JPS5910423B2 - High strength cermet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a titanium carbide-based cermet having high strength.

Conventionally, titanium carbide (hereinafter referred to as TiC) as a hard phase-forming component is generally contained as a main component, and this is bonded with one or two or more of the five iron group metals as a bonding phase-forming component. So-called cermets have been used as cutting tools, wear-resistant tools, etc. because they maintain high hardness from low to high temperatures and therefore have excellent wear resistance.

Recently, attention has been paid to a cermet in which the TiC-based cermet contains titanium nitride (hereinafter referred to as TiN) to improve its strength.

However, the above-mentioned TiN-containing Ti
All cermets, including C-based cermets, do not have sufficient strength, and if subjected to high stress or exposed to high temperatures during use, they may undergo brittle fracture or plastic deformation. However, its use was limited due to the corrosion caused by corrosion.

For this reason, conventional research on cermets has focused primarily on improving strength, and studies have focused on adjusting the hard phase particle size, the content of binder phase-forming components, and added components, but sufficient results have not yet been obtained. The current situation is that this is not the case.

From the above-mentioned viewpoint, the present inventors have developed a cermet that has relatively high strength among conventional cermets, that is, one or two iron group metals as a bonding phase forming component.
Species or more: 5 to 30%, Zr and H as hard phase forming components
f, V, Nb, Ta, and Cr carbides and nitrides, Mo and W carbides, and titanium nitride (hereinafter referred to as ZrC, ZrN, HfC, and Hf, respectively).
N, VC, VN, NbC.

NbN, T a C, T aN, Cr3c2. C
r2 N, M02 C.

One or more of the following: WCl and TiN, collectively referred to as metal carbon/nitride; 5
We focused on a cermet consisting of ~50%, titanium carbide as a hard phase-forming component, and unavoidable impurities; the rest (more than % by weight), and further improved the strength of this cermet to achieve a sufficiently high strength. In order to obtain a cermet, we conducted research focusing on the relationship between the average grain size of the binder phase and strength, which had not received any attention in the past, and found that (a) if the average grain size of the binder phase is incorporated above a certain lower limit; The high temperature strength of cermets will be significantly improved.

(b) When the crystal grain size of the binder phase becomes extremely coarse and becomes close to a single crystal, it will have extremely high strength not only at high temperatures of 500°C or higher, but also at lower temperatures.

(c) The crystal grain size of the binder phase changes depending on the cooling rate after sintering, the component composition, the hard phase grain size, etc., but when the content of the binder phase forming components is constant, it mainly depends on the cooling rate after sintering. be affected by speed.

(d) In the cooling process after sintering at a predetermined temperature, the temperature range from the generation of solid nuclei of the binder phase to the completion of solidification, that is, the temperature range of a predetermined width above and below the eutectic temperature. By slowly cooling the area at a cooling rate of about 0.05°C/min or less, the grain size of the binder phase can be arbitrarily coarsened. The above temperature range is cooled at a normal cooling rate (approximately 5°C/min or more)
For example, the transverse rupture strength at 1000°C should always be at least 10% higher than that of a cermet cooled at 1000°C.

The findings shown in (a) and (d) above were obtained.

Therefore, this invention was made based on the above knowledge, and includes one or two iron group metals as binder phase forming components.
5 to 30%, one or more of metal carbons and nitrides as hard phase forming components; 5 to 50%, titanium carbide and inevitable impurities as hard phase forming components; the remainder; (more than % by weight), the average crystal grain size of the binder phase with respect to the content of the binder phase-forming component is calculated by the curve shown in the relationship diagram between the average crystal grain size of the binder phase and the content of the binder phase'-forming component in the attached drawing. The feature is that the strength is improved by setting it in an upper range.

In addition, in the cermet of the present invention, the reason why the average crystal grain size of the binder phase relative to the content of the binder phase forming component is set in a range above the curve shown in the attached drawings as described above is due to the empirical effect based on the seed experiment. It is established that
In fact, the cermet of the present invention having an average grain size of the binder phase in the range above the above curve exhibits higher strength at high humidity and normal humidity than the conventional cermet. It is understood that the particle size is included in the range below the curve.

Next, the cermet of the present invention will be explained using Examples and in comparison with Comparative Examples.

Example 1 As raw material powders, Tic powder, ZrC powder, and H
fC powder, VC powder, NbC powder, TaC powder, Cr3
C2 powder, Mo2 C powder, WC powder, ZrN powder, H
fN powder, VN powder, NbN powder, TaN powder, Cr2
N powder, TiN powder, Ni powder, Co powder, and Fe powder were prepared, and these raw material powders were each blended into the composition shown in Table 1, mixed in a wet ball mill for 72 hours, and dried. After that, the powder compacts are press-formed under normal conditions, and then these compacts are sintered in vacuum at the temperature shown in Table 1. After sintering, the eutectic is determined from the sintering humidity. After normal cooling at a cooling rate of about 5°C/min up to a temperature of +10°C, slow cooling at a cooling rate of 0.02°C/min in the temperature range from eutectic temperature +10°C to eutectic temperature -10°C, Subsequently, the cermets 1 to 15 of the present invention having substantially the same composition as the blended composition were manufactured by normal cooling at a cooling rate of about 0.degree. C./min.

For comparison purposes, Comparative Cermets 1 to 1 were made using the same material except that after sintering, they were normally cooled at a cooling rate of approximately ℃/min.
5 was manufactured.

Next, the binder phase average grain size and high-temperature transverse rupture strength of the resulting cermets 1 to 15 of the present invention and comparative cermets 1 to 15 were measured, and the measurement results are shown in Table 1.

The average grain size of the binder phase was determined by measuring the grain size of the entire wide side of a high-temperature transverse rupture strength measurement specimen with the dimensions shown below with the polished surface thermally etched, and expressed as the average value. .

In addition, the high temperature transverse rupture strength is as follows: Specimen size: 4m, X8zllll×
24mm, distance between fulcrums, 20mm, test temperature: 1000
°C, stress increase rate: 1 kg/2 seconds, test atmosphere:
The test was conducted under the conditions of argon gas, number of test pieces: 3, and test mode: 3-point bending of the polished surface, and the results were expressed as an average value.

As shown in Table 1, it is clear from the relative comparison between the cermet of the present invention and the comparative cermet, which have the same component composition and sintering humidity but different cooling flexibility after sintering. It can be seen that the cermets of the invention whose average grain size lies in the range above the curve shown in the accompanying drawings have a higher high temperature transverse rupture strength (high temperature strength) than the comparative cermets which lie below said curve.

Example 2 The humidity range from eutectic temperature +10°C to eutectic temperature -10°C is approximately 0
．． The cermet 16 of the present invention was manufactured under substantially the same conditions as the cermet 1 of the present invention in Example 1, except that the cermet 16 was slowly cooled at a cooling rate of 0.07°C/min.

Regarding this cermet 16 of the present invention, under the same conditions as in Example 1, the average grain size of the binder phase and the temperature of 1000° C.
When the high temperature transverse rupture strength was measured, the average crystal grain size of the binder phase was 10.1 mm, and the high temperature transverse rupture strength was 125 kg/mm.
In addition, room temperature bending crab 265 kg/am2
showed that.

In addition, comparison cermet 1 is room temperature bending crab 230kg/
From the comparison of the above-mentioned inventive cermet 16 with the inventive cermet 1 and comparative cermet 1 in Example 1, it was found that in the cooling process after sintering, a temperature range of a predetermined width above and below the eutectic temperature was observed. It is clear that the more slowly the binder phase is cooled, the coarser the grain size of the binder phase becomes, and as the grain size becomes coarser, the high temperature and room temperature strengths increase proportionally.

As mentioned above, the cermet of the present invention has excellent strength especially at high temperatures, so it exhibits extremely excellent performance when used as cutting tools, wear-resistant tools, impact-resistant tools, etc. that require high-temperature strength. That's what I do.

[Brief explanation of drawings]

The attached drawings are diagrams showing the range of the present invention with respect to the content of the binder phase forming component and the average grain size of the binder phase.

Claims (1)

[Claims] 1. One or more iron group metals as a binder phase forming component; 5 to 30%; Zr, Hf, V, Nb as a hard phase forming component. Contains 5 to 50% of carbides and nitrides of Ta and Cr, carbides of Mo and W, and one or more of titanium nitride, with the remainder being titanium carbide as a hard phase forming component. In a cermet having a composition consisting of unavoidable impurities (more than % by weight), the average crystal grain size of the binder phase with respect to the content of the binder phase forming component is determined by the relationship diagram between the average crystal grain size of the binder phase and the content of the binder phase forming component in the attached drawing. A high-strength cermet whose strength is improved by setting the cermet to a range above the curve shown in .