JP2007038251A - Die for forging and producing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a long service life of a die for forging, regarding the die for forging, having a diffusion layer formed by diffusing carbide in Fe-based alloy on the surface of a substrate layer composed of the Fe-based alloy and higher hardness, in comparison with the substrate layer. <P>SOLUTION: On the surface of a preform body 52 composed of SKH51 (Fe-based alloy), at least one powder of metals which forms the carbide and diffuses in the inner part of SKH51, that is, Cr, W, Mo, V, Ni, Mn, is applied. After applying, a heat treatment is performed to the preform body 52 and thus, the preform body 52 having the diffusion layer 36a formed by diffusing the carbide of the above metal in the base material, is obtained. At the lower part of the diffusion layer 36a, the substrate layer 37 as the base material exists. Thereafter, an upper punch 26a for forging, having a prescribed shape can be produced by performing a finish-working. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a forging die having a diffusion layer formed by diffusing carbide in a Fe-based alloy on the surface of a base layer made of an Fe-based alloy and having a hardness higher than that of the base layer, and a method for manufacturing the same. About.

  The forging process is one of the forming processes widely adopted when obtaining a molded body having a desired shape. In the forging process, a forging die such as a punch or a die is used, and the workpiece is pressed by the forging die. The pressed meat of the workpiece causes plastic flow along a cavity formed by a punch and a die, and accordingly, the workpiece is formed into a molded body having a predetermined shape.

  A forging die is required to have sufficient wear resistance, corrosion resistance, strength, and the like for repeating the forging process described above several thousand to tens of thousands of times. If these properties are not sufficient, cracks and chips will easily occur, resulting in a forging die with a short life, and eventually the forging die will need to be replaced frequently, increasing capital investment. It is.

  The forging die is generally composed of high-speed tool steel (SKH) or alloy tool steel (SKD), that is, a steel material that is a kind of Fe-based alloy. Therefore, in order to improve the above-mentioned various properties, it is effective to provide a film on the surface by physical vapor deposition (PVD) method, chemical vapor deposition (CVD) method, plating, anodic oxidation or the like. It can be considered as well. However, in this case, there is a problem that it takes a long time to form a film and the film formation cost is high.

As an attempt to improve various characteristics of the surface of the steel material without providing a film, various surface treatments such as carburizing, sulfurizing, nitriding, carbonitriding and the like can be given (for example, see Patent Documents 1 and 2). Further, in Patent Document 3, although it is a cutting tool, if it is subjected to a mechanical treatment such as shot peening or shot blasting to give a compressive stress of 10 kgf / cm ² (approximately 0.1 MPa) to the surface, it has wear resistance. It has been reported that the fracture resistance can be improved.

JP 2003-129216 A JP 2003-239039 A JP-A-5-171442

  However, it is limited to the surface of a metal material that various characteristics improve by the conventional techniques as described in Patent Documents 1 to 3. For example, in nitriding or carburizing, the element diffuses from the surface of the metal material only a few μm and at most about 200 μm, and it is difficult to improve various internal characteristics. For this reason, even when applied to a forging die, it is difficult to say that the wear resistance and fracture resistance of the forging die are significantly improved.

  In addition, in the processing method according to the prior art, an interface exists between the formed nitride layer or the like and the metal material that is the base layer. For this reason, there is a concern that brittle fracture occurs from the interface under conditions where stress concentration occurs at the interface.

  The present invention has been made in order to solve the above-mentioned problems. Forging molds that are hard to cause brittle fracture because their hardness and strength are improved and the change in physical properties is gentle, so that stress concentration hardly occurs, and An object is to provide a manufacturing method.

In order to achieve the above object, a forging die according to the present invention is a forging die for forming a workpiece by pressurizing a workpiece,
An underlayer composed of an Fe-based alloy, and a diffusion layer that is located on the surface side of the underlayer and has a higher hardness than the underlayer by diffusing carbides in the Fe-based alloy;
The carbide is a metal element obtained by carbideizing at least one kind of carbide of Cr, W, Mo, V, Ni, Mn, or a solid solution of at least one of them and Fe. Is represented by M, the composition formula is M ₆ C, M ₂₃ C ₆ , (Fe, M) ₆ C or (Fe, M) ₂₃ C ₆ .

  When the carbides of Cr, W, Mo, V, Ni, and Mn diffuse into the Fe-based alloy, the hardness of the Fe-based alloy is improved by the same mechanism as that of the precipitation hardening type composite material. And in the die for forging which concerns on this invention, since this kind of carbide | carbonized_material has spread | diffused deep inside the Fe-based alloy which is a base material, the hardness and intensity | strength which were excellent to the inside are shown.

  In addition, this forging die has no interface between the diffused carbide and the underlayer. For this reason, stress concentration is unlikely to occur, so that brittle fracture is less likely to occur.

The composition formula of the carbides of Cr, W, Mo, V, Ni, and Mn is, for example, M ₆ C or M ₂₃ C ₆ when the metal element is represented by M. The carbide whose composition formula is expressed in this way is particularly excellent in the effect of improving the hardness of the Fe-based alloy.

Alternatively, a solid solution of at least one of Cr, W, Mo, V, Ni, and Mn and Fe is carbideized, and the composition formula is (Fe, M) ₆ C or (Fe, M) ₂₃ C ₆ It may be expressed. In this case, since the relative amount of the metal carbide as described above is reduced, it is possible to prevent the metal carbide from being excessively generated and the brittleness from being increased.

  Here, when the forging die is a punch, it is preferable that the diffusion layer is provided in a molding portion that presses at least the workpiece to plastically deform the workpiece. This is because it is sufficient that at least the various characteristics of the molded part are improved, and the cost can be reduced as compared with the case where the various characteristics are improved even to the part that does not contact the workpiece and does not press the workpiece. .

  On the other hand, when the forging die is a die having a molding portion into which the flesh of the workpiece that plastically flows flows, the diffusion layer is preferably provided in a portion where the cross-sectional area through which the meat passes decreases. Excessive stress is applied to the portion where the cross-sectional area is reduced as the workpiece flesh plastically flows. By improving the various characteristics of such a part, it is possible to avoid the occurrence of cracks and chips in the part.

Further, the present invention is a method for producing a forging die for forming a workpiece by molding a workpiece by pressing,
Applying a metal powder containing at least one of Cr, W, Mo, V, Ni, and Mn to the surface of a preform formed of an Fe-based alloy;
The Fe-based alloy coated with the metal powder is heat-treated so that at least carbon constituting the Fe-based alloy reacts with the metal, and when the metal element is represented by M, the composition formula is M ₆ C, M ₂₃ A carbide that is C ₆ , (Fe, M) ₆ C or (Fe, M) ₂₃ C ₆ and diffusing the carbide into the Fe-based alloy;
It is characterized by having.

  By passing through such a process, a thick diffusion layer can be formed, and a forging die having no interface between the diffusion layer and the underlayer can be produced. The obtained forging die is excellent in hardness and strength due to the presence of the diffusion layer.

  As described above, Cr, W, Mo, V, Ni, and Mn powders are used as the metal powder because the hardness of the Fe-based alloy can be improved.

  For the reasons described above, when the forging die is a punch, the cross-sectional area is reduced in the case of a die having a molded portion into which the workpiece fluid flowing plastically flows into the molded portion that presses the workpiece. It is sufficient to provide a diffusion layer at the portion to be formed.

  According to the present invention, the carbide is diffused in the Fe-based alloy that is the base material of the forging die, so that a forging die having improved hardness and strength to the inside can be obtained. In addition, since the thickness of the diffusion layer is large, it is possible to improve the hardness and strength deep inside.

  Hereinafter, preferred embodiments of a forging die and a manufacturing method thereof according to the present invention will be described in detail with reference to the accompanying drawings.

  1A to 1D are manufacturing steps of a spider 10 (see FIG. 1D) manufactured using the forging die according to the present embodiment. The spider 10 will be described first. The spider 10 is used as a component of a triport type constant velocity joint (not shown) that is slidable in the axial direction, and has a hole 12 in which serrations are formed. The ring body 14 and three trunnions 16a to 16c that are spaced apart at equal angles along the circumferential direction of the ring body 14 and project outward in the radial direction are integrally formed. The spider 10 is fixed to one end of a drive shaft (not shown), and the trunnions 16a to 16c are slidably provided along a track groove (not shown) formed on the inner wall of the bottomed cylindrical outer ring member. . Each trunnion 16 a to 16 c is formed so as to gradually increase in diameter from the root portion close to the ring body 14 toward the radially outward direction of the ring body 14.

  The spider 10 is manufactured by the following process.

  First, in the first preparation step, spheroidizing annealing is performed on the workpiece 18 (see FIG. 1A) cut out to a predetermined length of a cylindrical body (billet). Thereby, the work 18 is softened and the following forging is facilitated. In the second preparation step, a lubricating chemical film made of, for example, zinc phosphate or the like is formed on the surface of the workpiece 18 by bonderite treatment, thereby imparting lubricity to the surface. Specifically, the chemical conversion coating for lubrication may be formed by immersing the workpiece 18 in a solvent in which zinc phosphate or the like is dissolved for a predetermined time.

  Next, as shown in FIG. 2, forging is performed on the workpiece 18 on which the chemical conversion coating for lubrication is formed using the forging die 20 according to the present embodiment. Thereby, as shown in FIG. 1B, an intermediate molded body 24 is formed in which three trunnions 16 a to 16 c are bulged and formed on the outer peripheral surface of the disk-shaped portion 22 in the radially outward direction.

  Subsequently, by performing piercing on the center of the disk-shaped portion 22 of the intermediate molded body 24, as shown in FIG. 1C, an inner burr is punched to form a hole portion 12 penetrating therethrough, which is not shown. After performing chamfering and lace processing such as serration of the hole 12 using a cutting device, the spider 10 as a manufactured product is completed through heat treatment steps such as carburizing quenching and tempering (see FIG. 1D).

  Next, the forging die 20 according to the present embodiment will be described.

  As shown in FIG. 2, the forging die 20 includes a forging upper punch 26a that is connected to a first pressing mechanism (not shown) so as to be displaceable in the vertical direction, and the forging upper punch 26a. And a forging lower punch 26b that is connected to a second pressing mechanism (not shown) and is displaceable in the vertical direction. The forging upper punch 26a and the forging lower punch 26b are configured in the same manner.

  The forging upper and lower punches 26a and 26b are manufactured using SKH51 as a raw material (base material), and are connected to the large-diameter portion 28 on one end side and the large-diameter portion 28 as shown in FIG. And a small diameter portion 32 connected to the reduced diameter portion 30, a small diameter portion 32 projecting from the small diameter portion 32 toward the other end side, and curved in a substantially circular arc shape. And a punch forming portion 34.

  In this case, a diffusion layer 36a formed by diffusing a metal carbide in the base material SKH 51 is provided on a partial surface including the end surfaces of the punch forming portion 34 and the small diameter portion 32 as shown in FIG. . Therefore, in the upper and lower forging punches 26 a and 26 b, the end surfaces of the punch forming portion 34 and the small diameter portion 32 have the base layer 37 and the diffusion layer 36 a made of a base material, and the diffusion layer 36 a is formed on the base layer 37. It has become a form.

  Further, the forging die 20 has an upper die 38 connected to a lifting mechanism (not shown) and a lower die 40 positioned and fixed to a fixing die (not shown). The upper die 38 and the lower die 40 include The first portion 41 for forming the disk-shaped portion 22 and the curved concave portion 42 for forming the trunnions 16a to 16c are provided. Among these, into the recess 42, meat that is plastically flowed by being pressed from above and below by the forging upper and lower punches 26a and 26b flows.

  Further, first and second die forming portions 44a and 44b bulged in a cross-sectional arc shape in the direction in which the upper die 38 and the lower die 40 approach each other are formed at portions close to the concave portion 42, respectively. The As can be understood from FIG. 2, the separation distance between the first die forming portion 44 a and the second die forming portion 44 b, in other words, the cross-sectional area through which the meat of the plastically flowing workpiece 18 passes is the disc-shaped portion 22. It is smaller than the cross-sectional area of the first portion 41 to be molded.

  In this case, in the surface layer portions of the first and second die forming portions 44a and 44b, similarly to the upper and lower punches 26a and 26b for forging, a diffusion layer 36b formed by diffusing metal carbide in the base material SKH51. Is provided. That is, the first and second die forming portions 44a and 44b in the upper die 38 and the lower die 40 have a base layer made of a base material and a diffusion layer 36b, similarly to the upper and lower punches 26a and 26b for forging. The diffusion layer 36b is formed on the top.

  And as FIG. 2 shows, the diffusion layer 36b is provided in the site | part where the cross-sectional area through which the meat | flesh of the workpiece | work 18 passes reduces.

  The diffusion layers 36a and 36b will be described. As described above, the diffusion layers 36a and 36b are formed by diffusing a metal carbide in the base material SKH51.

  As a metal element that forms carbide, an element that improves the hardness of SKH51, specifically, Cr, W, Mo, V, Ni, and Mn is selected. The diffusion layers 36a and 36b formed by diffusing such metal element carbides exhibit high hardness and high strength. Therefore, in the upper and lower punches 26a and 26b, the end surfaces of the punch forming portion 34 and the small-diameter portion 32, and the first die forming portion 44a and the second die forming portion 44b in the upper die 38 and the lower die 40 are placed in other parts. Hardness and strength are higher than those.

Carbides, when represents a metal element in _{M, Cr 6 C, W 6} C, carbides and represented by M ₆ C as such Mo ₆ C, a carbide represented by M ₂₃ C _6. This type of carbide is most excellent in improving the hardness and strength.

If M ₆ C or M ₂₃ C ₆ is excessively present, the forging die 20 becomes brittle. Therefore, it is preferable to generate carbides of solid solution of Fe and metal elements of the above-described metal elements and forging punches 26a and 26b for forging, which are steel materials, upper die 38 and lower die 40. That is, the carbide may be represented by (Fe, M) ₆ C, (Fe, M) ₂₃ C ₆ or the like. When such carbides are generated, the relative amounts of M ₆ C and M ₂₃ C ₆ are reduced, so that the upper and lower punches 26a, 26b, the upper die 38 and the lower die 40 for forging are reliably avoided from being brittle. Will be able to.

  Here, the thickness of the diffusion layers 36a and 36b, in other words, the diffusion distance of the carbide, the depth of the upper and lower punches 26a and 26b for forging, the upper die 38 and the lower die 40 reaches at least 0.5 mm (500 μm). Usually, it may reach 3 to 7 mm (3,000 to 7000 μm), and may reach 15 mm (15000 μm) at the maximum. This value is remarkably large while the diffusion distance of elements in nitriding, carburizing, etc. is several tens of μm, at most about 200 μm. That is, in the present embodiment, the carbide can be diffused to a deeper portion than the element introduced by the surface treatment method according to the prior art.

  In the portion where the diffusion layers 36a and 36b are provided, the hardness is improved to the depth at which the carbide is diffused. That is, the hardness and strength of the forging upper and lower punches 26a and 26b, the upper die 38, and the lower die 40 are increased deeply, and as a result, the internal wear resistance is improved and deformation is difficult.

  As will be described later, the diffusion layers 36a and 36b are formed by generating carbides from metal elements diffused from the surface of the base material. For this reason, the carbide | carbonized_material density | concentration is the highest on the surface, and it reduces gradually as it goes inside the base material.

  Further, since the carbide concentration gradually decreases in this way, there is no clear interface between the diffusion layers 36 a and 36 b and the base layer 37. For this reason, since it can avoid that stress concentration arises, it can avoid that brittleness increases with diffusing a metallic element. In FIG. 4, a boundary line is provided between the diffusion layer 36 a and the base layer 37 for convenience in order to clarify that the diffusion layer 36 a exists.

  In this case, the columnar workpiece 18 is loaded into a positioning cavity formed by the lower die 40 and the lower forging punch 26b, and the first and second pressing mechanisms (not shown) are driven to move the upper and lower punches 26a for forging, The workpiece 18 is pressurized by displacing the members 26b in the direction in which they approach each other. The upper die 38 and the lower die 40 are brought into contact with each other by urging a lifting mechanism (not shown) substantially simultaneously with the upper and lower punches 26a, 26b for forging to lower the upper die 38, and the upper and lower dies 38, 40 are brought into contact with each other. A trunnion molding cavity is formed by the recesses 42, 42.

  At that time, the workpiece 18 pressed by the forging upper and lower punches 26a and 26b is plastically deformed, and a meat flow is generated in which the plastically deformed meat flows in the trunnion forming cavity, and the upper die 38 and the lower die In order to flow into the trunnion molding cavity in a state of being suitably squeezed by the first and second die molding portions 44a and 44b provided in the die 40, the meat plastically deformed to every corner of the trunnion molding cavity Is filled.

  As described above, the end surfaces of the punch forming portion 34 and the small diameter portion 32 of the upper and lower punches 26a and 26b for forging, the first die die forming portions 44a and 44b of the upper die 38 and the lower die 40 are diffused layers 36a and 36b. Therefore, high hardness and high strength and toughness are ensured. Therefore, these portions are not easily worn even if the forging process is repeated, and defects are not easily generated. That is, the life of the forging die 20 can be extended by providing the diffusion layers 36a and 36b.

  The forging upper punch 26a having the diffusion layer 36a can be manufactured as follows.

  First, as shown in FIG. 5 (b), a cylindrical workpiece W made of SKH 51 shown in FIG. 5 (a) is cut by a cutting tool 50 to correspond to the shape of the upper punch 26a for forging. The preform 52 is shaped.

Next, as shown in FIG. 5C, a metal powder to be diffused is applied to the surfaces of the punch forming part 34 and the small diameter part 32 on the surface of the preform 52. For example, if W is diffused, powder mixed with W powder may be applied, and if Cr is diffused, powder mixed with Cr powder may be applied. The coating amount of the powder may be, for example, to the amount W ₆ C and Cr ₆ C, etc. are produced.

  The powder is applied by applying a coating agent 54 prepared by dispersing the powder in a solvent. As the solvent, it is preferable to select an organic solvent that easily evaporates, such as acetone or alcohol. And powder, such as W and Cr, is disperse | distributed to this solvent.

  Here, an oxide film is usually formed on the surface of the base material SKH 51. In order to diffuse W, Cr, etc. in this state, a great amount of heat energy must be supplied so that W, Cr, etc. can pass through the oxide film. In order to avoid this, it is preferable to mix the coating agent 54 with a reducing agent capable of reducing the oxide film.

  Specifically, a substance that acts as a reducing agent on the oxide film and does not react with SKH51 is dispersed or dissolved in a solvent. Preferable examples of the reducing agent include nitrocellulose, polyvinyl, acrylic, melamine, and styrene resins, but are not particularly limited thereto. Note that the concentration of the reducing agent may be about 5%.

  The coating agent 54 in which the above substances are dissolved or dispersed is applied to the surfaces of the punch forming portion 34 and the small diameter portion 32 by a brush coating method using a brush 56 as shown in FIG. Of course, you may make it employ | adopt well-known coating techniques other than the brush coating method.

  Next, heat treatment is performed on the preform 52 in which the coating agent 54 is applied to the surfaces of the punch forming portion 34 and the small diameter portion 32. This heat treatment can also be performed by applying a burner flame 58 from one end face side of the preform 52 as shown in FIG. Of course, heat treatment may be performed in an inert atmosphere in a heat treatment furnace.

  In this temperature rising process, the reducing agent begins to decompose at about 250 ° C., and carbon and hydrogen are generated. The oxide film of the preform 52 is reduced under the action of carbon and hydrogen and disappears. For this reason, it is not necessary for W, Cr, or the like to pass through the oxide film, so that the time required for diffusion can be shortened and the thermal energy can be reduced.

When the temperature is further increased, C, Fe, which are constituent elements of SKH51, which is the base material, C generated by decomposition of the reducing agent, W, Cr, and the like react with each other, and W ₆ C, Cr ₆ C, W ₂₃ C ₆ , Cr ₂₃ C _{6 and the} like are generated. When Fe is involved, (Fe, W) ₆ C, (Fe, Cr) ₆ C, (Fe, W) ₂₃ C ₆ , (Fe, Cr) ₂₃ C _{6 and the} like are also generated.

Some of the generated carbides such as W ₆ C, Cr ₆ C, (Fe, W) ₆ C, and (Fe, Cr) ₆ C are immediately decomposed and returned to Fe, W, and Cr. Among these, W and Cr are next combined with C and Fe, which are constituent elements of the base material existing on the inner side of the base material, and C existing in a free state on the inner side of the base material. Thus, W ₆ C, Cr ₆ C, (Fe, W) ₆ C, (Fe, Cr) ₆ C and the like are newly generated. These W ₆ C, Cr ₆ C, (Fe, W) ₆ C, and (Fe, Cr) ₆ C are also immediately decomposed and returned to W and Cr, and then the base material existing further inside the base material. Are combined with C and Fe, which are constituent elements of C, and C which is present in a free state on the inner side of the base material, and again W ₆ C, Cr ₆ C, (Fe, W) ₆ C, (Fe, Cr ) ₆ C etc. are generated. In this way, the carbide is repeatedly decomposed and produced, so that the carbide diffuses deep inside the base material.

In this way, W ₆ C, Cr ₆ C, (Fe, W) ₆ C, and (Fe, Cr) ₆ C can be diffused inside the base material, and as a result, diffusion layers 36 a and 36 b are formed. (See FIG. 2 and FIG. 4). Note that the carbide concentration gradually decreases, and a clear interface does not occur between the carbide diffusion reaching end portion and the underlayer. Therefore, since brittle fracture can be avoided, the toughness of the site where the diffusion layers 36a and 36b are formed can be ensured. The thickness of the diffusion layers 36a and 36b, that is, the diffusion distance of carbides, extends up to a depth of about 15 mm from the surface.

  Finally, as shown in FIG. 5E, the preformed body 52 is finished with a cutting tool 50 to obtain a forging upper punch 26a. Similarly, the forging lower punch 26b can be produced.

  The upper punch 26a for forging thus obtained was cut along the longitudinal direction, and the C-scale Rockwell hardness (HRC) measured from the surface side to the inside of the cut surface was determined as the HRC of ordinary SKH51. In addition, it is shown in FIG. From FIG. 6, it is clear that in this case, the hardness increases from the surface to the inside of 2 mm.

  Similarly, the strength of the test piece of the JIS Z 2201 No. 4 test piece in which the diffusion layer 36a is formed is significantly improved as compared with the test piece of the same size in which the diffusion layer 36a is not formed. Specifically, the tensile strength of the test piece in which the diffusion layer 36a is not formed is about 1800 MPa, whereas the tensile strength of the test piece having the diffusion layer 36a is about 2200 MPa, which is about 1.2 times.

  Similarly to the above, carbides of Mo, V, and Ni can be diffused into the base material.

  The diffusion layer 36b of the upper die 38 and the lower die 40 can be formed by applying a heat treatment after applying a powder containing a metal to be diffused, as in the case of forming the diffusion layer 36a.

  In the above-described embodiment, the forging die 20 for manufacturing the spider 10 is illustrated and described, but the present invention is not particularly limited to this. For example, the present invention can be applied to a forging die for forging an outer ring member of a tripod type constant velocity joint (not shown), an outer ring member of a barfield type constant velocity joint (not shown), an inner ring and the like.

  Using SKH51, which is a high-speed tool steel, and SKD11, which is a die steel, a cylindrical body having a bottom diameter of 80 mm and a height of 80 mm was produced.

  On the other hand, a powder of a substance belonging to Group III-VIII of the periodic table (particle size 10-70 μm) is added to an acetone solution of 10% epoxy resin at a ratio shown in FIG. B was prepared.

  Thereafter, coating agent A was applied to the entire surface of the cylindrical body of SKH51, and coating agent B was applied to the entire surface of the cylindrical body of SKD11. In addition, application | coating was performed by brush coating and the thickness of the coating agents A and B was 1 mm.

  After the coating agent was naturally dried, a quenching treatment was performed by holding at 1000 to 1180 ° C. for 2 hours, and then a tempering treatment was performed by holding at 500 to 600 ° C. for 2 hours.

  Each cylindrical body was cut in the height direction, and HRC was measured every 0.5 mm along the height direction from the center of the bottom surface. The relationship between the distance from the surface and HRC is shown in FIG. 8 or FIG. 9 in a graph together with uncoated SKH51 and SKD11. Considering the measurement error of HRC, it is clear from these FIG. 8 or FIG. 9 that the hardness of each cylindrical body is increased to a depth of about 6 mm from the bottom surface.

Moreover, when the produced carbide was identified, it was confirmed to be (Fe, W) ₆ C, (Fe, W) ₂₃ C ₆ , (Fe, Cr) ₆ C, (Fe, Cr) ₂₃ C ₆ . .

1A to 1D show a manufacturing process of a spider manufactured using the forging die according to the present embodiment. It is a schematic longitudinal cross-sectional explanatory drawing which shows the state which has shape | molded the intermediate molded object with the metal mold | die for forging which concerns on this Embodiment. It is a general | schematic whole perspective view of the punch for forging which comprises the metal mold | die for forging of FIG. FIG. 4 is an enlarged vertical cross-sectional view of a main part of the forging punch in FIG. 3. FIG. 4 is a flow explanatory diagram showing a manufacturing process of the forging punch of FIG. 3. It is a graph which shows HRC measured toward the inside from the surface of the cut surface of the obtained forging punch. It is a chart which shows the composition and ratio of a coating agent. It is a graph which shows the relationship from the distance from the surface, and HRC in the test piece made from SKH51. It is a graph which shows the relationship from the distance from the surface in a test piece made from SKD11, and HRC.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Spider 14 ... Ring body 16a-16c ... Trunnion 20 ... Forging metal mold 26a, 26b ... Forging punch 32 ... Small diameter part 34 ... Punch molding part 36a, 36b ... Diffusion layer 37 ... Underlayer 38, 40 ... Die 41 ... 1st part 42 ... Recess 44a, 44b ... Die forming part 52 ... Pre-formed body 54 ... Coating agent 58 ... Burner flame

Claims (6)

A forging die for forming a workpiece by pressurizing a workpiece,
An underlayer composed of an Fe-based alloy, and a diffusion layer that is located on the surface side of the underlayer and has a higher hardness than the underlayer by diffusing carbides in the Fe-based alloy;
The carbide is a metal element obtained by carbideizing at least one kind of carbide of Cr, W, Mo, V, Ni, Mn, or a solid solution of at least one of them and Fe. A forging die, wherein the composition formula is M ₆ C, M ₂₃ C ₆ , (Fe, M) ₆ C, or (Fe, M) ₂₃ C ₆ , when M is represented by M.   2. The forging die according to claim 1, wherein the forging die is a punch, and the diffusion layer is provided at a molding portion that presses at least the workpiece to plastically deform the workpiece. Forging die.   The forging die according to claim 1, wherein the forging die is a die having a molding part into which the meat of the workpiece that plastically flows flows, and the diffusion layer has a reduced cross-sectional area through which the meat passes. A die for forging characterized by being provided at a portion to be made. A method for manufacturing a forging die for forming a workpiece by pressurizing a workpiece,
Applying a metal powder containing at least one of Cr, W, Mo, V, Ni, and Mn to the surface of a preform formed of an Fe-based alloy;
The Fe-based alloy coated with the metal powder is heat-treated so that at least carbon constituting the Fe-based alloy reacts with the metal, and when the metal element is represented by M, the composition formula is M ₆ C, M ₂₃ A carbide that is C ₆ , (Fe, M) ₆ C or (Fe, M) ₂₃ C ₆ and diffusing the carbide into the Fe-based alloy;
A method for producing a forging die, comprising:   5. The manufacturing method according to claim 4, wherein the preform is a punch preform, and the diffusion layer is provided at a molding portion that presses at least the workpiece to plastically deform the workpiece. A method for producing a forging die.   5. The manufacturing method according to claim 4, wherein the preform is a die having a molding portion into which the flesh of the workpiece that plastically flows flows, and the diffusion layer is disposed at a portion where a cross-sectional area through which the meat passes decreases. A method for producing a forging die, comprising: providing a forging die.

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