JP5865487B2 - Casting member and method for manufacturing the same, die casting sleeve, and die casting apparatus - Google Patents

Description

  The present invention relates to a casting member and a manufacturing method thereof, a die casting sleeve, and a die casting apparatus.

Conventionally, casting members (for example, molds and sleeves) used in contact with molten metal used for die casting of aluminum, magnesium, and alloys thereof are hot tool steels that are resistant to thermal fatigue. (Hot work tool steel) is used as a base material.
When such a casting member undergoes significant erosion to the molten metal during use, the frequency of repairing the casting member increases, and the life of the casting member is shortened.
Therefore, for the purpose of improving the erosion resistance of the casting member, a method of forming a nitrided layer in the portion of the casting member that contacts the molten metal, or a further oxide on the nitrided layer. A method for forming a layer has been proposed (see, for example, JP-A-2005-28398, JP-A-2003-13199, and JP-A-64-31957).

However, in a casting member having a structure in which a nitride layer and an oxide layer in contact with a molten metal are sequentially provided on a base material, the oxide layer is peeled off during repeated use, so that it is resistant to erosion during repeated use. May decrease.
Accordingly, an object of the present invention is to provide a casting member that maintains excellent resistance to melting even during repeated use, a manufacturing method thereof, and a die casting sleeve and a die casting apparatus provided with the casting member. is there.

The inventor has a basic structure of a casting member having a structure in which a nitride layer and an oxide layer are sequentially provided on a base material made of hot tool steel, and by specifying the configuration of the nitride layer, The knowledge that the said subject can be solved was acquired, and this invention was completed based on this knowledge.
That is, specific means for solving the above problems are as follows.

<1> A casting member used in contact with a molten metal, wherein the base material is made of hot tool steel, and nitrogen is diffused in the base material in contact with the base material, and the Vickers hardness is Nitrogen diffusion layer having a thickness of 200 μm or more and 400 μm or less, consisting of a nitrogen diffusion layer that is 50 HV or more higher than the Vickers hardness of the base material, and a nitrogen compound layer that is in contact with the nitrogen diffusion layer and is composed of a nitrogen compound containing iron and having a thickness of 5 μm to 40 μm An oxide layer containing an oxide containing iron in contact with the nitrogen compound layer and in contact with the molten metal, the oxide layer being in contact with the nitrogen compound layer and the nitrogen compound and the oxide It is the member for casting containing the mixed layer which consists of.
<2> The casting member according to <1>, wherein the oxide is at least one selected from a complex oxide having a structure in which a part of iron contained in magnetite is replaced with chromium, wustite, hematite, and magnetite. It is.
<3> The casting member according to <1> or <2>, wherein at least one of the oxides is a complex oxide having a structure in which a part of iron contained in magnetite is replaced with chromium .
<4 > The casting layer according to any one of <1> to < 3 >, wherein the mixed layer is a layer having a structure in which the oxide is formed in a pore of a porous structure made of the nitrogen compound. It is.

< 5 > A method for producing a casting member according to any one of <1> to < 4 >, wherein a base material preparation step of preparing a base material made of hot tool steel, and the base material A nitride layer forming step of forming a nitride layer by nitriding the surface by exposure to an atmosphere gas containing ammonia gas and nitrogen gas under heating at 450 ° C. to 600 ° C., and the nitride layer of the base material An oxide layer forming step of forming the oxide layer by subjecting the formed surface to an oxidizing atmosphere by exposing it to an oxidizing atmosphere under heating at 450 ° C. or higher and 600 ° C. or lower. is there.
< 6 > The method for producing a casting member according to < 5 >, wherein the atmospheric gas further contains carbon dioxide gas.
<7> The amount of the carbon dioxide gas in the atmospheric gas is 3% by volume or more and 20% by volume or less with respect to the total of the ammonia gas, the nitrogen gas, and the carbon dioxide gas. It is a manufacturing method of the member for casting.
<8> the oxide layer formation step, the nitride layer is formed surface of the base material is exposed to water vapor atmosphere as the oxidizing atmosphere under heating at 600 ° C. or less 480 ° C. or higher <5> ~ <7> The manufacturing method of the member for casting as described in any one of 7> .
<9> The nitride layer forming step is a method for producing a casting member according to any one of < 5 > to <8>, wherein the surface of the base material is exposed to the atmospheric gas for 20 hours or more and 40 hours or less. .
<10> For the casting according to any one of < 5 > to <9>, in the oxide layer forming step, the surface of the base material on which the nitride layer is formed is exposed to an oxidizing atmosphere for 1 hour or more. It is a manufacturing method of a member.

<11> A die casting sleeve provided with the casting member according to any one of <1> to < 4 >.
<12> A die casting apparatus including the casting member according to any one of <1> to < 4 >.

  ADVANTAGE OF THE INVENTION According to this invention, the member for casting and the manufacturing method of the member which were excellent in the fracturing resistance also in the time of repeated use, the sleeve for die-casting provided with the said member for casting, and a die-cast apparatus can be provided.

In the sample 2 which is an example of this invention, it is an optical microscope image (50-times multiplication factor) which shows the cross section of each layer. In sample 2 which is an example of the present invention, it is a graph which shows the relation between distance d (micrometer) from the interface of an oxide layer and a nitrogen compound layer, and Vickers hardness (Vickers hardness (HV)). In sample 2 which is an example of the present invention, it is a scanning electron microscope image (magnification 3000 times) showing a section of each layer. In the sample 7 which is a comparative example, it is a scanning electron microscope image (magnification 3000 times) which shows the section of each layer.

  Hereinafter, the casting member, the manufacturing method thereof, the die casting sleeve, and the die casting apparatus of the present invention will be described in detail.

<Casting member>
The casting member of the present invention is a casting member that is used in contact with a molten metal, and is formed of a base material made of hot tool steel and nitrogen (N) in the component of the base material in contact with the base material. Is diffused and has a Vickers hardness of 50 HV or more higher than the Vickers hardness of the base material, and a nitrogen compound layer having a thickness of 5 μm or more and 40 μm or less made of a nitrogen compound containing iron (Fe) in contact with the nitrogen diffusion layer A nitride layer having a thickness of 200 μm or more and 400 μm or less, and an oxide layer in contact with the molten metal containing an oxide containing iron (Fe) in contact with the nitrogen compound layer.

  In this specification, “Vickers hardness” refers to Vickers hardness measured according to JIS Z 2244 (1998).

Conventionally, as a casting member used in contact with molten metal, a nitride layer formed by nitriding the surface of a base material on a base material made of hot tool steel, and a base formed with a nitride layer 2. Description of the Related Art A casting member having a structure in which a nitride layer forming surface of a material is formed by oxidation treatment and an oxide layer that comes into contact with molten metal in use (during casting) is known (for example, Japanese Patent Application Laid-Open No. 2005-2005). -28398). This oxide layer contains an oxide containing iron. This oxide is a compound that is chemically stable and has low reactivity with molten metal. For this reason, by providing the casting member with the oxide layer, the melt resistance of the casting member is dramatically improved.
However, in the casting member provided with the oxide layer, the oxide layer is peeled off during repeated use (when casting is repeated. The same applies hereinafter), thereby reducing the melt resistance of the casting member. There is a case. The reason for the oxide layer peeling off during repeated use is that the thermal expansion coefficient of the oxide containing iron is larger than the thermal expansion coefficient of the base material (for example, hot tool steel). It is considered that a tensile stress acts on the oxide layer during the cooling process after casting, and the oxide layer is easily cracked by the tensile stress.

With respect to the above, in the casting member of the present invention, the peeling of the oxide layer during repetitive use is suppressed, and as a result, excellent melt resistance is maintained even during repetitive use.
The reason why this effect is achieved is assumed as follows.
That is, the casting member of the present invention is provided with an oxide layer as a layer (that is, the outermost surface layer) that comes into contact with the molten metal when the casting member is used, and from the nitrogen diffusion layer and the nitrogen compound layer. When the thickness of the resulting nitrided layer is as thick as 200 μm or more, excellent melt resistance is exhibited from the beginning of use.
Furthermore, the casting member of the present invention includes a nitrogen diffusion layer having excellent adhesion to the base material as a layer in contact with the base material, and the two layers between the nitrogen diffusion layer and the oxide layer. By interposing a nitrogen compound layer having a thickness of 5 μm or more excellent in adhesion, peeling of the oxide layer during repeated use is suppressed.
For the above reasons, it is presumed that in the casting member of the present invention, excellent melt resistance in the initial stage of use is maintained even during repeated use.

  In addition, as above-mentioned, it cannot be overemphasized that the member for casting of this invention is excellent not only in the time of repeated use but in the initial stage of use at the time of use.

By the way, in the conventional casting member, the nitrogen compound layer is generally not provided as much as possible because the nitrogen compound layer is generally more brittle than the nitrogen diffusion layer. For example, when forming a nitride layer by nitriding a base material, even if the nitrogen compound layer is formed by nitriding the base material, the nitrogen compound layer is formed as much as possible. The casting layer was used in a state where the compound layer was removed and the nitrogen compound layer was not present.
On the other hand, in the casting member of the present invention, as described above, a nitrogen compound layer having a thickness of 5 μm or more is intentionally interposed between the nitrogen diffusion layer and the oxide layer. As a result, when the nitrogen compound layer is not provided (that is, when the oxide layer is provided directly on the nitrogen diffusion layer) or when the thickness of the nitrogen compound layer is less than 5 μm, it is repeatedly used. Peeling of the oxide layer at the time is suppressed, and as a result, a decrease in the melt resistance during repeated use is suppressed.

In the present invention, the thickness of the nitride layer composed of the nitrogen diffusion layer and the nitrogen compound layer is 200 μm or more and 400 μm or less.
As a result of studies by the present inventors, it has been clarified that the melt resistance of the casting member is remarkably improved when the thickness of the nitride layer is 200 μm or more.
If the thickness of the nitrided layer is less than 200 μm, the melt resistance may decrease. From this viewpoint, the thickness of the nitride layer is 200 μm or more, preferably 250 μm or more.
On the other hand, if the thickness of the nitride layer exceeds 400 μm, the crack development resistance of the nitride layer decreases (that is, the crack progresses quickly when a heat crack occurs). On the other hand, when the thickness of the nitride layer exceeds 400 μm, the time required for forming the nitride layer becomes long (for example, 50 hours or more), and the productivity of the casting member decreases. From these viewpoints, the thickness of the nitride layer is 400 μm or less, preferably 350 μm or less.

In the present invention, the thickness of the nitride layer is the sum of the thickness of the nitrogen diffusion layer and the thickness of the nitrogen compound layer.
A method for measuring the thickness of the nitride layer, the thickness of the nitrogen diffusion layer, and the thickness of the nitrogen compound layer will be described later.

In the present invention, the thickness of the nitrogen compound layer is not less than 5 μm and not more than 40 μm.
When the thickness of the nitrogen compound layer is less than 5 μm, the oxide layer is easily peeled off. Furthermore, when the thickness of the nitrogen compound layer is less than 5 μm, when the oxide layer is formed, oxygen diffuses to the interface between the nitrogen compound layer and the nitrogen diffusion layer, and an oxide is formed at the interface. In some cases, the adhesion between the nitrogen compound layer and the nitrogen diffusion layer may also decrease (see FIG. 4 described later). From these viewpoints, the thickness of the nitrogen compound layer is 5 μm or more, preferably 10 μm or more.
On the other hand, when the thickness of the nitrogen compound layer exceeds 40 μm, the above-mentioned crack resistance of the nitrogen compound layer is lowered. From this viewpoint, the thickness of the nitrogen compound layer is 40 μm or less, preferably 30 μm or less, and more preferably 25 μm or less.

In the present invention, the thickness of the nitrogen compound layer refers to a section obtained by cutting the casting member along the thickness direction of each layer (nitride layer and oxide layer; the same shall apply hereinafter), nital (1% by volume of nitric acid). Nitrogen alcohol solution containing 5% by volume or less), and the cross section after the corrosion is observed with a scanning electron microscope (hereinafter also referred to as “SEM”), and this SEM image (see, for example, FIG. 3) Refers to the value measured based on
According to this measurement, since the interface between the nitrogen compound layer and the other layer becomes clear due to the corrosion, the thickness of the nitrogen compound layer can be measured. Here, the other layers are an oxide layer (a mixed layer when a mixed layer is present in the oxide layer) and a nitrogen diffusion layer.
For an example of measuring the thickness of the nitrogen compound layer, Example 1 (FIGS. 1 and 3) described later can be referred to.

In the present invention, the thickness of the nitride layer refers to a value measured as the distance from the interface between the oxide layer and the nitrogen compound layer to the interface between the nitrogen diffusion layer and the base material.
In the present invention, the thickness of the nitrogen diffusion layer refers to a value measured as the distance from the interface between the nitrogen compound layer and the nitrogen diffusion layer to the interface between the nitrogen diffusion layer and the base material.
Here, “distance” refers to the distance in the thickness direction of the nitrogen diffusion layer (the same applies hereinafter).
In addition, the interface between the oxide layer and the nitrogen compound layer and the interface between the nitrogen compound layer and the nitrogen diffusion layer are determined by an SEM image.
Further, the interface between the nitrogen diffusion layer and the base material is based on the relationship between the interface between the oxide layer and the nitrogen compound layer or the surface of the casting member and the Vickers hardness (see, for example, FIG. 2). It is determined as a position showing Vickers hardness 50HV higher than the Vickers hardness of the base material.
For an example of measuring the thickness of the nitride layer and the thickness of the nitrogen diffusion layer, Example 1 (FIGS. 1 to 3) described later can be referred to.

  Next, each component of the casting member of the present invention will be described.

(Base material)
The casting member of the present invention includes a base material made of hot tool steel.
There is no restriction | limiting in particular as said hot tool steel, For example, the alloy tool steel material for hot molds among the alloy tool steel materials prescribed | regulated by JISG4404 (2000), Unexamined-Japanese-Patent No. 2009-221594 Known hot tool steels described in JP 2008-095190 A, JP 2008-095181 A, JP 2006-213990 A, International Publication No. 2010/074017 pamphlet, and the like can be used. .
Among these, from the viewpoint of availability and the like, among the alloy tool steel materials defined in JIS G 4404 (2000), an alloy tool steel material for a hot die is preferable, and among these, JIS G 4404 (2000). SKD4, SKD5, SKD6, SKD61, and SKD8 are more preferable, and SKD61 is particularly preferable.
Further, as the hot tool steel, a hot tool steel having a novel composition obtained by improving the composition of a known hot tool steel may be used.
Further, as the hot tool steel, a hot tool steel that has been subjected to quenching and tempering may be used.

Further, from the viewpoint of including a composite oxide ((Fe, Cr) ₃ O ₄ ) having a structure in which a part of Fe contained in magnetite is replaced with Cr in the oxide layer described later, the above hot tool steel is used. It is also preferable to use a hot work tool steel containing 1 mass% or more of Cr (preferably 2 mass% or more, more preferably 4 mass% or more, particularly preferably 4.80 mass% or more). In the hot tool steel containing 1% by mass or more of Cr, the upper limit of the Cr content is, for example, 5.50% by mass.

The base material may contain inevitable impurities other than the hot tool steel.
For example, a trace amount of nitrogen may be diffused as an inevitable impurity in a region including a contact surface with the nitrogen diffusion layer in the base material (for example, a distance d in FIG. 2 described later is 300 μm or more and 350 μm or less). Area).
The base material may be hot tool steel that has been quenched and tempered.

(Nitride layer)
The casting member of the present invention includes a nitride layer.
The nitride layer is composed of a nitrogen diffusion layer that is in contact with the base material, and a nitrogen compound layer that is in contact with the nitrogen diffusion layer.
Hereinafter, details of these layers will be described.

-Nitrogen diffusion layer-
The nitrogen diffusion layer is a layer in which nitrogen is diffused in the component of the base material.
This nitrogen diffusion layer is a layer with high hardness. Specifically, the Vickers hardness of the nitrogen diffusion layer is 50 HV or more higher than the Vickers hardness of the base material.
This nitrogen diffusion layer itself also has the effect of improving the melt resistance of the casting member.

  This nitrogen diffusion layer is a layer in which nitrogen is diffused (solid solution) in a matrix composed of the components of the base material. In the nitrogen diffusion layer (in the matrix), a part of the diffused nitrogen may be combined with the nitride forming element in the component of the base material to form a fine nitride.

  When the Vickers hardness varies depending on the distance from the surface of the casting member (or the interface between the oxide layer and the nitrogen compound layer) in the base material, the above “Vickers hardness of the base material” The Vickers hardness of the area | region where the change of Vickers hardness when the distance from the surface (or interface of an oxide layer and a nitrogen compound layer) of a member changes 25 micrometers is 10 HV or less.

-Nitrogen compound layer-
The nitrogen compound layer is a layer in contact with the nitrogen diffusion layer, and is a layer having a thickness of 5 μm or more and 40 μm or less made of a nitrogen compound containing iron (Fe).
Since this nitrogen compound layer is a layer having excellent adhesion to the nitrogen diffusion layer and adhesion to the oxide layer, by providing this nitrogen compound layer, peeling of the oxide layer during repeated use ( Hereinafter, it is also simply referred to as “exfoliation of the oxide layer”.

  More specifically, regarding the adhesion between the nitrogen compound layer and the nitrogen diffusion layer, since the nitrogen compound layer is a layer in contact with the nitrogen diffusion layer, an oxide (for example, iron oxide) is interposed between the nitrogen compound layer and the nitrogen diffusion layer. ) Does not exist. Thereby, since peeling of both at the interface between the nitrogen compound layer and the nitrogen diffusion layer is suppressed, peeling of the oxide layer from the casting member is suppressed.

Moreover, the nitrogen compound containing iron, which constitutes the nitrogen compound layer, is a substance that has low reactivity with the molten metal and has high resistance to erosion with respect to the molten metal. For this reason, the nitrogen compound layer itself also has the effect of improving the melt resistance of the casting member.
The nitrogen compound containing iron is not particularly limited as long as it is a compound in which at least iron (Fe) and nitrogen (N) are covalently bonded. For example, γ′-Fe ₄ N, ε-Fe _2-3 N And composite nitrides containing iron and other elements other than iron.
The nitrogen compound containing iron contained in the nitrogen compound layer may be one type or two or more types.
Further, the nitrogen compound layer may contain inevitable impurities in addition to the nitrogen compound containing iron.

(Oxide layer)
The casting member of the present invention includes an oxide layer containing an oxide containing iron as a layer in contact with the nitrogen compound layer. When the casting member is used, the surface of the oxide layer comes into contact with the molten metal.
The oxide containing iron is not particularly limited as long as it is a compound in which at least iron (Fe) and oxygen (O) are covalently bonded. For example, FeO (also called wustite), Fe ₂ O ₃ (hematite) And iron oxide such as Fe ₃ O ₄ (also called magnetite). Among these, as the iron oxide, Fe ₃ O ₄ (magnetite) is particularly preferable from the viewpoint of excellent corrosion resistance.
As oxide containing iron, composite oxide containing elements other than iron and iron (e.g., described later _{(Fe, Cr) 3 O 4} ) can be cited.
The oxide containing iron contained in the oxide layer may be only one type or two or more types.

The oxide layer preferably includes a mixed layer containing the nitrogen compound and the oxide as a layer in contact with the nitrogen compound layer.
Thereby, since the adhesiveness of the oxide layer containing this mixed layer and a nitrogen compound layer can be improved more, peeling of an oxide layer can be suppressed more.
Here, the content of the oxide containing iron in the mixed layer is preferably 10% by mass or more, more preferably 20% by mass or more, and further preferably 30% by mass or more with respect to the entire mixed layer. And particularly preferably 40% by mass or more. Further, the content of the oxide is preferably 90% by mass or less, more preferably 80% by mass or less, still more preferably 70% by mass or less, and particularly preferably 60% by mass with respect to the entire mixed layer. % Or less.
Further, the content of the nitrogen compound in the mixed layer is preferably 10% by mass or more, more preferably 20% by mass or more, still more preferably 30% by mass or more, particularly with respect to the entire mixed layer. Preferably it is 40 mass% or more. The content of the nitrogen compound is preferably 90% by mass or less, more preferably 80% by mass or less, still more preferably 70% by mass or less, and particularly preferably 60% by mass with respect to the entire mixed layer. % Or less.

  The preferred mode for forming this mixed layer is that the nitrogen compound layer is first formed as a layer having a porous structure on the surface layer portion, and then oxidized on the nitrogen compound layer (the surface layer portion side having a porous structure). In this embodiment, the pores of the porous structure are oxidized by forming a physical layer, and oxides are formed in the pores. In this embodiment, the surface layer portion (having a porous structure) of the nitrogen compound layer, which was a part of the nitrogen compound layer at the time before forming the oxide layer, is mixed as described above after the oxide layer is formed. Layer (ie part of the oxide layer). In the mixed layer of this embodiment (for example, the mixed layer 42 in FIG. 3), the anchor effect is exhibited in a region including the interface with the nitrogen compound layer (that is, the mixed layer) in the oxide layer. Adhesion with the physical layer is further improved, and as a result, peeling of the oxide layer is further suppressed.

  The content of the oxide containing iron in the oxide layer is preferably 10% by mass or more, more preferably 20% by mass or more, and further preferably 30% by mass or more with respect to the entire oxide layer. And particularly preferably 40% by mass or more. Further, the content of the oxide is preferably 90% by mass or less, more preferably 80% by mass or less, still more preferably 70% by mass or less, and particularly preferably 60% by mass or less with respect to the entire oxide layer. It is below mass%.

In addition, as at least one of the oxides containing iron, a complex oxide having a structure in which part of Fe contained in magnetite (Fe ₃ O ₄ ) is replaced by Cr (hereinafter referred to as “(Fe, Cr) ₃ O ₄ ”) is preferable. Here, (Fe, Cr) ₃ O ₄ is a compound having a spinel structure, like magnetite (Fe ₃ O ₄ ).
When the oxide layer contains (Fe, Cr) ₃ O ₄ , adhesion between the oxide layer and the nitrogen compound layer is further improved, and peeling of the oxide layer is further suppressed.
Moreover, as a method of forming the oxide layer containing (Fe, Cr) ₃ O ₄ , as described above, Cr is 1% by mass or more (preferably 2% by mass or more, more preferably 4% by mass or more, particularly It is preferable to use a base material made of hot tool steel containing 4.80% by mass or more), forming the nitride layer on the base material, and then forming an oxide layer. According to this method, Cr can be easily supplied from the base material to the oxide layer to be formed, and (Fe, Cr) ₃ O ₄ can be easily contained in the oxide layer.

Although there is no restriction | limiting in particular in the thickness of the said oxide layer, From a viewpoint of improving a melt-proof property more, 1 micrometer or more is preferable and 2 micrometers or more are more preferable.
Further, the thickness of the oxide layer is preferably 20 μm or less, more preferably 10 μm or less, from the viewpoint of further suppressing peeling during repeated use.

  The nitride layer and the oxide layer described above are formed by subjecting the base material to surface treatment (for example, by sequentially performing nitriding and oxidizing treatment). It is preferable that

More specifically, the nitride layer is preferably a layer formed by nitriding the base material.
Examples of the nitriding treatment include a treatment in which the surface of the base material is exposed to an atmospheric gas containing ammonia gas and nitrogen gas (preferably further carbon dioxide gas) under heating.
In addition, the nitriding method can be a known method, but the nitrided layer can be formed by adjusting the nitriding conditions.
More preferable conditions for the nitriding treatment will be described later.

The oxide layer is preferably a layer formed by performing an oxidation treatment on the nitride layer forming surface side of the base material on which the nitride layer is formed.
Examples of the oxidation treatment include treatment exposed to an oxidizing atmosphere (for example, an air atmosphere or a water vapor atmosphere, preferably a water vapor atmosphere) under heating.
In addition, the oxidation treatment method can be a known method.
Examples of the treatment exposed to the water vapor atmosphere include known treatments called homotreatment and steam treatment.
More preferable conditions for the oxidation treatment will be described later.

  The casting member of the present invention may appropriately include known components in addition to the components described above.

The casting member of the present invention is a member used in contact with molten metal.
As this molten metal, a known aluminum alloy (for example, an aluminum alloy for die casting) can be suitably used. In addition, the casting member of the present invention can be expected to be effective when a melted metal is used which is a known zinc alloy (for example, a die casting zinc alloy).

  Further, the casting member of the present invention can be suitably used for die casting. For example, it can be used as mold components such as inserts and cores, core pins, sleeves, and the like, which are components of the die casting apparatus. Among these, the sleeve is an application in which higher resistance to melting damage is important because high-temperature molten metal has been in contact for a long time. Therefore, the casting member of the present invention having excellent melt resistance is optimal for a die casting sleeve.

<Die-casting sleeve, die-casting device>
The die casting sleeve of the present invention includes the casting member of the present invention.
The die casting apparatus of the present invention includes the casting member of the present invention (preferably as a die casting sleeve).
According to the die-casting sleeve or the die-casting apparatus of the present invention, it is possible to perform die-casting while maintaining excellent melt resistance from initial use to repeated use. Thereby, the repair frequency of the casting member can be reduced, and the life of the casting member can be extended.

<Method for producing casting member>
Although there is no restriction | limiting in particular in the method of manufacturing the casting member of this invention, For example, the base material preparation process which prepares the base material which consists of hot tool steel, and the surface of the said base material is 450 degreeC or more and 600 degrees C or less A nitride layer forming step of forming a nitride layer by nitriding by exposure to an atmospheric gas containing ammonia gas and nitrogen gas under heating, and a surface of the base material on which the nitride layer is formed is 450 ° C. or higher and 600 ° C. A method for producing a casting member including an oxide layer forming step in which an oxide layer is formed by oxidation treatment by exposure to an oxidizing atmosphere under heating at a temperature of 0 ° C. or lower is suitable.

  In the present manufacturing method, the hot tool steel, the base material, the nitrided layer, the oxide layer, and the like are as described in the above-mentioned section “Casting member”, and the preferred ranges are also the same.

(Nitride layer forming process)
In the nitriding layer forming step, the surface of the base material is subjected to nitriding treatment by exposure to an atmosphere gas containing ammonia gas and nitrogen gas under heating at 450 ° C. or higher and 600 ° C. or lower to form the nitride layer on the base material. It is a process.
This step can be performed by a normal nitriding method using a furnace.
In this step, the exposure time to the atmospheric gas is not particularly limited, but is preferably 20 hours or longer, more preferably 24 hours or longer, still more preferably 30 hours or longer, and particularly preferably 36 hours or longer. If the time is 20 hours or more, the thickness of the formed nitride layer can be easily adjusted to 200 μm or more, and the thickness of the formed nitrogen compound layer can be easily adjusted to 5 μm or more.
Further, the exposure time to the atmospheric gas is preferably 40 hours or less. When the time is 40 hours or less, the thickness of the formed nitride layer is easily adjusted to 400 μm or less, and the thickness of the formed nitrogen compound layer is easily adjusted to 40 μm or less.

Moreover, it is preferable that the said atmospheric gas contains a carbon dioxide gas further from the point which forms a nitrogen compound layer easily.
In this case, the amount of carbon dioxide gas in the atmospheric gas is preferably 3% by volume or more, and more preferably 5% by volume or more with respect to the total of ammonia gas, nitrogen gas, and carbon dioxide gas. The amount of the carbon dioxide gas is preferably 20% by volume or less, and more preferably 15% by volume or less based on the total of ammonia gas, nitrogen gas, and carbon dioxide gas.

  Moreover, although the heating temperature in this process is 450 degreeC or more and 600 degrees C or less, it is preferable that they are 500 degreeC or more and 600 degrees C or less, and it is more preferable that they are 540 degreeC or more and 600 degrees C or less. If the heating temperature is 500 ° C. or higher, it is easy to adjust the thickness of the formed nitride layer to 200 μm or higher.

(Oxide layer formation process)
In the oxide layer forming step, the surface of the base material on which the nitride layer is formed is oxidized by exposing it to an oxidizing atmosphere under heating at 450 ° C. or higher and 600 ° C. or lower, and the oxide layer is formed on the nitride layer. It is a process of forming a layer.
This step can be performed by a normal oxidation treatment method using a furnace.
In this step, the time for exposure to the oxidizing atmosphere is not particularly limited, but is preferably 1 hour or longer and more preferably 1.5 hours or longer from the viewpoint of more suitably producing iron oxide.
Although there is no restriction | limiting in particular in the upper limit of the time exposed to oxidizing atmosphere, From viewpoints, such as productivity, this time is 5 hours or less, 3 hours or less are more preferable, and 2 hours or less are especially preferable.

The oxidizing atmosphere is not particularly limited as long as it is an atmosphere capable of oxidizing iron, and examples thereof include an air atmosphere and a water vapor atmosphere.
As the oxidizing atmosphere, a steam atmosphere is preferable because Fe ₃ O ₄ (further, Fe ₃ O ₄ and (Fe, Cr) ₃ O ₄ ) can be easily generated.

Moreover, although the heating temperature in this process is 450 degreeC or more and 600 degrees C or less, it is preferable that they are 480 degreeC or more and 600 degrees C or less, and it is more preferable that they are 500 degreeC or more and 600 degrees C or less. If the heating temperature is 480 ° C. or higher, _Fe 3 _{O 4} (more _{(Fe, Cr) 3 O 4} ) can be more easily generated.

Moreover, this manufacturing method may have another process as needed.
Examples of the other steps include a step of quenching and tempering the base material prior to the nitride layer forming step.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
Below, the measurement of Vickers hardness was performed on the conditions of 50 g of load based on JISZ2244 (1998).

[Example 1]
Samples 1 to 9 were produced as casting members, and the melt resistance (melting rate) during repeated use was evaluated.
Hereinafter, the details will be described focusing on the sample 2.

<Preparation of Sample 2>
A hot tool steel of SKD61 defined in JIS-G-4404 (alloy tool steel) was processed into a cylindrical shape having a diameter of 10 mm and a height of 90 mm to obtain a base material.
This base material was quenched and tempered, and adjusted to have a Rockwell hardness (HRC) specified in JIS G 0202 of about 45 HRC.
Nitriding treatment and oxidation treatment under the conditions shown in Table 1 were sequentially performed on the entire surface of the base material after the hardness adjustment, and a nitride layer and an oxide layer were sequentially formed on the entire surface of the base material to obtain Sample 2.
Here, the nitriding treatment was performed in a reactor having a total pressure of 101 kPa into which an atmospheric gas having the composition shown in Table 1 was introduced.
The oxidation treatment was performed in a reactor having a total pressure of 101 kPa into which water vapor was introduced.

  In the heating condition column of Table 1, “h” indicates time. For example, “36h” indicates “36 hours”.

<Measurement of sample 2>
The produced sample 2 was cut along the thickness direction (depth direction) of the nitride layer and the oxide layer, and the following measurements were performed on the obtained cross section.
The measurement results are shown in Table 1 below.

(Measurement of nitrogen compound layer thickness)
The cross section was polished, and then the cross section was corroded with nital (nitric acid ethanol solution containing 5% by volume of nitric acid). Then, this cross section was observed with SEM (magnification 3000 times) (see FIG. 3), and the thickness of the nitrogen compound layer was measured based on the contrast in this SEM image.

(Measurement of thickness of nitride layer and nitrogen diffusion layer)
First, the position (depth) inside the base material was estimated based on the contrast of the optical microscope image (FIG. 1) of the cross section.
Next, in the cross section, Vickers hardness at each measurement point was sequentially measured in accordance with JIS Z 2244 (1998) from the surface side of the casting member to the base material side. By this series of Vickers hardness measurements, the relationship between the distance d from the interface between the oxide layer and the nitrogen compound layer (the distance in the thickness direction of each layer) and the Vickers hardness was determined (FIG. 2).
Based on this relationship, the measured value when the change in Vickers hardness when the distance d was changed by 25 μm inside the base material was 10 HV or less was defined as “Vickers hardness of base material”. Furthermore, the position showing the Vickers hardness 50 HV higher than the “Vickers hardness of the base material” was set as the position of the interface between the nitrogen diffusion layer and the base material.

Next, based on the above Vickers hardness measurement results, optical microscope observation results, and SEM observation results, the distance from the interface between the oxide layer and the nitrogen compound layer to the interface between the nitrogen diffusion layer and the base material is determined. The distance was the thickness of the nitride layer.
Further, the distance from the interface between the nitrogen compound layer and the nitrogen diffusion layer to the interface between the nitrogen diffusion layer and the base material was determined, and this distance was defined as the thickness of the nitrogen diffusion layer.

FIG. 1 is an optical microscope image (magnification 50 times) showing a cross section of Sample 2 taken along the thickness direction of a nitride layer and an oxide layer.
FIG. 2 is a result of measuring Vickers hardness in a cross section obtained by cutting the sample 2 along the thickness direction of the nitride layer and the oxide layer, and the distance from the interface between the oxide layer and the nitrogen compound layer. It is a graph which shows the relationship between d (micrometer) and Vickers hardness (Vickers hardness (HV)).

As shown in FIG. 1, in the sample 2, it is confirmed that the nitrogen diffusion layer 32 is formed on the base material 10, and the nitrogen compound layer 34 and the oxide layer 40 are formed on the nitrogen diffusion layer 32. It was.
Further, from FIG. 2, in Sample 2, the position where the Vickers hardness is 50 HV higher than the Vickers hardness (about 430 HV) of the base material, that is, the position where the distance d is 300 μm, is the base material 10 and the nitrogen diffusion layer 32. Interface.

FIG. 3 is an SEM image (magnification 3000 times) showing a cross section of each layer of sample 2.
As shown in FIG. 3, in the sample 2, it was confirmed that the nitrogen compound layer 34 is interposed between the oxide layer 40 including the surface of the sample 2 and the nitrogen diffusion layer 32. Specifically, the nitrogen compound layer 34 and other layers were distinguished by the difference in solubility in nital.
The nitride layer 30 in the sample 2 includes a nitrogen diffusion layer 32 and a nitrogen compound layer 34.
In addition, a mixed layer 42 was confirmed on the interface side with the nitrogen compound layer 34 in the oxide layer 40. 3 that the mixed layer 42 has a structure in which an oxide is formed in the porous pores.

(Component analysis of oxide layer)
The components of the oxide layer were analyzed by an X-ray diffraction test.

<Evaluation of melting rate (%) of sample 2>
About the sample 2 produced above, the melting loss rate (%) was evaluated as follows. This evaluation shows that the lower the erosion rate (%), the better the erosion resistance during repeated use.
First, an aluminum alloy ADC12 (JIS-H-5302) for die casting was melted to form a molten metal, and the temperature of the molten metal was maintained at 700 ° C.
Next, the weight of the sample 2 is measured (the weight measured here is hereinafter referred to as “weight before immersion”), and a portion from one end surface of the sample 2 after the weight measurement to 40 mm is measured. And immersed in the above-mentioned 700 ° C. molten metal (hereinafter, this state is referred to as “initial state”). From this initial state, the sample 2 was moved up and down with an amplitude of 20 mm at 90 times per minute for 5 hours (that is, the portion from one end surface of the sample 2 to 20 mm was always immersed in molten metal during this exercise). doing).
The sample 2 after the above 5 hours of movement was taken out of the molten metal, and this sample 2 was alkali washed. The sample 2 after the alkali cleaning was dried, and the weight of the dried sample 2 was measured (the weight measured here is hereinafter referred to as “weight after immersion”).
Based on the above “weight before immersion” and the above “weight after immersion”, the erosion rate (%) was calculated according to the following formula 1.
The calculated melt loss rate (%) is shown in Table 1 below.

  Melting rate (%) = ((Weight before immersion−Weight after immersion) / (Weight before immersion)) × 100 Formula 1

<Production, Measurement, and Evaluation of Sample 1 and Sample 3 to Sample 9>
In the preparation, measurement, and evaluation of Sample 2, the conditions of nitriding treatment and oxidation treatment were changed as shown in Table 1 below, and Sample 1, Sample 3 to Sample 9 were prepared, measured, and evaluated.
Here, in Samples 4, 6, and 8, the water vapor atmosphere in the oxidation treatment of Sample 2 was changed to an air atmosphere.
Sample 8 was subjected to nitriding treatment, and then the formed nitrogen compound layer was removed by shot blasting, and oxidation treatment was performed after the removal.
Sample 9 was not oxidized.
The results of measurement and evaluation are shown in Table 1 below.

  As shown in Table 1, the samples 1 to 5 which are examples of the present invention have a lower erosion rate (%) than the samples 6 to 9 which are comparative examples, and are resistant to erosion during repeated use. It was confirmed to be excellent.

Specifically, in Sample 1, the thickness of the nitrided layer was thinner than that of Sample 9, but due to the formation of the oxide layer, the melting loss rate was lower than that of Sample 9.
Sample 2 is a sample obtained by extending the time of nitriding treatment in Sample 1 and further increasing the thickness of the nitride layer. This sample 2 showed a lower melting rate than the sample 1.
In samples 1 and 2, the X-ray diffraction analysis, as a component of the oxide layer, in addition to the magnetite _(Fe 3 _{O 4),} a part of the Fe contained in magnetite _(Fe 3 _{O 4)} is replaced with Cr structure Complex oxide ((Fe, Cr) ₃ O ₄ ) was detected.

Sample 3 and sample 4 are obtained by changing the oxidation treatment conditions of sample 2.
Among these, in Sample 3 with a lower oxidation treatment temperature, magnetite (Fe ₃ O ₄ ) was detected as a component of the oxide layer, but (Fe, Cr) ₃ O ₄ ) was not detected, and Sample 2 and In comparison, the erosion rate was slightly higher.
In addition to magnetite (Fe ₃ O ₄ ), hematite (Fe ₂ O ₃ ) was also detected in the oxide layer of Sample 4 in which the atmosphere of the oxidation treatment was an air atmosphere. In this sample 4, the melting loss rate was slightly higher than in samples 2 and 3.

Sample 5 is obtained by changing the nitriding conditions of sample 3.
Specifically, the sample 5 is prepared by using the nitriding atmosphere gas (mixed gas of ammonia gas, carbon dioxide gas, and nitrogen gas) in the sample 3 as a conventional atmosphere gas (mixed ammonia gas and nitrogen gas) similar to the sample 9. Gas).
In this sample 5, the melting rate was slightly higher than that of the sample 3.

Samples 6 to 8 which are comparative examples are samples in which an oxide layer is formed on a nitride layer, as in the present invention.
However, in Sample 6, since the time for the nitriding treatment was short and the nitrided layer was thin, almost no improvement in melt resistance was seen compared to Sample 9.

Sample 7 is a sample in which the nitriding time was further shorter than that of sample 6 and the nitride layer was thin, and in addition, the nitrogen compound layer was also thin.
In this sample 7, during the evaluation of the erosion rate, in addition to the early peeling at the interface between the oxide layer and the nitrogen compound layer, the peeling also occurred at the interface between the nitrogen compound layer and the nitrogen diffusion layer, The erosion rate was high.

FIG. 4 is an SEM image (magnification 3000 times) showing a cross section of each layer of the sample 7.
As shown in FIG. 4, in the sample 7, as in the sample 2 (FIG. 3), the nitrogen compound layer 34 and the oxide layer 40 were sequentially formed on the nitrogen diffusion layer 32.
However, in the sample 7 in which the nitrogen compound layer 34 is thin, the oxide layer 50 shown in dark black in the SEM image is formed between the nitrogen diffusion layer 32 and the nitrogen compound layer 34.
In the sample 7, the presence of the oxide layer 50 reduces the adhesion between the nitrogen diffusion layer 32 and the nitrogen compound layer 34, and early peeling occurs at the interface between the nitrogen diffusion layer 32 and the nitrogen compound layer 34. It is thought to have happened.

  In Sample 8 where no nitrogen compound layer was present, the oxide layer was peeled off. And since there was no nitrogen compound layer under the peeled oxide layer, it resulted in a large melting loss rate.

[Example 2]
<Preparation of sleeve for die casting>
As a die casting sleeve, a sleeve A (untreated) and a sleeve B (untreated) having dimensions (outer diameter × inner diameter × length) as shown in Table 2 were prepared. The base material of the sleeve is SKD61.

First, nitriding treatment was performed on the surfaces of these sleeves under conditions of 530 ° C. × 36 h at an atmosphere gas flow ratio of ammonia: nitrogen = 1: 1 to form nitrided layers. The structure of the formed nitride layer was substantially the same as the structure of the nitride layer in Sample 9 (Comparative Example) in Table 1.
Thus, sleeve A (comparative example) and sleeve B (comparative example) were obtained.

Next, the sleeve A (comparative example) and the sleeve B (comparative example) were oxidized (520 ° C. × 1.5 h in a water vapor atmosphere) to form an oxide layer on the nitride layer in each sleeve.
The configuration of the formed oxide layer was substantially the same as the configuration of the oxide layer in Sample 1 of Table 1.
Thus, sleeve A (invention example) and sleeve B (invention example) were obtained.

<Evaluation (Die Casting)>
-Evaluation of sleeve A (example of the present invention)-
The sleeve A (example of the present invention) was loaded into a 1650 t cold chamber type die casting apparatus, and die casting of an aluminum alloy ADC12 (JIS-H-5302) for die casting was performed. Then, the number of shots until the melt damage increased and the sleeve had to be replaced was counted, and this number of shots was defined as the “number of possible shots”.

-Evaluation of sleeve A (comparative example)-
In the evaluation of sleeve A (invention example), sleeve A (invention example) was changed to sleeve A (comparative example), except that sleeve A (invention example) was changed to sleeve A (invention example). ) Was evaluated.

-Evaluation of sleeve B (example of the present invention)-
The sleeve B (example of the present invention) was loaded into a 650 t cold chamber type die casting apparatus, and die casting of an aluminum alloy ADC12 (JIS-H-5302) for die casting was performed. Then, the number of shots until the melt damage increased and the sleeve had to be replaced was counted, and this number of shots was defined as the “number of possible shots”.

-Evaluation of sleeve B (comparative example)-
In the evaluation of sleeve B (invention example), sleeve B (invention example) was changed to sleeve B (comparative example), except that sleeve B (invention example) was changed to sleeve B (invention example). ) Was evaluated.

  The above evaluation results are shown in Table 2 below.

As shown in Table 2, the sleeve A (comparative example) had a large melting loss after 60,000 shots and needed to be replaced, but the sleeve A (example of the present invention) could be used up to 120,000 shots. .
Further, in the evaluation of the sleeve B having a diameter smaller than that of the sleeve A, the sleeve B (comparative example) had a large melting loss at the time of 30,000 shots, and the sleeve B (example of the present invention) had to be replaced up to 60,000 shots. Could be used.

The entire disclosure of Japanese Application 2012-084683 is incorporated herein by reference.
All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually described to be incorporated by reference, Incorporated herein by reference.

Claims (12)

A casting member used in contact with molten metal,
A base material made of hot tool steel,
Nitrogen diffusion layer in contact with the base material and nitrogen diffused into the base material, the Vickers hardness is 50HV or more higher than the Vickers hardness of the base material, and a nitrogen compound containing iron in contact with the nitrogen diffusion layer A nitride layer composed of a nitrogen compound layer having a thickness of 5 μm or more and 40 μm or less, and a thickness of 200 μm or more and 400 μm or less;
An oxide layer in contact with the molten metal containing an oxide containing iron in contact with the nitrogen compound layer;
With
The said oxide layer is a member for casting containing the mixed layer which consists of the said nitrogen compound and the said oxide in contact with the said nitrogen compound layer.   2. The casting member according to claim 1, wherein the oxide is at least one selected from a composite oxide having a structure in which a part of iron contained in magnetite is replaced with chromium, wustite, hematite, and magnetite.   The casting member according to claim 1 or 2, wherein at least one of the oxides is a composite oxide having a structure in which a part of iron contained in magnetite is replaced with chromium. The mixed layer, casting member according to any one of claims 1 to 3 wherein the oxide pores of the porous structure consisting of the nitrogen compound is a layer of the formed structure. A method for producing the casting member according to any one of claims 1 to 4 ,
A base material preparation step for preparing a base material made of hot tool steel;
A nitride layer forming step of forming the nitride layer by performing nitriding treatment by exposing the surface of the base material to an atmosphere gas containing ammonia gas and nitrogen gas under heating at 450 ° C. or higher and 600 ° C. or lower;
An oxide layer forming step of forming the oxide layer by subjecting the surface of the base material on which the nitride layer is formed to an oxidizing atmosphere by heating at 450 ° C. or higher and 600 ° C. or lower;
The manufacturing method of the member for casting containing this. The method for producing a casting member according to claim 5 , wherein the atmospheric gas further contains carbon dioxide gas. The casting member according to claim 6, wherein an amount of the carbon dioxide gas in the atmospheric gas is 3% by volume or more and 20% by volume or less with respect to a total of the ammonia gas, the nitrogen gas, and the carbon dioxide gas. Manufacturing method. The said oxide layer formation process exposes the surface in which the said nitride layer of the said base material was formed to the water vapor | steam atmosphere as said oxidizing atmosphere under the heating of 480 degreeC or more and 600 degrees C or less . A manufacturing method of the member for casting given in any 1 paragraph . The nitride layer forming step, the manufacturing method of the cast member according to the surface of the base material in any one of the atmospheric gas in the exposed 20 hours or more 40 hours or less claims 5 to claim 8. The production of a casting member according to any one of claims 5 to 9, wherein in the oxide layer forming step, the surface of the base material on which the nitride layer is formed is exposed to an oxidizing atmosphere for 1 hour or more. Method. A die-casting sleeve comprising the casting member according to any one of claims 1 to 4 . The die-casting apparatus provided with the member for casting of any one of Claims 1-4 .