JP2971203B2 - Sintered materials for tools - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered material for a tool used for cutting or plastic working of a hard material such as hardened steel or cemented carbide, or a heat-resistant alloy.

[0002]

2. Description of the Related Art When machining hardened steel or a high-hardness material such as a nickel-base heat-resistant alloy or a cobalt-base heat-resistant alloy, a carbide powder of a high melting point metal such as tungsten is generally mixed with an iron-based metal such as iron, cobalt or nickel. Sintered cemented carbide has been used. In recent years, in addition to the above-mentioned cemented carbide being used 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 ( A device using a sintered body or the like has been developed. Sintered diamond is obtained by sintering diamond particles at a high temperature and high pressure using a cemented carbide as a binder, but is fundamentally unsuitable for processing steel or the like having a strong affinity for carbon. In this regard, since the CBN sintered body having the second highest hardness after diamond has little reaction with iron-based metals, it is possible to use nickel-based materials in addition to high-hardness materials such as hardened steels and cemented carbides, in addition to all types of workpieces other than diamond. It is effective for processing heat-resistant alloys and cobalt-based heat-resistant alloys.

In a conventional CBN sintered body, a ceramic such as titanium carbide or titanium nitride serving as a binder phase is independently mixed with CBN powder particles, and a metal component is added to improve sinterability. Most are sintered below. As the material of the binder phase, in addition to the above materials, carbides of silicon or zirconium, nitrides of silicon or zirconium, intermetallic compounds of aluminum and titanium, and intermetallic compounds of aluminum and zirconium are known.

[0004]

In the case of a tool using a conventional CBN sintered body, the hardness of the binder phase decreases in a high-temperature region.
CBN powder particles are likely to fall off from the binder phase, often leading to a decrease in wear resistance. In addition, when such a tool is incorporated into a processing machine that performs automatic operation for a long time, the occurrence of sudden tool loss should be absolutely avoided in terms of damage to the processing machine and a decrease in equipment operation rate. However, this type of conventional CBN sintered body pursues high wear resistance, but cannot be said to have sufficient toughness.

[0005] In view of such circumstances, an object of the present invention is to provide a sintered material for a tool which has an improved ability to carry CBN powder particles of a binder phase, and particularly has improved wear resistance at high temperatures. I do.

[0006]

As a result of various studies to achieve the above object, as a binder phase, a needle-like crystal of zirconium oxide, aluminum nitride and silicon carbide is mainly composed of titanium nitride and aluminum oxide. It has been found that the use of a mixed powder having a constant ratio of CBN as a subcomponent increases the ability of the binder phase to support CBN powder, thereby improving wear resistance and chipping resistance. The present invention has been made based on this finding, and the sintered material for a tool according to the present invention has 40 to 70% by volume of cubic boron nitride powder and 15 to 70% by volume of titanium nitride which is a main component of a binder phase. 45% by volume, and 15 to 35% by volume of a powder mixture of needle-like crystals of aluminum oxide, zirconium oxide, aluminum nitride, and silicon carbide, which are subcomponents of the binder phase. The composition of the auxiliary component is 50 to 65% by volume of aluminum oxide, 1 to 5% by volume of zirconium oxide, 20 to 40% by volume of aluminum nitride, and 5 to 15% by volume of silicon carbide needle crystals. I do.

Here, the present invention will be described in comparison with a conventional CBN sintered tool.

First, the state of wear of a conventional CBN sintered tool will be described with reference to the drawings. FIGS. 4A and 4B schematically show how the flank and the rake face of the CBN sintered tool are worn when cutting hardened steel. As shown in both figures, in the cutting process, when the CBN particles 11 of the tool tip 10 drop off from the bonding phase 12 and the dropped CBN particles 11 pass through the boundary between the work material 13 and the flank 10a, It is considered that a streak a is left on the flank 10a, and the streak a determines the flank wear width (V _B ), that is, the wear resistance. In the figure, 10b indicates a rake face. And
The falling off of the CBN grains 11 is caused by abrasion of a portion of the cutting edge portion having a function of supporting the CBN grains 11 in contact with the work material 13 of the bonding phase 12, and external force (cutting force, thermal stress, etc.) is reduced. At the stage where the force for supporting the CBN particles 11 is exceeded, the CB
It is considered that the CBN particles fall off from the cutting edge portion 10 due to the separation between the N particles 11 and the binder phase 12 at the grain boundary or the breakage of the binder phase 12. Further, from such a fact, it is considered that in the CBN sintered tool, the CBN grains have a function as a cutting edge, and the binder phase has a function as a carrier of the cutting edge.

From such a viewpoint, the function of the CBN grains and the binder phase when a CBN sintered tool is produced from the sintered material for a tool according to the present invention will be considered. First, CB as a cutting blade
Since N grains have hardness next to diamond and have low reactivity with iron group metals, which are disadvantages of diamond, they can be expected to have high abrasion resistance. It is considered to be sufficient.

On the other hand, it is considered that the binder phase needs to have the following four characteristics in view of the wear mechanism described above. That is, in order to increase the wear resistance of the binder phase and to suppress the retreat speed of the binder phase at the cutting edge due to wear, the hardness at the cutting edge temperature during cutting is high, and the work material (steel, Low reactivity with iron group metals). Also, CB
In order to make it difficult for the N grains and the binder phase to fall off due to peeling at the grain boundary, they mutually diffuse and react with the CBN grains and firmly adhere to each other. For this reason, it is required that the sinterability be good (densify at a low sintering temperature), and the strength and toughness be high.

Therefore, the binder phase according to the present invention will be considered for each of these characteristics. FIG. 1 shows the hardness of various binder phases of a CBN sintered tool. Generally, carbides, borides, and transition metals of Groups 4a, 5a, and 6a of the periodic table are used.
High hardness of nitride. Titanium nitride (hereinafter, referred to as TiN) used in the present invention is contained therein and has high hardness, and aluminum oxide (hereinafter, alumina or Al) is used.
₂ O ₃ ) shows a high value of hardness at the cutting edge temperature during cutting, and thus it is considered that the binder phase in the present invention satisfies the above characteristics.

FIG. 2 shows the free energy of formation (ΔG _T °) for steel at the cutting edge temperature of various bonding phases.
When such free energy of formation is used as an index of reactivity with steel and the like, carbides and nitrides of transition metals of Groups 4a, 5a and 6a of the periodic table, ie, TiN and aluminum nitride (hereinafter referred to as AlN) used in the present invention. Oxides such as alumina and zirconium oxide (hereinafter referred to as ZrO ₂ or zirconia) used in the present invention are presumed to have low reactivity, and it is considered that the binder phase used in the present invention satisfies the characteristics described above. Conceivable.

When the reactivity between the binder phase and the CBN particles is similarly evaluated by using the free energy of formation as an index, the possibility of reacting at the sintering temperature (1400 to 1800 ° C.) is as follows. Among the carbides, borides and nitrides of the transition metals of Groups 4a, 5a and 6a, TiN, AlN,
In addition to niobium nitride (hereinafter referred to as NbN), it is limited to several types. Therefore, the present invention provides T as a main component of the binder phase.
Since iN and AlN are included as one component of the subcomponent, it is considered that the above-described characteristics are also provided.

Next, in order to examine the above-mentioned properties relating to the soundness of the sintered body, CBN using only TiN as a binder phase was used.
A cutting tool was manufactured and a cutting test was performed. Manufactured CBN
The sintering tool contains 50 volume% of CBN particles having a particle size of 1 to 3 μm,
50% by volume of TiN powder having a particle size of 0.5 to 2 μm are mixed by a ball mill, and a pressure of 50 kbar (hereinafter, referred to as Kb) and a sintering temperature of 1400 to 1750 are obtained by using a conventionally known ultra-high pressure generator. °, and sintering time of 0.5 to 30 minutes, ultra-high pressure sintering, and this was bladed in a tool shape. Cutting test this [workpiece SUJ2 (hardness H _RC 6
2 or more), cutting speed 100m / min, feed 0.1min /
rev, a notch of 0.1 mm], it did not reach the wear resistance and chipping resistance of the conventional CBN sintered tool regardless of the conditions such as the sintering temperature and the sintering time. Also, such CBN
When the fracture surface of the sintered tool was observed under a microscope, it was observed that the fracture surface was broken at the TiN grain boundary.

Therefore, in the present invention, the sinterability is high,
Further, a sintered body having high soundness is obtained by adding alumina having the above-mentioned characteristics to TiN, and further adding AlN having the above-mentioned characteristics and having high activity at the time of sintering. In the present invention, the sinterability is improved by adding a small amount of zirconia to alumina, and the toughness is improved by adding silicon carbide needle-like crystals (hereinafter referred to as SiC needle-like crystals). ing. As described above, in the present invention, it is considered that the above-described characteristics are satisfied by using a binder phase in which a specific amount of alumina, zirconia, AlN, and SiC needle crystals are added to TiN.

Next, the operation of the present invention will be described. CBN is mainly used as a sintered material for tools.
If it is less than 0% by volume, it becomes difficult to reflect the hardness of CBN itself, and sufficient abrasion resistance cannot be obtained. On the other hand, if the CBN exceeds 70% by volume, a part of the CBN undergoes phase transition to hexagonal crystal during sintering, and the sinterability deteriorates.

On the other hand, TiN, which is the main component of the binder phase, has the characteristics of high melting point, high hardness, and low reactivity with steel. It is one of the materials showing the highest values at the cutting edge temperature. Also, it is considered that TiN shows a sharp decrease in hardness from around 1000 ° C., and becomes soft and easily flows in a high temperature range above the sintering temperature (1400 ° C.). Therefore, it can be assumed that TiN can flow between CBN grains during sintering, which is effective for densification of the sintered body.
Furthermore, since TiN can be expected to react with CBN particles,
Adhesion between the binder phase and the CBN particles occurs, and a sintered body having high soundness and good characteristics is obtained.

Alumina, which is a subcomponent of the binder phase,
It has high melting point, high hardness, and low reactivity with steel. As described above, it has excellent properties similar to TiN as a material component of the binder phase, but cannot be expected to have reactivity with CBN particles.
Therefore, when alumina is used as the main component of the binder phase, it is necessary to add a metal component or the like in order to improve the reactivity with CBN particles. In the present invention, AlN having high activity during sintering is used. Sinterability is greatly improved by the addition. Thereby, the soundness as a CBN sintered material is improved, and a material having high wear resistance and fracture resistance as a tool material can be provided. In the present invention, alumina and AlN
Is added and sintered so as to fill a gap between main components of a CBN sintered material composed of CBN grains and TiN grains, and has a role of bonding the TiN grains and the TiN grains between the grains. Fulfill.

Considering the role of alumina, it is essential that the sinterability of alumina itself be good, and it is necessary to further improve the toughness. However, in the present invention, zirconia and carbonized alumina are used in the present invention. The sinterability and toughness are improved by using a composition to which silicon needle crystals are added as a secondary component of the binder phase.

Here, the composition of the subcomponent will be described. As described in the above description, the binder phase of the CBN sintered material itself needs to be a tool having high wear resistance. Therefore, the composition cannot be arbitrarily selected, but its composition becomes important. Therefore, a tool material with only the binder phase in which the composition was changed was prototyped, and the wear resistance was evaluated by a cutting test. The conditions were a cutting speed of 170 m / min and a feed of 20 μm /
Spindle rotation, cut 20μm, work material SUJ2 (hardness H
_RC 62).

First, the composition was examined by limiting the components to alumina and aluminum nitride. When the volume percentage of aluminum nitride relative to the volume percentage of alumina was 1/3 or less, the brittleness of alumina appeared and the flank wear width became 70 μm or more. Similarly, when the ratio is 4/5 or more, the hardness of aluminum nitride is low, and the flank wear width is 70 μm or more. From this study, it was found that it was necessary to mix alumina and aluminum nitride as auxiliary components in a range of 3: 1 to 5: 4 (volume ratio).

Next, from the same experiment, if the amount of needle-like crystals added to the two-component system mixed in the above-mentioned appropriate range is less than 5% by volume, the effect of the addition does not appear.
When the content is 5% by volume or more, it is recognized that the sinterability is reduced and the toughness is reduced.

Further, the effect of changing the amount of zirconia added to the ternary system in which SiC needle crystals were added to the above two components was examined. FIG. 3 shows the results of the test. When zirconia was added in less than 1% by volume, the effect of the addition was not exhibited. On the other hand, when added in more than 5% by volume, the sinterability was relatively low. It was recognized that the abrasion resistance was deteriorated due to poor quality. The evaluation of the wear resistance was performed under the same conditions as described above.

Next, the composition (mixing ratio) of the CBN grains and the main and subcomponents of the binder phase will be described. In the gap generated when the CBN particles and the main component of the binder phase are mixed, the auxiliary components (alumina 50 to 65% by volume and zirconia 1 to 5% by volume)
And AlN 20 to 40% by volume, SiC needle-like crystals 5 to 15
% By volume) and the sub-components fill the gaps between the main components of the CBN grains and the binder phase after sintering, and the sub-component sintered bodies are connected in a network in the sintered body. It is considered that the addition of 15% by volume or more of the auxiliary component is theoretically necessary to achieve the above.

Considering the mixing ratio of the CBN particles and the main component of the binder phase, as described above, the minimum content of the CBN particles is desirably 40% by volume, and the subcomponent of the binder phase has the minimum amount (15% by volume). In the case of, the ratio of the main component is maximized. Therefore, the maximum mixing ratio of the binder phase main component is 45% by volume.
Becomes On the other hand, in order to form a structure in which the main component of the binder phase itself is connected in a network like the subcomponent, it is necessary to add the main component in an amount of 15% by volume or more.

Further, if the added amount of the sub-component in the binder phase exceeds the added amount of the main component, the original wear resistance is impaired, so that the maximum ratio of the sub-component is 35% by volume.

The sintered material for a tool of the present invention described above is
It can be manufactured using a conventionally known ultrahigh pressure sintering apparatus.
That is, first, the CBN powder and the main component and the subcomponent of the binder phase are mixed at a predetermined mixing ratio by a ball mill or the like to obtain a uniform mixed powder. Next, the mixed powder is compacted by a compacting press or the like, and this is filled in a container made of a high melting point metal such as zirconium. Thereafter, the temperature is set to 1400 to 1800 ° C. and the pressure is set to 4 by the ultra-high pressure sintering technique described in, for example, New Ceramics (1988), Vol.
After maintaining the pressure and temperature at 0 to 60 Kb for 0.5 to 30 minutes, the pressure is removed by cooling to produce a sintered body.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

CBN having a particle size in the range of 1 to 3 micrometers (hereinafter referred to as μm) synthesized by a non-catalytic method.
And a mixed powder of TiN having an average particle diameter of 0.5 to 1.5 μm, alumina, zirconia, AlN, and SiC needle crystal having an average particle diameter of 0.3 μm (volume ratio of 57: 3: 30: 10 ) And their volume ratio is 45: 30: 2
5 (= CBN: TiN: Al ₂ O ₃ / ZrO ₂ , Al
N and SiC needle-shaped crystals) are charged into a small planetary motion mill lined with tungsten carbide (hereinafter abbreviated as WC) based cemented carbide to further promote the mixing thereof. For the purpose, an amount of methyl alcohol corresponding to 35% of the total volume of these powder particles was added into the mill, and the mixture was covered and 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 (hereinafter referred to as "NaCl") powder is pressed into a cylindrical body having an inner diameter of 8 millimeters and a length of 10 millimeters to form a NaCl container body. And a 20 μm-thick zirconium foil is adhered to the inner surface of the lower cover, and a WC-based cemented carbide disk having a diameter of 7.8 mm and a thickness of 2 mm is placed in the lower cover. Have things ready.

After the drying is completed, the raw material powder is compacted in advance to a thickness of 6 mm by a powder compacting press or the like, and is charged onto the disk in the container body in an inert gas atmosphere. . Then, a disk made of the same WC-based cemented carbide as described above is placed thereon, and a thickness of 20 mm is further placed thereon.
After stacking a zirconium foil having a thickness of μm, the upper lid made of NaCl prepared in the same manner as above is fitted into the container main body, and the raw material powder is sealed in a container composed of the container main body, the lower lid, and the upper lid.

Next, the above-mentioned container was attached to an ultrahigh pressure generator, a pressure of 50 Kb and a temperature of 1650 ° C. were maintained for 30 minutes, the raw material powder was sintered, and a circle having a WC-based cemented carbide bonded to both ends was obtained. A columnar sintered material for a tool was obtained. Then, the sintered material for the tool is cut out in a state where the disc is bonded to finish a cutting edge for a cutting tool, and this is inserted into a square WC-based cemented carbide chip prepared in advance through a silver solder. Rake angle 0 °, clearance angle 5 °, nose radius of curvature 1
Millimeter cutting tools were created.

Using this cutting tool, a cutting speed of 170 m / min, a cutting depth of 20 μm, and a high carbon bearing steel (SUJ2) in the form of a round bar having a Rockwell hardness of 62 were obtained.
After turning by a distance equivalent to a length of 100 meters so that the feed speed of the cutting tool is 20 μm per revolution of the spindle, the wear width of the flank of the cutting edge and the C
The Vickers hardness of the BN sintered material was measured by changing the ratio of each particle constituting the raw material powder. During this turning, cutting oil was sprayed and supplied.

The same cutting test was performed by changing the volume% of the composition of the present embodiment and the results are shown in Tables 1 and 2. Incidentally, the composition obtained by adding a metal component to titanium nitride was used as a binder phase. The commercially available CBN sintered tool used has a Vickers hardness of 2500 and the wear width of the flank of the cutting edge is 45 μm.
Met.

[0034]

[Table 1]

[0035]

[Table 2]

As is evident from the results shown in Tables 1 and 2, those containing 40 to 70% by volume of CBN powder, 15 to 45% by volume of the main component of the binder phase, and 15 to 35% by volume of the subcomponent. (Sample number: 2-6, 9-13, 16-20, 22
-29), since the wear width of the flank of the cutting edge falls within the range of 32 to 39 μm and has good wear resistance,
Improvement of properties such as high temperature hardness of binder phase, non-reactivity with work material,
It was confirmed that the effect of improving the sinterability by adding alumina / zirconia, AlN and SiC needle-like crystals appeared. In the case where the CBN powder particles are less than 40% by volume (Sample No .: 1) or more than 70% by volume (Sample No .: 30), the cutting edge is chipped.
In the case where the particle size of the powder is in the range of 40 to 70% by volume, the cutting edge can be subjected to turning without causing any chipping.

[0037]

According to the sintered material for a tool of the present invention, the main component is TiN, which has high hardness at high temperatures, and AlN which enhances the activity during sintering, and alumina which has good sinterability and high toughness. / Since a binder having zirconia and SiC needle-shaped crystals as sub-components is used, the carrying capacity of CBN particles in the binder phase is improved as compared with the conventional one, and in particular, the wear resistance at high temperatures is improved and the soundness is improved. As a result, an improved sinterability can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing the hardness of a binder phase material of a CBN sintered tool.

FIG. 2 is an explanatory view showing the reactivity of a binder phase material of a CBN sintered tool with a work material.

FIG. 3 is an explanatory diagram showing an experimental result when zirconia is added to alumina.

FIG. 4 is a schematic diagram for explaining wear of the CBN sintered tool and an enlarged view of a portion A thereof.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Tool edge 10a Flank 10b Rake face 11 CBN grain 12 Bonding phase 13 Work material

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hideo Tsunoda 1-1, Akunouramachi, Nagasaki-shi, Nagasaki Mitsubishi Heavy Industries, Ltd. Nagasaki Research Laboratory (72) Inventor Fukushi Yamada 2-5-1 Marunouchi, Chiyoda-ku, Tokyo (56) References JP-A-55-62862 (JP, A) JP-A-63-201064 (JP, A) JP-A-2-282443 (JP, A) JP-A-1-172270 ( JP, A) JP-A-55-158175 (JP, A) JP-A-5-51267 (JP, A) JP-A-4-26555 (JP, A) JP-A-4-26554 (JP, A) (58) ) Surveyed field (Int.Cl. ⁶ , DB name) C04B 35/58

Claims (1)

(57) [Claims] C. 1. 40 to 70% by volume of cubic boron nitride powder particles
And 15 to 45% by volume of titanium nitride as a main component of the binder phase
And 15 to 35% by volume of a mixed powder of acicular crystals of aluminum oxide, zirconium oxide, aluminum nitride, and silicon carbide, which are subcomponents of the binder phase, and the composition of the subcomponent of the binder phase. Is aluminum oxide 50-6
5% by volume, 1 to 5% by volume of zirconium oxide, 20 to 40% by volume of aluminum nitride, and needle-like crystals of silicon carbide 5 to 5%
A sintered material for a tool, which has a ratio of 15% by volume.