JPH10237624A - Casting member excellent in molten al resistance, and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a casting member excellent in molten Al resistance, improved in erosion resistance to Al alloy without deteriorating heat retaining property, wear resistance, and heat cycle resistance, by regulating the amount of oxygen in a coating layer containing Cr and N to a specific percentage or below, at least in the outermost surface. SOLUTION: The amount of oxygen in a coating layer is regulated, at least in the outermost surface, to <=10 atomic %. When it exceeds the above percentage, the formation of an A/N reaction layer is inhibited and also a Cr oxide formed by incorporation of oxygen becomes deteriorated in thermal stability and liable to be decomposed. The amount of N in the coating layer is regulated, at least in the outermost surface, to 30-55 atomic %. The thickness of the coating layer is regulated to 5-20μm. It is preferable that a part or the whole of a base material is made of Ti alloy. The amount of oxygen in the coating layer can be regulated to <=10 atomic % by forming the coating layer on the surface of the base material by a PVD process at >=2μm/hr film-forming rate. It is preferable to use an arc ion plating process as the PVD process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting member (for example, a mold, a plunger sleeve, a plunger tip, Child pin, gate, etc.)
And a useful method for producing such castings.

[0002]

2. Description of the Related Art Die casting methods include gravity die casting, low pressure casting (differential pressure casting), high pressure casting (melt forging),
There is a die casting method and the like. Among them, the die casting method is often used for manufacturing an Al alloy casting.

[0003] In the die casting method, a molten metal is injected into a metal mold under pressure and molded. In the high-pressure casting method, a molten metal injected into a mold is further pressed to mold. Casting members used in these methods are used under more severe environments than casting members used in other gravity mold casting methods and low pressure casting methods.

[0004] Such a casting member used in a portion that comes into contact with the molten metal does not suffer from (a) melting damage due to contact with the molten metal, and (b) wear occurs under high temperature sliding conditions. (C) heat cracks do not occur under the conditions of the heat cycle of heating and cooling. That is, the casting member needs to be excellent in erosion resistance, wear resistance, and heat cycle resistance.

[0005] By the way, as a casting member used in the Al die-casting method, a die steel represented by SKD61 has been conventionally used. However, in recent years, since the heat conductivity is small and the molten metal is excellent in heat insulation, In place of the die steel, a Ti alloy such as Ti-6Al-4V is also expected to be promising. However, even when this Ti alloy was used, it could not be said that it had sufficient characteristics for erosion resistance and wear resistance.

[0006] For these reasons, various techniques have been proposed for improving the characteristics of a casting member using a Ti alloy as a base material. For example, Japanese Patent Application Laid-Open No. 64-44256 proposes a method of forming a titanium nitride film by a nitriding treatment, an oxide film by an oxidation treatment, etc. on the surface of a base material. Also, Japanese Patent Application Laid-Open Nos. H4-222469 and 4-25
In Japanese Patent No. 1650, an inner cylinder made of a composite material of Ti or a Ti alloy and ceramics is fitted inside a member such as a plunger sleeve, and a titanium boride layer is formed inside the inner cylinder by a boring treatment. For example, a method of forming titanium carbide by a gas carburizing method has been proposed. Further, Japanese Patent Application Laid-Open No. H4-222467 proposes a method of inserting an inner cylinder made of a composite material of a Ti alloy and a ceramic into a sleeve made of a Ti alloy such that the ceramic content increases toward the inner surface side. Have been.

[0007] However, these methods have been dominated by a surface treatment method in which a coating layer is formed on the surface of a Ti alloy base material by diffusion treatment. In these methods, since the diffusion coefficients of various elements into the Ti alloy are small, it is necessary to perform a diffusion treatment up to a high temperature exceeding 900 ° C. For example, in JP-A-64-44256, the nitriding temperature at the time of forming a titanium nitride film is 930 ° C. In addition, Japanese Patent Application Laid-Open Nos.
In the boring process (975 ° C.) and the carbonization process (1000 ° C.) described in No. 50, the processing temperature is 900
It is higher than ° C.

In the Ti-6Al-4V alloy, which has low thermal conductivity and is expected to be used as a casting member, the β transformation point of the crystal structure is 950 which is the β transformation point of pure Ti. When the heat treatment is performed in a temperature range of about 800 to 900 ° C. below 900 ° C. and exceeding 900 ° C., the occurrence of thermal strain and a decrease in strength of the member become remarkable. Therefore, the casting member heat-treated at a temperature exceeding 900 ° C. as described above has a problem that it cannot be applied to a member requiring a dimensional accuracy such as a sleeve.

On the other hand, in the technique disclosed in Japanese Patent Application Laid-Open No. Hei 4-224067, although the problem of occurrence of thermal distortion of the member does not occur, the structure of the sleeve becomes complicated, and the strength is reduced due to the use of ceramics. There is. In addition, there is a problem that the cost increases due to the complicated structure.

The above-mentioned Japanese Patent Application Laid-Open No. 64-44256 discloses a method suggesting the application of a sputtering method, an ion plating method or an ion implantation method as a method instead of the heat treatment in a temperature range exceeding 900 ° C. However, the point is how to apply these methods in which the coating substance directly comes from the evaporation source to the coating surface to form a uniform film on the inner surface of a cylindrical member such as a sleeve or a sprue. Was not specifically described.

In order to solve the above-mentioned technical problems, Japanese Patent Application Laid-Open No. 8-109331 discloses that a casting member (die-casting member) used for a portion that comes into contact with a molten metal has Cr and N on a base material surface. Forming a coating layer containing
As a preferred condition, it discloses that the N content in the coating layer is 30 to 55 atomic% at least on the outermost surface of the coating layer, and that the base material is partially or entirely made of a Ti alloy. This casting member was able to form a coating layer containing Cr and N at 900 ° C. or lower, so that a Ti alloy excellent in heat retention could be used as a base material. Further, by forming a coating layer containing Cr and N on the surface of this Ti alloy, a casting member excellent in all of erosion resistance, wear resistance and heat cycle resistance was obtained.

Further, the method of manufacturing the casting member uses a cylindrical base material and a rod-shaped Cr evaporation source, and inserts the Cr evaporation source into the base material, and performs arc ion plating in an N ₂ atmosphere. It discloses that a uniform film can be formed with good throwing power by forming the coating layer on the inner wall surface of the base material by performing the (AIP) method.

[0013]

Problems to be Solved by the Invention
The casting member in which the Ti-6Al-4V alloy is used as a base material in Japanese Patent Publication No. 1 is a casting member excellent in heat retention, excellent in erosion resistance, wear resistance and heat cycle resistance. However, even with such a casting member, the Al
When used for casting alloys, there have been cases in which the casting members are eroded. Further, the casting member may be melted by the rise of the casting temperature, the rise of the pressure during casting, or the change of the composition of the Al alloy. For this reason, there is a problem that the casting member in which the erosion has occurred must be replaced, and the productivity in the casting process decreases. Therefore, the present invention provides
(1) a cast member used for a part in contact with the alloy,
To provide a casting member excellent in molten Al resistance, in which the erosion resistance of an Al alloy is further improved without impairing heat retention, abrasion resistance and heat cycle resistance, and for producing this casting member. It provides a useful method.

[0014]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have made intensive studies to further improve the erosion resistance of a cast member used for a portion in contact with a molten Al alloy. . As a result of investigating the erosion resistance of the coating layer containing Cr and N in the molten aluminum, an AlN reaction layer was formed at the interface between the coating layer containing Cr and N and the molten aluminum, and this reaction layer was protected by the molten aluminum. It has been found that it acts as a film and exhibits excellent erosion resistance to molten aluminum. Further, the amount of oxygen in the coating layer containing Cr and N greatly contributes to the formation of the AlN reaction layer. That is, as the amount of oxygen in the coating layer increases, the protective film AlN
Based on the idea of inhibiting the formation of a reaction layer, Cr and N
By finding that the oxygen content in the coating layer containing 10% by mass or less can improve the erosion resistance of the cast member used in the portion in contact with the molten Al alloy, the present invention has been completed.

[0015] The invention according to claim 1 of the present invention is a casting member used for a portion in contact with a molten Al alloy, wherein a coating layer containing Cr and N is formed on the surface of a base material. The amount of oxygen in the coating layer is at least 10 at the outermost surface.
Atomic% or less. When the oxygen content in the coating layer is at least 10 atomic% at the outermost surface, the erosion resistance of the cast member can be improved. If the amount of oxygen in the coating layer is 10 atomic% or more, the formation of the AlN reaction layer is hindered, and the chromium oxide formed by containing oxygen has poor thermal stability and is likely to be decomposed. Conceivable. In addition, an excessive oxygen content will reduce the hardness of the coating layer, which is less desirable than the wear-resistant aspect. Further, in order to further improve the erosion resistance of the cast member, the amount of oxygen in the coating layer containing Cr and N is preferably set to 5 atomic% or less.

The term "at least the outermost surface of the coating layer" means that the oxygen content of the entire coating layer does not necessarily need to be 10 atomic% or less, and the outermost surface in contact with the molten metal has an oxygen content of at least 10 atomic%. %, The effect is exhibited. Therefore, it is a matter of course that a coating layer having an oxygen content exceeding 10 atomic% may be formed in a portion other than the outermost surface. However, the oxygen content of the entire coating layer is preferably 10 atomic% or less, more preferably 5 atomic% or less. Thereby, defects of the coating layer can be reduced and the quality of the coating layer can be stabilized.

According to a second aspect of the present invention, in the constitution of the first aspect, the N content in the coating layer is at least 30 to 55 atomic% at the outermost surface. N in coating layer
When the amount is at least 30 to 55 atomic% at the outermost surface, the erosion resistance of the cast member can be further improved. When the N content in the coating layer is in the range of 30 to 55 atomic%, a coating layer of a single phase of CrN, which is a crystal having a rock salt structure and having chemical stability, can be formed. Improve the quality. The N content in the coating layer is preferably 40 atomic%. By setting the N content to 40 atomic% or more, the erosion resistance of the CrN coating layer to molten Al can be remarkably improved. Further, by setting the N content in the coating layer to 40 atomic% or more, the hardness of the coating layer increases, and the wear resistance of the coating layer can be improved.

According to a third aspect of the present invention, the thickness of the coating layer is 5 to 20 μm.
m. By setting the thickness of the coating layer to 5 to 20 μm, the erosion resistance of the coating layer of the cast member can be stabilized. The thickness of the coating layer is not particularly limited, but is most preferably 5 to 20 μm. That is, if the thickness of the coating layer is too small, the base material may be melted due to defects reaching the base material such as pinholes inevitably existing in the coating layer. Therefore, the thickness is preferably at least 5 μm or more. The above-mentioned defects tend to decrease as the thickness increases, and when the thickness is 8 μm or more, the number of the defects decreases to a level where there is no practical problem.
m is more preferable. On the other hand, if the thickness is too large, the effect is not only saturated, but also the time required for forming the coating layer becomes long. Therefore, the thickness is suitably 20 μm or less, preferably 15 μm or less.

According to a fourth aspect of the present invention, in the configuration of the first or second or third aspect, the base material is partially or entirely made of a Ti alloy. By making the base material partially or entirely made of a Ti alloy, the heat retaining property and the heat cycle property of the cast member can be improved.

The type of the base material on which the coating layer is formed is not particularly limited. However, by changing the base material from a conventionally used die steel to a Ti alloy, the heat retaining property and the heat retaining property of the cast member can be improved. The heat cycle resistance can be further improved.

That is, the thermal conductivity of SKD61 is 28.
The thermal conductivity of Ti-6Al-4V is 7.1 W / m · K, which is less than 1/4 of SKD61, whereas the thermal conductivity of Ti-6Al-4V is 9 W / m · K. The heat retention becomes better as compared with the case where the die steel is used.

The Ti alloy has a thermal expansion coefficient closer to that of CrN than that of an Fe-based alloy such as SKD61. For example, the thermal expansion coefficients of Ti-6Al-4V, SKD61 and CrN are each 8.8 × 10 ^{−6 /} K, 11.3 ×
10 ⁻⁶ / K and 2.39 × 10 ⁻⁶ / K. Therefore, by applying the Ti alloy to the base material, even when used under a thermal cycle, the thermal stress caused by the difference in the thermal expansion coefficient between the coating layer and the base material becomes smaller than when SKD or the like is used. In addition, cracks are less likely to occur in the coating layer. In addition,
The part to which the Ti alloy is applied includes "part"
This is because such a case is assumed because not all of the casting members use a Ti alloy, and it is rather common to apply a Ti alloy to some of them.

According to a fifth aspect of the present invention, there is provided a cast member having excellent molten Al resistance according to any one of the first to fourth aspects, wherein the casting member is formed by a PVD method at a film forming rate of 2 μm / hr or more. The method is characterized in that the coating layer is formed on a material surface. 2 μm / hr by PVD method
By forming the coating layer on the surface of the base material at the above-described film forming rate, the amount of oxygen in the coating layer can be reduced to 10 atomic% or less, and oxygen remaining in the film forming apparatus and the wall of the film forming apparatus can be reduced. Of oxygen adsorbed on the coating layer can be suppressed.

The PVD method includes an arc ion plating (AIP) method, a hollow cathode method, a sputtering method and the like, and it is preferable to use the AIP method in the method of the present invention. The AIP method can increase the film forming rate to a maximum of about 10 μm / hr and can obtain a coating layer with a small amount of oxygen.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to Table 1. Table 1 shows the production method of the casting member of the present invention and the test results of the casting member.

A machined Ti-6Al-4V or SKD61 washed and used as a base material was used to form a coating layer shown in Table 1 to produce various casting members.
The AIP method, the sputtering method, and the ion nitriding method for comparison were used for forming the coating layer. Test material 1 and test materials 3-5
Formed a coating layer on the inner surface of the cylindrical test material shown in FIG. Further, the test material 2 and the test materials 6 to 12 each formed a coating layer on the upper surface of the flat test material. In addition, only the AIP method was used for forming the coating layer on the inner surface of the cylindrical test material. This is because it is difficult to form a uniform coating layer on the inner surface of the cylindrical test material by the sputtering method.

[0027]

[Table 1]

The method of forming the CrN coating layer on the inner surface of the cylindrical test material is as follows. As shown in FIG. While inserting a rod-shaped evaporation source 3 made of Cr, using the base material 1 as the counter electrode 2 and changing the film formation rate in the N ₂ atmosphere to 0.3 to 10 μm / hr,
The P method was performed. Samples 2, 8, and 9 were formed on the upper surface of a plate-like test material by using a Cr target (plate-like) with N ₂ as a reaction gas and changing the film formation rate by AIP method.
A coating layer was formed. For the test materials 6, 7, 10, and 11, a CrN coating layer was formed on the upper surface of the flat test material by reactive DC sputtering using a Cr target (flat) with N ₂ as a reaction gas. The SKD61 base material of the test material 12 was subjected to a nitriding treatment (550 ° C.) to form a Fe nitride film.

With respect to each of the obtained test materials, the composition of the coating layer (outermost surface), the thickness of the coating, and the erosion resistance were examined.
Table 1 shows the results. The coating layer composition is EPMA and A
It was measured by using ES together, the crystal structure of the film layer was investigated by X-ray diffraction, and the film thickness was measured by SEM.
The erosion resistance was evaluated by an immersion test in a molten Al alloy (JIS standard AC8C). The test temperature was 750 ° C,
The immersion time was measured at two levels of 3 hr and 6 hr, and the amount of erosion was measured from the change in film thickness before and after the test, and evaluated according to the following criteria. ◎: no erosion: erosion of less than 20% of coating layer △: erosion of 20% or more of coating layer ×: 100% erosion of coating layer XX: erosion of base material

The crystal structures of the coating layers of the test materials 1 to 11 other than the test material 12 are all CrN single phase, and the N content of the coating layer is 40 to 53.5 atomic%, which is a preferable N of the present invention. It was confirmed that the amount was within the range.

It was confirmed that the oxygen content of the coating layer decreased as the film formation speed increased (see Test Materials 1 to 6). In each of the test materials having a film formation rate of 2 μm / hr or more in this example, the oxygen content of the coating layer was 10 atom% or less, and the film formation rate was 2 μm / hr or less.
It is clear that the amount of oxygen in the coating layer on the surface of the base material can be reduced to 10 atomic% or less by setting it to at least μm / hr. In order to reduce the oxygen content of the coating layer to 5 atomic% or less,
The film forming speed needs to be 5 μm / hr or more.

Next, the measurement results of the erosion resistance will be described. Test materials 1 to 4 in which the oxygen content of the coating layer is 10 atomic% or less,
In the case of 8 to 10, no erosion was observed after 3 hours of immersion, and good erosion resistance was exhibited. With the immersion time of 6 hours, no erosion was observed in the test materials 1 to 3, and the test material 8 also had a practically problematic erosion amount. It has been found that the preferable range of the oxygen content of the coating layer is 5 atomic% or less, and the more preferable range is 1 atomic% or less.

Further, according to the present embodiment, the thickness of the coating layer is 5 μm.
Above, it is clear that there is no problem of erosion resistance.

Furthermore, Ti-6A which is excellent in erosion resistance
For the test materials 1, 3, and 4 using the l-4V alloy as the base material, the wear resistance, the heat cycle resistance, and the throwing power were examined. The abrasion resistance test was performed by using a pin-on-disk type sliding friction tester, using SKD61, which had been subjected to nitriding treatment, as a pin of a mating material, and sliding 1000 m at a temperature of 400 ° C. and a load of 10 kg / cm ^2. The subsequent wear was measured. The heat cycle resistance test was performed using a heat cycle tester having a high temperature bath (650 ° C.) and a low temperature bath (cold water).
A reciprocating test of both tanks was repeated so that one cycle was about 2 minutes, and a heat cycle was applied to the test material. The evaluation was made based on the number of cycles at which cracks occurred. The throwing power was evaluated by the coverage of the coating layer.

No wear of the coating layer was observed in any of the test materials, and no cracks were observed after 1000 thermal cycles. Further, the coverage was 100%. From the above results, it was confirmed that the test materials 1, 3, and 4 using the Ti-6Al-4V alloy as the base material had excellent wear resistance, heat cycle resistance, and throwing power.

The casting member of the present invention having excellent resistance to molten Al and the method for producing the same are not limited to the present embodiment.
As a casting member, in addition to the die casting method described in the embodiment, other die casting methods such as a gravity die casting method, a low pressure casting method (differential pressure casting method), and a high pressure casting method (a molten metal forging method).
Can be used. Further, the method of forming the coating layer of the casting member is not limited to the AIP method and the sputtering method of the embodiment, but may be another PVD method. further,
Depending on the material used for the base material of the casting member, a method of forming the coating layer at 900 ° C. or higher, such as a CVD method, may be used to reduce the oxygen content of the coating layer to 10 atomic% or less. By reducing the oxygen content of the coating layer to 10 atomic% or less, the erosion resistance of the casting member can be improved.

[0037]

As described above, the cast member of the present invention makes it possible to further improve the erosion resistance of an Al alloy without impairing the heat retention, abrasion resistance and heat cycle resistance. is there. Further, the method of the present invention can reduce the amount of oxygen in the coating layer, and as a result, makes it possible to manufacture a cast member having excellent erosion resistance in an Al alloy.

[Brief description of the drawings]

FIG. 1 is a schematic view for explaining one method of forming a coating layer according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylindrical base material 2 Counter electrode 3 Cr evaporation source

Claims (5)

[Claims] A casting member comprising a coating layer containing Cr and N formed on a surface of a base material and used in a portion coming into contact with a molten Al alloy, wherein the amount of oxygen in the coating layer is at least A casting member having excellent resistance to molten Al, characterized by being 10 atomic% or less at the outermost surface. 2. The casting member according to claim 1, wherein the N content in the coating layer is at least 30 to 55 atomic% at the outermost surface. 3. The casting member according to claim 1, wherein said coating layer has a thickness of 5 to 20 μm. 4. The base material is partially or entirely made of Ti.
The casting member according to claim 1, 2 or 3, which is made of an alloy. 5. A method for producing a cast member having excellent resistance to molten Al according to claim 1, wherein
Forming a coating layer on the surface of the base material at a deposition rate of 2 μm / hr or more by a method.