JP2578679B2 - TiCN-based cermet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a TiCN-based cermet excellent in wear resistance and toughness, and particularly to a cermet suitable as a cutting tool.

(Prior art) In recent years, as sintered bodies for cutting, Periodic Tables IVa, Va, V
Cermets composed of a hard phase composed of a double carbonitride of a group Ia element and a binder phase composed of an iron group metal have come to be used.

As such a cermet, a TiC-based cermet containing TiC as a main component has been mainly used until now, but since the TiC-based cermet has poor fracture resistance compared to a cemented carbide used as a tool material since ancient times. In addition, a so-called TiCN-based cermet in which toughness is improved by adding a nitride to this system has been proposed.

A representative example of this TiCN-based cermet is JP-B-59-5120.
No. 1 is cited, and here, a cermet composed of a hard phase composed of (Ti, W, Ta, Mo) CN and a binder phase composed of Ni and Co is disclosed, and the hard phase has a core rich in Ti or nitrogen. And W,
It is stated to exhibit a cored structure composed of Ta, Mo and a peripheral part rich in carbon. Further, according to this prior art, Mo or Mo ₂ C as a hard phase forming component is indispensable 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. It is a component. Further, TaC is an essential component from the viewpoint of practicality because it has an effect of improving the oxidation resistance of the cermet and suppressing the progress of crater wear as a cutting tool.

Also, carbon (C) and nitrogen (N) forming a hard phase
It is a major factor in determining the toughness and hardness of the cermet, and recently, attempts have been made to increase the toughness of the cermet by adding a large amount of nitrogen.

However, recently, improvements have been made to the above-mentioned TiCN-based cermet by further changing the structure of its surface to further increase wear resistance and toughness. For example, JP-B-59-14534 discloses that a toughened softened layer is formed on the surface to be fired by introducing nitrogen into the furnace at a temperature lower than the liquid phase appearance temperature during firing. Is performed in a reducing atmosphere containing CO to form a layer having a higher hardness than the inside.

However, each of these prior arts only examines either hardness or toughness, and is insufficient in cutting performance as a material for a tool that requires both high hardness and high toughness.

In view of this, the present applicant has proposed in Japanese Patent Application Laid-Open No. 2-15139 a TiCN-based cermet in which a modified layer of high hardness and high toughness is formed on the surface of a sintered body by controlling the timing of introducing nitrogen during sintering.

(Problems to be Solved by the Invention) However, the cermet disclosed in Japanese Patent Laid-Open No.
It shows excellent wear resistance and chipping resistance when cutting at medium speeds with cutting speeds of 100 to 200 m / min, but wear resistance and chipping resistance when cutting at high speeds where the cutting speed exceeds 200 m / min. It was revealed that the deterioration was large.

(Means for Solving the Problems) As a result of studying the above problems, the present inventors have used Ti and W as metal components for forming a hard layer, and added them as essential components so far. By using Nb instead of Mo and Ta, the heat resistance of the hard layer can be greatly improved, and from the inside to the surface (Ti / T
It was found that by forming a composition gradient so that the (i + W) ratio becomes small, a cermet having high hardness and high toughness on the surface and excellent wear resistance and chipping resistance even at high speed cutting can be obtained. This has led to the present invention.

That is, the present invention comprises a hard phase containing Ti, W, and Nb as essential components, and a binder phase made of an iron group metal, and the contents of Mo and Ta are each 0.5% by weight or less (0% or less). ), And from the overall composition of the cermet, the composition (atomic ratio) of the other components excluding the iron group metal, Mo, Ta and unavoidable impurities is represented by [(Ti) a (Nb)
b (W) c] (CuNv) 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 ratio represented by c / (a + c) increases from the inside to the surface. With such a configuration, the surface layer portion from the surface to 500 μm is larger than the inside. It is characterized by forming a hard part having high toughness and high hardness.

 Hereinafter, the present invention will be described in detail.

Although the TiCN-based cermet of the present invention is basically composed of a hard phase and a binder phase, in the present invention, the composition of other components other than the iron group metal in the overall composition of the cermet falls within the above range. The reason is set as follows.

First, Ti, which is a main component forming a hard phase, exists as approximately TiCN in a sintered body, and its amount is a major factor that determines the strength and hardness of a cermet. Abrasion resistance and affinity for metals, which are features of a cermet tool less than 0.5, become insufficient, and if it exceeds 0.95, fracture resistance becomes poor. In addition,
It is particularly desirable that (a) satisfies 0.70 ≦ a ≦ 0.9.

In the cermet, W, which is the same essential component of Ti, acts as WC to improve the bonding phase and wettability of the hard phase, suppress the grain growth, and increase the strength and toughness. W) When composed of CN, there is a problem that properties such as abrasion resistance, oxidation resistance, and fracture resistance do not reach a practical level. Therefore, carbides such as Mo and Ta have been used as an essential component for the purpose of strengthening the hard phase and improving various properties.However, as will be apparent from the examples described later, Mo ₂ C itself, the hard phase It was found that the properties were inferior to those of TiC or TiCN, which are the main components, so that they did not greatly contribute to the improvement of the properties of the cermet, and tended to deteriorate the properties in some cases. Especially,
This tendency was remarkable at high speed cutting.

Therefore, was subjected to study as a component in place of Mo ₂ C, due to such carbides Nb has its own superior properties compared to the Mo ₂ C characteristics of the cermet, can in particular greatly improve the heat resistance It was found that the wear resistance and chipping resistance during high-speed cutting can be improved. Therefore, if the combined amount (b + c) of Nb and W is less than 0.05, the fracture resistance becomes insufficient, and if it is more than 0.5, the wear resistance is poor and the reactivity with the work material tends to be high. The value of (b + c) is
It is particularly desirable that 0.1 ≦ b + c ≦ 0.30. Also,
The ratio of the amount of Nb (b) to the total amount of W and Nb (b + c) (b /
b + c) In the above formula, abrasion resistance and oxidation resistance smaller than 0.4 are inferior, and conversely, when it is larger than 0.95, fracture resistance is reduced.

In addition, according to the cermet in the present invention, the addition of Mo should be rather avoided, and the amount is 0.5% by weight in the cermet.
It is desirable to make the following.

On the other hand, the sinterability greatly depends on the amount of the binder phase in the system, but if the binder phase is the same, the sinterability decreases due to the addition of TaC, and high-temperature sintering is required. The wear resistance of the cermet is degraded due to the large crystal grain size. Therefore, it is desirable that the content of Ta be 0.5% by weight or less as in the case of Mo.

On the other hand, the amount of nitrogen and carbon is very important as a factor determining the hardness and toughness of the cermet, especially as the amount of nitrogen increases, the toughness tends to improve,
If the amount of nitrogen is excessive, a problem arises in that gas due to decomposition of nitride during firing remains in the voids in the sintered body. Therefore, in the above formula, if the nitrogen content (v) is smaller than 0.4, the toughness is reduced and the fracture resistance becomes insufficient, and if it exceeds 0.6, voids are generated in the sintered body and reliability becomes poor.

If the ratio (z) of the content of nitrogen and carbon to the content of Ti, W, and Nb is less than 0.8, the sinterability deteriorates and voids remain. If the ratio is more than 1.0, free carbon is generated and the strength is reduced. Scrub results. Desirably, 0.85 ≦ z ≦ 1.0.

In the present invention, as the iron group metal forming the binding phase,
Ni and / or Co may be mentioned, and preferably composed of Ni and Co. In particular, the molar ratio of Co / Ni + Co is preferably 0.5 to 0.9 from the viewpoint of improving wear resistance.

The iron group metal is desirably present in the system at a ratio of 3 to 30% by weight, particularly 5 to 20% by weight.

Further, the cermet of the present invention is greatly characterized by having a composition gradient from the surface to the inside as shown in FIG. 1, and specifically has a specific property that W is more abundant on the surface than the inside. . Also, Ti tends to be slightly richer in the inside than in the surface, contrary to W. Therefore, the atomic ratio (c / a + c) between the Ti amount (a) and the W amount (c) has a composition gradient that increases from the surface to the inside. Specifically, it is desirable that the ratio of the (c / a + c) value between the surface portion and the central portion is 1.1 or more. In addition, Nb, which is a hard phase forming component, has a tendency similar to that of W, and the iron group metal forming the binder phase is poor in the vicinity of the surface as compared to the inside, but precipitates on the extremely surface portion and forms an iron group metal layer. May be formed.

Due to such a composition gradient, as shown in FIGS. 2 and 3, a hard layer having higher hardness and higher toughness than the inside is formed near the surface, particularly in the surface layer up to 500 μm from the surface. Thereby, the wear resistance and fracture resistance of the cermet can be remarkably improved.

Further, as another factor in which the TiCN-based cermet of the present invention has excellent properties, the hard phase is composed of a core portion rich in Ti and nitrogen, and a peripheral portion rich in W, Nb, and carbon around the core portion. It has a cored structure. According to this cored structure, the characteristics of the peripheral portion can be improved by using Nb instead of the conventionally used Mo or Ta as the peripheral component.

As a method for producing the cermet of the present invention, for example, first, the above-mentioned Ti, W, Nb carbide, nitride, carbonitride powder and iron group metal powder in the final sintered body the above-mentioned ratio After weighing and mixing so as to obtain, molding is performed by means such as press molding, extrusion molding, injection molding, and the like, followed by firing.

In the firing, it is necessary to adjust the firing conditions so as to form the composition gradient and the cored structure as described above. Specifically, this is fired at a temperature of 1400 to 1600 ° C. in a vacuum, in an atmosphere of nitrogen or in a reducing atmosphere,
First, in the temperature raising process, a vacuum atmosphere of about 10 ^-1 torr is used up to a temperature at which a liquid phase due to the added iron group metal appears, and a pressure is set to a high vacuum atmosphere of 10 ^-3 torr or less above the liquid phase appearance temperature. Change abruptly. As described above, by changing the degree of vacuum, the nitride existing on the surface of the molded body is rapidly decomposed to form a carbon-rich phase near the surface. As a result, of the hard phase-forming components, W and the like which are easily bonded to carbon move to the surface portion. Also, metal components near the surface migrate to the inside or seep to the surface of the sintered body,
May volatilize.

Such a movement of the components also occurs during normal firing, but according to the present invention, a specific structure that cannot be obtained under normal conditions can be formed by the above-described operation.

Further, according to the present invention, it is used in the above manufacturing method.
Examples of the Ti compound-based raw material powder include TiC, TiCN, and TiN, but when a large amount of TiN powder is used, TiN is contained in the final sintered body.
However, the TiN phase itself has very poor wettability with metal, so that the interface between the TiN phase and the binder phase tends to be a starting point for fracture. Will reduce the performance. Therefore,
Consideration should be given to using TiC or TiCN powder instead of the raw material and a large amount of TiCN so that the TiN phase is not formed.

It is also possible to carry out a solid solution treatment before molding and sintering each raw material powder, or it is desirable not to carry out the solid solution treatment because the above-mentioned cored structure is hardly formed.

According to the present invention, Zr and H are further added for the purpose of improving the characteristics with respect to the system comprising the (Ti, W, Nb) (C, N) and iron group metals.
By adding carbides, nitrides, carbonitrides, and the like such as f, Cr, and V, and substituting a part of Ti, W, or Nb with a homologous metal, the characteristics can be improved. By substituting the portion with V, the action and effect of Nb can be further promoted, and in particular, the high-speed machinability of the cermet can be greatly improved. The Nb / V atomic ratio is desirably 0.2 to 1.0, and particularly desirably 0.25 to 0.5.

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

(Example) After weighing and mixing each of the powders of TiC, TiCN, WC, NbC, VC and Ni.Co as the raw material powder so that the composition of the final sintered body becomes the ratio shown in Table 1, 1.5ton / It was pressed into a chip shape for TNGA160408 at a pressure of cm ² and fired at a temperature of 1400 to 1600 ° C. for 1 hour in a vacuum atmosphere. At this time, the sample Nos. ^{1 to 12} were kept at a pressure of 10 ^-1 torr up to the liquid phase appearance temperature (1350 ° C), and were fired at a pressure of 10 ^-3 torr above the liquid phase appearance temperature. As a comparative example, the pressure was 10
^-1 torr was changed to 50 torr, and for sample No. 14, the pressure was 10 ^-1 t
Maintained at orr and fired.

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

For each sample, XMA analysis was performed to determine the Ti and W
Of the sintering couple and (c / a +
c) I ₁ and I ₂ respectively, and the ratio of I ₂ / I ₁ was determined. For sample No. 2, the composition distribution with respect to the depth of the sintered body of Ti, W, and Nb was examined and is shown in FIG.

Further, using a Vickers hardness tester, the presence or absence of a difference in properties between the surface portion and the inside of the sintered body was checked, and a sample No. of the present invention was used.
For samples Nos. 2, 4, 8 and out of range, the changes in hardness and toughness with respect to the depth of the sintered body were examined.
Shown in the figure.

Next, a wear test was performed using the respective samples under the following cutting conditions, and the flank wear amount after cutting and a defect test were performed to determine the number of non-defect corners.

(Wear test) Work material SCM435 Cutting speed 300m / min Depth of cut 2mm Feed 0.3mm / rev Cutting time 10min (Wear test) Work material SCM435 (with 4 grooves) Cutting speed 100m / min Depth of cut 2mm Feed 0.3mm / rev Cutting Table 1 shows the characteristics evaluation results for a time of 1 min.

According to Tables 1 and 2, in samples Nos. 17 and 18, which do not contain Nb but contain Ta or Mo, the wear amount is as large as 0.4 mm or more in the high-speed wear test. In addition, even in the system to which Nb was added, Sample No. 15 in which the amount was too large had poor fracture resistance and wear resistance, and Sample No. 16 in which the Nb amount was less than 0.4 in the (Nb / Nb + W) ratio showed hardness and hardness. Although a phase having higher toughness than that of the inside was formed, practical characteristics as high-speed machinability were not obtained. Furthermore, even when the composition satisfies the range of the present invention, the concentration of W was not formed in Sample No. 14 in which the pressure was constant during firing, and the pressure was not sufficient in terms of characteristics, and the pressure during firing was increased. No concentration gradient was formed even in sample No. 13.

In contrast to these comparative examples, Samples Nos. 1 to 12 of the present invention
In each case, a concentration gradient of W is formed between the central portions of the surface portions as shown in FIG. 1, the concentration ratio of W (I ₂ / I ₁ ) is 1.1 or more, and the hardness and toughness are shown in FIG. As shown in FIG. 3, a modified portion having high hardness and high toughness on the surface was formed.
The hardness of the modified portion was 5% or more of the internal hardness, and the toughness was 20% or more of the internal toughness. In the cutting test, the wear rate was excellent at 0.3 mm or less in the high-speed cutting test, and the fracture resistance test was also good.

(Effects of the Invention) As described in detail above, the TiCN-based cermet of the present invention is a component excluding the iron group metal, in which Nb is essentially added instead of Mo and Ta which have been conventionally used as essential components, and the W content is To provide a cermet having high strength, hardness, high-speed machinability, and excellent fracture resistance by forming a rich concentration gradient on the surface and forming a modified portion having excellent hardness and toughness on the surface. Can be.
Thus, when used as a tool, applicable cutting conditions can be expanded and the service life of the tool can be extended.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the composition distribution of Ti, W and Nb elements of the TiCN-based cermet of the present invention with respect to the depth of a sintered body, and FIG. FIG. 3 is a diagram showing a change in hardness with respect to the depth of the sintered body, and FIG. 3 is a diagram showing a change in hardness with respect to the depth of the sintered body in the sample of the example.

Claims (2)

(57) [Claims] 1. A hard phase containing Ti, W and Nb as essential components, and a binder phase made of an iron group metal,
And the contents of Mo and Ta are each 0.5% by weight or less (0% by weight).
), And from the overall composition of the cermet, the composition (atomic ratio) of the other components excluding the iron group metal, Mo, Ta and unavoidable impurities is represented by [(Ti) a (Nb) b
(W) c] (CuNv) 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 a ratio represented by c / (a + c) increases from the inside to the surface. 2. The Ti according to claim 1, wherein a modified portion having higher toughness and higher hardness than the inside is present in the surface layer portion up to 500 μm from the surface.
CN cermet.