JP2003205352A - Member for molten metal, composed of sintered alloy having excellent corrosion resistance and wear resistance to molten metal, its producing method and machine structural member using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a member for molten metal having extremely excellent corrosion resistance and parting property to the molten metal and excellent in thermal fatigue characteristic, mechanical characteristic and wear resistance, and its producing method. <P>SOLUTION: This member is made of Mo<SB>2</SB>FeB<SB>2</SB>type double boride base hardening sintered alloy as a base material and formed of stable and close nitride film or oxide film and the nitride film consisting essentially of B, Mo, Fe, Cr and nitrogen on this surface, and used as the member for molten metal. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a member for molten metal made of a sintered alloy having excellent corrosion resistance and wear resistance to molten metal, a method for producing the same, and a mechanical structural member using the same. More specifically, in a sintered alloy mainly composed of Mo ₂ FeB ₂ type double boride, by forming a nitride or a nitride and an oxide on the surface of the sintered alloy,
The present invention relates to a member for molten metal having significantly improved wear resistance, corrosion resistance, and releasability, a manufacturing method thereof, and a mechanical structural member using the member for molten metal.

[0002]

2. Description of the Related Art A typical member used in direct contact with molten metal is a member for die casting machine parts. Die casting machine is a plunger, sleeve,
It is composed of a molding die and is used in direct contact with a molten metal, such as aluminum, zinc, or magnesium. Therefore, the properties commonly required for these parts are corrosion resistance to molten metal such as not being eroded (melted) by molten metal and not forming a reaction layer,
It has wear resistance and heat fatigue resistance. Conventionally, tool steel and hot work tool steel (SKD) have been used as members for these parts.
No. 61) was used, but there was a problem that the life was short because the corrosion resistance to molten metal was not sufficient.

Therefore, in addition to having high hardness and high strength, M which exhibits excellent corrosion resistance to molten metal
o ₂ FeB ₂ type double boride type hard sintered alloy (Japanese Patent Publication No. 60-5
7499 publication) is applied to die casting parts,
We were able to obtain a significant life extension. However, it has been found that when this member is used for a long period of time, the reaction between the metal binding phase of the member and the molten metal proceeds, which causes a problem that corrosion resistance and releasability are deteriorated.

In recent years, attempts have been made to form a thermal spray coating of ceramics such as alumina or zirconia on the surface of a member in order to improve the corrosion resistance and the releasability of molten metal. However, in these thermal spray coatings, cracks such as heat check and heat cracks and peeling are likely to occur, and the expected improvement in durability has not been obtained.

Further, JP-A-5-148588 and JP-A-9-217167 disclose that the corrosion resistance of members is improved by providing an oxide film on the surface of steel, cast iron and stainless steel. There is. However, the formed oxide film has problems such as weak adhesion to members, very thinness, and low hardness, and it is difficult to apply it to plungers and sleeves that require wear resistance strength.

[0006]

DISCLOSURE OF THE INVENTION In the present invention, the Mo ₂ FeB ₂ type double boride-based hard sintered alloy has improved corrosion resistance to molten metal and releasability, and exhibits extremely excellent durability. By developing a hard sintered alloy, it has extremely excellent corrosion resistance to molten metal, releasability, and thermal fatigue properties, mechanical properties, and excellent wear resistance members for molten metal, and a method for producing the same. And it aims at providing the machine structural member using them.

[0007]

For the molten metal of the present invention
In the member for molten metal with excellent corrosion resistance, the base metal is hard-fired
On the surface of the base metal that is in direct contact with the molten metal
It is characterized in that a nitride film is formed. More hope
As a preferable form, the base material is Mo.₂FeB₂Type compound boride
And a Fe-based binder phase, which is a hard sintered alloy,
The nitride film mainly contains metallic elements such as Mo, Cr, Fe and B and nitrogen.
Body (Fe, Mo, Cr, B)_mN _nType of compound nitriding
It is characterized by being a film made of a material.

Further, as a more specific constituent component of the hard-sintered gold, B of 3 to 7.5%, 21 to 79.9%.
Of Mo, 2 to 30% of Cr, and the balance of 10% or more of Fe and unavoidable impurities, and 0.1 to 8% of M with respect to the total composition of the hard sintered alloy.
n, further, a part of the Mo content contained in the hard sintered alloy is replaced with W of 0.1 to 30% with respect to the total composition, and the hard sintered alloy is also formed. Part of the Mo content contained in is replaced with 0.1 to 20% of Nb with respect to the total composition, and further, part of the Mo content contained in the hard sintered alloy, A total of 0.1% to 30% of W and Nb is substituted for the total composition, and a part or all of the Nb content contained in the hard sintered alloy is Zr, Ti, Ta, Substituting any one or more of Hf, and a portion of the Fe content contained in the hard sintered alloy with respect to the total composition, either Ni and / or Co, or 0.1% to 20% of the total amount of both substituted, further hard sintered alloy Some of the Cr content to be contained, or the like to become replaced by 0.1 to 25% of V with respect to the total composition can be employed.

Further, in the method for producing a member for molten metal according to the present invention, any one of the above hard sintered alloys is heated in a nitrogen atmosphere or a reducing atmosphere containing nitrogen to form a nitride film on the surface thereof. Alternatively, one of the above hard sintered alloys is heated in the air or in an atmosphere containing oxygen to form an oxide film on the surface thereof, and then heated in a reducing atmosphere containing nitrogen to form an oxide film. Reduce to form a nitride film, or heat any of the above hard sintered alloys in the air or in an atmosphere containing oxygen to form an oxide film on the surface and then heat in a nitrogen atmosphere. However, a nitride film is formed below the oxide film. The pressure of the reducing atmosphere containing nitrogen or the nitrogen atmosphere is 0.1 to 1.
5 MPa is desirable. Further, the mechanical structural member of the present invention,
A machine structural member characterized by using a member for molten metal created by using the method for manufacturing a member for molten metal according to any one of the above, wherein the mechanical structural member is a member for an injection molding machine or a molten metal casting apparatus. It is a member.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, B, M is formed on the surface of a hard sintered alloy of Mo ₂ FeB ₂ type double boride system (hereinafter referred to as a base material).
By forming a stable and dense nitride film or oxide film and nitride film mainly containing o, Fe, Cr and nitrogen, it is extremely excellent against molten metal when used as a member for molten metal. It is intended to provide a member for molten metal having corrosion resistance and releasability. In the hard sintered alloy which is the base material of the member for molten metal of the present invention, B, Mo,
By limiting the Cr content within a certain range, a fine two-phase microstructure of a double boride and a Fe-based binder phase is obtained, and not only excellent strength and heat resistance (heat fatigue resistance) are obtained, It is possible to densely and stably form the above-mentioned nitride film or the surface treatment layer composed of the nitride film and the oxide film. Further, by containing Mn in the base material, the mechanical properties of the base material, the corrosion resistance and the self-repairing property of the surface treatment layer are improved, and by containing Nb, Zr, Ti, Ta, and Hf, The corrosion resistance and wear resistance of the surface-treated layer are improved, the thermal shock resistance and high temperature strength of the base material are improved by containing Ni and / or Co, and the mechanical properties of the base material are improved by containing V. And the self-healing property of the surface treatment layer is further improved. The present invention will be described in detail below.

The present inventors have reached the present invention by using Mo ₂
A hard sintered alloy mainly composed of FeB ₂ type double boride has sufficient corrosion resistance and wear resistance that it can withstand in a corrosive atmosphere in which a molten resin or molten metal is used or in an environment such as a high temperature range. I was finding that. However, in recent years, various fillers such as glass fibers and ferrite particles have been added in order to impart high performance to the resin, and further improvement in wear resistance of mechanical structural members used for injection molding of molten resin has been required. . For molten metal,
When contacting with the molten metal for a long time, the Fe-based binder phase reacts with the molten metal, and the corrosion resistance and release (peeling) properties tend to decrease, and further wear resistance, corrosion resistance, and release to the molten metal are exhibited. It was found that improvement in moldability (peelability) is necessary. As a result of various studies, formation of a dense and stable nitride film or a surface treatment layer composed of a nitride film and an oxide film on the surface of a hard sintered alloy mainly composed of Mo ₂ FeB ₂ type double boride. According to the above, it was found that the surface hardness is increased while maintaining the strength of the base material, and the corrosion resistance to the molten metal and the molten resin, the releasability, and the abrasion resistance are significantly improved even when used for a long time.

This is because the nitride film is mainly composed of metal elements of Mo, Cr, Fe and B, which are main constituent elements of the base metal, and nitrogen (Fe, Mo, Cr, B) _m N _n type. It is a stable and dense film made of composite nitride, and the oxide film also has Mo, Cr, F, which are the main constituent elements of the base metal.
e and B are mainly composed of a metal element and oxygen (F
e, Mo, Cr, B) _x O _y type composite oxide, which is a stable and dense film, and these surface treatment layers constitute a protective film to significantly improve the corrosion resistance and wear resistance to molten metal. This is to improve. Furthermore, by forming an oxide film in advance before forming the nitride film and nitriding while reducing this oxide film, nitriding is promoted by the oxide layer previously generated, and the nitride film is formed. A thicker film can be formed.

The hard sintered alloy used for the member for molten metal according to the present invention includes, in addition to the above four elements, Mn, W and N selectively.
In some cases, b, Zr, Ti, Ta, Hf, Ni, Co, and V are added. In this case, the nitride film or oxide film formed on the alloy surface is added to Mo, Cr, Fe, and B. And the above-mentioned selectively added element and nitrogen or oxygen. Mo, Cr, Fe, B for nitrides and oxides
In the case of not containing, the bonding strength of the surface treatment layer is weak, and the adhesiveness with the base material is lowered, so that cracks and peeling are likely to occur, and abrasion resistance is also insufficient. As a compound nitride,
Specifically, (Fe, Cr) ₃ Mo ₃ N, Fe ₃ N, Cr
_{N, Cr 2 N, MoN,} Mo 2 N, BN and the like. As the complex oxide, specifically, (Fe, M
o, Cr, B) ₂ O ₃ , (Fe, Mo, Cr, B) ₃ O ₄ ,
(Fe, Mo, Cr, B) O, (Fe, Mo, Cr,
B) O ₃ , (Fe, Mo, Cr, B) O _{2.7 to 2.9} , (F
e, Mo, Cr, B) O _{2 and the} like.

Since the above composite nitride is obtained by nitriding a Mo ₂ FeB ₂ type double boride, the alloy composition of the base material is mainly Mo, Cr, Fe and B.
_It must be a hard sintered alloy composed of ₂ FeB ₂ type complex boride. In the above hard sintered alloy, B is an indispensable element for forming the double boride and the surface treatment layer which are the hard phase of the base material of the molten metal member of the present invention. Also, B
The surface-treated layer containing is effective in improving the adhesion to the base material. If the amount of B is less than 3%, the ratio of the hard phase is 35.
%, The mechanical properties are inferior. On the other hand, if it exceeds 7.5%, the ratio of the hard phase exceeds 95%, and the strength and the thermal shock resistance decrease. Therefore, the B content is limited to 3 to 7.5%.

Mo, like B, is an essential element for forming a double boride and a surface treatment layer. In the base material, a part of the base material forms a solid solution in the binder phase of the hard alloy to improve the mechanical strength of the base material. However, the upper limit of the appropriate amount (79.9)
%), An intermetallic compound such as M ₆ C type carbide is formed to reduce the strength of the base material. On the other hand, if the content is less than 21%, Fe borides such as Fe ₂ B are formed, so that the strength of the base material decreases. Therefore, the Mo content is limited to 21 to 79.9%.

Like Mo, Cr does not only dissolve in the hard phase in the base metal uniformly in the binder phase to improve the mechanical properties, but also in the surface treatment layer, Cr is stable and dense. It is an essential element for the formation of complex oxides that are combined with. However, if the content exceeds 30%, an intermetallic compound such as chromium carbide (Cr ₃ C ₂ ) is formed and the strength of the base material is reduced. On the other hand, if it is less than 2%, the amount of Cr in the surface treatment layer becomes insufficient, and the corrosion resistance decreases. Therefore, the Cr content is limited to 2 to 30%.

Mn suppresses the grain growth of the double boride of the base material,
By refining the alloy structure, the mechanical properties are significantly improved. Further, by adding Mn, it is possible to obtain a sintered body having a good shape with less shape loss during sintering, and it is possible to obtain a near-net structure. Further, since Mn has a strong affinity with oxygen, it brings self-repairing property of the surface treatment layer and enhances the durability of the member. If the content is less than 0.1%, the effect of improving the properties is not recognized, and if it exceeds 8%, the mechanical properties of the base material deteriorate. Therefore, the Mn content is limited to 0.1 to 8% with respect to the entire composition.

W is an element that can be replaced with Mo and has the effect of improving the strength of the base material. But Mo
If the amount of substitution with is less than 0.1% with respect to the total composition, the effect is not recognized. On the other hand, 30 for Mo and the total composition
Not only will the effect not be observed even if substitution is made in excess of%, but the specific gravity of the base material will increase and the product weight will increase.
Therefore, the substitution amount of W for Mo is limited to 0.1 to 30% with respect to the total composition.

Nb is an element capable of substituting for Mo, and forms a solid solution with the complex boride of the base material and partly forms other hard particles (borides, oxides, carbides, and nitrides). And improve the mechanical properties. However, if the content is less than 0.1%, no improvement effect is observed, and if the content exceeds 20%, the sinterability of the hard alloy decreases, leading to a decrease in strength, and an expensive element. Therefore, the cost is increased. Therefore, the content of Nb is limited to 0.1 to 20% with respect to the entire composition. Further, Mo can be replaced with both W and Nb. In this case, it is preferable that the total of both W and Nb be replaced by 0.1 to 30% with respect to the total composition.

Zr, Ti, Ta, and Hf are M like Nb.
It is an element that can be replaced with o and improves mechanical properties like Nb. Therefore, a part or all of the Nb content can be replaced with any one kind or two or more kinds of these elements.

When Ni and / or Co form a solid solution in the Fe-based binder phase, the thermal shock resistance and high temperature strength of the hard alloy are improved. If the substitution amount with respect to the Fe content is less than 0.1%, the improving effect is not recognized, and even if the content exceeds 20%, the effect of improving the characteristics is not recognized.
Therefore, the content of Ni and / or Co is limited to 0.1 to 20% with respect to the total composition.

V is an element capable of substituting for Cr, and the mechanical properties of the base material are improved by containing it in a small amount. Further, in the surface treatment layer, the effect of improving self-repairing property is brought about. If it is less than 0.1%, its property improving effect is not recognized, and if it exceeds 25%, when an oxide film is formed, the adhesiveness of the film is reduced, causing impurities to be mixed into the molten metal. Can be. Therefore, the V content is limited to 0.1 to 25% with respect to the entire composition.

The hard alloy of the present invention contains, in addition to the above-mentioned constituent elements,
The balance is composed of Fe. Fe is an element that forms the complex boride and the binder phase, and is essential for forming the complex nitride that forms the surface treatment layer. In the hard alloy of the present invention, when the Fe content is less than 10%, not only the double boride cannot be sufficiently formed, but also F in the binder phase is not formed.
The e content is insufficient and the strength decreases. Therefore, the hard alloy of the present invention needs to contain 10% or more of Fe. Needless to say, if the hard alloy of the present invention cannot contain 10% or more of Fe, the content of each element other than Fe is reduced within the allowable range to contain 10% or more of Fe.

The main unavoidable impurity elements contained in the hard sintered alloy of the present invention are P, S, C, etc., and in order to maintain the strength of the hard sintered alloy, their content is as small as possible. It is desirable to do. When the total content of these elements is 1% or less, the influence on the mechanical properties is relatively small.

Next, a method of manufacturing the molten metal member of the present invention will be described. First, a method of manufacturing a hard alloy that is a base material will be described. (1) Fe, Mo, Cr, Mn, or W, Nb, Zr, Ti, Ta, Hf, Ni, C
Powder of B alloy consisting of B and one or more elements of o and V, or (2) Powder consisting of B alloy powder and alloy of one or more of these elements, or (3) B
Simple substance and Fe, Mo, Cr, Mn, or even W, N
b, Zr, Ti, Ta, Hf, Ni, Co, V, one or more kinds of simple substance powders, or (4) powder of B simple substance and an alloy of one or more kinds thereof, Compounded so as to have the alloy composition described above, wet-milled in an organic solvent using a vibrating ball mill, etc., and then granulated and molded, and the molded body is non-oxidized in vacuum, in a reducing gas, or in an inert gas. It is manufactured by liquid phase sintering in a neutral atmosphere.

The complex boride which forms the hard phase of the above hard alloy is formed by the reaction of the above-mentioned raw material powder during sintering, but it is previously added with Mo and Fe, and further selectively as described above. Complex boride consisting of elements, or B
By reacting the powder of a simple substance with the powders of Mo and Fe and the above-mentioned selectively added elements in a furnace,
₂ FeB ₂ type complex boride is produced, and Fe having a bonding composition is further added.
Powders of Mo, Ni, Co, and powders of the above-mentioned selectively added elements may be used so as to have a predetermined alloy composition.

Liquid phase sintering is usually carried out at a sintering temperature of 1373 to 1673K for 5 to 90 minutes. If the sintering temperature is less than 1373 K, the liquid phase does not sufficiently appear, a sintered body with many pores is obtained, and sufficient strength cannot be obtained. On the other hand, the sintering temperature is 16
If it exceeds 73 K, the liquid phase appears sufficiently, but the crystal grains become coarse and the strength decreases. Further, if the sintering time is less than 5 minutes, the diffusion of elements is not sufficient and the density is not sufficiently increased. On the other hand, even if it is sintered for more than 90 minutes, no further increase in strength is observed, and in some cases, the strength may decrease. By sintering under the sintering conditions in which the liquid phase described above appears, the voids disappear and a hard alloy having a density of almost 100% is obtained. As a method of eliminating the pores without causing the liquid phase to appear, a hot isostatic pressing method, a hot pressing method,
There are current sintering methods and the like, and the voids can be eliminated by using these methods. Further, these methods may be used in combination with the liquid phase sintering method.

The hard sintered alloy, which is the base material of the molten metal member of the present invention obtained as described above, is used not only as a single sintered body but also as a composite material by being joined to a steel material. Is also possible. That is, the hard sintered alloy of the present invention can be used not only by brazing to a steel material like a cemented carbide, but also by directly joining with a steel material without using a brazing material, and a strong adhesion can be obtained. can get. Further, it is also possible to apply a sinter joining method of joining sinter and steel at the same time, the steel does not cause strength deterioration due to heat damage, and the composite material is used as a member for die casting of molten metal such as aluminum. When used, only in a portion where corrosion resistance and wear resistance to the molten metal are required, by using the hard alloy that is the mother phase of the member for molten metal of the present invention to the minimum necessary, molds etc. It becomes possible to manufacture the member at a low price.

Next, a method for producing a member for molten metal according to the present invention, which comprises forming a surface treatment layer on the surface of the base material obtained as described above, will be described. When only the nitride film is formed on the surface of the above-mentioned molten metal member, the obtained base material is machined into a desired shape, the surface is washed and degreased, and then nitrogen of 0.1 to 1.5 MPa is applied. 773 to 18 in an atmosphere or a reducing atmosphere containing nitrogen
A nitride film is formed by holding at a temperature of 73K for 5 minutes to 50 hours. If the treatment temperature is less than 773K, it is not possible to form a nitride film having a sufficient thickness to obtain excellent corrosion resistance and wear resistance even if the treatment is performed for a long time. On the other hand, when the treatment temperature is higher than 1873K, the nitride film is peeled off. When the treatment time is less than 5 minutes, the formation of a nitride film having a sufficient thickness is not recognized, and even when the treatment is performed for more than 50 hours, not only the growth of the nitride film is saturated and peeling occurs, This leads to higher costs. Therefore, the nitriding treatment is 773 to 187.
5 minutes to 50 hours at a temperature of 3K, preferably 973 to 16
Do at 73K for 1-30 hours. The pressure of the atmosphere needs to be higher than the atmospheric pressure so that the atmosphere outside the processing tank does not enter the atmosphere, and if the pressure is increased, the film thickness tends to be thicker. It is preferable to perform the treatment under a pressure of ˜1.5 MPa.

As an alternative method of forming only a nitride film,
The obtained base material is machined into a desired shape, and after cleaning and degreasing the surface, first, in the air or in an oxygen atmosphere, 77
Hold at a temperature of 3 to 1873K for 5 minutes to 50 hours to form an oxide film. The oxide film forming means includes a high temperature atmospheric oxidation method and a high temperature wet hydrogen oxidation method, but is not particularly limited. If the treatment temperature is less than 773K, it is not possible to form an oxide film having a sufficient thickness to obtain excellent corrosion resistance even if the treatment is performed for a long time. On the other hand, 18
When the treatment temperature is higher than 73 K, the oxide film is peeled off. When the treatment time is less than 5 minutes, formation of an oxide film having a sufficient thickness is not recognized, and even if the treatment is performed for more than 50 hours, not only the oxide film grows saturated and peels off, This leads to higher costs. Then, in a reducing atmosphere containing nitrogen of 0.1 to 1.5 MPa, 7
Hold at a temperature of 73-1673 K for 1-40 hours. As described above, when an oxide film is formed by heating in the air or in an atmosphere containing oxygen and then heated in a reducing atmosphere containing nitrogen, even if nitriding treatment is performed under the same conditions, nitriding treatment alone is more effective. A thick nitride film can be obtained, and it becomes easy to increase the film thickness.

When the nitriding treatment is performed after forming the oxide film, the nitride film may be formed on the surface of the base material, that is, the lower layer of the oxide film. When performing this process,
After machining the base material and washing and degreasing the surface in the same manner as above, first, in the air or in an oxygen atmosphere, 773-
Hold at a temperature of 1873K for 5 minutes to 50 hours to form an oxide film. The oxide film forming means includes a high temperature atmospheric oxidation method and a high temperature wet hydrogen oxidation method, but is not particularly limited. If the treatment temperature is less than 773K, it is not possible to form an oxide film having a sufficient thickness to obtain excellent corrosion resistance even if the treatment is performed for a long time. On the other hand, 1873
When treated at a treatment temperature exceeding K, peeling of the oxide film occurs. When the treatment time is less than 5 minutes, formation of an oxide film having a sufficient thickness is not recognized, and even if the treatment is performed for more than 50 hours, not only the oxide film grows saturated and peels off, This leads to higher costs. Therefore, the oxidation treatment is performed at a temperature of 773 to 1873K for 5 minutes to 50 hours, preferably at 973 to 1673K for 1 to 30 hours. In this way, an oxide film is obtained. Then, nitriding is performed in the same manner as above. The nitride film is formed at the interface between the sintered alloy base material and the oxide film. In this way, a two-layer coating having an oxide coating on the nitride coating is obtained. When the oxide film is present on the nitride film in this way, the oxide exhibits a lubricating effect and wear resistance is further improved. Hereinafter, the present invention will be specifically described with reference to examples.

[0032]

EXAMPLES Example 1 B powder and metal powder are shown in Table 1.
After adjusting so as to have the content of hard sintered alloy components shown in Tables 1 to 4, wet mixing and pulverization was performed in acetone for 25 hours using a vibrating ball mill. The powder after crushing with a ball mill is dried and granulated, and the obtained fine powder is press-molded into a predetermined shape, and then heated at a temperature rising rate of 10 K / min in a vacuum with a vacuum degree of ≦ 1.3 Pa. , At temperatures of 1373 to 1673 K for 3
After heating for 0 minutes, the furnace was cooled to obtain a hard sintered alloy.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

[Table 4]

The obtained hard sintered alloy was processed into a desired shape, degreased, heated under the heating conditions shown in Tables 5 to 9 and then cooled in a furnace to form a composite nitride film on the surface of the hard sintered alloy. Alternatively, a surface-treated layer composed of a two-layer film of a composite nitride and a composite oxide was formed to obtain a member for molten metal. For comparison, some hard sintered alloys were subjected to the following characteristic evaluation without being subjected to the above heat treatment. The strength, the corrosion resistance to molten metal, and the wear resistance of the hard and hard alloys and the members for molten metal shown in Tables 5 to 9 obtained as described above were evaluated as follows.

[Strength] Specimens were cut out from as-sintered hard hard alloys and members for molten metal obtained by subjecting hard sintered alloys to heat treatment in the atmosphere, and bending strength (3) was measured based on JIS H5501. The point bending test) was measured. The larger the transverse rupture strength is, the better the strength is, and those having a bending strength of more than 1.5 GPa are the subject of the present invention. The results are shown in Tables 10-14.

[Corrosion Resistance] 10 mm × a hard sintered alloy as-sintered, or a member for molten metal in which a composite nitride film or a two-layer film of a composite nitride and a composite oxide is formed on the hard sintered alloy. A test piece was prepared by cutting into a size of 10 mm × 100 mm, and this test piece was heated and melted at 993 K (aluminum alloy for die casting: JIS-A
After being immersed in DC10) for 6 hours, the test piece was cut out in a cross section perpendicular to the longitudinal direction, the cross section was observed with an optical microscope, and the depth at which the test piece was eroded from the surface by molten aluminum was measured. The corrosion resistance was evaluated by. ◯: Erosion depth <5 μm, good releasability Δ: Erosion depth ≧ 5 μm and <30 μm, somewhat poor releasability ×: Erosion depth ≧ 30 μm, poor releasability results are shown in Tables 10-14. Items with # in the table are
It refers to those in which the effect of improving the effect is not observed even if the specific element is added more than necessary.

[Sliding Property and Abrasion Resistance] A hard sintered alloy whose surface is mirror-polished by a pin-on-disk method, and a hard sintered alloy having a composite nitride film or a composite nitride and a composite oxide two layers The following pins were placed on a test piece prepared from a member for molten metal on which a film was formed, and the following loads were applied, and the sample was rotated and slid at the following times. The test was carried out by applying an aluminum pin (JIS-5052) load of 1 N and rotating at 1000 times, and the width of the wear mark of the sample after the test was measured by a scanning electron microscope. Was evaluated. ◯: Wear width <500 μm Δ: 500 μm ≧ wear width <1000 μm ×: wear width ≧ 1000 μm The results are shown in Tables 10-14.

[0041]

[Table 5]

[0042]

[Table 6]

[0043]

[Table 7]

[0044]

[Table 8]

[0045]

[Table 9]

[0046]

[Table 10]

[0047]

[Table 11]

[0048]

[Table 12]

[0049]

[Table 13]

[0050]

[Table 14]

As shown in Tables 10 to 14, the member for molten metal of the present invention is excellent in strength, corrosion resistance against molten metal and wear resistance.

(Example 2) Ni ₂ B powder, Mo ₂ B ₅ powder, pure Mo powder, carbonyl Ni powder, pure Cr powder and pure Mn powder were made to have the component contents shown in composition No. 16 in Table 1. Was mixed in aceto, and the mixture was pulverized and mixed in acetone using a vibrating ball mill until the average particle size became 1.0 μm. Next, the mixed powder was pressed into a cylindrical shape by using the cold isostatic pressing method (CIP). Then, raise the temperature to 1573K in vacuum and 2
After holding for 0 minutes, the furnace was cooled to obtain a sintered body. Next, the cylindrical sintered body was fitted to a core material of alloy tool steel (SCM440), heated in vacuum at 1473K for 20 minutes, and diffusion-bonded to obtain a composite material. After cutting the sintered body portion of this composite material into the shape of an injection molding screw, it was subjected to 13 MPa in a mixed atmosphere consisting of 0.5 MPa hydrogen: 10% and nitrogen 90%.
It was kept at 73 K for 3 hours to form a nitride film. The injection molding screw thus obtained was loaded into an injection molding machine and subjected to polypropylene injection molding work.
After using 3000 times, no corrosion holes were formed on the surface, and almost no wear was observed.

Example 3 The same raw material powder as described above was blended so as to have the same composition as described above, and a cylindrical sintered body was prepared under the same conditions as above. After cutting this sintered body into a predetermined sleeve shape, it was heated in a nitrogen atmosphere of 0.5 MPa at 1173 K for 3 hours to form a nitride film on the surface. This was shrink-fitted to the inner circumference of the outer cylinder of alloy tool steel (SKD61) to obtain a die casting sleeve. This die casting sleeve was loaded into an aluminum die casting machine and was used for casting molten aluminum.
Even after 0 times of use, no cracks and the like were generated on the surface and almost no wear was observed.

[0054]

INDUSTRIAL APPLICABILITY The present invention contains Mo, Cr, Fe and B, and limits the content of Mo, Cr and B within a certain range,
Or further Mn, W, Nb, Zr, Ti, Ta, H
A composite nitride film or a composite oxide film is formed on the surface of a hard sintered alloy composed of fine double boride and an Fe-based binder phase, which contains f, Ni and / or Co, V and the like as appropriate. It is a member for molten metal formed by forming a two-layer film of a composite nitride film, and exhibits excellent corrosion resistance and wear resistance against molten metal and molten resin. When the molten metal member of the present invention is applied to a die casting sleeve for aluminum casting, cracks and wear are hardly generated.
Further, when the molten metal member of the present invention is applied to a screw of a resin injection molding machine, corrosion holes and wear do not occur. As described above, the member for molten metal of the present invention can be favorably applied not only to the mechanical structural member of molten metal but also to the mechanical structural member of molten resin.

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) C22C 38/58 C22C 38/58 C23C 8/10 C23C 8/10 8/26 8/26 8/34 8 / 34 // B29C 45/60 B29C 45/60 (72) Inventor Yuji Yamazaki 1 1296 Higashitoyoi Shimomatsu City, Yamaguchi Prefecture Toyo Kohan Co., Ltd. Technical Research Institute (72) Kenichi Takagi 2 Yonbancho, Chiyoda-ku, Tokyo 2 Address 12 Toyo Kohan Co., Ltd. F term (reference) 4F206 AA11 AJ02 AJ07 AJ14 JA07 JD01 JQ07 JQ11 4K028 AA02 AB03 AC08 CC02 CD01

Claims (18)

[Claims] 1. A molten metal excellent in corrosion resistance to molten metal, characterized in that the base material is made of a hard sintered alloy, and a nitride film is formed on the surface of the base material that is in direct contact with the molten metal. Parts. 2. The base material is Mo ₂ FeB ₂ type double boride and F.
A member for molten metal having excellent corrosion resistance to molten metal according to claim 1, which is a hard sintered alloy composed of an e-based bonded phase. 3. The nitride film formed on the surface of the hard-bonded gold is a (Fe, Mo, Cr, B) _m N _n- type composite nitride mainly composed of metal elements of Mo, Cr, Fe and B and nitrogen. A member for molten metal having excellent corrosion resistance to molten metal according to claim 1 or 2, wherein the member is composed of 4. The hard sintered alloy is 3 to 7.5% by weight.
B (21% to 79.9%, hereinafter)
O, 2 to 30% of Cr, and the balance of 10% or more of Fe and unavoidable impurities.
2. A member for molten metal having excellent corrosion resistance to the molten metal according to 2 or 3. 5. The total composition of the hard sintered alloy,
The member for molten metal having excellent corrosion resistance to molten metal according to claim 4, which contains 0.1 to 8% of Mn. 6. The method according to claim 4, wherein a part of the Mo content contained in the hard sintered alloy is replaced with W of 0.1 to 30% with respect to the total composition. 5. A member for molten metal having excellent corrosion resistance to the molten metal according to item 5. 7. The method according to claim 4, wherein a part of the Mo content contained in the hard sintered alloy is replaced with 0.1 to 20% of Nb with respect to the total composition. 5. A member for molten metal having excellent corrosion resistance to the molten metal according to item 5. 8. A part of the Mo content contained in the hard sintered alloy is replaced by 0.1 to 30% in total of both W and Nb with respect to the total composition. A member for molten metal having excellent corrosion resistance to the molten metal according to claim 4 or 5. 9. A part or all of the Nb content contained in the hard sintered alloy is replaced with any one kind or two kinds or more of Zr, Ti, Ta, and Hf. A member for molten metal having excellent corrosion resistance to the molten metal according to claim 7. 10. A portion of the Fe content contained in the hard sintered alloy is Ni and / or Co with respect to the total composition.
A member for molten metal having excellent corrosion resistance to molten metal according to any one of claims 4 to 9, which is formed by substituting 0.1 to 20% of either one or both in total. 11. The method according to claim 4, wherein a part of the Cr content contained in the hard sintered alloy is replaced with V of 0.1 to 25% with respect to the total composition. A member for molten metal having excellent corrosion resistance to the molten metal according to any one of 1. 12. The hard sintered alloy according to any one of claims 1 to 11 is heated in a nitrogen atmosphere or a reducing atmosphere containing nitrogen to form a nitride film on the surface thereof. A method for manufacturing a member for molten metal. 13. The hard sintered alloy according to claim 1, which is heated in the air or in an atmosphere containing oxygen to form an oxide film on the surface of the hard sintered alloy, and then the reducing property containing nitrogen. A method for producing a member for molten metal, which comprises heating in an atmosphere to reduce an oxide film to form a nitride film. 14. The hard sintered alloy according to claim 1 is heated in the atmosphere or in an atmosphere containing oxygen to form an oxide film on the surface, and then heated in a nitrogen atmosphere. Then, a method for producing a member for molten metal is characterized in that a nitride film is formed under the oxide film. 15. The reducing atmosphere containing nitrogen or the nitrogen atmosphere has a pressure of 0.1 to 1.5 MPa.
15. The method for manufacturing a member for molten metal according to any one of 1 to 14. 16. A machine structural member using a member for molten metal produced by the method for manufacturing a member for molten metal according to claim 12. 17. The mechanical structural member according to claim 16, wherein the mechanical structural member is a member for an injection molding machine. 18. The mechanical structure member according to claim 16, wherein the mechanical structure member is a member for a molten metal casting apparatus.