JP2686335B2 - Sintered materials for tools - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a sintered material for a tool used in cutting or plastic working a high hardness material such as hardened steel or cemented carbide or a heat resistant alloy. Regarding

<Prior Art> When processing hardened steel or high hardness materials such as nickel-base heat-resistant alloys and cobalt-base heat-resistant alloys, generally, carbide powder of refractory metal such as tungsten (W) is used for iron (Fe) or cobalt ( Cemented carbides that have been sintered and bonded with iron-based metals such as Co) and nickel (Ni) have been used.

In recent years, the above-mentioned cemented carbide is being adopted not as a tool but as an object to be processed, and in order to meet strict requirements for processing conditions, sintered diamond and cubic boron nitride ( CBN) sintered products have been developed. Sintered diamond is obtained by sintering diamond powder particles at a high temperature and high pressure using a cemented carbide as a binder, but is fundamentally unsuitable for processing steel having a strong affinity for carbon (C). In this regard, the CBN sintered body, which has the second highest hardness after diamond, has little reaction with iron-based metals, and therefore, in addition to high-hardness materials such as hardened steel and cemented carbide, nickel-based It is effective for processing heat-resistant alloys and cobalt-based heat-resistant alloys.

Most conventional CBN sintered bodies are obtained by mixing ceramics such as titanium carbide and titanium nitride as a binder with CBN powder and sintering them under high temperature and high pressure. As the binder, in addition to the above, nitrides of silicon and zirconium (Zr),
Further, intermetallic compounds of aluminum (Al) and titanium (Ti), intermetallic compounds of Al and Zr, etc. are known.

<Problems to be Solved by the Invention> In a tool using a conventional CBN sintered body, the hardness of the binder phase decreases in a high temperature region, so when the tool itself is processed at high temperature, CBN powder particles easily fall off from the phase, often leading to reduced wear resistance. In addition, when such a tool is installed in a processing machine that performs automatic operation for a long time, it is absolutely necessary to avoid sudden tool loss from damage to the processing machine, etc. However, the conventional CBN sintered body of this type pursues a high hardness, and cannot be said to have sufficient toughness.

The present inventors have found that aluminum oxide (alumina: Al
₂ O ₃ ) has the same room temperature hardness as titanium nitride, titanium boride, etc., and the hardness in the high temperature range of 600 to 800 ° C. is higher than these. It has also been found that Al ₂ O ₃ is effective as a binder for CBN.

At this time, in order to improve the wettability of the grain boundary between the CBN grains and the binder, and at least one of Al and Ti powder grains was added for the purpose of improving the adhesiveness. As a result of investigating the effect of the amount of added metal, it was found that the metal powder particles added to improve the properties of the grain boundary have low sinterability with respect to the binder phase. As a countermeasure against this, the idea of coating the surface of CBN grains with metal so that the metal is present only at the grain boundaries between the CBN grains and the binder phase was confirmed by experiments.

<Means for Solving the Problems> The present invention has been made based on such experimental results,
40-90% by volume of cubic boron nitride powder particles, and 5-55% by volume
A mixture of zirconium oxide powder particles and aluminum oxide powder particles to which needle-like crystals of silicon carbide were added was pressurized in the range of 40 to 60 kbar with an ultra-high pressure generator, while the temperature was in the range of 1200 to 1800 ° C. A sintered material for a tool obtained by heating and sintering is characterized in that a powder of cubic boron nitride is coated with a metal film. The cubic boron nitride is characterized in that its grain size is in the range of 1 to 3 micrometers, and the film thickness of the metal is in the range of 10 to 1000 angstroms.

In this case, a mixture of cubic boron nitride powder particles coated with a metal film, zirconium oxide powder particles and aluminum oxide powder particles to which needle-like crystals of silicon carbide were added was uniformly mixed and stirred. Then, this is charged into a container of high melting point material, and while being pressurized in the range of 40 to 60 kilobar (Kb) by an ultrahigh pressure generator such as a belt type ultrahigh pressure generator, 1200 to
The sintered material for tools is obtained by heating in the range of 1800 ° C and maintaining this state for about 0.5 to 30 minutes.

<Action> Cubic boron nitride is the main material as a sintered material for tools, and if it is less than 40% by volume, it becomes difficult to reflect the hardness of cubic boron nitride itself, and sufficient abrasion resistance is obtained. I can't. On the contrary, this cubic boron nitride contains 90% by volume.
If it exceeds 1.0, part of the hexagonal crystals undergo phase transition during sintering to deteriorate the sinterability, so that minute chipping or chipping occurs due to deterioration in toughness.

On the other hand, since a mixture of zirconium oxide and aluminum oxide exhibits the property as a binder of cubic boron nitride, if the content of these is less than 5% by volume or less than 4% by volume, the cubic boron nitride content in the sintered material for tools will be reduced. If the amount is too large, the sinterability deteriorates, leading to deterioration in wear resistance and toughness. On the other hand, if this mixture exceeds 55% by volume or 50% by volume, the amount of cubic boron nitride will be too small, and the hardness of cubic boron nitride itself should be reflected in the sintered material for tools. Becomes difficult, and the wear resistance is also deteriorated. As a general tendency, the toughness is improved as the ratio of zirconium oxide to aluminum oxide is increased, and conversely, the hardness of the binder phase is increased as the ratio of aluminum oxide is increased. From the above tradeoffs,
1 to 30 zirconium oxide to aluminum oxide
It is desirable that the content be within a volume% ratio, and a range of 1 to 10 volume% is particularly preferable.

Regarding the thickness of Al coated on the surface of the cubic boron nitride particles, if the thickness is 10 angstroms or less, the effect of improving the wettability of the cubic boron nitride particles and the binder phase by the addition of metal, improving the adhesive strength, etc. does not appear, and conversely 100 If the thickness is thicker than angstrom, the cubic boron nitride grains and the binder phase remain at the grain boundaries after sintering, and the strength of the grain boundaries is reduced, so that the wear resistance deteriorates.

<Example> 1 to 3 micrometers (μ
m) cubic boron nitride (CBN) with a grain size in the range of 10 angstrom (Å), 100 Å, 1000 Å with aluminum (Al) coated on its surface by vacuum deposition, and the average grain size. Is composed of zirconium oxide (ZrO ₂ ) and aluminum oxide (Al ₂ O ₃ ) each having a volume ratio of 0.3 μm, and the volume ratio of these is adjusted to 4:96 (= ZrO ₂ : Al ₂ O ₃ ). Silicon carbide (SiC) needle crystals to improve the toughness of the phase and tungsten carbide (WC)
It is charged into a small planetary motion type mill lined with a base cemented carbide, and the amount of methyl alcohol corresponding to 35% of the total volume of these powder particles is added to the mill for the purpose of promoting the mixing of these, With the lid on, these were kneaded for 3 hours. Then, the lid of the mill was removed in an inert gas atmosphere, and the mill was heated to 120 ° C. to evaporate the methyl alcohol, and the kneaded raw material powder was dried.

On the other hand, a sodium chloride (NaCl) powder particle is pressure-molded into a cylindrical shape with an inner diameter of 8 mm and a length of 10 mm, and a NaCl lower lid made in the same manner is integrally formed on the container body. A zirconium foil having a thickness of 20 μm is attached to these inner surfaces, and a disk made of WC-based cemented carbide having a diameter of 7.8 mm and a thickness of 2 mm is placed therein.

Then, the raw material powder after completion of the drying is charged in the inert gas atmosphere onto the disk in the container body so as to have a thickness of 6 mm, and is compacted with a protruding rod. Place the same WC-based cemented carbide disk as
Also, after stacking a 20 μm thick zirconium foil on this, insert the NaCl upper lid created in the same way as above into the container body, and seal the raw material powder in the container consisting of these container body, lower lid and upper lid. To do.

Next, the above-mentioned container was attached to the ultra-high pressure generator, and 50 Kb
The pressure was maintained at a temperature of 1650 ° C. for 30 minutes, and the raw material powder was sintered to obtain a cylindrical sintered material for a tool having a WC-based cemented carbide bonded to both ends. Then, this sintered material for tools is cut out in a state where the discs are bonded to finish the cutting edge for the bite, and this is prepared in advance with a rectangular WC-based cemented carbide tip through silver solder. A bite having a rake angle of 0 °, a clearance angle of 5 ° and a nose radius of curvature of 1 mm was prepared.

Rockwell hardness (C scale)
Is 62 round bar shaped high carbon bearing steel (SUJ2) with a cutting speed of 170 meters per minute, a depth of cut of 20 μm and a bite feed rate of 20 μm per revolution of the spindle.
After turning at a distance equivalent to the length of the meter, the wear amount of the flank of the cutting edge and the Vickers hardness of the CBN sintered material that constitutes this cutting edge, the ratio of each powder grain that constitutes the raw material powder. It changed and measured. The cutting oil was spray-supplied during the turning process.

These measurement results are shown in Table 1 and Table 2. By the way, when using a commercially available CBN sintered material using titanium nitride as a binder, the Vickers hardness is 2500, and the flank wear width of the cutting edge is It was 40 μm.

Incidentally, in this example, by coating the CBN grains with Al, the adhesion between the CBN grains and the grain boundary of the binder phase was improved, and compared with the Al-added CBN sintered material produced by the conventional inventors, Improvement in wear resistance was observed. That is, CB with Al added
The CBN sintered material having the same composition as No. 13 in Table 2 as the N sintered material had a flank wear width of 34 μm, whereas the flank wear width was 28 μm in the present example. CBN The effect of Al coating on the grains is shown.

The above-mentioned sintered materials for tools have high hardness at high temperatures
_Since a binder consisting mainly of ₃ O ₃ is used, wear resistance can be improved especially at high temperatures.
By applying the coating, the adhesion between CBN grains and the binder phase is improved, and the retention capacity of the CBN grains by the binder phase is improved compared to the conventional one. Further, in the case where SiC needle crystals are added to the binder phase, it is possible to increase the toughness of the binder phase by fiber reinforcement, and it is possible to provide a sintered material for tools with improved wear resistance and less chipping and chipping.

<Effects of the Invention> Since the sintered material for a tool of the present invention uses a binder mainly composed of aluminum oxide, which has a high hardness at high temperatures, it is possible to improve wear resistance at high temperatures. Further, since the surface of the cubic boron nitride was coated with a metal, the adhesion between the cubic boron nitride grains and the binder phase was improved, and the retention capacity of the cubic boron nitride grains by the binder phase was improved.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiro Fukaya 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries Ltd. Hiroshima Research Laboratory (72) Inventor Hideo Tsunoda 1-1, Atsunoura-cho, Nagasaki-shi, Nagasaki Prefecture No. Mitsubishi Heavy Industries Ltd. Nagasaki Research Institute (72) Inventor Fukushi Yasuda Marunouchi 2-5-1-5, Chiyoda-ku, Tokyo Mitsubishi Heavy Industries Ltd. (56) Reference JP-A-2-302371 (JP, A) Sho 61-168569 (JP, A)

Claims (2)

(57) [Claims] 1. A powder of 40 to 90% by volume of cubic boron nitride,
A mixture of 5 to 55% by volume of zirconium oxide powder and aluminum oxide powder, to which needle-like crystals of silicon carbide are added, is pressurized in the range of 40 to 60 kbar by an ultra-high pressure generator, while the temperature is 1200 to 1800 ° C. A sintered material for a tool, which is obtained by heating and sintering in the range of 1., wherein a powder of cubic boron nitride is coated with a metal film. 2. The sintered material for a tool according to claim 1, wherein the cubic boron nitride has a grain size in the range of 1 to 3 μm, and the metal film thickness is 10 to 1000 angstroms. Sintered material for tools characterized by being in the range.