JPS5948858B2 - Sintered hard alloy with excellent corrosion resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sintered hard alloy which has excellent corrosion resistance and is particularly suitable for use in the manufacture of decorative parts.

In general, the main properties required for decorative parts are (1) a beautiful surface, (2) no corrosion due to sweat during use, and (3) no corrosion due to contact with hard objects during use. It is possible to improve things such as not causing scratches on the surface.

Conventionally, stainless steel and materials whose surfaces are plated with gold or other materials have been used in many cases to manufacture decorative parts such as watch sides, but these materials have the above properties (1) and The above property (
3) was not satisfactory.

Therefore, recently, materials 4a and 5a of the periodic table have been used as materials for manufacturing decorative parts with scratch-proof properties.
A so-called sintered cemented carbide has been proposed, in which one or more carbides of group 6a transition metals are combined with one or more iron group metals, and has not been put into practical use. ing.

Among them, as bonded phase forming components, one or two of Ni and CO: 3 to 20%, Mo: 0.1 to 5%, Cr: 0.3 to 5%, and further include Contains vanadium carbide (hereinafter referred to as VC): 0.1 to 2% as a hard phase-forming component, and tantalum carbide (also a hard phase-forming component).
(hereinafter referred to as Tac), niobium carbide (hereinafter referred to as NbC)
, and one or more of tungsten carbide (hereinafter referred to as WC), and the remainder of unavoidable impurities. Since it satisfies (3) above, it is of high value as a material for decorative parts.

That is, for example, the conventional sintered hard alloy containing TaC as a main component exhibits a deep pale golden color that is different from that of gold-plated materials, and the conventional sintered hard alloy containing NbC as a main component The hard alloy has a deep silvery white color, and the above-mentioned conventional sintered hard alloys containing WC as a main component have a deep copper color, so these alloys are used for manufacturing decorative parts. If you do so, it will give you a sense of luxury.

However, although the conventional sintered hard alloys have the above properties (1) to (3), for example, when used as a watch side for a long period of time, they may leave fingerprint marks on the polished surface. If sweat or corrosive substances adhere to it, it may become cloudy, and depending on its intended use, it does not exhibit satisfactory corrosion resistance.

From the above-mentioned viewpoint, the present invention provides a sintered hard alloy which has excellent corrosion resistance compared to the above-mentioned conventional sintered hard alloy, which has been practically used mainly as a material for decorative parts. All of them contain, as bonded phase forming components, one or two of Ni and Co: 3 to 20%, Mo: 0.1 to 5%, Cr: 0.3 to 5%, and further V as a hard phase forming component if necessary
In the binder phase of a sintered hard alloy containing C: 0.1 to 2%, and the remainder consisting of one or more hard phase forming components of TaC, NbC, and WC and inevitable impurities, Nitrogen: 0.01 to 0.5%, is characterized by a sintered hard alloy that has been given excellent corrosion resistance by solid solution.

Next, the reason why the composition range of the sintered hard alloy of the present invention is limited as described above will be explained.

(a) Ni and C.

If its content is less than 3%, it cannot function as a binding metal satisfactorily, while if it is contained in excess of 20%, it becomes soft and the desired high hardness cannot be achieved. The content is set at 3 to 20%.

(b) M.

In the sintering process of alloy production, the Mo component improves the wettability between the hard phase and the binder phase, combines with free carbon in the raw material mixed powder to form carbide, and further dissolves the carbide into the binder phase. It also has the effect of suppressing precipitation from the binder phase, thereby forming a fine and uniform alloy structure, improving hardness and strength, and improving the corrosion resistance of the binder phase. If the content is less than 0.1%, the desired effect cannot be obtained, while if the content exceeds 5%, the alloy strength will decrease, so the content should be reduced to 0.1 to 5%.
It was determined that

(C) Cr The Cr component has the effect of improving corrosion resistance, but if the content is less than 0.3%, the desired effect cannot be obtained, whereas if the content exceeds 5%, the desired effect cannot be obtained. , the alloy strength will decrease, so if the content is 0.3 to 5.
It is set as 0%.

(a) VC The Mo component has the effect of further improving the hardness and strength of the alloy, so it is included as necessary when these properties are required, but the content is 0.1%. If the content is less than 2%, the desired effect of improving the above action cannot be obtained, while if the content exceeds 2%, the alloy properties will be impaired. Therefore, the content is set at 0.1 to 2%.

(e) Nitrogen If nitrogen (hereinafter referred to as N) is dissolved as a solid solution in the binder phase of an alloy containing a Cr component in the above range, the corrosion resistance of the alloy will be significantly improved without changing the color tone or decreasing the hardness. If the content is less than 0.01%, the desired effect of improving corrosion resistance cannot be obtained, while if the content exceeds 0.5%, the alloy strength will be significantly reduced. ~0.5
%.

Furthermore, the alloy of the present invention can be manufactured by a normal powder metallurgy method, but in order to form a solid solution of N in the binder phase, it is necessary to activate the surface of the raw material powder during sintering. It is preferable to use decomposed ammonia gas as the sintering atmosphere; however, if decomposed ammonia gas cannot be used due to reasons such as the sintering furnace, most of the sintering process is performed in a vacuum to remove the raw material powder. The oxide on the surface may be reduced and activated, and then N2 gas may be introduced.

The reason why corrosion resistance is improved when N is dissolved in the binder phase is not well understood, but it is thought to be like a famous dog.

That is, in general, when this type of sintered hard alloy is corroded, it is the binder phase that is corroded, and it is known that the corrosion resistance of the binder phase tends to be better as the alloy carbon content is lower. However, in the alloy of the present invention, the amount of carbon can be adjusted to the extent that it is normally necessary for a person skilled in the art to do so, and the alloy has better corrosion resistance than conventional low carbon alloys in which N is not solidly dissolved in the binder phase. be.

Therefore, the reason why the alloy of the present invention has excellent corrosion resistance is not due to the amount of carbon in the alloy, but due to the large change in phase equilibrium due to solid solution of N in the binder phase, or the effect of solid solution N itself. It seems to be.

Next, the alloy of the present invention will be explained using examples.

Example 1 As raw material powders, TaC powder and Ni powder with an average particle size of 1.5 μm, NbC powder with an average particle size of 1.4 μm, and average particle size of 1.3 μm
1.7 μm of Co powder and Mo powder, and 1.7 μm of Cr
These raw material powders are blended to have the final component composition shown in Table 1, each blended powder is mixed in a wet ball mill, and after drying, a green compact is formed. The powder compact is sintered under the conditions of vacuuming the temperature during the heating process up to 1400°C, introducing N2 gas at 100 torr when the temperature reaches 1400°C, and holding this temperature for 1 hour. Invention alloys 1 to 5 were each produced.

In addition, for comparison purposes, comparative alloys were prepared under the same manufacturing conditions as those for the invention alloys 1 to 5, except that the sintering temperature was 1400°C and the sintering was performed in vacuum without introducing N2 gas. 1 to 5 were manufactured.

Invention alloys 1 to 5 and comparative alloys 1 to 5 obtained as a result
Regarding 5, the N content was analyzed using the kale-tar method and an oxygen/nitrogen simultaneous analyzer, and the difference was determined from the N content after the bonded phase was dissolved and removed with an aqueous solution of acid or salt.
The amount of solid solution N in the bonded phase was determined.

The results are also shown in Table 1. Next, the invention alloys 1 to 5 and comparative alloys 1 to 5 were treated with artificial sweat (pH 4.7) in accordance with ISO (International Organization for Standardization) standards.
The lower half of the mirror-polished specimen was immersed for 24 hours in the artificial sweat, which was maintained at a temperature of 40°C ± 2°C, using as a corrosive liquid (the value is arbitrarily adjusted and controlled by the amount of caustic soda added), A corrosion resistance test was conducted to observe the cloudiness of the polished surface of the specimen after immersion.

The test results are shown in Table 1.

As shown in Table 1, Comparative Alloys 1 in which the amount of solid solute N in the binder phase is lower than the range of this invention.
Alloy 1 of the present invention has a higher amount of solid solute N in the binder phase than alloys 1 to 5.
It is clear that all of Nos. 5 to 5 exhibit excellent corrosion resistance.

Example 2 In the sintering process, the temperature was raised to 1000°C in a vacuum, the temperature was raised from 1000°C to 1400°C, and the sintering temperature was maintained at 1400°C for 1 hour at a pressure of 3Q.
Alloys 6 and 7 of the present invention were manufactured under the same conditions as those for Alloys 1 and 5 of the present invention in Example 1, except that they were carried out in a stream of decomposed ammonia gas at Qtorr.

Regarding the above-mentioned invention alloys 6 and 7, the amount of solid solution N in the binder phase was measured under the same conditions as in Example 1.
Invention alloy 6: 0.15% by weight, Invention alloy 7: 0.1
3% by weight, and even in a corrosion resistance test under the same conditions as in Example 1, no clouding occurred on the polished surface of the specimen, indicating excellent corrosion resistance.

Further, in a corrosion resistance test under the same conditions except that the pH value of artificial sweat was 2.5, the invention alloys 6 and 7 exhibited excellent corrosion resistance.

Example 3 Each raw material powder had an average particle size of 1.5 μm (7)
Using WC powder, Ni powder, VC powder, 1.3 μm CO grain powder, MO grain powder and 1.7 μm Cr powder, these raw powders were made to have the final component composition shown in Table 2. Inventive alloys 8 to 10 and comparative alloys 6 to 8 were produced from these blended powders under the same mixing, molding, and sintering conditions as in Example 1.

The amount of dissolved N in the binder phase and the corrosion resistance test results of the invention alloys 8 to 10 and comparative alloys 6 to 8 are shown in Table 2.

These measurement results were obtained under the same conditions as in Example 1.

As shown in Table 2, alloys 8 to 10 of the present invention exhibit significantly superior corrosion resistance compared to comparative alloys 6 to 8, which have a low amount of solid solute N in the binder phase, as in Example 1. is clear.

As mentioned above, the sintered hard alloy of the present invention not only satisfies all the properties required for kimono parts, but also has particularly excellent corrosion resistance. In addition to exhibiting excellent corrosion resistance when used in industrial applications, it also exhibits excellent performance when used in the manufacture of parts such as mechanical seals and various nozzles that require corrosion and wear resistance.

Claims (1)

[Claims] 1 Contains, as bonded phase forming components, one or two of Ni and Co: 3 to 20%, Mo: 0.1 to 5%, Cr: 0.3 to 5%. and one or two of tantalum carbide, niobium carbide, and tungsten carbide as hard phase forming components.
Species and unavoidable impurities: Remaining: In a sintered hard alloy consisting of the following, nitrogen: 0 in the binder phase.
．． A sintered hard alloy with excellent corrosion resistance, characterized in that the corrosion resistance is improved by solid solution of 0.01 to 0.5% (or more by weight). 2 Contains one or two of Ni and Co: 3 to 20%, Mo: 0.1 to 5%, Cr: 0.3 to 5% as binder phase forming components, and further contains hard phase formation Contains vanadium carbide: 0.1 to 2% as a component, and consists of one or more of tantalum carbide, niobium carbide, and tungsten carbide as hard phase forming components, and the remainder of inevitable impurities. In sintered hard alloys, nitrogen: 0 in the binder phase
．． A sintered hard alloy with excellent corrosion resistance, characterized in that the corrosion resistance is improved by solid solution of 0.01 to 0.5% (or more by weight).