JP4387331B2 - Ni-Fe base alloy and method for producing Ni-Fe base alloy material - Google Patents

Description

  The present invention is used for a material requiring high temperature strength, such as a generator member or an aircraft member, and has a particularly good forgeability and fatigue characteristics, and a Ni-Fe base alloy using the alloy. The present invention relates to a method for manufacturing a material.

Precipitation-strengthened Ni-based alloys are widely used for various generator members, aircraft members, and the like because they have high structural stability and excellent mechanical properties from cryogenic temperatures to high temperatures.
As a feature of this precipitation strengthened Ni-base alloy, it is generally manufactured by a combination of solution treatment and aging treatment. The solution treatment is a manufacturing process in which precipitates inevitably generated in a manufacturing process up to the previous stage, for example, a forging process, are once dissolved in a matrix. The aging treatment is a manufacturing process in which a specific precipitate appears so as to obtain a desired mechanical property by performing a heat treatment for a predetermined time at a predetermined temperature determined by the alloy composition. This particular precipitate is determined by the alloy composition and aging conditions.

A typical example of a precipitated phase mainly appearing in a matrix of austenite (hereinafter referred to as γ) is a gamma prime phase composed of Ni ₃ (Al, Ti) in the case of Inconel 706 (trademark of Incoalloys, the same applies hereinafter). (Hereinafter referred to as γ ′) or / and a co-precipitation phase (hereinafter referred to as γ′−γ ″) of γ ′ and a gamma double prime phase composed of Ni ₃ Nb (hereinafter referred to as γ ″) matched. Finely deposited. On the other hand, in the case of Inconel 718 (trademark of Incoalloys), strengthening of the alloy has been achieved by γ ″. The reason why the precipitated phases appear in this way is fundamentally because the composition of each alloy is different. It is said that there is.

Further, with respect to γ ′ and γ ″ contributing to the strengthening, there is also a precipitation phase that appears mainly in the vicinity of the grain boundary and pins the γ grain boundary. In the case of Inconel 706, an eta phase (hereinafter referred to as Ni ₃ Ti) In the case of Inconel 718, it is known that there is a delta phase (hereinafter referred to as δ) composed of Ni ₃ Nb. This is due to the difference in the composition of each alloy as in the case of contributing γ ′ and γ ″. For example, in order to precipitate the δ phase, the present applicant has proposed an alloy in which Nb is positively added (see Patent Document 1).
Japanese Patent Laid-Open No. 10-237574

  By the way, in recent years, with an increase in power generation efficiency, gas turbine members for power generation and the like have been increased in size, and further improvement in low cycle fatigue characteristics is desired in order to further improve the reliability of the members. In recent years, it has become clear that inconel 706 and 718 of the forging die Ni—Fe base alloy has various problems with respect to these problems.

That is, such a member is generally manufactured through steps such as steel ingot manufacturing, forging, heat treatment, and machining, but in Inconel 706, since η is solid solution at 980 ° C. or higher, it is 980 ° C. or higher. Grain refinement cannot be expected by grain boundary pinning during forging.
On the other hand, in Inconel 718, δ having a γ grain boundary pinning effect is precipitated. The solid solution temperature of δ is 1000 ° C. or higher, and can be used for a heat treatment for refining crystal grains during forging. In order to precipitate this δ, it is necessary to add at least 1.5% or more of Nb having a specific gravity of 8.56 as shown in Patent Document 1. However, since Nb is the heaviest element among the strengthening elements, a large amount of Nb tends to stay in the lower part of the liquid phase part during the production of the steel ingot, that is, during solidification, and remarkably promotes segregation. Therefore, a large amount of Nb can be manufactured with a relatively small segregation problem if it is a small member such as a blade for power generation or aircraft, but it is of a ton order such as a turbine rotor or a gas turbine disk. It is unsuitable for large-size member production.
From such a point of view, it is desired to develop a Ni—Fe-based alloy that can pin the γ grain size at a higher temperature, has low segregation, and has high segregation ability and excellent crystal grain refining ability.

The present invention has been made in view of the above circumstances, and is a Ni-Fe group that has low segregation and excellent crystal grain refining ability using a new intermetallic compound in place of δ or γ ″ -Ni ₃ Nb. It is an object to provide an alloy and a Ni—Fe based alloy material using the alloy.

V can be combined with a Ni ₃ Nb intermetallic compound to generate Ni ₃ V (Nb) -δ or γ ″ that is stable at higher temperatures. Therefore, the present invention solves the above-described problems. Therefore, we focused on using V, which has a specific gravity of 5.98, which is lower than that of Nb, which has a specific gravity of 8.56. By adding Ni ₃ V (Nb) by addition, a new Ni—Fe based alloy having low segregation and excellent crystal grain refining ability has been developed.

That is, the invention of the Ni-Fe-based alloy of the present invention is, in mass%, Ni: 24.0-55.0%, Cr: 13.0-21.0%, Al: 0.05-5.0% Ti: 3.0% or less, Nb: 0.1-3.0%, V: 2.0-12.0%, C: 0.005-0.1%, B: 0.015% or less And the balance is made of Fe and inevitable impurities.

The invention of the Ni—Fe base alloy according to claim 2 is, in mass%, Ni: 24.0 to 55.0%, Cr: 13.0 to 21.0%, Mo: 0.1 to 5.0% Al: 0.05-5.0%, Ti: 3.0% or less, Nb: 0.1-3.0%, V: 2.0-12.0%, C: 0.005-0. 1%, B: 0.015% or less, with the balance being Fe and inevitable impurities.

  The invention of the Ni—Fe based alloy according to claim 3 is characterized in that, in the invention according to claim 1 or 2, the V content is 2.0 to 10.0% by mass%.

  According to a fourth aspect of the present invention, there is provided a method for producing a Ni—Fe based alloy material comprising hot forging a Ni—Fe based alloy having the composition according to any one of claims 1 to 3 and then solidifying the intragranular precipitated phase. A solution treatment is performed, followed by an aging treatment.

  Below, the effect | action of the component prescribed | regulated by this invention and the reason for limitation are demonstrated. In addition, all the contents in the following mean the mass%.

Ni: 24.0-55.0%
Ni is an important element that stabilizes γ as a matrix of the alloy and combines with Al, Ti, and Nb to form a γ ′, γ ″ phase. In order to exert the effect, at least 24.0. However, excessive addition leads to an increase in the cost of the entire alloy, resulting in a higher price than conventional alloys, so the amount added is in the range of 24.0 to 55.0%. For the same reason, it is desirable that the lower limit is 35.0% and the upper limit is 45.0%.

Cr: 13.0-21.0%
Cr is an essential element for enhancing oxidation resistance, corrosion resistance, and strength, and at the same time, is necessary for maintaining nonmagnetic properties. In order to exert these effects, an addition amount of at least 13.0% is necessary. However, excessive addition deteriorates the stability of γ which is a matrix, precipitates a TCP phase such as a σ phase, and lowers the toughness. Therefore, the addition amount is limited to the range of 13.0 to 21.0%. For the same reason, it is desirable that the lower limit is 15.0% and the upper limit is 20.0%.

Mo: No addition or 0.1 to 5.0%
Since Mo has a specific gravity of 10.28 and is strongly segregated, it is an element unsuitable for the production of large steel ingots. Therefore, it is desirable that no additives be added in the present invention material. Therefore, when Mo is not actively added, the amount of Mo as an impurity amount is less than 0.1%. However, from the viewpoint of preventing segregation, 0.05% or less is desirable when not added, and further 0.02% or less is desirable. On the other hand, Mo is also an element that dissolves in the matrix and strengthens the matrix itself, and if added at about 0.1%, it contributes only to strengthening without degrading the segregation due to the steel ingot size. It becomes possible to make it. Nevertheless, excessive addition still promotes segregation, so when Mo is positively added, the addition amount is preferably 0.1 to 5.0%.

Al: 0.1 to 5.0%
Al combines with Ni to precipitate γ 'and contributes to strengthening of the alloy. Further, by forming an Al ₂ O ₃ protective film, it contributes to an improvement in oxidation resistance and corrosion resistance, and also contributes as a deoxidizing element in the steel ingot. Therefore, it is necessary to add at least 0.05% or more. However, excessive addition leads to coarsening of the γ ′ phase, and ductility decreases accordingly. Therefore, the addition amount is limited to a range of 0.05 to 5.0%. For the same reason, it is desirable that the lower limit is 0.05% and the upper limit is 3.0%.

Ti: 3.0% or less Ti, like Al, binds to Ni and precipitates γ ', contributing to strengthening of the alloy. It also contributes to corrosion resistance and deoxidation elements. However, excessive addition precipitates η and reduces ductility. Therefore, the addition amount is limited to a range of 3.0% or less. In order to obtain the above effect, it is desirable to add 0.1% or more. For the same reason, it is more desirable that the lower limit is 0.1% and the upper limit is 1.5%.

Nb: 0.1-3.0%
Nb combines with Ni to precipitate γ ″ and contribute to strengthening of the alloy. Further, δ precipitates on the high temperature side and contributes to crystal grain refinement by grain boundary pinning, so it is contained in an amount of 0.1% or more. However, since Nb is the heaviest element among the strengthening elements, it is an element that tends to stay in the lower part of the liquid phase part during the production of a steel ingot, that is, during solidification, and is likely to segregate. It causes coarsening and promotes segregation. Therefore, the added amount is 0.1 to 3.0%. For the same reason, it is desirable that the lower limit is 0.60% and the upper limit is 2.5%.

V: 2.0 to 12.0%
V, like Ni ₃ Nb, binds to Ni and precipitates Ni ₃ V-γ ″ and contributes to strengthening of the alloy. Further, δ precipitates even on the high temperature side and contributes to grain refinement by grain boundary pinning. In particular, by adding Nb and V in combination, Ni ₃ V (Nb) having higher temperature stability than Ni ₃ Nb is generated, whereby the solid solution temperature range of Ni ₃ Ti-η and Ni ₃ Nb-δ Even when forging is performed, grain refinement by γ grain boundary pinning can be achieved, so the addition of V contributes to the improvement of ductility, toughness, and low cycle fatigue properties by grain refinement, and Nb has a specific gravity of 8. 56, while V has a specific gravity of 5.98, segregation during solidification is unlikely to occur, but excessive addition of V generates an embrittled phase composed of Cr and V and easily oxidizes. Because of the large amount during forging heating Therefore, the grain boundary becomes brittle and the hot workability decreases, so the amount added is 2.0 to 12.0%, preferably 2.0 to 10.0%. For the same reason, it is more desirable to set the lower limit to 7.0% and the upper limit to 10.0%.

C: 0.005-0.1%
C forms Ti and TiC, and Cr and Mo form M ₆ C, M ₇ C ₃ and M ₂₃ C ₆ type carbides to suppress the coarsening of the alloy. In particular, M ₆ C and M ₂₃ C ₆ have a function of strengthening the grain boundaries by precipitating an appropriate amount of carbides at the grain boundaries. For these actions, C is contained in an amount of 0.005% or more. However, if carbon is excessively contained, too much Cr carbide precipitates at the grain boundary during the stabilization treatment, which weakens the grain boundary and lowers the ductility. Therefore, the addition amount of C is limited to a range of 0.005 to 0.1 wt%. For the same reason, it is more desirable that the lower limit is 0.005% and the upper limit is 0.01%.

B: 0.015% or less B segregates at the grain boundary to strengthen the matrix, and promotes high-temperature strength and ductility. However, the addition of a large amount facilitates the formation of borides and conversely weakens the grain boundaries. Therefore, the addition amount of B is limited to a range of 0.015 wt% or less. In addition, in order to acquire the said effect | action, it is desirable to contain 0.001% or more. Furthermore, for the same reason, it is more desirable that the lower limit is 0.001% and the upper limit is 0.005%.

As described above, according to the Ni—Fe based alloy of the present invention, Ni: 24.0 to 55.0%, Cr: 13.0 to 21.0%, Al: 0.05 by mass%. -5.0%, Ti: 3.0% or less, Nb: 0.1-3.0%, V: 2.0-12.0%, C: 0.005-0.1%, B: 0 0.15% or less, further containing Mo: 0.1 to 5.0% if desired, and the balance is made of Fe and inevitable impurities, so that it can be manufactured with low segregation, and for hot forging. Even when it is used, crystal grain refinement by grain boundary pinning can be sufficiently obtained.
That is, the Ni—Fe base alloy of the present invention produces a Ni—Fe base alloy having lower segregation and superior crystal grain refining ability than Ni—Fe base alloys containing Nb represented by Inconel 706 and 718. It is possible to expand the application range by increasing the size of generator members and aircraft members and improving low cycle fatigue characteristics.

  Moreover, according to the manufacturing method of the Ni-Fe base alloy material of the present invention, after hot forging the Ni-Fe base alloy having the above composition, a solution treatment for dissolving the intragranular precipitated phase is performed, Since the aging treatment is performed, an alloy material with low segregation and crystal grain refinement can be obtained, and a material excellent in ductility, toughness, and low cycle fatigue characteristics can be obtained.

Hereinafter, an embodiment of the present invention will be described.
The Ni—Fe-based alloy of the present invention can be prepared by adjusting the alloy components so as to have a prescribed composition. In addition, this invention alloy can be produced by a conventional method, The manufacturing method is not specifically limited.
The Ni—Fe-based alloy can be subjected to a heat treatment such as a diffusion heat treatment as necessary. Examples of the diffusion heat treatment include a heating temperature of 1150 to 1200 ° C. and a holding time of 3 to 70 hours. Thereafter, it is subjected to hot forging.
Hot forging can be performed by heating to 940 to 1150 ° C., for example, and the present invention is not particularly limited with respect to the conditions in the forging process.

  After hot forging, solution treatment is performed. In the solution treatment, heating is performed at a temperature higher than the recrystallization temperature to cause the intragranular precipitation phase such as γ ′ and γ ″ to form a solid solution. However, at this time, the temperature is preferably equal to or lower than the temperature at which crystal grain coarsening starts. In the solution treatment after the forging, the temperature is not less than the recrystallization temperature of the alloy and the temperature at which the intragranular precipitation phase such as γ ′ and γ ″ is solid-solved and not more than the temperature at which the grain coarsening starts. Is desirable. Although this temperature has some differences with components, for example, a temperature of 940 to 1020 ° C. can be exemplified. The solution treatment can be performed by holding for 1 to 3 hours. After the heating, it is desirable to rapidly cool at 0.5 ° C./min or more.

After the solution treatment, an aging treatment is performed to improve mechanical properties. Examples of the aging treatment include a treatment of heating at 700 to 800 ° C. for 24 to 100 hours.
The Ni—Fe-based alloy material obtained as described above has a fine crystal structure, and for example, a structure having a crystal grain size number of 5.5 or more is obtained.

  The Ni-Fe based alloy of the present invention is suitable for precipitation strengthened alloys that are exposed to high temperatures such as turbine rotors and turbine disks, and is particularly excellent in forgeability, low segregation, and ductility associated with grain refinement, It is suitable for large members that can be expected to improve toughness and low cycle fatigue characteristics. However, the application of the present invention is not limited to a turbine member such as a turbine rotor or a turbine disk, and the present invention can be used for various applications by utilizing the characteristics.

Hereinafter, embodiments of the present invention will be described in detail. A 50 kg steel ingot in which an alloy having the composition shown in Table 1 (remainder: impurities) was melted in a vacuum induction melting furnace was obtained. The steel ingot was subjected to diffusion treatment at 1175 ° C. × 70 hours, and then made into a plate material having a thickness of 30 mm × 120 mm × L by hot forging (heating temperature 1020 ° C.). An optimum solution treatment temperature region in which the intragranular precipitation phase was solidified for each test material and no crystal grain coarsening occurred was selected.
In addition, in order to grasp the optimum solution treatment temperature region of each test material, each test material was held at 900 to 1100 ° C. for 1 hour, and then the water-cooled test material was used, from the microstructure observation and hardness measurement results. Judgment was made based on the obtained static recrystallization behavior and grain growth behavior.

FIG. 1 shows the change in crystal grain size of the as-forged material and the specimens held at 900 ° C. to 1100 ° C. for 1 hour after forging. Comparative material No. 5 (Inconel 706), comparative material No. 6 (Inconel 718), the intragranular precipitated phase was dissolved at the same time as recrystallization, and grain growth started. In Comparative Example No. 5 from 960 ° C. In No. 6, grain growth started at 1000 ° C.
However, since the invention material has a grain growth start temperature of 980 ° C. to 1020 ° C. and has shifted to the high temperature side, the crystal grains can maintain a finer state on the high temperature side than the comparative material. Furthermore, among the inventive materials, the crystal grain size in the optimum solution treatment temperature region becomes finer as the amount of V added increases. Therefore, in the inventive material, since the δ phase due to Ni ₃ V (Nb) exists stably in a higher temperature range, the grain refinement by γ grain boundary pinning is achieved. Since refinement of crystal grains greatly improves ductility, toughness, and fatigue strength, it is desirable that the optimum solution treatment temperature be not less than the recrystallization temperature and not more than the grain growth start temperature.

  In FIG. 2, the hardness change of each test material hold | maintained at 900 to 1100 degreeC for 1 hour after forging and forging is shown. Comparative material No. 5 (Inconel 706), comparative material No. 6 (Inconel 718), the intragranular precipitation phase solution temperature is comparative material No. No. 5 from 960 ° C. 6 is from 1000 ° C. However, the invention material No. 1-No. In all cases, intragranular precipitation phase solid solution started at 940 ° C. The fact that the solid solution temperature of the intragranular precipitation phase of the inventive material exists on the lower temperature side than the comparative material reduces the deformation resistance on the lower temperature side and improves the forgeability in the high temperature region.

  FIG. 3 shows a comparison of the static recrystallization behavior, grain growth behavior, and solid solution temperature of the intragranular precipitation phase of the comparative material and the inventive material. The region where the solidification of the intragranular precipitated phase is achieved while suppressing the coarsening of the crystal grains of the comparative material is Comparative Material No. 6 at 960 ° C. and comparative material No. No. 7 is only 1000 ° C. Nos. 1 and 4 are 900 ° C. to 980 ° C. In 2 and 3, the range of 940 ° C. to 1020 ° C. is greatly expanded. This means that the process window in the forging of the material of the present invention is significantly larger than that of the comparative material, and crystal grain refinement by forging in a higher temperature range can be achieved.

It is a figure which shows the change of the crystal grain size accompanying the solution temperature rise of a comparative material and invention material. It is a figure which shows the change of the hardness accompanying the solution temperature rise of a comparative material and invention material. It is the schematic which put together the static recrystallization behavior, the grain growth behavior, and the intragranular precipitation phase solution temperature in the inventive material and the comparative material.

Claims (4)

In mass%, Ni: 24.0-55.0%, Cr: 13.0-21.0%, Al: 0.05-5.0%, Ti: 3.0% or less, Nb: 0.1 -3.0%, V: 2.0-12.0%, C: 0.005-0.1%, B: 0.015% or less, the balance consisting of Fe and inevitable impurities Characteristic Ni-Fe base alloy. In mass%, Ni: 24.0-55.0%, Cr: 13.0-21.0%, Mo: 0.1-5.0%, Al: 0.05-5.0%, Ti: 3.0% or less, Nb: 0.1 to 3.0%, V: 2.0 to 12.0%, C: 0.005 to 0.1%, B: 0.015% or less, A Ni—Fe base alloy characterized in that the balance consists of Fe and inevitable impurities.   The Ni-Fe base alloy according to claim 1 or 2, wherein the V content is 2.0 to 10.0% by mass.   After hot forging the Ni-Fe base alloy having the composition according to any one of claims 1 to 3, a solution treatment for dissolving the intragranular precipitation phase is performed, and then an aging treatment is performed. A method for producing a Ni—Fe based alloy material.

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