JP3422957B2 - Tough fine-grain cemented carbide - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine-grain cemented carbide material having excellent strength and toughness used in the field of cutting and wear-resistant parts . [0002] Conventionally, so-called fine-grain cemented carbides having an average grain size of less than 1 µm have been widely used because of their higher strength and toughness than alloys having an average grain size larger than that. However, there if often is lead to catastrophic destruction and try to investigate the usage details, the cause is been assumed to lead to lowering of fracture toughness value K _1C as a reactionary up dramatically Hardness Was. However, the sudden fracture is not only caused by a substantial decrease in fracture toughness, but as has been pointed out in the past, the WC (hereinafter referred to as “coal coal”) having a grain growth of 2 μm or more, referred to.) it is found many cases to induce the catastrophic destruction become a starting point of destruction. As already discussed, even if a cemented carbide is manufactured by a sintering method using a WC powder having a particle size of less than 1 μm as a raw material, part of the sintering process causes significant grain growth and the appearance of a giant coal. Seems inevitable. [0003] Naturally, it is desirable to reduce the number of giant coals. Therefore, studies using various grain growth inhibitors have been conventionally conducted. V, Ta,
It has been practiced to add an appropriate amount of one or more of them in the form of a metal or a compound such as a carbide or a nitride with Cr or the like. By doing so, the value of the coercive force, which is a measure of the average particle size of the carbide, is increased, and the coarsening of the particle size of the sintered cemented carbide as a whole has been suppressed. However, although the addition of V, Ta, Cr, etc. has a great effect on the refinement of the average particle size, it is difficult to reduce the number of giant coals scattered in some places to a certain value or less, which is a major problem. Was. Incidentally, there is JP-A 11-241138 discloses an example having the specified quality of the cemented carbide by using a coercive force. [0004] That is, it is an object of the present invention to simultaneously reduce not only the average particle size of the fine-grained cemented carbide but also the number of giant coals to a certain value or less. This makes it possible to improve the toughness of the cemented carbide and to avoid sudden fracture phenomena, which is industrially significant. [0005] The present inventors have SUMMARY OF THE INVENTION, the number of巨炭, coercive force, saturation magnetization, Co content, the alloy carbon content,
The following conclusions were reached as a result of further detailed examination of the type and amount of the grain growth inhibitor. That is, mainly
In a tough, fine-grained cemented carbide comprising WC and Co,
The tough fine-grain cemented carbide is made of Cr, Ta and V metals and / or
Containing two or more selected from these compounds,
The weight ratio of the total content of Ta and V to the Co content is
0.04 to 0.3, the saturation of the tough fine-grained cemented carbide
The magnetization is expressed as a ratio to the Co content per 1% by weight of Co.
1.44 to 1.74 μTm ³ / kg, coercive force is 336
00 to 52000 A / m, in section observation with an optical microscope
0 or more WC particles with a maximum diameter of 2 μm or more per 1 mm ²
A tough, fine-grained cemented carbide characterized by the presence of 5 or less
It is. In the present invention, even if an excessive amount of the grain growth inhibitor is added, the amount of the giant coal does not decrease below a certain value unless the saturation magnetization is within a certain range. Saturation magnetization relates to the amount of Co and C in the alloy. It has also been found that the coercive force, which is a measure of the average particle size, also contributes to the saturation magnetization, and that the coercive force decreases rapidly when the saturation magnetization exceeds a certain value. Furthermore, as for the number of giant coals, it has been found that the frequency of sudden destruction increases when the number of those having a maximum diameter exceeding 2 μm is 6 or more per 1 mm ² by microscopic cross-sectional tissue observation. There are several possible causes of the formation of coal, such as agglomeration of the raw material WC powder, segregation of carbon, and non-uniform dispersion of the grain growth inhibitor. The repetition of solid solution and precipitation induces or promotes grain growth. Therefore, it is generally assumed that the larger the Co content, the higher the frequency of the generation of the giant coal. However, as a result of intensive studies by the inventors, if the value obtained by dividing the saturation magnetization (μTm ³ / kg) by the Co content (% by weight) is in the range of 1.44 to 1.74, the amount of Co in the alloy is determined. Regardless, the number of giant coals can be kept to a very low value. Further, the value of the coercive force is 336.
It is possible to fall within the range of 00 to 52000 A / m. In other words, the saturation magnetization of the alloy is determined by the Co content (% by weight).
If the value obtained by dividing by 1. exceeds 1.74, the coercive force drops sharply. This means that the average grain size of WC increases and the toughness decreases. When the value obtained by dividing the saturation magnetization by the Co content (% by weight) is less than 1.44, a decarburized phase may appear and the performance of the alloy becomes unstable. The grain growth inhibitor is C
The addition of r, Ta, V metal or a compound of these elements is good, but the amount thereof is in the range of 0.04 to 0.3 in which the total weight% as the metal content is divided by the Co content (weight%). Desirably. If it is more than this, the toughness is reduced, and if it is less, the effect of suppressing the grain growth becomes weak. Hereinafter, the present invention will be described specifically with reference to Examples. [0007] In order to adjust the C content of WC powder, Co powder, compounds of Cr, Ta, V, and alloys having various average particle diameters, appropriate amounts of powder C are mixed as shown in Table 1. The mixture was mixed in an alcohol containing paraffin wax at a ratio of 1.2% by weight to the amount of powder using an attritor for 4 hours, dried and granulated using a spray dryer, and then press-molded. [Table 1] The pressed body was appropriately sintered under appropriate sintering conditions, and various physical properties were measured. Further, a cross-sectional observation with a microscope was performed, and the number of WC particles having a maximum diameter of 2 μm or more was counted.
Also, 30 samples of bending force were measured and the bending force was 3000MPa.
The following numbers were determined. Table 2 shows the results. [Table 2] From Table 2, it can be seen that, in Example 1 of the present invention in which the average grain size of the fine-grained cemented carbide and the number of giant coals were controlled, a high transverse rupture strength was stably obtained, and none had a transverse rupture strength of 3000 MPa or less. . In addition, in comparison of the same particle size (sample numbers 4 to 8 ), as the saturation magnetization becomes higher, the transverse rupture force becomes 3000MP.
The number of coals having a bending strength of 3000 MPa or less is increasing, because the number of coals is large. This means that the sudden destruction phenomenon described as the subject of the present invention can be reduced, and stable strength can be obtained. As is clear from the results in Table 2, those having a value obtained by dividing the saturation magnetization (μTm ³ / kg) by the Co content (% by weight) of less than 1.44 (Comparative Example 4 ) have a deflective strength. In many cases, the performance is unstable. This is probably because a decarburized phase appeared in the alloy structure. Conversely, when the value obtained by dividing the saturation magnetization (μTm ³ / kg) by the Co content (% by weight) exceeds 1.74 (Comparative Example 8 ), the number of giant coals increases and the transverse rupture strength is also unstable. Becomes However, even when the value obtained by dividing the saturation magnetization (μTm ³ / kg) by the Co content (% by weight) does not exceed 1.74, the number of coals increases due to other factors, and the transverse rupture strength becomes unstable. There are cases. Sample number of comparative example
No. 9 is an example in which the number of giant coals increased due to a shortage of the grain growth inhibitor. Although Sample No. 10 and 1 1 is an example of leading to decrease in toughness too many grain growth inhibitors, it is remarkable particularly lowering of toughness in greater Comparative Example 1 1 coercivity. On the other hand, it is clear that the transverse rupture force of the example of the present invention is relatively stable. According to the present invention, not only the average grain size of the fine-grain cemented carbide but also the number of giant coals can be reduced to a certain value or less at the same time. It is possible to avoid any destructive phenomenon, which is industrially significant.

Claims (1)

(57) [Claims 1] A tough, fine-grained cemented carbide mainly composed of WC and Co, wherein the tough, fine-grained cemented carbide is Cr, Ta
And two kinds selected from V metals and / or their compounds
Including the above, the Co content of the total content of the Cr, Ta and V
The weight ratio to the amount is 0.04 to 0.3, and the saturation magnetization of the tough fine-grained cemented carbide is a ratio to the Co content,
1.44 to 1.74 μTm ³ / k per 1% by weight of Co
g, a coercive force is 33600 to 52000 A / m, and 0 to 5 WC particles having a maximum diameter of 2 μm or more per 1 mm ² in cross-sectional observation with an optical microscope are present in a tough, fine-grained cemented carbide.