JP6855864B2 - Titanium plate press die and titanium plate press molding method - Google Patents

Description

The present invention relates to a press die for a titanium plate and a press molding method for a titanium plate.

Titanium is used in seawater heat exchangers because it has excellent corrosion resistance and is not particularly corroded by seawater. Among them, plate materials are often used in plate heat exchangers. This type of plate heat exchanger is constructed by stacking a plurality of wavy plates. In order to improve the heat transfer efficiency, press molding is performed to make the surface of the plate uneven. In recent years, in order to further improve the heat transfer efficiency, due to needs such as thinning of the plate thickness and complication of the surface uneven shape, the moldability is more excellent from the viewpoint of preventing local constriction or cracking during the press molding. Is now required. In addition, titanium has the property of easily adhering to other metals, and there is a risk of seizure marks on the titanium plate during press molding, thus preventing adhesion to the mold. There is also a need. Further, it is also desired to suppress the wear of the mold and improve the life of the mold.

In order to prevent press cracking and adhesion of the titanium plate and further prevent wear of the mold, it is necessary to reduce the friction coefficient between the titanium plate and the mold. As a means for reducing the coefficient of friction, for example, it is conceivable to improve the lubricity of the surface of the titanium plate. Regarding this point, for example, the method described in Patent Document 1 (Japanese Unexamined Patent Publication No. 63-174949) is known. This method requires a large number of steps such as forming an iron-zinc alloy layer of the lubricant carrier and then treating with zinc phosphate to apply the lubricant, resulting in low productivity.
Further, there is also a method in which an organic lubricating film typified by Millbond is formed on the surface of the titanium plate, and then press molding is performed in a state where the lubricating oil is further applied. However, in this method, it is necessary to apply and dry the Millbond solution to form a lubricating film, which requires a large number of steps and low productivity. Further, in an organic lubricating film such as Millbond, the peeled press debris may cause a pressing defect after press working, which may impair the appearance quality of the molded product after processing.

Further, when forming a titanium plate into a shape suitable for a plate heat exchanger, a plane strain state may be included as a deformed state of the titanium plate. The plane strain state is a deformation state in which distortion is caused only in one of the X-axis direction and the Y-axis direction, and the amount of distortion of the other orthogonal to one direction is 0. In general, molding including a plane strain state is molding in a severe state for the material, and press cracking is likely to occur. Therefore, it is more desired to reduce the coefficient of friction between the titanium plate and the mold.

Japanese Unexamined Patent Publication No. 63-174949

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a press die for a titanium plate, which does not generate press cracks or seizure marks and has less wear. In addition, press cracking and seizure marks do not occur, shape defects of the molded product due to die wear are unlikely to occur, the appearance quality after processing is excellent, and press molding of a titanium plate with excellent productivity is also possible. The challenge is to provide a method.

As a result of studying a die for press molding of a titanium plate having a surface having a surface having excellent wear resistance and adhesion resistance and a low surface friction coefficient, the present inventors have conducted an alloy usually used as a material for the die. A tool steel is used as a base material, a CrN film is formed on the base material, a diamond-like carbon film is formed on the base material, and a Cr film and an intermediate film are arranged between the CrN film and the diamond-like carbon film. It was found that by doing so, it is possible to improve the wear resistance, the adhesion resistance and the low friction resistance of the surface, improve the moldability of the titanium plate, and improve the life of the mold.
The gist of the present invention is as follows.

[1] A press die used for press molding of a titanium plate.
A base material and a surface treatment film formed on the surface of the base material are provided.
The base material is by mass%
C: 1.00 to 2.30%,
Si: 0.10 to 0.60%,
Mn: 0.25 to 0.80%,
P: 0.030% or less,
S: 0.030% or less,
Cr: Containing 4.80 to 13.00%,
The balance is made of steel with a composition of iron and impurities.
The surface treatment film includes a CrN film formed on the substrate, a Cr film formed on the CrN film, an intermediate film formed on the Cr film, and diamond formed on the intermediate film. It consists of a like carbon film,
The thickness of the CrN film is 0.5 μm to 5 μm (excluding 5 μm).
The interlayer film contains Cr and carbon, and when the total of Cr and carbon is 100% by mass, the Cr concentration at the interface on the Cr film side is 80% by mass or more, and C at the interface on the diamond-like carbon film side. The film has a concentration of 80% by mass or more, and the Cr concentration gradually decreases along the film thickness direction from the Cr film side toward the diamond-like carbon film side.
In the diamond-like carbon film, the ratio I ₁₃₈₀ / I ₁₅₄₀ of the absorption intensity I ₁₃₈₀ at a wave number of ^{1380 cm-1 and} the absorption intensity I ₁₅₄₀ ^{at a wave number of 1540 cm-1} measured by Raman spectroscopy is the film thickness from the film surface. For pressing titanium plates, 0.5 to 0.7 in the 20% depth range and 0.3 to 0.5 in the 20% depth range from the interface between the diamond-like carbon film and the intermediate film. Mold.
[2] In the diamond-like carbon film, the Vickers hardness in the range of 20% depth from the film surface is 3000 to 3500, and the range of 20% depth from the interface between the diamond-like carbon film and the intermediate film. The Vickers hardness of the titanium plate according to [1], which has a Vickers hardness of 2500 to 3000.
[3] The titanium plate press die according to [1] or [2], wherein the diamond-like carbon film has a thickness of 0.5 μm to 2 μm.
[4] The titanium plate press die according to any one of [1] to [3], wherein the CrN film has a Vickers hardness of 800 to 2000.
[ 5 ] The titanium plate press die according to any one of [1] to [4 ], wherein the Cr film has a thickness of 5 nm to 100 nm.
[ 6 ] The titanium plate press die according to any one of [1] to [5 ], wherein the interlayer film has a thickness of 30 nm to 1000 nm.
[ 7 ] The press die for a titanium plate according to any one of [1] to [6 ], wherein a nitride layer is formed on the surface of the base material and the CrN film is formed on the nitride layer. Type.
[ 8 ] The titanium plate press die according to [7 ], wherein the nitrided layer has a thickness of 0.5 μm to 5 μm.
[ 9 ] The titanium plate press die according to [7 ] or [ 8 ], wherein the average nitrogen concentration of the nitrided layer is 0.10 to 0.50% by mass.
[ 10 ] The press of a titanium plate according to any one of [7 ] to [ 9 ], wherein the nitrogen concentration distribution in the nitrided layer has a concentration gradient that decreases from the surface layer of the nitrided layer in the depth direction. Mold.
[ 11 ] The titanium plate press die according to any one of [7 ] to [ 10 ], wherein the Vickers hardness of the nitrided layer is 800 to 1200.
[ 12 ] The base material is further increased in mass%.
Mo: 0.70 to 1.20%,
V: 0.15-1.00%,
W: 0.60 to 0.80%,
The titanium plate press die according to any one of [1] to [ 11], which comprises.
[ 13 ] The titanium plate press die according to any one of [1] to [12 ], wherein the base material is a punch and a die.
[ 14 ] A method for press-molding a titanium plate, wherein the titanium plate is press-molded using the titanium plate press die according to any one of [1] to [13].
[15] When press-molding the titanium plate, including the plane strain state as deformation of the titanium plate, [14] the press molding method of the titanium plate according to.

According to the present invention, it is possible to provide a press die for a titanium plate, which does not generate press cracks or seizure marks and has less wear. Further, according to the present invention, press cracks and seizure marks do not occur, shape defects of the molded product due to wear of the mold are unlikely to occur, appearance quality after processing is excellent, and productivity is also excellent. It is possible to provide a press forming method for a titanium plate.

FIG. 1 is a schematic side view showing a main part of a plate heat exchanger according to an embodiment of the present invention. FIG. 2 is an exploded perspective view showing a main part of the plate heat exchanger according to the embodiment of the present invention. FIG. 3 is a process diagram illustrating a press molding method for a titanium plate according to an embodiment of the present invention. FIG. 4 is a diagram illustrating a method of press molding a titanium plate according to an embodiment of the present invention, and is a schematic view showing a titanium plate before molding. FIG. 5 is a diagram illustrating a method of press-molding a titanium plate according to an embodiment of the present invention, and is a schematic view showing a titanium plate after molding. FIG. 6 is a graph showing the relationship between the stroke amount of the punch during press molding and the thickness of the titanium plate. FIG. 7 is a graph showing the results of component analysis in the punch of the press die of Example 1. FIG. 8 is a graph showing the results of component analysis in the punch of the press die of Example 1. FIG. 9 is a graph showing the results of component analysis in the punch of the press die of Example 1. 10 (a) is a photomicrograph of the surface layer of the punch of Example 1, and FIGS. 10 (b) and 10 (c) are Raman spectra of the surface layer of the punch of Example 1. FIG. 11 (a) is a photomicrograph of the surface layer of the punch of Comparative Example 1, and FIGS. 11 (b) and 11 (c) are Raman spectra of the surface layer of the punch of Comparative Example 1. FIG. 12 is a schematic cross-sectional view showing a press die of Example 1 and Comparative Example 1.

Hereinafter, a press die for a titanium plate and a press molding method for the titanium plate according to the embodiment of the present invention will be described.
In addition, since this embodiment is described in detail in order to better understand the purpose of the press die for the titanium plate and the press molding method of the titanium plate of the present invention, the present invention will be described unless otherwise specified. It is not limited.

FIG. 1 shows a main part of the plate heat exchanger according to the present embodiment, and FIG. 2 shows an exploded perspective view of the main part of the plate heat exchanger.
As shown in FIGS. 1 and 2, the plate heat exchanger is configured by stacking wavy plates in the plate thickness direction. By stacking the wavy plates, a flow path through which the fluid flows is formed between the plates. By flowing a high-temperature fluid and a low-temperature fluid through each flow path, heat exchange is performed between the respective fluids via the plate. The plate is made of a titanium plate.

More specifically, as shown in FIG. 1, the plate heat exchanger is configured by stacking plates 1A to 1E made of titanium plates at predetermined intervals. Each of the plates 1A to 1E is a corrugated plate in which a flat original plate (titanium plate) is formed in a wavy shape, and may be a corrugated plate having a constant wavelength and amplitude, or corrugated plates having different wavelengths and amplitudes. May be good. In the example shown in FIG. 1, the wavelength and amplitude are the same between the plates 1A to 1E. Further, the plates 1A to 1E are fastened with fastening bolts (not shown) in a stacked state. Further, a gasket (not shown) for preventing the outflow of fluid is provided on the outer peripheral portion of each of the plates 1A to 1E.

With the above configuration, the flow path 2A is formed between the plates 1A and 1B, the flow path 2B is formed between the plates 1B and 1C, and the flow path 2C is formed between the plates 1C and 1D. A flow path 2D is formed between the plates 1D and 1E. As shown in FIG. 1, the flow directions of the fluids in the respective flow paths 2A to 2D are opposite to each other between the adjacent flow paths. Then, for example, a low-temperature fluid (for example, seawater) is circulated in the flow paths 2A and 2C, and a high-temperature fluid (for example, hot water or steam) is circulated in the flow paths 2B and 2D, so that the plates 1A to 1E are respectively. Heat exchange is performed between the hot fluid and the cold fluid via.

Each plate 1A to 1E is manufactured by press-molding a titanium plate. The titanium plate in this embodiment is not particularly limited, and may be either a pure titanium plate or a titanium alloy plate. For example, the following pure titanium plate or titanium alloy plate can be used. However, the titanium plates listed below are merely examples, and pure titanium plates or titanium alloy plates other than those listed below may be used.

As the pure titanium plate, for example, an industrial pure titanium plate can be used. Pure industrial titanium includes 1 to 4 types of JIS standard, and corresponding Grades 1 to 4 of ASTM standard, and pure titanium for industrial use specified by DIN standard 3.7025, 3.7035, 3.7055. It shall be. That is, the industrial pure titanium targeted in the present invention has a mass% of C: 0.1% or less, H: 0.015% or less, O: 0.4% or less, N: 0.07% or less, Fe: 0.5% or less, consisting of the balance Ti.

As the titanium alloy plate, an α-type titanium alloy, an α + β-type titanium alloy, and a β-type titanium alloy can be used.
Examples of the α-type titanium alloy include highly corrosion-resistant alloys (ASTM Grade 7, 11, 16, 26, 13, 30, 33, or titanium materials containing a small amount of JIS species corresponding to these and various elements), Ti-. 0.5Cu, Ti-1.0Cu, Ti-1.0Cu-0.5Nb, Ti-1.0Cu-1.0Sn-0.3Si-0.25Nb, Ti-0.5Al-0.45Si, Ti- 0.9Al-0.35Si, Ti-3Al-2.5V, Ti-5Al-2.5Sn, Ti-6Al-2Sn-4Zr-2Mo, Ti-6Al-2.75Sn-4Zr-0.4Mo-0. There are 45Si and the like.

Examples of the α + β type titanium alloy include Ti-6Al-4V, Ti-6Al-6V-2Sn, Ti-6Al-7V, Ti-3Al-5V, Ti-5Al-2Sn-2Zr-4Mo-4Cr, Ti-6Al. -2Sn-4Zr-6Mo, Ti-1Fe-0.35O, Ti-1.5Fe-0.5O, Ti-5Al-1Fe, Ti-5Al-1Fe-0.3Si, Ti-5Al-2Fe, Ti-5Al There are -2Fe-0.3Si, Ti-5Al-2Fe-3Mo, Ti-4.5Al-2Fe-2V-3Mo and the like.

Further, examples of the β-type titanium alloy include, for example, Ti-11.5Mo-6Zr-4.5Sn, Ti-8V-3Al-6Cr-4Mo-4Zr, Ti-10V-2Fe-3Mo, Ti-13V-11Cr-3Al. , Ti-15V-3Al-3Cr-3Sn, Ti-6.8Mo-4.5Fe-1.5Al, Ti-20V-4Al-1Sn, Ti-22V-4Al and the like.

Next, an example of the method for molding the titanium plate of the present embodiment will be described. The following examples describe examples of manufacturing the plates 1A to 1E of the plate heat exchangers shown in FIGS. 1 and 2, but the present invention is not limited to this, and the present invention is not limited to this. Widely applicable.

FIG. 3A shows a titanium plate and a press die before molding, and FIG. 3B shows a titanium plate and a press die after molding. First, as shown in FIG. 3A, a titanium plate 11a and a press die 21 are prepared. The press die 21 includes a punch 22 and a die 23. The punch 22 includes a punch plate 22a and a plurality of protrusions 22b attached to the lower surface of the punch plate 22a at equal intervals. Further, the die 23 includes a die plate 23a and a plurality of protrusions 23b attached to the upper surface of the die plate 23a at equal intervals. Then, when the punch 22 descends to the bottom dead center, the tip of the protrusion 23b of the die 23 penetrates between the protrusions 22b of the punch 22, and the protrusion of the punch 22 between the protrusions 23b of the die 23. The protrusions 22b and 23b are positioned so that the tip of the portion 22b penetrates. The protrusions 22b and 23b are the base materials in the present invention and are made of a steel material having a predetermined component, and a surface treatment film is formed on the surfaces of the protrusions 22b and 23b (base material). The surface treatment film is composed of a CrN film, a Cr film, an intermediate film, and a laminated film of a diamond-like carbon film. The base material and the surface-treated film will be described later, but by forming the surface-treated film on the protrusions 22b and 23b (base material), the friction coefficient with respect to the titanium plate 11a becomes small, and the titanium plate 11a during press molding Lubricity is improved.

As shown in FIG. 3A, the titanium plate 11a before molding is arranged between the punch 22 and the die 23. Both ends of the titanium plate 11a in the plate length direction (left-right direction in the drawing) are restrained by wrinkle presses (not shown). Further, the titanium plate 11a may or may not be constrained in the plate width direction.

Next, as shown in FIG. 3B, the punch 22 is lowered toward the die 23, and the tip of the protrusion 22b of the punch 22 is inserted between the protrusions 23b of the die 23. The titanium plate 11a is located on the protrusions 23a of the die 23 with both ends in the left-right direction constrained in the drawing, and the protrusions 22b and 23b come into contact with the titanium plate 11a as the punch 22 descends. Further, by pushing the protrusions 22b and 23b into the titanium plate 11a, bending deformation is performed at a plurality of positions of the titanium plate 11a, and finally a wavy titanium plate 11b is obtained.

At the time of molding, it is preferable to use an emulsion-based or soluble oil-based lubricant used for ordinary press molding of titanium plates. It is preferable to use a lubricant because the friction between the titanium plate 11a and the press die 21 is further reduced. From the viewpoint of lubrication performance and ease of removing the lubricant adhering to the product, a soluble oil-based lubricant, which is a water-soluble cutting fluid, is most suitable.

FIG. 4 shows the titanium plate 11a before molding, and FIG. 5 shows the titanium plate 11b after molding. In FIGS. 4 and 5, the titanium plates 11a and 11b are shown in a plan view and a side view. As shown in FIGS. 4 and 5, the plate width w2 of the titanium plate 11b after molding is substantially unchanged from the plate width w1 before molding. On the other hand, since the titanium plate 11a is bent and deformed at a plurality of locations while both ends in the plate length direction are restrained, the length L2 along the surface of the titanium plate 11b in the longitudinal direction after molding is the titanium plate before molding. With respect to the length L1 along the surface in the longitudinal direction of 11a, the length is extended by the amount of wavy deformation. In addition, the plate thickness is partially reduced because both ends are stretched while being restrained. That is, when the titanium plate 11b after molding is formed into a wavy shape, it is deformed and distorted along the plate length direction, but is not deformed in the plate width direction orthogonal to the plate length direction and the amount of distortion is large. It is 0, which is a so-called plane distortion state.

Next, the base material and the surface treatment film applied to the press die 21 according to the present embodiment will be described. The base material is mass%, C: 1.00 to 2.30%, Si: 0.10 to 0.60%, Mn: 0.25 to 0.80%, P: 0.030% or less, S. It is made of a steel material containing 0.030% or less, Cr: 4.80 to 13.00%, and having a steel composition in which the balance is composed of iron and impurities. A surface treatment film is provided on the surfaces of the protrusions 22b and 23b made of this base material. The surface treatment film includes a CrN film formed on the surface of the base material, a Cr film formed on the CrN film, an intermediate film formed on the Cr film, and a diamond-like carbon film formed on the intermediate film. Are stacked in this order. A nitride film may be formed on the surface of the base material, and a surface treatment film may be formed on the nitride film. In the diamond-like carbon film, the ratio I ₁₃₈₀ / I ₁₅₄₀ of the absorption intensity I ₁₃₈₀ at a wave number of ^{1380 cm-1 and} the absorption intensity I ₁₅₄₀ ^{at a wave number of 1540 cm-1} measured by Raman spectroscopy is the film thickness from the film surface. In the range of 20% depth, it becomes 0.5 to 0.7, and in the range of 20% depth from the interface between the diamond-like carbon film and the intermediate film, the ratio I ₁₃₈₀ / I ₁₅₄₀ becomes 0.3 to 0.5. ing.

[Structure of base material]
First, regarding the component composition of the base material of the present embodiment, the reasons for limiting each element will be described in detail. In the following description, unless otherwise specified, "%" represents mass%. In addition, the balance of the basic components and selected elements shown below consists of iron and unavoidable impurities.

(C: carbon) 1.00 to 2.30%
C is an element necessary for forming carbides and ensuring the hardness of the base material. Further, since it forms a hard carbide by combining with Cr, Mo, V and the like, it is important as an element that enhances quenching and tempering hardness and constitutes wear resistance. Therefore, in this embodiment, C is contained in an amount of 1.00% or more. From the viewpoint of ensuring hardness, it is preferable to contain 1.4% or more.
On the other hand, when the C content exceeds 2.30%, the toughness is significantly deteriorated. Therefore, in the present embodiment, the C content is limited to 2.30% or less. From the viewpoint of ensuring toughness, the upper limit of the C content is preferably 2.20%, more preferably 2.00% or less.

(Si: Silicon) 0.10 to 0.60%
Si is contained as an antacid. Further, Si is contained because it has an effect of increasing softening resistance during high-temperature tempering. From these viewpoints, Si is contained in an amount of 0.10% or more. On the other hand, if the Si content exceeds 0.60%, the hot workability and toughness may be lowered, and non-metal inclusions may be increased. Therefore, the Si content is set to 0.60% or less. From the viewpoint of ensuring the toughness of the base material, the upper limit of the Si content is preferably 0.50%.

(Mn: manganese) 0.25 to 0.80%
Mn is an element having a deoxidizing effect like Si, and is an element that improves hardenability and at the same time increases retained austenite. From this point of view, Mn is contained in an amount of 0.20% or more. From the viewpoint of ensuring the hardness of the base material, it is preferable to contain 0.30 or more. In consideration of the balance with toughness, the upper limit of the amount of Mn is set to 0.8% in this embodiment. Preferably, it is 0.6% or less.

(P: Phosphorus) 0.030% or less (S: Sulfur) 0.030% or less Both P and S are impurity elements that are preferably not present in steel. Therefore, the content of both P and S is limited to 0.030% or less. More preferably, it is limited to 0.020% or less.

(Cr: Chromium) 4.80 to 13.00%
Cr is a demanding element that improves the wear resistance of the base material by binding with C and forming carbides. Further, in the present embodiment, since the CrN film (hard film) is formed on the base material of the press die 21, it is very important for ensuring the adhesion with the CrN film. From these viewpoints, the amount of Cr is 4.80% or more, preferably 8.00% or more, and more preferably 11.00% or more.
On the other hand, if Cr is added excessively, the toughness may deteriorate due to the formation of coarse carbides, so the upper limit of the amount of Cr is set to 13.000%. It is preferably 12.50% or less.

In the present embodiment, Mo: 0.70 to 1.20% and V: 0.15 to 1.00% may be further contained in the above component composition.

(Mo: molybdenum) 0.70 to 1.20%
Mo has the effect of improving the temper softening resistance and imparting wear resistance to the base material by forming carbides. From these viewpoints, Mo is preferably contained in an amount of 0.70% or more, more preferably 0.80% or more.
On the other hand, if Mo is added excessively, the toughness of the base material may be deteriorated. From this, it is preferable that Mo is contained in an amount of 1.20% or less, and more preferably 1.10% or less.

(V: vanadium) 0.15-1.00%
V is effective for improving the hardenability of the base material, suppressing tempering and softening, and further refining the carbide. Therefore, V is preferably contained in an amount of 0.15% or more, more preferably 0.20% or more.
On the other hand, if V is added in excess, cold workability may be impaired. Therefore, V is preferably contained in an amount of 1.00% or less, more preferably 0.50% or less.

Further, in the present embodiment, W: 0.60 to 0.80% may be further contained in the above component composition.

(W: Tungsten) 0.60 to 0.80%
Like V, W is effective in improving the hardenability of the base material, suppressing tempering and softening, and further miniaturizing carbides. Therefore, it is preferable that W is contained in an amount of 0.6% or more. On the other hand, if W is added in excess, cold workability may be impaired. Therefore, it is preferable that W is contained in an amount of 0.80% or less.

In the present embodiment, the balance other than the above-mentioned elements is substantially composed of Fe, and a small amount of elements such as impurities that do not impair the action and effect of the present invention can be added.

In the press die of the present embodiment, a material having the above-mentioned component composition is used as the material of the base material, but among them, from the viewpoint of being cheaper and ensuring a good balance between wear resistance and adhesion resistance. , JIS G 4404, SKD1, SKD2, SKD10, SKD11 or SKD12 (all within the above component composition range) are preferably used, and among these, SKD11 is more preferable.

[CrN film]
The hardness of the base material having the above-mentioned component composition is about 500 to 600 in Vickers hardness. That is, when the titanium plate is press-molded with the base material as it is without forming a film or the like on the base material, the hardness of the base material itself can be secured, so that the wear resistance is relatively good. However, with regard to adhesion resistance, the material of the titanium plate may be seized on the base material, which may cause a large number of defects in the press die.

Therefore, in the present embodiment, it has been found that it is important to form a CrN film on the surface of the base material. By forming the CrN film on the surface of the base material, the adhesion between the press die 21 and the titanium plate 11a can be ensured, and the adhesion resistance can be improved.

The thickness of the CrN film is not particularly limited, but can be 0.5 μm to 5 μm. If the CrN film is made too thin, unevenness may occur during film formation, resulting in insufficient adhesion resistance. Further, if the CrN film is made excessively thick, the hardness is improved, but cracks are likely to occur in the film, which may make the film brittle, and the manufacturing cost is high from an economical point of view, which is not preferable. From these facts, the thickness of the CrN film is preferably 0.5 μm to 5 μm.

The method for forming the CrN film is not particularly limited, but it is preferable to use the PVD method (physical vapor deposition method) because the adhesion to the substrate can be ensured and the hardness of the formed film can be improved. Although the CrN film according to the present embodiment can be formed by another vapor deposition method (for example, a CVD method), the CrN film may have insufficient hardness or the CrN film may be excessively thick. It is preferable to use the PVD method as the film forming method.

The Vickers hardness of the CrN film is preferably in the range of 800 to 2000. The hardness of the CrN film is preferably high from the viewpoint of improving the wear resistance of the press die 21. Therefore, in the present embodiment, the Vickers hardness of the CrN film is preferably 800 or more, and more preferably 1500 or more. On the other hand, since an excessive increase in the hardness of the CrN film may cause cracks, the Vickers hardness of the CrN film is preferably 2000 or less.

The CrN film may have a single-layer structure or a multi-layer structure in which two or more layers are laminated. However, as described above, if the film thickness of the CrN film becomes too thick, cracks may occur, and the multi-layer structure causes a decrease in productivity and an increase in manufacturing cost. Therefore, the CrN film is used. It is preferable to have a single layer structure.

[Cr film and interlayer film]
In the present embodiment, it is preferable to arrange the Cr film and the intermediate film between the CrN film and the diamond-like carbon film. Although the diamond-like carbon film has relatively high adhesion to the CrN film, when the titanium plate is repeatedly press-molded using the press die of the present embodiment, the diamond-like carbon film is repeatedly impacted, which causes the diamond-like carbon film to be repeatedly impacted. , The diamond-like carbon film may peel off from the CrN film. Therefore, by forming a Cr film on the CrN film, forming an intermediate film on the Cr film, and further forming a diamond-like carbon film on the Cr film, the diamond-like carbon film can be peeled off even when repeatedly impacted. Suppress. Further, by providing the interlayer film, it is possible to have an inclined structure from Cr to C alone, and the durability can be improved.

The thickness of the Cr film is preferably in the range of 5 nm to 100 nm, more preferably in the range of 10 nm to 100 nm, further preferably in the range of 10 nm to 70 nm, and particularly preferably in the range of 10 nm to 40 nm. If the thickness of the Cr film is too thin, it becomes impossible to suppress the peeling of the diamond-like carbon film. Further, if the thickness of the Cr film is too thick, seizure will occur when the DLC film is peeled off, which is not preferable. The interface between the CrN film and the Cr film can be easily identified by measuring the Cr concentration distribution in the thickness direction. Since the Cr concentration in the CrN film is about 81% by mass and the Cr concentration in the Cr film is 100%, the Cr concentration in the thickness direction may be analyzed and the position where the Cr concentration suddenly changes may be set as the interface. Since the Cr concentrations are close to each other, the Cr film exhibits high adhesion to the CrN film. As a Cr analysis method, a thin film sample having a thickness capable of transmitting electron beams is prepared, and analysis is performed by scanning transmission electron microscope observation (STEM: SCANNING TRANSMISSION ELECTRON MICROSCOPY) and characteristic X-ray analysis.

The intermediate film contains Cr and carbon, and when the total of Cr and carbon is 100%, the Cr concentration gradually decreases along the film thickness direction from the Cr film side to the diamond-like carbon film side. In this intermediate film, for example, the amount of Cr at the interface with the Cr film is 80 to 100% by mass, and the amount of Cr at the interface with the diamond-like carbon film is less than 0 to 20% by mass. In other words, this interlayer film has a C content of less than 0 to 20% by mass at the interface with the Cr film and an C content of 80 to 100% by mass at the interface with the diamond-like carbon film. In the interlayer film, the Cr concentration and the C concentration gradually change along the thickness direction. The rate of change of the Cr concentration and the C concentration in the thickness direction may change continuously in a linear shape, continuously in a curved line, or discontinuously in a stepped manner. May be good.

Since the amount of Cr at the interface with the Cr film is 80 to 100% by mass, the intermediate film has a high affinity with the Cr film composed of 100% Cr, and the intermediate film has high adhesion to the Cr film. Shown. Further, since the amount of Cr at the interface with the diamond-like carbon film is less than 0 to 20% by mass and the amount of C is 80 to 100% by mass, the intermediate film is a diamond-like carbon film made of 100% C. The interlayer film shows high adhesion to the diamond-like carbon film. As described above, the interlayer film is interposed between the Cr film and the diamond-like carbon film to enhance the adhesion of these films.

The thickness of the interlayer film is preferably in the range of 30 nm to 1000 nm, more preferably in the range of 30 nm to 500 nm, further preferably in the range of 50 nm to 250 nm, and particularly preferably in the range of 60 nm to 180 nm. If the thickness of the interlayer film is too thin, the Cr concentration and the C concentration change rapidly along the thickness direction, and there is a possibility that the adhesion between the Cr film and the diamond-like carbon film cannot be ensured. Further, if the thickness of the interlayer film is too thick, the film becomes brittle and the durability is lowered, which is not preferable.

The interface between the intermediate film and the Cr film can be easily identified by measuring the Cr concentration distribution in the thickness direction. Here, the Cr concentration of the Cr film is approximately 100% by mass, and in the intermediate film, the Cr concentration decreases toward the diamond-like carbon film side. Therefore, the Cr concentration in the thickness direction is measured and the Cr concentration begins to decrease. The position may be the interface.
Further, the interface between the interlayer film and the diamond-like carbon film can also be easily identified by measuring the Cr concentration distribution in the thickness direction. In the intermediate film, the Cr concentration decreases toward the diamond-like carbon film side, and in the diamond-like carbon film, the Cr concentration becomes 0% by mass. Therefore, the Cr concentration in the thickness direction is analyzed and the Cr concentration becomes 0%. The position may be the interface. As in the case of the Cr film, the Cr analysis method is performed by scanning transmission electron microscopy (STEM: SCANNING TRANSMISSION ELECTRON MICROSCOPY) using a thin film sample and characteristic X-ray analysis.

By arranging the Cr film and the intermediate film on the CrN film, peeling of the diamond-like carbon film is suppressed even when an impact is repeatedly applied to the press die 21.

The method for forming the Cr film is not particularly limited, but it is preferable to use the PVD method (physical vapor deposition method) because the adhesion with the CrN film can be ensured.
Further, as the method for forming the intermediate film, it is preferable to use the PVD method (physical vapor deposition method) as in the case of the Cr film. In this case, Cr and carbon targets are prepared respectively, the interlayer film is grown by a sputtering method, and the sputtering conditions for each target are changed during the growth of the film, so that Cr is formed from the Cr film toward the diamond-like carbon film side. The concentration may be decreased and the C concentration may be increased.

[Diamond-like carbon film (DLC film)]
Since the titanium plate press die 21 is used in a harsh environment and conditions, it is required to have not only wear resistance and adhesion resistance but also excellent low friction resistance to the titanium plate.
Therefore, in the present embodiment, in order to realize low friction, a Cr film and an intermediate film are laminated on the CrN film, and further, ^{carbon in the sp 2} hybrid orbital (sp ² structure) and ^{carbon in the sp 3} hybrid orbital (sp ^{3) are laminated.} A high-hardness diamond-like carbon film (DLC film) made of (structure) is formed.
However, since the interlayer film is a film containing Cr and carbon, the crystal structure of carbon in the intermediate film is different from the crystal structure of carbon in the DLC film, and the intermediate film has a lower hardness than the DLC film. .. For this reason, simply forming a high-hardness DLC film on the interlayer film causes a hardness difference (strength discontinuity) between the intermediate film and the DLC film (intersection), and the intermediate film and the DLC film As a result of the stress being easily concentrated at the interface, the adhesion between the intermediate film and the DLC film cannot be sufficiently ensured, and the DLC film may be peeled off during press molding of the titanium plate.
Therefore, it is important to control the hardness distribution (hardness gradient) in the film thickness direction of the DLC film so as to alleviate the difference in hardness between the intermediate film and the DLC film.

Specifically, in a diamond-like carbon film, the ratio I ₁₃₈₀ / I ₁₅₄₀ of the absorption intensity I ₁₃₈₀ at a wave number of ^{1380 cm-1 and} the absorption intensity I ₁₅₄₀ ^{at a wave number of 1540 cm-1 measured by Raman spectroscopy is obtained.} 0.5 to 0.7 in the region 20% deep from the surface (upper layer region), and 0.3 to 0 in the region 20% deep from the interface between the DLC film and the intermediate film (lower layer region). controls 5 and so as, the proportion of sp ³ structure toward the intermediate layer side to impart hardness gradient as decreasing (hardness decreases) from the film surface.

As described above, I ₁₃₈₀ is the absorption intensity at a wave number of 1380 cm- ¹ measured by Raman spectroscopy, the so-called “D band”, and the other I ₁₅₄₀ is a wave number of 1540 cm measured by Raman spectroscopy. ^It is the absorption intensity at -1, the so-called “G band”, and can be used as a guideline ^{for sp 3} _{structure by calculating I 1380} / I ₁₅₄₀ (D / G).

Diamond-like carbon are those as percentage of carbon of sp ³ hybrid orbital (diamond structure) is relatively large, those proportions of carbon sp ² hybrid orbital (graphite structure) is relatively large mixed. That is, when the number of sp ³ structures increases, the property becomes closer to diamond (high hardness), and ^{when the number of sp 2} structures increases, the properties become closer to graphite (soft).

Therefore, as the lower region of the intermediate layer side is made soft, the upper region is a membrane surface side from that hard, by controlling the proportion of sp ³ structure and sp ² structure in DLC film, the thickness direction of the DLC film The hardness difference between the interlayer film and the DLC film can be alleviated by increasing the hardness gradient in the film.
Since the Vickers hardness at the interface on the DLC film side of the intermediate film is about 1200 to 2400, it is desirable that the lower layer region of the DLC film has a Vickers hardness of about 2500 to 3000 and the upper layer region is about 3000 to 3500.

In this way, by making the upper layer region of the DLC film ^{hard with an increased proportion of sp 3} structure, excellent wear resistance to the titanium plate can be exhibited, and this upper layer region is an sp ² hybrid orbital (graphite). Since it also contains some carbon (structure), low friction can be ensured. On the other hand, the lower region of the DLC film by as soft with reduced proportion of sp ³ structure, can be relaxed hardness difference between the intermediate film, it can be secured peeling resistance.
Further, since the DLC film has a low affinity for titanium, the adhesion resistance to the titanium plate can be improved.

In addition, I ₁₃₈₀ / I ₁₅₄₀ can be measured by Raman spectroscopy. Raman spectroscopic analysis irradiates the sample surface with laser light or the like, disperses the Raman scattered light emitted by it, and clarifies the structure and bonding state of the molecules on the sample surface from the difference in wavelength between the incident light and the Raman scattered light. It is a method to make.

The film thickness of the DLC film is not particularly limited and is preferably in the range of 0.5 μm to 2.0 μm, but it may be appropriately determined depending on the manufacturing method, its conditions, the usage environment of the press die, and the like.

The DLC film according to this embodiment can be formed by a plasma CVD method.
^{In order to control the ratio of the sp 3} structure and the sp ² structure in the DLC film as described above, each condition (deposition condition) of the plasma CVD method may be adjusted. ^{Specifically, the ratio of the sp 3} structure and the sp ² structure in the DLC film can be adjusted by appropriately adjusting the type and ratio of the reaction gas, the substrate temperature, the cathode voltage, the degree of vacuum, and the like. That is, as long as the above-mentioned hardness gradient is given in the film thickness direction of the DLC film, the film may be formed while appropriately adjusting the film forming conditions, and the film is formed under certain conditions from the start of the film formation. You may.

The reaction gas can be a mixed _{gas of CH 4} and H _{2 , or only CH 4} gas. When a mixed gas as a reaction gas, by adjusting the flow rate of each gas can adjust the proportion of sp ³ structure and sp ² structure, it may be adjusted each of the other conditions in the case of using only the CH ₄ gas.
Further, since it is important that the DLC film in the present embodiment has a sp ³ structure and an sp ² structure in a desired ratio, it is not preferable that a large amount of H (hydrogen) is mixed in the film. Therefore, it is better to suppress _{H 2} as a reaction gas to an appropriate amount.
Since the film forming conditions described above are affected by the type and specifications of the plasma CVD apparatus used, the ratio of the ^{sp 3} structure and the sp ^{2 structure may be adjusted while examining the Raman peak of the DLC film being generated.}

In addition, dirt may adhere to the surface of the interlayer film until the interlayer film is formed on the substrate and the DLC film is formed. Therefore, in the present embodiment, it is desirable to perform plasma cleaning on the surface of the intermediate film before forming the DLC film to decompose and remove stains on the surface before forming the DLC film. Thereby, the adhesion between the interlayer film and the DLC film can be further improved.

[Nitriding layer]
The press die 21 according to the present embodiment is a press die by forming a CrN film, a Cr film and an intermediate film on a base material, and further forming a high-hardness diamond carbon film on the film. The wear resistance, adhesion resistance, and low friction resistance of 21 are ensured. However, a hardness difference (strength discontinuity) occurs between the high hardness CrN film and the relatively soft base material (interface), and as a result, stress tends to concentrate at the interface between the CrN film and the base material. Depending on the thickness of the CrN film, sufficient adhesion between the CrN film and the base material may not be ensured.
Therefore, as a result of the examination by the present inventors, the hardness difference is increased by providing another layer capable of connecting the CrN film and the base material between the high hardness CrN film and the relatively soft base material. It was found that it can be relaxed, and the adhesion between the CrN film and the substrate and the strength of the press die can be compatible with each other.
In general, the maximum shear stress is not the outermost surface but the maximum just below the surface (surface layer). From the viewpoint of "contact stress of Hertz", the maximum shear stress is directly below the surface of the press die, that is, between the CrN film and the base material. It is preferable to further provide a high hardness layer between them to ensure the wear resistance of the press die.

From the above, it is preferable to provide a nitride layer obtained by plasma nitriding the surface layer of the base material between the base material and the CrN film. By forming the nitrided layer on the surface layer of the base material in this way, the difference in hardness between the CrN film and the base material can be alleviated, and stress concentration can be suppressed. As a result, the adhesion and strength between the CrN film and the base material can be improved, the peeling of the CrN film can be reduced, and the adhesion resistance can be improved.

The thickness of the nitrided layer is not particularly limited, but in the present embodiment, it can be 0.5 μm to 5 μm.
In order to reduce the difference in strength between the high hardness CrN film and the relatively soft base material, it is preferable to secure a thickness of the nitrided layer of 0.5 μm or more. More preferably, it is 1 μm or more. On the other hand, if the thickness of the nitrided layer is made too thick, the time required for the plasma nitriding process becomes long, the productivity is lowered, and the manufacturing cost is also high. Further, if the thickness of the nitrided layer is excessively increased, the surface roughness of the base material becomes large, and it becomes necessary to polish the surface of the base material before forming the CrN film. From these viewpoints, the thickness of the nitrided layer is preferably 5 μm or less.

The average nitrogen concentration in the nitrided layer is preferably 0.10 to 0.50% by mass.
If the nitrogen concentration in the nitrided layer is too low, the effect of improving the strength is small and sufficient wear resistance may not be obtained. Therefore, the average nitrogen concentration in the nitrided layer may be 0.10% by mass or more. preferable. More preferably, it is 0.20% or more.
On the other hand, if the nitrogen concentration in the nitrided layer is too high, the surface of the nitrided layer tends to be embrittled and cracks may occur. For this reason, the average nitrogen concentration in the nitrided layer is preferably 0.50% by mass or less. More preferably, it is 0.40% or less.

Further, it is preferable that the nitrogen concentration distribution in the nitrided layer has a concentration gradient that decreases from the surface layer of the nitrided layer toward the depth direction.
As described above, it is not preferable that the strength difference occurs inside the press die from the viewpoint of the adhesion between the CrN film and the base material and the strength. Therefore, it is preferable that the difference in strength between the CrN film, the surface layer of the base material, and the inside of the base material, that is, the strength gradient along the depth direction of the base material is gentle. For that purpose, it is preferable to control the concentration distribution of nitrogen in the nitrided layer formed between the CrN film and the base material so as to have a concentration gradient that decreases from the surface layer of the nitrided layer toward the base material side.

In order to control the nitrogen concentration distribution so that the gradient decreases from the surface layer of the nitrided layer toward the depth direction, the plasma nitriding treatment on the surface layer of the base material for forming the nitrided layer is divided into a plurality of times. Moreover, the nitrogen concentration distribution in the nitrided layer may be adjusted by performing each treatment under different conditions.

The "nitriding layer" can be discriminated (determining the boundary between the base material and the "nitriding layer") by a glow discharge emission analyzer (GDS). Specifically, first, in the surface layer of the base material nitrided by the plasma nitriding treatment, the analysis region is set to 1 mm in diameter, and normal glow discharge emission analysis is performed. Continuing the analysis in the depth direction, the region up to the point where the amount of nitrogen in the analysis region exceeds the average nitrogen concentration of the base material (base material) is defined as the "nitriding layer". That is, the glow discharge emission analysis is performed in the depth direction, and the boundary between the base material and the "nitriding layer" is determined at the point where the amount of nitrogen drops to the average nitrogen concentration of the base material.

The average nitrogen concentration in the nitrided layer can also be measured using GDS. In this embodiment, the analysis region has a diameter of 1 mm, analysis is performed in the depth direction using GDS, and the QDP (Quantitative Depth Profile) method specified in JIS K 0150 is applied to each depth of 50 nm. Measure the nitrogen concentration. This makes it possible to obtain the nitrogen concentration distribution in the nitrided layer. Further, the average nitrogen concentration of the entire nitrided layer can be obtained by calculating the average of each nitrogen concentration at each depth of 50 nm.

The press forming method of the press die 21 and the titanium plate according to the present embodiment has been described above, but before the CrN film is formed (before the plasma nitriding treatment is performed), the surface texture of the base material is good. Therefore, it is desirable to mirror-polish the surface of the base material in order to ensure the film-forming property of the CrN film. As a result, the adhesion between the CrN film and the base material can be improved, and as a result, excellent adhesion resistance can be obtained.

FIG. 6 graphically shows the relationship between the stroke amount of the punch and the thickness of the titanium plate. The graph of FIG. 6 is a result obtained by a simple simulation of a case where a titanium plate is press-molded with the press die shown in FIG. With both ends of the pure titanium plate with a thickness of 0.5 mm restrained in the longitudinal direction and both ends of the pure titanium plate in the longitudinal direction supported from below by two rolls, one roll is placed in the center of the titanium plate in the longitudinal direction. It shows the reduction behavior of the thickness of the titanium plate when it is bent and molded by lowering it from the upper side. The processed titanium plate is in a plane-distorted state. The stroke amount of the punch on the horizontal axis of FIG. 6 is the lowering amount of the roll arranged on the upper side, and the plate thickness on the vertical axis is the minimum plate thickness at the portion subjected to the bending process. By changing the type of roll, the coefficient of static friction μ between the titanium plate and the roll is set to 0.05 and 0.1. Looking at the stroke amount when the plate thickness is reduced to 0.3 mm (reduction rate 40%), it is 4.3 mm when the static friction coefficient μ is 0.1, but when the static friction coefficient μ is 0.05, it is 4.3 mm. The stroke amount has increased to 4.5 mm. In this way, by increasing the coefficient of static friction between the mold and the titanium plate to improve the lubricity, the stroke amount can be increased, and it becomes possible to process the mold into a desired shape without causing cracks.

Since the surface-treated film according to the present embodiment is formed on the titanium plate pressing die of the present embodiment, the space between the titanium plate and the pressing die is higher than that in the case where the surface-treated film is not formed. Lubricity can be greatly improved. This makes it possible to suppress cracking of the titanium plate during press molding in the titanium plate press molding method.

Further, according to the press die of the titanium plate of the present embodiment, the press die 21 is formed by forming a CrN film, a Cr film, an intermediate film and a diamond-like carbon film (DLC film) on the base material. Lubricity, wear resistance and adhesion resistance can be improved. Further, in the DLC film, the difference in hardness between the intermediate film and the DLC film can be alleviated by inclining the hardness in the film thickness direction of the DLC film. As a result, by making the upper layer region of the DLC film hard, excellent wear resistance to the titanium plate 11a can be exhibited ^{, and carbon of the sp 2} hybrid orbital (graphite structure) is also contained to some extent, resulting in low friction. Sex can be secured. By making one lower layer region soft, the hardness difference with the interlayer film can be alleviated, and peeling resistance can be ensured.

Further, by providing a nitride layer between the base material and the CrN film, the hardness difference (strength discontinuity) between the high hardness CrN film and the relatively soft base material can be eliminated, and CrN can be eliminated. Sufficient adhesion between the film and the base material can be ensured.

Further, in the press molding method of the titanium plate of the present embodiment, even if the deformed state of the titanium plate after molding includes a plane strain state, cracking after press molding, adhesion of the titanium material, and wear of the mold Can be prevented. That is, in the press forming method of the titanium plate of the present embodiment, the surface treatment film enhances the lubricity between the protrusions 22b and 23b and the titanium plate 11a, so that the protrusions 22b and 23b are bent while the titanium plate 11a is restrained. Even when the above is performed, the titanium plate 11a does not slide and adhere on the surface of the protrusions during the bending process, and the titanium plate 11a is stretched without being restricted by the protrusions 22b and 23b, and can be formed into a desired shape. Further, even if the protrusions 22b and 23b collide with the titanium plate 11a due to the lowering of the punch 22 and an impact is applied to the surface-treated film and the base material, the DLC film is peeled off because the surface-treated film has the Cr film and the intermediate film. Without impairing lubricity, adhesion resistance and wear resistance. As a result, even when the deformed state of the titanium plate after molding includes the plane strain state, it is possible to prevent cracking after press molding, adhesion of the titanium material, and wear of the mold.

Further, when molding a titanium plate, by applying a lubricant to the titanium plate and then press-molding, the lubricity between the titanium plate and the press die can be further improved.

Further, according to the press die according to the present embodiment, the life of the die can be remarkably improved, the frequency of die replacement can be reduced, and the manufacturing cost can be significantly reduced. Further, by reducing the frequency of mold replacement, it is possible to prevent a decrease in yield due to position adjustment at the time of mold replacement, and to improve the yield by improving molding dimensional accuracy.

The present invention is not limited to the above embodiment, and can be applied to any mold as long as it is used for press molding of a titanium plate.

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to the conditions used in the following examples.

<Press die>
(Example 1)
First, the present invention uses the tool steel SKD11 (C, Si, Mn, Cr, Mo, V, P, S, residual iron and impurities specified in JIS G 4404 as the base material for the die and punch of the press die. (Steel included in the range of) was adopted, and after forming into a predetermined shape, quenching and tempering were performed.
Next, the obtained substrate surface was subjected to nitriding treatment to form a nitride layer having a thickness of 25 μm and an average nitrogen concentration of 0.20% by mass on the surface layer of the substrate.
As the nitriding treatment, a radical nitriding treatment was used in which a highly reactive active species generated by DC glow discharge was used in a mixed gas atmosphere of ammonia and hydrogen (NH ₃ , H _{2, Ar).} The treatment temperature was set to 500 ° C., and the treatment was carried out for 3 hours.
Next, a 1.5 μm CrN film (single layer) was formed on the surface layer (nitrided layer) of the base material subjected to the nitriding treatment by a PVD vapor deposition method.

The components of the die and punch were analyzed from the surface of the CrN film in the depth direction using a glow discharge emission analyzer (GDS). The analysis results are shown in FIGS. 7 to 9. The horizontal axis in FIGS. 7 to 9 indicates the depth (μm) from the surface of the CrN layer, and the vertical axis indicates the concentration (mass%) of each component.
As shown in FIGS. 7 and 8, it can be seen that a CrN layer having a thickness of 1.5 μm is formed on the surface layer of the base material. Further, FIG. 9 is a graph showing the vertical range of the graph of FIG. 7 changed in order to confirm the concentration behavior of the element contained in a small amount in the depth direction. From the graph of FIG. 9, it can be seen that a nitride layer is formed between the CrN film and the base material. Further, as is clear from the graph, the nitrogen concentration gradually decreases from the CrN film side to the base material side, and the hardness fluctuation in the nitrided layer in the depth direction is also gradual. I understand. Although FIGS. 7 to 9 show the analysis results of the punch, the same analysis results as those of FIGS. 7 to 9 were obtained for the die.

Next, the surfaces of the die and punch (CrN film) were subjected to plasma cleaning in advance to remove stains, and then a Cr film and an intermediate film were formed by the PVD method. The thickness of the Cr film was 10 to 40 nm, and the thickness of the intermediate film was 60 to 180 nm. Further, when the total of the Cr concentration and the C concentration of the intermediate film is 100% by mass, the Cr concentration at the interface with the Cr film is 100% by mass, and the outermost surface (the surface that becomes the interface with the diamond-like carbon film). The film was formed so that the Cr concentration and the C concentration linearly changed along the film thickness direction so that the Cr concentration in the film was 0% by mass.

Next, the surface of the interlayer film was subjected to plasma cleaning to remove stains, and then a diamond-like carbon film (DLC film) was formed on the interlayer film. The film thickness was 1.0 μm.
The DLC film was formed by the plasma CVD method. A capacitively coupled high-frequency plasma CVD apparatus was used as the apparatus, and the temperature was set to 500 ° C. A high frequency power supply of 13.56 MHz was used as the power supply for plasma generation. As the reaction gas, a mixed gas of _{CH 4} and H _{2 was used.} At this time, _{by changing the mixing ratio of the mixed gas of CH 4} and H ₂ , the hardness of the film gradually increased from the interface with the interlayer film toward the surface.

(Comparative Example 1)
Using the tool steel SKD11 used in Example 1 as a base material, a nitride layer and a CrN film (single layer) were formed in the same manner as in Example 1. Next, a diamond-like carbon film (DLC film) was formed on the CrN film by an ion plating method to a thickness of 1.0 μm. Dies and punches were manufactured in this way.

<Raman spectroscopy>
The ratio of carbon in the ^{sp 2} hybrid orbital to carbon in the sp ^{3 hybrid orbital (sp 3} / sp ² ) on the surface layers of the dies and punches obtained in Example 1 and Comparative Example was measured by Raman spectroscopy.
The results are shown in FIGS. 10 (a) to 10 (c) and 11 (a) to 11 (c), Tables 1 and 2.

FIG. 10 (a) shows a micrograph of the surface layer of the punch of Example 1, and FIGS. 10 (b) and 10 (c) show the Raman spectrum of the DLC film of the punch of Example 1. FIG. 11 (a) shows a micrograph of the surface layer of the punch of Comparative Example 1, and FIGS. 11 (b) and 11 (c) show the Raman spectrum of the DLC film of the punch of Comparative Example 1. In the figure, "near the surface" is the surface layer of the DLC film, "inside the DLC film" is the inside of the DLC film, and "near the interface" is the Raman spectrum near the interface between the DLC film and the intermediate film.
Table 1 shows the Raman band parameters of Example 1, and Table 2 shows the Raman band parameters of Comparative Example 1.

As is clear from Tables 1 (a) to 10 (c), the DLC film obtained in Example 1 has an increase in _{I 1380} / I _{1540 from the intermediate film toward the DLC film.}
That is, it can be seen that the hardness slope increases as the hardness increases from the intermediate film to the DLC film.
That is, it can be seen that the hardness slope increases as the hardness increases from the intermediate film to the DLC film.

On the other hand, as is clear from FIGS. 11A to 11C and Table 2, the DLC film obtained in Comparative Example 1 had a large _{I 1380} / I _{1540 both “near the surface” and “inside the DLC film”.} It can be seen that the hardness gradient is not imparted in the film thickness direction.
Although FIGS. 10 to 11 show the analysis results of the punch, the same analysis results as those of FIGS. 10 to 11 were obtained for the die.

Next, the Vickers hardness of the nitrided layer, the CrN film, and the DLC film obtained in Example 1 and Comparative Example 1 was measured. The base material and the nitrided layer were measured with a microphone mouth bit force hardness tester. Further, the CrN film, the Cr film, the intermediate film, and the DLC film were subjected to an extremely low load indentation test by a nanoindentation (indentation) method, and converted to bite hardness. Specifically, when a load of 0.005 to 0.1 mN is applied for 20 seconds using a triangular pyramidal indenter (perco-pitch indenter) according to the nanoindentation (pushing) method (load 20s, holding 5s, unloading). The indentation hardness of 20s) was determined as the nanoindentation hardness. At this time, the measurement was performed under the condition that the pushing depth was 10 times or more.
In addition, the measurement by surface grinding and the side (cross-section) pushing by embedded polishing were used together. From the obtained nanoindentation hardness, the biting hardness was calculated by the following conversion formula.
Hv = 0.0945 x H _IT
However, the Hv in the formula the bit force Ichisu hardness, H _IT means respectively nanoindentation hardness.

For each layer and film, three points were measured in cross section and the average was taken as "Vickers hardness". The nitrided layer was measured near the interface with the substrate (region up to a depth of 2 μm: inner region) and near the interface with the CrN film (region up to a depth of 2 μm: outer region). The DLC film includes a region from the film surface to 0.20 t (near the surface), a region from the interface between the DLC film and the intermediate film to 0.20 t (near the interface), and the center of the DLC film in the film thickness direction (DLC film). Measurements were taken at a total of 3 locations (inside).
The results are shown in Table 3. As shown in Table 3, in Example 1, the average Vickers hardness of each layer and each film was 1000 for the nitrided film, 2000 for the CrN film, 1200 for the Cr film (not shown in Table 3), and the intermediate film was 2000 (not shown in Table 3), the "near the interface" of the DLC film is 2500, the "inside of the DLC film" is 3000, and the "near the surface" of the DLC film is 3500. The slope was given. The DLC may be about 2000 to 2400 in order to reduce crack fracture in the surface layer.

Further, as shown in Table 3, the Vickers hardness was measured in the same manner as in Example 1 in each of the “near the surface”, “inside the DLC film”, and “near the interface” of the DLC film obtained in Comparative Example 1. "Near the interface" was 4000, "Inside the DLC film" was 4000, and "Near the interface" was 4000, and the hardness distribution was uniform in the film thickness direction.

<Evaluation of press molding>
The press moldability was evaluated by press molding the titanium plate using the dies and punches of Example 1 and Comparative Example 1.
FIG. 12 shows a schematic cross-sectional view of the press die used in the test. The press die shown in FIG. 12 is composed of a punch 21, a die 22, and a wrinkle pressing pad 23. The punch 21 is provided with three protrusions 21a at equal intervals. Further, the die 22 is provided with two protrusions 22a and 22a. The tip of the protrusion on the die 21 and the punch 22 is a curved surface having a radius of curvature of 3.0 mm when viewed in cross section. The protrusions 21a of the punch 21 and the protrusions 22a of the die 22 are positioned so that the gap between the protrusions 21a and 22a becomes 1.5 mm when the punch 21 descends to the bottom dead center. The dimension of the punch 21 in the width direction in the drawing was 36 mm, and the height of each protrusion of the punch 21 and the die 22 was 10 mm. A wrinkle pressing pad 23 is arranged above the outer peripheral portion of the die 22. The die 22 is provided with a material inflow prevention bead 22b so as to surround the punch 21. As a result, the titanium plate that has undergone the molding process is in a plane strain state.

Using the press die shown in FIG. 12, a titanium plate having a thickness of 0.5 mm was press-molded. As the titanium plate, a titanium plate made of JIS Class 1 titanium was used. When the press die of Example 1 was used, only rust preventive oil (trade name: Knoxlast, manufactured by Parker Kosan Co., Ltd.) was applied to the titanium plate as a lubricant, and press molding was performed. When the press die of Comparative Example 1 was used, the same lubricant as in Example 1 was applied to the titanium plate surface-treated by Millbond and press-molded. By press molding, the titanium plate was molded into a wavy shape as shown in FIG. At this time, the punch 21 was pushed in so that the amplitude of the wave was 2.5 mm at the target value.

As a result of press molding, both Example 1 and Comparative Example 1 were formed into a wavy shape as shown in FIG. 2, and the radius of curvature of the cross section of one and the other protruding portion was in the range of 3.05 to 3.11 mm, and the amplitude was increased. Was 4.8 mm, and the shape almost as intended was obtained. No cracking with Example 1 and Comparative Example 1 occurred.
The minimum value of the plate thickness was 0.38 mm in Example 1 and 0.37 mm in Comparative Example 1, and there was no significant difference between the two.
As described above, the titanium plate press-molded using the press die of Example 1 was not subjected to the mill bond treatment, but as in Comparative Example 1, it did not cause cracks and was as intended. It has become possible to mold into a shape.

Further, the durability test was performed by applying the mold of the present invention to the punch of the Eriksen test specified in JIS Z 2247. That is, a punch for the Eriksen test was manufactured in the same manner as in Example 1 above, except that the shape of the base material of the punch was the shape specified in JIS Z 2247. Then, a JIS 1 type titanium plate having a thickness of 0.5 mm was used as a test piece, and a punch was pushed into the test piece until a through crack was generated. This was repeated 200 times. As a result, although the film thickness of the DLC film formed on the surface of the punch was slightly reduced, the DLC film itself did not peel off, and the durability was good.

1A-1E ... Plate (titanium plate), 11a, 11b ... Titanium plate, 21 ... Press die, 22 ... Punch, 22a ... Punch plate, 22b ... Projection (base material), 23 ... Die, 23a ... Die plate , 23b ... Protrusion (base material).

Claims (15)

A press die used for press molding of titanium plates.
A base material and a surface treatment film formed on the surface of the base material are provided.
The base material is by mass%
C: 1.00 to 2.30%,
Si: 0.10 to 0.60%,
Mn: 0.25 to 0.80%,
P: 0.030% or less,
S: 0.030% or less,
Cr: Containing 4.80 to 13.00%,
The balance is made of steel with a composition of iron and impurities.
The surface treatment film includes a CrN film formed on the substrate, a Cr film formed on the CrN film, an intermediate film formed on the Cr film, and diamond formed on the intermediate film. It consists of a like carbon film,
The thickness of the CrN film is 0.5 μm to 5 μm (excluding 5 μm).
The interlayer film contains Cr and carbon, and when the total of Cr and carbon is 100% by mass, the Cr concentration at the interface on the Cr film side is 80% by mass or more, and C at the interface on the diamond-like carbon film side. The film has a concentration of 80% by mass or more, and the Cr concentration gradually decreases along the film thickness direction from the Cr film side toward the diamond-like carbon film side.
In the diamond-like carbon film, the ratio I ₁₃₈₀ / I ₁₅₄₀ of the absorption intensity I ₁₃₈₀ at a wave number of ^{1380 cm-1 and} the absorption intensity I ₁₅₄₀ ^{at a wave number of 1540 cm-1} measured by Raman spectroscopy is the film thickness from the film surface. For pressing titanium plates, 0.5 to 0.7 in the 20% depth range and 0.3 to 0.5 in the 20% depth range from the interface between the diamond-like carbon film and the intermediate film. Mold. In the diamond-like carbon film, the Vickers hardness in the range of 20% depth from the film surface is 3000 to 3500, and the Vickers hardness in the range of 20% depth from the interface between the diamond-like carbon film and the intermediate film. The dies for pressing a titanium plate according to claim 1, wherein the dies are 2500 to 3000. The titanium plate press die according to claim 1 or 2, wherein the diamond-like carbon film has a thickness of 0.5 μm to 2 μm. The press die for a titanium plate according to any one of claims 1 to 3, wherein the Vickers hardness of the CrN film is 800 to 2000. The press die for a titanium plate according to any one of claims 1 to 4 , wherein the Cr film has a thickness of 5 nm to 100 nm. The titanium plate press die according to any one of claims 1 to 5 , wherein the interlayer film has a thickness of 30 nm to 1000 nm. The press die for a titanium plate according to any one of claims 1 to 6 , wherein a nitride layer is formed on the surface of the base material, and the CrN film is formed on the nitride layer. The titanium plate press die according to claim 7 , wherein the nitrided layer has a thickness of 0.5 μm to 5 μm. The titanium plate press die according to claim 7 or 8 , wherein the average nitrogen concentration of the nitrided layer is 0.10 to 0.50% by mass. Concentration distribution of nitrogen in the nitride layer has a concentration gradient that decreases along the depth direction from the nitride layer surface, a press die of the titanium plate as claimed in any one of claims 7 to 9 .. The Vickers hardness of the nitrided layer is 800 to 1200, a press mold for titanium plate according to any one of claims 7 to 10. The base material is further increased in mass%.
Mo: 0.70 to 1.20%,
V: 0.15-1.00%,
W: 0.60 to 0.80%,
The titanium plate press die according to any one of claims 1 to 11, which comprises. The titanium plate press die according to any one of claims 1 to 12 , wherein the base material is a punch and a die. A method for press-molding a titanium plate, wherein the titanium plate is press-molded using the titanium plate press die according to any one of claims 1 to 13. The method for press-molding a titanium plate according to claim 14 , wherein when the titanium plate is press-molded, a plane strain state is included as a deformed state of the titanium plate.

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