JPH0332502A - Cermet tool - Google Patents

Abstract

PURPOSE:To improve the abrasion resistance and defective resistance of a cermet tool by composing it of composition including a quantity of nitrogen, and providing a specified rigidity difference and toughness difference between its flank and its rake face. CONSTITUTION:A molded body in the form of a tool is produced consisting of 70-95wt.% a right material phase component of an atomic ratio of 0.4-0.6 as expressed by nitrogen/(carbon+nitrogen) including Ti by 50-80wt.% as converted to carbide, nitride or carbonitride, and a group IVa metal by 10-40wt.% as converted to carbide, and 5-30wt.% a binder phase component. The molded body is installed in a vacuum furnace to be baked, and by introducing nitrogen gas at a specified timing of baking, a highly rigid layer having a rigidity gradient is formed in the surface of the sintered body. A flank A of a cermet tool has a layer 1 of a high rigidity, and by polishing this surface, the rigidity of a rake face A is reduced to expose an inner surface 2 of a high toughness. A rigidity difference and a toughness difference are thus produced between the flank A and the rake face B, thereby both the abrasion resistance and the defective resistance of the tool can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cermet tool with excellent wear resistance and fracture resistance.

[Prior art]

Conventionally, cemented carbide whose main component is WC-Co has been mainly used as a sintered body for cutting, but recently T
Cermet sintered bodies whose main components are carbides, nitrides, and carbonitrides are used.

Such a cermet-based sintered body has TiC as a main component, an iron group metal as a binder phase, and a material from periodic table IV.
The mainstream was TiC7f5-method, in which carbides, nitrides, and carbonitrides of group metals such as a, Va, and Via were added as hard components. However, since such a TiC4 sintered sintered body is inferior in heat resistance and toughness, it was proposed to further include nitrides such as TiN and carbonitrides in the above composition. This is intended to provide toughness to the sintered body due to TiN itself having high toughness, and to improve thermal shock resistance and thermoplastic deformability due to its high thermal conductivity.

When such a cermet sintered body is used for tools, high wear resistance and chipping resistance are required, and various improvements have been made.

For example, in Japanese Patent Publication No. 59-14534, nitrogen is introduced into the furnace below the liquid phase appearance temperature to form a softened layer with high toughness on the surface of the sintered body, and in Japanese Patent Publication No. 59-17176, nitrogen is introduced into the furnace at a temperature below the temperature at which the liquid phase appears, and in Japanese Patent Publication No. 59-17176, nitrogen is introduced into the furnace at a temperature below the temperature at which the liquid phase appears, and a softened layer with high toughness is formed on the surface of the sintered body. Furthermore, it is possible to form Hard II having a specific hardness by firing, as disclosed in Japanese Patent Publication No. 1983-
According to No. 34618, it is proposed to obtain a cermet having uniform mechanical properties both on the surface and inside by exposing the cermet to a CO atmosphere when the temperature is lowered after firing.

[Problem that the invention seeks to solve]

However, from knowledge of wear resistance during high-speed cutting, the cutting tools described in Japanese Patent Publications No. 59-14534 and Japanese Patent Publication No. 60-34618 have low surface hardness and are therefore unsatisfactory in terms of performance. On the other hand, although Japanese Patent Publication No. 59-17176 discloses a method of forming a hard layer on the surface, the surface hardness is at most 2000 in bisocurce hardness (Hν).
Only up to Kg/mm2 has been achieved.

Therefore, in Japanese Patent Application No. 63-243623, the present inventors proposed a cermet sintered body with excellent wear resistance and a surface hardness of 2000 or more. If the toughness is improved, the toughness decreases and the fracture resistance becomes inferior, so there is a problem that the applications of such cermets are limited to some areas.

[Means for solving problems]

The present inventors have discovered that in cutting tools that normally consist of a flank face and a rake face, wear occurs mainly on the flank face, and chips are more likely to occur on the rake face, and that - tools with high hardness are used for boat fishing. Focusing on the fact that toughness improves as hardness decreases, we designed the flank face of the cutting tool to have high hardness and the rake face to have low hardness, thereby increasing the wear resistance and durability of the tool. It is possible to improve the chipping property and extend the life of the tool, and as a material for making the cutting tool with the above structure, Ti is used in an amount of 50 to 80% by weight in terms of carbide, nitride, or carbonitride. Contains Na metal of the periodic table at a ratio of 10 to 40 weight Mχ in terms of carbide, and has an atomic ratio of (nitrogen/carbon + nitrogen) of 0.
．． 70 to 95% by weight of a hard phase component ranging from 4 to 0.6% by weight, and 5 to 30% by weight of a binder phase component mainly composed of iron group metals.
It has been found that by using a cermet having a weight of 2, it is possible to obtain a cutting tool with excellent wear resistance and chipping resistance.

The present invention will be explained in detail below.

The cermet of the present invention contains Ti as a hard phase component in an amount of 50 to 80% by weight in terms of carbide, nitride, or carbonitride.
In particular, 55 to 65% by weight and periodic table Vi of W, Mo, etc.
10 to 40% by weight of group a metal, especially 15% by weight in terms of carbide.
30% by weight.

In such a hard phase component, the amount of TiO is 50% by weight.
If it is less than 80w, the wear resistance will decrease, and if it exceeds 80wt, the sinterability will decrease, which is not preferable. In addition, Group Vra metals have the effect of suppressing grain growth and improving wettability with the binder phase, but if it is less than 10!1 ffiχ, the above effects cannot be obtained,
The hard phase becomes coarse and hardness and strength decrease. Also, 40
If the weight exceeds 2, unhealthy phases such as η phase will occur and sintering will become difficult.

In addition to the above, hard phase components include Ta and Nb for the purpose of improving crater wear resistance, and Zr, V, Hf, etc. for the purpose of improving plastic deformation resistance in terms of nitrides, carbides, and carbonitrides. Although it is possible to contain it in a proportion of 5 to 40% by weight, if it exceeds 40% by weight, it is not preferable because it tends to deteriorate wear resistance and significantly increase the occurrence of bores and voids.

On the other hand, the binder phase is mainly composed of iron group metals such as Fe, Co, and Ni, and may partially contain hard phase forming components.

The sintered body as a whole has a hard phase component of 70 to 95% by weight and a binder phase component of 5 to 30% by weight.

The compositional feature of the present invention is that the atomic ratio expressed by (nitrogen/carbon + nitrogen) in the hard phase component is 0.4 to 0.
．． 6, especially in the range of 0.4 to 0.5. That is, if the atomic ratio is less than 0.4, no improvement in toughness or wear resistance can be expected, and the object of the present invention cannot be achieved; if it exceeds 0.6, bores and voids will occur in the sintered body. Reliability as a tool decreases.

An example of manufacturing a tool having flank and rake surfaces with different hardness using a cermet having such a composition will be described. First, the composition is Ti as carbide 1, 50 to 80% by weight in terms of nitride or carbonitride, Via of the periodic table.
A hard phase component 70 to 95 containing Group metal in a proportion of 10 to 40% by weight in terms of carbide and having an atomic ratio expressed by (nitrogen/carbon + nitrogen) in the range of 0.4 to 0.6.
% by weight and a binder phase component of 5 to 30 parts Iz.

Specifically, raw material powders include TiC, TiN, and T1CN.
etc., and as group IV a systems, WC, Mo, C, phylum oC
Of course, it is also possible to use these compounds, or a combination of these composite carbides, composite carbides, composite carbonitrides, etc. Note that if TiC is used as a Ti-based material, the sinterability will decrease and partial grain growth may occur.
N) or a combination of Ti(CN) and TiN is more preferred.

The obtained shaped rod is placed in a vacuum furnace and transferred to firing.

Firing is carried out at a firing temperature of 1400 to 1700°C. According to the present invention, firing is first heated in a vacuum furnace at a pressure of 0.5 Torr or less, and then heated at a pressure of 70 Torr or more, particularly 100 to 200 Torr, at a predetermined time. Introduce nitrogen gas.

This nitrogen gas is introduced during the temperature raising process at a temperature higher than the liquid phase appearance temperature of the iron group metal, especially at a stage when the theoretical density ratio has become denser than the initial formed rod by about 5χ or more. That is, a film is formed on the surface of the molded rod by the liquid phase at a temperature higher than the liquid phase appearance temperature. By introducing nitrogen gas after this film is formed, it suppresses the decomposition of nitrides and prevents a decrease in the wettability of the binder phase and hard phase particles, resulting in the formation of bores in the sintered body.
It is possible to prevent voids from remaining.

However, the timing of introducing nitrogen gas is after reaching the maximum sintering temperature.
In particular, in the vicinity where the theoretical density ratio exceeds 90χ, the effect of suppressing the decomposition of nitrides is not substantially obtained, and vF and the surface of the viscous material become rough.

After the temperature in the furnace reaches the maximum sintering temperature, the nitrogen gas is maintained for a predetermined time and then immediately returned to vacuum to continue firing.

This is because if the pressure is further increased after reaching the maximum sintering temperature,
A coarse-grained, brittle nitride layer containing almost no metal is formed on the surface of the sintered body, causing roughness on the sintered surface and significantly reducing the toughness of the surface.

In this way, by introducing nitrogen gas at a specific time during firing, a very hard layer having a hardness gradient is formed on the surface of the sintered body as shown in FIG. This is because pressure is generated between the inside of the molded body and the atmosphere in the furnace after nitrogen gas is introduced. Then, when the vacuum is suddenly returned, the bonding metal near the surface of the formed rod moves inward, and the amount of bonding phase decreases near the back surface compared to the inside, which is thought to increase the hardness.

The hardness of this surface area largely depends on the pressure of nitrogen gas introduced during firing. For example, in order to obtain a Vickers hardness of 2000 or more, the nitrogen gas pressure must be adjusted to approximately 70To
It is sufficient to set it to rr or more.

The above-mentioned cermet of the present invention has high toughness, high hardness, and excellent heat resistance because it contains a large amount of nitrogen, and in particular, the surface portion has high hardness, so it has very excellent wear resistance. On the other hand, the toughness is slightly inferior to that of the inside. On the other hand, the hardness of the inside is inferior to that of the surface,
It has the property of high toughness.

Therefore, according to the present invention, in the cross-sectional view of the cermet sintered body shown in FIG. By removing the hard layer, the hardness of the rake face is lowered and the highly tough interior 2 is exposed to the surface. As a result, a hardness difference and a toughness difference occur between the groove face and the flank face B.

In this polishing process, as shown in Figure 1, a hardness gradient is formed from the surface of the cermet to the inside.
By adjusting the amount of adjustment of the polishing die, the hardness of the rake face can be set appropriately.

In addition, the hardness of the flank surface is desirably 2000 or higher on the Pinocurs hardness, since the flank surface itself greatly contributes to the wear characteristics of the tool.On the other hand, the hardness of the rake surface is desirable, since it greatly contributes to the chipping property of the tool. Although toughness is desired, the rake face is also required to have moderate wear resistance, so it is desirable to have a Pinkers hardness of 1500 or more.
In particular, it is preferable that the difference in hardness between the flank face and the rake face is 200 or more.

The invention will now be explained with the following examples.

[Example 1] Composition 1 (wt%) ai2 (wt 2) Ti(CN) 50 Ti was prepared using powder with an average particle size of 1 to 1.5 μm as the raw material powder to the composition shown in Table 1 below. (CN) 58Ti
N 8 WC12 WC8MozC8 MozC10NbC6 TaC12VC2 Ni 6 Ni 7Co
6 Co 7 These two types of blends were ground with a vibrating mill, the binder was added, the bottom of the press was shaped into a TNMA332 chip shape, and the mixture was heated at 300°C.
After removing the binder, it was fired.

For firing, the temperature is raised in a vacuum furnace, and after the appearance of a liquid phase, nitrogen gas is heated at 1350°C to 100 Torr for composition 1 and 15 Torr for composition 2.
The pressure was introduced at 0 Torr, and after reaching the maximum sintering temperature of 1500° C., it was held for 5 minutes and immediately returned to vacuum. Note that the temperature was maintained at 1500° C. for 1 hour and then cooled.

The obtained sintered body was quantitatively analyzed for carbon and nitrogen in the hard layer, and the N 2 /(C+N) atomic ratio was found to be 0.5 for composition 1 and 0.45 for composition 2.

In addition, after polishing off the metal components slightly precipitated on the surface of this sintered body, the Vickers hardness was measured and found to be 2350 for Composition 1 and 2400 for Composition 2.

In addition, a characteristic measurement sample prepared in exactly the same manner as above was polished at an angle of approximately 5°, and the polished surface was
When Pinkers hardness was measured in the vertical direction at different distances (depths) from the surface, it was found that all sintered bodies had a hardness gradient in which the hardness decreased from the surface to the inside.

The rake faces of the cermets of compositions 1 and 2 thus obtained were polished with varying amounts of polishing to obtain several types of cutting tools with different rake face hardnesses as shown in Table 2.

The obtained cutting tool was subjected to a wear resistance test and a chipping resistance test under the following conditions.

Work material cutting speed notch sending cutting time Wear resistance test SCM435■ V = 300m/m1n d = 2mm f=0.3mm/rev T = 6 minutes later Flank wear amount compare The results are shown in Table 1.

[Margin below]

Fracture resistance test 545C■5+nm x4 V = 100m/ m1nd = 1.5mm f = 0.2mm /rev T = 1 minute Cut 5 corners and calculate the number of no-breakage corners Results shown in Table 1 of Honzoto Table According to No. 1, which did not undergo any polishing,
No. 1.5 sample with polished rake face, No. 2~
Both samples 4 and 6.7 have the same wear resistance, but
It can be seen that the fracture resistance is greatly improved.

〔Effect of the invention〕

As described above in detail, the cermet tool of the present invention has a composition system that contains a large amount of nitrogen, and by providing a specific hardness difference and toughness difference between the flank and rake faces, the wear resistance of the tool is improved. , the fire resistance can be greatly improved, and the life of the tool can be extended.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the hardness distribution of the cermet I sintered body used in the present invention, and FIG. 2 is a cross-sectional view of the cermet sintered body used in the present invention. A: Rake face B: Relief face

Claims (1)

[Claims] 50 to 80% by weight of Ti in terms of carbide, nitride or carbonitride, 1% by weight of Group IVa metal of the periodic table in terms of carbide.
Nitrogen/(
70 to 95% by weight of a hard phase component having an atomic ratio of 0.4 to 0.6 (carbon + nitrogen) and 5 to 30% by weight of a binder phase component whose main component is an iron group metal. 1. A cermet tool characterized in that the Vickers hardness of the flank face of the tool is higher than the hardness of the rake face.