METHOD FOR MANUFACTURING FINE FREE CARBON DISPERSION TYPE CEMENTED CARBIDE, CUTTING TIP WITH EXCHANGEABLE CUTTING EDGE, MACHINED PRODUCT FORMED FROM ALLOY, AND METHOD FOR MANUFACTURING SAME

Abstract

The present invention relates to a cemented carbide and coated cemented carbide which contain free carbons, and provides a cemented carbide which enables to remove or reduce the disadvantages of the free carbons even if the cemented carbide contains the free carbons, specifically to decrease in the strength is reduced by finely dispersing the free carbons even if the cemented carbide contains the free carbons and to obtain a beautiful mirror surface on a mirror-finished surface by finely dispersing free carbons in the cemented carbide. The present invention is a cemented carbide composed of tungsten carbide (WC) and cobalt (Co), which contains carbon in such an amount range that no solid carbon is contained in a liquid phase while the liquid phase is present at a high temperature, characterized in that the maximum diameter of the pores resulting from the free carbons is 20 m or smaller.

Claims

1-7. (canceled)

8. A method for manufacturing a cemented carbide composed of tungsten carbide (WC) and cobalt (Co), wherein: the cemented carbide contains 0.02 mass % or more to 0.15 mass % or less of free carbons; free carbons are finely dispersed in the cemented carbide; shrinkage during sintering occurs evenly; the cemented carbide in which a maximum diameter of pores resulting from the free carbons is 20 m or smaller is defined as Cemented carbide A; the cemented carbide in which a maximum diameter of pores resulting from the free carbons is 15 m or smaller is defined as Cemented carbide B; the cemented carbide in which a maximum diameter of pores resulting from the free carbons is 10 m or smaller is defined as Cemented carbide C; the Cemented carbide A, B or C to which chromium carbide or chromium nitride is added in an amount of 2 to 18 mass % based on cobalt (Co) content is defined as Cemented carbide D; the Cemented carbide A, B, C or D in which a part of tungsten carbide (WC) is replaced by any one or combinations of: a carbide, a nitride or a carbonitride of transition metal of groups 4 and 5 in the periodic table; and a double carbide or a double carbonitride of tungsten (W) with the carbide, the nitride or the carbonitride of the transition metal is defined as Cemented carbide E; and the Cemented carbide E in which a -free layer is formed on a surface of the cemented carbide and the -free layer has a thickness of 1 to 30 m is defined as Cemented carbide F, the Cemented carbide A, B, C, D, E or F in which a lattice constant of an fcc in a binder phase (Co phase) of the cemented carbide is 3.560 or higher is defined as Cemented carbide G, the method is characterized in that, when manufacturing any of the Cemented carbides A, B, C, D, E, F and G, after sintering a mixed powder for producing the cemented carbide at a sintering temperature not lower than a liquid-phase appearance temperature, the method comprises: a step of rapidly cooling from the temperature not lower than the liquid-phase appearance temperature; or a step of reheating to the temperature not lower than the liquid-phase appearance temperature and then rapidly cooling.

9. The method for manufacturing the cemented carbide according to claim 8, wherein, in the step of rapidly cooling and the step of reheating and rapidly cooling, a cooling rate from the temperature not lower than the liquid-phase appearance temperature to 800 C. is set to 30 C./min or higher.

10. A method for manufacturing a coated cemented carbide, wherein the cemented carbide manufactured by the method for manufacturing the cemented carbide according to claim 8 is used as a base material when manufacturing the coated cemented carbide.

11. An edge replacement-type cutting tip formed of a cemented carbide composed of tungsten carbide (WC) and cobalt (Co), wherein: the cemented carbide contains 0.02 mass % or more to 0.15 mass % or less of free carbons; free carbons are finely dispersed in the cemented carbide; shrinkage during sintering occurs evenly; dimensional accuracy is improved; the cemented carbide in which a maximum diameter of pores resulting from the free carbons is 20 m or smaller is defined as Cemented carbide A; the cemented carbide in which a maximum diameter of pores resulting from the free carbons is 15 m or smaller is defined as Cemented carbide B; the cemented carbide in which a maximum diameter of pores resulting from the free carbons is 10 m or smaller is defined as Cemented carbide C; the Cemented carbide A, B or C to which chromium carbide or chromium nitride is added in an amount of 2 to 18 mass % based on cobalt (Co) content is defined as Cemented carbide D; the Cemented carbide A, B, C or D in which a part of tungsten carbide (WC) is replaced by any one or combinations of: a carbide, a nitride or a carbonitride of transition metal of groups 4 and 5 in the periodic table; and a double carbide or a double carbonitride of tungsten (W) with the carbide, the nitride or the carbonitride of the transition metal is defined as Cemented carbide E; the Cemented carbide E in which a -free layer is formed on a surface of the cemented carbide, and the -free layer has a thickness of 1 to 30 m is defined as Cemented carbide F; and the Cemented carbide A, B, C, D, E or F in which a lattice constant of an fcc in a binder phase (Co phase) of the cemented carbide is 3.560 or higher is defined as Cemented carbide G, the edge replacement-type cutting tip is characterized in that the edge replacement-type cutting tip is formed of any of the Cemented carbides A, B, C, D, E, F and G, or any of coated cemented carbides using the Cemented carbide A, B, C, D, E, F or G as a base material.

12. A cemented carbide machined product such as tools, molds and parts formed of a cemented carbide composed of tungsten carbide (WC) and cobalt (Co), wherein: the cemented carbide contains 0.02 mass % or more to 0.15 mass % or less of free carbons; free carbons are finely dispersed in the cemented carbide; shrinkage during sintering occurs evenly; dimensional accuracy and/or machinability is improved; the cemented carbide in which a maximum diameter of pores resulting from the free carbons is 20 m or smaller is defined as Cemented carbide A; the cemented carbide in which a maximum diameter of pores resulting from the free carbons is 15 m or smaller is defined as Cemented carbide B; the cemented carbide in which a maximum diameter of pores resulting from the free carbons is 10 m or smaller is defined as Cemented carbide C; the Cemented carbide A, B or C to which chromium carbide or chromium nitride is added in an amount of 2 to 18 mass % based on cobalt (Co) content is defined as Cemented carbide D; the Cemented carbide A, B, C or D in which a part of tungsten carbide (WC) is replaced by any one or combinations of: a carbide, a nitride or a carbonitride of transition metal of groups 4 and 5 in the periodic table; and a double carbide or a double carbonitride of tungsten (W) with the carbide, the nitride or the carbonitride of the transition metal is defined as Cemented carbide E; the Cemented carbide E in which a -free layer is formed on a surface of the cemented carbide, and the -free layer has a thickness of 1 to 30 m is defined as Cemented carbide F; and the Cemented carbide A, B, C, D, E or F in which a lattice constant of an fcc in a binder phase (Co phase) of the cemented carbide is 3.560 or higher is defined as Cemented carbide G, the cemented carbide machined product is characterized in that any of the Cemented carbides A, B, C, D, E, F and G is machined by one or combinations of following machining methods: an electric discharging, grinding/polishing or cutting.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0118] FIG. 1 illustrates a WC-Co pseudo-binary vertical sectional view (reprinted from Hisashi Suzuki, Cemented Carbide and Sintered Hard Material (1986), p. 96, FIG. 1.112 (b), Maruzen Publishing Co., Ltd.).

DESCRIPTION OF EMBODIMENTS

[0119] <Definition of Size of Pore Resulting from Free Carbon, and Measurement Method Thereof>

[0120] The degree of the free carbon generation in the cemented carbide is judged in accordance with C02 to C08 in Appendix 4 of the quality standard CIS006C of Japan Cemented Carbide Tool Manufacturer's Association. When free carbons are generated in a generally produced cemented carbide, the state is as shown in Appendix 4. The grade ranges from C02 that the free carbons are smallest in number and size to C08 that the free carbons are largest in number and size, and even in C02 with the fewest free carbons, the maximum diameter is about 70 m. As shown in the photograph of the free carbons in Appendix 4, the pore of the free carbon is shaped in such a manner that several small dots aggregate in a dendritic form to form one pore, and the size of this aggregate was measured as the size of the pore. The size of the free carbon pore is generally supposed to be 25 m or larger (Non-Patent Document 4, p. 283 to 284).

[0121] In the present invention, for measurement of the size of the free carbon pore, a test sample was polished in accordance with the method described in CIS006C, and similarly observed and measured with a 100-power microscope in the same manner as in Appendix 4 of CIS006. In addition, a case that nets resulting from free carbons with a size of 20 m or larger could not be observed in a visual field (about 0.070.1 mm) with the same size as in Appendix 4 successively in two visual fields, or a case that 10 visual fields are randomly observed and pores resulting from free carbons with a size of 20 m or larger could not be observed in 7 visual fields, are defined as cemented carbides with free carbon pores having a maximum diameter of 20 m or smaller. The cemented carbides with free carbon pores having maximum diameters of 15 m or smaller and 10 m or smaller were also determined in the same measurement method.

[0122] However, note that if a pore resulting from free carbons is a small pore of 20 m or smaller, the pore may be difficult to distinguish from the A-type pore. In order to ascertain whether the pore results from free carbons, it is also necessary to concurrently observe and confirm the pore at a high magnification of several hundreds or higher, as also described in paragraph 0003. In addition, as shown in Tables 2, 4, 6, 7, 8, 9 of Examples, generally chemical analysis (free carbon %) is concurrently carried out, and thus, if there are free carbons, it can be confirmed that the pore results from free carbons.

<Method for Fining Free Carbon>

[0123] FIG. 1 shows a WC-Co pseudo-binary vertical sectional view (reprinted from Hisashi Suzuki, Cemented Carbide and Sintered Hard Material (1986), p. 96, FIG. 1.112 (b), Maruzen Publishing Co., Ltd.).

[0124] There are two types of precipitation of free carbons in the cemented carbide. According to FIG. 1,

(1) when the carbon content in the cemented carbide is 6.3% or more in terms of WC, the composition is WC+liquid (L)+carbon (C) at the time of appearance of a liquid phase. When the cemented carbide is cooled and solidified while kept in this composition, the composition is WC++C.
(2) when the carbon content is 6.13% to 6.3% in terms of WC, the composition is WC+liquid (L) at the time of appearance of a liquid phase, however when the cemented carbide is cooled while kept in this composition, the composition is WC++C. Since the theoretical carbon content of WC is 6.13%, the content in terms of free carbons is 0.01 to 0.17%.

[0125] Here, represents the binder phase mainly composed of Co in the crystal structure fcc (typically referred to as Co phase). The present invention is applied to only in the case of (2). In the case of (1), this range is not generally used for the cemented carbide, because carbons in the liquid phase remain as they are also at the time of appearance of the solid phase, and excessive free carbons are present. However, Patent Document 4 relates to the range of (1), which has been developed for a special application.

[0126] In the case of (2), when the cemented carbide is converted from the liquid phase to the solid phase at a temperature of the melting point or lower, free carbons (C-type pore) precipitate from the liquid phase. The cemented carbide according to the present invention can be realized by finely dispersing the sizes of the precipitated free carbons. Specifically, the cemented carbide is rapidly cooled from the liquid phase to finely disperse precipitation of the free carbons.

[0127] Theoretically, the quicker the rapid cooling is, the finer the free carbons are. However, if the cooling rate is too high, the internal stress may remain and the furnace may deteriorate depending on the product. Hence, there are limits according to the actual circumstances.

[0128] Also, the size of the free carbon is affected not only by the amount of free carbons in the cemented carbide but also by the composition and the shape/size of the sintered compact, and the like.

[0129] Thus, it is desirable to previously select the optimum cooling rate in accordance with the actual circumstance. In terms of facility, a rate of 100 C./min can be sufficiently achieved because of the advanced gas rapid-cooling technology, and examples of 1000 C./min and 10000 C./min have been also reported (Patent Documents 2 and 3). Normally, when the free carbons are examined by a 100-power microscope on the basis of CIS006C, the C-type pore is observed, but when the free carbons are finely dispersed, the pore looks like the A type in some cases. Thus, for ascertaining whether the pore results from free carbons, a method in which the pore is concurrently observed and confirmed at a high magnification of several hundreds or higher is also used, as also described in paragraph 0003. Furthermore, the pore can be confirmed by chemical analysis (free carbon %) as shown in Tables 2, 4, 6, 7, 8, and 9 of Examples.

<Cooling Method>

[0130] For sintering and reheating, vacuum furnaces are normally used. Recently, there have been many vacuum furnaces equipped with a device capable of performing forced cooling with inert gas. It is convenient to use this kind of vacuum furnace for production. The cooling rate can be increased by increasing the gas amount or increasing the gas pressure, and the cooling rate can be controlled depending on the actual circumstance. When a large amount of cemented carbide (product) is charged in a large furnace, the gas amount and the gas pressure should be increased, and when the charged amount is small and the product shape is also small, the gas amount and the gas pressure may be small. The inert gas may be Ar or N.sub.2 gas. The cooling effect of N.sub.2 is slightly larger than that of Ar, and also N.sub.2 is industrially advantageous in respect of cost.

[0131] Hereinafter, the best embodiment for carrying out the present invention will be explained on the basis of Examples. Note that the present invention is not limited to the following embodiments, and known changes can be added to the present invention within a scope substantially equal to or equivalent to the scope of the present invention.

Example 1

[0132] An example of the WC-Co-based material will be described below.

[0133] Mixed powders before sintering were prepared by a process in which commercially available raw materials were blended in the composition of (Table 1), mixed in a wet ball mill in accordance with a common method using alcohol, and dried. Samples with Cr.sub.3C.sub.2 added were designated as A, and samples with no addition were designated as B. In A2 and B2, the carbon contents were larger than that in A1 and B1 by 0.14%, and in B4 and B5, the carbon contents were larger than that in B1 by 0.10% and 0.18% respectively.

TABLE-US-00001 TABLE 1 Added amount Sam- WC(4 m) Co Cr2C3 of carbon ple (%) (%) (%) (%) A1 84.5 15 0.5 0 A2 84.5 15 0.5 0.14 B1 85 15 0 0 B2 85 15 0 0.14 B4 85 15 0 0.1 B5 85 15 0 0.18

[0134] A lubricant for press was added to these mixed powders, and all powders were pressed at 1 ton/cm.sup.2, and vacuum-sintered. Although the used mixed powders were the same, names of the samples were classified depending on the sintering conditions and heating conditions. The sintering conditions and characteristic values of the samples are shown in (Table 2).

[0135] Here, the slow cooling in the sintering conditions refers to a step in which the sample is vacuum-sintered at 1380 C., held for 1 hour, then cooled, and cooled (slowly cooled) from 1350 C. to 800 C. at 10 C./min.

[0136] In addition, the rapid cooling in the sintering conditions refers to a step in which the sample is vacuum-sintered at 1380 C., held for 1 hour, then cooled, and cooled (rapidly cooled) from 1350 C. to 800 C. at 30 C./min by introducing an inert gas, and the strong rapid cooling refers to a step in which the sample is cooled (strongly and rapidly cooled) from 1350 C. to 800 C. at 50 C./min by introducing an inert gas.

[0137] The reheating and rapid cooling in the sintering conditions refers to a step in which the sintered compact is reheated in a vacuum furnace at 1340 C. for 15 minutes, and cooled (rapidly cooled) from 1340 C. to 800 C. at 30 C./min by introducing an inert gas, and the reheating and strong rapid cooling refers to a step in which the sintered compact is reheated in a vacuum furnace at 1340 C. for 15 minutes, and cooled (strongly and rapidly cooled) from 1340 C. to 800 C. at 50 C./min.

[0138] Herein, the method for measuring the maximum diameter (m) of the pore in (Table 2) accords to the above-described <Definition of Size of Pore Resulting from Free Carbon, and Measurement Method Thereof>.

TABLE-US-00002 TABLE 2 Transverse Vickers Maximum Free rupture, hard- diameter Sam- carbon strength ness of pore ple (%) (MPa) (Hv) (m) Sintering conditions A11 0 3230 1130 10 Slow cooling of A1 A21 0.08 3050 1020 100 Slow cooling of A2 A22 0.05 3200 1110 15 Reheating and rapid cooling of A21 A23 0.06 3220 1110 15 Rapid cooling of A2 B11 0 3200 1110 10 Slow cooling of B1 B21 0.08 3070 1000 100 Slow cooling of B2 B22 0.07 3170 1070 20 Reheating and rapid cooling of B21 B23 0.06 3220 1100 10 Reheating and strong rapid cooling of B21 B24 0.07 3185 1090 15 Rapid cooling of B2 B41 0.06 3090 1020 70 Slow cooling of B4 B42 0.04 3200 1100 10 Reheating and strong rapid cooling of B41 B51 0.12 3000 980 150 Slow cooling of B5 B52 0.1 3160 1070 20 Reheating and rapid cooling of B51

[0139] A11, A21, B11, B21, B41 and B51 are under a sintering condition of slow cooling. The samples (A11, B11) whose added amount of carbon is 0 in (Table 1) had no free carbon also after sintering, and their pores were evaluated as type A in Appendix 1 of CIS006C, and classified as A02 or lower. The samples (A21, B21, B41, B51) with carbon added had free carbons also after sintering, and their pores were evaluated as type C in Appendix 4 of CIS006C, and classified as C02 to C06.

[0140] In relation to A21 and B21, as described more specifically, powders were sintered, then polished so as to have a mirror surface, and microscopically observed at magnification of 100, and as a result, both samples were evaluated as around C04 in accordance with CIS006C. That is, large free carbon pores of 80 to 100 m and small free carbon pores of about 25 m were found in a mixed state in A21 and B21.

[0141] Also, A22 and B22 were prepared by a process in which the A21 and B21 (sintered compact) were reheated in the same vacuum furnace, held at 1340 C. for 15 minutes, cooled, and cooled (rapidly cooled) from 1340 C. to 800 C. at a cooling rate of 30 C./min. The samples were polished by a method according to CIS006C in the same manner as for other samples, and the states of these cemented carbide pores were microscopically observed at magnification of 100.

[0142] The maximum diameter of the pore of A22 was 15 m or smaller, and the maximum diameter of the pore of B22 was 20 m or smaller. The transverse rupture strength and the hardness were also measured. A23 and B24 were prepared by a process in which a mixed powder was vacuum-sintered under the same conditions as described above and then cooled (rapidly cooled) at 30 C./min. Also, the mixed powders for B4 and B5 were similarly vacuum-sintered and then cooled. The sintering conditions and the results are shown in (Table 2).

[0143] When A11 and B11 with the sintering condition of slow cooling and 0% carbon addition amount were compared with A21 and B21 with the sintering condition of slow cooling and 0.14% carbon addition amount, A21 and B21 had a decreased transverse rupture strength and hardness because the free carbons precipitated. However, even if free carbons appear similarly to A22, A23, B22 and B24, the free carbons can be finely dispersed by changing the sintering conditions to rapid cooling or reheating and rapid cooling, and when the pore becomes smaller, the transverse rupture strength becomes equivalent to that of A11 and B11 without free carbons. Also, hardness of A21 and B21 tends to be slightly lower compared to that of A11 and B11 without free carbons, but there is almost no difference.

[0144] B52 had a slightly large amount of pores, and one pore having a maximum diameter of 20 to 25 m was observed in each of two visual fields out of ten visual fields. B23 was prepared by a process in which B21 is reheated to 1340 C. and strongly and rapidly cooled to 800 C. at 50 C./min, and B23 had pores improved compared to that in B22, the sizes of the pores in B23 were small and all of them were 10 m or smaller. Also, sizes of all pores in B42 were 10 m or smaller.

[0145] As described above, normally, when the cemented carbide contains free carbons which cause pores, the produced cemented carbide has low transverse rupture strength and hardness compared to a cemented carbide without free carbons by cooling with a general sintering conditions/cooling method (slow cooling). However, even if the cemented carbide contains free carbons, the free carbon pores in the cemented carbide are dispersed by rapid cooling or strong rapid cooling after sintering, or by slow cooling after sintering and then reheating and rapid cooling or reheating and strong rapid cooling. As a result, a cemented carbide having a transverse rupture strength and a hardness equivalent to those of the cemented carbide without free carbons can be produced.

Example 2

[0146] An example of a material for cutting tools will be described below.

[0147] Mixed powders before sintering were prepared by a process in which commercial raw materials were blended in the composition of (Table 3), subjected to a wet ball milling and dried in accordance with a general method using alcohol. A lubricant for press was added to all of these mixed powders, which were pressed at 1 ton/cm.sup.2. C11 and C21 were vacuum-sintered at 1400 C., held for 1 hour, then cooled, and cooled (slowly cooled) from 1380 C. to 800 C. at 10 C./min (corresponding to slow cooling in the sintering conditions).

[0148] On the other hand, C23 was vacuum-sintered at 1400 C., held for 1 hour, then cooled, and cooled (strongly and rapidly cooled) from 1380 C. to 800 C. at 50 C./min by introducing an inert gas (corresponding to strong rapid cooling in the sintering conditions).

[0149] In addition, C22 is prepared by reheating and rapidly cooling C21. The reheating and rapid cooling in the sintering conditions refers to a step in which the sample is held in a vacuum furnace at 1380 C. for 30 minutes and cooled at 30 C./min. C22 did not have pores with sizes of 20 m or larger. The sizes of the pores in C23 were 10 m or smaller. The results are shown in Table 4.

TABLE-US-00003 TABLE 3 WC (2 m) Co TiC TaNbC Cr2C3 Added amount Sample (%) (%) (%) (%) (%) of carbon (%) C1 73 10 8.5 8.5 0 0 C2 73 10 8.5 8.5 0 0.22

TABLE-US-00004 TABLE 4 Transverse Vickers Maximum Free rupture hard- diameter Sam- carbon strength ness of pore ple (%) (MPa) (Hv) (m) Sintering condition C11 0 2195 1470 10 Slow cooling of C1 C21 0.08 2040 1400 90 Slow cooling of C2 C22 0.1 2150 1430 20 Reheating and rapid cooling of C21 C23 0.06 2190 1460 10 Strong rapid cooling of C2.

[0150] In addition, C11, C21, C22 and C23 as base materials were CVD-coated with TiC with a thickness of 7 m. C11 had an phase with a thickness of 1 to 3 m at the boundary between the TiC coat and the base material, but C21 had no phase. Data for verifying Non-Patent Document 3 was obtained. Also C22 and C23 had no phase at the boundary between the TiC coat and the base material, and the same result as for C21 was obtained. That is, even if free carbons are finely dispersed in the base material, the effect for reducing the phase is same.

Example 3

[0151] An example of a cemented carbide having a -free layer on its surface, which is frequently used for a CVD base material will be described below.

TABLE-US-00005 TABLE 5 WC Co TiC TaNbC TiN Added amount Sample (%) (%) (%) (%) (%) of carbon (%) E 87.5 5 2 5 0.5 0 F 87.5 5 2 5 0.5 0.18

TABLE-US-00006 TABLE 6 Transverse Vickers Maximum Free rupture hard- diameter Sam- carbon strength ness of pore ple (%) (MPa) (Hv) (m) Sintering conditions E1 0 1510 10 Slow cooling of E F1 0.1 1440 90 Slow cooling of F F2 0.07 1490 15 Rapid cooling of F

[0152] Mixed powders before sintering were prepared by a process in which commercial raw materials were blended in the composition of (Table 5), mixed in a wet ball mill and dried in accordance with a general method using alcohol. A lubricant for press was added to these mixed powders, all of which were pressed at 1 ton/cm.sup.2. E1 and F1 were vacuum-sintered at 1400 C., held for 1 hour, then cooled, and cooled (slowly cooled) from 1380 C. to 800 C. at 10 C./min (corresponding to slow cooling in the sintering conditions).

[0153] On the other hand, F2 was vacuum-sintered at 1400 C., held for 1 hour, then cooled, and cooled (rapidly cooled) from 1380 C. to 800 C. at 30 C./min by introducing an inert gas (corresponding to rapid cooling in the sintering conditions). The results are shown in (Table 6). All of the samples E1, F1 and F2 had the -free layer with a thickness of 10 to 20 m on the surface. Even if the free carbons are finely dispersed, the -free layer can be made. These samples had -free layers on their sintered surface, and the transverse rupture strength was not measured.

Example 4

[0154] Experiments on the dimensional accuracy of the edge replacement-type cutting tip were carried out.

[0155] A lubricant for press was added to mixed powders of C1 and C2 in (Table 3) in Example 2, which was pressed at 1 ton/cm.sup.2 into a plurality of edge replacement-type cutting tips model no. SNMA432, sintered, and dimensional accuracy was measured. Results in (Table 7) were obtained. The sintering conditions are the same between G11 and C11, between G21 and C21, between G22 and C22, between G23 and C23.

[0156] The dimensional difference inside the tip in (Table 7) refers to a difference between the maximum value and the minimum value when four sides of one SNMA432 (square) are measured with a micrometer.

[0157] The difference between maximum and minimum values in 10 samples in (Table 7) refers to a value obtained by subtracting the minimum value from the maximum value when four sides of ten SNMA432s are measured.

TABLE-US-00007 TABLE 7 Difference between Maximum Dimensional maximum and minimum Sample Free diameter difference dimensions in (model no. carbon of pore inside the tip 10 samples SNMA432) Sintering condition (%) (m) (mm) (mm) G11 Slow cooling of C1 0 10 0.07 0.12 G21 Slow cooling of C2 0.08 90 0.05 0.09 G22 Reheating and rapid 0.1 20 0.05 0.09 coding of G21 G23 Strong rapid cooling 0.08 10 0.04 0.07 of C2

[0158] In G22 and G23 having finely dispersed free carbons, dimensional unevenness is smaller than that in G11 without free carbons.

[0159] G11, G22 and G23 were coated with 2 m TiC.sub.2+3 m TiN by ion plating which is one type of PVD, and subjected to the same measurement. Both the PVD-coated G22, G23 and the PVD-coated G11 had the same dimensional difference inside the tip and difference between maximum and minimum values in 10 samples as those before the coating. The coated G22 and G23 had smaller dimensional unevenness than that of the coated G11.

[0160] Furthermore, G11, G22, G23 were coated with TiC with a thickness of 7 m by a CVD method, and subjected to the same dimensional measurement for comparison. As expected, the dimensional unevenness was almost the same as before coating, and the coated G22 and G23 had smaller dimensional unevenness than that of G11.

Example 5

[0161] Cylindrical cemented carbide sintered compacts were prepared, and compared and investigated for the dimensional accuracy.

[0162] A lubricant for press was added to mixed powders of B1, B2 and B4 in Example 1, and pressed at 1 ton/cm.sup.2 to prepare a plurality of sintered compacts having an outer diameter of 50D, an inner diameter of 20d and a height of 50 (unit: mm), and compared for the dimensional accuracy. The results are shown in (Table 8).

TABLE-US-00008 TABLE 8 Dimensional Difference between Maximum difference in maximumand minimum Sample Free diameter one sintered outer diameters Cylindrical carbon of pore compact in 3 samples product Sintering condition (%) (m) (mm) (mm) H11 Slow cooling of B1 0 10 0.5 0.7 H21 Slow cooling of B2 0.08 100 0.3 0.4 H24 Rapid cooling of B2 0.07 15 0.2 0.3 H41 Slow cooling of B4 0.06 70 0.25 0.3 H42 Reheating and strong 0.06 10 0.2 0.25 rapid cooling of H41

[0163] The sintering conditions took over those for the B1, B2 and B4 powders. In the dimensional measurement, the outer diameter of the sintered compact was measured, and the difference between the maximum diameter and the minimum diameter was determined in order to judge whether or not the dimensional accuracy was good. The difference between the maximum and minimum outer diameters of one sintered compact, and the difference between the maximum and minimum diameters of three sintered compacts were indicated. It can be seen that H24 and H42 having finely dispersed free carbons have better dimensional accuracy than that of H11 without free carbons.

Examples 6

[0164] The machining efficiencies in preparing cemented carbide machined products were compared.

[0165] Circumferences of H11 and H24 in (Example 5) as work materials were cut by a lathe. As a cutting tool, model no. TNGA432 of a polycrystalline diamond sintered compact was used. Cutting was carried out under a condition of cutting velocity (v)=15 m/min, feeding rate (f)=0.1 mm/rev and cutting depth (d)=0.1 mm.

[0166] In relation to the time to remove the sintered skin on the circumference, naturally, H11 having many distortions and large stock allowance required 1.5 times more time than H24 with less distortion.

[0167] Furthermore, in order to compare the machinability between H11 and H24, the sintered skin was removed, then the tool was changed with a new tool, cutting was performed for 20 minutes under the same condition, and progress states of wear were compared between the both tools.

[0168] An amount of the tool wear (flank wear) due to cutting of H11 was 0.11 mm, and in the case of H24, it was 0.08 mm. This indicates that H24 has better machinability than that of H11. That is, the cemented carbide according to the present invention has not only a good dimensional accuracy for the sintered compact, but also an excellent machinability. Consequently, it was confirmed that cemented carbide machined products with low machining cost could be provided.

Example 7

[0169] The relationship between the lattice constant of the fcc in the binder phase (Co phase) and the cutting performance was investigated.

[0170] The C1 powder in (Example 2) was pressed into the SNMA432 at 1 ton/cm.sup.2, vacuum-sintered at 1400 C., held for 1 hour, and then rapidly cooled (very strongly and rapidly cooled) at a cooling rate of 70 C./min. The sample was numbered as G24. Also in (Example 4), the mixed powder was the same as in (Example 2), and as samples, G11, G21, G22 and G23 in (Example 4) and the above G24 were used, and compared for the lattice constant and the cutting performance. X-ray diffraction using Cu as the target was used for measuring the lattice constant.

TABLE-US-00009 TABLE 9 Sample Maximum Lattice Flank Shear drop on rake face (model no. Free carbon diameter of constant wear of coated cemented SNMA432) Sintering condition (%) pore (m) () (mm) carbide (mm) G11 Slow cooling of C1 0 10 3.555 0.4 0.025 G21 Slow cooling of C2 0.08 90 3.55 0.55 0.034 G22 Reheating and 0.1 20 3.562 0.35 0.023 rapid cooling of C21 G23 Strong rapid 0.08 10 3.568 0.25 0.02 cooling of C2 G24 Very strong rapid 0.06 10 3.571 0.2 0.016 cooling of C2

[0171] The flank wear of the tip was measured under a cutting (lathe cutting) condition of work material: SCM3, cutting velocity v=120 m/min, feeding rate f=0.4 mm/rev, cutting depth d=2 mm, and cutting time t=30 min.

[0172] Furthermore, G11, G21 to G24 were PVD-coated with 2 m TiC+3 m TiN, and subjected to a cutting test. Under a cutting (lathe cutting) condition of work material: SK5, v=100 m/min, f=0.5 mm/rev, d=2 mm, and t=30 min, the coated cemented carbides using G11, G21 to G24 were compared for the level of plastic deformation (shear drop on edge rake face) of the blade after test. The results are shown in (Table 9).

[0173] The performance of G21 containing free carbons in the conventional form was inferior to that of G11. However, it is found that both the cemented carbide and coated cemented carbide having a high lattice constant and finely dispersed free carbons are naturally superior to G21, but they are superior to G11 without free carbons.