JP7452172B2 - Method for manufacturing hot forged materials - Google Patents

Description

The present invention relates to a method for manufacturing a hot forged material using a heated die.

In forging heat-resistant alloys, the forging material is heated to a predetermined temperature in order to reduce deformation resistance. Since heat-resistant alloys have high strength even at high temperatures, hot forging dies used for forging them are required to have high mechanical strength at high temperatures. In addition, in hot forging, if the temperature of the hot forging die is about the same as room temperature, the workability of the forging material decreases due to heat removal, so for example, forging of difficult-to-work materials such as Alloy 718 and Ti alloy This is done by heating a hot forging die together with the raw material. Therefore, a hot forging die must have high mechanical strength at a high temperature that is the same as or close to the temperature at which the forging material is heated. As a hot forging die that satisfies this requirement, a Ni-based super heat-resistant alloy that can be used for hot forging in the atmosphere at a die temperature of 1000° C. or higher has been proposed (see, for example, Patent Documents 1 to 3).
Hot forging of difficult-to-process materials includes hot die forging, which uses a mold heated to a temperature close to that of the forging material, and forges at a strain rate of, for example, 0.01 to 0.1/sec, and forging materials. By using a mold heated isothermally, isothermal forging is applied, which allows forging at a strain rate slower than hot die forging, for example, 0.001/sec or less. As for hot forging performed in the atmosphere using a die made of Ni-based super heat-resistant alloy proposed in Patent Documents 1 to 3, an example of isothermal forging is shown in Non-Patent Document 1, and an example of hot die forging is shown in Patent Document 1. 4. By making the hot forged material into a shape close to the final shape, it is possible to improve the yield and reduce processing costs.In terms of forging material costs, the hot forged material has uneven deformation due to heat removal by the die. Isothermal forging is advantageous because it does not exist. On the other hand, the lower the temperature of the mold, the higher the high-temperature strength of the mold and the longer the life of the mold. Therefore, hot die forging, which has a relatively low mold temperature, is advantageous in terms of mold cost. If the forging conditions such as strain rate that affect the structure of the hot forged material are within the allowable range, when choosing between hot die forging and isothermal forging, there are operating costs that depend on equipment costs and the number of forging processes in addition to these costs. The one with the lowest manufacturing cost including the following will be selected.

Japanese Unexamined Patent Publication No. 62-50429 Special Publication No. 63-21737 US Patent No. 4,740,354 Japanese Patent Application Publication No. 3-174938

Transactions of the Iron and Steel Institute of Japan Vol.28(1988) No.11 P.958-964

When a Ni-based super heat-resistant alloy such as Mar-M200, which is shown as a conventional alloy in the example of Patent Document 2, is used in a mold, the upper limit of a general mold in hot die forging of difficult-to-process materials on an actual machine The temperature is about 900°C from the viewpoint of mold life. The general heating temperature for difficult-to-work materials is 1000 to 1150°C, so the mold temperature is 100 to 250°C lower than the hot forging material. In order to make the hot-forged material into a shape close to the final shape, it is advantageous to have a smaller temperature difference between the mold temperature and the hot-forged material. By applying a Ni-based super heat-resistant alloy, which has excellent properties and is advantageous in terms of mold service life, to a mold for hot die forging, the temperature difference with the hot forging material can be reduced. In order to fully obtain the effect of increasing the mold temperature, the mold temperature in this case needs to be 950° C. or higher.
The temperature near the surface of the hot forging material heated in the heating furnace decreases during transportation. If the difference between the heating temperature of the hot forging material and the mold heating temperature is small, if the hot forging material whose temperature near the surface has decreased during transportation is placed on the lower die, the temperature near the surface of the hot forging material will be lower than that of the metal. The temperature will be lower than the heating temperature of the mold. If hot forging is performed in this state, metal will be generated near the top and bottom surfaces of the hot forging material that come into contact with the upper and lower dies (a pair of upper and lower dies are referred to as "molds") during hot forging. While the temperature of the hot forging material increases due to heating by the mold, the temperature of the side surface of the hot forging material that is not in contact with the mold remains low. When hot forging is performed under such temperature unevenness, the areas near the top and bottom surfaces, where deformation resistance is relatively low, are preferentially deformed, resulting in double barreling-like forging defects on the sides of the hot forged material. More likely. Note that the upper and lower bottom surfaces in the present invention refer to the surfaces of the hot forging material that are in contact with the upper mold and the surfaces that are in contact with the lower mold. In addition, the double barreling forging defect referred to in the present invention refers to the hot forging material expanding in a curved shape in the outer circumferential direction on the side surface of the forging material after general upsetting forging of a cylindrical forging material. It refers to an elliptical depression on the side surface of a forged material, which is created by the barreling part that occurs near the top and bottom surfaces of the forged material. FIG. 1 illustrates the double barreling-like forging defect referred to in the present invention, including the hot forging process.
Generally, when this forging defect occurs, the volume of the cut-off portion other than the final shape in the hot forged material increases, resulting in a decrease in yield.

The above-mentioned problems tend to become particularly noticeable when large-sized forged materials are obtained. Therefore, in hot die forging, which uses a Ni-based super heat-resistant alloy for the mold, which has excellent high-temperature strength and is advantageous in terms of mold life, in addition to changing the mold material, a manufacturing method that does not cause double barreling-like forging defects is applied. There is a need to do so.
As a first method for this purpose, a decrease in the surface temperature of the hot forging material during transportation can be suppressed by shortening the transportation time. However, even in general hot die forging where the mold temperature is 900° C. or lower, the conveyance time can be shortened. Therefore, it is more effective to consider methods other than shortening the transportation time.
Patent Document 4 discloses hot die forging in which a forging material is coated with a metal material having a melting point higher than the forging temperature and then forged. If this method is used, it is possible to carry out hot die forging without causing double barreling defects even when the die temperature is 950° C. or higher. However, the method of Patent Document 4 requires coating the hot forging material before forging and removing the coating after forging, which reduces productivity.
The reality is that in hot die forging where the mold temperature is 950° C. or higher, there has been no proposal for a method for producing hot forged materials that prevents double barreling defects from occurring without reducing productivity.
An object of the present invention is to provide a method for manufacturing a hot forged material that can prevent double barreling defects from occurring.

The present inventor investigated the occurrence of double barreling-like forging defects in hot die forging where the mold temperature is 950° C. or higher, found temperature conditions that can suppress double-barreling-like forging defects, and arrived at the present invention.
That is, in the present invention, both the upper mold and the lower mold are made of a Ni-based super heat-resistant alloy, and the hot forging material is pressed in the atmosphere by the lower mold and the upper mold to form a hot forged material. In the method for producing a hot forged material including a hot forging step, a material heating step of heating the hot forging material to a heating temperature within a range of 1025 to 1150° C. in a heating furnace; A mold heating step of heating the mold to a heating temperature within a range of 950 to 1075° C., and a conveyance step of conveying the hot forging material from the inside of the heating furnace to above the lower mold by a manipulator, and A value obtained by subtracting the heating temperatures of the upper mold and the lower mold from the heating temperature of the hot forging material is 75° C. or higher, and the hot forging material is used during hot forging in the hot forging step. This is a method for producing a hot forged material in which the strain rate is always 0.001/sec or more.
Further, the composition of the Ni-based superheat-resistant alloy is, in mass%, W: 7.0 to 16.0%, Mo: 1.0 to 11.0%, Al: 5.0 to 7.5%, selected Elements: Cr: 7.5% or less, Ta: 7.0% or less, Ti: 7.0% or less, Nb: 7.0% or less, Co: 15.0% or less, C: 0.25% or less , B: 0.05% or less, N: 0.015% or less, Zr: 0.8% or less, Hf: 0.8% or less, rare earth elements: 0.2% or less, Y: 0.2% or less, It is preferable that Mg: 0.03% or less, Ca: 0.03% or less, and the balance is Ni and inevitable impurities.
Further, it is preferable that a lubrication coating is provided on the surface of the hot forging material by applying a liquid lubricant before the hot forging material is heated to the heating temperature in the heating furnace.

According to the present invention, it is possible to prevent double barreling-like forging defects from occurring.

FIG. 2 is a diagram showing a double barreling-like forging defect caused by hot forging. It is a schematic diagram which illustrated each process of the manufacturing method of the hot forging material based on this invention, and the flow between processes. FIG. 2 is a schematic diagram showing the effect of preventing double barreling-like forging defects by applying the method for producing hot forged material according to the present invention.

Embodiments of the present invention will be described in detail below.
<Material for hot forging>
First, a hot forging material (hereinafter also referred to as raw material) used in the method for producing a hot forging material of the present invention will be described.
INDUSTRIAL APPLICATION This invention is suitable for the manufacturing method of the hot forging material which hot forges the raw material for hot forging which consists of a difficult-to-process material. Typical examples of difficult-to-process materials include Ni-based super heat-resistant alloys containing Ni as a main component and Ti alloys containing Ti as a main component. Note that the term "main component" as used in the present invention refers to the element having the highest content in mass %. The shape and internal structure of the material for hot forging are not particularly limited, but any shape or internal structure that is generally suitable for a material for hot forging may be used. In addition, the "Ni-based super heat-resistant alloy" as used in the present invention is a Ni-based alloy, also called superalloy, heat-resistant superalloy, or superalloy, which is used in a high temperature range of 600°C or higher, and includes γ', etc. Refers to an alloy that is strengthened by precipitated phases.
In order to prevent the occurrence of double barreling-like forging defects, the shape of the hot forging material in the present invention is determined by setting the height of the material when it is placed in the mold to the maximum width of the material. The value divided by (diameter) is preferably 3.0 or less, more preferably 2.8 or less, and particularly preferably 2.5 or less. This is because if this value exceeds 3.0, there is a high possibility that other forging defects such as buckling will occur in addition to double barreling defects.
Further, the surface of the material for hot forging may have a surface state in which scale is formed, but in order to uniformly apply the lubricant, it is preferably a metal surface that has been degreased and cleaned after machining.

In addition, during hot forging, the surface of the hot forging material and the die come into contact with each other at high temperatures and high stress loads. A lubricant or mold release agent is used to suppress mold wear. In hot forging in the air at a mold temperature of 950°C or higher, as in the present invention, graphite-based lubricants, boron nitride-based mold release agents, glass-based lubricants are used as lubricants or mold release agents. A mold release agent is also used.
In the present invention, it is preferable to use a glass-based liquid lubricant in which glass frit is dispersed in a dispersant such as water, from the viewpoint of reducing molding load and coating workability. The glass frit is preferably borosilicate glass, which has an advantageous viscosity in terms of reducing molding load. Further, from the viewpoint of suppressing chemical reactions that promote oxidative corrosion between the hot forging material and the mold, it is preferable that the alkali component content of the glass in this liquid lubricant be low.
The glass-based liquid lubricant mentioned above can be applied to the surface of the hot forging material by, for example, spraying, brushing, or dipping the entire surface of the hot forging material, or spraying or brushing the mold surface. and supplied between the hot forging material and the die. Among these, spray coating is the most preferred coating method from the viewpoint of controlling the thickness of the lubricating film. The hot forging material before the lubricant is applied may be heated to a temperature higher than room temperature before the application operation in order to promote volatilization of a dispersant such as water contained in the liquid lubricant.
The thickness of the glass-based lubricant film formed by coating is preferably 100 μm or more in order to form a continuous lubricant film during hot forging. If the thickness is less than 100 μm, the lubricating film may be partially damaged, and in addition to deterioration of lubricity due to direct contact between the hot forging material and the die, there is a risk that the die may be more likely to wear out or seize. Further, from the viewpoint of suppressing a temperature drop during transportation of the material for hot forging, it is preferable that the lubricating film be thick. However, if the lubricating film is too thick, when forging is performed using a mold with a complexly shaped die surface, there is a risk that the forged product will fall out of dimensional tolerance due to glass deposits on the die surface. . Therefore, the thickness of the lubricating film is preferably 500 μm or less.

<Mold>
Next, the mold used in the present invention will be explained. The term "mold" as used in the present invention refers to a pair of upper and lower molds.
The material of the mold used in the present invention is a Ni-based super heat-resistant alloy that has excellent high-temperature strength and is advantageous in terms of mold life. In addition to Ni-based super heat-resistant alloys, fine ceramics and Mo-based alloys can be used as mold materials with excellent high-temperature strength. However, molds made of fine ceramics are expensive. Furthermore, if the mold is made of a Mo-based alloy, it must be used in an inert atmosphere, which requires dedicated large-scale and special equipment. Therefore, these are disadvantageous in terms of manufacturing cost compared to Ni-based super heat-resistant alloys. For the above reasons, the material of the mold used in the present invention is a Ni-based super heat-resistant alloy.
Among the Ni-based super heat-resistant alloys that have excellent high-temperature strength, the Ni-based super heat-resistant alloys having the alloy composition described below not only have excellent high-temperature compressive strength but also are suitable for hot forging even in high-temperature atmospheric atmospheres. This alloy has sufficient strength to be used as a mold.
The composition of a preferable Ni-based super heat-resistant alloy for hot forging molds will be explained below. Note that the unit of chemical composition is mass %. The preferred composition of the Ni-based superheat-resistant alloy is, in mass%, W: 7.0 to 16.0%, Mo: 1.0 to 11.0%, Al: 5.0 to 7.5%, and as selected elements. , Cr: 7.5% or less, Ta: 7.0% or less, Ti: 7.0% or less, Nb: 7.0% or less, Co: 15.0% or less, C: 0.25% or less, B : 0.05% or less, N: 0.01% or less, Zr: 0.8% or less, Hf: 0.8% or less, rare earth elements: 0.2% or less, Y: 0.2% or less, Mg: 0.03% or less, Ca: 0.03% or less, the remainder being Ni and inevitable impurities.

<W: 7.0-16.0%>
W is dissolved in solid solution in the austenite matrix and also in the gamma prime phase (γ' phase) whose basic form is Ni ₃ Al, which is a precipitation strengthening phase, thereby increasing the high temperature strength of the alloy. On the other hand, W has the effect of lowering the oxidation resistance and the effect of making harmful phases such as TCP (Topologically Close Packed) phase more likely to precipitate. From the viewpoint of increasing high-temperature strength and further suppressing deterioration in oxidation resistance and precipitation of harmful phases, the content of W in the Ni-based superheat-resistant alloy in the present invention is set to 7.0 to 16.0%. In order to more reliably obtain the effect of W, a preferable lower limit is 10.0%, a preferable upper limit of W is 15.0%, an even more preferable upper limit is 12.0%, and more preferably 11.0%. It is.
<Mo: 1.0-11.0%>
Mo is dissolved in solid solution in the austenite matrix and also in the gamma prime phase whose basic form is Ni ₃ Al, which is a precipitation-strengthening phase, thereby increasing the high-temperature strength of the alloy. On the other hand, Mo has the effect of reducing oxidation resistance. From the viewpoint of increasing high-temperature strength and further suppressing deterioration of oxidation resistance, the content of Mo in the Ni-based superheat-resistant alloy in the present invention is set to 1.0 to 11.0%. In addition, in order to suppress the precipitation of harmful phases such as TCP phase due to the addition of W and Ta, Ti, and Nb, which will be described later, a preferable lower limit of Mo should be set in consideration of W and the contents of Ta, Ti, and Nb, which will be described later. is preferable, and in order to more reliably obtain the effect of Mo when Ta is contained, the preferable lower limit is 2.5%, the more preferable lower limit is 4.0%, and more preferably 4.5%. On the other hand, when Ta, Ti, and Nb are not contained, the preferable lower limit of Mo is 7.0%, and the more preferable lower limit is 9.5%. Further, a preferable upper limit of Mo is 10.5%, and a more preferable upper limit is 10.2%.
<Al: 5.0-7.5%>
Al combines with Ni to precipitate a gamma prime phase consisting of Ni ₃ Al, increases the high temperature strength of the alloy, forms an alumina film on the surface of the alloy, and has the effect of imparting oxidation resistance to the alloy. On the other hand, if the Al content is too high, the eutectic gamma prime phase is excessively produced, which also has the effect of lowering the high temperature strength of the alloy. From the viewpoint of increasing oxidation resistance and high-temperature strength, the Al content in the Ni-based superheat-resistant alloy in the present invention is set to 5.0 to 7.5%. In order to more reliably obtain the effect of Al, the preferable lower limit is 5.5%, and the more preferable lower limit is 6.1%. Further, a preferable upper limit of Al is 6.7%, and a more preferable upper limit is 6.5%.

<Cr: 7.5% or less>
The Ni-based superheat-resistant alloy in the present invention can contain Cr. Cr promotes the formation of a continuous layer of alumina on or inside the alloy, and has the effect of improving the oxidation resistance of the alloy. The dimensional tolerance of hot forged materials is larger than that of isothermal forging, and in the case of hot die forging where the mold heating temperature is low, the importance of oxidation resistance is relatively low and the addition of Cr is not essential. In the Ni-based super heat-resistant alloy, Cr is added as necessary. Note that this does not prevent its inclusion as an impurity. Further, if it is necessary to add Cr, addition of Cr in an amount exceeding 7.5% must be avoided since it also reduces the compressive strength of the alloy at temperatures above 1000°C. A preferable lower limit for reliably obtaining the effect of Cr is 0.5%, a more preferable lower limit is 1.3%, and a preferable upper limit of Cr is 3.0%.
<Ta: 7.0% or less>
The Ni-based superheat-resistant alloy in the present invention can contain Ta. Ta solidly dissolves in the gamma prime phase consisting of Ni ₃ Al by replacing Al sites, increasing the high temperature strength of the alloy, and increasing the adhesion and oxidation resistance of the oxide film formed on the alloy surface. It has the effect of improving the oxidation resistance of the alloy. Compared to isothermal forging, the dimensional tolerance of hot forged materials is larger, and in the case of hot die forging where the mold heating temperature is low, the importance of oxidation resistance and high temperature strength is relatively low, so the addition of Ta is not essential. In addition, Ta is expensive, and if a large amount is added, the mold cost will be high. Therefore, in the Ni-based superheat-resistant alloy according to the present invention, Ta is added as necessary. Note that this does not prevent its inclusion as an impurity. In addition, if it is necessary to add Ta, if the Ta content is too high, it will tend to precipitate harmful phases such as TCP phase, or excessively generate eutectic gamma prime phase, reducing the high-temperature strength of the alloy. Since it also has some effects, it is necessary to avoid adding it in an amount exceeding 7.0%. A preferable lower limit for reliably obtaining the effect of Ta is 0.5%, and a more preferable lower limit is 2.5%. A preferable upper limit of Ta is 6.5%. In addition, when Ta is contained together with Ti or Nb, which will be described later, if the total content of these elements is large, high-temperature strength will decrease due to precipitation of harmful phases and excessive formation of eutectic gamma prime phase. The total content of these elements is preferably 7.0% or less.

<Ti: 7.0% or less>
The Ni-based superheat-resistant alloy in the present invention can contain Ti. Similar to Ta, Ti dissolves in the gamma prime phase composed of Ni ₃ Al by substituting Al sites, thereby increasing the high-temperature strength of the alloy. Furthermore, since it is a cheaper element than Ta, it is advantageous in terms of mold cost. Compared to isothermal forging, the dimensional tolerance of hot forged materials is larger, and in the case of hot die forging where the mold heating temperature is low, the importance of high temperature strength is relatively low, so the addition of Ti is not essential. Therefore, in the Ni-based superheat-resistant alloy according to the present invention, Ti is added as necessary. Note that this does not prevent its inclusion as an impurity. In addition, if it is necessary to add Ti, if the Ti content is too high, it will tend to precipitate harmful phases such as TCP phase, or it will generate excessive eutectic gamma prime phase, reducing the high-temperature strength of the alloy. Since it also has some effects, it is necessary to avoid adding it in an amount exceeding 7.0%. A preferable lower limit for reliably obtaining the effect of Ti is 0.5%, and a more preferable lower limit is 2.5%. A preferable upper limit of Ti is 6.5%. In addition, when Ti is contained together with the above-mentioned Ta or the below-mentioned Nb, if the total content of these elements is large, the high-temperature strength will decrease due to precipitation of harmful phases and excessive formation of eutectic gamma prime phase. Therefore, the total content of these elements is preferably 7.0% or less.
<Nb: 7.0% or less>
The Ni-based superheat-resistant alloy in the present invention can contain Nb. Like Ta and Ti, Nb dissolves in the gamma prime phase consisting of Ni ₃ Al by substituting Al sites, thereby increasing the high-temperature strength of the alloy. Furthermore, since it is a cheaper element than Ta, it is advantageous in terms of mold cost. Compared to isothermal forging, the dimensional tolerance of hot forged materials is larger, and in the case of hot die forging where the mold heating temperature is low, the importance of high temperature strength is relatively low, so the addition of Nb is not essential. Therefore, in the Ni-based superheat-resistant alloy according to the present invention, Nb is added as necessary. Note that this does not prevent its inclusion as an impurity. In addition, if it is necessary to add Nb, if the Nb content is too high, it will tend to precipitate harmful phases such as TCP phase or excessively generate eutectic gamma prime phase, reducing the high-temperature strength of the alloy. Since it also has some effects, it is necessary to avoid adding it in an amount exceeding 7.0%. A preferable lower limit for reliably obtaining the effect of Nb is 0.5%, and a more preferable lower limit is 2.5%. A preferable upper limit of Ti is 6.5%. In addition, when Nb is contained together with the above-mentioned Ta or Ti, if the total content of these elements is large, high-temperature strength will decrease due to precipitation of harmful phases and excessive formation of eutectic gamma prime phase. The total content of these elements is preferably 7.0% or less.
<Co: 15.0% or less>
The Ni-based superheat-resistant alloy in the present invention can contain Co. Co dissolves in the austenite matrix and increases the high temperature strength of the alloy. Compared to isothermal forging, the dimensional tolerance of hot forged materials is larger, and in the case of hot die forging where the mold heating temperature is low, the importance of high temperature strength is relatively low, so the addition of Co is not essential. Therefore, in the Ni-based superheat-resistant alloy of the present invention, Co is added as necessary. Note that this does not prevent its inclusion as an impurity. Moreover, if the content of Co is too high, since Co is an expensive element compared to Ni, the cost of the mold will increase, and it will also have the effect of making harmful phases such as TCP phase more likely to precipitate. Therefore, addition of more than 15.0% must be avoided. A preferable lower limit for reliably obtaining the effect of Co is 0.5%, and a more preferable lower limit is 2.5%. The preferred upper limit is 13.0%.

<C and B>
The Ni-based superheat-resistant alloy in the present invention can contain one or two elements selected from C and B. C and B improve the strength of the grain boundaries of the alloy, increasing high temperature strength and ductility. Therefore, in the Ni-based superheat-resistant alloy according to the present invention, one or two elements selected from C and B are also added as necessary. Note that this does not prevent its inclusion as an impurity. Furthermore, if the content of C and B is too large, coarse carbides and borides are formed, which also has the effect of reducing the strength of the alloy. From the viewpoint of increasing the strength of the grain boundaries of the alloy and suppressing the formation of coarse carbides and borides, the upper limit of the C content in the present invention is 0.25%, and the upper limit of the B content is 0.05%. It is. A preferable lower limit for reliably obtaining the effect of C is 0.005%, and a more preferable lower limit is 0.01%. Moreover, a preferable upper limit is 0.15%. A preferable lower limit for reliably obtaining the effect of B is 0.005%, and a more preferable lower limit is 0.01%. Further, a preferable upper limit is 0.03%.
When economy and high-temperature strength are particularly required, it is preferable to add only C, and when ductility is particularly required, it is preferable to add only B. When both high temperature strength and ductility are particularly required, it is preferable to add C and B at the same time.
<N>
When containing Ti and C mentioned above, it is preferable that N is intentionally contained. This is because the nitrides formed together with Ti act as precipitation nuclei of MC carbides having a similar crystal structure, giving the MC carbides a desirable shape and finely dispersing them, thereby increasing the tensile strength. On the other hand, if the N content becomes too large, microporosity derived from N will occur excessively and the tensile strength will decrease. Therefore, the N content in the present invention is set to 0.015% or less. When Ti and C are contained, the content is preferably 0.0006% or more, more preferably 0.001% or more, in order to increase the tensile strength. Further, a preferable upper limit of N is 0.009%, and a more preferable upper limit is 0.008%.

<Other optional additive elements>
The Ni-based superheat-resistant alloy in the present invention can contain one or more elements selected from Zr, Hf, rare earth elements, Y, Ca, and Mg. Note that this does not prevent its inclusion as an impurity. Zr, Hf, rare earth elements, and Y suppress the diffusion of metal ions and oxygen at the grain boundaries by segregation to the grain boundaries of the oxide film formed on the alloy surface. Suppression of this grain boundary diffusion reduces the growth rate of the oxide film, and also improves the adhesion between the oxide film and the alloy by changing the growth mechanism that promotes peeling of the oxide film. That is, these elements have the effect of improving the oxidation resistance of the alloy by reducing the growth rate of the oxide film and improving the adhesion of the oxide film.
Further, the alloy contains a considerable amount of S (sulfur) as an impurity. This S decreases the adhesion of the oxide film by segregation at the interface between the oxide film formed on the alloy surface and the alloy and by inhibiting the chemical bonding thereof. Ca and Mg form sulfides with S and have the effect of improving the adhesion of the oxide film and improving the oxidation resistance of the alloy by preventing segregation of S.
Note that among the rare earth elements, it is preferable to use La. This is because La has a large effect of improving oxidation resistance. In addition to suppressing the above-mentioned diffusion, La also has the effect of preventing the segregation of S, and these effects are excellent, so that La is preferably selected from among the rare earth elements. Further, since Y also exhibits the same effects as La, addition of Y is also preferable, and it is particularly preferable to use two or more types containing La and Y.
If good mechanical properties are required in addition to oxidation resistance, it is preferable to use Hf or Zr, particularly preferably Hf. Further, when adding Hf, since Hf has a small effect of preventing segregation of S, oxidation resistance is further improved by adding Mg in addition to Hf at the same time. Therefore, when mechanical properties as well as oxidation resistance are required, it is more preferable to use two or more elements including Hf and Mg.

If the amounts of the above-mentioned Zr, Hf, rare earth elements, Y, Ca, and Mg are too large, intermetallic compounds with Ni etc. will be formed excessively and the toughness of the alloy will decrease, so these arbitrary additions are not recommended. It is preferable that the elements are contained in suitable amounts. In addition, Zr and Hf form carbides together with C to increase tensile strength.
From the above, the upper limit of each content of Zr and Hf in the present invention is 0.8%. The preferable upper limit of the content of each of Zr and Hf is 0.5%, more preferably 0.2%, and even more preferably 0.15%. When not containing C, the preferable upper limit of Zr and Hf is 0.2%, more preferably 0.1%.
Since the rare earth element Y has a higher effect of lowering toughness than Zr and Hf, the upper limit of the content of each of these elements in the present invention is 0.2%, the preferable upper limit is 0.1%, and Preferably it is 0.05%, more preferably 0.02%. When containing Zr, Hf, rare earth elements, and Y, the preferable lower limit is 0.001%. The preferred lower limit for fully exhibiting the effects of containing Zr, Hf, rare earth elements, and Y is 0.005%, and more preferably 0.01% or more.
Moreover, since it is sufficient to contain only the amount of Ca and Mg necessary to form sulfide with the impurity S contained in the alloy, the contents of Ca and Mg are each 0.03% or less. A preferable upper limit is 0.02%, more preferably 0.01%. On the other hand, in order to more reliably exhibit the effects of Mg addition, the lower limit is preferably 0.005%. Further, since Mg has a smaller effect of reducing toughness and ductility than Ca, it is preferable to use only Mg alone when the S content is low and there is no need to contain a large amount of these elements.
The additive elements other than those described above are Ni and unavoidable impurities. In the Ni-based superheat-resistant alloy according to the present invention, Ni is a main element constituting the gamma phase, and together with Al, Ta, Ti, Nb, Mo, and W constitutes the gamma prime phase. In addition, unavoidable impurities are assumed to be P, N, O, S, Si, Mn, Fe, Cu, etc., and if the ingot is cast in a furnace normally used for Ni-based alloys, V, Re, etc. Ru is assumed. P, O, and S may be contained as long as they are each 0.003% or less, and Si, Mn, Fe, Cu, V, Re, and Ru may be contained as long as they are each 0.5% or less. It doesn't matter if you stay there. Further, the Ni-based alloy of the present invention can also be called a Ni-based heat-resistant alloy. Note that, among the unavoidable impurity elements, the content of S in particular is preferably 0.015% or less, and more preferably 0.0010% or less.

By the way, the shape of the mold used in the present invention is not limited, and the shape may be selected depending on the shape of the hot forging material or the hot forging material.
Further, in the present invention, from the viewpoint of improving workability, at least one of the molding surface or side surface of the mold can be coated with an antioxidant coating layer, if necessary. This prevents oxidation of the mold surface due to contact between atmospheric oxygen and the base material of the mold at high temperatures and the accompanying scale scattering, thereby preventing deterioration of the working environment and deterioration of the shape. The aforementioned antioxidant is preferably an inorganic material made of one or more of nitrides, oxides, and carbides. This is to form a dense oxygen-blocking film using a coating layer of nitride, oxide, or carbide to prevent oxidation of the mold base material. The coating layer may be a single layer of nitride, oxide, or 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.

Next, the "material heating process" and the "mold heating process" will be explained. In order to prevent the above-mentioned double barreling-like forging defects, (1) the heating temperature of the hot forging material, (2) the heating temperature of the mold, and (3) the temperature difference therebetween are very important.
The present inventor investigated the occurrence of double barreling-like forging defects in hot die forging where the die temperature is 950°C or higher, and found that the main cause of the occurrence was a temperature drop near the surface of the hot forging material during transportation and a It was found that deformation occurs preferentially near the top and bottom surfaces of the material during hot forging due to recuperation of heat near the top and bottom surfaces of the material due to the die. Therefore, it is important to appropriately manage the above-mentioned (1) to (3).
<Material heating process>
Using the hot forging material described above, the hot forging material is heated to a predetermined temperature. An example of the subsequent steps is illustrated in FIG. The mold heating step and the material heating step may be performed simultaneously. However, the transport process is performed after all of these processes are completed, and the forging process is performed after this transport process is completed.
The material for hot forging is heated to the desired material temperature using a heating furnace. In the present invention, a material for hot forging is heated in a heating furnace to a heating temperature within the range of 1025 to 1150°C. This heating brings the temperature of the hot forging material to the heating temperature. The heating time may be longer than the time at which the entire hot forging material reaches a uniform temperature. The lower limit of the heating temperature is set at 1025° C., which is slightly higher, in anticipation of a temperature drop near the surface of the material for hot forging during transportation to a hot forging device (hot press machine). If the heating temperature is less than 1025°C, double barreling-like forging defects are likely to occur. On the other hand, if the temperature exceeds 1150° C., a problem arises in that the metal structure of the hot forging material becomes coarse. Note that the actual heating temperature is preferably determined within the range of 1025 to 1150°C depending on the material of the hot forging material.

<Mold heating process>
In the present invention, the mold used for hot forging is also heated to a heating temperature within the range of 950 to 1075°C. This heating brings the temperature of the mold to the heating temperature. At this time, if the mold is made of a Ni-based super heat-resistant alloy having the above-mentioned preferred composition, it can be heated to the target temperature in the atmosphere. The heating temperature of the mold was set to 950 to 1075° C. because this is the temperature necessary to perform hot die forging and to prevent double barreling-like forging defects. Outside this range of 950 to 1075°C, double barreling-like forging defects may occur. In heating the mold, it is sufficient that at least the surface temperature of the pressing surface of the mold reaches the desired temperature.
Then, the value obtained by subtracting the heating temperature of the mold from the heating temperature of the hot forging material is set to be 75° C. or higher. If the temperature difference obtained by subtracting the heating temperature of the mold from the heating temperature of the hot forging material is less than 75℃, when the hot forging material is placed on the lower mold, the temperature will drop during transportation and the hot forging The temperature near the surface of the material becomes lower than the temperature of the mold surface. If forging is performed in this state, during hot forging, the heat from the mold will recuperate near the top and bottom of the hot forging material, while the temperature will rise and fall near the side surface of the hot forging material where no recuperation occurs. The temperature becomes lower than that near the bottom, resulting in uneven temperature and the resulting difference in deformation resistance, and the areas near the top and bottom, where deformation resistance is relatively low, are preferentially deformed, resulting in double barreling-like forging defects. . Therefore, when the material for hot forging is placed on the lower mold, the temperature near the surface of the material for hot forging is higher than the temperature of the surface of the mold. The temperature difference after subtracting the temperature is set to 75° C. or more to intentionally create a temperature difference between the two to prevent double barreling-like forging defects from occurring.
Regarding the heating of the mold, there are methods of heating the mold to a predetermined temperature using a heating furnace, induction heating, resistance heating, etc., and then transporting the mold to a hot forging device, a heating furnace provided in the hot forging device, and an induction heating device. The predetermined temperature may be set by heating to a predetermined temperature using a resistance heating device or the like, or by a combination of these methods. Further, it is preferable to heat the mold until immediately before the start of pressing in the hot forging process. In addition, if it is possible to continue heating the upper die and/or lower die during hot forging, heating the die during hot forging will allow you to adjust the forging conditions when continuing hot die forging. It can be kept constant and stable production can be performed.

<Transportation process>
After the hot forging material is heated to a target temperature, it is conveyed by a manipulator to a position above the heated lower die. Generally, a manipulator used to transport hot forging materials has a pair of gripping fingers for gripping the hot forging materials from the left and right sides, and is capable of gripping and transporting a predetermined weight. Those that are possible are used, and it is preferred in the present invention to use manipulators with similar functions.
In addition, regarding conveyance by a manipulator, the shorter the conveyance time, the better from the viewpoint of suppressing the occurrence of double barreling-like forging defects. In addition to the above-mentioned temperature difference condition of the present invention, in order to suppress the temperature drop during conveyance, double barreling The occurrence of such forging defects can be more reliably prevented.
Further, the gripping jig for gripping the hot forging material is heated to 950°C or higher and within the temperature range of minus 50°C to +100°C, which is the heating temperature of the hot forging material, and the gripping jig is It is preferable to transport the hot forging material using a tool. This is because the gripping jig heated to an appropriate temperature can suppress the temperature drop on the surface of the hot forging material due to contact with the manipulator's gripping fingers or exposure of the side surface of the hot forging material to the atmosphere during transportation. It is possible to reliably suppress the occurrence of double barreling-like forging defects.
<Hot forging process>
Hot forging is performed using hot forging materials and dies (lower die and upper die) heated to the predetermined temperatures described above. Hot forging is performed by placing a hot forging material on a lower mold and pressing the hot forging material in the atmosphere with the lower mold and the upper mold. Thereby, it is possible to obtain a hot forged material in which double barreling-like forging defects are prevented from occurring. If the hot forging operation time is long, even if a temperature difference is created between the heating temperature of the hot forging material and the mold, the upper and lower bottom areas will regenerate during the hot forging operation, while the hot forging The temperature of the side surface of the forging material decreases, causing a double barreling-like forging defect. In order to prevent double barreling-like forging defects, the strain rate of the hot forging material during hot forging must always be 0.001/sec or more. In order to more reliably prevent double barreling-like forging defects, the strain rate is preferably always 0.005/sec or more, and more preferably always 0.01/sec or more.

The invention will be explained in more detail in the following examples.
First, examples of Ni-based super heat-resistant alloys that are preferable as mold materials used in the present invention will be shown. Ingots of Ni-based super heat-resistant alloys shown in Table 1 were manufactured by vacuum melting. The Ni-based super heat-resistant alloy having the composition shown in Table 1 has excellent high-temperature compressive strength properties as shown in Table 2. In addition, the P and O contained in the ingot shown in Table 1 were each 0.003% or less. Moreover, Si, Mn, and Fe are each 0.03% or less.
The high-temperature compressive strength (compressive yield strength) shown in Table 2 was measured at a strain rate of 10 ^-3 /sec at 1100°C. Under these conditions, if it is 300 MPa or more, it can be said that it has sufficient strength as a mold for hot forging. The compressive yield strength of the Ni-based superheat-resistant alloy having the composition shown in Table 1 shown in Table 2 is 489 MPa at the highest value and 332 MPa at the lowest value. Therefore, it can be seen that all of these have sufficient strength as a mold for hot forging. In addition, No. 1 was also tested under the test conditions of strain rate 10 ^-2 /sec and strain rate 10 ^-1 /sec, and the value in the former was 570 MPa and the value in the latter was 580 MPa, and even under conditions of relatively high strain rate. It was confirmed that it has excellent compressive yield strength. Further, the high-temperature compressive strength of the composition shown in Table 1 when used at a temperature of 1100° C. or lower is equal to or higher than the value shown in Table 2.
Among the Ni-based superheat-resistant alloys shown in Table 1, No. An upper mold and a lower mold having the composition No. 1 were produced.

No. of Table 1 Using the Ni-based super heat-resistant alloy molds (lower mold and upper mold) shown in 1, hot die forging was performed in the air at a mold heating temperature of approximately 1000°C and a hot forging material heating temperature of approximately 1100°C. Ta.
The hot forging material is made of a Ni-based super heat-resistant alloy, and the high-temperature compressive strength of the hot forging material is less than or equal to that of the Ni-based super heat-resistant alloy shown in Table 1. The shape is a cylinder with a diameter of about 300 mm and a height of about 600 mm.The surface of the hot forging material is machined, and the machined surface is lubricated with liquid glass containing borosilicate glass frit. The lubricant was applied by brushing to a thickness of about 400 μm. Thereafter, the hot forging material and the die were heated to a predetermined temperature.

After the temperature of the hot forging material and the gripping jig used for transportation reaches 1100°C and the temperature of the mold reaches 1000°C, the heated hot forging material is transferred to a heating furnace by a manipulator using the gripping jig. It was taken out and placed on the lower mold. After that, hot die forging was performed in which the hot forging material was pressed using a lower die and an upper die. The compression ratio is about 70%. Further, the strain rate is always 0.001/sec or more, and is approximately 0.01/sec throughout the forging operation. The maximum load was approximately 4000 tons. Note that when the hot forging material was placed on the lower mold, the temperature near the surface of the hot forging material was higher than the temperature of the mold surface. The mold was heated also during hot forging.
For comparison, hot die forging was carried out under the same conditions except that the mold heating temperature was 1040°C. The difference between the hot forging material and the mold heating temperature when the mold heating temperature is 1000°C is about 100°C, and when the mold heating temperature is 1040°C, it is about 60°C. When the hot forging material of the comparative example was placed on the lower mold, the temperature near the surface of the hot forging material was lower than the temperature of the mold surface.
FIG. 3(a) is a conceptual diagram of the appearance of a hot forged material manufactured by hot die forging under conditions in which the difference in heating temperature between the hot forging material and the die of the present invention is about 100°C. (b) shows a conceptual diagram of the appearance of a hot forged material manufactured by hot die forging under conditions in which the difference in heating temperature between the hot forged material and the mold is approximately 60° C. in a comparative example.
The difference between the inventive example and the comparative example is only the mold heating temperature, and although the productivity of the two is almost the same, as is clear from FIGS. 3(a) and 3(b), the inventive example By hot die forging under temperature conditions, it is possible to obtain a hot forged material without forging defects.

Claims (3)

Both the upper mold and the lower mold are made of Ni-based super heat-resistant alloy, and the hot forging process is performed in which the hot forging material is pressed in the atmosphere by the lower mold and the upper mold to form a hot forged material. In the method of manufacturing hot forged material including,
a material heating step of heating the hot forging material to a heating temperature within a range of 1025 to 1150° C. in a heating furnace;
a mold heating step of heating the upper mold and the lower mold to a heating temperature within a range of 950 to 1075°C;
When the hot forging material is conveyed to above the lower mold by a manipulator, a gripping jig for gripping the hot forging material is attached to the clamping part of the manipulator, and the gripping jig is configured to transport the hot forging material to the upper die. The gripping jig has a cover that covers the side surface of the material, and the gripping jig is heated to 950°C or higher and within a temperature range of -50°C to +100°C, which is the heating temperature of the hot forging material. a conveyance process of conveying the hot forging material exposed to the atmosphere using a tool ;
including;
The value obtained by subtracting the heating temperature of the upper mold and the lower mold from the heating temperature of the hot forging material is 75° C. or higher, and the strain of the hot forging material during hot forging in the hot forging step A method for producing a hot forged material, characterized in that the speed is always 0.001/sec or more. The Ni-based super heat-resistant alloy contains, in mass%, W: 7.0 to 16.0%, Mo: 1.0 to 11.0%, Al: 5.0 to 7.5%, and Cr as a selected element. : 7.5% or less, Ta: 7.0% or less, Ti: 7.0% or less, Nb: 7.0% or less, Co: 15.0% or less, C: 0.25% or less, B: 0 .05% or less, N: 0.015% or less, Zr: 0.8% or less, Hf: 0.8% or less, rare earth elements: 0.2% or less, Y: 0.2% or less, Mg: 0. 2. The method for producing a hot forged material according to claim 1, wherein the composition has a composition of 0.03% or less, Ca: 0.03% or less, and the remainder consisting of Ni and unavoidable impurities. 2. A lubricant coating is provided on the surface of the hot forging material by applying a liquid lubricant before the hot forging material is heated to the heating temperature in the heating furnace. 2. The method for producing a hot forged material according to 2.