JP2011147946A - Warm/hot forging die and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a warm/hot forging die in which wear during a forging work and also thermal fatigue crack are suppressed and the large crack and chipping of the die are prevented, and which is excellent in durability and to provide a method of manufacturing the same. <P>SOLUTION: The warm/hot forging die has a designed surface to which a wear resisting coating film is given. The wear resisting coating film is a multilayer film in which a first layer (0&lt;x&lt;1) composed of (Al<SB>x</SB>Cr<SB>1-x</SB>)N and a second layer (0&lt;y&lt;1) composed of (Ti<SB>y</SB>Al<SB>1-y</SB>)N are alternately laminated and the thickness of each layer of the adjacent first layer and second layer is at least &le;15 nm and the thickness of all the coating film of the multilayer coating film is 1-20 &mu;m. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a hot forging die and a manufacturing method thereof, and in particular, a hot forging die having excellent wear resistance and thermal fatigue properties such as oxidation resistance and heat check resistance and the like. It relates to a manufacturing method.

  In a cutting tool, a cold mold, etc., the wear resistance is improved by a surface hardening process such as nitriding or shot peening. In recent years, with demands for higher processing accuracy, surface hardening treatments with higher wear resistance have been demanded, and as one of them, surface hardening treatments that impart a high-hardness surface film to the material to be treated by the PVD method Has been done.

  For example, in Patent Document 1, although an Al oxide film formed by the PVD method is very excellent in wear resistance, it is difficult to form a stable film, while nitrides such as Ti, Hf, and Zr are stable. Although it is possible to form a coated film, it is said that the wear resistance, particularly the wear resistance in high-speed cutting applications, is insufficient. In addition, in this document, a first layer made of one or more compounds of nitride, oxide, carbide, carbonitride, and boride of a predetermined metal element containing Al and Si, and Al and Si And a second layer made of a nitride, oxide, carbide, carbonitride and / or boride of an alloy made of two kinds of metal elements of a predetermined metal element containing a predetermined number of metal elements by a PVD method. It discloses that a multi-layer coating having a thickness of 4 to 50 nm and a total coating thickness of 0.5 to 10 μm is applied to the material to be treated. Such a multilayer film can be stably formed by the PVD method, has high hardness and good wear resistance, and is excellent in interfacial consistency, and is therefore a film with little peeling. It states that the treated material can give excellent wear resistance.

  As in the above-mentioned Patent Document 1, generally, by giving a multilayer coating to the tool steel by the PVD method, it is possible to suppress propagation of cracks generated in the surface or the multilayer coating in the stacking direction at the multilayer interface. In addition, impact resistance and the like can be improved as compared with a single layer coating. That is, it is possible to prevent the occurrence of cracking and peeling of the film against the impact received during use as a tool, and as a result, it is possible to provide more excellent wear resistance.

For example, in Patent Document 2, a PVD method is used to form a first layer made of TiC _x N _1-x (0 ≦ x ≦ 0.6), (Al _y Ti _1-y ) (N _z C _1-z ) ( 4 or more layers stacked alternately adjacent to each other and the second layer of 0.56 ≦ y ≦ 0.75, 0.6 ≦ z ≦ 1), and the total coating thickness of the multilayer coating is 0.6 to A wear-resistant coating for machine tools that is 12 μm is disclosed. As described above, it is stated that the multilayer coating structure can alleviate and prevent the growth of cracks generated near the surface, prevent the coating from cracking and peeling, and provide excellent wear resistance.

  Furthermore, a film formed by an ion plating method, which is a kind of PVD method, is considered to be more excellent in wear resistance because it is dense and has high hardness. On the other hand, for example, in Patent Document 3, such a dense film has a high residual compressive stress. Therefore, when the film is formed to be thicker than a certain degree, the adhesion with the material to be treated is lowered, and the wear resistance is well balanced. It states that it is difficult to form a film having a practical thickness that can be improved. Furthermore, in this document, the first layer made of Ti nitride (or carbonitride) and the second layer made of TiAl nitride (or carbonitride) are alternately arranged with different orientations. A tool is disclosed in which a multilayer coating having a predetermined intermediate layer disposed between a first layer and a second layer is applied by an ion plating method. By laminating two types of films with different orientations, a dense and practically hard film with a practical thickness can be formed without increasing the residual compressive stress, and therefore the adhesion to the material to be treated is impaired. It states that it can provide a highly abrasion-resistant film.

  In this document, the reason why the film formed by the ion plating method has a high residual compressive stress is that a preferential growth orientation is given by crystal growth. That is, a film having a columnar crystal structure is formed, but one columnar crystal particle becomes a single crystal having very few internal defects, and such crystals continuously form a film to increase the thickness of the film. Along with this, the residual compressive stress increases.

  Incidentally, mechanical wear during forging has become a problem in hot forging dies as well as cutting tools. In order to suppress this wear during forging, a mold is used by repeatedly applying a lubricant to the mold design surface for each forging process. On the other hand, because the mold design surface is repeatedly heated by contact with the high-temperature forged material and cooled by the application of the lubricant, thermal fatigue cracks such as heat check and heat crack are caused by thermal stress. As a result, problems such as large cracks and chipping of the mold occurred. Therefore, it has been studied to perform surface hardening treatment on the mold design surface of such a hot forging mold.

  For example, in Patent Document 4, after a polishing material is sprayed together with compressed air on a hot mold alloy steel such as SKD61 to form a nanocrystalline structure without a layered processed structure on the surface layer near the surface, plasma nitriding is performed. 1 discloses a hot forging die in which nitrogen is diffused below the surface layer and a hard ceramic layer made of chromium nitride (CrN) or the like is formed on the outermost surface by a PVD method including an ion plating method. He states that by applying a nanocrystalline structure without a layered structure, high hardness and toughness can be improved, and wear loss and thermal fatigue cracks on the mold design surface are suppressed. The hard ceramic layer made of chromium nitride (CrN) is not a wear-resistant film against mechanical wear but a film mainly for imparting resistance to melting damage.

JP-A-7-205361 JP-A-6-136514 JP-A-10-76407 JP 2008-223122 A

  Also in the hot forging die, a surface hardening treatment for imparting a high hardness surface film to the die material by the PVD method is being studied in accordance with a demand for higher processing accuracy. Here, it is also required to prevent large cracks and chipping of the mold due to thermal fatigue cracks as well as mechanical wear during forging.

  The present invention has been made in view of such circumstances, and its purpose is to suppress thermal fatigue cracks such as heat check as well as wear during forging and prevent large cracks and chips of the mold. The present invention provides a hot forging die having excellent durability and a method for producing the same.

  The inventor has an oxidation resistance temperature of 1000 ° C. or higher, which is higher than TiN and CrN used for general wear-resistant coatings, and has high hardness, and thus has excellent wear resistance such as AlCrN films and TiAlN films. Research on nitride films was underway. In order to provide durability against thermal fatigue cracks such as heat check in addition to wear during forging, a multi-layered film in which the above-mentioned nitride films are alternately laminated is formed to provide a film with higher wear resistance. I thought that I might be given. Therefore, the present inventors have studied how to form a multilayer coating to be applied to a use of a hot forging die that is harsh in a use environment, particularly in a use temperature environment, as compared with a general tool use, and have reached the present invention.

Therefore, the hot forging die according to the present invention is a hot forging die in which a wear-resistant coating is provided on the mold design surface, and the wear-resistant coating is formed by (Al _x Cr _1-x ) N first layer (where 0 <x <1) and (Ti _y Al _1-y ) N second layer (where 0 <y <1) are alternately arranged The thickness of each of the adjacent first and second layers is at least 15 nm or less, and the total thickness of the multilayer coating is 1 μm or more and 20 μm or less. Features.

According to this invention, it is possible to provide a hot forging die having excellent durability, which can suppress thermal fatigue cracks as well as wear during forging and prevent large cracks and chipping of the die. Here, having a high hardness even in a wide temperature range such as 1000 ° C. or higher from 400 ° C. at the time of heat forging _{(Al x Cr 1-x)} N gives especially high abrasion resistance during forging. Moreover, even in an oxidizing atmosphere within the same temperature range, stable (Al _x Cr _1-x ) N and (Ti _y Al _1-y ) N can reduce surface irregularities due to oxidation, which can cause thermal fatigue cracks. Prevents large cracks and chipping of the mold due to thermal fatigue cracks. That is, after forming a multilayer coating by combining these (Al _x Cr _1-x ) N and (Ti _y Al _1-y ) N coatings, each layer has a size of not more than about a size capable of developing into a large crack, that is, 15 nm or less. By laminating, it is possible to reduce the occurrence of latent cracks of such a size and prevent large cracks and chips of the mold. Further, the total film thickness is set to a range that provides both wear durability and adhesion, that is, a total film thickness of 1 μm to 20 μm. As described above, it is possible to provide a hot forging die having excellent durability, which can suppress thermal fatigue cracks as well as wear during forging and prevent large cracks and chips of the die.

  In the above-described invention, a nitrogen diffusion layer may be included in the foundation of the wear-resistant film. According to this invention, the adhesiveness between the wear-resistant film and the base can be improved, and the residual compressive stress generated inside the wear-resistant film can be reduced. The generation of cracks on the surface can be prevented. That is, it is possible to provide a hot forging die having excellent durability. In the nitrogen diffusion layer, when a part of the compound layer of the element in the mold material and nitrogen is formed, it is preferable to remove the compound layer by polishing or the like.

A method for producing a hot forging die according to the present invention is a method for producing a hot forging die in which a wear-resistant film by an ion plating method is provided on a die design surface, wherein N is placed in a vacuum chamber. A step of forming a reactive gas atmosphere, and a first target material made of Al _x Cr _1-x (where 0 <x <1) and a second material made of Ti _y Al _{1-y in the} vacuum chamber. A target material (provided that 0 <y <1) are arranged to face each other, and a first atmosphere zone and a second atmosphere zone in which the constituent atoms of the target material are ionized are formed independently on the front part of each. And a deposition step of rotating the mold design surface so as to alternately pass through the first atmosphere zone and the second atmosphere zone at regular intervals. .

  According to this invention, as described above, along with wear during forging, thermal fatigue cracks can be suppressed and large cracks and chipping of the mold can be prevented, and a hot forging mold having excellent durability can be stably produced. It can be provided.

  Furthermore, the above-described invention may include a nitriding treatment step of providing a nitrogen diffusion layer on the mold design surface prior to application of the abrasion-resistant film by an ion plating method. According to this invention, the adhesiveness between the wear-resistant film and the base can be improved, and the residual compressive stress generated inside the wear-resistant film can be reduced. Generation of cracks on the surface can be prevented, and a hot forging die having excellent durability can be stably provided.

It is a perspective view of the test piece used for the verification test of this invention. It is a figure of the apparatus used with the manufacturing method by this invention. It is a figure of the apparatus used for the verification test of this invention. It is a side view of the test piece used for the verification test of this invention. It is a figure which shows the forge process in the verification test of this invention. It is a figure of the measurement part of the test piece used for the verification test of this invention. It is a figure which shows various conditions and test data of the verification test of this invention. It is a figure which shows the test data of the verification test of this invention. It is a graph of the test data of the verification test of this invention. It is a transmission electron micrograph of the typical structure | tissue in the verification test of this invention. It is a figure which shows the test data of the verification test of this invention.

  About the test in the test piece (Examples 1-7) which provided the film | membrane on the manufacturing conditions similar to the metal mold | die for hot forging as an Example by this invention, and the test piece (Comparative Examples 1-16) as a comparative example, This will be described with reference to FIGS.

As shown in FIG. 1, in both the example and the comparative example, the test piece 1 is made of a plate material having a thickness of 5 mm obtained by refining an SKD61 equivalent material defined in JIS standard to 48 HRC. An annular body provided with a 5 mm through hole 1a. A plurality of test pieces 1 are prepared. For the test piece 1 of Example 7 to be described later, NH ₃ gas is heated to 500 ° C. in a mixed atmosphere of 20 vol% NH ₃ gas and 80 vol% H ₂ gas, and 10 Plasma nitriding treatment was carried out for a time.

  Next, as shown in FIG. 2, the test piece 1 is placed and fixed on a rotating stage 10 in the reaction chamber 5 of the ion plating apparatus. On the other hand, here, the targets 11 and 12 are arranged along the wall surface of a reaction chamber (not shown) so as to face each other with the rotary stage 10 in between. Except for some test pieces, nitrogen gas was introduced into the reaction chamber so as to have a partial pressure of 1 to 5 Pa in order to generate nitride. A multi-arc PVD apparatus M500C-600 (product name) manufactured by Nissin Electric Co., Ltd. was used for the ion plating treatment of each test piece 1. The targets 11 and 12 for each test piece and various conditions for ion plating are summarized in FIG.

  Although details of the ion plating are omitted, when a vacuum arc discharge is generated to start the processing, the constituent atoms of the targets 11 and 12 are evaporated and ionized to form an atmosphere zone in front of each. When the rotary stage 10 is rotated (see R1 in FIG. 2), the test piece 1 passes through this atmosphere zone alternately. In the hot forging die as an example according to the present invention, the treated surface of the test piece 1 corresponds to the die design surface, and the die design surface passes through the atmosphere zone. Note that the processing surface of the test piece 1 may be further rotated with respect to the rotary stage 10 as indicated by R2 in FIG. The specimen 1 after the ion plating process is removed from the rotary stage 10 and taken out from the reaction chamber 5 of the ion plating apparatus.

  As shown in FIG. 3, the test piece 1 after the ion plating treatment is repeatedly transferred to a heating / cooling test apparatus (heat check test apparatus) 20. That is, the small diameter portion of the support portion 22 is inserted into the through hole 1 a of the test piece 1, and fixed between the test piece 1 and the holder 23 from above and below. In this state, the outer peripheral surface of the test piece 1 is rapidly heated to 700 ° C. by the high frequency coil 21. Subsequently, cooling water 24 is jetted from a water outlet (not shown) to rapidly cool to room temperature. This heating and cooling cycle is repeated 1000 times in total. The test piece 1 after repeated heating and cooling was removed from the test apparatus 20 and cut along a plane perpendicular to the central axis.

  One of the cut test pieces 1 was filled with resin, the cut surface was polished, and the cut surface was observed with an optical microscope (100 times). The number of cracks and the length of each crack were measured over the entire circumference, and this is shown in FIG. FIG. 9 shows the number of cracks observed in Examples 1 to 3 and Comparative Example 13. In addition, it is judged that heat check resistance is inferior, ie, a thermal fatigue characteristic is inferior, so that there are many long cracks.

Furthermore, the transmission electron microscope observation of the cross section which crossed the multilayer film in the test piece 1 was performed. In particular, FIG. 10 shows a transmission electron micrograph of a cross section across the multilayer film obtained under the conditions shown in Example 1 of FIG. Here, a multi-layered film with gray and white contrast is observed. From the result of elemental composition analysis, the gray-colored portion is (Al _x Cr _1-x ) N (0 <x <1, hereinafter “ (Al—Cr) -based nitride layer ”) and the portion that appears white is (Ti _y Al _1-y ) N (0 <y <1, hereinafter,“ (Ti—Al) -based nitride ” Called “layer”).

  Moreover, about the test piece separately ion-plated, the elemental composition analysis and hardness measurement were performed about the process coating. The elemental composition analysis was performed using a high frequency glow discharge spectroscopic analyzer (GD-OES) PROFILER 2 (product name) manufactured by Horiba, Ltd. The hardness was measured using Nano Indenter XP (product name) manufactured by MTS Systems Corporation at an indentation depth of 300 nm, and the measured value [GPa] was converted to HV hardness. These results are also shown in FIG.

  In FIG. 7, “composition”, “composition 1”, and “composition 2” all represent the composition of the target 11 or 12. Comparative Examples 1 to 6 are cases where only one target 11 is used, and a plurality of coatings having the same composition are formed. Hereinafter, such a film is referred to as a “single composition film”. On the other hand, Examples 1 to 7 and Comparative Examples 7 to 15 are cases where two types of targets 11 and 12 are used, and a plurality of layers of films having different compositions are formed. Hereinafter, such a film is referred to as a “different composition multilayer film”. Moreover, the comparative example 16 does not perform an ion plating process, and does not have a surface film with a to-be-processed material.

  By the way, in the ion plating process, it is predicted that one layer is formed each time the test piece 1 passes through the atmosphere zone in the reaction chamber 5 described above. Here, when the rotary stage 10 makes one round, it passes through the atmosphere zone formed by the two targets 11 and 12, so that two layers are formed. That is, the number of films constituting the multi-layer coating is expressed by [type of coating (here, two types derived from targets 11 and 12)] × [number of rotations per minute] × [ion plating processing time (minutes)]. Desired. This could be confirmed from a transmission electron microscope image as shown in FIG.

  Therefore, the thickness of one layer in FIG. 7 is obtained as follows. For example, the thickness of the whole different composition multilayer film can be measured by optical microscope observation and electron microscope observation of the cross section of the test piece 1 described above. For example, in the case of the test piece 1 of Example 1, it was about 4.4 μm (4400 nm, see FIG. 10). In the ion plating process, the rotary stage 10 rotates at 5 rpm and is processed for 70 minutes. Therefore, when the number of films of different composition multilayer coating is calculated as described above, 2 × 5 × 70 = 700 layers are obtained. That is, dividing the thickness of the different composition multilayer film by this yields 4400 ÷ 700 = 6.3 nm.

  On the other hand, when the thickness of a pair of gray and white layers constituting the film is measured from the transmission electron micrograph of FIG. 10, it is 12.4 nm. If the thicknesses of the gray and white layers are equal, [((Al—Cr) -based nitride layer thickness + (Ti—Al) -based nitride layer thickness) / 2] = 6.2 nm In this case, the value almost coincides with the value obtained from the thickness of the whole multilayer film with different composition and the conditions of the ion plating treatment. Therefore, the thickness of one layer in FIG. 7 is obtained from the thickness of the latter multi-component multilayer film as a whole and the conditions of the ion plating treatment (such as the number of rotations of the test piece 1).

  By the way, apart from the above, a punch wear test was performed using a punch test piece 30 as shown in FIG. The punch test piece 30 is made of a bar material tempered with JIS SKD61 to 50 HRC, and similarly to the above, the punch tip 30a is subjected to the same plasma nitriding treatment and ion plating treatment as shown in FIG. Created. In the punch wear test, the punch tip 30a of the punch test piece 30 was struck against the workpiece 32 made of S53C heated to 820 ° C., and after hot working for processing the hole 33 was repeated 5000 times, The wear amount α (see FIG. 6) was measured. Processing was performed using a horizontal high-speed forging machine at a forging speed of 85 spm and a lubricating oil amount of 3 L / min. In addition, as shown in FIG. 5, the workpiece 32a made of S53C is first forged, followed by a two-step process (forging) in which the punch test piece 30 is hit and the hole 33 is processed. did.

  As shown in FIG. 6, the punch test piece 30 after being processed 5000 times has a wear amount α (mm) at a position of 0.2 mm from the foremost end of the punch tip portion 30 a at 90 ° intervals along the circumferential direction. The point was measured. The wear amount α shown in FIG. 11 is an average value of four points.

  Next, measurement results of the manufacturing conditions, configuration and hardness of the coating shown in FIG. 7, measurement of the crack length related to the heat check resistance shown in FIG. 8, and measurement of the wear amount α related to the wear resistance shown in FIG. .

  In Comparative Examples 1, 2 and 6 in which a single composition film using only one type of target mainly composed of Ti-based or Cr-based nitride or carbonitride is formed, as shown in FIG. Compared to Examples 1 to 7, the wear amount α tends to be relatively large as shown in FIG.

  On the other hand, in Comparative Examples 3 to 5 in which a single composition film using only one type of target mainly composed of (Ti—Al) nitride or (Al—Cr) nitride is formed, FIG. As shown, the wear amount α can be significantly reduced compared to Comparative Examples 1, 2, and 6. In particular, the film of Comparative Example 3 has a very small number of cracks as compared to the films of Comparative Examples 3 and 4 as shown in FIG. That is, it provides extremely high heat check resistance. Thus, a single composition film using only one type of target mainly composed of (Ti—Al) -based nitrides has only one type of target mainly composed of (Al—Cr) -based nitrides. Compared to the single composition film used, the heat check resistance is superior. This is considered to be because cracks are less likely to occur because the former has higher oxidation resistance and higher toughness due to lower hardness than the latter. Moreover, the coating films of Comparative Examples 4 and 5 are higher in hardness than Comparative Example 3 as shown in FIG. 7, and give a smaller wear amount α as shown in FIG.

  By the way, although the multilayer coating by the ion plating method can provide high wear resistance because of the dense coating, on the other hand, cracks grow due to high residual compressive stress due to thermal fatigue, impact force during forging, etc. Easy to peel. In the single composition coatings as in Comparative Examples 1 to 6, the residual compressive stress is continuous in the coating and easily peels at once. Therefore, by selecting and combining two types from the above targets and forming a different composition multilayer film, the residual stress becomes discontinuous between layers and is difficult to peel off. Even if peeling occurs, one layer at a time However, it is considered that the amount of wear becomes smaller as a result of repeated peeling. Therefore, a different composition multilayer film was formed as follows.

  In Comparative Examples 7 and 8 in which different composition multilayer coatings were formed using two types of targets of Cr-based nitride and Ti-based nitride, the number of cracks was relatively large as shown in FIG. The length tends to be long. Further, as shown in FIG. 11, the wear amount α tends to be relatively large. That is, it is predicted that the films of Comparative Examples 7 and 8 are insufficient in both heat chuck resistance and wear resistance during forging.

  In Comparative Examples 9 to 11 where different composition multilayer films were formed using two types of targets of Cr-based nitride and (Ti-Al) -based nitride, as shown in FIG. There are many numbers and the length tends to be long. On the other hand, as shown in FIG. 11, the wear amount α tends to be relatively smaller than those of Comparative Examples 7 and 8, and is very small in Comparative Example 9.

  Further, in Comparative Example 12 in which the different composition multilayer film was formed using two types of targets of Cr-based nitride and (Al—Cr) -based nitride, as shown in FIG. There are many numbers and the length tends to be long. On the other hand, as shown in FIG. 11, the wear amount α is very small as in Comparative Example 9. That is, it is predicted that the coating films of Comparative Examples 9 to 12 have good wear resistance during forging, but are insufficient in heat chuck resistance.

  Therefore, in Examples 1 to 7 in which different composition multilayer films are formed using two types of targets of (Ti—Al) -based nitride and (Al—Cr) -based nitride, as shown in FIG. Further, it can be seen that the number of cracks is relatively small, and the wear amount α tends to be relatively small as shown in FIG.

  Specifically, in Examples 1 to 3 and Comparative Example 13, when the thickness is further changed, as shown in FIG. 9, the number of cracks abruptly increases around 15 nm. That is, if the thickness of each multilayer film is 15 nm or less, the heat check resistance is greatly improved. In a hard film such as (Ti—Al) -based nitride or (Al—Cr) -based nitride, each layer has a crack size of not more than about 15 nm, that is, 15 nm or less. The number of cracks of such a size can be reduced, and as a result, large cracks and chips of the mold can be prevented. Think.

  Furthermore, in Example 2 and Comparative Examples 14 and 15, when the total film thickness is changed, as shown in FIGS. 8 and 11, the number of cracks is greatly increased, even if it is too thin or too thick, centering around 10 μm. The amount of wear increases. This is because when the film is thin as in Comparative Example 14, the film is worn out immediately, and for example, the same film as in Comparative Example 16 is not applied. On the other hand, if the thickness is too thick, the residual compressive stress generated inside is high, and the probability of peeling of the film is increased. If the film is completely peeled off, the same results as in Comparative Example 16 are obtained. That is, the total film thickness is within a range that provides both wear durability and adhesion, that is, 1 μm or more and 20 μm, preferably 2 μm to less than 8 μm, thereby suppressing thermal fatigue cracks along with wear during forging. In addition, it is possible to provide a hot forging die that can prevent large cracks and chipping of the die and has excellent durability.

Further, as one example, an Al _0.7 Cr _0.3 layer was provided on a material to be treated (mold) in an Ar atmosphere using an Al _0.7 Cr _0.3 target, and then the test was performed. In Example 6 in which a different composition multilayer coating similar to Example 3 was provided, that is, an Al _0.7 Cr _0.3 layer was provided between the different composition multilayer coating and the material to be treated, as shown in FIG. In particular, there is a tendency to reduce long cracks.

  Further, in Example 7 in which the nitriding treatment for providing the nitrogen diffusion layer on the material to be treated of the different composition multilayer coating was performed, as shown in FIG. . This is a film / underlying interface against thermal fatigue due to repeated heating and cooling by forming an inclined part with increased hardness and reduced thermal expansion coefficient from the inside to the surface of the non-nitrided material. This is because cracks can be prevented from occurring. That is, the adhesion between the film and the base can be improved. In addition, it is possible to reduce the compressive residual stress generated inside the coating rather than to form a coating on the unnitrided base material to be processed, and to suppress the occurrence and development of cracks.

  As described above, by applying the different composition multilayer coatings according to Examples 1 to 7 described above to the mold design surface of the hot forging die, particularly, high wear resistance and oxidation resistance are provided, and heat check resistance, etc. A mold having excellent thermal fatigue characteristics can be provided. In other words, in a general specification application in a hot forging die, even a thin film can provide sufficient durability.

From the above, the hot forging die in which the wear-resistant coating is provided on the die design surface in the present example is the first layer (Al _x Cr _1-x ) N formed by ion plating ( A multilayer film in which 0 <x <1) and a second layer (0 <y <1) made of (Ti _y Al _1-y ) N are alternately laminated is given, and the adjacent first layer and the second layer The thickness of each of the two layers is at least 15 nm or less, and the total thickness of the multilayer coating is 1 μm or more and 20 μm or less. Thereby, it is possible to provide a hot forging die having excellent durability that can suppress thermal fatigue cracks as well as wear during forging and prevent large cracks and chips of the die.

  In addition, as one example, by providing a nitrogen diffusion layer on the base of the wear-resistant coating, the adhesion between the wear-resistant coating and the base is improved, and the residual compressive stress generated inside the wear-resistant coating is reduced. This can reduce the occurrence of cracks and peeling of the film during forging, and the generation of cracks on the film and its surface. That is, it is possible to provide a hot forging die having excellent durability.

On the other hand, the method for producing a hot forging die in which a wear-resistant film by an ion plating method is provided on the die design surface in the present embodiment includes a step of forming a reactive gas atmosphere of N in a vacuum chamber, In the vacuum chamber, a first target material (0 <x <1) made of Al _x Cr _1-x and a second target material (0 <y <1) made of Ti _y Al _1-y are opposed to each other. And independently forming a first atmosphere zone and a second atmosphere zone in which constituent atoms of the target material are ionized at respective front portions, and the first atmosphere zone and the second atmosphere zone. A deposition step of rotating the mold design surface so as to alternately pass through the atmosphere zone at regular intervals. As a result, in a wide temperature range from 400 ° C to 1000 ° C during hot forging, it is possible to suppress thermal fatigue cracks as well as wear during forging and prevent large cracks and chipping of the mold, and it has excellent durability. Forging dies can be provided stably.

  Furthermore, as one embodiment, a nitriding treatment step of providing a nitrogen diffusion layer on the mold design surface prior to the application of the wear resistant film by the ion plating method is included. According to this, it is possible to improve the adhesion between the wear-resistant film and the base, and to reduce the residual compressive stress generated inside the wear-resistant film, and to prevent cracking and peeling of the film during forging, and the film and its Generation of cracks on the surface can be prevented, and a hot forging die having excellent durability can be stably provided.

  Up to this point, the representative embodiments according to the present invention and the modifications based thereon have been described, but the present invention is not necessarily limited thereto. Those skilled in the art will recognize a variety of alternative embodiments and modifications without departing from the scope of the appended claims.

1 Test piece 10 Rotating stage 11, 12 Target 20 Repeated heating / cooling test device (heat check test device)
30 punch specimen

Claims (4)

A mold for hot forging with a wear-resistant coating on the mold design surface,
The wear-resistant film is formed by a first layer made of (Al _x Cr _1-x ) N (where 0 <x <1) and (Ti _y Al _1-y ) N by an ion plating method. Two layers (where 0 <y <1) are alternately laminated, and the thickness of each of the adjacent first and second layers is at least 15 nm or less, and the multilayer The hot forging die, wherein the total thickness of the coating is 1 μm or more and 20 μm or less.   The hot forging die according to claim 1, further comprising a nitrogen diffusion layer as a base of the wear-resistant film. A method for producing a mold for hot forging in which a wear-resistant film by an ion plating method is provided on a mold design surface,
Forming a reactive gas atmosphere of N in the vacuum chamber;
In the vacuum chamber, a first target material made of Al _x Cr _1-x (where 0 <x <1) and a second target material made of Ti _y Al _1-y (where 0 <y <1 And the first atmosphere zone and the second atmosphere zone in which the constituent atoms of the target material are ionized are formed independently on the front portions, respectively,
A hot forging mold characterized by including a deposition step of rotating the mold design surface so as to alternately pass through the first atmosphere zone and the second atmosphere zone at regular intervals. Manufacturing method.   The method for producing a hot forging die according to claim 3, further comprising a nitriding treatment step of providing a nitrogen diffusion layer on the die design surface prior to application of the wear-resistant film by an ion plating method. .