JP2502322B2 - High toughness cermet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a high-toughness cermet suitable as a material for a cutting tool capable of high-speed cutting.

[Conventional technology]

In recent years, IVa, Va, VIa of the periodic table of titanium, tantalum, molybdenum, tungsten, chromium, zirconium, etc.
A double-carbonitride of at least one kind of transition metal selected from the group is used as a hard phase, and this is combined with a binder phase of a heat-resistant metal such as nickel or cobalt to be used as a cutting tool material.

Such cermets are conventional tungsten, titanium,
Compared with a sintered hard alloy in which double carbide such as tantalum is used as a hard phase and this is bonded with a metal such as nickel or cobalt,
Since the thermal fatigue resistance toughness is remarkably improved, it is almost impossible to use the conventional sintered hard alloy, and the application is being expanded to the area where only so-called cemented carbide containing tungsten carbide as the main component is not used.

However, in the field of cutting tools, where higher speed cutting is more and more demanded, the above-mentioned thermite has a drawback that crater wear that occurs on the rake face of the tool during high speed cutting is very likely to progress. Crater wear is a phenomenon in which the hard phase of the thermite is excavated in particle units and falls off. Generally, crater wear is improved by roughening the structure, but the hardness of the thermite decreases as the structure becomes rougher, so this method of improvement was naturally limited. Therefore, the inventors of the present invention, as a high toughness thermite capable of reducing crater wear during high-speed cutting, previously formed a double carbonitride having a hard phase component mainly composed of titanium, and then added nickel or cobalt to this powder. A high toughness thermite manufactured by a method of mixing powders and sintering was proposed (see Japanese Patent Publication No. 5-64695).

However, although this high-toughness thermite can uniformly disperse nitrogen in the hard phase, it has a drawback that when the nitrogen content increases, the grindability of the thermite by the grindstone remarkably decreases.

[Problems to be solved by the invention]

In view of such conventional circumstances, it is an object of the present invention to provide a high toughness thermite as a cutting tool, which reduces crater wear during high speed cutting and at the same time improves grindability.

[Means for solving problems]

The high-toughness thermite of the present invention comprises a hard phase composed of a double carbonitride of at least two transition metals selected from the IVa, Va, and VIa groups of the periodic table containing titanium as a main component and tungsten as an essential component, Nickel and cobalt and a binder phase containing unavoidable impurities, the weight ratio of nickel and cobalt in the binder phase Ni / (Ni + Co) is 0.3 to 0.8, and the atomic ratio of nitrogen and carbon contained in the whole is N / (C + N) is 0.3
.About.0.6, the cobalt content A weight% and the nickel content B weight% and the saturation magnetic amount C gauss of the cermet
cm ³ / g satisfies the relationship of C ≧ 0.73 × (20.2 × A + 6.8 × B), and yellow or brown particles are absent or 0.01 volume% or less even if they are present.

In order to produce the high-toughness thermite of the present invention, Ti or Ti is used as a raw material powder of titanium and tungsten which are essential components.
(CN) powder or WC powder is not used as it is, but it is made into a double carbonitride by subjecting it to solid solution treatment at a temperature higher than the sintering temperature in a nitrogen atmosphere together with other hard substance powders. Mix with powder of nickel and cobalt and sinter. At that time, the saturation magnetic amount of the obtained high toughness thermite is controlled, and as a method thereof, a method of adjusting the amount of carbon mixed with the raw material powder, a method of using carbon or nitrogen as the sintering atmosphere, a metal in the raw material powder, There is a method of mixing powdery titanium or powder of titanium carbide or nitride.

Incidentally, the raw material powder may contain inevitable impurities such as iron mixed in the manufacturing process in a range not affecting the characteristics,
Further, carbon powder can be mixed in order to improve the sinterability as is usually done.

[Action]

The present inventors have variously studied the improvement of the grindability of the high toughness thermite proposed in the above Japanese Patent Publication No. 5-64695, and as a result, the grindability is better as the hard phase component dissolved in the binder phase is smaller. I found out that Therefore, the saturation magnetism was adopted as a parameter showing the purity of the binding metals nickel and cobalt, and the relationship between the saturation magnetism of the thermite and the grindability was examined. The saturation magnetic quantity of pure cobalt is 2020 G (gauss) cm ³ / g, the saturation magnetic quantity of pure nickel is 680 Gcm ³ / g, and the saturation magnetic quantity of the cermet containing these is the weight fraction of cobalt or nickel. It decreases as the rate decreases or the purity of cobalt or nickel decreases.

Therefore, the cobalt content A weight% and the nickel content B weight%, and the saturation magnetic amount C gauss cm of the cermet
^The present invention was found by finding that the cermet exhibits good grindability in the range where C ≧ 0.73 × (20.2 × A + 6.8 × B) with ³ / g. Is.

A higher nickel / cobalt weight ratio Ni / (Ni + Co) is preferred, but if this value exceeds 0.8, the hardness of the cermet decreases, and if it is less than 0.3, the crater wear resistance cannot be improved by increasing the interfacial strength. . Further, in the cermet, the greater the content of nitrogen, the lower the sinterability, but
According to the present invention, the sinterability is good even if the nitrogen content is large, and the atomic ratio N / (C + N) of nitrogen and carbon can be set in the range of 0.3 to 0.6. If this value is less than 0.3, the toughness of the cermet is reduced, and if it exceeds 0.6, the wear resistance of the cermet is reduced.

However, in order to obtain the effect of improving the toughness and strength of the thermite, it is important that nitrogen is uniformly dispersed in the hard phase. In conventional nitrogen-containing sintered hard alloys, yellow or brown particles can be observed in the hard phase structure by an optical microscope due to nitrogen segregation. These yellow or brown particles are titanium nitride or carbonitride, and as long as these particles appear, pores are likely to be generated due to decomposition in the high concentration part of nitrogen, and the effect of nitrogen content is sufficiently exerted in the low concentration part. It was found that the characteristics deteriorate, such as not being performed. However, as described in JP-B-5-64695, a double carbonitride having a hard phase component mainly composed of titanium is formed in advance, and the double carbonitride powder is mixed with a powder of nickel or cobalt and baked. According to the binding method, nitrogen can be uniformly dispersed, and no yellow to brown particles are present. Even if yellow or brown particles are present, if they are 0.01 vol% or less, they have no effect on the effect of improving strength and toughness.

Further, in the high-toughness thermite of the present invention, by having a structure containing substantially no molybdenum, the cutting characteristics can be further improved without deteriorating the grindability of the thermite.

〔Example〕

Example 1 In a ball mill, 70% by weight of a commercially available Ti (CN) powder having an average particle size of 2 μm (C / N ratio 5/5), 10% by weight of TaC powder and 20% by weight of WC powder having almost the same particle size were used. Mix for 10 hours, nitrogen partial pressure 400 torr
Was subjected to a solid solution treatment at 1800 ° C. for 1 hour in a nitrogen gas stream to form a double carbonitride (TiTaW) CN containing Ti as a main component. It was confirmed by X-ray diffraction that the peaks of TaC and WC had disappeared in this double carbonitride.

After grinding this double carbonitride with a ball mill for 20 hours,
0 mesh or less Ni powder and Co powder and, if necessary, free C powder were added to obtain the composition shown in Samples 1 to 5 in Table 1, a solvent was further added, and the mixture was mixed in a wet ball mill for 20 hours. 3% by weight of camphor was added to the obtained mixed powder, and the mixture was pressed and molded at ² t / cm ² . The green compact was sintered at 1500 ° C. for 1 hour in a nitrogen gas stream with a nitrogen partial pressure of 10 torr.

Also, as samples 6 to 8, the same Ti (CN) powder, TaC as above
Powder and WC powder without solid solution treatment
The powder, Co powder and, if necessary, free C powder were mixed and sintered in the same manner as above.

When each of the obtained samples was observed with an optical microscope for the presence of yellow to brown particles, the presence of yellow particles was confirmed in Comparative Examples 6 to 8.

The hardness (Hv), fracture toughness (K ₁ c) and strength (kg / mm ² ) of each of the thermites of Samples 1 to 7 were measured, and the crater wear depth (mm) under cutting condition 1 in Table 2 was measured.
And flank wear amount (mm), chip damage rate (%) under cutting condition 2, saturated magnetic amount (Gcm ³ / g), and grinding resistance Fn in the normal direction by a grinding test under the conditions shown in Table 4. (N / mm) was measured and the results are shown in Table 3. The cermets of the present invention (Samples 2 to 4) are comparative cermets (Samples 1 and 5).
It was found that the crater wear resistance and the toughness are particularly excellent in comparison with the above-mentioned items.

Table 4 Grinding wheel: Resin bond diamond grinding wheel (# 200) Grinding method: Surface plunge grinding Grinding speed: 40m / sec Feed: 0.20mm / sec Depth of cut: 0.02mm Example 2 64% by weight of commercially available Ti (CN) powder having an average particle size of 2 μm, 8% by weight of TaC powder, 20% by weight of WC powder and 8% of Mo ₂ C powder having almost the same particle size.
% With a ball mill for 10 hours, nitrogen partial pressure 400tor
In a nitrogen stream of r, solid solution treatment was performed at 1800 ° C. for 1 hour to form a double carbonitride containing Ti as a main component. It was confirmed by X-ray diffraction that the peaks of TaC, Mo ₂ C and WC disappeared in this double carbonitride.

This Mo-containing double carbonitride was crushed in a ball mill for 20 hours, and then Ni powder, Co powder and free C powder of 100 mesh or less were added to obtain the composition shown in Samples 9 and 10 of Table 5, and a solvent was further added. In addition, the mixture was mixed for 12 hours with a wet attritor. 3% by weight of camphor was added to the obtained mixed powder, and the mixture was pressed at ² t / cm ² . This green compact was sintered at 1450 ° C. for 1 hour in a nitrogen gas stream with a nitrogen partial pressure of 10 torr.

The characteristics and cutting performance of each sample were measured in the same manner as in Example 1, and the results are shown in Table 6. Comparing the sample 10 in which the double carbonitride contains Mo and the sample 3 in Example 1 having an approximate composition except that the double carbonitride does not contain Mo, the cermet of the sample 3 containing no Mo is more preferable. It can be seen that it has excellent cutting performance.

Furthermore, the samples 3a, 3-b, 9-a, 9 of the same composition as the sample 3 of the first embodiment and the samples 9, 10 of the present embodiment, respectively, in which only the saturation magnetic amount was changed. -B, 10
-A and 10-b were produced, and a grinding test was performed on each sample under the same conditions as in Example 1 to obtain a grinding resistance Fn in the normal direction.
Was measured. The results are shown in Table 7 together with the saturation magnetic amount.

From Table 7, between the Co content A (% by weight) and the Ni content B (% by weight) in the sample and the saturation magnetic amount C (Gcm ³ / g),
It can be seen that Samples 3, 9 and 10 in which the relationship of C ≧ 0.73 × (20.2 × A + 6.8 × B) exists exhibit better grindability than other samples in which the above relationship does not hold.

〔The invention's effect〕

According to the present invention, it is possible to provide a high-toughness thermite as a cutting tool, which is excellent in crater wear resistance during high-speed cutting and also excellent in grindability, and can achieve a low processing cost.

Claims (1)

(57) [Claims] 1. A hard phase comprising a double carbonitride of at least two transition metals selected from the IVa, Va, and VIa groups of the periodic table containing titanium as a main component and tungsten as an essential component, and nickel and cobalt. And a binder phase containing unavoidable impurities, and the weight ratio of nickel and cobalt in the binder phase is Ni.
/ (Ni + Co) is 0.3 to 0.8, the atomic ratio N / (C + N) of nitrogen and carbon contained in the whole is 0.3 to 0.6, the cobalt content A weight% and the nickel content B weight% And the saturation magnetic amount C gauss cm ³ / g of Cermet is C ≧ 0.73 ×
A high toughness thermite satisfying the relationship of (20.2 x A + 6.8 x B), wherein yellow or brown particles are absent or 0.01 volume% or less even if they are present.