JPH0835031A - Sintered hard alloy having super hard film and tool for plastic working - Google Patents

Abstract

PURPOSE:To produce a sintered hard alloy having a super hard film excellent in wear resistance by subjecting a sintered compact, formed under specific conditions and consisting of WC and Fe-C alloy, to immersion treatment in a molten borax bath in which Group Va elements are dissolved. CONSTITUTION:A sintered hard alloy, which is a sintered compact consisting of WC and 2.5-50wt.% Fe-C alloy and in which the amount of C in this Fe-C alloy is regulated to >=0.25wt.%, is prepared. This sintered hard alloy is immersed in a molten borax or borate bath in which one or >=2 kinds among the group Va and VIa elements are dissolved, and a super hard layer consisting of a carbide film of >=about 5mum film thickness is formed on the sintered hard alloy. By this method, the sintered hard alloy can be coated with the stable and uniform super hard layer in a short period of time, and the sintered hard alloy having extremely excellent wear resistance can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention includes various tools such as cutting tools such as cutting tools and drills, wear-resistant tools such as dies and drawing dies, and impact-resistant tools such as bits.
The present invention relates to a cemented carbide and a tool for plastic working, which is suitable for a member for applications requiring ultra-high pressure and corrosion resistance, and is provided with a suitable super-hard coating.

[0002]

2. Description of the Related Art As a conventional coated cemented carbide having a surface treatment, a WC-Co type cemented carbide obtained by liquid phase sintering by mixing Co powder as a binder with carbide powder containing WC as a main component. The base material is a base material on which hard ceramics have been formed by PVD or CVD treatment, or the base material is immersed in a borax sand or borate salt bath in which a carbide-forming element is melted. In some cases, carbides are formed by a treatment for reacting the carbide-forming element with C in the cemented carbide (hereinafter referred to as K-TD treatment).

[0003]

Among the above-mentioned coated cemented carbides, the ones subjected to PVD treatment do not have sufficient adhesion of the formed coating, and when they are used as a tool for plastic working to which surface pressure is applied, etc. Since the film peels off in a short time, it was not suitable for such use.

Further, in the case of the CVD treatment or the K-TD treatment, since these treatments are all high temperature treatments,
Part of the carbon in the matrix is consumed and η
The (Co ₃ W ₃ C) phase occurs. Since this η phase is extremely brittle, it deteriorates the toughness of the cemented carbide material, and when it is used for a plastic working tool that is also subject to surface pressure, the coating film peels off in a relatively short time, resulting in a long life. It was hard to get.

The present invention advantageously solves the above-mentioned problems and has a long life because the η phase is not generated even if the carbide coating treatment is carried out at a high temperature, and the growth rate of the carbide coating is relatively fast. It is an object of the present invention to provide a cemented carbide and a tool for plastic working having a superhard coating, which is advantageous in use in fields requiring good wear resistance because of its good properties.

[0006]

Means for Solving the Problems As a result of intensive research and development on coated cemented carbides, the inventors have found that Fe-containing Fe powder containing 0.25 wt% or more of C as a binder in a carbide powder whose main component is WC.
Molten bath of borax or borate in which carbide forming element of Va group or VIa group of the periodic table is dissolved in cemented carbide obtained by mixing 2.5 to 50% of C type powder and sintering. It has been found that the superhard coating alloy and the superhard coating plastic working tool having no significant η phase and significantly improved wear resistance can be obtained by performing a treatment for forming a carbide by immersing in the steel. The present invention is based on the above findings.

That is, the present invention is a cemented carbide formed by coating a cemented carbide layer on the surface, wherein the cemented carbide is WC.
Sintered body with Fe-C alloy contained in the range of 2.5 to 50 wt% and the amount of C in the Fe-C alloy is 0.25 wt% or more, and the superhard layer is Va group or VIa group. A cemented carbide with a superhard coating, characterized by the elemental bond of being a carbide coating formed by immersion treatment of borax or borate in which one or more elements are dissolved in a molten bath ( The first invention).

Further, the present invention is a cemented carbide obtained by forming a cemented carbide layer on the surface, wherein the cemented carbide is one of carbides of IVa group, Va group and VIa group elements in addition to WC. Or 2
A sintered body of a Fe-C alloy containing at least 2.5% by weight and a Fe-C alloy contained in the range of 2.5 to 50 wt%, and the amount of C in the Fe-C alloy is 0.25 wt% or more; And a super hard coating having an ultra-hard coating characterized by the elemental bond of a carbide coating formed by immersion treatment of borax or borate in which one or more VIa group elements are dissolved in a molten bath. It is a hard alloy (second invention).

In the present invention, it is preferable that the carbide coating is one kind or two or more kinds of V carbide, Nb carbide and Cr carbide (third invention).

Further, the present invention is a plastic working tool (fourth invention) characterized by using a cemented carbide having the superhard coating of the first invention, the second invention or the third invention.

[0011]

In the present invention, a Fe-C type alloy is used as the binder. By using such an Fe-C alloy, since C as a carbide source is supplied from the Fe-C alloy when forming the carbide coating, it is possible to effectively suppress the generation of the η phase. it is conceivable that.

The amount of C in this Fe-C alloy is 2.5 wt% or more. The reason is based on the following experiments. Particle size 1
Fe powder and C powder having a particle diameter of 5 μm or less were added to 1.5 μm WC powder in an amount of 10 wt% in total. that time,
0 to 2% in the amount converted to Fe-C alloy by changing the amount of C
The amount was set to various values. After mixing these powders,
Press molding at room temperature with a pressure of ² t / cm ² and then in vacuum 14
Sintering was performed at 00 ° C. In addition, during this sintering, Fe powder and C
Interdiffuses with the powder to form a Fe-C alloy. This sintered body
Immerse in a borax bath containing Fe-Nb at 1000 ° C for 10 hours
-TD treatment was performed. With respect to the obtained carbide-coated cemented carbide, the thickness of the Nb carbide coating was examined, and the relationship with the amount of C in the Fe—C based alloy binder is shown in FIG. As is clear from FIG. 1, when the amount of C in the Fe—C alloy is 0.25 wt% or more, a uniform film can be stably obtained. When abrasion resistance is required for tools and the like, the film thickness must be about 5 μm or more.

The proportion of such Fe--C alloy binder in the cemented carbide is limited to 2.5 to 50 wt%. This is because if the Fe-C based alloy binder is less than 2.5 wt%, a good carbide coating cannot be obtained, while if it exceeds 50 wt%, the initial strength as a cemented carbide is no longer exhibited.

The Fe-C based alloy binder is not particularly limited with respect to other requirements as long as the C content is 0.25 wt% or more. As described above, using Fe powder and C powder,
It may be sintered and diffused. However, it is more preferable to use Fe-C alloy powder. Examples of the Fe-C alloy powder include structural steel, spring steel, bearing steel, die steel,
Any powder satisfying the C content, such as stainless steel or high-speed steel, may be used.

Regarding carbide as a raw material of cemented carbide,
In addition to WC alone, in addition to WC, IVa group, Va group and
Carbides of VIa group elements (eg TiC, NbC, TaC, Zr
C, HfC, VC, Cr ₃ C ₂ , Mo ₂ C) may be added alone or in combination.

The particle size of the Fe-C alloy powder and the carbide powder such as WC varies depending on the sintering method used, but a powder of 100 mesh or less is generally used.

Further, the sintering method is as follows:
Any of IP molding-vacuum sintering method, hot press sintering method, various discharge sintering methods, and the like may be used. If the HIP treatment is further performed after the sintering, a more reliable alloy can be obtained.

Next, the Fe-C type binder cemented carbide obtained by sintering is subjected to K-TD treatment. As described above, this K-TD treatment is performed using the Va group and VIa group elements (for example, V, Nb, C).
By immersing the cemented carbide in a molten bath of borax or borate in which one or more of r) are dissolved, C in the matrix of the cemented carbide and Va group and VIa group in the molten salt A carbide is formed on the outermost surface of the cemented carbide from the reaction with the element. The processing temperature should be above 800 ℃ and below the melting temperature. In the present invention, since the Fe alloy containing C is used as the binder, C is smoothly supplied from the matrix and a uniform carbide coating having good adhesion is formed in a relatively short time. As a result, it is possible to easily obtain an ultra-hard coated tool having no η phase.

[0019]

【Example】

(Example 1) To WC powder having a particle size of 1 to 1.5 μm, SUJ 2 powder having a particle size of 5 μm or less was variously added as a binder in a range of 5 to 30 wt%, and mixed and pulverized with a ball mill for 60 minutes. Then, using a C type, discharge sintering at a pressure of 500 kg / cm ² was performed at 1200 ° C. in a high vacuum of 10 ⁻⁴ torr or less to obtain a 9 × 5 × 25 mm carbide tip (for microstructure observation). . All the cemented carbides were good sintered products. These cemented carbides were subjected to K-TD treatment by immersing them in a borax melting bath at 1000 ° C. in which ferrovanadium was dissolved for 16 hours. Also, for comparison, Co was used as a binder, and the WC-Co with various amounts of Co was changed.
Cemented carbide was also manufactured under the same conditions and subjected to K-TD treatment under the same conditions.

The thickness of the obtained superhard coating is shown in FIG. 2 in relation to the amount of binder added. As is clear from FIG. 2, all the cemented carbides using the Fe—C alloy binder according to the present invention have a VC phase of 5 μm or more. On the other hand, in the cemented carbide using the Co binder, the VC coating is thin in all cases.

3 and 4 show photographs of the metallographic structure near the surface of the superhard coated cemented carbide. FIG. 3 shows the case of the Fe—C based alloy binder described above, and FIG. 4 shows the case of using the Co binder. From the comparison between FIG. 3 and FIG. 4, it can be seen that in the cemented carbide using the Fe—C alloy binder, the coating is thick and uniformly coated with good adhesion. On the other hand, in the case of the Co binder, the coating is thin, and the η phase, which is revealed by black corrosion under the coating, is observed. In the coated cemented carbide using Co binder, peeling of the coating was also observed during polishing for observing the structure.

(Example 2) 30 wt% of SKD 11 powder having 200 mesh under as a binder was mixed with WC powder having a particle size of 1 to 1.5 μm and mixed and pulverized with a ball mill for 60 minutes.
Add 0.2% paraffin and load into a metal mold to apply a pressure of 2 t /
It was pressure-formed at cm ² and then vacuum-sintered at 1400 ° C. for 1 hour to produce a 30 mmφ × 30 mm sintered block. The sintered product was good with no cracks. 6.42 mm from such a sintered product
After making φ drawing die, K at 1000 ℃ for 5-10 hours
-TD treatment was applied to give a VC coating and a VC-NbC composite coating.

With the thus obtained super hard coating die, SKH
Cold drawing of 35 materials, surface reduction rate 16%, drawing speed 50m / mi
I went with n. For comparison, a life comparison was performed between a drawing die that was not subjected to a coating treatment and a drawing die having a JIS D-2 composition in which a TiN surface coating was formed by PVD or CVD. Table 1 shows the results.

[0024]

[Table 1]

As is clear from Table 1, all the dies coated with Co as a binder and having a surface coating had a short life, and peeling of the coating was observed in the CVD and PVD treated dies. On the other hand, all the dies according to the present invention exhibited a life of 5 to 10 times as long as those of the dies not subjected to the coating treatment, and no peeling of the coating was observed.

Example 3 0.5% of VC having a particle size of 1 to 3 μm was added to WC having a particle size of 1 to 1.5 μm, and 10 wt% of SKD 11 powder having a particle size of 10 μm or less was added as a binder to the mixed powder. After mixing by hand, 0.2% paraffin is added as a lubricant, and then pressure-molded with a metal mold at a pressing force of 1 t / cm ²
Vacuum sintering was performed for an hour to obtain a block of 30 mmφ × 30 mm.
A φ8 mm cold rear extrusion die was produced from this sintered block, and then subjected to K-TD treatment at 1000 ° C. for 5 hours to perform VC coating.

With the ultra-hard coated die thus obtained, SUS 43
Extrusion rate of 0 ferritic stainless steel equivalent to 0
Cold forging processing was performed at 55%. Commercially available rear extrusion die (W
(C-Co uncoated cemented carbide) caused seizure after about 200 times and required re-polishing, whereas the K-TD treated die according to the present invention had a life of about 20,000 to 30,000 times. Indicated.

[0028]

EFFECTS OF THE INVENTION The superhard coated cemented carbide of the present invention uses an Fe--C type alloy as a binder, and the coating treatment is a dipping treatment in a borax or borate bath. In conventional cemented carbide, brittleness
Since long-life could not be obtained due to the exfoliation of the coating due to the formation of phases, the cemented carbide and the composition processing which can coat the super-hard coating uniformly in a short time and have extremely excellent wear resistance. The tool for use was obtained.

[Brief description of drawings]

FIG. 1 is a graph showing the thickness of a Nb carbide coating in a carbide-coated cemented carbide in relation to the amount of C in a Fe—C based alloy binder.

FIG. 2 is a graph showing the relationship between the thickness of a superhard coating and the amount of binder added.

FIG. 3 is a photograph of a metallographic structure in the vicinity of the surface of the cemented carbide with a superhard coating when the Fe—C based alloy binder is used.

FIG. 4 is a photograph of a metallographic structure in the vicinity of the surface of a cemented carbide with a cemented carbide when a Co binder is used.

Claims (4)

[Claims] 1. A cemented carbide obtained by coating a cemented carbide layer on the surface, wherein the cemented carbide contains Fe and WC in the range of 2.5 to 50 wt%.
A sintered body with a -C alloy, and the amount of C in this Fe-C alloy is 0.25 wt% or more, and the superhard layer dissolves one or more of the Va group and VIa group elements. A cemented carbide having a superhard coating, characterized in that it is a carbide coating formed by dipping borax or borate in a molten bath. 2. A cemented carbide formed by coating a cemented carbide layer on the surface, the cemented carbide being one or more of carbides of IVa group, Va group and VIa group elements in addition to WC. And a Fe-C-based alloy containing 2.5 to 50 wt% of C and the Fe-C-based alloy has a C content of 0.25 wt% or more, and the superhard layer is a Va group or VIa group. A cemented carbide having a superhard coating, characterized by the elemental bond of being a carbide coating formed by immersion treatment of borax or borate in which one or more group elements are dissolved in a molten bath. . 3. The carbide coating comprises V carbide, Nb carbide and Cr.
A cemented carbide having a superhard coating according to claim 1 or 2 which is one or more kinds of carbides. 4. A plastic working tool characterized by using a cemented carbide having the cemented hard coating according to claim 1, 2 or 3.