JPH0525937B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a cermet for cutting tools such as throw-away inserts. Conventionally, it is known that this type of cermet is generally inferior in toughness compared to cemented carbide, and in order to improve this toughness, titanium nitride (TiN) or titanium carbonitride {Ti(C,N)} has been added to TiC-based cermet. Attempts have been made to improve toughness by adding C. However, although such a method improves the toughness to a certain extent, it has not been possible to improve the toughness to a level comparable to that of cemented carbide, and it has not yet been possible to sufficiently improve the toughness of this type of cermet. The current situation is that this is not the case. By the way, the conventional
When titanium nitride (TiN) or titanium carbonitride {Ti(C,N)} is added to a TiC-based cermet, its toughness is measured by the average number of impacts until fracture in an intermittent cutting test, and the toughness is approximately 800 to 880. In contrast, an example of cemented carbide has a far superior number of times of 2,400 times. Accordingly, the present invention has found that by improving the structure of the cermet substrate itself, the toughness of the cermet substrate can be significantly improved to a level comparable to or even higher than that of the above-mentioned cemented carbide. In the present invention, the surface layer of the cermet base is thicker than the surface.
By firing the material so that it is dense with a diameter of 0.01 to 2.00 mm and has pores occupying an area of 10 to 50% of the surface area of the sintered body, cracks occur in the dense surface layer due to impact. In this case, the inward propagation of the crack is blocked by the porous material to prevent the crack from extending inward or to the whole body, thereby preventing damage to the whole body. When the occupied area of the pores is less than 10%, that is, when the number of pores is small, the number of pores facing the crack occurrence position is small, so the effect of preventing the crack from progressing is small, and conversely, when the area occupied by the pores is less than 50% The toughness of the sintered body as a whole deteriorates extremely. When the thickness of the dense surface layer exceeds 2.00 mm, the area occupied by the dense layer increases and approaches the conventional case where the entire surface layer is dense, and the effect of preventing the development of cracks is small, and the thickness is less than 0.01 mm.
If it is less than mm, the area occupied by the pores becomes too large and the toughness of the sintered body as a whole deteriorates. Hereinafter, the structure of a cermet sintered body in which the present invention is applied to a triangular throw-away insert and the state of occurrence of cracks will be explained based on the drawings. FIG. 1 is a cross-sectional view showing the basic structure of the insert base in a sintered state, and FIG. 2 is a longitudinal cross-sectional view of the same insert base. Insert base 1 is TiC
It is made of {or TiN, Ti(C,N)} based sintered body, the surface layer is formed of a dense material 2 over a certain thickness T, and the inside is formed of a porous material 3 having a certain occupied area as shown in the figure. By making the sintered body of the insert into such a structure, as _shown in _FIG . The tip reaches one pore in the porous substance 3, and this pore can prevent the tip of the crack _C1 from advancing any further. In comparison, in the case of the conventional cermet shown in Fig. 4, which is entirely dense 4, its toughness depends on the manufacturing method or composition itself of the sintered body, and even if it has a certain degree of toughness, if When a crack C ₂ occurs on the surface layer, since there is no structural barrier at the tip to suppress crack propagation, it easily propagates into the entire sintered body 5 and causes damage to the entire sintered body. . From the above, in the case of the present invention, if the thickness T of the dense surface layer of the sintered body 1 is too thin, the volume occupied by the pores becomes too large and the overall toughness deteriorates. on the other hand,
If the thickness T of the dense surface layer is too large, the volume occupied by the dense layer becomes too large, and the range of crack development becomes long, approaching the low toughness characteristics of the conventional example. Also,
If the area occupied by the pores of the porous material is too small, the number of pores occupied by the crack will decrease in proportion to the location where the crack occurs, and the range of crack development will become larger or the crack will be allowed to grow inward. On the other hand, if the area occupied by the pores of the porous material is too large, the overall toughness will deteriorate. Furthermore, the average diameter of the pores is suitably in the range of 0.5 μm to 5 μm; if it is too large, the overall toughness will deteriorate, and if it is too small, the effect of suppressing crack growth will be reduced. Next, an example of a suitable manufacturing method for obtaining the above sintered body will be explained. Example 1 TiC, TiN, WC, Mo ₂ C and
Weigh Ni so that it has the composition range shown in Table 1,
A suitable solvent such as acetone is added to this, and wet mixing is performed using a vibrating mill to create a mixed slurry. An appropriate amount of a pore agent such as polyethylene is added to this mixed slurry and side mixing is performed. After the mixing is completed, the mixture is dried, the solvent is evaporated off, paraffin wax is added, and the mixture is granulated by 40 mesh passes. The powder thus obtained is molded at a pressure of 1000 to 2000 Kg/ ^cm2 , then calcined at a temperature of around 300°C to remove wax, and then fired at a firing temperature of 1500°C in a non-oxidizing atmosphere. do. The pore agent is 500~1000
It melts at ℃, leaving the part of the molded body occupied by the pore agent as pores. At this time, since the sintered body shrinks slightly, a pore agent having a particle size slightly larger (approximately 1.2 times) than the desired pore diameter (described later) is used in the slurry. Furthermore, a mixed slurry similar to the above without adding the pore agent is applied to the entire surface of the fired body. The thickness of the slurry to be applied is determined appropriately depending on the shrinkage rate during firing. Thereafter, after the applied slurry is sufficiently dried, it is fired at a firing temperature of 1500°C to form a sintered body having a porous interior and a dense surface layer. In this way, the composition range of TiC and TiN was adjusted to 40:20.
For two sets of cermet compositions containing 20:40% by weight or 20:40% by weight, the thickness of the dense surface layer was determined by adjusting the amount of slurry applied to the porous fired body, and the amount of the pore agent added was determined. Adjust the area occupied by the pore in the sintered body, and the inscribed circle diameter is 9.5 mm.
Samples 1 to 8 shown in Table 1 were used as triangular inserts having a thickness of 4.8 mm, and the average number of impacts until the sintered body broke was determined by an interrupted cutting test for each sample.

【table】

[Table] Sample numbers 1 and 5 in Table 1 have no pore agent added and the pore occupied area is 0%, and correspond to conventional cermets. Sample numbers 1 and 5 have an average number of impacts before breakage of about 800 and 880, while sample numbers 2, 3, 4, 6, 7, and 8 have an area occupied by porous pores inside the sintered body. cermet is 10 to 50%, and the average number of impacts before breakage is over 1380, which shows that the toughness is significantly improved compared to the conventional cermet with 0% pore occupation area, especially sample numbers 3 and 7. It can be seen that the toughness of the steels with the same number of impacts has been improved to 2340 and 2400, comparable to the toughness of the cemented carbide mentioned above. In addition, even in the case of sample numbers 3a, 3b, 7a, and 7b, which have the same pore occupation area of 30% as sample numbers 3 and 4 above, the thickness of the dense surface layer is less than 0.01 mm or
It is understood that if it exceeds 2.00 mm, the number of impacts will be less than 900 and the toughness will deteriorate. Example 2 NbC, TiC, WC, TiN, Mo ₂ as starting materials
Weigh C and Ni so that they fall within the composition range shown in Table 2, add a suitable solvent such as acetone,
Wet mixing is performed using a vibrating mill to create a mixed slurry. A suitable amount of a pore agent is added to this mixed slurry in the same manner as described above, followed by molding and firing to obtain a molded fired body having pores. A similar mixed slurry without the addition of a pore agent as described above is applied to the entire surface of this sintered body, and this is fired to obtain a sintered body having pores inside and a dense surface layer. In this way, the above composition is set as an appropriate composition range of the cermet, and the amount of slurry applied to the porous fired body is adjusted to determine the thickness of the dense surface layer.
In addition, the area occupied by the pores in the sintered body was determined by adjusting the amount of the pore agent added, and the inscribed circle diameter was determined in the same manner as above.
Samples 9 to 16 shown in Table 2 were prepared as triangular inserts each having a diameter of 9.5 mm and a thickness of 4.8 mm, and the average number of impacts until the sintered body fractured was determined using the same interrupted cutting test for each of these samples.

【table】

[Table] Sample numbers 9 and 13 in Table 2 have no pore agent added and the pore occupied area is 0%, and correspond to conventional cermets. Sample numbers 9 and 13 have toughness with an average number of impacts before fracture of about 930 and 900, while sample numbers 10, 11, 12, 14, 15 and 16 have toughness due to the occupation of porous pores inside the sintered body. Area is 10-50%
The average number of impacts before breakage was 1380 or more, which shows that the toughness is far superior to that of conventional cermets with 0% pore occupation area.In particular, sample numbers 11 and 15 have an average number of impacts of 2430 and above. It is understood that toughness is not only superior to that of 2620 and Sample Nos. 3 and 7 of Example 1, but also greater than that of the cemented carbide described above. In addition, sample numbers 11a, 11b, 15a and 15b have the same pore occupation area of 30% as sample numbers 11 and 15 above.
Even if the thickness of the surface layer is less than 0.01mm or
It is understood that if it exceeds 2.00% mm, the number of impacts will be 900 or less, and the toughness will deteriorate as in Example 1. Example 3 Sample numbers 3, 7, 11 and 15 of Examples 1 and 2 above
When the average number of impacts until the sintered body breaks due to an interrupted cutting test was similarly calculated for cases where the average diameter of the pores inside the sintered body was less than 0.5 μm and more than 5 μm, the average number of impacts until the sintered body fractured was determined. When the diameter was less than 0.5 μm, it was repeated 800 to 900 times, and when it exceeded 5 μm, the toughness was extremely deteriorated. In other words, if the average diameter of the pores is too small, the tip of the crack will develop regardless of the presence of pores, and the effect of suppressing crack growth will be lost.On the other hand, if the average diameter of the pores is too large, the toughness of the entire sintered body will deteriorate. This is to do so. From the above Examples 1, 2, and 3, the TiC-based cermet and other NbC-containing cermets also have a dense surface layer from the surface to a thickness of 0.01 to 2.00 mm, and an inner surface area of 10 to 2.00 mm of the surface area of the sintered body. The sintered body, which has a porous structure with an area occupied by 50% pores, has far superior toughness compared to conventional cermets that do not have the above-mentioned pores inside, and has a toughness comparable to that of cemented carbide. It was found that the improvement was the same or even better. In addition, the average pore diameter of the pore quality is
It is also understood that outside the range of 0.5 μm to 5 μm, the toughness is extremely degraded. When such a sintered body is used as a cermet for a cutting tool such as a throw-eye insert, a cutting tool with high toughness and excellent durability can be provided.

[Brief explanation of the drawing]

Figures 1 to 3 show the structure of a cermet sintered body and the state of crack occurrence in which the present invention is applied to a triangular throw-away insert. Figure 1 is a cross-sectional view of the insert, and Figure 2 is a similar insert. FIG. 3 is an enlarged partial explanatory view showing a crack occurrence state, and FIG. 4 is an enlarged partial explanatory view showing a crack occurrence state of a conventional insert in which the entire sintered body is dense. 1...Insert base, 2...Dense material, 3...
Pore quality, T...surface layer thickness.

Claims (1)

[Claims] 1. The surface layer of the cermet substrate is 0.01 to 0.01 thicker than the surface.
It is dense over 2.00mm, and the inside has a sintered body surface area.
A high-toughness cermet characterized by being fired to form a porous material having an area occupied by 10 to 50% of the bore. 2. The high toughness cermet according to claim 1, wherein the pores have an average pore diameter of 0.5 μm to 5 μm.