JP6924377B2 - Hot forging dies and their manufacturing methods and forging material manufacturing methods - Google Patents

Description

The present invention relates to a hot forging die and a method for manufacturing the same, and a method for manufacturing a forging material using such a hot forging die.

In recent years, due to the demand for higher efficiency of steam turbines, turbine blades (hereinafter simply referred to as "blades") used in steam turbines have also become longer. In the case of producing a long blade material exceeding about 1500 mm, the mainstream method is to sandwich the material between the upper mold and the lower mold and form the blade material by large-scale press forging.
For example, Japanese Patent Application Laid-Open No. 4-46651 (Patent Document 1) has a three-dimensional shape formed by matching the striking surfaces of an upper mold and a lower mold having a three-dimensionally shaped engraved surface with each other. The invention of a method for manufacturing a blade for forging using an excellent cavity is disclosed. The upper mold and the lower mold disclosed here are made of one metal material and are integrally formed (see, for example, FIGS. 2 and 4 of Patent Document 1).
On the other hand, in Japanese Patent Application Laid-Open No. 2014-208379 (Patent Document 2) by the applicant of the present application, it is a hot forging die for a long material, and the hot forging die has a plurality of heats. There is a proposal for a hot forging die, which is an integral assembly in which pieces of a die forging are arranged in a row in the longitudinal direction of a long material. This proposal is an excellent proposal that can be applied to increasing the size of products (hot forged materials). According to this proposal, it is preferable that several hot forging die pieces are integrated by a tie rod.

Japanese Unexamined Patent Publication No. 4-46651 Japanese Unexamined Patent Publication No. 2014-208379

According to the study of the present inventor, when an attempt is made to integrally manufacture a hot forging die used in a large-scale hot forging device having a scale of tens of thousands of tons, the weight of the material exceeds 50 tons. .. It is difficult to perform heat treatment using such a heavy object as a material to obtain a predetermined characteristic.
Furthermore, in the case of a split die that is assembled using a nesting die, it is said that if the die is press-fitted like a shrink fit, compressive stress will be applied to the nesting die and the die will crack. The risk can also be reduced. However, there is no proposal to fix the nesting die by shrink fitting in the split die in which the nesting die has a square prism shape.
An object of the present invention is to prevent cracking of a hot forging die by shrink-fitting a hot forging die having a square column shape as a nesting die, which can be applied to a large-sized product. It is an object of the present invention to provide a mold, a method for producing the mold, and a method for producing a forging material using such a hot forging die.

The present invention has been made in view of the above-mentioned problems.
That is, the present invention relates to a hot forging die that presses a hot forging material into a forging material.
The hot forging die has at least a nesting die and a master die for accommodating the nesting die.
The nesting mold has a die-engraved surface for pressing the hot forging material and has a square columnar outer shape.
The mother die has a storage portion for accommodating the nesting die and has a square columnar outer shape.
The nested mold has a chamfered shape at a corner extending along a direction of being inserted into the master mold.
The nesting die and the master die are hot forging dies having a structure that is shrink-fitted and integrated.
Preferably, the nesting mold is an assembly of a plurality of nesting mold pieces.
More preferably, the structure has a build-up layer of a Ni-based superheat-resistant alloy on the engraved surface of the nested mold piece. It is also preferable that at least one of the nesting mold pieces is a nesting mold piece made of a Ni-based super heat-resistant alloy.
In the above hot forging die, it is preferable that at least a part of the edge portion of the die carved surface is provided with a split member that can be attached to and detached from the nesting die.
Further, in such a hot forging die, it is preferable that the split member has a higher hot strength than the nesting die.

Further, the present invention relates to a method for manufacturing a hot forging die, which presses a hot forging material into a forging material.
The hot forging die has at least a nesting die and a master die for accommodating the nesting die.
The nesting mold has a square columnar outer shape, has a die-engraved surface for pressing the hot forging material, and has a chamfered shape at a corner portion extending along a direction of being inserted into the master mold. ,
The mother die has a square columnar outer shape, and has a storage portion for accommodating the nesting die.
This is a method for manufacturing a hot forging die in which the nesting die and the mother die are shrink-fitted and integrated.
Preferably, the nesting mold is an assembly of a plurality of nesting mold pieces.

The method for producing a forged material of the present invention is characterized in that a heated hot forging material is hot forged using the above-mentioned hot forging die to obtain a forged material.

The hot forging die of the present invention is a die for hot forging that is integrated by shrink-fitting a nesting die having a square columnar outer shape into a mother die having a square columnar outer shape. It is possible to prevent the mold from cracking and use a hot forging die that can be applied to increasing the size of the product.
Further, according to the method for producing a forging material of the present invention using such a mold, it is possible to reduce the cost related to the mold when, for example, a large forging material is obtained by hot forging.

It is a figure which shows an example of the nesting die of the hot forging die of this invention. It is a figure which shows an example of the hot forging die of this invention. It is a figure which shows an example at the time of fixing the nesting die of the hot forging die of this invention with a fastening member. It is a figure which shows an example of the nesting die piece used for the hot forging die of this invention. It is a figure which shows another example of the hot forging die of this invention. FIG. 5 is a partial cross-sectional view of a nested type of the embodiment shown in FIG.

First, a hot forging die for shrink fitting will be described. Usually, in a hot forging die having a structure in which a nesting die is press-fitted by shrink fitting, for example, as shown in the WO2013 / 147154 pamphlet proposed by the applicant of the present application, an annular or truncated cone-shaped die is used. It is generally a combination. This is because if it is an annular mold, it expands and contracts in the diameter direction, stress is uniformly applied to the entire outer circumference, and it can be firmly integrated by press fitting. On the other hand, for example, when an attempt is made to hot forge a long forged material such as a blade, the combination of the annular and truncated cone-shaped dies as described above can be used as a mold for hot forging the long material. Is unsuitable. Further, there is also a method of integrating the nesting die with a tie rod as in Patent Document 2 described above, but when it is used in a large hot forging device of tens of thousands of tons, cracking of the die is more reliably prevented. It is advantageous to be able to do it. Therefore, in the present invention, the hot forging die used when the forging material is rod-shaped and is used as a long hot forging material by hot forging is produced by shrink fitting. The "hot forging" referred to in the present invention also includes constant temperature forging and hot dies.

The hot forging die of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view of a nesting die 2 constituting the hot forging die of the present invention. As described above, for example, a rod-shaped forging material is hot forged to form a long blade. It is molded into a shape. Therefore, the overall outer shape of the hot forging die 1 (outer shape of the mother die 3) and the outer shape of the nesting die 2 shown in FIG. 2 are square columns. It should be noted that the outer circumference of the hot forging die 1 may be slightly uneven, for example, a collar portion for fixing to a hard plate, and as shown in FIG. 1, the collar portion may be processed. The nesting type fixing frame 23 of another member corresponding to the above may be provided.
In the hot forging die 1 of the present invention, at least the nesting die 2 and the master die 3 provided with the storage portion 31 for accommodating the nesting die 2 are indispensable. As shown in FIG. 2, the surface of the nesting mold 2 has a concave (drilled portion) mold-engraved surface 21 according to the product shape. In the present invention, the dug portion will be described as a "mold carved surface". Further, the outer shape of the nesting type 2 is a square columnar shape. The term "square pillar" as used herein includes, for example, a rectangular parallelepiped as well as a quadrangular pyramid shape.
In the present invention, the corner portions 24 (having four corner portions 24 in FIG. 1) extending along the direction of insertion into the mother mold of the nested mold (hereinafter, simply referred to as the insertion direction) have a chamfered shape. .. The corners may be chamfered in a straight line, or may have an R shape. This chamfered shape is imparted in order to prevent excessive stress concentration on the corner portion 24 and prevent cracking of the nested mold. The nested mold has a carved surface on its surface and processes the forging material. Therefore, the corners of the nesting type that directly receives the forging load at the time of forging are chamfered to alleviate the stress concentration on the corners. The chamfered shape in the present invention is formed for such a purpose, and is different from the square shape that is inevitably formed due to restrictions on mold processing and the like. For example, even if there is a minute rounded shape at the corner portion extending along the direction perpendicular to the insertion direction, the chamfered shape in the present invention is larger than the rounded shape. The size of the chamfered shape may be determined according to the size of the forging load, the size of the nesting mold, and the like. In this case, the size of the chamfered portion means the length removed from each side by one chamfered portion. For example, the size of the chamfered portion can be R10 to R50. It is preferable that the corners of the mother die 3 corresponding to this are also processed according to the chamfered shape of the corners 24 of the nesting die.

In the master mold 3 of the present invention, the nesting mold 2 is press-fitted by shrink fitting, and it is necessary to apply an appropriate stress to the surface in contact with the nesting mold 2. In particular, when the nesting mold is long in the longitudinal direction according to the length of the forging material, such as a rectangular parallelepiped, the thickness of the base mold portion in contact with it (symbol W in FIG. 2) is excessively thin. Since the compressive stress applied to the nesting mold becomes low and the crack prevention effect due to shrink fitting may be insufficient, for example, the height of the nesting mold (IW in FIG. 1) is 1.0 to 2. It is preferable that the thickness is about 0 times that of the nesting type and the thickness is W. Further, the size of the nesting mold and the master mold should be determined by calculating the shrink fit ratio while considering the length of the forging material.

Further, in the nesting mold 2 of the present invention, a plurality of nesting mold pieces 22 are arranged in a row in a row in the longitudinal direction of the nesting mold (direction perpendicular to the direction of being inserted into the master mold), for example, and the assembly body is inserted. It can be a child type. Thereby, the size of each nesting mold piece 22 can be reduced. Therefore, when overlaying the engraved surface, the nested metal piece 22 is individually provided with an arbitrary thickness and shape at a desired location without preparing a new large overlay welding machine. An overlay layer can be formed. Further, the nesting mold piece 22 shown in FIG. 2 may be further divided (as in the mold piece 27) as shown in FIG. In this case, if the die-engraved surface side is preliminarily subjected to aging treatment to obtain a nickel-based superheat-resistant alloy-made nesting die piece 22 whose strength is sufficiently increased, and the die is placed in a place where the largest forging load is applied, the die can be formed. It is also possible to greatly improve the life.
Further, even if some of the nested mold pieces are excessively worn, it is possible to replace or repair only the nested mold pieces. This makes it possible to obtain a hot forging die that is economically advantageous.
As the material of the nesting die piece, basically, for example, hot mold steel such as SKD61 and SKT4 specified by JIS can be used except for the position where a large forging load is applied. When increasing the strength of the mold, a Ni-based superheat-resistant alloy such as Alloy718 or a high-speed tool steel can be selected. Further, in the present invention, a die for hot forging can be formed by combining die pieces made of different materials according to the magnitude of the load applied to each die piece. By combining these, the life of the hot forging die can be improved. As the material of the master mold, steel for hot dies such as SKD61 and SKT4 specified by JIS is sufficient.

Further, the length of the nesting mold piece 22 used in the present invention (the length in the longitudinal direction of the long member) may be uneven. This is because, for example, in the case of a blade or the like, a twisting action acts on the material to be forged during hot forging. Therefore, for example, the nesting die piece 22 at a place where high stress is applied withstands stress. By setting the length and conversely, the location where the stress is low is the length of the die piece, which is advantageous in terms of cost, it is applied to the entire hot forging die when the nesting die piece 22 is assembled. The stress can be dispersed and the mold cost can be reduced. In addition, if necessary, it is preferable to verify the location where the stress of each mold piece is applied in advance by simulation and determine the division location. If it is unavoidable to divide even the location where the stress is high, it is necessary to divide. For example, as shown in FIG. 4, the height direction of the mold piece is further divided diagonally to relieve stress, or a protruding collar portion 26 for receiving the load of adjacent mold pieces is provided. Is effective.
Further, the length of each die piece in the longitudinal direction should be determined in consideration of the stress applied to the hot forging die and the material strength of the die piece itself. In particular, when used in a large-scale hot forging device with a scale of tens of thousands of tons, the stress applied to the die piece also increases, and if the length becomes excessively short, the die piece may break. The length is preferably at least 100 mm or more.

Further, in the present invention, the nesting mold 2 can be an assembly body of four or more nesting mold pieces 22. As described above, the stress can be dispersed by making the length of the nesting mold piece 22 (the length in the longitudinal direction of the long material) non-uniform. For example, in the transition from the initial stage to the final stage of forging, the stress applied to the assembled hot forging die differs depending on each die piece. Therefore, for example, in the case of a blade, the vicinity of the root and the boss portion By dividing the vicinity and the vicinity of the cover portion and further dividing the vicinity into a plurality of mold pieces, stress can be more reliably dispersed. In particular, when the hot forging die of the present invention is used when used in a large-scale hot forging device having a scale of tens of thousands of tons, it is preferable to divide the nesting die 2 into five or more nesting die pieces 22. , More preferably, 7 or more.
Further, in the present invention, when the nesting mold 2 is composed of four or more nesting mold pieces 22, the weight of one nesting mold piece can be reduced. When an attempt is made to use a conventional integrated die for hot forging of a large product, the cooling rate at the time of quenching inevitably decreases, and a metal structure such as bainite that inhibits toughness appears and the toughness deteriorates. On the other hand, in the present invention, for example, even when hot mold steel such as SKD61 and SKT4 specified in JIS is used as the mold piece, it is cooled at the time of quenching the mold piece. It is possible to increase the speed. As a result, it is possible to sufficiently exhibit the excellent high-temperature strength and high toughness of hot mold steels such as SKD61 and SKT4, and it is possible to obtain a mold piece having both high strength and high toughness. can. Therefore, it is preferable to use four or more nested mold pieces so that the weight can be reduced.

Further, in the present invention, a build-up layer of a Ni-based superheat-resistant alloy may be formed on the engraved surface of the nesting mold piece.
If the overlay layer of the Ni-based superheat-resistant alloy is selected from a material capable of increasing the strength at a location where a large load is applied during hot forging, the life of the die piece can be extended. Further, if the overlay layer of the Ni-based superheat-resistant alloy to be used is selected to have a lower thermal conductivity than the material of the die piece, the effect of preventing the temperature of the material to be forged to drop during hot forging can be obtained. Be done.
In order to obtain the above-mentioned two effects of extending the life and preventing temperature decrease, for example, it is preferable to form a build-up layer made of a Ni-based superheat-resistant alloy, and in particular, B: 0 to 0 in mass%. .02%, C: 0.01 to 0.15%, Mg: 0 to 0.01%, Al: 0.5 to 2%, Si: 0 to 1%, Mn: 0 to 1%, Ti: 1 ~ 3%, Cr: 15-22%, Co: 2-15%, Nb: 0-3%, Mo: 3-7%, Ta: 1-7%, W: 3-7%, and Ta alone Alternatively, it is preferable to use an alloy containing 1 to 7% of Ta + 2Nb in total and the balance being Ni and impurities.

Further, as shown in FIG. 5, it is also preferable that at least a part of the edge portion of the concave engraved surface is provided with a split member that can be attached to and detached from the nesting type. FIG. 6 is an enlarged partial cross-sectional view of the left side portion of the cross section at the position AA in FIG. In the embodiment shown in FIGS. 5 and 6, a split member 28 that can be attached to and detached from the nesting mold 2 forming the die carving surface is arranged at the edge portion of the concave die carving surface 21 according to the product shape. ..
When forging a die with a die having a die-engraved surface, the die-engraving is done to prevent meat shortage and to prevent the pressing force from suddenly increasing at the end of the reduction by the upper and lower dies and causing an overload. Generally, a gap (burr path) is provided between the upper die and the lower die to allow the forging material to protrude beyond the edge of the surface. In this case, the wear and damage of the mold at the edge of the engraved surface becomes particularly remarkable, and the degree of wear and damage between the edge of the engraved surface and the inner part of the engraved surface near the center. Will be very different. On the other hand, as in the embodiment shown in FIG. 5, if the edge portion where the wear is severe is made removable, only the split member is replaced when the split member becomes unusable due to the wear or the like. do it. Therefore, the mold replacement work is greatly simplified and the material loss is also reduced.

Further, by adopting a structure in which the split member 28 has a higher hot strength than the nested mold, the life of the mold can be further extended. The hot strength referred to here is the strength at the temperature reached by the mold surface during hot forging, and for example, the tensile strength at a temperature of 500 ° C. can be used as an index thereof. As the material of the dividing member 28, a Ni-based super heat-resistant alloy such as Alloy718, high-speed tool steel, or the like can be used. Of these, Ni-based super heat-resistant alloys are particularly preferable. Even when an expensive material such as a Ni-based super heat-resistant alloy is used, only the part of the dividing member needs to be replaced, so that the maintenance and replacement costs of the mold can be significantly reduced.
The area occupied by the dividing member of FIG. 5 can be composed of one dividing member, but as shown in FIG. 5, the dividing member is composed of a plurality of divided member pieces arranged adjacent to each other, that is, the divided member is composed of a plurality of divided members. By arranging the divided member pieces in a divided state, it is possible to minimize the parts to be replaced due to wear or the like. Further, it can be expected that the stress at the time of forging is dispersed and the maximum stress applied to the divided member is reduced.

As shown in the partial cross-sectional view of FIG. 6, a part of the dividing member 28 arranged at the edge of the die-engraved surface is formed in a direction perpendicular to the engraving direction (forging pressure direction: z-direction) of the die-engraved surface. It is exposed on the carved surface and forms a part of the carved surface. The other part of the dividing member 28 is exposed on the upper surface in the z direction and forms a part of the beam path 28. Placing the removable split member 28 on the z-direction end of the concave die-carved surface and the edge including the burrs, which are severely damaged such as wear, is very effective in reducing the mold cost related to replacement and the like. Is the target.
In the embodiment shown in FIG. 5, the dividing member is arranged on the long side along the longitudinal direction. The dividing member may be arranged over the entire circumference of the engraved surface, but as shown in FIG. 5, it may be arranged at least in a part where the wear is severe.

From the portion of the upper surface of the dividing member 28 that constitutes the beam path, there is an inclined portion that inclines downward as it goes away from the engraved surface, and a surface that continues beyond the inclined portion and forms the beam path. A burrs 29 are formed, which are composed of surfaces located below. In the embodiment shown in FIG. 6, at the position where the above-mentioned burrs 29 are formed, the dividing member 28 is detachably fixed to the nesting type by bolts 30 from above.
Further, the dividing member 28 projects below the split member 28 in a direction perpendicular to the engraving direction (z direction) of the engraved surface (a direction perpendicular to the edge of the engraved surface, which is the y direction in FIG. 6). The nested type has a convex portion having a rectangular cross section, and the nested type is provided with a concave portion that can be fitted with the convex portion. Concavities and convexities are formed in each of the divided member and the nesting type by the convex portion and the concave portion. By fitting the unevenness of the dividing member 27 to the unevenness of the nesting type, the dividing member 28 is constrained in the engraving direction (z direction) of the engraved surface. Therefore, even if a strong upward frictional force acts on the split member during forging, the fixed state of the split member can be stably maintained. It is possible to use a configuration that does not utilize the restraint due to the fitting of the unevenness shown in FIG. 6, but by using the configuration shown in FIG. 6, in addition to fixing the bolt at the position of the burrs, it is closer to the carved surface. Since the dividing member is restrained at the position in the engraving direction of the engraved surface, the reinforcing member can be fixed more firmly.
When the nested mold is composed of an assembly of a plurality of nested mold pieces, a dividing member can be arranged on each nested mold piece. In such a case, the number of nested pieces for arranging the dividing members may be one or two or more. Further, the number of dividing members arranged in one nested piece may be one or two or more.

When forming a build-up layer of a Ni-based super heat-resistant alloy, an alloy layer made of a solid-melt reinforced heat-resistant alloy different from the build-up layer is built-up welded between the mold piece and the build-up layer. It is preferable to improve the weldability and alleviate the stress generated between the base material of the mold piece and the striking surface.
The solid solution strengthened heat-resistant alloy referred to in the present invention is, for example, a composition capable of solid-solving an alloy element to strengthen a matrix among alloys having a composition shown in JIS-G4901 or G4902. It may be an alloy having the alloy or the alloy described in ASTM-A494.
A typical component range is C: 0.15% or less, Cr: 15 to 30%, Co: 0 to 3%, Mo: 0 to 30%, W: 0 to 10%, Nb in mass%. : 0 to 4%, Ta: 0 to 4%, Ti: 0 to 1%, Al: 0 to 2%, Fe: 0 to 20%, Mn: 0 to 4%, and the balance consists of Ni and impurities. It is an alloy.

As a typical example of manufacturing (assembling) the hot forging die of the present invention described above, first, a nesting die having a square columnar outer shape and a die carved surface for pressing the forging material is prepared. As described above, the hot forging material is a long product, and therefore has a round bar shape. The nesting die to be prepared is often a rectangular parallelepiped, and the forging load and its distribution are calculated in advance, and the number, shape, and material of the nesting die pieces required to withstand the forging load are used. For places where durability is particularly required, prepare a nesting mold piece itself or a mold having a built-up layer of Ni-based superheat-resistant alloy formed on the die-engraved surface, or further divide the nesting mold piece. It is preferable that the die carved surface is a mold piece made of a Ni superheat resistant alloy that has been previously subjected to solution heat treatment and aging treatment. Considering that the dimensions of the nesting mold are determined by calculating the heat shrinkage of the nesting mold and the master mold, a mold piece of Ni-based superheat resistant alloy is used only near the die carved surface that receives a large forging load. It is preferable to use or to form a build-up layer because the heat shrinkage calculation becomes easy.
In addition, chamfering is performed on the four corners (four corners extending along the direction of insertion into the mother die) of the assembled nesting mold, and the parts are fastened and integrated by a fastening member 25 such as a tie rod as an integral body. Chamfer type 2 (Fig. 3). As shown in FIG. 3, the shape of the nesting die piece constituting the nesting die is different from that having a flange portion that receives the forging load in consideration of the forging load, or, for example, a Ni-based superheat resistant alloy. An assembly body with the mold piece 27 may be provided.

Next, a master mold having a square columnar outer shape and having a storage portion for storing the nesting mold is prepared. The corners of the storage portion of the mother mold may be processed according to the chamfered shape of the corner portion 24 of the nesting mold. The width of the mother mold is about 1.0 to 2.0 times the height of the nest mold so that the mother mold and the nest mold can be firmly integrated by shrink fitting. The thickness is preferable.
Then, the mother die and the nesting die can be shrink-fitted and integrated to form a hot forging die having a square columnar outer shape.
According to the present invention described above, overlay welding can also form a desired overlay layer at an arbitrary position, is economically excellent, and can be applied to increasing the size and strength of products.

1 Hot forging die 2 Nested die 21 Die carved surface 22 Nethered die piece 23 Nethered die fixing frame 24 Square 25 Fastening member 26 Flange 27 Die piece 28 Divided member 29 Burr 30 Bolt 3 Master mold 31 Storage section 32 Corner

Claims (8)

In a hot forging die that presses a hot forging material into a forging material,
The hot forging die has at least a nesting die and a master die for accommodating the nesting die.
The nesting mold has a die-engraved surface for pressing the hot forging material and has a square columnar outer shape.
The mother die has a storage portion for accommodating the nesting die and has a square columnar outer shape.
The nested mold has a chamfered shape at a corner extending along a direction of being inserted into the master mold.
The said the entering-subtype mold have a structure that is integral with the shrink fit,
A hot forging die characterized in that at least a part of the edge portion of the die carved surface is provided with a split member that can be attached to and detached from the nesting die. The hot forging die according to claim 1, wherein the nesting die is an assembly of a plurality of nesting die pieces. The hot forging die according to claim 2, wherein a build-up layer of a Ni-based superheat-resistant alloy is provided on the engraved surface of the nested die piece. The hot forging die according to claim 2 or 3, wherein at least one of the nested die pieces is a nested die piece made of a Ni-based superheat-resistant alloy. The hot forging die according to any one of claims 1 to 4, wherein the split member has a higher hot strength than the nested die. In the method of manufacturing a hot forging die that presses a hot forging material into a forging material,
The hot forging die has at least a nesting die and a master die for accommodating the nesting die.
The nesting mold has a square columnar outer shape, has a die-engraved surface for pressing the hot forging material, and has a chamfered shape at a corner portion extending along a direction of being inserted into the master mold. ,
The mother die has a square columnar outer shape, and has a storage portion for accommodating the nesting die.
At least a part of the edge portion of the engraved surface is provided with a split member that can be attached to and detached from the nesting die.
A method for manufacturing a hot forging die, which comprises shrink-fitting the nesting die and the mother die to integrate them. The method for manufacturing a hot forging die according to claim 6 , wherein the nesting die is an assembly of a plurality of nested die pieces. A method for producing a forged material, which obtains a forged material by hot forging a heated hot forging material using the hot forging die according to any one of claims 1 to 5.

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