JP7228124B2 - Method for manufacturing hot worked material - Google Patents

Description

The present invention relates to a method for producing a hot-worked material made of a Ni-based alloy, and in particular, from a Ni-based alloy having a γ″ phase as a strengthening phase (γ″ strengthening type or γ′/γ″ composite strengthening type). It relates to a method for producing a hot-worked material.

Ni-based alloys are known in which a γ' (gamma prime) phase, which is an intermetallic compound composed of Ni ₃ (Ti, Al, Nb, Ta), is precipitated in a matrix (γ phase). High-strength forged alloys in which such precipitates are precipitated at a high molar ratio of 40% or more are used for aircraft engine members and the like. On the other hand, such alloys, which exhibit high strength at high temperatures, lack hot workability, but undergo dynamic recrystallization by applying high strain rate plastic working below the solid solution temperature of the γ' phase. Therefore, a working method for ensuring hot workability has been proposed.

For example, in Patent Document 1, in a method for producing a hot-worked material made of a Ni-based alloy that performs plastic working at a high strain rate exceeding 1.0 / sec at a solid solution temperature of the γ' phase or less, before plastic working, The ingot is heated to a temperature equal to or higher than the solid solution temperature of the γ' phase to once dissolve the γ' phase into a single phase of the γ phase, and then at a cooling rate of less than 300°C/h to lower than the solid solution temperature by at least 300°C. It discloses a manufacturing method in which a γ' phase is precipitated and a uniformly coarsened structure is obtained by cooling to a temperature. It states that the greater the degree of coarsening of the γ' phase, the more the dynamic recrystallization is promoted by a large strain rate in the subsequent plastic working, and the effect of improving the plastic workability becomes remarkable.

By the way, it is difficult to apply plastic working at a high strain rate to a large forged member, and the working method using dynamic recrystallization as described above cannot be used. Therefore, a method has been proposed in which the precipitated γ' phase is overaged to coarsen to ensure hot workability.

For example, in Patent Document 2, after homogenization heat treatment in which an ingot is held in a temperature range of 1130 to 1200° C. for at least 2 hours, it is gradually cooled to a temperature at which the γ' phase precipitates at a cooling rate of 0.03° C./second or less. to promote the growth of the γ' phase, then heat treatment is performed by raising the temperature to the γ' phase solid solution temperature of 950 to 1160 ° C. or less and maintaining it for 2 hours or more, and further, the cooling rate is 0.03 ° C./sec or less. It is said that the γ' phase is grown by cooling at . The average grain size of the primary γ' phase obtained at this time is 1 μm or more, and high hot workability can be obtained.

JP 2017-179592 A WO2016/152985

As a Ni-based alloy with excellent high-temperature mechanical strength, a Ni-based alloy utilizing the strengthening of the precipitated γ″ (gamma double prime) phase by interfacial matching strain, such as Inconel 718 (trade name), is also known. There is also a demand for a working method that ensures hot workability for alloys, and like the above alloys that use the γ' phase as a strengthening phase, it is possible to ensure hot workability by growing the γ″ phase. There is expected.

By the way, the tetragonal γ″ phase is a metastable phase of Ni ₃ Nb. In other words, in such an alloy system, it is also necessary to control the balance between the γ″ phase and the δ phase.

The present invention has been made in view of the above circumstances, and an object of the present invention is to produce a Ni-based alloy containing at least Nb and having a γ″ phase made mainly of Ni ₃ Nb as a strengthening phase. The object of the present invention is to provide a method for manufacturing a hot-worked material.

A method for producing a hot-worked material according to the present invention is a method for producing a hot-worked material made of a Ni-based alloy containing at least Nb and having a γ″ phase made of Ni ₃ Nb as a strengthening phase, and comprising: First, after a homogenization heat treatment in which the ingot is held at a temperature of 1050 ° C. or higher, it includes a cooling step of cooling to a temperature of 820 ° C. or lower at a cooling rate of 50 ° C./h or lower, and intermetallic compound particles composed of γ″ phase. It is characterized by precipitation and growth.

According to this invention, by precipitating and growing particles of an intermetallic compound consisting of a γ″ phase, hot workability is ensured, and a Ni-based alloy having a γ″ phase consisting of Ni ₃ Nb as a strengthening phase is formed. Hot worked materials can be produced.

In the above invention, the cooling step may further include a holding heat treatment step of heating to a temperature of 850 to 970° C. and then holding at this temperature. According to this invention, the particles of the intermetallic compound composed of the γ″ phase can be sufficiently grown, and the hot workability can be ensured more reliably.

In the above invention, the intermetallic compound particles may have an average particle diameter of 0.1 μm or more. According to this invention, it is possible to obtain a Ni-based alloy that is excellent in high-temperature mechanical strength while ensuring hot workability due to the grown intermetallic compound particles of the γ″ phase.

Another method for producing a hot-worked material according to the present invention is a method for producing a hot-worked material made of a Ni-based alloy containing at least Nb and having a γ″ phase made of Ni ₃ Nb as a strengthening phase, Prior to hot working, the ingot is homogenized at a temperature of 1050° C. or higher, followed by a cooling step of cooling to a temperature of 850-970° C. at a cooling rate of 50° C./h or less, followed by holding at this temperature. and a holding heat treatment step for precipitating and growing intermetallic compound particles of δ phase.

According to this invention, by precipitating and growing intermetallic compound particles composed of the δ phase, which is a stable phase, hot workability is ensured, and a Ni-based alloy having a γ″ phase composed of Ni ₃ Nb as a strengthening phase is produced. A hot-worked material consisting of can be produced.

In the above invention, the intermetallic compound particles may have an average particle size of 1.0 μm or more. According to this invention, it is possible to obtain a Ni-based alloy that is excellent in high-temperature mechanical strength while ensuring hot workability due to the grown intermetallic compound particles of the δ phase.

In the above invention, the holding time of the holding heat treatment step may be one hour or more. According to this invention, it is possible to obtain a Ni-based alloy that is excellent in high-temperature mechanical strength while ensuring hot workability by sufficiently growing particles composed of an intermetallic compound.

In the above invention, the room temperature hardness of the ingot to be subjected to the hot working may be HV450 or less. According to this invention, it is possible to easily obtain a Ni-based alloy having excellent high-temperature mechanical strength while ensuring hot workability.

In the above-described invention, the Ni-based alloy may be characterized by having a chemical composition that includes 2 to 10% by mass of Nb and 3% or less of each of Al and Ti. According to this invention, it is possible to obtain a Ni-based alloy that is excellent in high-temperature mechanical strength mainly due to the γ″ phase while maintaining hot workability by sufficiently growing grains composed of an intermetallic compound.

1 is a table of chemical compositions of alloys used in an example of a method for producing a hot-worked material according to the present invention. FIG. 2 is a heat treatment diagram showing an example of a method for manufacturing a hot-worked material. 1 is a list of thermal histories and room-temperature hardness measurement results of hot-worked materials. 1 is a microstructure photograph of Example 1. FIG. 3 is a microstructure photograph of Examples 2 and 3. FIG. It is a microstructure photograph of Examples 4 to 6.

A method for producing a hot-worked material made of a Ni-based alloy as one embodiment according to the present invention will be described with reference to FIGS. 1 and 2. FIG.

The Ni-based alloy targeted here contains at least Nb, and has a chemical composition that secures the high-temperature strength required as a member by using a γ″ phase consisting mainly of Ni ₃ Nb as a strengthening phase. there is

For example, as shown in FIG. 1, as an example of the chemical composition of such a Ni-based alloy, Nb may be included in the range of 2 to 10% by mass. Also, Al and Ti may be contained in an amount of 3% by mass or less, respectively.

Such Ni-based alloys, which are mainly required to have high-temperature strength with the γ″ phase as the strengthening phase, are generally said to lack hot workability. In order to ensure the properties, the inventors have come up with the idea of precipitating and growing particles of an intermetallic compound consisting of a γ″ phase prior to hot working.

Specifically, as shown in FIG. 2, a cooling step of cooling the ingot to a temperature T2 of 820° C. or less at a cooling rate of 50° C./h or less through a homogenization heat treatment step of holding the ingot at a temperature Te of 1050° C. or higher. to precipitate and grow particles of the intermetallic compound as described above.

Here, as in the heat history A1, after slowly cooling to a temperature T2 of 820 ° C. or less in the first cooling step, which is the cooling step described above, the temperature is continuously cooled to 500 ° C. or less at a cooling rate of 50 ° C./h or less. It may be slowly cooled to the temperature T1. As a result, the particles of the intermetallic compound composed of the γ″ phase can be precipitated and grown as described above. It tends to precipitate and grow. As a result, it is possible to obtain a hot-worked material that ensures hot workability. With such a hot-worked material, it is possible to obtain a member that is excellent in high-temperature mechanical strength while ensuring hot-workability.

On the other hand, after slowly cooling to a temperature T2 of 820° C. or less in the first cooling step, heating again to a temperature Tr of 850 to 970° C. and then holding it within this temperature range like the heat history A2 including a holding heat treatment step may be processed. In this case, the growth of the intermetallic compound particles of the γ″ phase is promoted, and the growth of the intermetallic compound particles of the γ″ phase is easier than in the case of the thermal history A1. Further, by lengthening the holding time of the holding heat treatment step, an intermetallic compound composed of the δ phase can also be precipitated. This also makes it possible to obtain a hot-worked material that ensures hot-workability.

The inventors of the present application also conceived of precipitating and growing particles of an intermetallic compound composed of the δ phase, which is a stable phase, prior to hot working as a method of ensuring hot workability.

Specifically, as shown in the thermal history B of FIG. It includes a cooling step of cooling to Tr, followed by a holding heat treatment step of holding the temperature Tr as it is. According to such a thermal history B, particles of an intermetallic compound consisting of the δ phase can be precipitated and grown. It should be noted that, unlike the particles of the intermetallic compound composed of the γ″ phase, the particles of the intermetallic compound composed of the δ phase are precipitated by generating precipitation nuclei at the grain boundaries, and grow toward the inside of the crystal grains. There is a tendency.

This also makes it possible to obtain a hot-worked material that ensures hot workability, and to obtain a member that is excellent in high-temperature mechanical strength. By adjusting the holding time in the holding heat treatment step, the growth of the intermetallic compound particles of the δ phase can be controlled, and a member having desired mechanical properties can be obtained.

The hot-worked material obtained by the above thermal histories A1, A2, and B has a room temperature hardness (room temperature hardness) of the ingot of HV 450 or less, so that the hot workability is sufficiently high as a guideline. It is preferable that it can be secured. Further, by growing the particles of the intermetallic compound composed of the δ phase to an average particle size of 1.0 μm or more, or by growing the particles of the intermetallic compound composed of the γ″ phase to an average particle size of 0.1 μm or more. It is preferable to obtain sufficient growth of intermetallic compound particles and to ensure sufficient hot workability as a guideline.In order to obtain such hot-worked materials, for example, It can be considered that the holding time in the holding heat treatment step is set to 1 hour or more, and after the particles of the intermetallic compound composed of the δ phase or the γ″ phase are precipitated, they can be sufficiently grown, and the hot It is preferable because workability can be ensured.

[Mechanical test and structure observation]
A hardness test was conducted on the hot-worked material of the Ni-based alloy produced by the above-described production method, and the structure was observed. These results will be described with reference to FIGS.

Using a Ni-based alloy having the chemical composition shown in FIG. 1, a hot-worked material was produced as follows so as to have the thermal history shown in FIG.

For Comparative Example 1, an ingot made of a Ni-based alloy having the above composition was subjected to homogenization heat treatment at 1180° C. for 4 hours, heated to 1120° C., and then bloomed forging to create an octagonal billet of 650×1700H. , air-cooled. Cracks were generated by such air cooling, but the cooling rate by this air cooling was 500° C./h.

For Examples 1 to 6, test pieces of 10 mm×10 mm×10 mm were cut out from the ingots described above, subjected to the heat history described above, and subjected to hardness tests and structural observations. As for the heat history, the cooling rate was adjusted assuming a large member.

In the structure observation, the surface of the test piece was mirror-polished, the polished surface was subjected to electric corrosion with a 10% oxalic acid aqueous solution, and then observed with a SEM (scanning electron microscope), and a photograph of the structure was taken (Fig. 4). 6).

Regarding the hardness test, after the holding heat treatment process, in addition to measuring the hardness of the sample after performing the second cooling process (slow cooling to 500 ° C. at 20 ° C./h), after the holding heat treatment process (second cooling The hardness was also measured in the same manner for the samples that were water-cooled and tissue-frozen prior to the process). In addition, microscopic observation was performed on the tissue frozen sample and the sample after the second cooling step. Here, in Example 1, the heat history A1 (see FIG. 2) in which the holding heat treatment step is not provided and the cooling (slow cooling) to 500° C. or less is provided only in the first cooling step. In "Sa", the hardness is measured for a sample whose structure is frozen by water cooling (rapid cooling) from the time it reaches 900°C.

Referring to FIG. 3 together with FIG. 4, in Example 1, the hardness of the slowly cooled sample was increased compared to the frozen tissue sample. Although cracks are likely to occur during slow cooling due to such a difference in hardness, it is considered that hot workability as a hot-worked material can be ensured. In addition, almost no precipitates could be observed in the frozen specimen after the holding heat treatment process, and it was observed that intermetallic compound particles of the γ″ phase were precipitated and grown in the subsequent cooling process.

Referring to FIG. 3 in conjunction with FIG. 5, Examples 2 and 3 are given thermal histories B (see FIG. 2), respectively. In the final product, the γ″ phase, which is to be obtained as the strengthening phase, is a metastable phase and changes to the δ phase by isothermal holding at around 900°C. It should be noted that if the grains of the intermetallic compound of the γ″ phase are similarly coarsely grown, they do not contribute much to the increase in hardness. In Example 2, the sample was held isothermally at 900° C. for 30 hours in the holding heat treatment step, and particles of an intermetallic compound mainly composed of the γ″ phase that did not contribute to the increase in hardness were precipitated, and the hardness was reduced to 407 HV compared to 417 HV in Example 1. In Example 3, which was held isothermally for 100 hours, many particles of the intermetallic compound due to the δ phase were precipitated, and the hardness could be suppressed to 317 HV. It is believed that this was also ensured by Example 2, but the longer holding time as in Example 3 facilitates the growth of particles of the intermetallic compound composed of the δ phase, which is advantageous for ensuring hot workability. .

Further, referring to FIG. 6 together with FIG. 3, Examples 4 to 6 are given thermal histories A2 (see FIG. 2), respectively. Once cooled to 800° C., intermetallic compound particles mainly composed of γ″ phase are precipitated, and by heating and maintaining at 900° C., such intermetallic compound particles can be grown, Mainly coarse γ″ phase intermetallic compound particles can be obtained, and an increase in hardness can be suppressed.

In Example 4 in which the holding time in the holding heat treatment step was set to 10 hours, particles of a relatively coarse intermetallic compound of the γ″ phase were obtained (see FIG. 6(a)), and after cooling, the particles of the metal compound of the γ″ phase were further coarsened. The hardness could be suppressed to 353 HV by growing into intermetallic particles (see FIG. 6(b)). The same was true in Example 5 in which the holding time was 30 hours. In Example 6, in which the holding time was 100 hours, relatively coarse intermetallic compound particles of the γ″ phase could be precipitated (see FIG. 6(e)), but the growth of such intermetallic compound particles was very small. However, it is considered that the hardness could be suppressed to 322HV and the hot workability as a hot-worked material could be ensured.

As described above, the particles of the intermetallic compound consisting of the γ″ phase can be precipitated and grown by the thermal history A1 or A2, and the particles of the intermetallic compound consisting of the δ phase can be precipitated and grown by the thermal history B. Note that since the intermetallic compound particles grow even in the cooling (second cooling) after the holding heat treatment step, slow cooling is preferable, and the cooling rate may be, for example, 50° C./h or less.

Although representative embodiments of the present invention have been described above, the present invention is not necessarily limited thereto, and a person skilled in the art will be able to make modifications without departing from the spirit of the present invention or the scope of the appended claims. , one may find various alternatives and modifications.

Claims (6)

A method for producing a hot-worked material made of a Ni-based alloy containing at least Nb and having a γ″ phase made of Ni ₃ Nb as a strengthening phase,
Prior to hot working,
After the homogenization heat treatment in which the ingot is held at a temperature of 1050 ° C. or higher, it includes a cooling step of cooling to a temperature of 820 ° C. or lower at a cooling rate of 50 ° C./h or lower, and intermetallic compound particles consisting of γ″ phase are precipitated. A method for producing a hot-worked material , wherein the intermetallic compound particles are grown to have an average particle size of 0.1 μm or more . 2. The method for producing a hot-worked material according to claim 1, wherein said cooling step further includes a holding heat treatment step of heating to a temperature of 850 to 970° C. and then holding said temperature. A method for producing a hot-worked material made of a Ni-based alloy containing at least Nb and having a γ″ phase made of Ni ₃ Nb as a strengthening phase,
Prior to hot working,
After the homogenization heat treatment in which the ingot is held at a temperature of 1050° C. or higher, it is cooled to a temperature of 850 to 970° C. at a cooling rate of 50° C./h or less, followed by a cooling step, which is maintained at this temperature and consists of the δ phase. A method for producing a hot-worked material , comprising a holding heat treatment step for precipitating and growing intermetallic compound particles, wherein the intermetallic compound particles have an average particle size of 1.0 μm or more . 4. The method for producing a hot-worked material according to claim 2, wherein the holding time in the holding heat treatment step is one hour or more. 5. The method for producing a hot-worked material according to claim 1, wherein the ingot subjected to the hot working has a room temperature hardness of HV450 or less . One of claims 1 to 5 , wherein the Ni-based alloy contains 2 to 10% by mass of Nb and has a composition that can contain 3% or less of Al and Ti, respectively. A method for producing the hot-worked material described.

Images