JP6227517B2 - Cemented carbide - Google Patents

Description

  The present invention relates to a cemented carbide that exhibits excellent performance when used as a cutting tool or wear-resistant member.

Cemented carbide is widely used as a material for cutting and cutting tools for metal materials. Cemented carbides are iron, metal (Fe, Co, Ni) binders, Ti, Zr, Hf, V, Nb, Ta, which are metals of Group 4, Group 5 and Group 6 of the Periodic Table. , Cr, Mo, W carbide alloy sintered. In particular, the WC-Co system is most widely used for cutting tools.
In this cemented carbide, higher hardness can be obtained by suppressing the grain growth of the hard phase containing carbide particles such as WC. As this grain growth inhibitor, carbides such as VC, Cr ₃ C ₂ and TaC are known.
In Cited Document 1, a high-hardness cemented carbide containing 3 to 13% Co, 0.05 to 0.5% VC, 0.1 to 1.0% Al, and the balance of WC and inevitable impurities is used. It is disclosed.
In Cited Document 2, Co and / or Ni is 5 to 12% by weight, and the total amount of at least two of Cr ₃ C ₂ , VC, TaC, Mo, Ru, and Si is 0.1 to 3%, An ultrafine cemented carbide having a composition consisting of WC and inevitable impurities in the balance is disclosed.

  In particular, cemented carbide has been developed in recent years that adds a carbonitride phase to suppress WC phase grain growth. In Cited Document 3, the total of the WC phase, the carbonitride phase, and the binder phase is 100 vol%, the average particle size of the WC phase is 0.05 to 0.8 μm, and the average particle size of the carbonitride phase is 0. A cemented carbide of 0.03 to 1.1 μm is disclosed. Further, in Cited Document 4, a superphase having a second phase mainly composed of carbonitrides of one or more elements selected from the group consisting of Group 4 elements, Group 5 elements and Group 6 elements. A hard alloy is disclosed.

JP 2006-257469 A JP 2004-256863 A JP2012-251242 JP2012-229138

Inhibition of grain growth of WC is an indispensable material technology for producing ultrafine cemented carbide, and carbides such as VC, Cr ₃ C ₂ , TaC, and NbC are used as grain growth inhibitors. In particular, VC is widely used because it has a high effect of suppressing grain growth. By the way, although the mechanism by which VC suppresses the grain growth of WC has not been clarified, when part of WC and VC dissolve in the liquid phase during sintering and reprecipitates with cooling, VC is adsorbed to the WC step. Is believed to be happening. Therefore, in order to obtain a high grain growth suppressing effect, an addition amount close to the solubility limit in the binder phase is required, but in this case, a (W, V) C phase is generated and the strength of the material is reduced. There is a fear. It is also known that VC is segregated at the WC / Co interface, which causes a problem that the interface strength is lowered. In addition, TaC and NbC are hardly dissolved in the binder phase, so it can be said that the above problems are unlikely to occur. However, since the grain growth inhibitory effect is lower than that of VC, it is added in a large amount to obtain ultrafine carbide. As a result, there is a problem that characteristic values necessary for the tool such as strength and thermal conductivity are lowered.
An object of the present invention is to provide an ultrafine cemented carbide with high hardness without adding strength by adding ultrafine carbonitride particles that are difficult to dissolve in the binder phase.

  In order to solve the above-mentioned problems, the cemented carbide of the present invention has a first phase mainly composed of tungsten carbide (WC) having a raw material average particle size of 0.05 to 2.0 μm as a main component with respect to the entire cemented carbide. A second phase composed of carbonitride produced by carbonitriding Ti oxide during sintering, containing 0.1 to 30 wt% of the entire cemented carbide; A binder phase mainly composed of at least one selected from the group consisting of Ni and Fe is included in an amount of 0.5 to 30 wt% with respect to the entire cemented carbide, and includes a first phase and a carbonitride phase that are hard phases. The total of a certain second phase and a binder phase is 100 wt%, does not contain V other than inevitably mixed, and has an average WC grain size after sintering of 1.0 μm or less. .
  The cemented carbide of the present invention is characterized in that the raw material average particle diameter of the oxide is in the range of 5 to 100 nm.
  Further, the cemented carbide of the present invention further comprises Cr. ₃ C ₂ And add Cr ₃ C ₂ Is added in an amount of 0.1 to 20 wt% with respect to the entire binder phase.

The present invention, which is a means for solving the above problems, has the following specific effects.
In the cemented carbide of the present invention, the grain size of the WC phase can be reduced, and a cemented carbide with high hardness and high strength can be obtained.

Schematic diagram showing WC phase grain growth inhibition in liquid phase sintering SEM picture of material with carbonitride added SEM photograph of material produced by changing the amount of TiO ₂ added SEM photograph of material made by adding TiO ₂ and Cr ₃ C ₂ in combination

  The cemented carbide of the present invention consists of a WC phase and a binder phase containing at least one selected from the group consisting of Co, Ni and Fe, and consists of Ti, Zr, Hf, Nb, Ta, Cr, Mo and W. Having a carbonitride phase of at least one metal selected from the group.

  When the WC phase is less than 70 wt% with respect to the entire cemented carbide, the binder phase is relatively increased, and it becomes difficult to control the grain growth of the WC phase and the hardness of the cemented carbide decreases. It was set as 70-99.4 wt% with respect to the whole cemented carbide. In order to achieve this requirement, an amount of raw material powder that falls within this range may be blended. Among these, it is more preferable that the WC phase is 80 to 95 wt% with respect to the entire cemented carbide. Making the average particle diameter of the WC phase of the invention less than 0.05 μm is difficult to produce due to grain growth during sintering, and when the average particle diameter of the WC phase of the present invention exceeds 2.0 μm, Since the hardness and strength of the cemented carbide are lowered, the raw material average particle size of the WC phase of the present invention is determined to be 0.05 to 2.0 μm. In order to achieve this requirement, a raw material powder having a size within this range after sintering may be used. Among these, the average particle diameter of the WC phase is more preferably 0.1 to 1.0 μm.

The carbonitride phase in the cemented carbide of the present invention is at least one type of carbonitride selected from Ti, Zr, Hf, Nb, Ta, Cr, Mo and W. A hard ultra-fine cemented carbide can be produced, improving wear resistance.
Among them, the carbonitride phase may be a double carbonitride composed of two or more metal elements composed of Ti, Zr, Hf, Nb, Ta, Cr, Mo, and W. In particular, the carbonitride phase is more preferably a double carbonitride composed of at least one selected from Zr, Hf, Nb, Ta, Cr, Mo and W in addition to Ti as an essential component.
Specific examples of carbonitride include Ti (C, N), (Ti, Mo) (C, N), (Ti, W) (C, N), and the like.
Further, in addition to the carbonitride phase described above, it is preferable to contain a small amount of carbides such as Ti, Zr, Hf, Nb, Ta, Cr, and Mo, and it is particularly preferable to include a carbide of Cr. Thereby, grain growth of the hard phase can be further suppressed.

The grain growth of the WC phase in the cemented carbide is that the WC phase dissolved in the binder phase precipitates in the other WC phase at a high temperature during sintering, and the WC grains are grain-grown and completely dissolved during the cooling step. This is caused by reprecipitation of the WC phase that did not exist as a core. Therefore, in the cemented carbide of the present invention, the carbonitride phase is made to be present in the form of dots at the interface between the WC phase and the binder phase, so that precipitation with the WC phase as a core is less likely to occur during the cooling process. Thus, the grain growth of the WC phase is suppressed (pinning effect).
Here, in order to obtain a higher grain growth suppressing effect, a large number of carbonitride phases need to exist around the WC phase. However, if a large amount of the carbonitride phase is added, it may aggregate and the strength may be reduced. For this reason, in order to obtain a sufficient grain growth suppressing effect while maintaining a high strength, a large number of carbonitride phases are required with a small addition amount.
In order to satisfy this requirement, the carbonitride phase is preferably fine. For this purpose, the average particle size of the carbonitride phase is preferably in the range of 5 to 100 nm. When the average particle size of the carbonitride phase exceeds 100 nm, if not added in a large amount as described above, a sufficient grain growth suppressing effect cannot be obtained, and it becomes difficult to achieve both strength and hardness at a high level. Moreover, it seems that the carbonitride phase of less than 5 nm aggregates during the powder mixing and causes a decrease in strength. In order to achieve this requirement, a raw material powder having a size within this range after sintering may be used.

  Moreover, when the carbonitride phase in the cemented carbide of the present invention exceeds 30 wt% with respect to the entire cemented carbide, the strength is reduced due to aggregation of the carbonitride phase. Moreover, if it is less than 0.1 wt%, a sufficient grain growth suppressing effect cannot be obtained. Therefore, the carbonitride phase of this invention should just mix | blend the raw material powder of the quantity which falls in the range of 0.1-30 wt%.

The finer the carbonitride phase, the higher the effect of suppressing the grain growth. The generally produced carbonitride particles such as TiC, TaC, and Ti (C, N) have a particle size of 1 μm or more. Further, when the particle size of the carbonitride is smaller than this, impurities such as contamination increase, and the sinterability of the material is remarkably impaired, making it difficult to produce a satisfactory material. Therefore, finer carbonitride particles than TiC and Ti (C, N) that are generally produced can be obtained by adding finer oxides and carbonitriding during sintering. Thereby, the big grain growth inhibitory effect can be acquired and it becomes possible to make high intensity | strength and high hardness compatible.
FIG. 1 is a schematic diagram showing the grain growth suppression of the WC phase in the liquid phase sintering method.
(A) is a cemented carbide composed of a WC phase and a Co phase to which no grain growth inhibitor is added. (B) is a cemented carbide obtained by adding VC as a grain growth inhibitor to (a). (C) is a cemented carbide obtained by adding (Ti, Mo) (C, N) as a grain growth inhibitor to (a). (D) is a cemented carbide obtained by adding TiO ₂ as a grain growth inhibitor to (a).
Here, as shown in (a), in the cemented carbide to which the grain growth inhibitor is not added, the WC phase dissolved in the Co phase at a high temperature in sintering is regenerated using the coarse WC phase not dissolved as a core. Precipitation causes significant grain growth. As shown in (b), the material added with VC suppresses grain growth by adsorbing VC in the WC step when VC dissolves in the Co phase and reprecipitates at a high temperature. VC exists on the surface of the WC particle, and the WC / Co interface strength is lowered. At this time, a (W, V) C phase is generated, which may reduce the strength of the material.
As shown in (c), when a (Ti, Mo) (C, N) grain growth inhibitor is added, there is a grain growth inhibitory effect, but the grain growth inhibitory effect is large because the particle diameter of the grain growth inhibitor is large. tend to be inferior compared to the VC addition and TiO ₂ addition of alloy. Therefore, as shown in (d), by adding TiO ₂ powder that hardly dissolves in the binder phase and the hard phase even at high temperatures, no harmful phase is generated, and the strength of the material is not reduced. Can be obtained. Moreover, since TiO ₂ has a smaller particle size than general carbonitride, a large grain growth suppressing effect can be obtained with a small amount. However, TiO ₂ is an oxide, and a dense sintered body cannot be obtained by sintering in vacuum. Therefore, carbonitriding is performed by flowing nitrogen gas during sintering, and Ti (C, N) is used to improve sinterability.

An oxide made of at least one metal selected from Ti, Zr, Hf, Nb, Ta, Cr, Mo and W is used. In particular, oxides that change to carbonitrides during liquid phase sintering in a nitrogen atmosphere are good and are preferably fine particles. Moreover, when using for a cutting tool etc., what shows the outstanding performance is further desirable. For this reason, TiO ₂ is particularly preferred as the oxide.

The binder phase of the present invention is a metal mainly composed of at least one selected from the group consisting of Co, Ni and Fe. In the present invention, the metal mainly composed of at least one selected from the group consisting of Co, Ni and Fe is 50 wt% or more in total of at least one selected from the group consisting of Co, Ni and Fe. Means containing metal.
The binder phase of the present invention preferably contains 70 to 100 wt% in total of at least one selected from the group consisting of Co, Ni and Fe.
The binder phase of the present invention is more preferably made of Co as a main component because it is excellent in heat resistance, toughness, and adhesion to a coating. The bonded phase containing Co as a main component of the present invention means a bonded phase containing 50 wt% or more of Co with respect to the entire bonded phase.
Further, when Cr or Cr ₃ C ₂ is contained in the binder phase of the present invention in an amount of 0.1 wt% or more based on the entire binder phase, the hardness, strength and oxidation resistance of the binder phase are improved, and the WC phase and carbon Grain growth of the nitride phase is suppressed, and the hardness and strength of the cemented carbide are improved. However, it is difficult for Cr or Cr ₃ C ₂ to dissolve in the binder phase of the present invention in excess of 20 wt% with respect to the binder phase. Therefore, the amount of Cr or Cr ₃ C ₂ contained in the binder phase of the present invention is preferably 0.1 to 20 wt% with respect to the entire binder phase.
If the binder phase of the present invention is more than 30 wt% with respect to the entire cemented carbide, the strength of the cemented carbide decreases, so the binder phase of the present invention is set to 0.5 to 30 wt%. In order to achieve this requirement, an amount of raw material powder that falls within this range may be blended.

  Examples of the method for producing the cemented carbide of the present invention include the following methods. As a raw material powder, WC having an average particle diameter of 0.05 to 2.0 μm is weighed so as to be 70 to 99.4 wt% with respect to the cemented carbide, and Ti, Zr, Hf, Nb, Ta, Cr, Mo and The oxide of at least one metal selected from W is weighed so as to be 0.1 to 30 wt% with respect to the cemented carbide. In addition, as the binder phase, a metal mainly composed of at least one selected from the group consisting of Co, Ni, and Fe is weighed so that the total of the WC phase, the carbonitride phase, and the binder phase is 100 wt%. Also, 1 wt% or less of carbon powder or 1 wt% or less of tungsten powder may be added to the raw material powder so that free carbon or a decarburized phase does not occur after sintering. These together with an organic solvent are put into a ball mill or an attritor, and pulverized and mixed for a predetermined time. Then, after drying, it is formed into a predetermined shape.

  Next, the temperature is set to 1300 to 1500 ° C. in a nitrogen atmosphere, and sintering is performed for 60 to 120 minutes. Thereby, the added oxide is carbonitrided by carbon in the material and nitrogen during sintering. When the sintering temperature is less than 1300 ° C., the cemented carbide may be insufficiently densified. Moreover, when it becomes higher than 1500 degreeC or it sinters exceeding 120 minutes, it will become difficult to suppress the grain growth of a WC phase and a carbonitride phase. Furthermore, this is made into the temperature of 1300-1500 degreeC in inert gas atmosphere, and HIP processing is performed in the time for 60 to 120 minutes.

The hardness of the cemented carbide added with TiO ₂ , TaC, Cr ₃ C ₂ as an additive and the cemented carbide not added with carbonitride was measured. The composition and hardness are shown below.
As shown in Table 1, the cemented carbide added with TiO ₂ has a higher hardness than Comparative Examples 1, 2, and 3. FIG. 2 shows the SEM structure of these cemented carbides. It can be seen that the carbonitride-free material has significantly grown grains, whereas the carbonitride-added material has suppressed WC phase grain growth. Among them, the material to which TiO ₂ is added particularly suppresses grain growth and is a fine cemented carbide.

Furthermore, the hardness and structure of the cemented carbide with the added amount of TiO ₂ varied were evaluated.
It can be seen from Table 2 that the hardness increases as the added amount of TiO ₂ increases. In addition, as shown in FIG. 3, it can be seen that even a very small addition amount exhibits a grain growth suppressing effect. Furthermore, it turns out that the higher grain growth inhibitory effect is acquired by increasing addition amount.

In order to obtain a higher effect of suppressing grain growth, a cemented carbide in which TiO ₂ and Cr ₃ C ₂ were added in combination was produced. These were measured for hardness and strength. Furthermore, it compared with the Cr ₃ C ₂ simple substance addition product.
From Table 3, it can be seen that a cemented carbide with high hardness and high strength can be obtained by adding Cr ₃ C ₂ in combination. A material in which TiO ₂ and Cr ₃ C ₂ are added in combination and added in a total of 3 vol% is higher in hardness and strength than those in which 3 vol% is added by adding Cr ₃ C ₂ alone. FIG. 4 shows each SEM structure. It can be seen that a high grain growth suppression effect is obtained by the composite addition, and the material has a fine and uniform structure.

  Since a high grain growth inhibitory effect is obtained and it becomes possible to produce ultrafine cemented carbide, it is expected to be used for drawing dies and molding dies that require high wear resistance. In addition, since a material having high strength and high hardness can be obtained, it can be used for a cutting tool such as a micro drill.

Claims (3)

Including 70 to 99.4 wt% of the first phase mainly composed of tungsten carbide (WC) having a raw material average particle size of 0.05 to 2.0 μm, based on the entire cemented carbide;
Containing a second phase composed of carbonitride produced by carbonitriding an oxide of Ti during sintering with respect to the whole cemented carbide ;
Including 0.5 to 30 wt% of a binder phase mainly composed of at least one selected from the group consisting of Co, Ni and Fe , based on the whole cemented carbide ;
The sum of the second phase and the binder phase is a first phase and the carbonitride phase is a hard substance phase is 100 wt%, not including V other than those further inevitably mixed, average WC after sintering cemented carbide having a particle size is equal to or less than 1.0 micron m. The cemented carbide according to claim 1,
A cemented carbide characterized in that the raw material average particle diameter of the oxide is in the range of 5 to 100 nm . In the cemented carbide according to claim 1 or 2,
Further added _Cr 3 _{C 2,} the addition amount of _Cr 3 _{C 2} is cemented carbide, which is a 0.1-20 weight% with respect to the total binding phases.