JPH0413841A - Ticn-base cermet - Google Patents

Abstract

PURPOSE:To improve wear resistance and breaking resistance by selecting Nb instead of Mo as a hard component and allowing Nb to exist in the peripheral part of a structure with core in a cermet consisting of a hard phase having a structure with core and a binding phase. CONSTITUTION:This TiCN-base cermet is constituted of a hard phase having a structure with core and containing Ti, W, and Nb and a binding phase consisting of iron group metal. The composition of the remainder of the whole composition of the above cermet from which the above iron group metal is subtracted is represented by [(Ti)a(Nb)b(W)c](CuNv)z, where (a+b+c)=1, (a)=0.5 to 0.95, (b+c)=0.05 to 0.5, (b)/(b+c)=0.4 to 0.8, (v)=0.4 to 0.6, (z)=0.8 to 1, and (u+v)=1 are satisfied. Further, the core part in the structure having a core therein is enriched in Ti and N, and the peripheral part is enriched in W, Nb, and C.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a TiCN-based cermet with excellent wear resistance and toughness, and particularly to a cermet suitable as a cutting tool.

(Prior art) In recent years, as sintered bodies for cutting, sintered bodies from the periodic table No. 1 Va, Va,
Cermets that are composed of a hard phase made of a double carbonitride of a Vla group element and a binder phase made of an iron group metal have come to be used.

Until now, the mainstream of such cermets has been TiC-based cermets whose main component is TiC;
Because the base cermet has inferior fracture resistance compared to cemented carbide, which has been used as a tool material for a long time, so-called Ti has improved toughness by adding nitrides to this system.
A CN-based cermet was proposed.

As a typical example of this TiCN-based cermet,
No. 51201, where (Ti, W, Ta
, Mo) A cermet comprising a hard phase consisting of CN and a binder phase consisting of Ni and Co is disclosed, in which the hard phase has a core rich in Ti and nitrogen,
It is stated that it exhibits a cored structure composed of W, Ta, Mo, and a peripheral portion rich in carbon. Moreover, according to this prior art, Mo and MO2 are used as hard phase forming components.
C is considered an essential component as a hard phase component because it exists in the periphery of the cored structure and improves 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.

In addition, carbon (C) and nitrogen (N), which form the hard phase, are major factors that determine the toughness and hardness of cermets, and recently attempts have been made to increase the toughness of cermets by incorporating large amounts of nitrogen. is being done.

However, recently, various improvements have been made to the TiCN-based cermets, including improvements in the hard phase component and in the core or peripheral portion of the cored structure. For example, in Japanese Patent Publication No. 63-3017, Mo and Mo2C are 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. In addition, in JP-A-64-39342, it was proposed to add NbC in addition to Ti, Ta, and W as hard components to improve the thermal shock resistance and oxidation resistance of cermets. It has been proposed to improve sex.

(Problems to be Solved by the Invention) However, according to these prior art techniques, cermets have not been fundamentally improved, and the cutting characteristics of cemented carbide, which has been the mainstream tool material, still deteriorate. Remaining. Moreover, as cutting conditions become more severe, tool materials are required to have even higher properties.

Therefore, the present inventor conducted various studies on the composition of conventional cermets, and found that Mo and Mo2C as hard phase components.
Although the addition of MozC is effective in improving wettability with the binder phase, MozC itself has lower hardness, thermal conductivity, and
Since properties such as Young's modulus and oxidation resistance are greatly inferior, the presence of a peripheral portion containing Mo in a cored structure tends to cause a decline in wear resistance particularly as a tool material. Therefore, as in Japanese Patent Publication No. 63-3017, Mo is used as a hard phase forming component.
It is thought that it is better to have no additives, but
According to the structure of No. 3017, the precipitation of the TiN phase is caused by TiN
It was found that because the TiN phase itself has very poor wettability with the binder phase, the interface between the TiN phase and the binder phase becomes a breaking point within the sintered body and becomes a factor in deteriorating the strength.

On the other hand, according to JP-A No. 64-39342, although the oxidation-resistant effect of Nb is recognized, the oxidation-resistant effect due to the addition of Ta as a hard phase forming component is not exhibited in cermets containing a large amount of nitrogen. On the contrary, it inhibits sinterability,
It has been found that in order to obtain a dense body, it is necessary to set the sintering temperature high, which causes grain growth of the sintered body particles, which reduces the wear resistance of the cermet.

(Means for Solving the Problems) Based on the above findings, the present inventors investigated the composition of a cermet that has excellent wear resistance, chipping resistance, and oxidation resistance. As a result, Ti is the metal component forming the hard phase.
, W is an essential component, and instead of conventionally adding Mo and Ta, Nb is selected and these are blended in a specific range,
The present invention was based on the discovery that the presence of Nb together with W in the peripheral part of a cored structure can effectively modify the peripheral part, thereby improving wear resistance, chipping resistance, and oxidation resistance. reached.

That is, the present invention provides a TiCN-based cermet comprising a hard phase containing Ti, W and Nb as essential components and a binder phase consisting of an iron group metal, wherein the iron group metal in the overall composition of the cermet is Other component compositions excluding ((
T i)a (N b)b (W)c〕 (CuNv)
When expressed as z, a+b+c-Lo, 50≦a≦0.95
．． 0.05≦b+c≦0.5.0.40≦bZb+c≦
0.80.0.40≦v≦0.60.0.80≦2≦1
．． 0. In addition to satisfying u+v=l, the hard phase exhibits a cored structure, Ti and nitrogen are rich in the core, and W, Nb
It is characterized by having a structure in which carbon is rich in the periphery, and furthermore, the amount of Mo and Ta is 0.
It is characterized by being 5% by weight or less.

Next, the reason for setting the ratio of each metal element in the above range in the TiCN-based cermet of the present invention will be described.

First, as a component forming a hard phase, 'II exists in the sintered body as approximately TiCN, and the amount of Ti (a
) is less than 0.5, the wear resistance and affinity for metals, which are characteristics of cermet tools, will be insufficient, and the
．． If it exceeds 95, the fracture resistance will be poor. In addition, a
It is particularly desirable that 0.70≦a≦0.9.

Further, Nb and W are auxiliary components that form a hard phase, and both have the effect of suppressing the grain growth of the cermet, forming a fine crystal structure and increasing the strength and toughness of the cermet. Therefore, these contents (b+c) are 0.0
If it is less than 5, the chipping resistance will be insufficient, and if it is more than 0.5, the wear resistance will be poor and the reactivity with the work material will tend to be high. Note that (b+c) value is 0.10≦b+
It is particularly desirable that c≦0°30.

Among these, W is an essential component in order to improve the wettability of the hard phase with the binder phase and increase the toughness as WC, but when the hard phase is composed of (Ti, W)CN However, there is a problem in that properties such as wear resistance, oxidation resistance, and chipping resistance do not reach a practical level. Therefore, M was added for the purpose of strengthening the hard phase and improving the core properties.

Until now, carbides such as cermets and Ta have been used as essential components, but as mentioned above, M oz C itself has inferior properties compared to TiC and TiCN, which are the main components of the hard phase. It will cause it to deteriorate. 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 itself has superior properties as a carbide compared to M 02 C, so it greatly contributes to improving the properties of cermets, and since it does not affect the sinterability, it improves the wear resistance of cermets. It was found that the properties, oxidation resistance, and chipping resistance can be improved.

From this relationship, if the ratio of the amount of Nb (b) to the sum of W and Nb (b + C) (b / b + c) is less than 0.4 in the above formula, the wear resistance and oxidation resistance will be poor, On the other hand, if it is larger than 0.8, fracture resistance will decrease.

Furthermore, like Mo, Ta is said to have the effect of improving the oxidation resistance of the system and suppressing crater wear, and has traditionally been considered an essential component, but in the system of the present invention, it has almost no effect. , rather, it tends to impede sinterability.

Therefore, the amount of Ta in the TiCN-based cermet of the present invention is also 0.
It is desirable that the amount is 5% by weight or less.

On the other hand, the amount of nitrogen and carbon is a very important factor in determining the hardness and toughness of cermets. In particular, as the amount of nitrogen increases, the toughness tends to improve, but if the amount of nitrogen is excessive, A problem arises in that gas from the decomposition of nitrides remains in the sintered body in the voids.

Therefore, in the above formula, if the nitrogen content (v) is less than 0.4, the toughness will decrease and fracture resistance will be insufficient, and if it exceeds 0.6, voids will occur in the sintered body and reliability will be impaired. Become.

Furthermore, if the ratio (z) of the amount of nitrogen and carbon to the total amount of Ti, W, and Nb is smaller than 0.8, sinterability deteriorates and voids remain, and if it is larger than 1.0, free carbon is generated. This results in a decrease in strength. Preferably 0.8
5≦z≦1.0.

In the present invention, the iron group metal forming the binder phase includes N
i and/or Co, preferably Ni and C
In particular, it is preferable that the molar ratio of Co/Ni+Co is 0.5 to 0.9 from the viewpoint of improving wear resistance.

Further, it is desirable that the iron group metal is present in the system in an amount of 3 to 30% by weight, particularly 5 to 20% by weight.

The cermet of the present invention is produced by weighing and mixing the powders of carbides, nitrides, and carbonitrides of Ti, W, and Nb and the iron group metal powder so that the final sintered body has the above-mentioned ratio, and then press-forming and extruding the powder. After molding using a molding method such as molding or injection molding, it is fired.

In firing, it is necessary to adjust the firing conditions so that a cored structure is formed. Specifically, this is done in a vacuum, nitrogen atmosphere, or reducing atmosphere at a temperature of 1400 to 1600
Obtained by firing at a temperature of °C. Note that sinterability may be slightly reduced by suppressing the amount of Mo, which has excellent wettability with iron group metals, but in this case, increase the amount of iron group metals or increase the carbon powder by 0.05~3 Sinterability is improved by adding % by weight.

In addition, the Ti compound-based raw material powder used is Tic,
Examples include TiCN, TiN, etc., but if a large amount of TiN powder is used, it may remain as a TiN phase in the final sintered body as disclosed in JP-A-64-39342. This will deteriorate the mechanical properties of the cermet. Therefore, TiC and TiC can be used as raw materials.
When using N, care should be taken to avoid the formation of a TiN phase.

According to the present invention, carbides, nitrides, carbonitrides, etc. such as Zr5Hf, Cr and V are further added to the above system for the purpose of improving the characteristics, and in the above formula, part of Ti or Nb is added. It is possible to improve the characteristics by replacing a part of Nb with ■, and in particular, by replacing a part of Nb with ■, the effect of Nb is further promoted, and the wear resistance especially during high-speed cutting of cermet is greatly improved. I can do it. At this time, the Nb/V atomic ratio is preferably 1 to 10, particularly 1 to 5.

The invention will now be explained with the following examples.

(Example) TiC, T with an average particle size of 1 to 1.5 μm as raw material powder
iCN5WC,, NbC, VC, Ni, C.

After weighing and mixing each of the powders so that the composition of the final sintered body would be in the proportions shown in Table 1, 1.5 ton/c
It was press-molded into a chip shape for TNGA160408 at a pressure of m2. In addition, in the table, samples Nos. 17 and 18 have a VCt-Nb/V atomic ratio of 3 compared to sample No. 2.3.
．． It is replaced with an amount that becomes 0. Next, these molded bodies were fired for 1 hour in a vacuum atmosphere at a temperature of 1400-1600''C.

As a result, when the structure of the obtained sintered body was confirmed using an electron microscope, it was found that the hard phase in both cases had a cored structure, and no precipitation of TiN phase was observed. In addition, sample Nα2
The amount of elements in the core and periphery of the cored structure was investigated using TEM. The results are shown in FIGS. 1 and 2. According to these figures, a large amount of Ti exists in the core, and W,...
It can be seen that a large amount of Nb exists in the peripheral area.

The obtained sintered body was measured for three-point bending strength, Vickers hardness, and fracture toughness by the indentation method using a diamond indenter for Vickers hardness at a load of 20 kg in accordance with JISR1601.

Next, a wear test was performed using each sample under the cutting conditions shown below.
A chipping test was conducted to examine the amount of flank wear after cutting and the number of non- chipping corners.

(Wear test) Work material Cutting speed Cutting feed Cutting time (Defect test) Work material SCM435 (4 grooves) Cutting speed
100 m/min Depth of cut 2 mm Feed 0.3 mm/rev Cutting time 1 m1n The results are shown in Table 2.

(Comparative Example 1) TiC, T with an average particle size of 1 to 1.5 μm as raw material powder
Using each powder of iCN, WC, MO2C, Ni, Co(7), 2% by weight of Ni, 008% by weight and other components (T
io, 5sWo, o6Moo, +o) (Co, s, N
L45) A sintered body (sample No. 19) having a cored structure was obtained by firing in the same manner as in the example except that the mixture was weighed and mixed so as to have a composition of 0.90.

CM435 250m/min mm 0.3mm/rev 0m1n =14 The same characteristics as in the examples were measured for this sintered body.

The results are shown in Table 2.

(Comparative Example 2) TiC, T with an average particle size of 1 to 1.5 μm as raw material powder
i 2% by weight of Ni, 8% by weight of Co, and other components (
Tio, 85WO, 05T ao, 10) (C
As a result of firing in the same manner as in the example except that the composition was weighed and mixed so as to have a composition of 0.90,
Sintered body with cored structure (sample No. 20)
was gotten.

The properties of this sintered body were also measured in the same manner as in the examples. The results are shown in Table 2.

(The following is a blank space) According to Tables 1 and 2, sample Nα19.
No. 20 had a large amount of wear, and its chipping resistance was also inferior to the products of the present invention.

On the other hand, all the samples of the present invention show excellent cutting performance, but all the samples whose compositions of Tt, w, Nb, C, and N deviate from the range of the present invention yield satisfactory results. There wasn't.

(Effects of the Invention) As detailed above, the TiCN-based cermet of the present invention has excellent wear resistance by selecting Nb instead of Mo as the hard phase component and by allowing Nb to exist in the periphery of the cored structure. It exhibits excellent durability and fracture resistance, and can be used as a material for tools to extend its life.

[Brief explanation of drawings]

Fig. 1 shows the TEM analysis results of the core of the cored structure in the cermet of the present invention, and Fig. 2 shows the TEM analysis results of the periphery.
M analysis results are shown.

Claims (2)

[Claims] (1) A TiCN-based cermet consisting of a hard phase containing Ti, W and Nb and exhibiting a cored structure, and a binder phase consisting of an iron group metal, wherein the overall composition of the cermet indicates that the iron group metal and other component compositions excluding unavoidable impurities [(Ti)_a(Nb)_b(W)_c](C_u
When expressed as N_v)_z, a+b+c=1, 0.50≦
a≦0.95, 0.05≦b+c≦0.5, 0.40≦
b/b+c≦0.80, 0.40≦v≦0.60, 0.
80≦z≦1.0, u+v=1, and in the cored structure, Ti and nitrogen are rich in the core, and W, Nb
and a TiCN-based cermet characterized by carbon being abundant in the peripheral region. (2) The TiCN-based cermet according to claim 1, wherein the amount of Mo contained in the cermet is 0.5% by weight or less.