JP3154403B2 - Coating mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold most suitable for molding iron-based parts or aluminum alloy parts such as automobile parts and machine parts, and more particularly to a mold excellent in heat crack resistance and oxidation resistance. It is about type.

[0002]

2. Description of the Related Art A mold such as a forging die used for warm or hot forging and a mold used for casting has a high surface temperature (generally 500 ° C. or higher) during use. Damage due to oxidation of the steel and fatigue cracks due to repeated thermal stress occur, resulting in a "skin roughening" phenomenon called heat check. It is said that such rough surface progresses with an increase in the number of processes, and reaches the life of the mold when it becomes difficult to maintain the dimensional accuracy.

[0003] In order to delay such damage to the mold even a little, nitriding treatment (tufftriding treatment, gas nitriding treatment, ion nitriding treatment, sulphonitriding treatment, etc.) is widely used at present. The feature of nitriding treatment is to diffuse and infiltrate the element mainly composed of nitrogen into the surface of the steel mold base material to increase the surface hardness, introduce surface compressive stress, etc., and make the mold surface durable against heat check. Is to improve. However, the oxidation resistance of the mold surface cannot be improved by the nitriding treatment, and damage due to oxidation of the mold surface, that is, "generation of iron oxide on the mold surface → falling off of oxide scale → further oxidation progression Has not been suppressed.

A widely used surface treatment other than nitriding is the formation of a ceramic film such as titanium carbide, titanium nitride or titanium carbonitride by chemical vapor deposition (CVD) or physical vapor deposition (PVD). is there. Further, vanadium carbide or the like by a thermal reaction / precipitation method called a TRD method or a TD method is also used. But,
These titanium carbonitrides, vanadium carbides, and the like lose their oxidation resistance at around 500 to 600 ° C., and no remarkable effect has been obtained in suppressing the oxidation of the mold surface.

In order to overcome these drawbacks, a method is disclosed in which a surface hardening treatment such as a nitriding treatment is combined with a film forming treatment such as the above-mentioned vapor deposition method.

(1) Japanese Patent Application Laid-Open No. 62-103368 proposes a ceramic coating metal in which a nitride layer is formed on the surface of a metal substrate and a ceramic coating layer is coated. Discloses the law.

(2) In Japanese Patent Application Laid-Open No. H2-125861, ion nitriding treatment and ion plating are performed continuously in the same vacuum layer inner tank, and metal nitride, carbide, carbonitride, carbonitride And a method of forming one or more films of oxide or the like.

(3) Japanese Patent Application Laid-Open No. 5-984422 discloses a continuous process in which a high-frequency power source is used in a vacuum vessel to impinge on nitrogen ions that generate plasma to a workpiece to form a hardened layer and immediately perform ceramic coating as it is. A method is disclosed.

(4) In JP-A-8-35075, a metal member is ion-nitrided by glow discharge in an atmosphere of ammonia gas and hydrogen gas, and a hard coating is formed on the ion-nitrided layer by a PVD method. A method is disclosed.

[0010]

However, all of these prior arts merely disclose a processing method or merely disclose a material system. In particular, a material system that simultaneously satisfies the heat crack resistance and the heat oxidation resistance, and the material system did not provide satisfactory characteristics of mechanical properties.

Accordingly, a main object of the present invention is to provide a coated mold having both heat crack resistance and oxidation resistance of the mold surface.

[0012]

The present invention has achieved the above object by combining the formation of a hardened layer on the surface of a mold base material by nitriding treatment and the formation of a ceramic film having excellent oxidation resistance. Thus, a long-life mold is realized by a synergistic effect of the two surface modification technologies.

[0013] Namely, the present invention molds the mold base material having a nitrided layer on the surface portion and wherein the kite comprising the following 1 or more ceramic coatings selected from ~. (Ti _1-x , Cr _x ) N film (where x is an atomic ratio, 1.0 ≧ x ≧ 0.02) A titanium nitride film containing at least one of TiN and Ti ₂ N, and a chemical formula CrN and Cr ₂ N coating composition laminated alternately five times or more and a chromium nitride layer comprising at least one of two or more kinds of _{(Ti 1-x, Cr x} )
N thin film (where x is an atomic ratio and 1.0 ≧ x ≧ 0.0
2) The coatings laminated alternately four or more times, especially the table of the mold base material
Average value of compressive residual stress over a depth of 10 μm from the surface
Is not less than 0.2 GPa and not more than 1.5 GPa,
The average value of the compressive residual stress of the entire ceramic coating is 0.2
It is preferable to be not less than GPa and not more than 8 GPa .

Here, the mold of the present invention includes a forging die for warm or hot forging and a casting mold. Further, the mold base material is preferably JIS steel type SKH or SKD or a material equivalent to these.

As the nitriding treatment on the surface of the mold base material, many nitriding treatment methods such as a tuftride treatment, a gas nitridation treatment and an ion nitridation treatment can be applied. However, in many methods, a brittle compound “γ′-Fe ₄ N or ε-Fe” called a compound layer or an embrittlement layer is formed on the surface of the mold material after the nitriding treatment.
_{Since 2-3} N "is generated, it is desirable to remove such a compound layer by polishing. Note that when the ion nitriding treatment is used, the nitriding treatment can be realized without forming the above-described compound layer. The thickness of the nitrided layer is 50 μm or more,
It is preferably not more than 00 μm. The average value of the compressive residual stress of the nitrided layer over a depth of 10 μm from the surface of the mold base material is 0.2 GPa or more by optimizing the processing temperature during nitriding and the depth of the nitrided layer. It can be 5 GPa or less.

The ceramic film formed on such a nitriding layer has excellent oxidation resistance. Examples of the ceramic film having excellent oxidation resistance include a film obtained by adding a chromium element to titanium nitride. Oxidation resistance is greatly improved by adding chromium element to titanium nitride.
The amount of chromium added depends on the composition of the coating (Ti _1-x , C
r _x ) N (x is the atomic ratio), 1.0 ≧ x ≧
It needs to be 0.02. At this time, it is preferable that the composition of the coating of (Ti _1-x , Cr _x ) N be continuously or stepwise inclined toward chromium-rich from the base material side to the coating surface side. This ceramic coating
A film in which a titanium nitride layer having a chemical formula of at least one of TiN and Ti ₂ N and a chromium nitride layer having a chemical formula of at least one of CrN and Cr ₂ N are alternately laminated five times or more, or two or more types having different compositions. (Ti _1-x , Cr _x )
N thin film (where x is an atomic ratio and 1.0 ≧ x ≧ 0.0
Even if a coating is obtained by alternately laminating 2) four or more times, equivalent or longer mold life can be obtained.

The average value of the compressive residual stress of the entire ceramic film is 0.5 G by optimizing the conditions at the time of film formation.
It can be set to Pa or more and 8 GPa or less. The total thickness of the ceramic coating is preferably 0.5 μm or more and 40 μm or less.
It is more preferable that a titanium nitride film is interposed between the ceramic film and the mold base material.

The main reasons for limiting the configuration as described above are as follows. Nitriding treatment is said to have an excellent effect of improving heat crack resistance, but even if this treatment method is used alone, the life of the mold quickly reaches the limit due to the low oxidation resistance of steel. I will. It is essential that an appropriate compressive residual stress exists in the nitrided layer.

The residual stress is defined by an X-ray diffraction method (sin ²
The average value of the residual stress over a depth of 10 μm from the surface of the mold base material is 0.2 GP.
It is necessary to set a compressive stress of not less than a and not more than 1.5 GPa. If the compressive residual stress is smaller than 0.2 GPa or the tensile residual stress is not preferable, the effect of suppressing the generation of thermal cracks cannot be obtained. On the other hand, when the compressive residual stress exceeds 1.5 GPa, it is not preferable because crack generation is promoted.

The ceramic film formed on the surface of the mold is improved in oxidation resistance by adding a chromium element to a ceramic film based on titanium nitride instead of a conventional ceramic. At the same time, it is essential that a compressive residual stress exists in the coating, and the above-mentioned X
It is measured by the line diffraction method. Specifically, it is essential that the average value of the residual stress of the entire coating film is a compressive stress of 0.5 GPa or more and 8 GPa or less. The average value of the compressive residual stress is 0.
If the stress is less than 5 GPa or the tensile residual stress is obtained, the effect of suppressing the occurrence of thermal cracks is insufficient. On the other hand, if the compressive residual stress exceeds 8 GPa, it is not preferable because crack generation is accelerated.

The depth of the nitrided layer on the surface of the mold is 50 μm.
It is desirable that it is not less than m and not more than 500 μm. 50μ
If the processing is less than m, a remarkable effect cannot be obtained. Further, since a process for obtaining a nitrided layer exceeding 500 μm requires a considerably long time, it is not economical in terms of cost effectiveness.

The reason that the oxidation resistance of the coating can be improved by adding a chromium element to the titanium nitride ceramics is that chromium in the coating is oxidized in a high-temperature atmosphere at the time of using a mold, and the surface of the coating is oxidized. This is for forming a strong protective film of chromium oxide. Such a dense oxide film has the effect of greatly suppressing the progress of oxidation of the titanium nitride film, and greatly suppresses the oxidative wear of the mold surface. It is preferable that the composition of the coating film satisfies 1.0 ≧ x ≧ 0.02 when expressed as (Ti _1-x , Cr _x ) N (x is an atomic ratio). The upper limit of the composition x is 1.0 from the characteristics of the substance. When the composition x is less than 0.02, the effect of improving the oxidation resistance cannot be obtained.

Regarding the method of adding chromium to the titanium nitride ceramics, in addition to making the composition uniform in the coating thickness direction, the oxidation resistance can be further improved by devising as follows.

(A) The base material side is made of titanium rich (Ti _1-x ,
The oxidation resistance of the coating surface side is particularly improved by using a coating of Cr _x ) N and a coating surface of the coating film of chromium-rich (Ti _1-x , Cr _x ) N.

(B) A structure in which a titanium nitride film containing at least one of the chemical formulas TiN and Ti ₂ N and a chromium nitride film containing at least one of the chemical formulas CrN and Cr ₂ N are alternately repeated at least four times and laminated. Thus, even if one layer is worn away and disappears, the effect is maintained by the next layer showing a face.

(C) Two or more (Ti _1-x , Cr _x ) N thin films (where x is an atomic ratio and 1.0 ≧ x ≧ 0.02) having different compositions are alternately applied four times. By repeating the above-described structure, even if one layer is worn out and disappears, the effect is maintained by the next layer appearing.

The total thickness of the ceramic film is as follows:
The thickness is preferably 0.5 μm or more and 40 μm or less.
When the thickness is less than 0.5 μm, the effect of the coating treatment cannot be obtained.
On the other hand, when the thickness exceeds 40 μm, the coating is self-destructed by an impact during use, which is not preferable.

It is preferable to insert a titanium nitride film between the ceramic film and the base material since the adhesion between the nitrided layer on the surface of the base material and the ceramic film can be maximized.

[0029]

Embodiments of the present invention will be described below. (Test Example 1) φ40 × h made of JIS steel type SKD61
A 30 mm cylindrical block was made and heat treated by quenching and tempering to a Rockwell C scale hardness of 52. The end face of this block was polished to a roughness of 0.5Z or less.

The polished surface of this block was subjected to a surface treatment according to the present invention shown in Table 1 (Examples 1 to 16). For comparison, comparative examples shown in Table 2 were produced (Comparative Examples 1 to 13).

[0031]

[Table 1]

[0032]

[Table 2]

In Tables 1 and 2, details of the nitriding treatment or the method of forming the ceramic film are as follows. [Method 1] Tuftride treatment: temperature 550 ° C., time 30
Keep in salt bath for 20 minutes to 20 minutes, 25-45 depth on surface
A cured layer of 0 μm was obtained. 10μ depth generated on this surface
The compound layer of m was polished and removed to have a surface roughness of 0.5Z. In addition, what changed the residual stress of the hardened layer surface by changing the temperature of the tufted-ride process was also prepared.

[Method 2] Ion nitriding treatment: temperature 500
° C, time 15 minutes to 2 hours, nitrogen gas 60 flow%, hydrogen gas 40 flow%, processing tank pressure 2 Torr, DC voltage -100 V applied to the base material, high frequency power (13.56 MH)
z) Under the condition of 1000 W, a cured layer of 15 to 120 μm (including comparative examples) was obtained on the surface. No harmful compound layer was formed on this surface, but the surface roughened by the plasma treatment was lightly lapped to obtain a surface having a roughness of 0.5Z. In addition, what changed the compression residual stress of the hardened layer surface by changing the temperature of the ion nitriding process was also prepared.

[Procedure 3] Formation of (Ti _1-x , Cr _x ) N coating: First, the base T was formed by arc ion plating.
iN is formed to a thickness of about 0.5 μm, and subsequently to this film formation, (Ti _1−x , C
r _x ) N coating was formed. The conditions for forming the (Ti _1-x , Cr _x ) N coating are as follows: evaporation source: titanium-chromium alloy (Cr composition is 100 × atomic%) determined by target composition x, arc current 100 A, base material temperature 450 ° C. In a nitrogen atmosphere, the pressure in the vacuum chamber is 30 mTorr, the DC current voltage applied to the base material is -200 V, and the processing time is 30 minutes. As a result, the overall thickness of the coating was 3.6 μm. Similarly, by changing the processing time, (Ti _1-x , Cr _x ) N
A coating was formed. Also, by changing the metal composition of the evaporation source, x
= 0.03, 0.3 and 0.7 (Ti _1-x , Cr
_x ) An N film was formed. Further, a material in which the residual stress in the coating was changed by changing the temperature of the base material was also prepared.

[Method 4] Formation of TiN / CrN coating: Evaporation source made of pure titanium (containing 0.5% by weight or less of unavoidable impurities) or pure chromium (containing 0.5% by weight or less of unavoidable impurities) , And these two evaporation sources were arranged so as to face the inner wall of the vacuum chamber.
A rotary table was placed at the center of the two evaporation sources, and the base material was attached thereto. Using an arc ion plating method, the arc current of each evaporation source is 100 A, the base material temperature is 450 ° C., the atmosphere is nitrogen, the pressure in the vacuum chamber is 30 mTorr.
r, DC voltage applied to the base material -200 V, table rotation speed 0.3 rpm, processing time 20 minutes, thickness 2μ
m of TiN / CrN coating was formed. Repetitive returns the number of laminated was 6 times. In addition, a comparative example in which the number of laminations was changed 25 times and 500 times and the same number of times was 4 times and 500 times was produced by changing the number of rotations of the table. Further, a material in which the residual stress in the coating was changed by changing the temperature of the base material was also prepared.

[Method 5] (Ti _1-x , Cr _x ) N / (T
i _1-x ′, Cr _x ′) N film formation: Titanium-chromium alloys having different compositions were prepared one by one according to the method 4 and placed facing the inner wall of the vacuum chamber. The rotation speed of the table was 0.3 rpm. The other conditions are the same as those of the method 4. A processing time of 20 minutes and a thickness of 2 μm (Ti _{1 -x} , C
(r _x ) N / (Ti _1-x ′, Cr _x ′) N coating was formed. The number of times of lamination was 6 times. Further, the number of times of lamination is changed to 10, 80
Examples were also made, and a comparative example was made in which the number of table rotations was 0.15 rpm and the number of laminations was three. Further, a material in which the residual stress in the coating was changed by changing the temperature of the base material was also prepared.

[Method 6] (Ti _1-x , Cr _x ) N → (T
i _1-x ′, Cr _x ′) N Gradient composition film formation: Titanium-chromium alloy (Cr composition is 100 × atomic%, 100 × x) determined by the target compositions x and x ′ by arc ion plating. (Atomic%) with a distance of 3
Two units were arranged in parallel with an interval of 00 mm, arc current 100 A, base material temperature 450 ° C., nitrogen atmosphere, vacuum chamber pressure 30 mTorr, DC voltage −200 applied to the base material.
V and a processing time of 60 minutes, the base material was slowly translated in parallel between the two evaporation sources to obtain a (T
i _1-x , Cr _x ) N → (Ti _1-x ′, Cr _x ′) N Graded composition coating was formed. Here, x = 0.03, x '=
0.7. In addition, a material in which the residual stress in the coating was changed by changing the temperature of the base material was also prepared.

[Method 7] Formation of TiN film: A method similar to Method 3 was used to form TiN films having different thicknesses by changing the treatment time using an evaporation source made of titanium.

The measurement of the residual stress in the vicinity of the metal surface of the mold and in the coating was carried out by the X-ray diffraction method based on the sin ² ψ method. Then, for these examples and comparative examples, the entire surface treated surface was heated in air at 600 ° C. (60 ° C.).
Second) to underwater quenching (60 seconds). The damage of the treated surface was observed with an optical microscope after the thermal cycle was applied in units of 100 times. The test results are also shown in Tables 1 and 2.

As is clear from Tables 1 and 2, it was confirmed in the examples that the generation of thermal cracks was significantly suppressed.

Test Example 2 Example 4 in Test Example 1
6, 10 and 15 and Comparative Examples 5, 6, 10 and 13 were processed into warm forging die punches (JIS steel type SKH51, Rockwell C scale hardness 53), and the die was actually subjected to warm forging. The life was evaluated. During forging, the mold surface is 700
℃. The life was determined when the dimensional accuracy of the workpiece exceeded a specified range. Table 3 shows the life evaluation results. In each example, it was confirmed that the life of the mold was greatly improved.

[0043]

[Table 3]

Test Example 3 Example 4 in Test Example 2
6, 10 and 15 and Comparative Examples 5, 6, 10 and 13 were prepared by using an assembling pin (JIS steel type SKD6) for casting aluminum alloy.
1. Processed to a Rockwell C scale hardness of 51), and the life of the cast pin was actually evaluated at the time of casting an aluminum alloy. The casting method is gravity casting, and the surface of the blanking pin is 6
It had been heated to 70 ° C. The life was determined when the dimensional accuracy of the workpiece exceeded a specified range. Table 4 shows the life evaluation results. It was confirmed that the life of the cast pin was greatly improved in the product of the present invention.

[0045]

[Table 4]

[0046]

As described above, according to the present invention, it is possible to achieve both heat crack resistance and oxidation resistance, and it is difficult to achieve a mold such as a forging die or a mold used in a high temperature atmosphere, which was difficult to achieve with the prior art. Life extension can be achieved. In particular, it is expected to be used as a forging die of an iron-based part such as an automobile part or a machine part or a casting die of an aluminum alloy part.

Claims (7)

(57) [Claims] 1. A coating mold having a nitriding layer in which nitrogen is diffused and infiltrated on the surface of a mold base material, and a ceramic film formed on the nitriding layer. Any of
Coating mold, characterized in that the Kayori configuration. (Ti _1-x , Cr _x ) N film (where x is an atomic ratio, 1.0 ≧ x ≧ 0.02) A titanium nitride film containing at least one of TiN and Ti ₂ N, and a chemical formula CrN, Cr ₂ coating composition laminated alternately five times or more and a chromium nitride layer containing at least one of N different 2 or more of _{(Ti 1-x, Cr x} ) N
(Where x is an atomic ratio and 1.0 ≧ x ≧ 0.0
2) alternately laminated 4 or more times 2. A depth of 10 μm from the surface of the mold base material.
Average compressive residual stress over 0.2 GPa,
1.5 GPa or less, the average value of the compressive residual stress of the entire ceramic coating is
0.2 GPa or more and 8 GPa or less
2. The coating mold according to claim 1, wherein: 3. A ceramic coating comprising (Ti _1-x , Cr
_x ) N (where x is the atomic ratio, 1.0 ≧ x ≧
0.02), according to claim 1 or, wherein the composition of Cr in the coating is a gradient composition that increases toward the base material side to the coating surface
2. The coating mold according to 2 . 4. A TiN film is interposed between a surface of a mold base material and a ceramic film.
3. The coating mold according to any one of 3 . 5. The method according to claim 1, wherein the thickness of the nitrided layer is at least 50 μm.
The coating mold according to any one of claims 1 to 4 , wherein the thickness is 0 µm or less. 6. A thickness of the ceramic film is 0.5μm or more, according to claim 1 to 5, characterized in that at 40μm or less
The coated mold according to any one of the above. 7. A mold applications, the coating die according to any one of claims 1 to 6, characterized in that the casting of warm or hot forging or aluminum alloy ferrous component.