JP2014172091A - Cold-forging mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cold-forging mold excellent in durability where a membrane of high tenacity and seizure resistance is formed on the surface of a metal mold.SOLUTION: A cold-forging mold has a membrane 2 consisting of a nitride and a carbonitride selected from among Ti, Cr, and Al deposited on the surface of a mold base material 1; this membrane 2 is structured from a three-layered membrane formed of a bottom layer 2a, intermediate layer 2b, and top layer 2c in a direction from the mold surface to the membrane surface, where the bottom layer 2a consists mainly of Cr nitride or carbonitride, intermediate layer 2b consists mainly of Al, Ti, Cr nitride or carbonitride, and top layer 2c consists mainly of Al and Ti nitride or carbonitride; when a total atomic ratio of Al to Ti contained in the top layer 2c is 100, an atomic ratio of Al in the top layer 2c exceeds 55 and is 80 or less.

Description

  The present invention relates to a die for cold forging, particularly a die for cold forging having excellent durability by increasing the toughness and seizure resistance of a coating coated on the surface of the die. It is.

  Conventionally, jigs for metal working (hereinafter referred to as “molds”) have been improved in wear resistance and seizure resistance by nitriding the material. In recent years, in addition to nitriding treatment, coating of Ti or Cr nitride or carbonitride, Ti and Al, Cr and Al nitride or carbonitride, etc. on the mold surface by vapor phase coating such as PVD Improvements in wear resistance and seizure resistance have been studied.

  In order to improve the durability of the mold (prolong the life), various types of molds have been conventionally used in which the surface of the mold is coated with a film made of a nitride or carbonitride such as Ti, Al, Cr, etc. Technology has been proposed. For example, the inventions described in Patent Documents 1 to 6 below have been proposed.

  Patent Document 1 (Japanese Patent Application Laid-Open No. 2003-321864) discloses a film that covers parts, tools, molds, and the like that are exposed to high temperatures, has an oxidation resistance of 1000 ° C. or higher, and has good wear resistance. An invention related to a high hardness film has been proposed. The abrasion-resistant film described in Patent Document 1 is a nitride mainly composed of Al, Cr, and Si. In the same document, the atomic percentage of the metal component alone includes Cr of 20% to 75%, Si of 1% to 30%, the remainder being Al, and Al, Cr, and Si. Alternating film layer a nitride mainly composed of nitride and b layer composed of nitrides mainly composed of Ti and Al, in which atomic percent of only the metal component is 25% to 75% of Al and the rest is Ti It is disclosed that at least one layer is formed, the a layer is formed as the outermost layer, and further, a layer made of a nitride of Ti or Cr is provided between the film and the substrate.

Patent Document 2 (Japanese Patent Application Laid-Open No. 2008-174782) proposes an invention relating to a covering member and a forming tool having excellent wear resistance and seizure resistance. The forming jig described in Patent Document 2 has _a coating layer A (film thickness 1) made of Cr _1-X Mx (B _a C _b N _1-ab ) on the surface of an iron-based alloy substrate containing Cr. 10 .mu.m) is formed, thereon _{Ti 1-X-Y Cr X} Al Y L Z (B B C a N 1-a-B) consisting of coating layer B (thickness 2 to 10 [mu] m) is formed Hard film covering member for forming tool, wherein 0 ≦ x ≦ 0.7, 0 ≦ a ≦ 0.2, 0 ≦ b ≦ 0.5, M is W, V, Mo, Nb, Ti, Al 1 or more of 0 ≦ 1-XY ≦ 0.5, 0 <X ≦ 0.5, 0.4 ≦ Y ≦ 0.7, 0 ≦ Z ≦ 0.15, 0 ≦ A ≦ 0.5 , 0 ≦ B ≦ 0.2, L is one or more of Si and Y.

Patent Document 3 (Japanese Patent Application Laid-Open No. 2010-202917) proposes an invention related to a hard coating that is applied to a mold and a sliding member and has improved heat resistance and mechanical properties.
The hard film described in Patent Document 3 is a nitride film represented by the following general formulas (1-a), (1-b) and (1-c), and includes titanium (Ti), chromium (Cr), This is a hard nitride film in which the metal ratio of aluminum (Al) is a composition in the vicinity of a phase transformation where the film maintains cubic crystals.
(Ti, Al) N ... (1-a)
(Cr, Al) N ... (1-b)
(Ti, Cr, Al) N (1-c)
Also, paragraph 0029 of the same document describes that two steps of depositing an alloy or metal film (intermediate layer) and depositing nitride were performed for sample preparation. Further, in Table 1 of paragraph 0030 of the same document, when Ti: Cr: Al: Si is set to 20: 20: 55: 5 in an at% as a composition of (Ti, Cr, Al, Si) N as an embodiment, Discloses that a hardness value (GPa) of 32 was obtained.

Patent Document 4 (Japanese Patent Application Laid-Open No. 2010-284710) discloses an invention relating to a metal mold for plastic working such as forging and press working that has improved galling resistance and wear resistance. Has been proposed. The coated metal mold for plastic working described in Patent Document 4 is formed on the surface of a mold base with a nitride of Al _x Cr _y Si _z (where x, y, z represents an atomic ratio, x + y + z = 100, and x, y, z ≠ 0), and a hard film having a surface roughness according to JIS-B-0601 (2001) of 0.06 μm or less in terms of arithmetic average roughness Ra and a maximum height Rz of 1.0 μm or less is coated. This is a plastic working coating die.
Further, Patent Document 4 discloses that this hard coating is a lowermost layer made of Cr nitride, nitride of Al _x1 Cr _y1 Si _z1 (where x1 ≦ y1 and an intermediate layer composed of x1, y1, z1 ≠ 0) and an uppermost multilayer structure composed of nitride of Al _x2 Cr _y2 Si _z2 (where x2> y2 and x2, y2, z2 ≠ 0) It is also disclosed.

Patent Document 5 (Japanese Patent Application Laid-Open No. 2012-136775) proposes an invention related to a coating mold having excellent adhesion resistance. Here, the “adhesion resistance” indicates a property for preventing the workpiece from adhering to the mold surface (see paragraph 0007 of the same document).
The mold described in Patent Document 5 is a coated mold in which a hard film is coated on the surface by a sputtering method, and this hard film is coated with Ti or Ti nitride, carbide, charcoal coated on the mold substrate side. A layer made of any of nitrides and nitride of Al _x Cr _y Si _z coated on the mold surface side (where x, y, z indicate an atomic ratio, x + y + z = 100, and x> y, And b ≦ 3 ≦ z <20) and having a hardness of 35 GPa or more, Ti disposed between the a layer and the b layer, and Ti ratio decreasing from the a layer side toward the b layer side, Al _v Cr _w nitride containing Si increasing from the layer side toward the b layer side so as to approach the Si ratio of the b layer (provided that v and w indicate atomic ratios and v> w) And an intermediate layer. Further, the hard coating has a surface roughness (Ra) of 0.1 μm or less and a maximum height (Rz) of 0.8 μm or less.

Patent Document 6 (Japanese Patent Application Laid-Open No. 2005-42146) proposes an invention relating to a high-hardness film having excellent oxidation resistance even at 1000 ° C. or higher and good wear resistance.
The high-hardness film described in Patent Document 6 is a film that coats a base material to be processed such as a tool or a mold, and a coating layer made of a metal nitride formed on the outer surface of the base material; An underlayer made of a nitride of Ti or Cr between the coating layer and the object to be processed, and an intermediate layer provided at the interface between the coating layer and the underlayer, and the composition of the coating layer in contact with the intermediate layer And an intermediate layer having a mixed composition with the composition of the formation. Furthermore, it is disclosed that this coating layer is a film composed of a metal nitride mainly composed of Al, Cr and Si, and the intermediate layer has a thickness of 0.1 to 2 μm.
Further, in the document, the coating layer is a coating a layer of nitride mainly composed of Al, Cr and Si, and a nitride mainly composed of Ti and Al, and the atomic percentage of only the metal component is Al. It is also disclosed that one or more coating b layers each having a thickness of 25% to 75% and the remainder being Ti are alternately formed, and the a layer is formed as the outermost layer.

  Japanese Patent Laid-Open No. 2003-321764   JP 2008-174782 A   JP 2010-202917 A   JP 2010-284710 A   JP 2012-136775 A   Japanese Patent Laying-Open No. 2005-42146 (Patent No. 3621194)

  In recent years, molds for cold forging (hereinafter referred to as “cold forging molds”) used in particularly harsh environments are molds in a closed area and at a high speed (more than 50 shots per minute). Since the base material is repeatedly subjected to tension and compression, fine cracks are likely to occur on the mold surface as compared with molds for other uses. Therefore, the film formed on the mold surface is required to have toughness that is particularly impact-resistant among its characteristics. Further, since the cracks on the surface of the mold are mostly generated from the surface of the film, the toughness of the outermost layer is important in the film formed on the surface of the mold.

  As another form, the cold forging die is used for forging a workpiece by repeating shots at high speed in a closed region, so that the surface temperature of the die can be used for other purposes such as press molding. The reaction product (foreign matter) due to the lubricant and the molding powder tends to firmly adhere (adhere) to the mold surface. Due to this fixed (adhered) material, the molding load increases and eventually a dimensional defect occurs in the product (workpiece). As a countermeasure against the occurrence of dimensional defects, the adhesion resistance against foreign matters is particularly important among the characteristics of the film formed on the surface of the mold.

  The high-hardness film disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 2003-321864) is a nitride mainly composed of Al, Cr, and Si in order to have oxidation resistance of 1000 ° C. or higher. A film composed of two layers (a layer and b layer), which is a nitride film a layer mainly composed of Al, Cr, and Si, and nitrided mainly composed of Ti and Al And at least one layer of the metal component alone is formed by alternately forming one or more layers each having a Al content of 25% or more and 75% or less and the remainder being Ti, and forming the a layer as the outermost layer. A high-hardness film in which a layer made of a nitride of Ti or Cr is provided between the film and the substrate.

In the coating described in Patent Document 1, since the a layer, which is the outermost layer, is composed of a layer containing Si and a large amount of Cr, when applied to a cold forging die, There are problems like this. First, by containing Si in the outermost layer, the film has high hardness and high wear resistance, but on the other hand, the toughness of the outermost layer is lowered and cracks from the surface of the film are likely to occur. It tends to occur. Next, when the outermost layer contains a large amount of Cr (at least 20% and not more than 75% in terms of the atomic percentage of the metal component), the heat conduction on the mold surface is reduced, thereby enabling plastic processing of the metal at a high surface pressure. When implemented, the temperature of the mold surface rises and the amount of foreign matter attached increases, thus making it easy to cause abnormal product dimensions. Thus, by using the outermost layer containing Si and a large amount of Cr at the same time, the above-described problems become more prominent, and there is a limit to improving the durability of the cold forging die.
The a layer does not contain Ti (see paragraph 0015 (Table 3)). When the outermost layer is formed with a film mainly composed of nitrides and carbonitrides of Al and Ti, forging compared to the film made of nitride or carbonitride containing Cr described in Patent Document 1 described above It becomes possible to reduce adhesion of deposits on the mold surface during molding.

Patent Document 2 iron-base alloy base material surface containing Cr as disclosed in (JP 2008-174782 _{JP), Cr 1-x Mx (} B a C b N 1-a-b) consists of coating layer A ( thickness 1 to 10 [mu] m) is formed, thereon _{Ti 1-X-Y Cr X} Al Y L Z (B B C a N 1-a-B) consisting of coating layer B (thickness 2 to 10 [mu] m) is Similarly, a hard coating coated member for a forming tool, which is characterized by being formed, has poor film toughness and seizure resistance when applied to a cold forging die, and improves the durability of the die. Has its limits.

  The hard coating disclosed in Patent Document 3 (Japanese Patent Laid-Open No. 2010-202917) has a metal ratio of titanium (Ti), chromium (Cr), and aluminum (Al) in the vicinity of the phase transformation where the film maintains a cubic crystal. Similarly, when the hard nitride film having the composition is applied to a cold forging die, the film has poor toughness and seizure resistance, and there is a limit to improving the durability of the die.

The plastic working coating mold disclosed in Patent Document 4 (Japanese Patent Application Laid-Open No. 2010-284710) is a nitride of Al _x Cr _y Si _{z on} the surface of the mold base (where x, y, and z are atoms The surface roughness according to JIS-B-0601 (2001) is 0.06 μm or less in terms of arithmetic average roughness Ra, and the maximum height Rz is x + y + z = 100 and x, y, z ≠ 0) A mold coated with a hard coating of 1.0 μm or less, with excellent surface roughness and somewhat improved wear resistance, but with poor coating toughness and seizure resistance, durability of cold forging die There is a limit to the improvement of sex.

The coating mold disclosed in Patent Document 5 (Japanese Patent Application Laid-Open No. 2012-136775) includes an a layer made of Ti or Ti nitride, carbide, or carbonitride coated on the mold base side, Al _x Cr _y Si _z nitride coated on the mold surface side (where x, y, z indicate atomic ratio, x + y + z = 100, x> y, and 3 ≦ z <20), and the hardness is The b layer of 35 GPa or more, the Ti layer disposed between the a layer and the b layer, the Ti ratio decreasing from the a layer side to the b layer side, and the b layer from the a layer side to the b layer side An Al _v Cr _w nitride containing Si and increasing so as to approach the Si ratio (where v and w are atomic ratios and v> w) is provided with a coating film. However, when such a coating is applied to a cold forging die, the toughness and seizure resistance of the coating are poor, and there is a limit to improving the durability of the die.

  The high hardness film disclosed in Patent Document 6 (Japanese Patent Application Laid-Open No. 2005-42146) includes a coating layer made of a metal nitride formed on the outer surface of a base material to be processed, and the coating layer and the base material. An intermediate layer composed of a mixed composition of the composition of the underlayer composed of a nitride of Cr and an intermediate layer provided at the interface between the coating layer and the underlayer, the intermediate layer being in contact with the intermediate layer However, the film has poor toughness and seizure resistance, and there is a limit to improving the durability of the cold forging die.

  The technology related to the coating proposed in the above-mentioned patent document is the use of a press die that press-forms bending or drawing of a high-tensile material (high-tensile steel material), especially for a cold forging die. A peculiar film for solving the problem of cracks on the mold surface and adhesion of foreign substances has not been put into practical use yet, and further improvement of the durability of the cold forging mold is strongly desired.

  The present invention has been made in view of such circumstances, and the object thereof is to suppress the occurrence of cracks in a cold forging die as compared with the conventional die having a coating film, and perform cold forging. A film capable of suppressing the adhesion of foreign matters during molding is formed on the mold surface, and the number of shots indicating the durability (life) of the mold is increased from about 10,000 to 12000 from the conventional about 15000, The object is to provide a cold forging die that can be improved to 20000 or more.

The invention according to claim 1 of the present invention is a cold forging die in which a surface of a die base material as a base material is coated with a film made of nitride or carbonitride selected from Ti, Cr, and Al. In
The coating is composed of a coating layer that forms a lowermost layer, an intermediate layer, and an outermost layer sequentially from the surface side of the mold base,
The lowermost layer is a film mainly composed of a nitride or carbonitride of Cr, the intermediate layer is a film mainly composed of a nitride or carbonitride of Al, Ti and Cr, and the outermost layer is composed of Al and Ti. It is composed of a film mainly composed of nitride or carbonitride,
When the total atomic ratio of Al and Ti contained in the outermost layer is 100, the atomic ratio of Al of the outermost layer is more than 55 and not more than 80.

  The invention according to claim 2 of the present invention relates to the cold forging die according to claim 1, wherein when the total atomic ratio of Al, Ti and Cr contained in the intermediate layer is 100, The intermediate layer has a Cr atomic ratio of 50 or less, an Al atomic ratio of 45 to 65, and a Ti atomic ratio of 10 to 35.

  The invention according to claim 3 of the present invention relates to the cold forging die according to claim 1 or 2, wherein both or one of the intermediate layer and the outermost layer contains Si, When the total atomic ratio of Al, Ti, Cr and Si is 100 in the intermediate layer containing Si or the outermost layer, the atomic ratio of Si is 2 or more and 10 or less.

  The invention according to claim 4 of the present invention relates to the cold forging die according to claim 3, wherein the atomic ratio of Si contained in the intermediate layer is the number of Si atoms contained in the outermost layer. It is characterized by more than the ratio.

  A fifth aspect of the present invention relates to the cold forging die according to any one of the first to fourth aspects, wherein the intermediate layer is a nitride contained in the lowermost layer and the outermost layer. Or it is comprised from the mixed film containing a carbonitride.

  The invention according to claim 6 of the present invention relates to the cold forging die according to any one of claims 1 to 5, wherein the intermediate layer includes nitride or carbonitride contained in the lowermost layer. It is characterized by being comprised from the laminated film which laminated | stacked the film | membrane containing a thing and the film | membrane containing the nitride or carbonitride contained in the said outermost layer.

  Invention of Claim 7 of this invention is related with the metal mold | die for cold forging in any one of Claim 1-6, The film thickness of the said outermost layer is the film thickness of the whole said film layer. It is characterized by being 50% or more.

Invention of Claim 8 of this invention is related with the metal mold | die for cold forging in any one of Claim 1-7, Between said lowermost layer and said intermediate | middle layer, said lowermost layer and Interposing a film containing nitride or carbonitride contained in the intermediate layer,
A film containing a nitride or carbonitride contained in the intermediate layer and the outermost layer is interposed between the intermediate layer and the outermost layer.

  The invention according to claim 9 of the present invention relates to the cold forging die according to any one of claims 1 to 8, wherein the surface of the outermost layer is selected from Ti, Cr, Al, and Si. It is characterized by having an outer color adjusting coating layer made of one or more nitrides or carbonitrides.

  The invention according to claim 10 of the present invention relates to the cold forging die according to any one of claims 1 to 9, wherein the cold forging die is cold forging of a workpiece. It is a punch that is used for molding.

  The cold forging die according to the present invention is provided with a coating having excellent toughness and adhesion resistance on the outermost layer of the coating coated on the mold surface, and a coating coated on the surface of a conventional cold forging die. In addition, since cracks generated from the surface of the coating are suppressed, and adhesion of foreign matter to the surface of the mold is further suppressed, it can be suitably used as a cold forging mold having dramatically improved durability.

  It is sectional drawing for demonstrating the structural example of the membrane | film | coat formed in the metal mold | die surface about the metal for cold forging of this invention.   In order to explain the shape of the prototype cold forging punch in an example in which the cold forging punches to be used as the molds of the present invention and the comparative example were prototyped and subjected to cold forging to evaluate the durability. FIG.   It is a schematic diagram for demonstrating the state before mounting the prototype cold forging punch in a cold forging apparatus, and performing cold forging to a workpiece.   In FIG. 3, it is a schematic diagram for demonstrating a state when shape | molding by cold forging to the to-be-processed object.   In an example in which the punches of the present invention and the comparative example were prototyped and subjected to cold forging to evaluate the durability, the punch of sample number 2 according to the present invention was subjected to 12,000 shots of cold forging. It is a photograph figure which shows the state of the surface of this punch.   It is a SEM photograph figure when a bearing part of a punch concerning the present invention which performed cold forging of 12000 shot shown in Drawing 5 was imaged with a scanning electron microscope, (a) is a secondary electron image, (b) Indicates a backscattered electron image.   Similarly, in the example in which the punches of the present invention and the comparative example were prototyped and subjected to cold forging to evaluate the durability, the punch of sample number 7 according to the comparative example was subjected to cold forging of 5000 shots. It is a SEM photograph figure when the bearing part of this punch is imaged with a scanning electron microscope sometimes, (a) shows a secondary electron image, (b) shows a reflected electron image.   Similarly, in the example in which the punches of the present invention and the comparative example were prototyped and subjected to cold forging to evaluate the durability, 12,000 shots of cold forging were performed on the punch of sample number 19 according to the comparative example. It is a photograph figure which shows the state of the deposit | attachment sometimes attached to this punch.

  The cold forging die according to the present invention is a cold forging in which the surface of a die base material as a base material is coated with a film mainly composed of a metal nitride or carbonitride selected from Ti, Cr, and Al. This is a mold for inter-forging. As shown in FIG. 1, the cold forging die of the present invention has a film (film layer) 2 formed on the surface of a mold base 1 as a base material. From the surface of the base material 1 toward the surface of the coating layer 2, the coating of the lowermost layer 2a, the intermediate layer 2b, and the outermost layer 2c is laminated in order. The outermost layer 2 c is a film formed (film-formed) on the outermost side (surface side) of the film 2. The coating 2 is formed on at least the functional portion of the cold forging die, that is, at a portion (surface portion or the like) that contributes to forging by contacting with the workpiece at least during cold forging.

  In the cold forging die of the present invention, the lowermost layer 2a of the film 2 is a film mainly composed of a nitride or carbonitride of Cr, and the intermediate layer 2b is a nitride or charcoal of Al, Ti and Cr. The outermost layer 2c is composed of a nitride-based coating, the outermost layer 2c is composed of an Al and Ti nitride or carbonitride, and the outermost layer 2c has a total atomic ratio of Al and Ti of 100. In this case, the basic feature is that the atomic ratio of Al exceeds 55 and is 80 or less.

  The cold forging die of the present invention is for cold forging by forming the coating 2 composed of the lowermost layer 2a, the intermediate layer 2b, and the outermost layer 2c described above on the surface of the die base 1. It is possible to provide a die for cold forging which can improve the toughness of the coating film 2 formed on the surface of the die and can improve the seizure resistance, thereby greatly improving the durability.

Hereinafter, the characteristics of the film 2 provided in the present invention will be described in detail.
In cold forging, especially in severe forging where the cross-section reduction rate of the workpiece exceeds 50%, cracks generated on the surface of the die for cold forging and deposits adhering to the surface of this die However, it becomes a factor that varies the defect of the molded product size and the mold life. Therefore, when manufacturing products by such severe cold forging, it is extremely important to improve the crack resistance (toughness) and adhesion resistance (seizure resistance) of the coating formed on the mold surface. It has become.
In addition, the above-mentioned deposit is a foreign substance obtained by solidifying or semi-solidizing a lubricant for cold forging and powder generated from a workpiece during forging (forging), and in the following description, The “attachment” indicates this foreign matter. In addition, the die life described above may be referred to as “forging life” in the following description.

  In the cold forging die of the present invention having the coating 2, the outermost layer 2c, which is the outermost layer of the coating 2, is a coating composed mainly of nitrides or carbonitrides of Al and Ti, and further Al and Ti. When the total atomic ratio of 100 is taken as 100, by forming a film in which the atomic ratio of Al is more than 55 and 80 or less, cracks on the mold surface and adhesion of deposits are suppressed, and heat resistance is also improved. I was able to. As a result, deformation resistance during forging of the workpiece can be reduced, and the durability (forging life) of the cold forging die can be improved.

  Specifically, in the outermost layer 2c of the film 2 provided by the present invention, the content of Ti, Al, and Cr affects the crack generation state on the surface of the cold forging die and the amount of deposits attached. As a result of experiments on the influence, a film mainly composed of nitrides or carbonitrides of Al and Ti has a mold during forging of a workpiece as compared with a film made of nitride or carbonitride containing Cr. There was a tendency for the adhesion of deposits to the surface to decrease. Furthermore, when the total atomic ratio of Al and Ti in the outermost layer 2c is 100, cracks on the mold surface are greatly suppressed by forming a film in which the atomic ratio of Al exceeds 55 and is 80 or less. It was found that adhesion of deposits was reduced and the durability of the cold forging die was improved. This is because the film containing Cr has poor thermal conductivity, that is, its heat dissipation is inferior, so that during cold forging under high surface pressure, the temperature tends to rise on the film surface, which is the cause. It was speculated that this was because the deposits adhered to the mold surface.

Further, when the outermost layer 2c is composed of a film in which the atomic ratio of Al exceeds 55 and is 80 or less, the temperature increase on the surface of the film during forging is suppressed by suppressing the Cr content in the outermost layer 2c. In addition to the effect, the heat dissipation is further improved by improving the binding ratio of Al and nitrogen.
Furthermore, the reason why the generation of cracks was suppressed by configuring the outermost layer 2c with a film in which the atomic ratio of Al is more than 55 and not more than 80 is that the film structure of the outermost layer 2c is refined and the oxidation resistance is increased. It was speculated that this improved crack resistance.

  In order to maximize the toughness which is the crack resistance of the outermost layer 2c, it is preferable to set the film hardness of the outermost layer 2c to a range of 20 to 30 GPa as measured by an indentation hardness method. If it exceeds 30 GPa, the toughness of the film tends to decrease, and the film may peel off. If it is less than 20 GPa, the wear resistance is not sufficient. In order to control the film hardness of the outermost layer 2c, it can be controlled by the bias voltage applied to the mold substrate among the film forming conditions in addition to the Al content of the outermost layer 2c.

  In the present invention, the outermost layer 2c is a film in which the atomic ratio of Al exceeds 55 and is 80 or less, but the film made of a nitride of Ti and Al or a carbonitride has an Al content and film formation conditions. It has a cubic and hexagonal crystal structure. In the present invention, the content of Al is important in a coating made of Ti and Al nitride or carbonitride, and the crystal structure may be either cubic or hexagonal.

  For the above reasons, the outermost layer 2c is a film mainly containing a nitride or carbonitride of Ti and Al, suppressing the Cr content, and considering its content, more preferably the film hardness, Controlling the atomic ratio to be in the above-described atomic ratio range is extremely effective for improving the durability of the cold forging die.

As described above, the outermost layer 2c is composed of a film mainly composed of a nitride or carbonitride of Al and Ti, and when the total atomic ratio of Al and Ti is 100, the atomic ratio of Al is The film is over 55 and 80 or less. In the outermost layer 2c, when the Al content is 55 or less in atomic ratio, the hardness of the outermost layer 2c is increased, and cracks are likely to occur in the outermost layer 2c during forging of the work piece. It becomes impossible to improve the durability. On the other hand, when the Al content exceeds 80 in atomic ratio, the droplets of the coating 2 (the outermost layer 2c) increase and the surface roughness (surface roughness) becomes sharply rough. In addition, the durability of the cold forging die cannot be improved.
Furthermore, when the lowermost layer 2a constituting the film 2 in the present invention is formed of a film mainly composed of a nitride or carbonitride of Cr, the adhesion between the mold base 1 and the film 2 is improved. Simultaneously, the effect | action which suppresses further the crack generation of the outermost layer 2c is exhibited.

  The cold forging die of the present invention is provided with the above-described coating 2, and in particular, with the outermost layer 2c, the function of the outermost layer 2c, that is, seizure resistance, toughness (crack resistance). The film 2 is characterized in that the heat resistance is improved and the coating 2 is less prone to cracks.

  The intermediate layer 2b of the film 2 provided by the present invention is a film layer formed between the lowermost layer 2a and the outermost layer 2c so that the adhesion between the lowermost layer 2a and the outermost layer 2c is improved. It has a function for joining and a function for complementing the wear resistance of the coating 2.

In the present invention, the components of the intermediate layer 2b are mainly composed of Al, Ti, and Cr. When the total atomic ratio of Al, Ti, and Cr is 100, the atomic ratio of Cr is 50 or less, and the atomic ratio of Al is 45. It is preferable that the atomic ratio of Ti is 10 or more and 35 or less.
The wear of the film formed on the cold forging die proceeds from the outermost layer 2c. When a part of the outermost layer 2c is exposed due to wear, the intermediate layer 2b exerts an effect of suppressing the wear of the film 2.

  The intermediate layer 2b is a film (mixed film) formed by film formation using an alloy target containing a metal nitride or carbonitride component constituting the lowermost layer 2a and the outermost layer 2c. It is also good. As another film forming method in which the intermediate layer 2b is composed of a mixed film using this alloy target, for example, the film forming target of the lowermost layer 2a and the film forming target of the outermost layer 2c are discharged simultaneously in a film forming apparatus. Thus, by forming the film while rotating the mold base 1, a method of forming a mixed film in which components contained in both targets are mixed can be employed.

In the intermediate layer 2b, when the total atomic ratio of Al, Ti, and Cr is 100, if the atomic ratio of Cr exceeds 50, the progress of wear of the coating 2 is accelerated and the forging life of the mold tends to be shortened. Become. Further, if the atomic ratio of Al in the intermediate layer 2b is less than 45, the heat resistance of the intermediate layer 2b is lowered, so that the wear of the coating 2 is similarly accelerated and the forging life is shortened. On the other hand, when the atomic ratio of Al in the intermediate layer 2b exceeds 65, the progress of wear of the coating 2 is similarly accelerated and the forging life of the mold tends to be shortened.
Moreover, when the atomic ratio of Ti in the intermediate layer 2b is less than 10 and exceeds 35, the peel resistance of the outermost layer 2c is lowered, and the forging life of the mold tends to be shortened. From this, more preferable components of the intermediate layer 2b are as follows: when the total atomic ratio of Al, Ti and Cr is 100, the atomic ratio of Cr is 30 or less, the atomic ratio of Al is 50 or more and 60 or less, and the atomic ratio of Ti Is desirably 10 or more and 20 or less.

Furthermore, in the present invention, it is desirable to contain Si in both or one of the intermediate layer 2b and the outermost layer 2c. When Si is contained, when the total atomic ratio of Al, Ti, Cr and Si contained in the intermediate layer 2b and the outermost layer 2c is 100, the atomic ratio of Si should be 2 or more and 10 or less. preferable. Thus, by including Si in both or one of the intermediate layer 2b and the outermost layer 2c, the crystal grain size of the intermediate layer 2b and the outermost layer 2c can be further refined. At the same time as the hardness of the outermost layer 2c is improved, an effect of dispersing stress concentrated on the texture grain boundary of the film occurs during forging of the workpiece, and the effect of improving the durability of the cold forging die occurs. .
When Si is included in the outermost layer, when the total atomic ratio of Al, Ti, Cr and Si is 100, the atomic ratio of Cr is 5 or less, more preferably 1 or less. A decrease in toughness of the outermost layer 2c due to Si content can be suppressed.

  In the case where Si is contained in either or both of the intermediate layer 2b and the outermost layer 2c, when the total atomic ratio of Al, Ti, Cr, and Si in each layer is 100, Si atoms When the ratio is less than 2, the effect of containing Si, that is, the effect of refining the crystal grain size cannot be obtained significantly. On the other hand, if the atomic ratio of Si exceeds 10, the toughness of the film is extremely lowered, and conversely, the progress of crack generation is accelerated, and the durability of the cold forging die is lowered.

  Further, by configuring the content (atomic ratio) of Si contained in the intermediate layer 2b to be larger than the atomic ratio of Si contained in the outermost layer 2c, seizure resistance on the surface of the outermost layer 2c and the intermediate layer are increased. The balance of wear resistance due to 2b is optimal, and the durability of the cold forging die is greatly improved, which makes the embodiment of the film 2 particularly preferable in the present invention.

  Furthermore, in the present invention, the film thickness (layer thickness) of the outermost layer 2 c is preferably 50% or more of the film thickness of the entire film 2. The upper limit of the film thickness of the outermost layer 2c in the entire film 2 is preferably 75% or less. Thus, by making the film thickness of the outermost layer 2c 50% or more of the film thickness of the entire film 2, the outermost layer 2c exhibits the effects such as improvement of its toughness to the maximum, and a cold forging die Durability is greatly improved. Furthermore, the thickness of the lowermost layer 2a is made the thinnest. Specifically, the film thickness of the lowermost layer 2a is 15% or less of the film thickness of the entire film 2, and the film thickness of the intermediate layer 2b is 40% or less of the film thickness of the entire film 2 so that the durability is the highest. An excellent cold forging die can be obtained.

  In the present invention, when Cr is contained in the outermost layer 2c, the Cr content is 5 or less when the total atomic ratio of Al, Ti, and Cr in the outermost layer 2c is 100. Preferably there is. If the atomic ratio exceeds 5 and the seizure resistance decreases, the tendency of deposits to adhere to the mold surface during forging increases, and the forging life is shortened due to variations in forging life and abnormal product dimensions. Tend to be.

  In the present invention, when the lowermost layer 2a contains Ti and Al in addition to Cr, the Ti and Al content of the lowermost layer 2a is 100 when the total atomic ratio of Al, Ti and Cr is 100. The atomic ratio of Ti and Al is preferably 5 or less. The reason for this is to suppress a decrease in the toughness of the entire coating 2.

  In the present invention, the above-described mixed coating and other layers may be appropriately formed between the lowermost layer 2a, the intermediate layer 2b, and the outermost layer 2c constituting the coating 2. For example, a first intermediate mixed layer that forms a mixed film containing components contained in the lowermost layer 2a and the intermediate layer 2b is formed between the lowermost layer 2a and the intermediate layer 2b, and between the intermediate layer 2b and the outermost layer 2c. Alternatively, a second intermediate mixed layer that forms a mixed film containing the components contained in the intermediate layer 2b and the outermost layer 2c may be formed. As described above, when a film composed of the first intermediate mixed layer and the second intermediate mixed layer is provided, the toughness of the film 2 can be further improved.

Further, in the cold forging die of the present invention, for the purpose of adjusting the appearance color of the die, the upper layer of the outermost layer 2c has a thickness of 0.3 μm or less, and Ti, Cr, Al, You may coat | cover the coating layer for external color adjustment which consists of 1 or more types of nitride selected from Si, or carbonitride.
This appearance color adjusting coating layer is silver when Cr is the main component, dark blue when Al and / or Si is the main component, and gold when Ti is the main component, and Depending on the content of Ti, Cr, Al, and Si, the color can be adjusted to an intermediate appearance color between the above colors. Furthermore, when a dark-colored film mainly composed of Al and / or Si is coated on a silver-colored film mainly composed of Cr to a thickness of about 0.05 μm, an interference color is formed. The coating layer for appearance color adjustment is also effective for identifying whether or not the surface treatment is performed on whether or not the coating layer 2 is formed on the surface of the mold and whether or not the mold has already been used for forging. Become.

Next, the surface roughness (surface roughness) of the surface of the coating 2 in the cold forging die according to the present invention will be described. The surface roughness (Ra) of the surface of the outermost layer 2c of the coating 2 provided by the present invention is preferably 0.1 μm or less, and the maximum height (Ry) is preferably 1 μm or less.
The reason why the arithmetic average roughness (Ra) is preferably 0.1 μm or less and the maximum height (Ry) is preferably 1 μm or less is as follows.
Particulate defects called droplets inside the coating 2 become a starting point for cracking due to stress concentration after dropping, which greatly affects the durability of the mold. For this reason, the durability of the die for cold forging can be improved by defining the values of the surface roughness (Ra) and (Ry) of the outermost layer 2c as described above. Moreover, it is preferable that the area ratio of a droplet is 2% or less. The area ratio of the droplets can be obtained by measuring the area ratio of irregularities when the surface of the outermost layer 2c is observed at a magnification of about 3000 times with a scanning electron microscope or the like.

  As described above, the formation of the intermediate layer 2b constituting the film 2 is performed by simultaneously discharging two types of targets made of the metal composition of the lowermost layer 2a and the outermost layer 2c in the film forming apparatus and rotating the gold in the film forming apparatus. By forming a film on the surface of the mold substrate 1, a film containing a nitride or carbonitride of the metal component of the lowermost layer 2a and a film containing a nitride or carbonitride of the metal component of the outermost layer 2c are laminated. You may form the mixed film (henceforth "laminated film") which consists of the structure comprised. In this case, in the intermediate layer 2b, the stacking order of the layer (2b1) containing the metal component of the lowermost layer 2a and the layer (2b2) containing the metal component of the outermost layer 2c is not particularly limited. It is sufficient that the layers are laminated.

  The method for forming the laminated film as an embodiment of the above-described mixed film includes a film containing a nitride-containing or carbonitride-containing metal component of the lowermost layer 2a and a metal component nitride of the outermost layer 2c, The discharge current and the rotational speed of the mold base 1 are controlled so that the thickness of each coating containing carbonitride is 0.3 μm or less, and the nitride or carbonitride of the metal component of these lowermost layers 2a And an intermediate layer 2b having a laminated structure in which a unit layer containing a nitride or carbonitride of a metal component of the outermost layer 2c is sequentially laminated. At this time, the composition of each unit layer of the laminated structure is as follows: when the total atomic ratio of Al, Ti, Cr, and Si is 100, the unit layer (2b1) having an atomic ratio of Cr of 50 or more and Al Preferably, unit layers (2b2) having a composition having an atomic ratio of 50 or more are alternately stacked so that the composition and film thickness of the intermediate layer 2b have predetermined values. When the intermediate layer 2b having such a laminated (periodic) structure is formed, the toughness of the coating 2 can be further increased, and a cold forging die with improved durability can be obtained.

In the intermediate layer 2b having this laminated structure, the layer thickness (film thickness) of the particularly preferable unit layer is less than 0.1 μm. Here, since the unit layer having a Cr atomic ratio of 50 or more has a columnar crystal structure and the unit layer having an Al atomic ratio of 50 or more has a fine structure, in the intermediate layer 2b having this laminated structure, Unit layers having different particle sizes are alternately stacked. For this reason, since the intermediate layer 2b having a laminated structure has improved crack resistance, it is possible to contribute to improving the durability of the cold forging die.
In addition, the structure | tissue which makes this laminated structure can be confirmed by cross-sectional observation with a transmission electron microscope.

  In the cold forging die of the present invention, it is preferable to perform nitriding treatment on the surface of the mold base before forming the above-described coating 2 on the surface of the mold base 1. This is because, in order to improve the peel resistance of the film 2 formed on the cold forging die, it is preferable to perform nitriding treatment on the surface of the die base 1 in advance. When nitriding is performed on the surface of the mold base 1, plasma nitridation is preferable, in which a compound layer is not easily formed by nitriding, and the depth of the nitriding is 50 μm from the surface of the mold base 1 to the inside. The following is preferable.

[Prototype mold]
Next, an example in which a die for evaluating the performance of the cold forging die according to the present invention is made as a prototype, and an experiment for cold forging is performed to evaluate its durability will be described. As the mold for durability evaluation, 30 types of cold forging punches were prototyped and their durability was evaluated. The material of the prototype punch was a matrix type HSS (equivalent to JIS), which is a mold material, and the quenching temperature was 1150 ° C., the tempering temperature was 520 ° C. three times, and the hardness was adjusted to 65 HRC. And, in order to reduce the variation in the surface shape and surface portion properties of the punch (die) substrate after the heat treatment, after grinding and cutting to a predetermined shape, The functional part of the punch base material that becomes the contact part (contact part with the workpiece to be forged) is mirror-polished, the surface roughness (Ra) of the functional part is 0.03 μm, and the surface roughness (Ry) is 0. Adjusted to 3 μm.

FIG. 2 is a plan view showing the shape of a prototype punch (punch base material) 3. The punch 3 has a cylindrical shape, and a straight portion 3 a and a straight portion 3 a are formed along the axial center (longitudinal) direction. The bearing part 3b integrally formed in the lower end part of this is provided. Moreover, the diameter of the bearing part 3b is provided with the outer peripheral surface 3c and the bottom part 3d which were formed so that it might become a little larger than the diameter of the straight part 3a. For this reason, although not shown in FIG. 2, the straight part 3a and the bearing part 3b are integrally formed via the taper part. In addition, a minute R-shaped portion is formed at the ridgeline where the outer peripheral surface 3c and the bottom 3d intersect.
Since a normal cold forging punch has the above-described shape, the bearing portion 3b becomes a portion that is more easily damaged than the straight portion 3a. In particular, the outer peripheral surface portion 3c of the bearing portion 3b is easily damaged.
L shown in FIG. 2 indicates the length in the longitudinal direction (axial direction) of the straight portion 3 a and the bearing portion 3 b that are functional portions of the punch 3. In addition, the upper part of the longitudinal direction of the straight part 3a shown in FIG. 2 becomes a holding part for making the forging apparatus hold the punch 3.

On the surface of each prototype punch base 3 for cold forging, that is, the straight portion 3a, taper portion (not shown), and bearing portion 3b (outer peripheral surface 3c and bottom portion 3d) of the punch base 3 shown in FIG. The film having the specifications shown in Table 1 was formed (film formation) using a film forming apparatus having a plurality of arc evaporation sources.
In the following description of the embodiment, when “punch base material” is described, a prototype punch in which a film is not formed on the functional parts (straight part 3a, taper part, and bearing part 3b) of the punch base material is shown. When “punch” is simply described, a prototype punch (punch 3) in which a film is formed on this functional portion is shown.

Table 1 shows Ti, Cr, Al, Si contained in the lowermost layer 2a, the intermediate layer 2b, and the outermost layer 2c as the specifications of the film formed on the 30 types of prototype punch substrates (sample numbers 1 to 30). Ratio, that is, the value of the atomic ratio when the total atomic ratio of these elements is 100, and the film thickness (μm) of each layer of the lowermost layer 2a, intermediate layer 2b, and outermost layer 2c formed And surface roughness (Ra) and (Ry) indicating the surface roughness (surface roughness) of the surface of the outermost layer (outermost layer) 2c.
Also, in the column of the sample number, it is described which punch corresponds to the sample number, which corresponds to the punch of the example of the present invention, the comparative example, or the conventional example. Further, Table 1 shows the forging life (number of shots) which is an evaluation result of durability of the prototype punch.

  As shown in Table 1, the punch of the comparative example made for comparison with the inventive example formed only one layer, only two layers, and three layers of the lowermost layer, the intermediate layer, and the outermost layer. Examples of conventional punches that are also prototyped include punch examples in which no film is formed and punch examples in which only one layer of film is conventionally formed.

“Forging life” shown in the rightmost column of Table 1 indicates the number of shots obtained by performing a cold forging molding experiment on the durability of the prototype punch, and this forging life (number of shots) is as follows. Was defined as
That is, when the workpiece (workpiece material) 4 shown in FIG. 3 is formed by cold forging (rear extrusion molding) using the prototype punch 3, a product obtained by cold forging (see FIG. 4). The forged formed product 5) is judged whether or not vertical streaks are generated on the inner surface (inner peripheral surface) 5a of the inner surface 5a. The cumulative number of shots when an error of 0.01 mm occurred was defined as the forging life. In the column of forging life shown in Table 1, a value where the cumulative number of shots is less than 1000 is shown as the number of times rounded down as “000”, and the value of the number of shots is the value of the prototyped die (punch 3). The life (forging life) is shown.

The experimental conditions for cold forging and the evaluation method for the experimental results of the prototype punch 3 will be described in more detail.
The workpiece 4 for cold forging was made of S45C (carbon steel for machine structure), and the workpiece was subjected to annealing and bond treatment (phosphate treatment) during drawing. Then, using a commercially available part former, the steps of cutting, end face correction, and drawing are performed to form a cylindrical workpiece 4, and then the workpiece is inserted from the hole 6a of the die 6 shown in FIG. 4 was inserted onto the receiving punch 7, and the prototype punch 3 was shot up and down in the hole 6a of the die 6 in the F direction to form the workpiece 4 by cold forging. In this cold forging, forging is performed by a backward extrusion process in which the cross-section reduction rate of the work piece 4 is 70% and the forming depth is 2.5 times the diameter, and a cylindrical shape having a bottom portion 5b is formed. The durability of the punch was evaluated based on the measurement of the state of occurrence of vertical stripes on the inner peripheral surface 5a while forming the forged molded product 5 (see FIG. 4) sequentially and repeatedly. In this rear extrusion process, the molding load is 150 kgf / mm ² , the number of shots per minute is 60 shots, and the lubricating oil is a water-insoluble forging oil containing a sulfur-based extreme pressure additive used as a punch in the previous process. Directly supplied. The code | symbol 8 shown in FIG. 3 (FIG. 4) has shown the frame of cold forging.

  Next, the specifications regarding the film of the punch 3 that has been prototyped will be described with reference to Table 1. Sample Nos. 2 to 5, Sample Nos. 8 to 16, and Sample Nos. 20 to 24 form films composed of the lowermost layer 2a, the intermediate layer 2b, and the outermost layer 2c included in the present invention, and each of these films The atomic ratio of the elements contained in this indicates the punch of the present invention example included in the range defined by the present invention. Sample numbers 13, 14, 15, and 21 show punches of the present invention example in which a film containing Si is formed on both or one of the intermediate layer and the outermost layer.

  Sample No. 1 is a comparative example in which a film having only one outermost layer provided in the example of the present invention was formed (atomic ratios of Ti and Al are 40 and 60). Sample Nos. 6 and 7 have a film composed of the lowermost layer, the intermediate layer, and the outermost layer, but the atomic ratio of Al contained in the outermost layer is not included in the range defined in the present invention. A comparative example is shown. Sample number 17 has an atomic ratio of elements corresponding to the lowermost layer and the outermost layer provided in the present invention, but shows a comparative example not provided with an intermediate layer, and sample number 18 is the lowermost layer. A comparative example is shown in which a film comprising an intermediate layer and an outermost layer is provided, but the atomic ratio of Al contained in the outermost layer is not included in the range defined in the present invention. Sample No. 19 has a coating composed of a lowermost layer, an intermediate layer, and an outermost layer. The atomic ratio of Cr in the lowermost layer is 100, the atomic ratio of Ti in the intermediate layer is 5, and the atomic ratio of Cr is A comparative example is shown in which 65, the atomic ratio of Al is 30, the atomic ratio of Ti of the outermost layer is 10, the atomic ratio of Cr is 30, and the atomic ratio of Al is 60.

  Sample number 25 represents a conventional punch in which a film is not formed on the surface of the functional part of the punch base material, and sample numbers 26 to 30 are CrN, TiN, TiCN, TiAlN, and AlCrN, respectively, which have been conventionally performed. 1 shows a conventional punch in which one layer of a film made of

For the formation of the film on each punch base material, a base material holder having a rotation mechanism was provided in the chamber of the film forming apparatus, and the prototype punch base material was placed on this base material holder. Then, after evacuating the inside of the chamber of the film forming apparatus (exhausting to 1 × 10 ⁻³ Pa or less), the punch base was heated to about 430 ° C., and then sputter cleaning was performed using Ar ions. Thereafter, in the case of film formation with an arc evaporation source, a φ100 mm target is used, the arc current is in the range of 80 to 150 A, the bias voltage applied to the punch substrate is minus 45 V, and the N ₂ atmosphere has a total pressure of 4 Pa. In a mixed gas of (N ₂ + C ₂ H ₂ ), a nitride film or a carbonitride film was formed on the surface of the punch base material. The number of revolutions of the punch base was 4 revolutions per minute.

  In this film formation, for the sample numbers of the present invention example and the comparative example described as “-” in the “Manufacturing method” column of Table 1, first, the target (evaporation source) having the metal composition of the lowermost layer. Was used to form the lowermost layer on the punch substrate, and then the evaporation source was switched to form the intermediate layer. After the intermediate layer was formed, the outermost layer was formed with the target having the metal composition of the outermost layer.

  “Mixing” described in the “Manufacturing method” column of the intermediate layer in Table 1 indicates that the intermediate layer is composed of a laminated film as an embodiment of the “mixed film” described above. In addition, about the sample number of this invention example and the comparative example which are described as "mixing" in the column of the intermediate | middle layer of Table 1, using the target which has a metal composition of a lowermost layer, a lowermost layer is put on a punch base material. After forming the film, it shows that the mixed film, that is, the intermediate layer 2b having the laminated structure described above was formed by using the target having the composition of the lowermost layer and the target having the composition of the outermost layer simultaneously. Yes. And after forming the intermediate | middle layer 2b, the outermost layer was formed with the target which has a composition of outermost layer.

  When the intermediate layer is formed as a laminated structure as described above, as described above, the intermediate layer is strictly formed on the surface of the punch base placed on the rotation mechanism of the film formation apparatus, and the lowermost layer target for film formation and the outermost layer formation. Films made of nitride or carbonitride of each metal component of the film target are alternately laminated. In order to form the intermediate layer as this laminated structure, the lowermost layer deposition target and the outermost layer deposition target are simultaneously discharged based on the control of the deposition apparatus, and the arc current is changed in the range of 80 to 150A. However, the number of rotations of the rotation mechanism for forming each unit layer is controlled so that the thickness of the unit layer constituting the laminated structure and the composition thereof have predetermined values.

  In addition, in the functional part (straight part 3a, taper part, and bearing part 3b) of the punch base material 3 of sample numbers 1 to 30 (excluding sample number 25), the lowermost layer, the intermediate layer, After forming a film having a film thickness corresponding to the outermost layer, the surface of the functional part of the punch base material is mirror-polished again, and as shown in Table 1, the surface roughness (Ra) of the film on the surface of the functional part is determined. Thirty types of trial punches were manufactured by adjusting the surface roughness (Ry) to 0.6 μm, which is 0.1 μm or less, and 0.05 μm, which is 0.1 μm or less.

[Results of forging experiment using prototype punch]
Subsequently, a cold forging forming experiment was performed on the prototype punches according to sample numbers 1 to 30 based on the above-described cold forging experimental conditions. The results are shown in the “Forging life (number of shots)” column of Table 1. From the results of this forging life, the following matters became clear.

  (1) For sample numbers 2 to 5, sample numbers 8 to 16, and sample numbers 20 to 24 serving as examples of the present invention, the number of shots indicating the forging life was 15000 to 58000. FIG. 5 is a photograph taken when the number of shots reaches 12000 for the punch of sample number 2 which is an example of the present invention. FIGS. 6A and 6B are shots of the punch of sample number 2 similarly. It is a SEM photograph figure (magnification 65) when the outer peripheral surface of a bearing part when the frequency | count reaches 12000 is observed with a scanning electron microscope, Comprising: The secondary electron image and the reflected electron image are each shown. As shown in FIG. 5 and FIG. 6, damage such as peeling of the film did not occur on the straight portion 3a of the punch of sample No. 2 and the outer peripheral surface 3c of the bearing portion 3b, which are examples of the present invention.

  On the other hand, the number of shots showing the forging life of Sample No. 1, Sample No. 6 to 7 and Sample No. 17 to 19 serving as comparative examples is 7000 to 12000, which is lower than that of the present invention. It was. FIGS. 7A and 7B are SEM photographs of the outer peripheral surface of the bearing portion observed with a scanning electron microscope when the number of shots reaches 5000 for the punch of sample number 7 as a comparative example. And a secondary electron image and a reflected electron image, respectively. In FIGS. 7A and 7B, the vertical direction of the paper surface indicates the axial direction of the punch (forging direction).

7A and 7B, black portions (reference numeral “8”) extending in the horizontal direction of the paper surface indicate cracks generated on the outer peripheral surface 3c of the bearing portion 3b. The white portion of the peripheral area shows that the film is peeled off and the base material of the punch is exposed, that is, minute irregularities are generated in the peripheral area including the crack 8. Is shown. In the punch of Sample No. 7, which is a comparative example, the minute unevenness in the peripheral portion including these cracks 8 generated on the outer peripheral surface 3c of the bearing portion 3b expands as the number of forging shots increases, and the forging life is 10,000. The number of shots was determined.
In addition, as shown in Table 1, the number of shots indicating the forging life of the conventional punches (sample numbers 25 to 30) was 10,000 or less.

As a result, the punch of the present invention example has three layers on the base material, that is, the above-mentioned film made of nitride or carbonitride selected from Ti, Cr, Al, or Ti, Cr, Al, Si. When the film 2 composed of the lower layer, the intermediate layer, and the outermost layer is formed, and the atomic ratio of these elements contained in each of these three layers is defined within the above-mentioned range, the punch of the comparative example such as sample number 1 It was revealed that the forging life was improved by 2 to 4.8 times as compared with the above.
In particular, for Sample Nos. 2 to 5, Sample No. 10, Sample Nos. 13 to 16, and Sample Nos. 21 and 23, which are examples of the present invention, the number of shots indicating the forging life is 20000 or more, which has been conventionally performed. It has been clarified that the forging life is improved at least 2 to 10 times as compared with the conventional sample numbers 25 to 30. As described above, the reason why the forging life of the example of the present invention is improved is that the Al content of the outermost layer is more than 55 in atomic ratio and not more than 80, more preferably in the range of 60 to 80, as described above. It can be inferred that this is due to the suppression of cracks in the outermost layer 2c.

  (2) Sample No. 3, which is an example of the present invention, is a case where Cr is contained in the outermost layer in an atomic ratio of 5, but the forging life is reduced as compared with Sample No. 2 of the example of the present invention. Although the amount of wear of the punch of sample number 3 was small, it was observed that the amount of deposits deposited on the punch surface was larger than that of sample number 2. For this reason, the surface of the forged product was scratched by the deposits and exceeded the allowable range for the product. Furthermore, Sample No. 19, which is a comparative example, is a case where Cr is contained in the outermost layer, but the forging life is as short as 12000 compared to the present invention example, and a large improvement in durability can be confirmed even compared to the conventional example. There wasn't. This is because, although the amount of wear of the punch was small as in the case of Sample No. 3, significantly more deposits deposited on the surface of the punch were observed compared to the example of the present invention. For this reason, many flaws due to this deposit occurred on the surface of the forged product, which exceeded the allowable range as a product. Therefore, when Cr is contained in the outermost layer, the Cr content is preferably an atomic ratio with the upper limit being 5 or less.

  (3) Sample numbers 2 to 5 and 8 to 12 serving as examples of the present invention are cases in which the Cr content in the intermediate layer is set to any of the ranges of 10 to 75 in terms of atomic ratio. In Sample No. 4 with an atomic ratio of 10 and Sample No. 5 with a Cr content of 20 in atomic ratio, a high value of 35,000 or more shots for a forging life was obtained. On the other hand, in Sample Nos. 8 to 10 of the present invention example in which the Cr content was 30 to 75 in atomic ratio, the wear amount of the punch increased, so the number of shots for the forging life decreased to 16000 to 24,000. From this, when Ti, Cr, and Al are contained in the intermediate layer, it can be said that the atomic ratio of Cr content is more preferably 10 to 20 or less.

  (4) Sample Nos. 11, 12, and 20 that are examples of the present invention are cases where Ti or Al nitride or carbonitride is contained in the lowermost layer in addition to Cr, but sample numbers 2 that are examples of the present invention. The number of shots that resulted in the forging life decreased. This is because Sample Nos. 11, 12, and 20, especially Sample No. 20, could not maintain the dimensional tolerance of the product due to abnormal wear. Therefore, when Ti or Al nitride or carbonitride is contained in the lowermost layer in addition to Cr, it can be said that the atomic ratio of Ti or Al in the lowermost layer should be reduced to less than 5. However, Sample Nos. 11, 12, and 20 have a forging life 1.3 times or more that of Sample Nos. 25 to 30 as the conventional example, and the effect is not remarkable, but compared with that of Conventional Examples 25 to 30. It can be said that the forging life is long.

(5) As shown in Sample Nos. 13 to 15 and 21, which are examples of the present invention, when Si is contained in the intermediate layer and / or the uppermost layer in an atomic ratio within the range of 5 to 10, the forging life is increased. The number of shots shown is 40000 or more, and the forging life is remarkably improved as compared with other examples of the present invention. This means that if the intermediate layer and the uppermost layer, or one of them, contains Si in an atomic ratio of 5 or more and 10 or less, the wear resistance of the coating is improved by the action of refining the crystal grain size due to the addition of Si, It is believed that the number of shots has improved significantly. In particular, it is more preferable that the number of shots showing the forging life is 52000 to 58000 when the intermediate layer Si atomic ratio shown in sample numbers 15 and 21 is larger than that of the outermost layer.
Sample No. 16 was a case where the intermediate layer was formed using a target for forming the intermediate layer, and showed an excellent forging life similar to the case where the intermediate layer was formed as a mixed film.

  (6) Sample Nos. 22, 23, and 24 serving as examples of the present invention are cases where the film thicknesses of the lowermost layer, the intermediate layer, and the outermost layer are changed, but the forging lifetimes of the sample numbers 22 and 24 are 15000 and 17000. On the other hand, the forging life of Sample No. 2 and Sample No. 23 becomes 25000 and 22000, and if the film thickness ratio of the outermost layer exceeds 50% of the thickness of the entire coating 2 and is less than 75%, the forging life is longer. It can be said. This suggests that the balance of properties of the lowermost layer, the intermediate layer and the outermost layer affects the forging life, and the film thickness ratio of the outermost layer exceeds 50% with respect to the film thickness of the entire coating 2, It can be said that less than 75% is a preferable film thickness structure of the present invention. Furthermore, the film thickness ratio of each layer is such that the film thickness of the lowest layer is the thinnest and is 15% or less of the film thickness of the entire film 2, and the film thickness of the intermediate layer is 40% or less of the film thickness of the entire film 2 It can be said that it is preferable.

(7) Sample No. 1, which is a comparative example, consists of a single-layer film in which the lowermost layer and the intermediate layer are not formed. Therefore, this film partially peels off, and the film wears abnormally starting from the peeled portion. Due to the fact that the generation of streaks due to peeling of the film was confirmed on the surface of the forged product at a relatively early stage (number of shots: 7000), and the tolerance for the product was exceeded, the durability of the cold forging die was improved. It did not improve.
Sample numbers 6 and 7, which are comparative examples in which the Al content in the outermost layer is 55 and 40 in atomic ratio, have 12000 and 10,000 shots for the forging life, which is less than the forging life of the present invention. It was. As for the sample No. 7, the punch surface after forging was observed with a scanning electron microscope. As a result, as shown in FIGS. 7A and 7B, a large number of cracks 8 were observed in the direction perpendicular to the forging direction. As a result, the allowable dimension range of the product could not be maintained. From this result, it can be said that it is important that the Al content in the outermost layer is an atomic ratio exceeding 55.

  The punch of sample number 7 is a comparative example in which the Al content in the outermost layer 2c of the coating is 40 in terms of atomic ratio, and when the number of shots reaches 5000, it is shown in FIGS. 7 (a) and 7 (b). Thus, many cracks 8 were observed in the direction perpendicular to the forging direction, and the cracks 8 caused abnormal wear on the bearing portion (3b), thereby shortening the forging life. The crack 8 generated in a direction perpendicular to the forging direction is a crack 8 generated in the coating coated on the coating surface by repeating the elastic deformation of the base material surface by compression and tension during forging. The generation particularly depends on the Al content in the outermost layer, and was observed on the punch surface having a sample number of 55 or less in atomic ratio.

  (8) Since Sample No. 17 serving as a comparative example has no intermediate layer, the number of shots in which abnormal wear occurs due to peeling or the like on the outermost layer before the effect of the outermost layer is exerted, resulting in a forging life Became a low value of 12000. Similarly, Sample No. 18, which is a comparative example, formed a film consisting of three layers of a lowermost layer, an intermediate layer, and an outermost layer. However, since the Al content in the outermost layer was 50 in atomic ratio, it was perpendicular to the forging direction. A large number of cracks were observed in the direction of, so that the product dimension became abnormal, and the number of shots for the forging life was as low as 12000. Similarly, in Sample No. 19 serving as a comparative example, the Cr content in the outermost layer was set to 30 in atomic ratio, so that the deposit on the punch surface increased. For this reason, many flaws due to the deposits were generated on the surface of the forged product, and the number of forging shots exceeded the allowable range as a product at 12000, and could not be continued.

  FIG. 8 is a photograph showing the punch state when the number of forging shots reaches 12000 for sample number 19 as a comparative example. Sample No. 19 has a Cr content in the outermost layer of 30 as an atomic ratio, so that a large amount of deposit 9 adheres to the straight portion 3a of the punch during cold forging, and this deposit 9 is a workpiece. Scratches occurred on the inner peripheral surface 5a of the product 5. The adhesion amount of the deposit 9 greatly depended on the Cr content of the outermost layer.

  (9) In Sample Nos. 25 to 30 which are conventional examples, the number of shots for a forging life is 10000 or less. In Sample Nos. 26 and 30, it was observed that the deposits deposited on the punch surface were particularly large compared to the examples of the present invention, and as a result, the inner peripheral surface 5a of the forged product 5 was scratched by the deposits. Occurred and exceeded the allowable range for forged products. Sample Nos. 27 and 28 are inferior in wear resistance as compared with the examples of the present invention because the base material of the functional part on the punch surface was partially exposed. In sample No. 29, many cracks were observed in the direction perpendicular to the forging direction on the punched surface after forging, and the allowable dimension range of the product could not be maintained. As a result, cracks were more likely to occur than in the present invention example. Met.

In the above-described embodiment, at least one selected from Ti, Cr, Al, and Si for adjusting the appearance color on the outermost layer of the coating formed on the cold forging die (punch) of the present invention. Even when a coating for appearance color adjustment made of a nitride or carbonitride was applied, no major difference in forging life could be confirmed.
Further, in the present invention, for example, a film for improving wear resistance on the inner peripheral surface of the hole 6a of the die 6 constituting the cold forging die shown in FIG. 3 (FIG. 4), for example, It is preferable to form a film made of CrN, TiN, TiCN or the like that has been conventionally used.

As described in the results (1) to (9) of the above examples, the cold forging punch provided with the coating composed of three layers of the lowermost layer, the intermediate layer, and the outermost layer according to the present invention is a conventional example or Compared to the punch having the coating film of the comparative example, the number of shots (durability) at which the forging life is at least 1.5 times greater and the seizure due to the adhesion of foreign matter to the punch surface (functional part) is improved. Was confirmed.
In the above-described embodiment, an example was described in which the durability of the film formed on the surface of the punch was confirmed by performing cold forging by backward extrusion, but the present invention includes various types including a punch and a die. It can be applied to a cold forging die to provide a die that improves its durability. In particular, the present invention improves the adhesion resistance of the die surface by suppressing cracks generated from the coating surface peculiar to the die for cold forging and seizing, and is used at a cross-section reduction rate of 50 to 80% or more. The mold is suitable for a cold forging mold used for forward extrusion, backward extrusion, upsetting, and drawing.

  The material of the die applicable to the cold forging die of the present invention is, for example, die steel, matrix high speed steel, high speed tool steel, cemented carbide or the like. In addition, as a film forming apparatus for forming a film on the cold forging die of the present invention, an apparatus to which a PVD method (ion plating, sputtering, ion beam sputtering, etc.) is applied can be used.

  The cold forging die according to the present invention has higher film toughness than the conventional surface-coated mold layer, and has excellent peeling resistance and seizure resistance of the film, and has improved durability. It is useful as a mold for use.

1: Mold base 2: Film (film layer)
2a: Lowermost layer 2b: Intermediate layer 2c: Outermost layer 3: Punch 3a: Straight part 3b: Bearing part 3c: Outer peripheral surface (outer peripheral part)
3d: bottom (bottom)
4: Work piece (work material)
5: Forged molded product (product)
5a: Inner peripheral surface 6: Die 6a: Hole 7: Underlay punch 8: Crack 9: Deposit

Claims (10)

In the cold forging die in which the surface of the die base material as a base material is coated with a film made of nitride or carbonitride selected from Ti, Cr, Al,
The coating is composed of a coating layer in which a lowermost layer, an intermediate layer, and an outermost layer are formed sequentially from the surface side of the mold base,
The lowermost layer is a film mainly composed of a nitride or carbonitride of Cr, the intermediate layer is a film mainly composed of a nitride or carbonitride of Al, Ti and Cr, and the outermost layer is composed of Al and Ti. It is composed of a film mainly composed of nitride or carbonitride,
A die for cold forging, wherein the atomic ratio of Al in the outermost layer is more than 55 and not more than 80 when the total atomic ratio of Al and Ti contained in the outermost layer is 100.   When the total atomic ratio of Al, Ti, and Cr contained in the intermediate layer is 100, the atomic ratio of Cr in the intermediate layer is 50 or less, the atomic ratio of Al is 45 to 65, and the atomic ratio of Ti is The die for cold forging according to claim 1, wherein the die is 10 to 35.   The intermediate layer and / or the outermost layer contains Si, and when the total atomic ratio of Al, Ti, Cr and Si in the intermediate layer containing Si or the outermost layer is 100, Si The die for cold forging according to claim 1 or 2, wherein the atomic ratio is 2 or more and 10 or less.   The cold forging die according to claim 3, wherein an atomic ratio of Si contained in the intermediate layer is larger than an atomic ratio of Si contained in the outermost layer.   The said intermediate | middle layer is comprised from the mixed film containing the nitride or carbonitride contained in the said lowermost layer and outermost layer, The cold forging in any one of Claims 1-4 characterized by the above-mentioned. Mold.   The intermediate layer is composed of a laminated film obtained by laminating a film containing nitride or carbonitride contained in the lowermost layer and a film containing nitride or carbonitride contained in the outermost layer. The cold forging die according to any one of claims 1 to 4, wherein the die is for cold forging.   The cold forging die according to any one of claims 1 to 6, wherein the thickness of the outermost layer is 50% or more of the film thickness of the entire coating layer. Between the lowermost layer and the intermediate layer, interpose a film containing nitride or carbonitride contained in the lowermost layer and the intermediate layer,
The film according to any one of claims 1 to 7, wherein a film containing nitride or carbonitride contained in the intermediate layer and the outermost layer is interposed between the intermediate layer and the outermost layer. The cold forging die described.   The surface of the outermost layer is provided with an appearance color adjusting coating layer made of one or more nitrides or carbonitrides selected from Ti, Cr, Al, and Si. The cold forging die according to any one of 8.   The cold forging die according to any one of claims 1 to 9, wherein the cold forging die is a punch used for cold forging.