JPH0663052B2 - High toughness cermet tool - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cermet tool used for, for example, a throw-away insert or the like.

(Prior Art) A cermet sintered body containing carbides such as TiC as a main component is used as a material having excellent heat resistance and wear resistance, especially for a tool. The toughness was inferior to the cemented carbide containing WC as the main component.

Therefore, there is known a so-called TiCN-based cermet in which toughness is improved by adding titanium nitride (TiN) or titanium carbonitride (TiCN) to the TiC-based cermet in order to improve the toughness.

(Problems to be solved by the invention) However, although such a TiCN-based cermet can improve the toughness to some extent, it cannot improve the toughness to a degree comparable to that of a cemented carbide, and this type of cermet has not been improved yet. The current situation is that the toughness of the cermet has not been sufficiently fulfilled. By the way, when the toughness of a cermet obtained by adding TiN or TiCN to a conventional TiC-based cermet is evaluated by the average number of impacts to fracture by an intermittent cutting test,
It is about 800 to 880 times, while cemented carbide is far superior, about 2000 times or more.

(Means for Solving Problems) The present inventor pays attention to the structure of cermet itself containing TiC and TiN or TiCN as a main component, and forms a pore substance having a larger amount of pores than the surface layer inside. It was found that the toughness can be increased by this and the fracture resistance as a tool can be greatly improved.

According to the cermet tool of the present invention, first, in terms of composition, it is important that TiC and TiN, or TiCN as a main component, in particular, TiN based on the total amount of titanium carbide, nitride, and carbonitride. It is desirable to adjust the weight ratio to be 34 to 66% by weight. This is because if the substitution amount of TiN for TiC is small, the toughness of the cermet itself is significantly reduced, and if the substitution amount of TiN is excessive, the hardness of the cermet is reduced. It is known that these Ti compounds form a hard phase in the cermet, but as a component forming the hard phase, in addition to the above Ti compound, WC, Mo ₂ C, NbC carbides, nitrides, and Carbonitride and the like can be added. Also,
An appropriate amount of Ni, Co, or the like is mixed as a binding metal together with the hard phase.

Next, it is important for the cermet tool of the present invention that, in terms of structure, the inside has a pore quality containing more pores than the surface layer portion. The present invention, by thus providing pores inside the surface layer portion made of dense material, when the crack is generated in the dense surface layer portion by impact, it is possible to prevent the crack from inwardly propagating. The cracks are suppressed so that they do not extend inward or the whole, and damage to the whole is prevented. Therefore, the toughness can be improved by allowing the pores to exist inside, as compared with the conventional cermet having a dense surface layer and inside. However, if the average diameter of the pores is too large, the pores themselves become the origin of fracture and the fracture resistance decreases, and if the occupancy of the pores with respect to the internal surface area is too large, the strength and toughness deteriorate extremely. Therefore, the internal pores have an average diameter of 0.5 to 5
μm, occupancy rate of 50% or less to the internal surface area of pores
Most preferably, it is 10-30. The surface layer itself is preferably a dense material having substantially no pores, and when the thickness is small, the proportion of the pore material in the sintered body becomes large, and the strength as a whole, In addition, if the toughness is apt to deteriorate and the thickness of the surface layer portion is too thick, the structure becomes closer to the conventional one, and the effect of suppressing the development of cracks due to pores is reduced. Therefore, the thickness of the surface layer portion is preferably 0.01 to 2 mm.

Hereinafter, a structure of a cermet sintered body and a crack generation state in which the present invention is applied to a throw-away insert in a triangular shape will be described with reference to the drawings.

FIG. 1 is a transverse sectional view showing the basic structure of the insert base body, and FIG. 2 is a vertical sectional view of the same insert base body.
The insert substrate 1 is a TiCN-based cermet containing TiC and TiN or TiCN as a main component, and the surface layer portion 2 is composed of a dense material over a certain thickness T, and the inside 3 is a pore material containing a pore P. It is formed as shown.

With such a structure of the insert, as shown in FIG. 3, fine cracks (cracks) are formed in the surface layer portion 2 of the insert base body 1 which is made of a dense material due to an impact during cutting.
When C ₁ occurs, the energy of the crack can be diffused when the tip of the crack C ₁ reaches the pore P existing inside, and the progress of the crack can be prevented.

On the other hand, in the conventional sintered body 5 shown in FIG. 4 which is entirely dense, there is no structural barrier that suppresses the development of cracks C ₂ when the cracks C ₂ occur. The result is that the insert itself eventually becomes cracked or chipped.

Next, an example of a suitable production method for obtaining the above cermet will be described.

First, as a starting material, TiC, TiN or TiCN powder, if desired, a hard phase forming component such as WC, Mo ₂ C or NbC, and Ni or Co.
An iron group metal powder such as the above is mixed with a solvent such as acetone to form a slurry. An appropriate amount of a pore-forming agent such as polyethylene is added to this mixed slurry, mixed again, and then dried and sized.

This powder is molded into a desired tool shape by molding means such as press molding, and then fired in a non-oxidizing atmosphere at 1400 to 1600 ° C. At this time, 500 ~ 1000 ℃ in the heating process
The pore agent melts in the vicinity, and the portion occupied by the pore agent in the molded body remains as pores. After that, it is desirable to use a pore agent having a particle diameter slightly larger (about 1.2 times) than the pore diameter to be finally obtained in the slurry because it shrinks as the firing progresses.

Next, prepare a mixed slurry containing no pore agent,
Apply this to the entire surface of the sintered body, and after drying it, 1400
Bake in a non-oxidizing atmosphere at ~ 1600 ° C. The thickness of the slurry applied to the entire surface of the sintered body may be an appropriate thickness depending on the shrinkage rate during firing.

In this way, finally, a sintered body can be obtained in which the surface layer portion is dense and the inside is porous.

Hereinafter, the present invention will be described with reference to the following examples.

(Example) TiC, TiN, WC, Mo ₂ C and Ni powders were weighed so as to be in the composition range shown in Table 1, acetone was added thereto, and wet mixed by a vibration mill to prepare a slurry. .
An appropriate amount of a pore agent made of polyethylene having a particle size of 0.05 to 10 μm was added to this slurry and mixed again.

After the mixing was completed, the mixture was dried to remove the solvent by evaporation, paraffin wax was added, and the mixture was passed through a 40-mesh screen for sizing.
The powder thus obtained was molded under a pressure of 1000 to 2000 Kg / cm ² and then calcined at a temperature of around 300 ° C. to remove the wax. Then, it was fired at a firing temperature of 1500 ° C. in a non-oxidizing atmosphere. The pore agent melted at 500 to 1000 ° C., and the pore remained in the sintered body. Next, a slurry of the same composition containing a pore-forming agent was applied to the surface of the sintered body while changing the thickness as appropriate on the surface of the sintered body. Next, this was dried and then baked at a baking temperature of 1500 ° C. to form a dense surface layer portion.

The shape of the insert is TNMG332 as shown in Fig. 1.
Shaped.

An interrupted cutting test was performed on the obtained insert, and the average number of impacts until the cutting edge of the insert was damaged was measured. For the insert, the thickness of the dense surface layer portion was measured, and the average particle diameter of the pores inside the insert and the area occupied by the pores were determined.

According to Table 1, the number of impacts was 800 to 880 in the conventional samples No. 1 and No. 8 having no pore quality inside. In addition, sample Nos. 12 and 13 containing TiC or TiN as the main component and not containing both TiC and TiN have even worse impact resistance.
It was ~ 650 times.

On the other hand, according to the present invention, the sample having pores inside thereof exhibited extremely excellent impact resistance as compared with the conventional product and the comparative product. According to the product of the present invention, according to the relationship between the pore occupancy rate and the pore diameter, it can be seen that when the pore occupancy rate is the same, the smaller the pore diameter, the better the impact resistance.

(Effects of the Invention) As described above in detail, the cermet tool of the present invention has the surface layer portion made of dense material and the inside made of pore material,
Since it is possible to suppress the development of cracks and thereby improve the toughness as a sintered body and the fracture resistance, it is possible to improve the reliability as a tool and provide a tool with a long life. it can.

[Brief description of drawings]

FIGS. 1 and 2 show an example of a cermet tool of the present invention, showing a structure of a throw-away insert having a triangular diameter and a crack generation state. FIG. 1 is a cross-sectional view of the insert, and FIG. Similar insert longitudinal section, third
FIG. 4 is an enlarged partial explanatory view showing a crack generation state, and FIG. 4 is an enlarged partial explanatory view showing a crack generation state of a conventional insert. 1 ... Insert base 2 ... Surface layer 3 ... Inside P ... Pore C ... Crack

Claims (2)

[Claims] 1. A high-toughness cermet tool, which is a cermet tool containing TiC and TiN or TiCN as a main component, wherein the inside of the cermet is made of a pore material having more pores than the surface layer portion. 2. The high-toughness cermet tool according to claim 1, wherein the surface layer portion is substantially dense and has a thickness of 0.01 to 2.00 mm.