KR101630561B1 - Member for die casting and process for manufacturing same, sleeve for die casting, and die casting equipment - Google Patents

Abstract

In accordance with the present invention, there is provided a casting member for use in contact with a molten metal, comprising: a base material including a hot tool steel; a base material having a Vickers hardness of 50 HV or more higher than Vickers hardness of the base material in contact with the base material, A diffusion layer and a nitrogen compound layer having a thickness of 5 占 퐉 or more and 40 占 퐉 or less and containing a nitrogen compound which is in contact with the nitrogen diffusion layer and contains iron and a nitrogen compound layer which is in contact with the nitrogen compound layer and contains iron And an oxide layer containing an oxide which is in contact with the molten metal and is in contact with the molten metal.

Description

TECHNICAL FIELD [0001] The present invention relates to a casting member, a manufacturing method thereof, a sleeve for a die casting, and a die casting apparatus. [0002]

The present invention relates to a casting member, a method of manufacturing the same, a sleeve for die casting, and a die casting apparatus.

Molding members (e.g., molds, sleeves) used in contact with molten metal used in die casting such as aluminum, magnesium, alloys thereof, etc. are conventionally used as hot work tools steel is used as the base material.

Such a casting member, when the erosion of the molten metal progresses remarkably during use, increases the frequency of maintenance of the casting member, and also shortens the service life of the casting member.

Therefore, there is a method of forming a nitrided layer in a portion of the casting member in contact with the molten metal for the purpose of improving the erosion resistance of the casting member, or a method in which an oxide layer is further formed (See, for example, Japanese Patent Application Laid-Open Nos. 2005-28398, 2003-13199, and 64-31957).

However, in a casting member having a structure in which a nitride layer is formed on the base material and an oxide layer is in contact with the molten metal, the oxide layer is peeled off during repeated use, have.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a casting member which maintains excellent content handling even in repeated use, a method of manufacturing the same, and a die casting sleeve and a die casting apparatus provided with the casting member.

The inventors of the present invention have found that the basic structure of the casting member is structured such that the nitride layer and the oxide layer are sequentially provided on the base material including the hot tool steel and that the structure of the nitride layer is specified, Knowledge, and completed the present invention based on such knowledge.

Specifically, concrete means for solving the above problems are as follows.

A nitrogen diffusion layer which is in contact with the base material and nitrogen is diffused in the base material and Vickers hardness is higher than Vickers hardness of the base material by 50 HV or more; < 1 > a casting member used in contact with molten metal, And a nitrogen compound layer having a thickness of 5 占 퐉 or more and 40 占 퐉 or less and containing a nitrogen compound which is in contact with the nitrogen diffusion layer and contains iron and a nitrogen compound layer which is in contact with the nitrogen compound layer, And an oxide layer containing an oxide and contacting the molten metal.

&Lt; 2 > The casting member according to < 1 >, wherein the oxide layer comprises a mixed layer contacting the nitrogen compound layer and containing the nitrogen compound and the oxide.

<3> A 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 the magnetite is replaced with chromium.

&Lt; 4 > The nitride layer is a layer formed by nitriding the base material, and the oxide layer is a layer formed by oxidizing the base material on which the nitride layer is formed, Member.

<5> A method for producing a casting member according to any one of <1> to <4>, comprising the steps of: preparing a base material for preparing a base material containing hot tool steel; A nitriding layer forming step of nitriding the nitrided layer by exposure to an atmospheric gas containing ammonia gas and nitrogen gas under heating of the nitrided layer; And an oxide layer forming step of forming an oxide layer by an oxidation treatment by exposing the oxide layer to an oxidizing atmosphere.

<6> The method for producing a casting member according to <5>, wherein the atmospheric gas further comprises carbon dioxide gas.

The step of forming the oxide layer may include exposing the surface of the base material on which the nitride layer is formed to a steam atmosphere as the oxidizing atmosphere under heating at a temperature of 480 ° C. to 600 ° C., Member. &Lt; / RTI >

<8> The nitriding layer forming step is a method for producing a casting member according to any one of <5> to <7>, wherein the surface of the base material is exposed to the atmosphere gas for 20 hours to 40 hours.

<9> The oxide layer forming step is a method for manufacturing a casting member according to any one of <5> to <8>, wherein the surface of the base material on which the nitride layer is formed is exposed in an oxidizing atmosphere for 1 hour or more.

<10> A die casting sleeve having a casting member according to any one of <1> to <4>.

<11> A die casting apparatus comprising the casting member according to any one of <1> to <4>.

According to the present invention, it is possible to provide a casting member which maintains excellent content handling even in repeated use, a method for producing the casting member, and a die casting sleeve and a die casting apparatus provided with the casting member.

Fig. 1 is an optical microscopic image (magnification 50 times) showing a section of each layer in the sample 2 which is an example of the present invention.
2 is a graph showing the relationship between the distance d (占 퐉) from the interface between the oxide layer and the nitrogen compound layer and the Vickers hardness (HV) in the sample 2 which is an example of the present invention.
Fig. 3 is a scanning electron microscopic image (magnification 3000 times) showing a cross section of each layer in Sample 2 which is an example of the present invention.
4 is a scanning electron microscopic image (magnification 3000 times) showing a cross section of each layer in the sample 7 as a comparative example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the casting member of the present invention and its manufacturing method, the die casting sleeve, and the die casting apparatus will be described in detail.

&Lt; Casting member &

The casting member of the present invention is a casting member used in contact with a molten metal and includes a base material including a hot tool steel and a base material which is in contact with the base material and in which nitrogen (N) is diffused in the base material and Vickers hardness And a nitrogen compound layer having a thickness of not less than 5 占 퐉 and not more than 40 占 퐉 and containing a nitrogen compound containing iron (Fe) and in contact with the nitrogen diffusion layer higher than the Vickers hardness by not less than 50HV, And an oxide layer contacting the nitrogen compound layer and containing an oxide containing iron (Fe) and contacting the molten metal.

In the present specification, "Vickers hardness" refers to Vickers hardness measured in accordance with JIS Z 2244 (1998).

Conventionally, as a casting member used in contact with molten metal, a nitriding layer formed by nitriding the surface of a base material on a base material including hot tool steel and a nitriding layer forming surface of a base material on which a nitriding layer is formed are oxidized and formed And an oxide layer in contact with the molten metal at the time of use (at the time of casting) are successively formed on the molten metal (see, for example, Japanese Patent Application Laid-Open No. 2005-28398). The oxide layer contains an oxide including iron. These oxides are chemically stable and have low reactivity with molten metals. As a result, the oxide layer is formed on the casting member, so that the contentability of the casting member is remarkably improved.

However, in the casting member provided with the oxide layer, the oxide layer is peeled off at the time of repeated use (when casting is repeatedly carried out, the same is applied hereinafter), thereby deteriorating the content stability of the casting member have. The reason that the oxide layer peels off during repeated use is that the thermal expansion coefficient of the oxide containing iron is larger than the coefficient of thermal expansion of the base material (for example, hot tool steel) Tensile stress is applied to the oxide layer at the time of the cooling process, and the oxide layer tends to be broken by the tensile stress.

With respect to the above, in the casting member of the present invention, the peeling of the oxide layer at the time of repeated use is suppressed, and as a result, the excellent content property is maintained even in repeated use.

The reason why such an effect is exhibited is presumed as follows.

That is, the casting member of the present invention is characterized in that an oxide layer is formed as a layer (that is, the outermost layer) that is in contact with the molten metal at the time of using the casting member, and that the nitriding layer including the nitrogen diffusion layer and the nitrogen compound layer When the thickness is 200 mu m or more, excellent content luck is exhibited from the beginning of use.

The casting member of the present invention is characterized in that it has a nitrogen diffusion layer which is in contact with the base material and is excellent in adhesion with the base material and that a nitrogen compound layer having a thickness of 5 占 퐉 or more which is excellent in adhesion between the nitrogen diffusion layer and the oxide layer, The peeling of the oxide layer at the time of repeated use can be suppressed.

For these reasons, it is assumed that excellent castability at the initial stage of use of the casting member of the present invention is maintained even at the time of repeated use.

Further, as described above, it is a matter of course that the casting member of the present invention is excellent not only in repeated use but also in the initial stage of use.

However, in the conventional casting member, it is general that the nitrogen compound layer is not formed as much as possible because the nitrogen compound layer is generally thinner than the nitrogen diffusion layer. For example, when the base material is nitrided to form a nitride layer, a nitrogen compound layer is not formed as much as possible, or even if a nitrogen compound layer is formed by nitriding treatment of the base material, And the casting member was used in a state in which 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 탆 or more is interposed between the nitrogen diffusion layer and the oxide layer. As compared with the case where the nitrogen compound layer is not formed (that is, when the oxide layer is formed directly on the nitrogen diffusion layer) or when the thickness of the nitrogen compound layer is less than 5 mu m, the peeling of the oxide layer As a result, deterioration of the content handlability at the time of repeated use is suppressed.

In the present invention, the thickness of the nitride layer including the nitrogen diffusion layer and the nitrogen compound layer is 200 占 퐉 or more and 400 占 퐉 or less.

According to the study by the present inventors, it has become clear that when the thickness of the nitride layer is 200 탆 or more, the content loss of the casting member is remarkably improved.

If the thickness of the nitrided layer is less than 200 탆, the content loss may be deteriorated. From this viewpoint, the thickness of the nitride layer is 200 占 퐉 or more, but preferably 250 占 퐉 or more.

On the other hand, if the thickness of the nitrided layer exceeds 400 mu m, the crack development resistance of the nitride layer is lowered (that is, the crack progresses more rapidly when the heat crack is generated). When the thickness of the nitrided layer exceeds 400 占 퐉, the time required for forming the nitrided layer becomes longer (for example, 50 hours or more) and the productivity of the casting member is lowered. From this viewpoint, the thickness of the nitride layer is 400 mu m or less, preferably 350 mu m 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.

Methods 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.

Further, in the present invention, the thickness of the nitrogen compound layer is 5 占 퐉 or more and 40 占 퐉 or less.

If the thickness of the nitrogen compound layer is less than 5 mu m, the oxide layer tends to peel off. When the thickness of the nitrogen compound layer is less than 5 mu m, oxygen may diffuse to the interface between the nitrogen compound layer and the nitrogen diffusion layer to form an oxide at the interface, and the adhesion between the nitrogen compound layer and the nitrogen diffusion layer (See FIG. 4 to be described later). From this viewpoint, the thickness of the nitrogen compound layer is 5 占 퐉 or more, but preferably 10 占 퐉 or more.

On the other hand, when the thickness of the nitrogen compound layer exceeds 40 mu m, the crack resistance of the nitrogen compound layer is deteriorated. From this viewpoint, the thickness of the nitrogen compound layer is 40 占 퐉 or less, preferably 30 占 퐉 or less, and more preferably 25 占 퐉 or less.

In the present invention, the thickness of the nitrogen compound layer is preferably in the range of from 1 to 5% by volume (nitric acid) in a cross section cut along the thickness direction of each layer (nitriding layer and oxide layer, (Hereinafter referred to as &quot; SEM &quot;), and the cross section after corrosion is observed with a scanning electron microscope (hereinafter also referred to as &quot; SEM &Quot;. &lt; / RTI &gt;

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 layer is an oxide layer (a mixed layer when a mixed layer is present in the oxide layer) and a nitrogen diffusion layer.

As an example of measurement of the thickness of the nitrogen compound layer, it is possible to refer to Example 1 (Figs. 1 and 3) to be described later.

In the present invention, the thickness of the nitrided layer indicates a value measured as a distance from the interface between the oxide layer and the nitrogen compound layer to the interface between the nitrogen diffusion layer and the parent material.

In the present invention, the thickness of the nitrogen diffusion layer refers to a value measured as a 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, the "distance" refers to the distance in the thickness direction of the nitrogen diffusion layer (the same applies hereinafter).

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 SEM.

The interface between the nitrogen diffusion layer and the base material is preferably set so that the interface between the oxide layer and the nitrogen compound layer or the distance from the surface of the casting member to the Vickers hardness (for example, see FIG. 2) 50 HV &lt; / RTI &gt;

Examples of the measurement of the thickness of the nitride layer and the thickness of the nitrogen diffusion layer can be found in Example 1 (Figs. 1 to 3) described later.

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

(Base material)

The casting member of the present invention comprises a base material including hot tool steel.

The hot tool steel is not particularly limited and may be, for example, an alloy tool steel for an alloy tool steel specified in JIS G 4404 (2000), an alloy tool steel for a hot die, Japanese Patent Application Laid-Open Nos. 2009-221594, 2008-095190 A known hot tool steel disclosed in Japanese Patent Application Laid-Open No. 2008-095181, Japanese Patent Application Laid-Open No. 2006-213990, International Publication No. 2010/074017, etc. can be used.

Among them, from the viewpoint of availability and the like, alloy tool steels for hot dies among alloy steel steels specified in JIS G 4404 (2000) are preferable. Among them, SKD4 and SKD5 specified in JIS G 4404 (2000) , SKD6, SKD61 and SKD8 are more preferable, and SKD61 is particularly preferable.

As the hot tool steel, a hot tool steel of a new composition having improved the composition of a known hot tool steel may be used.

As hot tool steel, hot tool steel subjected to quenching and tempering may be used.

From the viewpoint of containing a complex oxide [(Fe, Cr) ₃ O ₄ ] having a structure in which a part of Fe contained in the magnetite is substituted with Cr in the oxide layer to be described later, (Preferably 2% by mass or more, more preferably 4% by mass or more, and particularly preferably 4.80% by 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.

Further, the base material may contain inevitable impurities in addition to the hot tool steel.

For example, in the base material, a trace amount of nitrogen may be diffused as an inevitable impurity in a region including a contact surface with the nitrogen diffusion layer (for example, a distance d in Fig. 2 to be described later is 300 mu m or more and 350 mu m or less .

The base material may be a hot tool steel subjected to quenching tempering.

(Nitride layer)

The casting member of the present invention comprises a nitride layer.

The nitride layer is composed of a nitrogen diffusion layer which is a layer in contact with the base material and a nitrogen compound layer which is in contact with the nitrogen diffusion layer.

Hereinafter, the details of these layers will be described.

- Nitrogen diffusion layer -

The nitrogen diffusion layer is a layer in which nitrogen is diffused into the components of the base material.

This nitrogen diffusion layer is a layer having a high hardness. Specifically, the Vickers hardness of the nitrogen diffusion layer is higher than the Vickers hardness of the base material by 50 HV or more.

This nitrogen diffusion layer itself also has an effect of improving the contentability of the casting member.

This nitrogen diffusion layer is a layer in which nitrogen is diffused (solidified) in a matrix containing a matrix component. In the nitrogen diffusion layer (in the matrix), a part of the diffused nitrogen may be combined with the nitride forming element among the components 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 "Vickers hardness of the base material" refers to the surface of the casting member Or the interface between the oxide layer and the nitrogen compound layer) is 25 mu m, the Vickers hardness of the region where the Vickers hardness change is 10HV 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 占 퐉 or more and 40 占 퐉 or less including a nitrogen compound containing iron (Fe).

Since this nitrogen compound layer is a layer having excellent adhesion with the nitrogen diffusion layer and adhesion with the oxide layer, the nitrogen compound layer is provided so that the peeling of the oxide layer (hereinafter also simply referred to as &quot; Is suppressed.

Regarding the adhesion between the nitrogen compound layer and the nitrogen diffusion layer, more specifically, since the nitrogen compound layer is in contact with the nitrogen diffusion layer, no oxide (for example, iron oxide) is present between the nitrogen compound layer and the nitrogen diffusion layer. As a result, the peeling of the both at the interface between the nitrogen compound layer and the nitrogen diffusion layer is suppressed, and further, the peeling of the oxide layer from the casting member is suppressed.

Further, the nitrogen compound containing iron constituting the nitrogen compound layer is a substance having a low content of reactivity with the molten metal and a high content of affinity to the molten metal. As a result, the nitrogen compound layer itself also has an effect of improving the content uniformity of the casting member.

As the nitrogen compounds, including iron, if at least a compound of iron (Fe) and nitrogen (N) is made in combination sharing is not particularly limited, for example, nitride, such as _{γ'-Fe 4 N, ε-} Fe 2 ~3 N Iron, and a complex nitride containing an element other than iron and iron.

The nitrogen-containing compound contained in the nitrogen compound layer may be one species or two or more species.

Further, the nitrogen compound layer may contain inevitable impurities in addition to the nitrogen compound including iron.

(Oxide layer)

The casting member of the present invention comprises an oxide layer containing an oxide including iron as a layer in contact with the nitrogen compound layer. When the casting member is used, the surface of the oxide layer is in 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 to each other. Examples thereof include FeO (also called uistite), Fe ₂ O ₃ (also called hematite ), Fe ₃ O ₄ (also referred to as magnetite), and the like. Among them, Fe ₃ O ₄ (magnetite) is particularly preferable as iron oxide because of excellent corrosion resistance.

As the oxide containing iron, a composite oxide containing elements other than iron and iron (for example, (Fe, Cr) ₃ O ₄ described later) is also exemplified.

The iron-containing oxide contained in the oxide layer may be one kind or two or more kinds.

It is preferable that the oxide layer includes a mixed layer containing the nitrogen compound and the oxide as a layer in contact with the nitrogen compound layer.

As a result, the adhesion between the oxide layer including the mixed layer and the nitrogen compound layer can be further improved, so that the peeling of the oxide layer can be further suppressed.

Here, the content of the iron-containing oxide in the mixed layer is preferably 10% by mass or more, more preferably 20% by mass or more, further preferably 30% by mass or more, It is preferably not less than 40% by mass. The content of the oxide is preferably 90% by mass or less, more preferably 80% by mass or less, further preferably 70% by mass or less, and particularly preferably 60% by mass or less, .

The content of the nitrogen compound in the mixed layer is preferably 10% by mass or more, more preferably 20% by mass or more, further preferably 30% by mass or more, and particularly preferably 30% 40% by mass or more. The content of the nitrogen compound is preferably 90% by mass or less, more preferably 80% by mass or less, further preferably 70% by mass or less, particularly preferably 60% by mass or less, to be.

In a preferred form of forming this mixed layer, first, the nitrogen compound layer is formed as a layer having a porous structure on the surface layer portion, and then an oxide layer is formed on the nitrogen compound layer (surface layer portion side having a porous structure) And oxidizes the holes of the porous structure to form oxides in the holes. 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 formation of the oxide layer is formed as a mixed layer (that is, a part of the oxide layer) after the formation of the oxide layer do. In the mixed layer of this type (for example, the mixed layer 42 in FIG. 3), an anchor effect is expressed in a region of the oxide layer including the interface with the nitrogen compound layer (that is, the mixed layer), so that the nitrogen compound layer and the oxide layer The adhesion is further improved, and further, the peeling of the oxide layer is further suppressed.

The content of the iron-containing oxide in the oxide layer is preferably 10% by mass or more, more preferably 20% by mass or more, further preferably 30% by mass or more, And particularly preferably not less than 40% by mass. The content of the oxide is preferably 90 mass% or less, more preferably 80 mass% or less, further preferably 70 mass% or less, and particularly preferably 60 mass% or less to be.

Also, as at least one kind of oxides containing iron, a composite oxide having a structure in which a part of Fe contained in magnetite (Fe ₃ O ₄ ) is substituted with Cr [hereinafter also 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 ).

Since the oxide layer contains (Fe, Cr) ₃ O ₄ , the adhesion between the oxide layer and the nitrogen compound layer is further improved, and the peeling of the oxide layer is further suppressed.

As a method of forming the oxide layer containing (Fe, Cr) ₃ O ₄ , it is preferable that the Cr content be 1 mass% or more (preferably 2 mass% or more, more preferably 4 mass% Particularly preferably 4.80% by mass or more), and the nitrided layer is formed on the base material, followed by forming the oxide layer. According to this method, Cr can easily be 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.

The thickness of the oxide layer is not particularly limited, but is preferably 1 m or more, and more preferably 2 m or more, from the viewpoint of further improving the content stability.

The thickness of the oxide layer is preferably 20 占 퐉 or less, more preferably 10 占 퐉 or less, from the viewpoint of further suppressing peeling in repeated use.

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

More specifically, it is preferable that the nitride layer is a layer formed by nitriding the base material.

As the nitriding treatment, the surface of the base material is exposed to an atmosphere gas containing ammonia gas and nitrogen gas (preferably, carbon dioxide gas) under heating.

In addition, the nitriding treatment can be performed by a known method, and the nitriding layer can be formed by adjusting the conditions of the nitriding treatment.

More preferable conditions of the nitriding treatment will be described later.

The oxide layer is preferably a layer formed by performing an oxidation treatment on the nitride layer formation side of the base material on which the nitride layer is formed.

The oxidation treatment includes a treatment in which an oxidizing atmosphere (for example, an atmospheric atmosphere or a steam atmosphere, preferably a steam atmosphere) is exposed under heating.

In addition, the oxidation treatment can be performed by a known method.

Examples of the treatment for exposing to the steam atmosphere include a known treatment such as homotreatment or steam treatment.

Further preferable conditions of the oxidation treatment will be described later.

The casting member of the present invention may appropriately include well-known constituent elements in addition to the above-described constituent elements.

Further, the casting member of the present invention is a member used in contact with molten metal.

As the molten metal, a well-known aluminum alloy (for example, an aluminum alloy for die casting, etc.) may be appropriately used. Further, the casting member of the present invention can be expected to have an effect when a molten metal obtained by melting a known zinc alloy (for example, zinc alloy for die casting) is used.

Further, the casting member of the present invention can be suitably used for die casting. For example, it can be used as a mold component such as an insert, a core, or the like, a core pin, a sleeve, or the like, which is a component of a die casting apparatus. Among them, the sleeve is used in which a high-temperature molten metal is in contact for a long time, so that a more excellent content property is emphasized. Therefore, the casting member of the present invention having excellent content handling properties is optimal for a die casting sleeve.

<Die casting sleeve, die casting device>

The die casting sleeve of the present invention comprises the casting member of the present invention.

In addition, 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 die casting apparatus of the present invention, die casting can be carried out while maintaining excellent content uniformity during repeated use from the initial use. As a result, the frequency of maintenance of the casting member can be reduced, and the service life of the casting member can be prolonged.

&Lt; Production method of casting member >

The method for producing the casting member of the present invention is not particularly limited, and for example, a base material preparing step of preparing a base material including a hot tool steel, A nitride layer forming step of forming a nitride layer by performing a nitriding treatment by exposing the nitride layer to an atmosphere gas containing nitrogen gas; and a step of exposing the surface of the base material on which the nitride layer is formed to an oxidizing atmosphere at 450 캜 to 600 캜 And an oxide layer forming step of forming an oxide layer by oxidation treatment is suitable.

In the present manufacturing method, the hot tool steel, the base material, the nitrided layer, the oxide layer, and the like are the same as those described in the section of "Casting Member", and the preferable range is the same.

(Nitriding layer forming step)

The nitriding layer forming step is a step of nitriding the surface of the base material by exposure to an atmospheric gas containing ammonia gas and nitrogen gas at a temperature of 450 DEG C to 600 DEG C to form the nitrided layer on the base material.

This step can be performed by a conventional nitriding method using a furnace.

In this step, the time for exposure to the atmosphere gas is not particularly limited, but is preferably 20 hours or more, more preferably 24 hours or more, still more preferably 30 hours or more, and particularly preferably 36 hours or more. When the time is 20 hours or more, the thickness of the formed nitride layer is easily adjusted to 200 탆 or more, and the thickness of the formed nitrogen compound layer is easily adjusted to 5 탆 or more.

The time for exposure 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 more easily adjusted to 400 탆 or less and the thickness of the formed nitrogen compound layer is more easily adjusted to 40 탆 or less.

Further, it is preferable that the atmospheric gas further includes carbon dioxide gas in view of easy formation of a nitrogen compound layer.

In this case, the amount of carbon dioxide gas in the atmospheric gas is preferably 3 vol% or more, more preferably 5 vol% or more, based on the total amount of ammonia gas, nitrogen gas, and carbon dioxide gas. The amount of the carbon dioxide gas is preferably 20 vol% or less, more preferably 15 vol% or less, based on the total amount of the ammonia gas, the nitrogen gas, and the carbon dioxide gas.

The heating temperature in this step is not less than 450 ° C and not more than 600 ° C, but preferably not less than 500 ° C and not more than 600 ° C, and more preferably not less than 540 ° C and not more than 600 ° C. If the heating temperature is 500 占 폚 or higher, the thickness of the formed nitride layer is more easily adjusted to 200 占 퐉 or more.

(Oxide layer forming step)

The oxide layer forming step is a step of oxidizing the surface of the base material on which the nitride layer is formed by exposing the surface of the base material to an oxidizing atmosphere at 450 캜 or higher and 600 캜 or lower and forming the oxide layer on the nitrided layer.

This step can be carried out by a conventional oxidation treatment method using a furnace.

In this step, the time for exposure to the oxidizing atmosphere is not particularly limited, but is preferably not less than 1 hour, more preferably not less than 1.5 hours, from the viewpoint of more suitably producing iron oxide.

The upper limit of the time for exposure to the oxidizing atmosphere is not particularly limited, but from the viewpoint of productivity, this time is preferably 5 hours or less, more preferably 3 hours or less, and particularly preferably 2 hours or less.

The oxidizing atmosphere is not particularly limited as long as it is an atmosphere capable of oxidizing iron, and examples thereof include an atmospheric atmosphere and a steam 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 easily.

The heating temperature in this step is not less than 450 ° C and not more than 600 ° C, but preferably not less than 480 ° C and not more than 600 ° C, and more preferably not less than 500 ° C and not more than 600 ° C. If the heating temperature is more than 480 ℃, Fe ₃ O _{4 [Further, (Fe, Cr) 3 O} 4] the can be easily generated more.

In addition, the present manufacturing method may have other steps, if necessary.

Other processes include a step of quenching and tempering the base material prior to the nitride layer forming step.

Example

Hereinafter, the present invention will be described concretely with reference to examples, but the present invention is not limited to these examples.

In the following, the Vickers hardness was measured in accordance with JIS Z 2244 (1998) under a load of 50 g.

[Example 1]

Samples 1 to 9 were prepared as a casting member, and the content dependency (loss factor) during repeated use was evaluated.

Hereinafter, the details of the sample 2 will be described.

&Lt; Production of sample 2 >

The hot tool steel of SKD61 specified by 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 form a base material.

This base material was subjected to quenching tempering and adjusted to a hardness of about 45 HRC by a Rockwell hardness (HRC) specified by JIS G 0202.

A nitriding layer and an oxide layer were sequentially formed on the entire surface of this base material to obtain a sample 2, on the entire surface of the base material after the hardness adjustment, with the nitriding treatment and the oxidation treatment under the conditions shown in Table 1 in sequence.

Here, the nitriding treatment was carried out in a reaction furnace with a total pressure of 101 kPa in which the atmosphere gas of the composition shown in Table 1 was introduced.

The oxidation treatment was carried out in a reaction furnace with a total pressure of 101 kPa into which steam was introduced.

In the heating conditions of Table 1, &quot; h &quot; represents time. For example, &quot; 36h &quot; indicates &quot; 36 hours &quot;.

&Lt; Measurement of sample 2 >

The fabricated sample 2 was cut along the thickness direction (depth direction) of the nitride layer and the oxide layer, and the following measurement was performed on the obtained cross section.

The measurement results are shown in Table 1 below.

(Measurement of Thickness of Nitrogen Compound Layer)

The cross section was abraded and subsequently the cross section was corroded with a nitrate (ethanol nitrate solution containing 5 vol% of nitric acid). Subsequently, this cross section was observed with an SEM (magnification: 3000 times) (see Fig. 3), and the thickness of the nitrogen compound layer was measured based on the contrast on this SEM.

(Measurement of Thickness of Nitride Layer and Nitrogen Diffusion Layer)

First, the position (depth) of the inside of the base material was estimated based on the contrast of the cross section of the optical microscope (Fig. 1).

Then, in the section, the Vickers hardness of each measurement point was measured sequentially from the surface side of the casting member toward the base material side in accordance with JIS Z 2244 (1998). The relationship between the distance d (the distance in the thickness direction of each layer) from the interface between the oxide layer and the nitrogen compound layer and the Vickers hardness was determined by this series of Vickers hardness measurement (FIG. 2).

Based on this relationship, the measured value when the variation of the Vickers hardness when the distance d was changed by 25 mu m in the inside of the base material was 10 HV or less was defined as &quot; Vickers hardness of the base material &quot;. In addition, the position showing the Vickers hardness of 50 HV higher than the "Vickers hardness of the base material" was defined as the position of the interface between the nitrogen diffusion layer and the base material.

Subsequently, as a result of the Vickers hardness measurement, the distance from the interface between the oxide layer and the nitrogen compound layer to the interface of the nitrogen diffusion layer and the base material was determined based on the results of the optical microscope observation and the SEM observation, and this distance was taken as the thickness of the nitride layer .

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 microscopic image (magnification 50 times) showing a section obtained by cutting the sample 2 along the thickness direction of the nitride layer and the oxide layer.

Fig. 2 shows the results of Vickers hardness measurement on a section obtained by cutting the sample 2 along the thickness direction of the nitrided layer and the oxide layer. The distance d (mu m) from the interface between the oxide layer and the nitrogen compound layer and the Vickers hardness hardness (HV)].

1, in the sample 2, the nitrogen diffusion layer 32 is formed on the base material 10, the nitrogen compound layer 34 and the oxide layer 40 are formed on the nitrogen diffusion layer 32 .

2, in the 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 m is set at the interface between the base material 10 and the nitrogen diffusion layer 32 Respectively.

3 is an SEM image (magnification 3000 times) showing a cross section of each layer of Sample 2. Fig.

As shown in Fig. 3, in the sample 2, it was confirmed that the nitrogen compound layer 34 was interposed between the oxide layer 40 including the surface of the sample 2 and the nitrogen diffusion layer 32. In detail, the nitrogen compound layer 34 and the other layer were distinguished from each other by the difference in solubility in and out.

The nitride layer 30 in the sample 2 is composed of the nitrogen diffusion layer 32 and the nitrogen compound layer 34.

In addition, the mixed layer 42 was confirmed on the interface side with the nitrogen compound layer 34 in the oxide layer 40. 3, it can be seen that the mixed layer 42 has a structure in which an oxide is formed in a porous hole portion.

(Component analysis of oxide layer)

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

&Lt; Evaluation of drag ratio (%) for sample 2 >

With respect to the sample 2 prepared as described above, the loss factor (%) was evaluated as follows. In this evaluation, the lower the drag ratio (%), the better the content handlability at the time of repeated use.

First, an aluminum alloy ADC12 (JIS-H-5302) for die casting was melted into a molten metal, and the temperature of the molten metal was maintained at 700 占 폚.

Subsequently, the weight of the sample 2 (hereinafter referred to as &quot; weight before immersion &quot;) was measured, and the portion from the one end face of the sample 2 after the weight measurement to 40 mm was immersed in the molten metal (Hereinafter referred to as &quot; initial state &quot;). From this initial state, the sample 2 was moved up and down by an amplitude of 20 mm for 90 hours per minute for 5 hours (that is, during this exercise, the portion up to 20 mm from one end face of the sample 2 was always immersed in molten metal have).

The sample 2 after the movement for 5 hours was removed from the molten metal, and the sample 2 was washed with alkali. The alkali-washed sample 2 was dried and the weight of the dried sample 2 was measured (the weight measured here is hereinafter referred to as &quot; weight after immersion &quot;).

(%) Was calculated based on the above-described &quot; weight before immersion &quot; and the &quot; weight after immersion &quot;

The calculated drag loss ratio (%) is shown in Table 1 below.

<Preparation, Measurement and Evaluation of Sample 1 and Sample 3 to Sample 9>

The conditions for the nitriding treatment and the oxidation treatment were changed as shown in the following Table 1 in the production, measurement and evaluation of the sample 2, and the production, measurement and evaluation of the sample 1 and the samples 3 to 9 were carried out.

Here, in the samples 4, 6 and 8, the steam atmosphere in the oxidation treatment of the sample 2 was changed to an atmospheric atmosphere.

In Sample 8, after the nitriding treatment, the formed nitrogen compound layer was removed by shot blasting, and oxidation treatment was performed after removal.

In the sample 9, the oxidation treatment was not performed.

The results of the measurement and evaluation are shown in Table 1 below.

As shown in Table 1, it was confirmed that Sample 1 through Sample 5 of the present invention had a lower loss ratio (%) than Sample 6 through Sample 9, which were comparative examples, and superior in content dependency at the time of repeated use.

Specifically, in Sample 1, although the thickness of the nitrided layer was thinner than that of Sample 9, since the oxide layer was formed, the sample loss was lower than Sample 9.

Sample 2 was a sample in which the nitriding treatment time in Sample 1 was extended to make the nitrided layer thicker. This sample 2 exhibited a lower loss factor than sample 1.

In Sample 1 and Sample 2, a composite of a structure in which a part of Fe contained in magnetite (Fe ₃ O ₄ ) was replaced with Cr in addition to magnetite (Fe ₃ O ₄ ) as a component of the oxide layer by X- Oxide [(Fe, Cr) ₃ O ₄ ] was detected.

And Sample 3 and Sample 4 were obtained by changing the oxidation treatment conditions of Sample 2.

(Fe ₃ O ₄ ) was detected as a component of the oxide layer, but (Fe, Cr) ₃ O ₄ was not detected in the sample 3 in which the oxidation treatment temperature was lowered. In comparison with the sample 2, This slightly increased.

In addition to magnetite (Fe ₃ O ₄ ), hematite (Fe ₂ O ₃ ) was also detected in the oxide layer of the sample 4 in which the atmosphere of the oxidation treatment was an atmospheric environment. In Sample 4, the drag ratio was slightly higher than that of Samples 2 and 3.

Sample 5 was obtained by changing the nitriding condition of sample 3.

Specifically, Sample 5 was prepared by mixing the atmosphere gas (ammonia gas, carbon dioxide gas and nitrogen gas mixed gas) of the nitriding treatment in Sample 3 with the same conventional atmosphere gas (mixed gas of ammonia gas and nitrogen gas) as Sample 9 It is a change.

In this sample 5, the drag ratio 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 the nitride layer as in the case of the present invention.

However, since the time for the nitriding treatment was short and the nitride layer was thin, the sample 6 showed almost no improvement in the content loss property as compared with the sample 9.

Sample 7 was a sample in which the nitriding treatment time was shorter than that of sample 6, the nitride layer was thinner, and the nitrogen compound layer was also thin.

In this sample 7, early peeling occurred at the interface between the oxide layer and the nitrogen compound layer during the evaluation of the drag ratio, and peeling also occurred early at the interface between the nitrogen compound layer and the nitrogen diffusion layer, and the drag ratio was high.

4 is an SEM image (magnification 3000 times) showing the cross section of each layer of the sample 7.

4, a nitrogen compound layer 34 and an oxide layer 40 were sequentially formed on the nitrogen diffusion layer 32 in the same manner as in the sample 2 (Fig. 3).

However, in the sample 7 in which the nitrogen compound layer 34 is thin, the oxide layer 50 which is shown in dark black in the SEM image was formed between the nitrogen diffusion layer 32 and the nitrogen compound layer 34. [

In the sample 7, the presence of the oxide layer 50 deteriorates the adhesion between the nitrogen diffusion layer 32 and the nitrogen compound layer 34 so that the nitrogen compound layer 34 can not be peeled off at the interface between the nitrogen diffusion layer 32 and the nitrogen compound layer 34 .

In the sample 8 in which the nitrogen compound layer was not present, the oxide layer was peeled off. Further, since there is no nitrogen compound layer under the peeled oxide layer, the drag ratio is large.

[Example 2]

<Fabrication of sleeve for die casting>

Sleeve A (untreated) and sleeve B (untreated) were prepared as shown in Table 2 as dimensions (outer diameter x inner diameter x length) as diecasting sleeves. The base material of the sleeve is all SKD61.

First, the surface of each of these sleeves was subjected to nitriding treatment under conditions of an atmospheric gas flow rate of ammonia: nitrogen = 1: 1 at 530 占 폚 for 36 hours to form a nitrided layer. The structure of the formed nitride layer was substantially the same as that of the nitride layer in the sample 9 (comparative example) shown in Table 1.

Thus, the sleeve A (comparative example) and the sleeve B (comparative example) were obtained.

Subsequently, the sleeve A (comparative example) and the sleeve B (comparative example) were subjected to oxidation treatment (520 DEG C x 1.5h in a steam atmosphere) to form an oxide layer on the nitride layer in each sleeve.

The constitution of the formed oxide layer was substantially the same as the constitution of the oxide layer in the sample 1 of Table 1.

As a result, the sleeve A (the invention example) and the sleeve B (the invention example) were obtained.

<Evaluation (Diecasting)>

- Evaluation of Sleeve A (Honor)

Sleeve A (an example of the present invention) was loaded in a 1650 t cold chamber type die casting apparatus, and die casting of aluminum alloy ADC12 (JIS-H-5302) for die casting was performed. Then, the number of shots until the replacement of the sleeve becomes necessary after the increase in the melting loss is counted, and the number of shots is determined as &quot; possible short number of times &quot;.

Evaluation of sleeve A (comparative example)

In the evaluation of the sleeve A (the invention example), the sleeve A (comparative example) was produced in the same manner as the evaluation of the sleeve A (the inventive example), except that the sleeve A ) Was evaluated.

- Evaluation of Sleeve B (Honor)

Sleeve B (the case of the present invention) was loaded in a 650-ton cold chamber type die casting apparatus, and die casting of aluminum alloy ADC12 (JIS-H-5302) for die casting was performed. Then, the number of shots until the elongation of the sleeve becomes large and the sleeve needs to be replaced is counted, and the number of shots is defined as &quot; the number of short shots. &Quot;

- Evaluation of sleeve B (comparative example)

In the evaluation of the sleeve B (inventive example), the sleeve B (comparative example) was obtained in the same manner as the evaluation of the sleeve B (the inventive example), except that the sleeve B (the inventive example) ) Was evaluated.

The results of the above evaluation are shown in Table 2 below.

As shown in Table 2, the sleeve A (comparative example) required a replacement due to a large melting loss at 60,000 shots, but sleeve A (the comparative example) could be used up to 120,000 shots.

Further, in the evaluation of the sleeve B which is smaller in diameter than the sleeve A, the sleeve B (comparative example) required a replacement due to a large melting loss at the expiration of 30,000 shots, but the sleeve B there was.

The disclosure of Japanese Patent Application No. 2012-084683 is hereby incorporated by reference in its entirety.

All publications, patent applications, and technical specifications described in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical specification was specifically and individually indicated to be incorporated by reference.

Claims (16)

A casting member used in contact with molten metal,
A base material including a hot tool steel,
A nitrogen diffusion layer having a thickness of not less than 200 탆 and not more than 400 탆 in contact with the base material and having a Vickers hardness of 50 HV or more higher than Vickers hardness of the base material in contact with the base material and nitrogen diffused in components of the base material, And a nitrogen compound layer having a thickness of 5 占 퐉 or more and 40 占 퐉 or less including a nitrogen compound containing iron,
And an oxide layer contacting the nitrogen compound layer and containing an oxide containing iron and contacting the molten metal
Wherein the oxide layer comprises a mixed layer comprising the nitrogen compound and the oxide in contact with the nitrogen compound layer. The method 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 the magnetite is substituted with chromium, austite, hematite and magnetite. The method according to claim 1,
Wherein at least one of the oxides is a composite oxide having a structure in which a part of iron contained in the magnetite is substituted with chromium. The method according to claim 1,
The nitride layer is a layer formed by nitriding the base material,
Wherein the oxide layer is a layer formed by oxidizing the base material on which the nitride layer is formed. The method according to claim 1,
Wherein the mixed layer is a layer of a structure in which an oxide is formed in a hole portion of a porous structure containing the nitrogen compound. 3. The method of claim 2,
Wherein the mixed layer is a layer of a structure in which an oxide is formed in a hole portion of a porous structure containing the nitrogen compound. A method for producing the casting member according to any one of claims 1 to 6,
A base material preparing step of preparing a base material including a hot tool steel,
A nitrided layer forming step of nitriding the surface of the base material by exposing the surface of the base material to an atmospheric gas containing ammonia gas and nitrogen gas under heating at 450 캜 to 600 캜 to form the nitrided layer,
And an oxide layer forming step of forming an oxide layer by exposing the surface of the base material, on which the nitride layer is formed, to an oxidizing atmosphere under heating at 450 캜 or more and 600 캜 or less. 8. The method of claim 7,
Wherein the atmospheric gas further comprises a carbon dioxide gas. 8. The method of claim 7,
Wherein the oxide layer forming step exposes the surface of the base material on which the nitride layer is formed to a steam atmosphere as the oxidizing atmosphere under heating at a temperature of 480 캜 or more and 600 캜 or less. 8. The method of claim 7,
Wherein the nitrided layer forming step exposes the surface of the base material to the atmospheric gas for 20 hours to 40 hours. 8. The method of claim 7,
Wherein the oxide layer forming step exposes the surface of the base material on which the nitride layer is formed to an oxidizing atmosphere for 1 hour or more. A sleeve for diecasting, comprising the casting member according to any one of claims 1 to 6. A die casting apparatus comprising the casting member according to any one of claims 1 to 6. 9. The method of claim 8,
Wherein the oxide layer forming step exposes the surface of the base material on which the nitride layer is formed to a steam atmosphere as the oxidizing atmosphere under heating at a temperature of 480 캜 or more and 600 캜 or less. 9. The method of claim 8,
Wherein the nitrided layer forming step exposes the surface of the base material to the atmospheric gas for 20 hours to 40 hours. 9. The method of claim 8,
Wherein the oxide layer forming step exposes the surface of the base material on which the nitride layer is formed to an oxidizing atmosphere for 1 hour or more.

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