JPH04231454A - Coated ticn-base cermet - Google Patents

Abstract

PURPOSE:To manufacture a TiCN-base cermet excellent in wear resistance and toughness by forming a specified coating film on the surface of a TiCN-base cermet in which specified amounts of Nb and V are added to a hard phase essentially consisting of Ti and W. CONSTITUTION:As for a TiCN-base cermet constituted of a hard phase essentially consisting of Ti and contg. at least W, Nb and V and a bonding phase constituted of iron-group metals, at the time of denoting the componental compsn. other than iron-group metals and inevitable impurities as [(Ti)a(Nb, V)b (W)c] (CuVv)z, a+b+c=1, 0.50<=a<=0.95, 0.05<=b+c<=0.5, 0.40<=b/(b+c)<=0.95, 0.40<=v<=0.60, 0.80<=z<=1.0 and u+v=1 are satisfied, and the atomic ratio of Nb to V (Nb/V) is regulated to 1 to 10. On the surface of the above TiCN-base cermet, a Ti-contg. hard film enriched with Ti compared to that in the cermet, having <=0.4mum average grain size and <=100ppm content of iron group metals is formed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a TiCN-based cermet with excellent wear resistance and toughness, and more particularly to a surface-coated cermet with an excellent finished surface of a workpiece as a cutting tool.

0002

[Prior Art] In recent years, as a sintered body for cutting,
a hard phase consisting of a double carbonitride of group a, 5a, and 6a elements;
Cermets composed of a binder phase made of iron group metals have come into use.

[0003] Such cermets have so far been made of Ti.
TiC-based cermets, whose main component is C, have been the mainstream, but this TiC-based cermet has inferior fracture resistance compared to cemented carbide, which has been used as tool material for a long time, so it is difficult to use such systems. A so-called TiCN-based cermet with improved toughness by adding nitride has been proposed.

The hard phase in this TiCN-based cermet is generally composed of double carbonitrides of Ti and W, and carbides and nitrides such as Mo and Ta are added as hard phase forming components. Mo and Mo2C are considered essential components as hard phase components because they improve the wettability of the hard phase with the binder phase. Furthermore, TaC improves the oxidation resistance of cermet and has the effect of suppressing the progress of crater wear when used as a cutting tool, so it has been regarded as an essential component from the point of view of practicality.

[0005] Carbon (C) and nitrogen (N), which form the hard phase, are major factors that determine the toughness and hardness of cermets.Recently, efforts have been made to increase the toughness of cermets by incorporating a large amount of nitrogen. Attempts are being made to do so.

However, recently various improvements have been made to TiCN-based cermets.
In No. 017, Mo and Mo2C are not added because they do not have the effect of improving wettability with the binder phase in systems containing a large amount of nitrogen and inhibit sinterability. A system in which a phase consisting of TiN is precipitated has been proposed, and it has also been proposed to add NbC as a hard component to improve the thermal shock resistance and oxidation resistance of cermet.

[0007]

[Problems to be Solved by the Invention] However, with these TiCN-based cermets, these technological improvements have not led to essential improvements in cermets, and up until now there has been no improvement in the quality of cemented carbide, which is the mainstream tool material. Deterioration of cutting properties still remains. Moreover, as cutting conditions tend to become stricter, tool materials with even higher properties are required.

Therefore, various studies were conducted on the composition of conventional cermets, and it was found that when Mo or Mo2C is added to a cermet that forms a cored structure, the Mo itself becomes Ti.
Since it is inferior to C in properties such as hardness, thermal conductivity, Young's modulus, and oxidation resistance, we thought it would be better not to add Mo from the viewpoint that it tends to cause a decrease in wear resistance especially when used as a tool material. It will be done.

Furthermore, according to the structure of Japanese Patent Publication No. 63-3017, the problem with the precipitation of the TiN phase is that since the TiN phase itself has poor wettability with metal, the interface with the binder phase becomes a source of fracture and the strength deteriorates. have.

On the other hand, the oxidation resistance effect of Ta has almost no effect on cermets containing a large amount of nitrogen, and on the contrary, it inhibits sinterability. It has been found that there is a problem in that the sintering temperature needs to be set particularly high, which causes grain growth of the sintered particles and reduces the wear resistance of the cermet.

Furthermore, there is a limit to the improvement in the quality of the finished surface of the workpiece due to the influence of the iron group metal as a binder phase component contained in the cermet.

0012

[Means for Solving the Problem] Based on the above knowledge, the present inventors investigated the composition of cermet with excellent wear resistance, chipping resistance, and oxidation resistance. Ti and W are essential components, and conventionally Mo and Ta have been added to them, but instead of these, Nb and V are selected and added within a specific range, and Mo and Ta in the system are added. It has been discovered that a TiCN-based cermet with excellent cutting properties can be obtained by minimizing the amount of Ta, and by forming a specific coating on the surface of this cermet, the properties of the cermet itself are not impaired. It was discovered that the quality of the finished surface after cutting the work material could be improved.

That is, the present invention provides at least Ti, W, N
It is composed of a hard phase containing b and V and a binder phase made of an iron group metal, and the other components excluding the iron group metal from the overall composition are [ (Ti) a (Nb, V) b (W
)c](Cu Nv )z, a+b+c=
1, 0.50≦a≦0.95, 0.05≦b+c≦0.
5, 0.40≦b/b+c≦0.95, 0.40≦v≦
0.60, 0.80≦z≦1.0, u+v=1, and the atomic ratio of Nb and V (Nb/V) is 1.
The surface of a TiCN-based cermet in the range of ~10 is coated with a hard film containing Ti, which is richer in Ti than the cermet, has an average particle size of 0.4 μm or less, and has an iron group metal content of 100 ppm or less. It is characterized by:

The coated TiCN-based cermet of the present invention basically consists of a base material consisting of a hard phase and a binder phase, and a hard coating layer formed on the surface of the base material.

In the cermet base material, Ti is a component that forms a hard phase and is present in the sintered body as approximately TiCN, but if the Ti amount (a) is less than 0.5, it is characteristic of a cermet tool. Abrasion resistance and low affinity for metals will be insufficient, and if it exceeds 0.95, chipping resistance will be poor. Note that a is 0.70≦a≦0
．． 9 is particularly desirable.

[0016] Nb, V, and W are auxiliary components that form a hard phase, and all have the effect of suppressing the grain growth of cermet, forming a fine crystal structure and increasing the strength and toughness of cermet. act. Therefore, the total amount of these (
If b+c) is less than 0.05, the chipping resistance will be insufficient, and if it is larger than 0.5, the wear resistance will be poor and the reactivity with the work material will tend to be high. Note that it is particularly desirable that the (b+c) value is 0.10≦b+c≦0.30.

Among these, W is an essential component for improving the wettability of the hard phase with the binder phase and increasing toughness as WC, but when the hard phase is (Ti, W)
When made of CN, there is a problem in that properties such as wear resistance, oxidation resistance, and chipping resistance do not reach a practical level. Therefore, carbides such as Mo and Ta have been used as essential components for the purpose of strengthening the hard phase and improving various properties, but as mentioned above, Mo2C itself is a main component of the hard phase, TiC or TiCN. Since its properties are inferior to that of cermet, it actually deteriorates the properties of the cermet. In addition, sinterability is greatly influenced by the amount of binder phase in the system, but when the binder phase is the same amount, the addition of TaC reduces sinterability, requiring high temperature firing, which causes crystallization. The wear resistance of the cermet deteriorates as the particle size of the cermet increases.

On the other hand, Nb is Mo2 as a carbide.
Since it has superior properties in itself compared to C, it greatly contributes to improving the properties of cermet, and it does not affect sinterability, so it has excellent wear resistance, oxidation resistance,
It was found that fracture resistance can be improved. Furthermore, V forms a hard phase together with Nb as VC, thereby enhancing the effect of adding Nb, and can greatly improve the wear resistance particularly during high-speed cutting of cermet.

From this relationship, the ratio (b/
If b+c) in the above formula is less than 0.4, the wear resistance and oxidation resistance will be poor, and if it is larger than 0.95, the chipping resistance will be reduced. Note that the atomic ratio of Nb/V is preferably 1 to 10, particularly 2 to 6.

On the other hand, the amount of nitrogen and carbon is a very important factor in determining the hardness and toughness of cermet, and especially as the amount of nitrogen increases, the toughness tends to improve. When this happens, a problem arises in that gas from decomposition of nitrides during firing remains in the sintered body in the voids. Therefore, in the above formula, if the nitrogen amount (v) is 0.
When it is less than 4, the toughness decreases and fracture resistance becomes insufficient, and when it exceeds 0.6, voids occur in the sintered body, resulting in a lack of reliability.

[0021] In addition, the amount of nitrogen and carbon is Ti, W, Nb, and V.
If the ratio (z) to the total amount is less than 0.8, the sinterability will deteriorate and voids will remain, and if it is larger than 1.0, free carbon will be generated, resulting in deterioration of strength. Desirably, 0.85≦z≦1.0.

[0022] The iron group metal forming the binder phase in the present invention includes Ni and/or Co, preferably composed of Ni and Co, particularly when the molar ratio of Co/Ni+Co is 0.5 to 0.9. It is preferable from the viewpoint of improving wear resistance. In addition, this iron group metal is 3 to 40% in the system.
Preferably, it is present in a proportion by weight, in particular from 5 to 30% by weight.

According to the above-mentioned cermet, when cutting is performed using, for example, structural alloy steel SCM435 as a work material, the iron group metals in the cermet and W in the hard phase react with the work material, causing the finished surface to deteriorate. It may get rough. Therefore, according to the present invention, the surface of such a TiCN-based cermet is coated with a hard film containing Ti.

In order to suppress the reactivity between the cermet base material and the workpiece material, this hard film has a Ti content richer than that of the base material, especially the Ti content in the surface layer. This makes it possible to suppress the reactivity of the cermet with the work material described above. In addition, when forming a hard film on the cermet surface, iron group metals that are abundant on the cermet surface diffuse into the hard film, which deteriorates the original properties of the hard film, such as hardness and non-reactivity with the workpiece material. I'll let you. Therefore, this hard film has an iron group metal content of 100%.
It is necessary to control it to below ppm, especially below 70 ppm.

Furthermore, the grain size of the crystals constituting the hard film is
It is a factor that influences the hardness and strength of the film, and the smaller the crystal grain size, the harder, higher strength, and higher toughness the film becomes. Therefore, according to the present invention, the crystal grain size of this hard film is set to 0.4 μm.
In particular, by controlling the thickness to 0.3 μm or less, it is possible to exhibit its original function as a hard film, and to prevent particle drop-off due to breakage in the film, and thus film peeling.

[0026] The Ti-containing hard film in which the Ti content is higher than that in the cermet includes TiC, TiN, Ti
CN or the like is suitable, and these films may contain oxygen depending on the case.

[0027] This hard film has a thickness of 1 to 10 on the cermet surface.
It is desirable to coat with a thickness of 1 μm.
If it is smaller, the effect of suppressing the reactivity with the work material will be small, and the surface of the work material will become rough, and if it is thicker than 10 μm, it will be easy to peel off during use due to the difference in thermal expansion between the base material and the coating layer.

Next, the method for manufacturing the above-mentioned coated TiCN-based cermet will be explained. First, powders of carbides, nitrides, and carbonitrides of Ti, W, and Nb and powders of iron group metals are used as raw material powders to form a final sintered body. Weigh and mix so that they are in the proportions mentioned above. After that, this mixed powder is press-molded,
After molding using well-known molding methods such as extrusion molding and injection molding,
Fire.

A high-density sintered body can be obtained by firing at a temperature of 1,400 to 1,600° C. in a vacuum, a nitrogen atmosphere, or a reducing atmosphere.

[0030] Note that the sinterability of the entire system may be slightly reduced due to the fact that Mo, which has excellent wettability with iron group metals, is not substantially added during firing. increase the amount or carbon from 0.05 to 3% by weight
Sinterability is improved by adding a certain amount.

Furthermore, TiC, TiCN, TiN, etc. can be mentioned as the Ti compound-based raw material powder to be used.
In some cases, N may remain as a TiN phase in the final sintered body, but this TiN phase itself has poor wettability with the binder phase, so the interface between the binder phase and the TiN phase becomes the starting point of cracks. It deteriorates the mechanical properties of cermet. Therefore, consideration should be given to using TiC or TiCN as a raw material and not adding a large amount of TiN powder to prevent the formation of a TiN phase.

According to the present invention, carbides, nitrides, carbonitrides, etc. such as Zr, Hf, Cr, etc. can be further added to the above system for the purpose of improving the characteristics.

Next, a hard film containing Ti is formed on the surface of the cermet obtained as described above. Specifically, chemical vapor deposition methods (CVD methods) such as thermal CVD, plasma CVD, and laser CVD, physical vapor deposition methods (PDV methods) such as sputtering and ion plating, or vapor phase impregnation methods are employed. However, in order to control the particle size of the hard film to 0.4 μm or less based on the present invention, ion plating, plasma CVD, and sputtering are preferable.

[0034] Also, the amount of iron group metal mixed into the hard film was reduced to 1
When limiting the amount to 00 ppm or less and considering the film adhesion strength, ion plating, plasma CVD, etc. are preferable.In particular, the ion plating method reduces the formation of crystal grains in the film due to the low film forming temperature. It is easy to control fineness, and since the diffusion of iron group metals from the base material is suppressed, mixing into the film can be prevented. Furthermore, during film formation, it is also necessary to consider eliminating parts made of iron group metals as much as possible in the equipment in the reactor.

[0035]

[Example] Average particle size as raw material powder is 1 to 1.5 μm
TiC, TiCN, WC, NbC, VC, Ni, and Co powders were weighed and mixed so that the composition of the final sintered body would be in the proportions shown in Table 1, and then sintered for TNGA160408 at a pressure of 1.5 ton/cm2. It was press-molded into a chip shape. For samples 14 and 15, Mo2 C and TaC were used instead of NbC and VC as comparative examples. Thereafter, these molded bodies were heated to 1400 to 1600°C.
It was baked at a temperature of 1 hour in a vacuum atmosphere.

When the structure of the obtained sintered body was observed, it was found that it was composed of a hard phase consisting of a double carbonitride mainly composed of Ti and W, and a binder phase.
No precipitation of iN phase was observed.

[0037] For the hard film, TiN, TiCN, and TiCNO films were formed to a thickness of 3 μm using the ion plating method with the base material temperature set at 300 to 700°C. Further, the average grain size of crystals in the film was measured by SEM observation, and the content of iron group metals in the film was measured by ICP analysis.

Next, each sample was subjected to a wear test and a chipping test under the following cutting conditions, and the amount of flank wear and the number of non- chipping corners after cutting were investigated. The results are shown in Table 2.

(Wear test) Work material SCM435 Cutting speed 200 m/min depth of cut
2mm Feed 0.3mm/rev Cutting time 10min

(Defect test) Work material SCM435 (4 grooves) Cutting speed 100 m/min depth of cut
2mm Feed 0.3mm/rev Cutting time 1min

[0041] In addition, for evaluation of the finished surface, a surface roughness meter was used to express the condition of the finished surface of the workpiece as Rmax. It was evaluated as ○.

[0042]

[Table 1]

[0043]

[Table 2]

According to Tables 1 and 2, samples Nos. 10 and 11, in which cermets containing Mo and Ta, which have been conventionally used as hard phase components, were used as base materials,
In both cases, the amount of wear was large, and the chipping resistance was also inferior to that of the products of the present invention.

On the other hand, all the samples of the present invention show excellent cutting performance, but the composition of the base material is Ti, W, and N.
No satisfactory results were obtained for any of the samples in which the compositions of b, C, and N deviated from the range of the present invention.

[0046]

Effects of the Invention As detailed above, the coated Ti of the present invention
CN-based cermet has M as a hard phase component in the base material.
By selecting Nb and V instead of o and Ta and further forming a predetermined film on the surface, it has excellent wear resistance and chipping resistance, and improves the quality of the finished surface after cutting the work material. It is possible to increase the lifespan of the tool as a tool material.

Claims (2)

[Claims] [Claim 1] Mainly composed of Ti, at least W and Nb
and a hard phase containing V and a binder phase consisting of an iron group metal, and the other components excluding the iron group metal and inevitable impurities from the overall composition are
, V)b (W)c](Cu Nv)z, a+b+c=1, 0.50≦a≦0.95, 0.0
5≦b+c≦0.5, 0.40≦b/b+c≦0.95
, 0.40≦v≦0.60, 0.80≦z≦1.0, u
+v=1 and the atomic ratio of Nb to V (Nb/V) is in the range of 1 to 10. On the surface of the TiCN-based cermet, the cermet is richer in Ti than the cermet and has an average particle size of 0.4 μm. Hereinafter, a coated TiCN-based cermet characterized by being coated with a hard film containing Ti with an iron group metal content of 100 ppm or less. 2. The coated TiCN-based cermet according to claim 1, wherein the contents of Mo and Ta in the cermet are each 0.5% by weight or less.