JP2808755B2 - Sintered body for high hardness tools - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a sintered body for a high hardness tool using cubic boron nitride (hereinafter abbreviated as cBN).

[Conventional technology]

cBN has the highest hardness next to diamond, and its sintered body is used for various cutting tools.

As an example of a cBN sintered body suitable for cutting tools,
No. 3631 discloses cBN in an amount of 80 to 40% by volume, with the balance being carbides, nitrides, borides, silicides of Group 4A, 5A, and 6A elements of the periodic table, or mixtures or mutual solid solution compounds thereof. There is disclosed a sintered body for a high-hardness tool in which the compound is a main component, and the compound forms a continuous binder phase in a sintered body structure. Although this sintered body generally shows high performance as a cutting tool, in applications where particularly severe impact force is applied, for example, continuous cutting of hardened steel, the cutting edge is liable to be broken due to insufficient strength or wear of the cutting edge. There were drawbacks.

Japanese Patent Application Laid-Open No. 62-228450 discloses a sintered body for a high-hardness tool in which the strength and wear of the cutting edge are improved in order to eliminate such chipping of the cutting edge. In this sintered body, the binder is 25 to
50% by weight of Al, a compound containing Ti such as a carbide of Ti, and Ti
Contained in a compound containing or as WC
It contains 40% by weight of W, which reacts with cBN during sintering to form aluminum boride, titanium boride, and the like, and the cBN and the binder or the binder are firmly bound.

However, even the sintered bodies described in Japanese Patent Publication No. 57-3631 and Japanese Patent Application Laid-Open No. 62-228450 still have the following problems as a tool for cutting cast iron. . For example, when cutting high-strength graphite cast iron or high-speed gray cast iron, problems such as rapid progress of cutting edge wear leading to a short life, and crater wear on the cutting edge resulting in chipping of the cutting edge. It was still left.

[Problems to be solved by the invention]

The present invention has been made in view of the above circumstances, and provides a sintered body for a high-hardness tool which is made of a cubic boron nitride sintered body, has excellent strength and wear resistance, and exhibits excellent cutting performance even for cast iron. With the goal.

[Means for solving the problem]

In order to achieve the above object, in a sintered body for a high-hardness tool of the present invention, a sintered body obtained by sintering 45 to 75% by volume of cubic boron nitride powder and the remaining binder powder at an ultra-high pressure is used. And wherein said binder is 4-20% by weight of Al and 5-20% by weight of Hf
With the balance being HfC and (Ti _1-x M _x ) C _z (where M represents an element of group 4A, 5A or 6A in the periodic table excluding Hf, and 0 ≦ x ≦ 0.15 and 0.55 ≦ z ≦ 0.9 Is contained in a range of 9: 1 to 1: 2 by volume ratio.

[Action]

The reason why the sintered body for a high-hardness tool of the present invention is excellent in strength and wear resistance is that the binder is 4 to 20% by weight of Al and 5 to 20% by weight of Hf, and HfC and the above (Ti _1- because it includes a _x M _x) C _z, it reacts with cBN during sintering under high temperature and high pressure boride aluminum (AlB _2), aluminum nitride (AlN),
And hafnium boride (HfB ₂ ) and titanium boride (TiB ₂ ), and further, Al reacts with HfC or a (Ti _1-x M _x ) C _z compound to produce these reaction products. Has excellent wear resistance
It is presumed that N and the binder are firmly joined or the binders are firmly joined to each other. It was confirmed by X-ray diffraction that a small amount of Al was present as aluminum oxide in the sintered body, but this did not hinder the operation and effect of the present invention at all.

In addition, HfC and (Ti _1-x M _x ) C _z compounds, and the above reaction products, can impart sufficient heat resistance and oxidation resistance to the high temperature of the cutting edge in cast iron cutting or the like. In addition to being able,
It has excellent wear resistance and high-temperature strength, and can improve and improve the strength, wear resistance, heat resistance, and the like of the binder itself.

If the content of Al in the binder is less than 4% by weight, the reaction between Al and cBN will be insufficient, and if the content of Hf is less than 5% by weight,
When the reaction between Hf and Al or (Ti _1-x M _x ) C _z becomes insufficient, the holding power of cBN by the binder is weakened. Conversely, Al or H
If the f content exceeds 20% by weight, HfC, which has higher abrasion resistance than AlB ₂ or HfB ₂ , although the amount of AlB ₂ or HfB ₂ generated increases and the bonding strength between cBN and the binder increases. And (Ti
Since the relative content of _1-x M _x) C _z compound is lowered, the wear resistance of the sintered body hardness of the binder itself is reduced is reduced.

HfC in the binder in _{(Ti 1-x M x)} C z compound and volume ratio of 9: 1 to 1: The reason for limiting the 2 range, 9: HfC relatively increases beyond 1, Al in the binder is HfC or (Ti _1-x M _x )
Even if it reacts with the _Cz compound, it will still be in excess, so the wear resistance left unreacted will be reduced, and conversely, if it exceeds 1: 2 (Ti _1-x
M _x ) When the C _z compound becomes relatively large, HfC and (Ti _1-x M _x )
Since the reaction between C _z compound becomes supersaturated, because Hf reduces the remaining wear-resistant as the metal component.

In the formula (Ti _1-x M _x ) C _z , x = 0, that is, M may not be included, but when x exceeds 0.15, the amount of TiC having excellent heat resistance and wear resistance relatively decreases. , The wear resistance and high-temperature strength are reduced, making it unsuitable as a tool.
The reason why z ≦ 0.9 is that if z is less than 0.55, the amount of free Ti increases and the strength and hardness of the binder itself decreases, and if z exceeds 0.9, the amount of free Ti becomes insufficient and the binder is bonded. This is because the power is reduced. When W is used as M, the abrasion resistance and strength of the binder are improved and good characteristics are exhibited.

Furthermore, by adding at least one iron group element to the binder, the strength and strength of the binder are further increased,
The characteristics of the sintered body are further improved. This is the iron group element and Ti
It is considered that the boride is strongly bonded by the binder due to its high wettability with borides such as B ₂ and AlB ₂ .

In the present invention, the reason for setting the amount of cBN to 45 to 75% by volume is that if the amount is less than 45% by volume, the strength and hardness of the sintered body decrease,
Also, due to the relatively large amount of the binder, the mechanical wear progresses rapidly due to the high hardness portions such as the high hardness graphite contained in the cast iron, the pearlite base in the matrix, and the base subjected to the austenitic treatment. This is because cracks due to falling or impact are likely to occur. Also, if the amount of cBN is 7
If it exceeds 5% by volume, cBN will come into contact with each other,
In the case of high-strength work materials or in the case of intermittent cutting in which high pressure is applied to the cutting edge, cracks occur at the contact points between particles, and furthermore, the amount of binder is relatively reduced. This is because the bonding strength is reduced and the strength of the sintered body is reduced.

Furthermore, in general wear of a cBN sintered body, it is considered that cBN is excellent in wear resistance, so that the binder is worn preferentially and cBN falls off. Therefore, in order to homogenize the structure and suppress preferential abrasion of the binder, it is preferable to adjust the particle size as follows. The average particle size of cBN is preferably as small as possible. In particular, if it exceeds 4 μm, the binder portion becomes large and wears preferentially. More preferably, by adjusting the particle size of cBN so that the cBN having a particle size of 1 μm or less is 35 to 80% by weight and the cBN having a particle size of 3 to 6 μm is 20 to 65% by weight, the small cBN particles are interposed between the large cBN particles.
The particles are filled to homogenize the tissue. In addition, the use of fine binder powder having an average particle size of the binder powder less than 1/3 of the average particle size of cBN also promotes uniform dispersion of the binder, thereby improving wear resistance. preferable.

〔Example〕

Example 1 HfC powder and carbide powder containing Ti, and Hf powder and Al
The powder is crushed and mixed using a cemented carbide pot and ball,
A binder powder having an average particle size of 0.8 μm or less and having a composition shown in Table 1 below was prepared. These binder powders and cBN powder having an average particle size of 2.5 to 4 μm are mixed at a volume ratio of 50:50, and the mixed powder is placed in a container made of Mo, and then placed in a vacuum furnace at 10 ^-4
After degassing by heating at torr and 1000 ° C. for 20 minutes, sintering was performed at a pressure of 55 Kb and a temperature of 1400 ° C. for 30 minutes.

When each of the obtained sintered bodies was identified by X-ray diffraction,
For all sintered bodies, peaks of cBN and carbides containing Hf, as well as peaks of HfB ₂ , AlB ₂ , AlN, and TiB ₂ were confirmed, and peaks of Mo and W carbides other than Hf were found depending on the sample. Was also recognized. When the structure of the sintered body was observed with a scanning electron microscope, it was confirmed that fine cBN particles were bonded to each other via a binder.

Further, each sintered body was processed into a cutting tip, and a cutting test was performed on a spheroidal graphite cast iron FCD45 material (hardness H _B = 200).
Cutting conditions are: cutting speed 300m / min, depth of cut 0.3mm, feed 0.2
mm / rev and cut dry for 20 minutes. The results are shown in Table 2.

Example 2 73% by weight of HfC powder, 12% by weight of TiC _0.75 powder, 10% by weight of Al powder, and 5% by weight of Hf powder were pulverized and mixed in the same manner as in Example 1 and averaged as shown in Table 3 below. A binder powder having a particle size was prepared. These binder powders were mixed with the cBN powders shown in Table 3, deaerated in the same manner as in Example 1, and sintered at a pressure of 50 Kb and a temperature of 1300 ° C. for 30 minutes to obtain a sintered body.

Each sintered body is processed into chips for cutting,
FCD100 member a cylindrical body the outer circumference of the (hardness H _B = 300), cutting speed 150
Cutting was performed in a dry manner at m / min, depth of cut of 0.15 mm, and feed of 0.15 mm / rev, and the cutting time until the flank wear width reached 0.3 mm was measured. The results are shown in Table 3.

[Effects of the Invention] According to the present invention, the strength, wear resistance, and heat resistance of the binder are improved, and the high hardness cBN is firmly joined with the binder, so that the strength and wear resistance are higher than before. It is possible to provide a sintered body for a high hardness tool which is excellent in quality.

The sintered body for high-hardness tools of the present invention is particularly effective for cutting high-strength graphite cast iron and high-speed cutting of gray cast iron, and is also suitably used for cutting hardened steel and heat-resistant alloys due to its high hardness. Can.

Claims (3)

(57) [Claims] 1. A sintered body obtained by ultra-high pressure sintering of 45 to 75% by volume of cubic boron nitride powder and the remaining binder powder, wherein the binder is 4 to 20% by weight of Al. And 5-20% by weight of Hf
With the balance being HfC and (Ti _1-x M _x ) C _z (where M represents an element of group 4A, 5A or 6A in the periodic table excluding Hf, and 0 ≦ x ≦ 0.15 and 0.55 ≦ z ≦ 0.9 Wherein the compound represented by the formula (1) is contained in a volume ratio of 9: 1 to 1: 2. 2. The cubic boron nitride powder of the sintered body has an average particle size of 4 μm or less, and at least 1 μm or less of cubic boron nitride powder is 35 to 80% by weight and 3 to 6 μm of cubic crystal. The sintered body for a high-hardness tool according to claim 1, wherein the sintered body contains 20 to 65% by weight of a boron nitride powder. 3. The hardening tool according to claim 1, wherein the average particle size of the binder is less than 1/3 of the average particle size of the cubic boron nitride powder. Union.