JP2009248237A - Titanium carbonitride-based cermet cutting tool excellent in wear resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a titanium carbonitride-based cermet cutting tool having a hard coating layer exhibiting excellent wear resistance during high-speed cutting. <P>SOLUTION: This cutting tool has a texture structure made of a mixing composition having 20-30% tungsten carbide, 5-10% one or more of tantalum carbide, niobium carbide, and vanadium carbide, 10-20% cobalt and the remainder made of titanium carbonitride and inevitable impurities, a body hard phase of a core structure and a metal bonding phase. In the metal bonding phase, a 2-20 area% tungsten carbide phase of hexagonal crystal crystalline structure is present, or 1-20 area% fine deposited and dispersed hard phase comprising a compound carbide of tungsten and cobalt of cubical structure is present, and the remainder is formed of a metal bonding phase formed mainly of Co. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  This invention, for example, is a titanium carbonitride base that exhibits excellent thermal shock resistance and fracture resistance and excellent wear resistance over a long period of time when used for high-speed cutting with high heat generation such as various steels and cast iron. The present invention relates to a (TiCN-based) cermet cutting tool (hereinafter simply referred to as a cermet tool).

Conventionally, as a cermet tool, Ti carbonitride, carbonitride mainly composed of Ti, or carbonitride mainly composed of Ti and M (where M is one or two of Ta, Nb, and V) A core composed of a core composed of a core composed of Ti, W and M as a main component, and 70 to 95 area%. There is known a cermet tool that is composed of a titanium carbonitride group (TiCN group) cermet (hereinafter simply referred to as cermet) composed of a binder phase mainly composed of Co and W and inevitable impurities.
Then, in order to improve the thermal shock resistance of the cermet tool, in the temperature range of 1400 to 1600 ° C., at a predetermined pressure _He, and fired at N 2, Ar, CO, CO 2 _atmosphere, W 6 _Co 6 C , W ₃ Co ₃ C, W ₄ Co ₂ C, and W ₉ Co ₃ C ₄ are known to produce η phases containing lower carbides.
Further, in order to improve the wear resistance of the cermet tool, it is kept in a temperature range of 1400 to 1550 ° C. and in an N ₂ atmosphere of _{20 to} 500 Torr, quenched, and then heated at 1100 to 1250 ° C. (W, It is also known to disperse and precipitate a fine precipitation-dispersed hard phase composed of Co) C.
JP 2000-135606 A JP 2000-237903 A

In recent years, there has been a strong demand for labor-saving, energy-saving, high-efficiency, and low-cost cutting, and there has been a remarkable improvement in the performance of cutting devices. Cutting conditions have become increasingly severe, and cermet tools are expected to have a longer service life.
Cermet tools are generally insufficient in thermal shock resistance and fracture resistance compared to carbide tools, especially when trying to improve wear resistance, thermal shock resistance and fracture resistance. In order to prolong the service life of cermet tools, it is necessary to improve wear resistance without reducing thermal shock resistance and fracture resistance. The conventional cermet tool is inferior in any of thermal shock resistance, fracture resistance and wear resistance, and cannot be said to have these characteristics in combination.

  In view of the above, the present inventors have conducted intensive research on a cermet tool having excellent wear resistance without deteriorating thermal shock resistance and fracture resistance. The following knowledge was acquired about the conditions etc. for producing | generating a structure | tissue.

(A) According to the above prior art (hereinafter, the techniques described in Patent Documents 1 and 2 are referred to as “prior art 1” and “prior art 2”, respectively), an arbitrary cermet firing temperature of 1400 to 1600 ° C. At least one of He, N ₂ , Ar, CO, and CO ₂ is introduced at a pressure of 760 Torr or less, and W ₆ Co ₆ C, W ₃ Co ₃ C, W ₄ Co ₂ C, and W ₉ are introduced. By generating an η phase containing a lower carbide such as Co ₃ C ₄ , thermal shock resistance is improved (prior art 1), and in a temperature range of 1400 to 1550 ° C. and in an N ₂ atmosphere of _{20 to} 500 Torr. The cermet is rapidly cooled after being fired and heated at 1100 to 1250 ° C. to improve the wear resistance by dispersing and precipitating a fine precipitation-dispersed hard phase composed of (W, Co) C (conventional technology). 2).
However, when firing the cermet raw material powder, for example,
(B) From room temperature to sintering temperature (1480-1600 ° C.), the temperature is raised in a vacuum atmosphere.
(B) After holding at the sintering temperature for 5 to 30 minutes in a vacuum atmosphere,
(C) introducing a mixed gas of nitrogen and hydrocarbon (for example, N ₂ —CH ₄ mixed gas), and heating and holding in the mixed gas atmosphere of nitrogen and hydrocarbon (200 to 400 Torr) for 30 to 60 minutes;
(D) After pulling vacuum, cool to room temperature,
When firing under the condition of
A sintered structure composed of a main hard phase (70 to 95 area%) having a core structure composed of a core part and a peripheral part and a binder phase (30 to 5 area%) is formed;
Further, in the binder phase (30 to 5 area%), a tungsten carbide (hereinafter referred to as h-WC) phase having a hexagonal structure fills the gap between the main hard phases and bonds the main hard phases to each other. Or a hard phase (hereinafter referred to as (W, Co) C) composed of a composite carbide of tungsten and cobalt having a cubic structure (hereinafter referred to as (W, Co) C) or the prior art 2 (Corresponding to a fine precipitation-dispersed hard phase composed of (W, Co) C) in (1), finely precipitated and dispersed, and the balance is composed of a metal-bonded phase mainly composed of cobalt.

(B) The h-WC phase formed in the binder phase under the above firing conditions is the cubic structure η phase formed in the prior art 1 or the cubic structure formed in the prior art 2. This is a tough hard phase having a hexagonal crystal structure completely different from the fine precipitation-dispersed hard phase composed of (W, Co) C, and the toughness of the cermet is improved by the formation of the h-WC phase. When the phases exist in a form that fills the gaps between the main hard phases and bonds the main hard phases, a network with excellent toughness of the main hard phases is formed, and the plastic deformation resistance of the cermet as a whole is improved. Great improvement.

(C) Therefore, the main hard phase having a core structure composed of the core portion and the peripheral portion, the binder phase and the binder phase, the gap between the main hard phases is filled, and the main hard phases are bonded to each other. A cermet tool having a tough and hard h-WC phase structure that exists in such a form can be used for high-speed cutting with high heat generation such as various steels and cast irons. As well as excellent wear resistance over a long period of time.

This invention has been made based on the above findings,
“(1)
(A)% by weight
Tungsten carbide: 20-30%
One or more of tantalum carbide, niobium carbide and vanadium carbide: 5 to 10%,
Cobalt: 10-20%
Titanium carbonitride and inevitable impurities: balance,
Having a composition of
(B) In structure observation with a scanning electron microscope,
Titanium carbonitride, carbonitride mainly composed of titanium, or a core composed of carbonitride mainly composed of titanium and M (where M is one or more of tantalum, niobium and vanadium) A cored structure composed of a carbonitride mainly composed of a portion, titanium, tungsten, and M (where M represents one or more of tantalum, niobium, and vanadium). Main hard phase: 70-95 area%,
The balance has a structure consisting of a binder phase: 30-5 area%,
(C) The binder phase is mainly composed of a tungsten carbide (h-WC) phase having a hexagonal crystal structure with an area ratio of 2 to 20 area%, with the balance being cobalt, where the area% of the binder phase is 100%. Consisting of a metal bonded phase,
A titanium carbonitride-based cermet cutting tool characterized by that.
(2)
In the (1) titanium carbonitride-based cermet cutting tool,
The binder phase (c) is composed of a tungsten carbide (h-WC) phase having a hexagonal crystal structure with an area ratio of 2 to 20 area%, and 1 to 20 area% when the area% of the binder phase is 100%. A fine precipitation-dispersed hard phase composed of a composite carbide of tungsten and cobalt ((W, Co) C) having a cubic structure with an area ratio of: and a metal binder phase mainly composed of cobalt.
The titanium carbonitride-based cermet cutting tool according to (1) above. "
It has the characteristics.

In the cermet tool of the present invention, the reason why the blending composition, structure and the like are limited as described above will be described below.
Tungsten carbide (WC);
In the cermet of this invention, if the blending ratio of WC is less than 20% by weight, the W content ratio in the binder phase (bonding phase) mainly comprising Co is insufficient, and the desired high-temperature hardness cannot be maintained, On the other hand, if the blending ratio exceeds 30%, the tungsten carbide (h-WC) phase having a hexagonal crystal structure is formed in the form of particles and does not take a form that bonds the main hard phases to each other. For this reason, the plastic deformation resistance is drastically lowered, and plastic deformation is likely to occur at the cutting edge due to this, so the blending ratio was determined to be 20 to 30% by weight.

One or more of tantalum carbide, niobium carbide and vanadium carbide (TaC / NbC / VC);
A part of TaC, NbC and VC is dissolved in the Co component which is a binder phase forming component during sintering, and the other part is dissolved in the periphery and core of the main hard phase. However, if the blending ratio (total amount of TaC, NbC, and VC) is less than 5% by weight, the desired improvement effect cannot be obtained in the above-described operation, If the content ratio exceeds 10%, the content ratio in the hard phase becomes too high, and this causes a decrease in the hardness of the main hard phase, so the blending ratio (total amount of TaC, NbC and VC) is 5 to 5%. It was determined as 10% by weight.

Cobalt (Co);
Co has the effect of improving the sinterability and forming a metallic binder phase mainly composed of Co to improve the strength of the cermet. However, if the blending ratio is less than 10% by weight, the desired sinterability is obtained. On the other hand, when the blending ratio exceeds 20% by weight, wear rapidly progresses. Therefore, the blending ratio is set to 10 to 20% by weight.

Titanium carbonitride (TiCN);
TiCN has the effect of forming a main hard phase during sintering and improving the hardness of the cermet tool, thereby contributing to the improvement of wear resistance. However, if the blending ratio is less than 40% by weight, the desired hardness is obtained. On the other hand, if the blending ratio exceeds 65%, the strength of the cutting tool is drastically reduced, and chipping and chipping are likely to occur during cutting. It is desirable to set it as 65 weight%, and it is still more desirable to set it as 50 to 55 weight%.

Main hard phase;
The main hard phase is titanium carbonitride, carbonitride mainly composed of titanium or titanium and M (wherein M represents one or more of tantalum, niobium and vanadium). A core made of nitride (hereinafter collectively referred to as (Ti, M) CN), titanium, tungsten, and M (where M is one or two of tantalum, niobium, and vanadium) It consists of a hard phase with a core structure composed of a peripheral part composed of a carbonitride (hereinafter referred to as (Ti, W, M) CN) mainly composed of the above, but the area ratio of the principal hard phase is If the area ratio is less than 70 area%, the ratio of the binder phase is relatively too large and wear resistance is lowered. On the other hand, if the area ratio exceeds 95 area%, the ratio of the binder phase is too small. Sinterability and strength decrease. From becoming, defining the area ratio of the main hard phase and 70-95 area%.

Bonded phase;
The area ratio of the binder phase is the same as in the case of the main hard phase, that is, if the area percentage of the binder phase exceeds 30 area%, the wear resistance decreases, while the area percentage of the binder phase is 5 areas. If it is less than%, the sinterability decreases and the strength decreases, so the area ratio of the binder phase was determined to be 30-5 area%.
In the present invention, the binder phase refers to a phase other than the main hard phase constituting the cermet. In addition to the metal bond phase composed of a Co-based solid solution phase in which W, Ta, Nb, and V are dissolved in Co, the main phase is used. A hexagonal crystal structure WC (h-WC) phase that exists in a form that fills the gap between the hard phases and bonds the main hard phases to each other, or, further, a composite carbide of W and Co with a cubic crystal structure (( The fine precipitation-dispersed hard phase composed of W, Co) C) is also referred to as a binder phase.

h-WC phase;
The h-WC phase having a hexagonal structure existing in the binder phase is, for example, heated at a cermet raw material powder under a vacuum to a sintering temperature (1480 to 1600 ° C.), particularly when cermet is fired. After heating and holding at the sintering temperature for 5 to 30 minutes in an atmosphere, a mixed gas of nitrogen and hydrocarbon (for example, N ₂ —CH ₄ mixed gas) is introduced, and the mixed gas atmosphere of nitrogen and hydrocarbon ( 200 to 400 Torr) is further heated and held for 30 to 60 minutes, vacuumed, and then cooled to room temperature in an inert gas such as Ar gas, so that W dissolved in the molten metal phase is converted into carbide. By precipitation, an h-WC phase is formed. However, in the case where heating and holding for 30 to 60 minutes is not performed in a mixed gas atmosphere of nitrogen and hydrocarbon (200 to 400 Torr) at a temperature within the range of 1480 to 1600 ° C., the conventional technique 1 In this invention, a cubic structure η phase represented by (3) is formed, or a fine precipitation-dispersed hard phase composed of (W, Co) C having a cubic structure represented by prior art 2 is formed. A h-WC phase having a hexagonal crystal structure is not formed. Although the mechanism of the formation of the h-WC phase is not sufficiently elucidated, the fact that the h-WC phase has a hexagonal crystal structure means that energy dispersive X-ray analysis using a transmission electron microscope ( The present inventors have confirmed by (TEM-EDS).
The h-WC phase is a tough hard phase, and, as schematically shown in FIG. 1, fills the gap between the main hard phases and bonds the main hard phases to each other. Therefore, the toughness of the cermet tool is improved and the plastic deformation resistance of the cermet tool is greatly improved. However, when the area ratio of the h-WC phase in the binder phase is less than 2 area%, the effect of improving toughness and plastic deformation resistance cannot be expected, while the area ratio of the h-WC phase is 20 area%. Exceeding the sinterability of the cermet and the strength decrease, the h-WC phase area ratio in the binder phase, that is, when the binder phase area percentage is 100%, the binder phase The area ratio of the h-WC phase occupying inside was determined to be 2 to 20 area%.

A fine precipitation-dispersed hard phase comprising a composite carbide of W and Co ((W, Co) C);
When the cermet is fired, after sintering and heating and holding in the temperature range of 1520 to 1600 ° C. and in a mixed gas atmosphere of nitrogen and hydrocarbon, when cooled, W dissolved in the molten metal phase is obtained. In the case of a cermet in which the h-WC phase is precipitated as carbide and precipitated in the main hard phase gap, but there is a large amount of Co and the proportion of WC is small (Co 15-20 and WC 20-25% by weight) A part of W dissolved in the metal is finely precipitated and dispersed in the binder phase as a composite carbide of W and Co ((W, Co) C). The fine precipitation dispersed phase composed of (W, Co) C is a hard phase having a cubic crystal structure, which further improves the wear resistance of the cermet tool. ) If the area ratio of the C fine precipitation-dispersed hard phase exceeds 20 area%, the toughness is drastically reduced and the cutting edge is liable to be damaged, while the (W, Co) C fine occupying the binder phase. When the area ratio of the precipitation-dispersed hard phase is less than 1 area%, the effect of improving the wear resistance cannot be expected. Therefore, the fine precipitated-dispersed hard phase having a cubic crystal structure in the binder phase and made of (W, Co) C. The area ratio was defined as 1 to 20 area%.
In addition, by performing firing under the conditions shown in the following examples, the h-WC phase is 2 to 20% by area in the binder phase, or further, a fine precipitation dispersed hard phase composed of (W, Co) C is bonded. It is possible to obtain a bonded phase structure in which 1 to 20% by area is present in the phase and the balance is a metal bonded phase mainly composed of Co.

  In the cermet tool of the present invention, the structure is composed of a main hard phase having a core structure composed of a core portion and a peripheral portion, and the remaining binder phase, and the binder phase has a hexagonal crystal structure. -The WC phase is present in such a form that the gap between the main hard phases is filled and the main hard phases are bonded to each other, or further, a fine precipitation dispersed hard phase comprising (W, Co) C having a cubic crystal structure. And the remainder is composed of a metallic binder phase mainly composed of Co, which is excellent in plastic deformation resistance even when used for high-speed cutting with high heat generation such as various steels and cast iron. It exhibits thermal shock resistance and fracture resistance, and exhibits excellent wear resistance over a long period of time.

  Next, the cermet tool of the present invention will be specifically described with reference to examples.

TiCN powder, WC powder, TaC powder, NbC powder, VC powder, and Co powder, all having an average particle diameter of 0.5 to 2 μm, are prepared as raw material powders, and these raw material powders are blended as shown in Table 1. Compounded in the composition, wet mixed in a ball mill for 24 hours, dried, and then pressed into a TNGA-shaped green compact at a pressure of 200 MPa. The green compact was subjected to the following sintering conditions:
(1) From room temperature to the heating temperature shown in Table 2, the temperature is raised in a vacuum atmosphere.
(2) After heating and holding at the heating temperature in a vacuum atmosphere for the time shown in Table 2 (shown as gas introduction time (min) in Table 2),
(3) A mixed gas of nitrogen and hydrocarbons shown in Table 2 was introduced into the sintering furnace, and similarly shown in Table 2 as a nitrogen-hydrocarbon mixed gas atmosphere (in Table 2, shown as sintering atmosphere pressure (Torr)) ), And held for heating only for the time shown in Table 2 (shown as heating holding time (min) in Table 2),
(4) From the sintering temperature, using Ar gas as an inert gas, cooling to room temperature at a cooling rate (° C./min) shown in Table 2.
The cermet of the present invention, which is sintered under the conditions consisting of the above steps (1) to (4), is subjected to honing processing of R: 0.07 mm on the cutting edge portion in the ISO standard / TNGA160408 chip shape shown in Table 3 Tools 1-10 were produced respectively.

For the purpose of comparison, the green compact having the composition shown in Table 1 was changed to various conditions shown in Table 4 (for example, the atmosphere gas in the sintering furnace was changed to N ₂ atmosphere or Ar atmosphere, and the atmosphere gas pressure was changed. The temperature is reduced, the heating and holding time in the gas atmosphere is extended, the reheating is performed after the cooling is completed), and the cutting edge portion is formed in the ISO standard / TNGA160408 chip shape shown in Table 5. R: Comparative cermet tools 1 to 10 subjected to honing of 0.07 mm were produced.

  For the cermet tools 1 to 10 and comparative cermet tools 1 to 10 obtained as a result, the structure of the cermet constituting the cermet tools 1 to 10 is observed with a scanning electron microscope (SEM), and each of the cermet tools present in the binder phase is observed. The area ratio of the phase (however, the area ratio when the area% of the binder phase is 100%), the crystal structure, and the morphology are measured with an electron beam backscattering diffractometer (SEM-EBSD) using a scanning electron microscope, The measurement results are shown in Tables 3 and 5, respectively.

Next, for the cermet tools 1 to 10 of the present invention and the comparative cermet tools 1 to 5 and 6 to 10, all of which are screwed to the tip of the tool steel tool with a fixing jig,
Work material: JIS / S35C round bar,
Cutting speed: 700 m / min,
Cutting depth: 0.5 mm,
Feed: 0.08 mm / rev,
Cutting time: 20 minutes,
Wet continuous high-speed cutting test (normal cutting speed is 350 m / min) of carbon steel under the conditions (referred to as cutting condition A),
Work material: JIS / SS330 round bar,
Cutting speed: 900 m / min,
Cutting depth: 0.5 mm,
Feed: 0.15 mm / rev,
Cutting time: 25 minutes,
Wet continuous high-speed cutting test (normal cutting speed is 400 m / min) of mild steel under the following conditions (referred to as cutting condition B),
Work material: JIS / FC250 round bar,
Cutting speed: 800 m / min,
Cutting depth: 0.5 mm,
Feed: 0.12 mm / rev,
Cutting time: 12 minutes,
A dry continuous high-speed cutting test of cast iron under the following conditions (referred to as cutting condition C) (normal cutting speed is 350 m / min),
In each cutting test, the flank wear width of the cutting edge was measured. The measurement results are shown in Table 6.

  From the results shown in Tables 3, 5, and 6, the cermet tools 1 to 10 of the present invention have a tungsten carbide (h-WC) phase having a hexagonal crystal structure in the binder phase in an amount of 2 to 20 area% (however, the above When the area% of the binder phase is 100%, the ratio of the area occupied in the binder phase is present (or, further, there is a fine precipitation dispersed hard phase composed of (W, Co) C having a cubic crystal structure, In particular, the h-WC phase is a tough hard phase, and the h-WC phase is present in a form that fills the gap between the main hard phases and bonds the main hard phases to each other. As a result, the toughness and plastic deformation resistance of cermet tools are greatly improved, and even when used for high-speed cutting with high heat generation such as various steels and cast iron, excellent plastic deformation resistance, thermal shock resistance, Abrasion resistance and long-lasting wear resistance In comparison cermet tools 1-5, only the cubic η phase is precipitated, so that the wear resistance is excellent, but the fracture resistance is inferior. In the cermet tools 6 to 10, although the wear resistance is excellent due to the presence of the fine precipitation-dispersed hard phase composed of (W, Co) C having a cubic structure, the thermal shock resistance is inferior. It is apparent that the tools 1 to 10 do not have improved wear resistance without deteriorating both thermal shock resistance and fracture resistance, and reach the service life in a relatively short time.

  As described above, the cermet tool of the present invention has excellent plastic deformation resistance not only in cutting processing under normal conditions such as various steels and cast iron, but also in high-speed cutting processing which is severe cutting conditions with high heat generation. Excellent heat resistance as well as thermal shock resistance and fracture resistance, and extended service life. As a result, it is possible to satisfy cutting and labor savings and cost reductions with sufficient satisfaction. It is.

In this invention cermet tool 1, it is a schematic explanatory drawing which shows that the h-WC phase exists in the form which fills the space | gap between main hard phases, and couple | bonds main hard phases.

Claims (2)

(A)% by weight
Tungsten carbide: 20-30%
One or more of tantalum carbide, niobium carbide and vanadium carbide: 5 to 10%,
Cobalt: 10-20%
Titanium carbonitride and inevitable impurities: balance,
Having a composition of
(B) In structure observation with a scanning electron microscope,
Titanium carbonitride, carbonitride mainly composed of titanium, or a core composed of carbonitride mainly composed of titanium and M (where M is one or more of tantalum, niobium and vanadium) A cored structure composed of a carbonitride mainly composed of a portion, titanium, tungsten, and M (where M represents one or more of tantalum, niobium, and vanadium). Main hard phase: 70-95 area%,
The balance has a structure consisting of a binder phase: 30-5 area%,
(C) The binder phase includes a tungsten carbide phase having a hexagonal crystal structure with an area ratio of 2 to 20 area% and a metal binder phase mainly composed of cobalt when the area% of the binder phase is 100%. Consist of,
A titanium carbonitride-based cermet cutting tool characterized by that. In the titanium carbonitride-based cermet cutting tool according to claim 1,
The binder phase (c) is composed of a tungsten carbide phase having a hexagonal crystal structure with an area ratio of 2 to 20 area% and a cubic with an area ratio of 1 to 20 area% when the area% of the binder phase is 100%. Consisting of a fine precipitation-dispersed hard phase composed of a composite carbide of tungsten and cobalt having a crystal structure, and a metal-bonded phase mainly composed of cobalt.
The titanium carbonitride-based cermet cutting tool according to claim 1.

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