JPWO2019107502A1 - Hot forging molds and methods for manufacturing forged products - Google Patents

Abstract

A Ni-base alloy for a hot die which has high high-temperature compressive strength and good oxidation resistance and can suppress deterioration of a working environment and shape deterioration, and a hot forging die and a hot forging die using the same. Provided is a method for manufacturing a forged product using a mold. By mass%, W: 7.0 to 15.0%, Mo: 2.5 to 11.0%, Al: 5.0 to 7.5%, Cr: 0.5 to 7.5%, and the balance is A hot forging die in which 80% or more of the surface of a Ni base alloy for a hot die composed of Ni and inevitable impurities is covered with an aluminum oxide layer. In addition to the above composition, Ta is further added. 7.0% or less, Zr: 0.5% or less, Hf: 0.5% or less, rare earth element: 0.2% or less, Y: 0.2% or less, Mg: 0. One or more elements selected from elements of up to 03% can be contained.

Description

  The present invention relates to a Ni-based alloy for hot dies, a hot forging die using the same, and a method for producing a forged product.

In forging a product made of a heat-resistant alloy, the forging material is heated to a predetermined temperature in order to reduce deformation resistance. Since a heat-resistant alloy has high strength even at high temperatures, a hot forging die used for forging requires high mechanical strength at high temperatures. Further, in hot forging, when the temperature of the hot forging die is lower than that of the forging material, the workability of the forging material is reduced due to heat removal. For example, a product made of a difficult-to-work material such as Alloy 718 or Ti alloy Forging is performed by heating a hot forging die together with the material. Accordingly, the hot forging die must have a high mechanical strength at a temperature equal to or close to the temperature at which the forging material is heated. As a hot forging die that satisfies this requirement, Ni-based superalloys that can be used for hot forging at a die temperature of 1000 ° C. or higher in the atmosphere have been proposed (see, for example, Patent Documents 1 to 5).
The hot forging referred to in the present invention includes hot die forging in which the temperature of the hot forging die is brought close to the temperature of the forging material and constant temperature forging in which the temperature is the same as that of the forging material.

JP 62-50429 A JP-A-60-221542 JP, 2006-069692, A JP, 2006-0669703, A U.S. Pat. No. 4,740,354

The Ni-based superalloy described above is advantageous in that it has a high high temperature compressive strength, but in terms of oxidation resistance, a fine scale of nickel oxide scatters from the mold surface during cooling after heating in the atmosphere. Therefore, there is a risk of work environment deterioration and shape deterioration. The problem of oxidation of the mold surface and the accompanying scattering of the scale is a big problem in maximizing the effect that it can be used in the atmosphere.
An object of the present invention is a Ni-based alloy for hot dies having high high temperature compressive strength and good oxidation resistance, and capable of suppressing deterioration of working environment and shape deterioration, and hot forging die using the same And a method for producing a forged product using the hot forging die.

The present inventor has studied the deterioration of the working environment and shape deterioration due to oxidation of the mold surface and the accompanying scale scattering, and has found a composition having high high temperature compressive strength and good oxidation resistance, and has reached the present invention.
That is, this invention is the mass%, W: 7.0-15.0%, Mo: 2.5-11.0%, Al: 5.0-7.5%, Cr: 0.5-7. 5%, the balance being a hot forging die in which 80% or more of the surface of the Ni-based alloy for hot die made of Ni and inevitable impurities is covered with an aluminum oxide layer.
In the present invention, in addition to the above composition, Zr: 0.5% or less, Hf: 0.5% or less, rare earth element: 0.2% or less, Y: 0.2% or less, Mg: 0.03 One or more selected from elements of% or less can be contained.
In the present invention, in addition to the above composition, 7.0% or less of Ta can be further contained.
In the present invention, in addition to the above composition, the total of one or two elements selected from Ti and Nb is 3.5% or less, and the total content of Ta, Ti and Nb is 1. It can be contained within a range of 0 to 7.0%.
Moreover, in this invention, in addition to the said composition, Co can be further contained 15.0% or less.
More preferably, in the hot forging die using the Ni-based alloy for hot die, an antioxidant coating layer is provided on at least one of the molding surface and the side surface of the hot forging die.

Moreover, this invention is the mass%, W: 7.0-15.0%, Mo: 2.5-11.0%, Al: 5.0-7.5%, Cr: 0.5-7 0.5%, Ta: 0 to 7.0%, Co: 0 to 15.0%, and the balance is a Ni-based alloy for hot molds composed of Ni and inevitable impurities.
Further, in the present invention, in addition to the above composition, further, by mass, Zr: 0.5% or less, Hf: 0.5% or less, rare earth element: 0.2% or less, Y: 0.2% or less Mg: One or more elements selected from elements of 0.03% or less can be contained.
In the present invention, in addition to the above composition, the composition further contains 3.5% or less in total of one or two elements selected from elements of Ti and Nb by mass%, Ta, Ti and Nb. The total content can be contained within a range of 1.0 to 7.0%.
In the present invention, the 0.2% compressive strength at a test temperature of 1000 ° C. and a strain rate of 10 ⁻³ / sec is preferably 500 MPa or more.
More preferably, the 0.2% compressive strength at a test temperature of 1100 ° C. and a strain rate of 10 ⁻³ / sec is 300 MPa or more.
The present invention is also a hot forging die using the Ni-based alloy for hot die.

The present invention also includes a first step of heating the forging material and a second step of hot forging the forging material heated in the first step using the hot forging die. This is a method for producing a forged product.
More preferably, in the method for producing a forged product, the second step is performed by heating the hot forging die to 1000 ° C. or higher.
In addition, the present invention provides a preheating of the Ni-based alloy for hot dies at 1000 ° C. or higher in the atmosphere before the step of heating the hot forging dies to 1000 ° C. or higher, so that the hot An aluminum oxide layer can be formed on 80% or more of the surface of the Ni-based alloy for molds.

  According to the present invention, it is possible to obtain a Ni-based alloy for hot molds having high high temperature compressive strength and good oxidation resistance. Thereby, deterioration of the working environment and shape deterioration in hot forging can be suppressed.

It is the figure which showed the oxidation resistance of the example of this invention and the comparative example on the test conditions which simulated long-time use of the metal mold | die. It is the figure which showed the surface of the test piece after hold | maintaining for 8 hours at 1100 degreeC in air | atmosphere of the example of this invention and a comparative example. It is a cross-sectional photograph which shows the backscattered electron image and element map of the oxide layer which were formed in the surface of the test piece after hold | maintaining at 1100 degreeC in the air | atmosphere of this invention example and a comparative example for 3 hours or 8 hours. It is the figure which showed the oxidation resistance of the example of this invention and the comparative example on the test conditions which simulated the heating and cooling by repeated use of a metal mold | die. It is the figure which showed the high temperature compressive strength of the example of this invention and the comparative example. It is the photograph which showed the antioxidant effect of the metal mold | die surface by application | coating of antioxidant.

Hereinafter, the Ni-based alloy for hot molds of the present invention will be described in detail. The unit of chemical composition is mass%. The Ni-based alloy for hot dies is used as a base material for the hot forging die of the present invention.
<W>
W forms a solid solution in the austenite matrix and also forms a solid solution in the gamma prime phase (γ ′ phase) based on Ni ₃ Al, which is a precipitation strengthening phase, to increase the high temperature strength of the alloy. On the other hand, W has an action of reducing oxidation resistance and an action of facilitating precipitation of harmful phases such as a TCP (Topologically Close Packed) phase. From the viewpoint of increasing the high temperature strength and further suppressing the decrease in oxidation resistance and the precipitation of harmful phases, the content of W in the Ni-based alloy in the present invention is 7.0 to 15.0%. A preferable lower limit for obtaining the effect of W more reliably is 10.0%, a preferable upper limit of W is 12.0%, and a more preferable upper limit is 11.0%.
<Mo>
Mo dissolves in the austenite matrix and also dissolves in the gamma prime phase based on Ni ₃ Al, which is a precipitation strengthening phase, to increase the high temperature strength of the alloy. On the other hand, Mo has the effect | action which reduces oxidation resistance. From the viewpoint of increasing the high temperature strength and further suppressing the decrease in oxidation resistance, the Mo content in the Ni-base superalloy according to the present invention is set to 2.5 to 11.0%. In order to suppress precipitation of harmful phases such as TCP phase accompanying the addition of W and Ta, Ti, and Nb described later, it is preferable to set a preferable lower limit of Mo in consideration of W, Ta, Ti, and Nb contents. The preferable lower limit for obtaining the effect of Mo more reliably is 4.0%, and the more preferable lower limit is 4.5%. Moreover, the upper limit of preferable Mo is 10.5%, More preferably, it is 9.0%, More preferably, it is 6.0%.

<Al>
Al binds to Ni to precipitate a gamma prime phase composed of Ni ₃ Al, increases the high temperature strength of the alloy, generates an alumina film on the surface of the alloy, and has an effect of imparting oxidation resistance to the alloy. On the other hand, when the content of Al is too large, an eutectic gamma prime phase is excessively generated, and the high temperature strength of the alloy is lowered. From the viewpoint of increasing the oxidation resistance and the high temperature strength, the Al content in the Ni-base superalloy according to the present invention is set to 5.0 to 7.5%. A preferable lower limit for obtaining the effect of Al more surely is 5.2%, and more preferably 5.4%. Moreover, the upper limit of preferable Al is 6.7%, More preferably, it is 6.5%, More preferably, it is 6.0%.
<Cr>
Cr has the effect of promoting the formation of a continuous layer of alumina on or in the alloy surface and improving the oxidation resistance of the alloy. Therefore, it is necessary to add 0.5% or more of Cr. Further, when Cr is added together with Al, W, etc., 3.0 to 7.5% of Cr achieves high compressive strength at 1000 ° C. as shown in Table 4 and FIG. . Furthermore, when the Cr content is 3.0% or less, high compressive strength can be obtained at temperatures from 1000 ° C. to 1100 ° C. in addition to 1000 ° C. However, the addition of Cr in a range exceeding 7.5% must be avoided because the compressive strength at 1000 ° C. or higher is lowered. The addition of Cr is not necessarily disadvantageous for the high temperature strength. When 0.5 to 7.5% Cr is added together with Al, W, etc., the high temperature strength is rather increased, and while maintaining the high high temperature strength, the acid resistance is improved. The present invention has clarified that the chemical property can be improved. A preferable lower limit for obtaining the effect of Cr more reliably is 1.0%, and more preferably 1.3%. On the other hand, when there is too much content of Cr, it may make it easy to precipitate harmful phases, such as a TCP (Topologically Close Packed) phase. In particular, when a large amount of elements that improve the high-temperature strength of alloys such as W, Mo, Ta, Ti, and Nb are contained, harmful phases are likely to precipitate. From the viewpoint of suppressing precipitation of harmful phases while maintaining the content of elements that improve oxidation resistance and improve high-temperature strength at a high level, the preferable upper limit of the Cr content in the present invention is 3.0%. It is. A more preferred upper limit is 2.0%.

<Ta>
The Ni-base superalloy according to the present invention can contain Ta. Ta is a solid solution in which Al sites are replaced with a gamma prime phase composed of Ni ₃ Al to increase the high temperature strength of the alloy, and to improve the adhesion and oxidation resistance of the oxide film formed on the alloy surface, In particular, it has the effect of further improving the oxidation resistance of the alloy under heat cycle conditions where the mold heating and cooling cycle is short. On the other hand, when there is too much content of Ta, there also exists an effect | action which makes it easy to precipitate harmful phases, such as a TCP phase. From the viewpoint of enhancing oxidation resistance and high-temperature strength and suppressing precipitation of harmful phases, the upper limit of Ta when Ta is contained in the present invention is 7.0%. When Ta is contained, a preferable lower limit for obtaining the effect more reliably is 0.5%, and a further preferable lower limit is 2.5%, and more preferably 5.0%. The upper limit of Ta is preferably 6.7%, more preferably 6.5%.

<Zr, Hf, rare earth element, Y and Mg>
The Ni-base superalloy according to the present invention can contain one or more elements selected from Zr, Hf, rare earth elements, Y and Mg. Zr, Hf, rare earth elements, and Y suppress diffusion of metal ions and oxygen at the grain boundary due to segregation at the grain boundary of the oxide film. The suppression of the grain boundary diffusion reduces the growth rate of the oxide film, and improves the adhesion between the film and the alloy by changing the growth mechanism that promotes the peeling of the oxide film. That is, these elements have the effect of further improving the oxidation resistance of the alloy, particularly under heat cycle conditions where the heating and cooling cycles of the mold are short, by reducing the growth rate and improving the film adhesion described above. In addition, rare earth elements, Y and Mg form S (sulfur) and sulfide, which lowers the adhesion of the coating by segregating at the interface between the oxide coating and the alloy and inhibiting their chemical bonding, and segregating S By preventing the adhesiveness, the adhesiveness is improved, and the oxidation resistance of the alloy is further improved particularly in a heat cycle condition where the heating and cooling cycles of the mold are short. S is an element that can be included as an impurity.
Of the rare earth elements, La is preferably used. This is because La has a great effect of improving oxidation resistance. La has an effect of preventing segregation of S in addition to the above-described suppression of diffusion, and since these effects are excellent, La is preferably selected from rare earth elements. In addition, Y has the same effect as La, so addition of Y is also preferable, and it is particularly preferable to use two or more kinds including La and Y.
In addition to oxidation resistance, in order to suppress mold cracking due to excessive thermal stress that occurs especially under heat cycle conditions where the heating and cooling cycles of the mold are short, rare earth elements, Y It is preferable to use Hf or Zr, which has a low effect of lowering toughness. Among Zr and Hf, it is particularly preferable to use Hf because Hf has a lower effect of lowering toughness and an effect of preventing cracking during casting. In the case of containing one or two of Zr and Hf without containing rare earth elements and Y, Zr and Hf are less effective in preventing segregation of S than rare earth elements and Y, so Mg is added simultaneously. Then, the oxidation resistance is further improved. Therefore, it is particularly preferable to use Hf and Mg at the same time in order to improve the oxidation resistance and toughness with a good balance.

If the amount of Zr, Hf, rare earth element, Y and Mg is too large, an intermetallic compound with Ni or the like is excessively generated and the toughness of the alloy is lowered. In the case, the content shown below is preferable.
From the viewpoint of enhancing the oxidation resistance and suppressing the decrease in toughness, the upper limit of each content of Zr and Hf when containing Zr and Hf in the present invention is 0.5%. The upper limit with preferable content of each of Zr and Hf is 0.3%, More preferably, it is 0.2%. The lower limit when Zr and Hf are contained is preferably 0.001%. A preferable lower limit for sufficiently exhibiting the effects of containing Zr and Hf is 0.01%, further preferably 0.05%, and more preferably 0.1% or more.
Since the rare earth element Y has a higher effect of lowering the toughness than Zr and Hf as described above, the upper limit of the content of each of these elements when the rare earth element Y is contained in the present invention is 0.2%. The upper limit is preferably 0.02%, more preferably 0.005%. The lower limit when the rare earth element and Y are contained is preferably 0.001%. A preferable lower limit for sufficiently exhibiting the effect of containing the rare earth element and Y is 0.002%, and more preferably 0.003% or more.
Further, since Mg only needs to be contained in an amount necessary for forming sulfide and sulfur contained as impurities in the alloy, the upper limit of the content when Mg is contained is 0.03%. When Mg is contained, the lower limit is preferably 0.001%. The upper limit of preferable Mg is 0.025%, More preferably, it is 0.02%. On the other hand, in order to exhibit the effect of adding Mg more reliably, the lower limit is preferably 0.005%.

<Ti and Nb>
The Ni-based alloy for hot molds in the present invention can contain one or two selected from Ti and Nb in a total range of 3.5% or less. Ti and Nb, like Ta, are dissolved in the form of substituting Al sites for the gamma prime phase composed of Ni ₃ Al to increase the high temperature strength of the alloy. Moreover, since it is an element cheaper than Ta, it is advantageous in terms of mold cost. On the other hand, if the content of Ti and Nb is too large, as with Ta, the effect of easily depositing a harmful phase such as a TCP phase and the effect of excessively generating a eutectic gamma prime phase and reducing the high temperature strength of the alloy is there. In addition, Ti and Nb have a weak effect of increasing the high temperature strength compared to Ta, and unlike Ta, do not have an effect of improving oxidation resistance.
From the above, from the viewpoint of suppressing the precipitation of the harmful phase and the decrease in the high temperature strength accompanying excessive formation of the eutectic gamma prime phase, while limiting the total content of Ta, Ti and Nb, It is desirable to replace Ta with Ti or Nb, which is advantageous in terms of mold cost, within a range in which the oxidation resistance is maintained at the same level as when only Ta is contained. In the present invention, when Ti and / or Nb is contained, the upper limit of the total content of Ta, Ti and Nb is set to 7.0%, and one or two kinds selected from elements of Ti and Nb are used. The upper limit of the content is preferably 3.5%. A preferable upper limit of the total content of Ta, Ti, and Nb is 6.5%, and a preferable upper limit of the content of one or two selected from the elements of Ti and Nb is 2.7%. Further, from the viewpoint of reliably obtaining the effect of increasing the high temperature strength, the lower limit of the total content of Ta, Ti and Nb is set to 1.0%, and from the viewpoint of reliably obtaining the effect of reducing the die cost, Ti The lower limit of the content of one or two selected from Nb elements is preferably 0.5%. A preferable lower limit of the total content of Ta, Ti, and Nb is 3.0%, and a more preferable lower limit is 4.0%. The minimum with preferable 1 type or 2 types of content selected from the element of Ti and Nb is 1.0%.
In selecting Ti and Nb, it is preferable to use Ti from the economical viewpoint, and Nb is preferably used when high temperature strength is particularly important. When emphasizing both mold cost and high temperature strength, it is particularly preferable to use Ti and Nb simultaneously.

<Co>
The Ni-based alloy for hot dies in the present invention can contain Co. Co dissolves in the austenite matrix and increases the high temperature strength of the alloy. On the other hand, if the content of Co is too large, Co is an expensive element compared to Ni, so that there is an effect of increasing the die cost and facilitating precipitation of harmful phases such as TCP phase. From the viewpoint of increasing the high temperature strength and suppressing the increase in mold cost and precipitation of harmful phases, Co can be contained in the range of 15.0% or less. In addition, when it contains Co, the preferable minimum for obtaining an effect reliably is 0.5%, More preferably, it is 2.5%. Moreover, a preferable upper limit is 13.0%, More preferably, it is 6.0%.
<C and B>
The Ni-based alloy for hot dies in the present invention contains one or two elements selected from C (carbon) of 0.25% or less and B (boron) of 0.05% or less. Can do. C and B improve the strength of the crystal grain boundaries of the alloy and increase the high temperature strength and ductility. On the other hand, when there is too much content of C and B, a coarse carbide | carbonized_material and boride are formed and there also exists an effect | action which reduces the intensity | strength of an alloy. From the viewpoint of increasing the strength of the crystal grain boundaries of the alloy and suppressing the formation of coarse carbides and borides, the C content in the case of containing C in the present invention is 0.005 to 0.25%, the content of B The amount is preferably 0.005 to 0.05%. A preferable lower limit for reliably obtaining the effect of C is 0.01%, and a preferable upper limit is 0.15%. A preferable lower limit for reliably obtaining the effect of B is 0.01%, a preferable upper limit is 0.03%, and a more preferable upper limit is 0.02%.
It is particularly preferable to use only C when importance is attached to economy and high-temperature strength, and it is particularly preferable to use only B when importance is attached to ductility. When both high temperature strength and ductility are emphasized, it is particularly preferable to use C and B at the same time.
Other than the additive elements described above, Ni and unavoidable impurities. In the Ni-base superalloy according to the present invention, Ni is a main element constituting a gamma phase and constitutes a gamma prime phase together with Al, Ta, Mo, W and the like. Of the inevitable impurity elements, particularly S is preferably 0.0030% or less. More preferably, it is preferably regulated to a range of 0.0010% or less to prevent segregation at the interface between the oxide film and the alloy and deterioration of the adhesion of the film due to inhibition of their chemical bonds.

As will be clarified in Examples described later, preferred compositions in the present invention include W, Mo, Al, Cr, Ta, Hf, and Mg, and the following ranges are considered to be particularly preferable. .
In mass%, W: 10.0-12.0%, Mo: 4.0-6.0%, Al: 5.0-6.5%, Cr: 1.0-3.0%, Ta: Hot mold having a composition of 2.5 to 6.7%, Hf: 0.01 to 0.3%, Mg: 0.001 to 0.025%, the balance being Ni and inevitable impurities Ni-base alloy.

<Oxide film>
In the present invention, it is important that 80% or more of the surface is covered with an aluminum oxide layer when heated to 1000 to 1100 ° C. in the atmosphere. The Ni-based alloy for hot dies of the present invention can be used for hot die forging and isothermal forging in the atmosphere. The temperature of 1000 ° C. is a temperature assuming hot die forging. Further, 1100 ° C. is a temperature assuming constant temperature forging. In addition, the surface said here points out the most important molding surface in a metal mold | die. Preferably, the molding surface and the side surface of the mold are covered with an aluminum oxide layer, and more preferably, the entire surface of the mold is covered.
In order to form an aluminum oxide layer on 80% or more of the surface of the Ni-based alloy for hot molds within this temperature range, for example, an oxide layer (oxide film) is formed by performing injection processing such as shot blasting. Can be promoted. However, if there is excessive component segregation in the Ni-based alloy for hot molds, the oxide film tends to be non-uniform. Therefore, component segregation is reduced, for example, homogenization heat treatment at 1100 to 1300 ° C. for about 10 to 100 hours performed after an antioxidant is applied to the entire surface of the casting material in an inert atmosphere or in the air. Is preferably applied in advance to prevent non-uniform formation of aluminum oxide. When the coating of the aluminum oxide layer is less than 80% of the surface, there arises a problem that the amount of scale scattering increases. Therefore, in the present invention, the area ratio of the aluminum oxide formed on the surface of the Ni-based alloy for hot dies is 80% or more. Preferably it is 90% or more, Most preferably, it is 100%. In order to confirm the coverage (area ratio) of the aluminum oxide layer of the present invention, it is preferable to observe at least a range of 25 mm ² with an optical microscope.
In addition, a mold that has been degreased and washed after machining is preliminarily heated at a temperature of 1000 ° C. or higher in the atmosphere, and 80% or more of the surface is covered with an aluminum oxide layer. It is possible to suppress the formation of an oxide layer of aluminum due to dirt such as oil and fat adhering to the surface during the attaching operation and the like, and the seizure between the mold and the member. The aluminum oxide layer formed on the molding surface has the effect of improving the wettability of the glass lubricant used as the lubricant. The upper limit of the preheating temperature may be 1150 ° C. Although the preheating time depends on the size of the hot forging die, approximately 10 minutes to 3 hours is sufficient.

<Hot forging die>
In the present invention, a hot forging die using the Ni-based alloy for hot dies having the above alloy composition and coated with an aluminum oxide layer within the range specified in the present invention may be constituted. it can. The hot forging die of the present invention can be obtained by sintering or casting alloy powder. Casting with a lower manufacturing cost is preferable to sintering of the alloy powder. Further, in order to suppress the occurrence of cracking of the material due to stress during solidification, it is preferable to use a sand mold or a ceramic mold as the mold.
Further, at least one of the molding surface and the side surface of the hot forging die of the present invention can be a surface having an antioxidant coating layer. Thereby, oxidation of the mold surface due to contact between oxygen in the atmosphere at high temperature and the mold base material and the accompanying scale scattering can be prevented, and deterioration of the working environment and shape deterioration can be prevented more reliably. The antioxidant described above is preferably an inorganic material composed of one or more of nitride, oxide, and carbide. This is because a dense oxygen barrier film is formed by a nitride, oxide, or carbide coating layer to prevent oxidation of the mold base material. Note that the coating layer may be a single layer of any one of nitride, oxide, and carbide, or may have a laminated structure of a combination of two or more of nitride, oxide, and carbide. Furthermore, the coating layer may be a mixture of two or more of nitrides, oxides, and carbides. In the present invention, in order to form the coating layer, conventional methods such as coating and spraying can be applied. However, the coating layer is preferably formed from an economical viewpoint. Since the film thickness can be easily increased by forming an oxygen barrier film by coating, contact between oxygen in the atmosphere and the base metal of the mold can be prevented more reliably, but the coating layer thickness is excessively increased. Since the effect is saturated, the thickness of the coating layer is preferably 100 to 200 μm. Further, the antioxidant before application is preferably a slurry that can be easily applied, and the application method is preferably simple brush application.
As described above, the hot forging die using the Ni-based alloy for hot die of the present invention described above has high high temperature compressive strength and good oxidation resistance, and oxygen and die in the atmosphere at high temperature. Oxidation of the mold surface due to the contact of the base material and scale scattering associated therewith can be prevented, and deterioration of the working environment and shape deterioration can be more reliably prevented.

<Method for manufacturing forged products>
A typical process in the case of producing a forged product using a hot forging die using the Ni-based alloy for hot die of the present invention will be described.
First, as a first step, the forging material is heated to a predetermined forging temperature. Since the forging temperature varies depending on the material, the temperature is adjusted appropriately. The hot forging die using the Ni-based alloy for hot die of the present invention has the characteristics that can be subjected to constant temperature forging or hot die forging even in the atmosphere at high temperature. It is suitable for hot forging of Ni-base super heat-resistant alloys and Ti alloys. A typical forging temperature is in the range of 1000 to 1150 ° C.
Then, the forging material heated in the first step is hot forged (second step) using the hot forging die. In addition, it is preferable to perform the second step by heating the hot forging die to 1000 ° C. or higher before hot forging. In the case of the above hot die forging or isothermal forging, the hot forging in the second step is preferably die forging. Further, as described above, the Ni-based alloy for hot dies according to the present invention can be hot forged in the atmosphere at a high temperature of 1000 ° C. or higher by using a component with particularly adjusted Cr content.

  The following examples further illustrate the present invention. Ingots of Ni-based alloys for hot molds shown in Table 1 were manufactured by vacuum melting using ceramic molds. The unit is mass%. In addition, P, N, and O contained in the following ingot are each 0.003% or less, and Si, Mn, and Fe are each 0.03% or less. No. in Table 1 1 to 20 are “examples of the present invention”, No. 21 and 22 are Ni-based alloys for hot molds having the composition of “Comparative Example”.

  A 10 mm square cube was cut out from each of the above ingots, and the surface was polished to the equivalent of No. 1000 to produce an oxidation resistance test piece, and the oxidation resistance was evaluated. In the oxidation resistance test, two types of tests were conducted: a test simulating long-time use and a test simulating repeated use when used in the atmosphere as a die for hot forging.

As an oxidation resistance test that simulates long-term use, the present invention example No. 1 to 20 and Comparative Example No. 1 Using the test pieces 21 and 22, the test pieces were placed in a ceramic crucible made of SiO ₂ and Al ₂ O ₃ and placed in a furnace heated to 1100 ° C. for a predetermined time at 1100 ° C. After the holding, the crucible containing the test piece was taken out of the furnace, and a heating test was performed in which the crucible was air-cooled with the same material covered immediately after taking out to prevent the scale from peeling off the crucible. In the heating test, in order to evaluate the oxidation resistance with respect to long-term use, each test piece was tested with a holding time of 3 hours and 8 hours to 20 hours. When preheating is assumed, the first heating (3 hours) corresponds to the preheating, and the second heating (8 hours and 20 hours) is performed at a high temperature accumulated when hot forging is repeatedly performed. The retention time is assumed.
For each test piece, the surface area of the test piece and the mass of the crucible containing the test piece were measured before the heating test, and after cooling to room temperature after the heating test, the mass of the crucible containing the test piece was measured. The mass change per unit surface area of the test piece after each test was calculated by subtracting the mass measured before the test from the mass measured after each test and dividing the value by the surface area measured before the test. The larger the mass change value, the larger the scale generation amount per unit area. The mass change was calculated as follows.
Mass change = (mass after test−mass before test) / surface area before test

Table 2 shows the mass change per unit surface area of the test piece calculated in the heating test for each holding time. The unit of mass change is mg / cm ² . In addition, FIG. 1 to 3, 7, 13, 17 and 20 and Comparative Example No. The relationship between the retention time at 1100 ° C. in the atmosphere of 21 and 22 and the mass change is shown.
From Table 2 and FIG. In Nos. 1 to 20, the amount of scale produced was suppressed and the weight change after 8 hours was less than half that of Comparative Examples 21 and 22 to which no Cr was added. It can be seen that it has excellent oxidation resistance.

In addition, FIG. 2 shows an example No. of the present invention held at 1100 ° C. in the atmosphere for 8 hours. 2 and 3 and Comparative Example No. 21 shows optical micrographs of 21. From the results of quantitative analysis of oxides formed on the surface by an energy dispersive X-ray analyzer and optical micrographs taken at a magnification of 100 times, oxides made of black aluminum oxide layer, green nickel, etc. The area ratio of the aluminum oxide analyzed by distinguishing is shown together in FIG. The measured area is 100 mm ² .
As shown in FIG. In Nos. 2 and 3, it can be seen that the addition of Cr promotes the formation of aluminum oxide, and more than 80% of the surface is covered with the aluminum oxide layer. No. Surfaces after the heating test at 1100 ° C. in the atmosphere of the examples of the present invention other than 2 and 3 are similarly covered with aluminum oxide. Comparative Example No. No. 22 is No. Like 21, the surface is not covered with aluminum oxide. Invention Example No. 1 shown in Table 2 and FIG. The good oxidation resistance of 1 to 20 is due to this aluminum oxide.

  In addition, FIG. 1 and 7 and Comparative Example No. 21. FE-EPMA backscattered electron image and Al, Mo, W, O elements observed near the surface from the cross-sectional direction after resin-embedding the sample after heating test at 1100 ° C. in the atmosphere Show the map. The shading in the element map image corresponds to the concentration of the element to be measured, and the whiter the concentration is. In addition, this invention example No. 1 and Comparative Example No. 21 is a sample after a holding time of 8 hours. 7 is a sample after 3 hours. Comparative Example No. In No. 21, a composite oxide composed of Al, Mo, and W is formed on the surface, and a continuous layer of aluminum oxide is not formed. In 1 and 7, it can be seen that a continuous layer of aluminum oxide is formed on the surface. From the above, it can be seen that the aluminum oxide on the surface of the example of the present invention forms a layer, and this layer was formed by the addition of Cr.

As an oxidation resistance test simulating repeated use, Example No. of the present invention. 1 to 8 and 10 and Comparative Example No. Using the 21 test pieces, the test pieces were placed on a ceramic container made of SiO ₂ and Al ₂ O ₃ and placed in a furnace heated to 1100 ° C. and held at 1100 ° C. for 3 hours. Later, a heating test was conducted in which the sample was taken out of the furnace and cooled by air. In order to evaluate the oxidation resistance to repeated use, the heating test was repeated 5 times by cooling and re-charging.
For each test piece, the surface area and mass of the test piece were measured before the first heating test, and after cooling to room temperature after the first to fifth heating tests, the surface scale was removed with a blower. The mass of was measured. By subtracting the mass measured before the first test from the mass measured after each test and dividing the value by the surface area measured before the first test, the mass change per unit surface area of the test piece after each test Was calculated. The larger the absolute value of the mass change value, the larger the amount of scale scattering per unit area. The mass change after each repetition was calculated as follows.
Mass change = (mass after test−mass before first test) / surface area before first test

Table 3 shows the mass change per unit surface area of the test piece calculated after each heating test. The unit of mass change is mg / cm ² . FIG. 4 shows the relationship between the number of heating tests and the mass change.
As shown in Table 3 and FIG. 1 to 8 and 10 have scale generation (scattering) smaller than that of the alloy of Comparative Example 21, the absolute value of the mass change value is small, and have good oxidation resistance even for repeated use. I understand that. Further, Example No. of the present invention in which Ta was added in addition to Cr. Nos. 4 and 8, and Example No. of the present invention in which La and Zr were added in addition to Cr. Nos. 2 and 3 are Nos. To which only Cr was added. Compared with 1, the scattering of the scale is suppressed.
In addition, Example No. of the present invention in which Hf was added in addition to Cr and Ta. 5 or Invention Example No. 5 with Mg added. No. 6 of the present invention example No. 6 to which only Cr and Ta were added. Compared with 4, scale scattering is further suppressed. Furthermore, Example No. of the present invention in which Hf and Mg were added simultaneously. 7 is an example of the present invention. It can be seen that the scattering of the scale is further suppressed as compared with 5 and 6. This is because the adhesion of the scale is improved by different mechanisms of Hf and Mg, and it can be seen that good results with very little mass change can be obtained. In addition, Example No. of the present invention in which La was added in addition to Cr and Ta. No. 10 of the present invention example No. 10 to which only Cr and Ta were added. Compared to 8, the scattering of the scale is further suppressed, and it can be seen that the oxidation resistance is equivalent to that of Invention Example 7 described above. This is because La has a mechanism for improving the adhesion between the scales of Hf and Mg.

Next, Example No. 1 to 20 and Comparative Example No. 1 A test piece collecting material having a diameter of 8 mm and a height of 12 mm was cut out from each of the ingots 21 and 22, and the surface thereof was polished to No. 1000 to prepare a compression test piece. Using this compression test piece, a compression test was performed at 900 ° C., 1000 ° C., and 1100 ° C. under conditions of a strain rate of 10 ⁻³ / sec and a compression rate of 10%. A 0.2% compressive strength was derived from the stress-strain curve obtained by the compression test, and the high temperature compressive strength was evaluated. This compression test is to test whether a mold for hot forging has a sufficient compressive strength even at high temperatures, and those with test temperatures of 900 ° C. and 1000 ° C. are mainly “hot die forging”. The test temperature of 1100 ° C. is mainly for confirming the application to “constant temperature forging”. At a test temperature of 1100 ° C. assuming constant temperature forging, it can be said that the strength is sufficient if it is 300 MPa or more. Preferably it is 350 MPa or more, More preferably, it is 380 MPa or more. In addition, at test temperatures of 900 ° C. and 1000 ° C. assuming hot die forging, it can be said that a strength of 500 MPa or more is sufficient. Preferably it is 550 MPa or more, More preferably, it is 600 MPa or more.

Table 4 shows an example of the present invention. 1 to 20 and Comparative Example No. 1 The 0.2% compressive strength in each test temperature of the test piece of 21 and 22 is shown. In addition, FIG. 1 to 3 and Comparative Example No. The relationship between each test temperature of 21 and 0.2% compressive strength is illustrated.
From Table 4, No. It can be seen that the compressive strength at a strain rate of 10 ⁻³ / sec at 1000 ° C. of 1 to 3 is 500 MPa or more. No. In 1 and 2, a compressive strength of 600 MPa or more is obtained. No. of preferable Cr amount For 1 and 2, 4 to 20, it can be seen that the compressive strength at a strain rate of 10 ⁻³ / sec at 1100 ° C. is 300 MPa or more. It can be seen that some of them obtained a compressive strength of 350 MPa or more and some obtained a compressive strength of 400 MPa or more. In addition, as shown in FIG. The compressive strength at 1000 ° C. of Nos. 1 to 3 is Comparative Example No. containing no Cr. In comparison with Example 21, it is equal to or greater than that of Example No. The compressive strength at 1000-1100 ° C. of Nos. 1 and 2 is Comparative Example No. It is clear that it is equal to or greater than 21. From the above, it can be seen that any of the alloys of the present invention has high high temperature compressive strength.

Next, as shown in Table 5, the composition of the Ni-based alloy for hot dies according to the present invention was satisfied, and an antioxidant composed of an oxide shown in Table 6 was applied to the surface with a thickness of approximately 150 μm. Using a hot forging die, the effect of preventing oxidation and scale scattering of the hot forging die by an antioxidant was evaluated.
FIG. 6 shows an appearance photograph of the surface of the hot forging die after heating the hot forging die coated with the antioxidant at 1000 ° C. or higher in the atmosphere. As can be seen from FIG. 6, it can be seen that there is no peeling of the antioxidant applied to the surface of the hot forging die. Also, no scattering of scale was confirmed. From this, it is understood that the oxidation of the mold and the scattering of the scale are prevented by the antioxidant.

From the above results, it can be seen that the Ni-based alloy for hot dies of the present invention has both sufficient oxidation resistance and high compressive strength at high temperatures even when used for hot forging in the atmosphere. . Accordingly, it can be seen that the hot forging die using the Ni-based alloy for hot die of the present invention is useful in forging of a product made of a heat-resistant alloy (for example, hot die forging or isothermal forging). . In particular, since scale generation can be significantly reduced, it is possible to suppress deterioration of the work environment and shape deterioration.
Further, when a hot forging die is manufactured using the Ni-based alloy for hot die of the present invention and an application layer of an antioxidant is formed on at least one of the molding surface or the side surface, the work is further improved. In addition to preventing environmental degradation, shape degradation can also be prevented. Therefore, it can be seen that the hot forging die made of the Ni-based alloy for hot die of the present invention is suitable for hot die forging and isothermal forging in the atmosphere.

The present inventor has studied the deterioration of the working environment and shape deterioration due to oxidation of the mold surface and the accompanying scale scattering, and has found a composition having high high temperature compressive strength and good oxidation resistance, and has reached the present invention.
That is, this invention is the mass%, W: 7.0-15.0%, Mo: 2.5-11.0%, Al: 5.0-7.5%, Cr: 0.5-7. Hot forging metal, in which at least 80% of the entire surface of a hot forging die using a Ni-based alloy for hot die made of Ni and inevitable impurities is covered with an aluminum oxide layer at 5%. It is a type.
In the present invention, in addition to the above composition, Zr: 0.5% or less, Hf: 0.5% or less, rare earth element: 0.2% or less, Y: 0.2% or less, Mg: 0.03 One or more selected from elements of% or less can be contained.
In the present invention, in addition to the above composition, 7.0% or less of Ta can be further contained.
In the present invention, in addition to the above composition, the total of one or two elements selected from Ti and Nb is 3.5% or less, and the total content of Ta, Ti and Nb is 1. It can be contained within a range of 0 to 7.0%.
Moreover, in this invention, in addition to the said composition, Co can be further contained 15.0% or less .

The present invention also includes a first step of heating the forging material and a second step of hot forging the forging material heated in the first step using the hot forging die. This is a method for producing a forged product.
More preferably, in the method for producing a forged product, the second step is performed by heating the hot forging die to 1000 ° C. or higher.
In addition, the present invention performs preheating of the Ni-based alloy for hot dies having the above-described composition at 1000 ° C. or higher in the air before the step of heating the hot forging die to 1000 ° C. or higher. The hot forging die can be obtained by forming an aluminum oxide layer of 80% or more on the entire surface of the Ni-based alloy for hot die .

Claims (15)

  In mass%, W: 7.0 to 15.0%, Mo: 2.5 to 11.0%, Al: 5.0 to 7.5%, Cr: 0.5 to 7.5%, the balance is A hot forging die characterized in that 80% or more of the surface of a Ni-based alloy for hot die made of Ni and inevitable impurities is coated with an aluminum oxide layer.   The Ni-based alloy for hot molds is mass%, Zr: 0.5% or less, Hf: 0.5% or less, rare earth element: 0.2% or less, Y: 0.2% or less, Mg: The hot forging die according to claim 1, further comprising one or more elements selected from 0.03% or less of elements.   The hot forging die according to claim 1 or 2, wherein the Ni-based alloy for hot die further contains 7.0% by mass or less of Ta.   The Ni-based alloy for hot dies further contains 3.5% or less in total of one or two elements selected from elements of Ti and Nb by mass%, and the contents of Ta, Ti and Nb The hot forging die according to claim 2 or 3, wherein a total sum of is 1.0 to 7.0%.   The hot forging die according to any one of claims 1 to 4, wherein the Ni-based alloy for hot die further contains 15.0% or less of Co by mass%.   The Ni-based alloy for hot molds further contains one or two elements selected from elements of C: 0.25% or less and B: 0.05% or less by mass%. The hot forging die according to any one of the above.   The hot forging die according to any one of claims 1 to 6, further comprising an antioxidant coating layer on at least one of a molding surface and a side surface of the hot forging die.   In mass%, W: 7.0 to 15.0%, Mo: 2.5 to 11.0%, Al: 5.0 to 7.5%, Cr: 0.5 to 7.5%, Ta: A Ni-based alloy for hot molds containing 0 to 7.0%, Co: 0 to 15.0%, and the balance being Ni and inevitable impurities.   The Ni-based alloy for hot dies according to claim 8, in mass%, Zr: 0.5% or less, Hf: 0.5% or less, rare earth element: 0.2% or less, Y: 0.2 Ni-based alloy for hot molds further containing one or more selected from elements of not more than% and Mg: not more than 0.03%.   The Ni-based alloy for hot dies according to claim 8 or 9, further containing, in mass%, 3.5% or less in total of one or two elements selected from elements of Ti and Nb, Ta Ni-based alloy for hot molds in which the total content of Ti and Nb is 1.0 to 7.0%. The Ni-based alloy for hot dies according to any one of claims 8 to 10, wherein a 0.2% compressive strength at a test temperature: 1000 ° C and a strain rate: 10 ^-3 / sec is 500 MPa or more. The Ni-based alloy for hot dies according to any one of claims 8 to 10, wherein a 0.2% compressive strength at a test temperature of 1100 ° C and a strain rate of 10 ^-3 / sec is 300 MPa or more. A first step of heating the forging material;
A forging product manufacturing method comprising: a second step of hot forging the forging material heated in the first step using the hot forging die according to any one of claims 1 to 7.   The manufacturing method of the forge product of Claim 13 which heats the said metal mold | die for hot forging to 1000 degreeC or more, and performs a 2nd process. Prior to the step of heating the hot forging die to 1000 ° C. or higher, the Ni die alloy for hot die is preheated to 1000 ° C. or higher in the atmosphere to obtain the Ni base alloy for hot die. The method for producing a forged product according to claim 14, wherein an aluminum oxide layer is formed on 80% or more of the surface of the forged product.

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