JPH075381B2 - Method for producing cubic boron nitride-based ultra-high pressure sintered body for cutting tool - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention has an excellent toughness, and is a cubic boron nitride (hereinafter referred to as cubic boron nitride) suitable for use as a cutting tool for intermittent cutting of hardened steel such as hardened steel. , CBN) based sintered body.

[Conventional technology]

In recent years, the switching from grinding of high hardness steel such as hardened steel to cutting with higher processing efficiency has progressed rapidly, and along with that, a sintered body based on CBN, which has high hardness, is a cutting tool material. It has come to be noted as, for example, CBN
Powder, one or both of Ti nitride powder and carbonitride powder, and Al powder are mechanically mixed, press-molded, and the molded body is sintered under ultrahigh pressure to produce a cutting tool. For producing a CBN-based sintered body for automobiles (see Japanese Patent Publication No. 57-3631), and a method in which a Co plate is brought into close contact with a CBN compact or an Al plate is further stacked on the Co plate It is exposed to high temperature under high pressure to infiltrate Co or further Al into the CBN compact, and at the same time sinter the CBN compact while producing compounds such as cobalt boride and aluminum nitride, and then cutting tools. A method of manufacturing a CBN-based sintered body for use in a vehicle has been proposed.

[Problems to be solved by the invention]

However, in addition to the above conventional Al powder, Ti nitride (hereinafter referred to as TiN) powder and carbonitride (hereinafter referred to as TiCN).
One or both of the powders (indicated below)
In general, it is difficult to prepare a mixed powder having a high degree of mixing, that is, high uniformity, by the method of sintering Ti compound powder) and CBN powder. Therefore, Al powder is mixed uniformly in the mixed powder. As a result, the strength of the obtained sintered body is insufficient, and when the sintered body is used as a cutting tool for cutting a cutting tool, particularly for intermittent cutting of hardened steel such as hardened steel, the cutting edge is likely to be chipped. There is a problem, and the above conventional method of infiltrating Co or further Al into a CBN compact by using a Co plate or an Al plate as an infiltrant at the same time as sintering the CBN compact has a melting point In order to generate cobalt boride, aluminum nitride, etc. while infiltrating high Co, it is necessary to sinter at a high temperature of 1400 ° C or higher. At such a high temperature, not only the surface of the CBN particles but also the inside thereof becomes unstable. However, the properties of the CBN particles themselves are lost. As a result, the characteristics of the resulting sintered body as a cutting tool, such as wear resistance, are impaired, and the strength of the sintered body cannot be expected to improve because the interface strength of the CBN particles does not rise. It was

[Findings based on research]

Therefore, the present inventors have conducted various studies to solve such problems, and as a result, on the surface of a molded body obtained by press molding a mixed powder composed of a Ti compound powder and a CBN powder, 3% of body capacity
In the state of closely contacting Al such as Al plate having the above capacity, these molded body and Al are exposed to high temperature under ultra high pressure, thereby simultaneously infiltrating Al into the molded body,
Al, a compound of Ti, when reacted with each other between CBN, Al uniformly penetrates throughout the voids of the molded body to form a sintered body having a uniform structure, the reaction with CBN particles Aluminum nitride (hereinafter referred to as AlN) and titanium boride (hereinafter referred to as TiB ₂ ) produced by the reaction while advancing near the surface of Ti compound particles and maintaining the characteristics of these particles. Binds the above particles firmly,
As a result of increasing the interfacial strength, the resulting cutting tool sintered body has significantly improved strength (toughness) while maintaining the characteristics originally possessed by Ti compound particles and CBN particles. , Was found.

[Means for solving problems]

This invention was invented based on the above findings, excellent characteristics originally provided in the CBN-based sintered body for cutting tools, for example, without damaging the wear resistance, for cutting tools with high toughness, In particular, for the purpose of providing a method for producing a CBN-based ultra-high pressure sintered body, which is suitable for use in intermittent cutting of hardened steel such as hardened steel, Ti compound powder: 30 to 60% by weight, CBN powder: a mixed powder having the following composition is prepared, and then,
While pressing the surface of the molded body obtained by press-molding this mixed powder with Al having a capacity of 3 to 10% of the capacity of this molded body, these molded body and Al were subjected to ultra high pressure. Exposed to high temperature, thereby infiltrating the molded body with Al, at the same time,
Al produced by the mutual reaction between the compound powder of Ti and the CBN powder and the constituents of these powders and Al.
A method for producing a CBN-based ultra-high pressure sintered body for a cutting tool, comprising combining Ti compound powder and CBN powder with AlN and TiB ₂ , characterized by being sintered together with N and TiB _2. is there.

[Specific Description of the Invention]

1. Ti compound powder These powders have the function of imparting welding resistance to the manufactured sintered body, but if the content is less than 30% by weight, the desired welding resistance can be secured. On the other hand, if it is contained in an amount of more than 60% by weight, the toughness is insufficient and the cutting edge is liable to be chipped.
Determined to be 60% by weight.

As the Ti compound powder, one having an average particle diameter of generally 0.02 to 5 μm, preferably 0.2 to 0.8 μm is used.

2. CBN powder CBN powder has the function of imparting wear resistance and heat resistance to the manufactured sintered body, and in the present invention, it is generally 0.2 to 10 μm.
CBN powder having an average particle size of m, preferably 1-5 μm is used.

3. Obtained Al The Al infiltrant can be used in various states such as powder, granules, chips, foil, and plate, but from the viewpoint of easy handling, foil or plate Al is generally used. When the capacity is less than 3% of the capacity of the infiltrated material, Al does not sufficiently spread in the material, while the Al content exceeds 10% of the capacity of the material.
Since Al will not be infiltrated into the compact and will remain in the compact, the volume of Al used as the infiltrant is set to 3 to 10% of the volume of the compact.

4. Sintering In the present invention, the reaction sintering under ultra-high pressure accompanied by infiltration of Al is based on a normal ultra-high pressure sintering method, that is, first, as a raw material powder, TiN powder, TiCN powder, and CBN powder are used. Is prepared, and one appropriately selected from these raw material powders is mixed in a predetermined composition, and mixed to prepare a mixed powder,
On the surface of the molded body obtained by press molding this mixed powder, separately prepared Al, for example, Al foil is closely contacted and inserted into a metal container, which is heated to a temperature of 400 to 600 ° C. for vacuum degassing. After filling the container with the ultrahigh pressure and high temperature generator, raise the pressure and temperature to 40: 7.
It can be manufactured through a basic process consisting of holding at 0 Kb and temperature: 800 to 1300 ° C. for a pressure and temperature for several minutes to several tens of minutes, cooling, and finally releasing the pressure.

Incidentally, in using the CBN-based ultra-high pressure sintered body produced according to the present invention as a cutting tool, alone or
Even when used as a throwaway chip in the state where it is compounded with a high-rigidity material such as WC-based cemented carbide or thermite, the tip of a holder made of WC-based cemented carbide or hardened steel You may use it in the state attached by brazing.

〔Example〕

Next, a method for producing a CBN-based sintered body according to the present invention will be described with reference to examples.

As raw material powders, CBN powder having an average particle diameter of 3 μm, TiN powder of 1 μm and TiCN powder of 1 μm were prepared, and these raw material powders were blended with each other at the blending ratio shown in Table 1, and then ball milled. Mixed in acetone for 5 hours to form a mixed powder.

Then, the mixed powder thus prepared was molded into a disk-shaped molded body having a diameter of 13 mm and a thickness of 1.5 mm at a pressure of ² ton / cm ² , and then a diameter was formed on these molded bodies: 13mm x thickness:
Overlapping the Al foil with the dimension of 0.1 mm,
By inserting the combination with the foil into the container of the ultra-high pressure and high temperature generator, pressure: 50 Kb, temperature: 1100 ℃, holding time: 15 minutes by ultra-high pressure sintering, according to the present invention CBN base Sintered bodies 1 to 8 were manufactured, and for comparison, the Al foil was not used and the thickness of the Al foil was replaced with:
Using only 0.03 mm Al foil, except that the volume ratio of the Al foil to the capacity of the molded body was set to 2% (conditions outside the scope of the present invention are indicated by * in Table 1), Comparative CBN-based sintered bodies 1 and 2 were respectively manufactured by the same method as described above, and further, without using the Al foil used in the above-mentioned examples, an Al powder having an average particle diameter of 0.5 μm in the mixed powder. And the molded body in the above example
It consists of powder only, Co foil with diameter: 13 mm × thickness: 0.05 mm and Al foil with diameter: 13 mm × thickness: 0.03 mm are stacked on this compact, and the sintering temperature is 1500 ° C only. By changing the above, conventional CBN-based sintered bodies 1 and 2 were manufactured by the same method as in the above example.

Then, the CBN-based sintered bodies 1 to 8 of the present invention obtained as a result are
Comparative CBN-based sintered bodies 1-2, and conventional CBN-based sintered bodies 1-2
For the purpose of evaluating the toughness, the fracture toughness value Kc is calculated,
For the purpose of evaluating wear resistance and impact resistance, cutting chips were cut from each of the above sintered bodies, brazed to a WC-based cemented carbide holder, and polished to finish, then the work material: hardened steel ( SCM-418, hardness: H _{R C:} 60) round bar (diameter: 200 mm), cutting speed: 150 meters / min, cut: 0.2 mm, feed: dry high hardness turning test under the conditions of 0.1 mm / rev. and workpiece: hardened steel with two cross-sectional L-shaped groove in the longitudinal direction symmetrically (SCM-440, hardness: H _{R C:} 45) round bar, cutting speed: 120 m / min, cut : 0.2 mm, feed: 0.1 mm / rev. Cutting time: 30 min, high-hardness steel interrupted cutting test was performed respectively, and in the above turning test, cutting was performed until the flank wear width of the cutting edge reached 0.1 mm. In the above-mentioned intermittent cutting test, the number of occurrences of defects among the six test cutting edges was measured, and these measurement results were first measured.
Shown in the table.

〔The invention's effect〕

From the results shown in Table 1, the present invention CBN-based sintered bodies 1 to 8
Have high toughness and excellent wear resistance and impact resistance (based on high toughness), and therefore interrupted cutting of hardened steel such as hardened steel that requires these properties in particular. CBN-based sintered body 1, which does not infiltrate Al at all, while exhibiting excellent cutting performance even in The comparative CBN-based sintered body 2 and the conventional CBN-based sintered bodies 1 and 2 in which the amount of infiltrated Al was insufficient were inferior in impact resistance due to low toughness, and also had wear resistance. Drop,
It can be seen that the cutting performance is remarkably inferior overall and that a cutting tool suitable for intermittent cutting of high hardness steel cannot be obtained.

As described above, according to the present invention, it is possible to produce a CBN-based sintered body having particularly high toughness and excellent wear resistance,
When used as a cutting tool for intermittent cutting of hardened steel such as hardened steel that requires these characteristics, it shows extremely excellent cutting performance, so that difficult-to-cut materials as described above become large parts. It is possible to provide a CBN-based sintered body for a cutting tool that can efficiently cut.

Claims (1)

[Claims] 1. A mixed powder having a composition of one or both of Ti nitride powder and carbonitride powder: 30 to 60% by weight, cubic boron nitride powder: balance, and Then,
While pressing the surface of the molded body obtained by press-molding this mixed powder with Al having a capacity of 3 to 10% of the capacity of this molded body, these molded body and Al were subjected to ultra high pressure. Exposed to high temperature, thereby infiltrating the molded body with Al, at the same time,
One or both of the Ti nitride powder and carbonitride powder, and the cubic boron nitride powder are produced by an interaction reaction between the constituents of these powders and Al, and aluminum nitride. And / or titanium nitride particles and / or carbonitride particles, and cubic boron nitride particles are bonded with aluminum nitride and titanium boride. For producing a cubic boron nitride-based ultra-high pressure sintered body for a cutting tool.