Hard sintered body for tools

A hard sintered body for tools is obtained by sintering under a superhigh pressure, a sinter powder mixture containing at least 20 percent by volume and not more than 70 percent by volume of cubic boron nitride powder and having a remainder formed of a binder powder mixture. The binder contains at least 2 percent by weight and not more than 20 percent by weight of Al and at least 2 percent by weight and not more than 20 percent by weight of W, and has a remainder formed of a Ti compound or compounds. The atomic ratio of Ti contained in the binder to a transition metal element or elements belonging to any of the groups IVa, Va and/or VIa of the periodic table including Ti is at least 2/3 and not more than 97/100. In the structure of the sintered body, cubic boron nitride crystals are bonded with each other through bonding phases formed by the binder. For forming the sintered body, at least one or more Ti compounds are selected from a group of TiN.sub.z, Ti(C,N).sub.z, TiC.sub.z, (Ti,M)N.sub.z, (Ti, M) (C,N).sub.z and (Ti,M)C.sub.z, wherein M represents a transition metal element or elements belonging to any one of the groups IVa, Va and/or VIa of the periodic table excluding Ti, and z is within the range of 0.1.ltoreq.z.ltoreq.0.40. Such a sintered body has an excellent crater wear resistance, so that it can be used for making tool inserts for high-speed cutting of steel or cast iron.

FIELD OF THE INVENTION 
The present invention relates to an improvement in a hard sintered body for 
tools made of cubic boron nitride, hereinafter referred to as CBN. 
BACKGROUND INFORMATION 
CBN is the hardest material next to diamond, and a sintered body prepared 
from the same is applied to various cutting tools. Japanese Patent 
Laying-Open No. 53-77811 (1978) discloses an example of such a CBN 
sintered body suitable for cutting tools. 
The sintered body disclosed in the above prior art contains 80 to 40 
percent by volume of CBN and has a remainder mainly formed of a carbide, 
nitride, boride or silicide of a transition metal belonging to the group 
IVa, Va or VIa of the periodic table or a mixture or solid solution 
compound thereof, with addition of Al and/or Si. In this CBN sintered 
body, the aforementioned compound forms continuous bonding phases in the 
structure of the sintered body. 
In the aforementioned hard sintered body for tools, a bonding compound is 
prepared from a carbide, nitride, boride or silicide of a transition metal 
belonging to any of the groups IVa, Va or VIa of the periodic table or a 
solid solution compound thereof. Since such a compound has an excellent 
thermal conductivity and a high hardness, the sintered body generally 
exhibits a high performance when the same is used in a cutting tool. 
However, when the sintered body which is disclosed in Japanese Patent 
Laying-Open No. 53-77811 (1978) and now on the market, is used for a 
high-speed cutting of steel, for example, so-called crater wear develops 
depending on the cutting conditions, to relatively shorten the life of the 
cutting tool. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a hard 
sintered body for tools, which is superior in crater wear resistance to 
the aforementioned conventional CBN sintered body and capable of 
high-speed cutting of steel. 
It has been found that this object has been attained by sintering a powder 
mixture containing at least 20 percent by volume and not more than 70 
percent by volume of CBN powder and having a remainder formed of binder 
powder described below, whereby the sintering takes place under CBN-stable 
conditions and under a superhigh pressure. 
According to the present invention there is provided a sintered body which 
is obtained by mixing CBN powder with a binder powder containing 2 to 20 
percent by weight of Al in the form of either Al or a compound of Al and 
Ti, and 2 to 20 percent by weight of W in the form of W, WC or a compound 
of W and Ti, or further containing 1 to 10 percent by weight of one or 
more metals from the iron group, and having a remainder formed of one or 
more Ti compound selected from a group of TiN.sub.z, TiC.sub.z, 
Ti(C,N).sub.z, (Ti,M)N.sub.z, (Ti,M)C.sub.z and (Ti,M)(C,N).sub.z, where M 
represents transition metal element(s) belonging to any one of the groups 
IVa, Va and/or VIa of the periodic table excluding Ti and wherein z is 
within the range of 0.1 z 0.40, such that the atomic ratio of Ti to a 
transition metal element or elements belonging to any one of the groups 
IVa, Va and/or VIa of the periodic table including Ti is at least 2/3 and 
not more than 97/100. This CBN binder powder mixture is sintered under a 
superhigh pressure. 
The CBN sintered body according to the present invention contains at least 
one or more Ti compounds selected from a group of TiN, TiC, Ti(C,N), 
(Ti,M)N, (Ti,M)C and (Ti,M)(C,N), titanium boride, aluminum boride, 
aluminum nitride, a tungsten compound and tungsten in addition to cubic 
boron nitride, or further containing one or more metal compounds from the 
iron group. In such a sintered body of the invention the CBN particles are 
joined to each other by bonding phases in the structure of the sintered 
body. 
For the following reasons a sintered body according to the present 
invention has an excellent crater wear resistance. 
It is generally considered that crater wear is developed since a binder is 
abraded due to friction on a tool cutting face caused by high-temperature 
shavings, whereby CBN particles are caused to fall out of the bonding and 
leave craters. In order to improve the crater wear resistance of a CBN 
sintered body, it is thus necessary to improve the wear resistance of the 
binder under a high temperature and strongly join the binder and CBN or 
constituents of the binder themselves with each other, while the strength 
of the binder and the junction strength between CBN and the binder or the 
constituents of the binder themselves must not be reduced under a high 
operating temperature which is applied to the tool cutting face during 
cutting. 
According to the present invention, the Ti compound or compounds and Al 
contained in the binder react with CBN during sintering under high 
temperature/high pressure to generate titanium boride, aluminum boride, 
titanium nitride and aluminum nitride, thereby to strongly join or bond 
CBN with the binder. In particular, excessive Ti contained in one or more 
Ti compounds selected from the group of TiN.sub.z, TiC.sub.z, 
Ti(C,N).sub.z, (Ti,M)N.sub.z, (Ti,M)C.sub.z and (Ti,M)C,N)hd z, where M 
represents a transition metal element belonging to any one of the groups 
IVa, Va and/or VIa of the periodic table excluding Ti, and wherein z is 
within the range of 0.1.ltoreq.z.ltoreq.0.40, easily reacts with CBN 
crystals to form TiB.sub.2 and TiN. 
The formation of TiB.sub.2 is beneficial since TiB.sub.2 has a high 
hardness, an excellent wear resistance and a high junction strength with 
CBN and the binder, and these characteristics do not deteriorate even if a 
high operating temperature is applied. The value of z in the above general 
formulas of the Ti compounds is within a range of 0.1.ltoreq.z.ltoreq.0.40 
since the formation of TiB.sub.2 is reduced if the value of z exceeds 0.40 
whereby the strength and the wear resistance of the binder are undesirably 
reduced. If the value of z is less than 0.1, on the other hand, the metal 
Ti remains in the binder contained in the sintered body, whereby the wear 
resistance of the binder deteriorates. 
The binder strength and the wear resistance of the binder are further 
increased by solution-treating or mixing a nitride or nitrides and 
carbo-nitride or carbo-nitrides of a transition metal or metals belonging 
to any one of the groups IVa, Va and/or VIa of the periodic table with a 
nitride and a carbo-nitride of Ti, to further improve the characteristics 
of the sintered body as compared to the case of preparing the binder only 
of a Ti compound or Ti compounds. The atomic ratio of Ti contained in the 
binder to metal or metals belonging to any one of the groups IVa, Va 
and/or VIa of the periodic table including Ti must be 2/3 to 97/100. If 
the Ti content is less than 2/3, the bond strength of the binder and CBN 
is reduced. When the atomic ratio exceeds 97/100, on the other hand, the 
wear resistance and strength of the binder are reduced. 
The binder contains 2 to 20 percent by weight of Al. The ability of the Al 
to improve the bond strength of the CBN particles and the binder is 
reduced if the Al content is less than 2 percent by weight, while the 
hardness of the binder itself is reduced if the Al content exceeds 20 
percent by weight, whereby the wear resistance is also reduced. 
The content of W in the form of W, WC or a compound of W and Ti is 2 to 20 
percent by weight. The strength of the binder is not improved if the W 
content is less than 2 percent by weight. If the content of the Ti 
compound or compounds is reduced and the W content exceeds 20 percent by 
weight, the junction strength of CBN and the binder is reduced. It has 
been found that the binder is improved in strength to exhibit excellent 
characteristics particularly when M represents tungsten in the 
aforementioned chemical formulas. 
The binder preferably contains 1 to 10 percent by weight of one or more 
metals of the iron group for further increasing the strength and hardness 
of the sintered body. This further improvement may be due to the fact that 
the metals of the iron group are highly wettable with borides such as 
TiB.sub.2 and AlB.sub.2, to attain a stronger bonding of the borides 
contained in the sintered body. If the content of the iron group metal or 
metals is less than 1 percent by weight, the characteristics are not 
improved. If the iron metal content exceeds 10 percent by weight, on the 
other hand, the binder strength itself and the binder hardness are 
reduced. The metals of the iron group include Fe, Co and Ni. 
In the sintered body according to the present invention, the CBN particles 
are held by bonding phases formed by the aforementioned binder. The CBN 
content is at least 20 percent by volume and not more than 70 percent by 
volume. If the content of the CBN particles is less than 20 percent by 
volume, the hardness of the CBN sintered body is reduced. If the content 
of the CBN particles exceeds 70 percent by volume, on the other hand, the 
toughness of the sintered body is reduced and performance of the cutting 
tool deteriorates. 
The hard sintered body according to the invention has excellent junction 
strength of CBN and the binder or constituents of the binder, whereby a 
particularly excellent crater wear resistance is achieved making the 
present sintered bodies suitable for high speed cutting tools for cutting 
steel or cast iron. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS AND OF THE BEST MODE

Example 1 
Nitride powder or carbo-nitride powder containing Ti was mixed with 
aluminum powder and WC powder to prepare a binder powder mixture having an 
average particle size of not more than 1 .mu.m. The mixing was performed 
in a container with a ball of cemented carbide in the container, as shown 
in Table 1. The binder powder mixture was then further mixed with CBN 
powder materials of not more than 3.mu.m in particle size in a volume 
ratio of 45:55 to prepare a sinter powder mixture for sintering. Circular 
plates of cemented carbide composed of WC - 10 wt. % Co were introduced 
into Mo vessels, which were then filled with the sinter powder mixture. 
The vessels were introduced into a superhigh pressure/temperature 
apparatus, and sintered under a pressure of 50 kb and a temperature of 
1250.degree. C. for 25 minutes. 
Sintered bodies thus obtained were examined by an X-ray diffraction, to 
observe peaks which are believed to be those of CBN, nitrides, carbides 
and carbo-nitrides containing Ti, TiB.sub.2, AlB.sub.2, AlN and borides 
and carbides of W, or W. 
Table 2 shows Vickers hardness values of these sintered bodies which were 
worked into inserts for cutting tools for cutting round bars of 100 mm in 
diameter made of SUJ2 (H.sub.RC :59 to 61). The cutting conditions were as 
follows: 
Cutting Speed: 210 m/min. 
Depth of Cut: 0.15 mm 
Feed Rate: 0.1 mm/rev. 
Type: Dry 
Table 2 also shows the time durations during which a tool of the invention 
could perform a cutting operation before cutting edge chipping occurred. 
Referring to Table 1, the column of "Atomic Ratio Ti:M" shows the atomic 
ratios of Ti to transition metal elements belonging to any of the groups 
IVa, Va and/or VIa of the periodic table excluding Ti. 
Referring to Tables 1 and 2, samples Nos. 8 to 12 were prepared as 
reference examples. The underlined values shown in Table 1 for the 
reference examples are out of the range of the composition according to 
the present invention. 
TABLE 1 
______________________________________ 
Atomic Ratio 
Sample No. 
Composition of Binder (wt. %) 
Ti:M 
______________________________________ 
Example 
1 75TiN.sub.0.1, 10Al, 15WC 
95.2:4.8 
2 70TiC.sub.0.2, 20Al, 10WC 
96.5:3.5 
3 75(Ti.sub.0.9 Zr.sub.0.1)N.sub.0.3, 5Al, 20WC 
92.9:7.1 
4 83(Ti.sub.0.8 W.sub.0.1 Hf.sub.0.1)(C.sub.0.2 N.sub.0.8).sub.0.4, 
1 84.1:15.9 
15Al.sub.3 Ti, 2WC 
5 75(Ti.sub.0.8 Cr.sub.0.15 M.sub.0.05)(C.sub.0.4 N.sub.0.6).sub.0. 
18, 77.7:22.3 
17Al, 2WC, 
6 75(Ti.sub.0.9 Nb.sub.0.05 V.sub.0.05)(C.sub.0.8 N.sub.0.2).sub.0. 
25, 84.5:15.5 
17Al, 2WC, 
7 83(Ti.sub.0.8 Ta.sub.0.1 Cr.sub.0.1)(C.sub.0.5 N.sub.0.5).sub.0.3 
3, 75.9:24.1 
2Al, 15WC, 
Reference 
Example 
##STR1## 96.6:3.4 
9 
##STR2## 11.2:22.8 
10 
##STR3## 70.7:29.3 
11 
##STR4## 
##STR5## 
12 
##STR6## 89.7:10.3 
______________________________________ 
TABLE 2 
______________________________________ 
Sample 
Vickers Cutting Durations Before 
No. Hardness Chipping (min.) 
______________________________________ 
Example 1 3400 55 
2 3350 48 
3 3450 52 
4 3300 59 
5 3300 57 
6 3450 53 
7 3400 51 
Reference 
8 2950 23 
Example 9 2900 22 
10 2800 14 
11 2850 18 
12 2800 15 
______________________________________ 
Example 2 
Powder materials of 76 percent by weight of (Ti.sub.0.9 Zr.sub.0.1) 
(C.sub.0.5 N.sub.0.5).sub.0.25, 12 percent by weight of Al and 12 percent 
by weight of WC were mixed with each other to obtain a binder powder 
mixture having particles of not more than 1 .mu.m in size. The binder 
powder mixture contains Ti and W in an atomic ratio of 86.1:13.9. This 
binder powder was mixed with CBN powder to prepare a sinter powder mixture 
as shown in Table 3. 
The sinter powder mixture thus obtained was sintered under a superhigh 
pressure similarly to Example 1 to obtain sintered bodies, which were made 
into inserts for cutting tools. The cutting tools with these inserts were 
used to cut outer peripheries of round bars of 300 mm in diameter made of 
SCM435 (H.sub.RC :22). The cutting conditions were as follows: 
Cutting Speed: 580 m/min. 
Depth of Cut: 0.6 mm 
Feed Rate: 0.2 mm/rev. 
Type: Dry 
Table 3 shows the time durations during which the cutting could be 
performed before cutting edge chipping occurred. Referring to Table 3, 
samples Nos. 18 and 19 were prepared as reference examples. The underlined 
values of the reference examples are out of the range of CBN content 
according to the present invention. 
TABLE 3 
______________________________________ 
cBN cBN Cutting Durations 
Sample Particle Content Before Chipping 
No. Size (vol. %) (min.) 
______________________________________ 
Example 13 not more 50 115 
than 5 .mu.m 
14 3.about.5 .mu.m 
40 105 
15 not more 70 103 
than 3 .mu.m 
16 " 50 121 
17 " 20 95 
Reference 
18 " --80 12 
Example 19 " --10 4 
______________________________________ 
Example 3 
Powder materials of (Ti.sub.0.9 V.sub.0.05 Nb.sub.0.05)(C.sub.0.2 
N.sub.0.8).sub.z having z values shown in Table 4 were mixed with Al 
powder materials and WC powder materials in ratios of 80:12:8 in weight 
percentage, to obtain binder powder mixtures having particle sizes of not 
more than 1 .mu.m. These binder powder mixtures were mixed with CBN powder 
materials having a particle size of 3 to 5.mu.m, in a volume ratio of 
50:50, to prepare a sinter powder mixture. 
The sinter powder mixture thus obtained was sintered under a superhigh 
pressure similarly to Example 1, to obtain sintered bodies. Table 4 also 
shows Vickers hardness values of these sintered bodies. 
The above sintered bodies were made into inserts for cutting tools, to cut 
outer peripheries of round bars of 80 mm in diameter made of SKD11:60). 
The cutting conditions were as follows: 
Cutting Speed: 230 m/min. 
Depth of Cut: 0.15 mm 
Feed Rate: 0.08 mm/rev. 
Type: Dry 
Table 4 also shows the time durations before cutting edge chipping of these 
inserts. 
Referring to Table 4, the column "Atomic Ratio Ti:M" shows the ratios of Ti 
contained in the binders to transition metal elements belonging to any one 
of the groups IVa, Va and/or VIa of the periodic table excluding Ti. 
Samples Nos. 20, 25, 26 and 27 were prepared as reference examples, 
whereby the underlined values are out of the range of the z values 
according to the present invention. 
TABLE 4 
______________________________________ 
Cutting 
Duration 
z-Value Before 
Sample in Ti Atomic Ratio 
Vickers 
Chipping 
No. Compound Ti:M Hardness 
(min.) 
______________________________________ 
Reference 
Example 
20 
##STR7## 87.7:12.3 2800 25 
Example 
21 0.1 87.7:12.3 3400 57 
22 0.2 87.6:12.4 3400 52 
23 0.3 87.6:12.4 3300 57 
24 0.4 87.5:12.5 3250 50 
25 
##STR8## 87.5:12.5 3150 48 
Reference 
Example 
26 
##STR9## 87.5:12.5 2950 27 
27 
##STR10## 
87.4:12.6 2950 24 
______________________________________ 
Example 4 
The binder powder mixtures shown in Table 5 were prepared in a similar 
manner as in example 1. These binder powder mixtures were further mixed 
with CBN powders having particle sizes of not more than 2 .mu.m in a 
volume ratio of 70:30, to obtain sinter powder mixtures. These sinter 
powder mixtures were sintered under a superhigh pressure and temperature 
similarly to Example 1, to obtain sintered bodies. Table 5 shows Vickers 
hardness values of these sintered bodies. 
Then the sintered bodies were made into inserts for cutting tools to cut 
outer peripheries of round bars of 70 mm in diameter made of carburizing 
steel of SNCM415 (H.sub.RC :58 to 61). The cutting conditions were as 
follows: 
Cutting Speed: 180 m/min. 
Depth of Cut: 0.1 mm 
Feed Rate: 0.08 mm/rev. 
Type: Dry 
Table 6 shows cutting-available times. 
Referring to Table 5, the column "Atomic Ratio Ti:M" shows the ratios of Ti 
contained in the binders to transition metal elements belonging to any one 
of the groups IVa, Va and/or VIa of the periodic table excluding Ti. 
Samples Nos. 31 to 33 were prepared as reference examples. The underlined 
values of these reference examples shown in Table 5 are out of the range 
of composition according to the present invention. 
TABLE 5 
______________________________________ 
Atomic Ratio 
Sample No. 
Composition of Binder (wt. %) 
Ti:M 
______________________________________ 
Example 
28 83(Ti.sub.0.9 Zr.sub.0.1)(C.sub.0.1 N.sub.0.9).sub.0.30, 
87.6:12.4 
8WC 
29 78(Ti.sub.0.95 Hf.sub.0.05)(C.sub.0.3 N.sub.0.7).sub.0.43, 
93.5:6.5 
18Al, 4WC 
30 79Ti(C.sub.0.5 N.sub.0.5).sub.0.12, 6Al, 15WC 
94.6:5.4 
Reference 
Example 
31 
##STR11## 78.1:21.9 
32 
##STR12## 88.1:11.9 
33 
##STR13## 78.9:21.1 
______________________________________ 
TABLE 6 
______________________________________ 
Cutting Duration 
Sample Before Chipping 
No. Vickers Hardness 
(min.) 
______________________________________ 
Example 28 3250 52 
29 3200 55 
30 3400 50 
Reference 
31 2950 11 
Example 32 2700 3 
33 2700 9 
______________________________________ 
Example 5 
Nitride or carbo-nitride powder materials containing Ti were mixed with 
aluminum powder materials, metal group powder materials and WC powder 
materials, to prepare a binder powder mixture having an average particle 
size of not more than 1 .mu.m. The mixture was prepared in a container 
holding a ball of cemented carbide, as shown in Table 7. The binder powder 
mixture was mixed with CBN powder materials having a particle size of not 
more than 3 .mu.m, in a volume ratio of 45:55, to prepare a sinter powder 
mixture. Circular plates of cemented carbide composed of WC - 10 wt. % Co 
were introduced into Mo vessels, which were then filled with the mixed 
powder materials. Then the vessels were introduced into a superhigh 
pressure/temperature apparatus, and sintered under a pressure of 51 kb and 
a temperature of 1300.degree. C. for 20 minutes. 
Sintered bodies thus obtained were examined by X-ray diffraction. Observed 
peaks are considered to be those of nitrides, carbides and carbo-nitrides 
containing Ti, TiB.sub.2, AlB.sub.2, AlN and borides and carbides of W, or 
W in all of the sintered bodies. Table 8 shows Vickers hardness values of 
these sintered bodies. 
The aforementioned respective sintered bodies were made into inserts for 
cutting tools, to cut outer peripheries of round bars of 100 mm in 
diameter made of SKD11 (H.sub.RC :60 to 62. The cutting conditions were as 
follows: 
Cutting Speed: 230 m/min. 
Depth of Cut: 0.2 mm 
Feed Rate: 0.12 mm/rev. 
Type: Dry 
Table 8 also shows the time durations during which cutting was performed 
before cutting edge chipping occurred. 
Referring to Table 7, the column "Atomic Ratio Ti:M" shows the atomic 
ratios of Ti to transition metal elements belonging to any one of the 
groups IVa, Va and/or VIa of the periodic table excluding Ti. 
Referring to Tables 7 and 8, samples Nos. 41 to 47 were prepared as 
reference examples, whereby the underlined values are out of the range of 
composition according to the present invention. 
TABLE 7 
______________________________________ 
Atomic Ratio 
Sample No. 
Composition of Binder (wt. %) 
Ti:M 
______________________________________ 
Example 
34 78(Ti.sub.0.9 W.sub.0.1)(C.sub.0.1 N.sub.0.9).sub.0.20, 
84.7:15.3 
15WC, 2Fe 
35 68(Ti.sub.0.8 V.sub.0.1 Hf.sub.0.1)(C.sub.0.5 N.sub.0.5).sub.0.30 
, 77.9:22.1 
15Al, Ti, 12WC, 5Ni 
36 82(Ti.sub.0.95 Cr.sub.0.05)(C.sub.0.8 N.sub.0.2).sub.0.10, 
94.4:5.6 
12Al, 2WC, 4Co 
37 62Ti(C.sub.0.9 N.sub.0.1).sub.0.40, 20Al, 8WC, 
96.6:3.4 
10Co 
38 65(Ti.sub.0.9 Cr.sub.0.1)C.sub.0.10, 7Al, 20WC, 
87.0:17.0 
8Ni 
39 79(Ti.sub.0.85 Nb.sub.0.05 Ta.sub.0.1)N.sub.0.25, 
78.9:21.1 
18WC, 1Fe 
40 79(Ti.sub.0.9 Mo.sub.0.1)(C.sub.0.4 N.sub.0.6).sub.0.33, 
88.4:11.6 
13Al, 5WC, 3Ni 
Reference 
Example 
41 
##STR14## 85.0:15.0 
42 
##STR15## 86.7:13.3 
43 
##STR16## 96.8:3.2 
44 
##STR17## 71.2:28.8 
45 
##STR18## 79.6:20.4 
46 
##STR19## 85.7:14.3 
47 
##STR20## 82.8:17.2 
______________________________________ 
TABLE 8 
______________________________________ 
Cutting Duration 
Sample Before Chipping 
No. Vickers Hardness 
(min.) 
______________________________________ 
Example 34 3300 61 
35 3250 58 
36 3400 65 
37 3200 60 
38 3400 59 
39 3300 55 
40 3250 54 
Reference 
41 3100 29 
42 3000 23 
43 2900 10 
44 2950 7 
45 3050 28 
46 2900 3 
47 3100 45 
______________________________________ 
Example 6 
Powder materials of Ti.sub.0.9 W.sub.0.1)N.sub.0.20, Al, WC and one or more 
metals of the iron group were mixed in ratios of 75:12:10:3 in weight 
percentage, to obtain a binder powder mixture having a particle size of 
not more than 1 .mu.m. This binder contains Ti and W in an atomic ratio of 
86.2:13.8. Such binder powder materials were mixed with CBN powder 
materials to form a sinter powder mixture as shown in Table 9. 
The sinter powder mixture thus obtained was sintered under a superhigh 
pressure and temperature similarly to Example 5, to obtain sintered 
bodies. The sintered bodies were made into inserts for cutting tools. 
The inserts were applied to cut outer peripheries of round bars of 300 mm 
in diameter made of SCM435 (H.sub.RC :22). The cutting conditions were as 
follows: 
Cutting Speed: 560 m/min. 
Depth of Cut: 1.0 mm 
Feed Rate: 0.5 mm/rev. 
Type: Dry 
Table 9 also shows the cutting duration before chipping of the cutting edge 
of the insert occurred. 
Samples Nos. 53 and 54 were prepared as reference examples, whereby the 
underlined values are out of the range of CBN contents according to the 
present invention. 
TABLE 9 
______________________________________ 
cBN cBN Cutting Durations 
Sample Particle Content Before Chipping 
No. Size (vol. %) (min.) 
______________________________________ 
Example 48 not more 60 105 
than 8 .mu.m 
49 3.about.5 .mu.m 
40 98 
50 " 70 112 
51 not more 50 125 
than 3 .mu.m 
52 " 20 94 
Reference 
53 " --10 5 
Example 54 " --80 13 
______________________________________ 
Example 7 
(Ti.sub.0.8 Zrhd 0.1Ta.sub.0.1)(C.sub.0.4 N.sub.0.6).sub.z powder materials 
having z values shown in Table 10 were mixed with Al, WC and Co powder 
materials in ratios of 70:15:12:3 in weight percentage to obtain a binder 
powder mixture having a particle size of not more than 1 .mu.m. The binder 
powder mixture was further mixed with CBN powder materials in a volume 
ratio of 40:60 to prepare a sinter powder mixture. 
The so obtained sinter powder mixture was sintered under a superhigh 
pressure and temperature similarly to Example 5, to obtain sintered 
bodies. Table 10 also shows Vickers hardness values of these sintered 
bodies. 
The sintered bodies thus obtained were made into inserts for cutting work, 
to cut outer peripheries of round bars of 80 mm in diameter made of SUJ2 
(H.sub.RC :60). The cutting conditions were as follows: 
Cutting Speed: 250 m/min. 
Depth of Cut: 0.13 mm 
Feed Rate: 0.10 mm/rev. 
Type: Dry 
Table 10 also shows cutting time durations before cutting edge chipping 
occurred. 
Referring to Table 10, the column "Atomic Ratio Ti:M" shows the ratios of 
Ti contained in the binders to transition metal elements belonging to any 
one of the groups IVa, Va and/or VIa of the periodic table excluding Ti. 
Samples Nos. 55, and 59 to 62 were prepared as reference examples, whereby 
the underlined values are out of the range of z values according to the 
present invention. 
TABLE 10 
______________________________________ 
Atomic Cutting Duration 
Sample Ratio Vickers 
Before Chipping 
No. z-Value Ti:M Hardness 
(min.) 
______________________________________ 
Reference 
Example 
55 
##STR21## 
75.7:24.3 
2800 25 
Example 
56 0.10 75.6:24.4 
3100 53 
57 0.25 75.5:24.5 
3400 68 
58 0.33 75.4:24.6 
3300 62 
Reference 
Examples 
59 
##STR22## 
75.3:24.7 
3250 55 
60 
##STR23## 
75.3:24.7 
3150 48 
61 
##STR24## 
75.2:24.8 
3000 20 
62 
##STR25## 
75.2:24.8 
2950 18 
______________________________________ 
Example 8 
The binder powder materials shown in Table 11 were prepared in a similar 
manner to Example 5, to form a binder powder mixture which was further 
mixed with CBN powder materials having a particle size of not more than 2 
.mu.m, in a volume ratio of 70:30, to obtain a sinter powder mixture. 
Then the sinter powder mixture was sintered under a superhigh pressure 
similarly to Example 5, to obtain sintered bodies. Table 11 shows Vickers 
hardness values of these sintered bodies. 
The sintered bodies were made into inserts for cutting tools, to cut outer 
peripheries of nitrided round bars of 100 mm in diameter made of SNCM645 
(H.sub.RC :67). The cutting conditions were as follows: 
Cutting Speed: 180 m/min. 
Depth of Cut: 0.07 mm 
Feed Rate: 0.08 mm/rev. 
Type: Dry 
Table 12 shows the cutting durations before chipping of the insert cutting 
edges. 
Referring to Table 11, the column "Atomic Ratio Ti:M" shows the ratios of 
Ti contained in the binders to transition metal elements belonging to any 
of the groups IVa, Va and/or VIa of the periodic table excluding Ti. 
Samples Nos. 66 to 68 were prepared as reference examples, whereby the 
underlined values are out of the range of composition according to the 
present invention. 
TABLE 11 
______________________________________ 
Sample Atomic Ratio 
No. Composition of Binder Ti:M 
______________________________________ 
Example 
63 74(Ti.sub.0.9 Mo.sub.0.1)(C.sub.0.3 N.sub.0.7).sub.0.10, 
85.2:14.8 
8Al, 15WC, 3Fe 
64 69(Ti.sub.0.9 V.sub.0.0)(C.sub.0.9 N.sub.0.1).sub.0.35, 
83.8:16.2 
4Al, 19WC, 8Ni 
65 74(Ti.sub.0.9 Nb.sub.0.1)N.sub.0.22, 18Al, 3WC, 
89.0:11.0 
5Co 
Reference 
Example 
66 
##STR26## 87.2:12.8 
67 
##STR27## 96.0:4.0 
68 
##STR28## 79.3:20.7 
______________________________________ 
TABLE 12 
______________________________________ 
Cutting Duration 
Sample Before Chipping 
No. Vickers Hardness 
(min.) 
______________________________________ 
Example 63 3350 58 
64 3300 62 
65 3400 55 
Reference 
66 3100 23 
Example 67 2950 15 
68 2700 4 
______________________________________ 
Although the present invention has been described and illustrated in 
detail, it is clearly understood that the same is by way of illustration 
and example only and is not to be taken by way of limitation, the spirit 
and scope of the present invention being limited only by the terms of the 
appended claims.