure which showed the process of the uniform compression test after performing forward extrusion and heat holding, and a reheat holding. It is the figure which showed the grain growth behavior of the crystal grain by the reheating holding | maintenance of FIG. 6 in relation to the initial δ phase. It is the figure which compared and showed the change of the microstructure by heating holding | maintenance about the thing of 5% of initial delta phases in FIG. 7, and the thing of 0%. It is the figure which showed typically the recrystallization behavior by forging.

Next, embodiments of the present invention will be described below.
(Deposition behavior of δ phase)
The precipitation behavior of the δ phase was examined when the δ phase precipitation treatment was performed on the Ni-base heat-resistant alloy having the chemical composition shown in Table 1.

First, ST treatment (solution heat treatment) was performed under the condition of holding 1050 × 1 hr. A sample whose particle size was adjusted to 4 (sample size: outer diameter φ12 mm × height 18 mm) was prepared. FIG. 1 shows the microstructure of this sample. The average particle size is 91.2 μm (by optical microscope measurement).
This sample was held at various temperatures ranging from 850 ° C. to 1000 ° C., and the precipitation behavior of the δ phase was examined by SEM (scanning electron microscope).
The precipitation behavior of the δ phase at temperatures of 900 ° C., 950 ° C., and 1000 ° C. is shown in FIG.

As shown in FIG. 2, the amount of precipitation of the δ phase decreases as the temperature increases from 900 ° C. to 950 ° C. to 1000 ° C., and at a temperature of 1000 ° C., not only the retention time of 36 hours has elapsed, but also 100 hours have elapsed. After that, the amount of precipitation of the δ phase is as low as 2% (represented as volume% when measured in area%).
Even at a temperature of 950 ° C., the amount of precipitation of the δ phase does not reach 4% when the holding time of 36 hours elapses.
On the other hand, at a temperature of 900 ° C., it exceeds 7% after 36 hours, and the δ phase is precipitated in a sufficient amount.
The temperature for the precipitation treatment of the δ phase is preferably in the range of 900 to 930 ° C.
In particular, the precipitation treatment of the δ phase can be particularly suitably performed under the condition of 915 ° C. × 36 hr.

(Solubility behavior of δ phase)
The sample subjected to ST treatment was subjected to δ phase precipitation under the condition of 915 ° C. × 36 hr, and a solid solution test sample (average particle size 91.2 μm) in which 6.7% of acicular δ phase was precipitated was obtained as 975 The solution was heated to various temperatures of 1050 ° C. to 1050 ° C. and held to examine the partial solid solution behavior of the δ phase.
The partial solid solution behavior of the δ phase at heating temperatures of 975 ° C., 1000 ° C., 1025 ° C., and 1050 ° C. is shown in FIG.

As shown in FIG. 3, at 1050 ° C., the δ phase immediately forms a solid solution, and even at 1025 ° C., the δ phase suddenly dissolves. Therefore, the heat treatment in the initial amount adjustment process of the δ phase, in which the acicular δ phase is partly dissolved with parting, in particular, the parting / partial solution treatment of the δ phase by heating is performed at less than 1025 ° C. good.
However, if the temperature is lower than 920 ° C., the partial solid solution of the δ phase does not proceed sufficiently, so the processing temperature is preferably 920 ° C. or higher.

(Recrystallization / grain growth behavior)
The Ni-base heat-resistant alloy material having the chemical composition shown in Table 1 is subjected to ST treatment (conditions of 1050 ° C. × 1 hr), followed by δ phase precipitation treatment (915 ° C. × 36 hr), and then a preliminary in the initial amount adjustment treatment of δ phase As a forging treatment, a test material having a size outer diameter of φ23.8 mm × a height of 48.0 mm was subjected to forward extrusion at a temperature of 980 ° C. and a surface reduction rate of 60% by high-temperature heating. After that, as the δ phase division / partial solid solution treatment by heating, the δ phase is partly dissolved with division by holding it again at 980 ° C. for 15 to 360 min, and the initial amount of δ phase is adjusted. It was.

FIG. 4 shows the relationship between the holding time (sec) and the precipitation amount (initial amount) of the δ phase together with the crystal grain size.
As shown in FIG. 4, the amount of the δ phase decreases due to partial solid solution as the holding time becomes longer. In FIG. 4, the amount of δ phase (initial amount) is 5% after holding for 15 min and 3% after holding for 360 min.
FIG. 5 shows the microstructure and δ phase precipitation state after holding at 980 ° C. × 15 min and after holding at 980 ° C. × 360 min.

As shown in these figures, ASTM No. 1 was originally set in a state before forward extrusion. The crystal grain size of 4 (average particle size: 91.2 μm) is 7.1 μm (when holding for 15 minutes) and 9.4 μm (when holding for 360 minutes) when reheated and held at 980 ° C. after forward extrusion. ) And the crystal grains are finer, but this is a finer crystal grain through forward extrusion.
After completing the initial amount adjustment processing of the δ phase as described above, the following uniform compression processing test is performed as a final forging process, and then reheating and holding are performed to determine the crystal grain growth behavior and the solid solution of the δ phase. The decrease behavior was investigated.
Here, the uniform compression processing test was conducted as follows.

As shown in FIG. 6, a cylindrical test piece having an outer diameter of 15 mm and a height of 22.5 mm was heated to 980 ° C. by high-frequency heating (heating rate: 10 ° C./sec), and then the same temperature was maintained for 30 sec (seconds). The temperature distribution was maintained and the temperature distribution was equalized, and then the specimen was compressed in the axial direction (vertical direction in the figure) at a strain (ε) speed of 10 / sec (strain ε = 0.4) (the reduction rate was 33%). .
Thereafter, reheating and holding at 980 ° C. were performed, and the grain growth behavior of the crystal grains and the δ phase reduction behavior with the lapse of the holding time were examined.
Here, the grain growth behavior and the δ phase decrease behavior were investigated for those in which the initial amount of the δ phase was 0%, 3%, and 5%, and the respective results were compared and shown in FIG.
Further, the microstructure after 10 sec, 1000 sec, and 3100 sec for the initial δ phase of 0% and 5% are also shown in FIG.
For the δ phase having an initial amount of 0%, the one obtained by directly extruding the ST-treated product without performing the δ-phase precipitation treatment was used.

These results of FIGS. 7 and 8 show that the grain growth of the crystal grains can be effectively suppressed as the initial δ phase increases to 3% and 5% as compared with the case where the initial δ phase is 0%. This indicates that the crystal grain size obtained can be made finer.
This result also shows that the final grain size can be controlled by changing the amount of the initial δ phase.
Incidentally, when the initial δ phase is 5%, the final crystal grain size (after 3100 sec) is about 10 μm. It is about 10.
On the other hand, when the initial δ phase is 3%, the final crystal grain size is a little less than 20 μm. It is about 8.
When the initial amount of δ phase is zero, the final crystal grain size is about 50 μm.
In this result, the final particle size difference between the δ phase of 0%, 3%, and 5% is the pinning effect by the δ phase.

Claims (3)

In mass%
Ni: 50-55%
Cr: 17-21%
Al: 0.2-0.8%
Ti: 0.6-1.2%
Nb: 4.7-5.6%
Mo: 2.8-3.3%
Co: ≤ 1.0%
C + Si + Mn + P + S + Cu + B: ≦ 1.1%
For the to-be-formed material made of the Ni-base heat-resistant alloy having the remaining Fe composition, a δ phase precipitation treatment is performed to precipitate the δ phase in a needle shape,
Thereafter, the forging material subjected to the δ phase precipitation treatment is heated at 920 to 1025 ° C. for less than 1 to 36 hours, and the precipitated acicular δ phase is partly dissolved together with separation, and the amount of precipitation of the δ phase Execute the initial amount adjustment process of δ phase to adjust
Thereafter, a forging step of repeating at least once the free forging and reheating at which the blow is performed at a recrystallization temperature or higher and a total reduction ratio of 33% or more,
A free forging method for a Ni-base heat-resistant alloy member, characterized in that a Ni-base heat-resistant alloy member having fine crystal grains is obtained. 2. The method for free forging a Ni-base heat-resistant alloy member according to claim 1, wherein the δ phase precipitation treatment is performed in a temperature range of 800 to 1020 ° C. and a time range of 0.1 to 36 hr. The free forging method of a Ni-base heat-resistant alloy member according to any one of claims 1 and 2, wherein the reheating is performed in a temperature range of 920 to 980 ° C.