JP2009066741A - Cutting tool made of wc-based cemented carbide excellent in chipping resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cutting tool made of WC-based cemented carbide, capable of achieving excellent chipping resistance in high-speed intermittent heavy cutting work in which high heat is generated, with large mechanical impact loads added repeatedly. <P>SOLUTION: The cutting tool made of surface-coated WC-based cemented carbide comprises a base member of WC-based cemented carbide having an average composition of 5-12% Co, 0.02-0.2% S, carbide-converted values of 1-5% TiC, 1-5% for one kind or two kinds of TaC and NbC, all in mass%, with WC for the rest. The inner side of the base member is substantially composed of a first hard phase comprising WC, a second hard phase comprising composite carbide solid solution and/or composite carbonitride solid solution of Ti, Ta and/or Nb and W, a dendritic carbosulfide precipitation phase, a binder phase, and unavoidable impurities. The surface side of the base member is composed of the first hard phase and the binder phase substantially, including less than 0.02% S. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention provides a substrate made of a WC-based cemented carbide even in cutting of steel or cast iron, particularly in high-speed intermittent heavy cutting that repeatedly generates a large mechanical load and thermal shock with high heat generation. A composite carbon sulfide precipitation phase containing one or both of dendritic Ti and Ta and Nb, which precipitates in the internal structure of the steel [hereinafter referred to as (Ti, Ta / Nb) CS precipitation phase] However, by suppressing the propagation of cracks generated in the WC-based cemented carbide substrate, a surface-coated WC-based cemented carbide cutting tool that exhibits excellent wear resistance and excellent fracture resistance (hereinafter referred to as the following) This is related to a coated carbide tool.

Conventionally, at least one of a Ti carbide layer, a nitride layer, a carbonitride layer, a carbonate layer, a nitride oxide layer, and a carbonitride oxide layer on the surface of a tool base made of a WC-based cemented carbide. Or in a coated carbide tool formed by vapor-depositing a hard coating layer composed of two or more Ti compound layers and an Al oxide layer,
(A) The inside of the substrate made of WC-based cemented carbide is
A first hard phase comprising WC;
A second hard phase composed of either or both of a composite carbide solid solution and a composite carbonitride solid solution containing Ti and Ta and / or Nb and W as main metal components;
Composed of a binder phase containing 5-12 wt% Co and 0.2-3 wt% Cr,
(B) On the other hand, the substrate surface layer having a width of 10 to 50 μm from the substrate surface of the substrate made of the WC-based cemented carbide is
The second hard phase does not exist, is composed of the first hard phase and a binder phase, and the binder phase contains 1.1 to 1 by weight ratio to the Co and Cr contents inside the substrate. Coated carbide tools containing Co, Cr of 0.5, 1.2 to 2.0 are known, and excellent fracture resistance when this coated carbide tool is used for intermittent heavy cutting It is known to exert.
JP 2000-126905 A

  In recent years, the performance of cutting equipment has been remarkable. On the other hand, there are strong demands for labor saving and energy saving in cutting work, as well as high efficiency and low cost, and accordingly, heavy cutting such as high feed and high cutting. However, the above-mentioned conventional coated carbide tool is processed under severer conditions, that is, accompanied by high heat generation and extremely large mechanical load and heat on the cutting edge. When used for high-speed interrupted heavy cutting where a mechanical impact is applied, for example, the crack generated in the cutting edge ridge line propagates or progresses, or chipping and chipping occur due to the penetration of the crack in the tool base, At present, the service life is reached in a relatively short time.

  Therefore, from the above viewpoint, the present inventors have provided coated carbide that exhibits excellent wear resistance as well as wear resistance even when high-speed intermittent heavy cutting is performed using a coated carbide tool. As a result of earnest research on tools, the following knowledge was obtained.

(A) When the above conventional coated carbide tool (see Patent Document 1) is used for normal interrupted cutting of various steels and cast irons, although excellent wear resistance and fracture resistance are exhibited, it is more severe. When used for various cutting conditions such as intermittent heavy cutting under high-speed conditions, cracks generated at the edge of the cutting edge propagate and propagate through the tool base, and this crack penetrates through the tool base. This causes cracks and chipping, but when manufacturing a WC-based cemented carbide tool substrate (hereinafter referred to as a cemented carbide substrate) by sintering, a specific raw material powder is blended in a certain proportion. The green compact obtained by blending was placed on a base plate coated with a carbon-based paste containing S in an amount of 1.5% by mass or more, and cooled to 1200 ° C. after sintering. When the speed is controlled to 1.5-3 ° C / min In the inside of the cemented carbide substrate formed by sintering (that is, on the inner side of a predetermined width within a range of 10 to 50 μm from the surface of the cemented carbide substrate (sintered body)), a carbon sulfide precipitation phase ((Ti, Ta / Nb) CS precipitation phase) is obtained in a dendritic structure (see FIG. 1). On the other hand, the carbon sulfide precipitation phase ((Ti, There is no precipitation of Ta / Nb) CS precipitation phase), and a zone with an S content of less than 0.02% by mass is formed (see FIG. 2).

(B) A coated carbide tool in which a hard coating layer is formed by vapor deposition on a cemented carbide substrate having a different structure as described above on the inner side and the surface side of the cemented carbide substrate is, for example, a high-speed intermittent heavy cutting process. Even when cracks occur in the coated carbide tool, the propagation of cracks is suppressed by the precipitation of dendritic (Ti, Ta / Nb) CS precipitates inside the carbide substrate. In addition, it is possible to prevent the cutting edge ridge line portion from being chipped and chipping. On the other hand, there is no (Ti, Ta / Nb) CS precipitate phase on the surface side of the carbide substrate, and the S content is 0. Since it is less than 0.02% by mass, the carbide substrate itself has excellent wear resistance. Further, on the surface of the carbide substrate, for example, a hard material having excellent wear resistance itself, such as a Ti compound layer and an Al oxide layer. Sufficient wear resistance due to vapor deposition of coating layer It is also ensured.

(C) Therefore, the coated carbide tool of the present invention in which the dendritic carbon sulfide composed of the (Ti, Ta / Nb) CS precipitate phase is precipitated only inside the carbide substrate is accompanied by high heat generation, Even when used for high-speed intermittent heavy cutting, where extremely large mechanical loads and thermal shocks are applied to the blade, it must exhibit excellent wear resistance and excellent fracture resistance.

This invention has been made based on the above findings,
“(A)% by mass,
Co: 5-12%
S: 0.02-0.2%
And in carbide equivalent value,
TiC: 1-5%
One or two of TaC and NbC: 1 to 5%,
WC: The rest
In a surface-coated WC-based cemented carbide cutting tool in which a hard coating layer is vapor-deposited on the surface of a WC-based cemented carbide substrate composed of a sintered body having an average composition consisting of:
(B) When observed in a cross section, the inner side from the predetermined width within the range of 10 to 50 μm from the surface of the substrate is
A first hard phase comprising WC;
A second hard phase composed of either or both of a composite carbide solid solution and a composite carbonitride solid solution containing Ti and Ta and / or Nb and W as main metal components;
A dendritic carbon sulfide precipitation phase containing Ti as a metal component, further containing either or both of Ta and Nb, and containing C and S as non-metal components combined with the metal component;
It consists of a sintered body consisting of a binder phase and inevitable impurities,
(C) The surface side from the predetermined width within the range of 10 to 50 μm from the substrate surface is
A sintered body composed of the first hard phase and the binder phase and having an S content of less than 0.02% by mass, wherein the second hard phase and the dendritic carbon sulfide precipitation phase do not exist. Consist of
A surface-coated WC-based cemented carbide cutting tool (coated carbide tool) with excellent fracture resistance characterized by "
It has the characteristics.

The coated carbide tool of the present invention will be described in detail below.
(A) Average composition of the carbide substrate;
(A) WC
The carbide substrate that is the tool substrate of the coated carbide tool of the present invention is, for example,
(A) The temperature is raised from room temperature to 1350 to 1550 ° C., which is a sintering temperature, at a rate of 1 to 5 ° C./min in a vacuum atmosphere of 100 Pa or less
(B) Next, in a vacuum atmosphere, the sintering temperature is maintained for 0.5 to 2 hours,
(C) Thereafter, the sintering temperature is gradually cooled to 1200 ° C. at a rate of 1.5 to 3 ° C./min.
Can be produced under the sintering conditions.
In the cemented carbide substrate (sintered body) manufactured under the above-mentioned sintering conditions, WC as a constituent component forms a first hard layer, and a composite carbide solid solution, composite carbonitride together with Ti, Ta, and Nb components. A second hard phase composed of a solid solution is formed and contributes mainly to improvement of wear resistance of the cemented carbide substrate.
However, if the WC content ratio in the cemented carbide substrate is too high, the content ratio of the W component in the binder phase also increases, and the high-temperature strength of the binder phase itself decreases. The ratio (average composition) is desirably 78 to 93% by mass (however, in terms of carbide).

(B) TiC, TaC / NbC
TiC, TaC and NbC, like the WC component, are solid-solved in a binder phase mainly composed of Co at the time of sintering, and a composite carbide solid solution or composite charcoal containing Ti and Ta and / or Nb and W as main metal components at the time of cooling. The nitride solid solution is precipitated to form a second hard phase, and has an effect of improving the high temperature strength of the cemented carbide substrate. However, the TiC content is less than 1% by mass, or one of TaC and NbC or If the total content of the two types is less than 1% by mass, a desired improvement effect cannot be obtained in the above action. On the other hand, if the content of TiC exceeds 5% by mass, or one or two of TaC and NbC If the total content of the seeds exceeds 5% by mass, the toughness decreases and defects are likely to occur. Therefore, the content (average composition) of TiC is 1 to 5% by mass (however, in terms of carbide), , TaC and N 1 to 5 mass% of one or the total content of the (average composition) of C and (where carbides converted value) was determined, respectively.

(C) Co
Co has the effect of improving the sinterability, forming a binder phase, and improving the strength of the cemented carbide substrate. However, if the content ratio is less than 5% by mass, the desired sinterability can be ensured. On the other hand, when the content ratio exceeds 12% by mass, wear proceeds rapidly, so the content ratio (average composition) is set to 5 to 12% by mass.

(D) S
S as a constituent component of the cemented carbide substrate is a dendritic (Ti, Ta / Nb) CS precipitate phase inside the substrate, that is, inside a predetermined width within a range of 10 to 50 μm from the surface of the carbide substrate. And even if a crack occurs in the coated cemented carbide tool by high-speed intermittent heavy cutting, the carbon sulfide precipitate phase exhibits an action of suppressing the propagation of the crack.
However, when the S content is less than 0.02% by mass, no dendritic precipitate is formed, so there is no effect of suppressing the propagation of cracks, while when the S content exceeds 0.2% by mass, The (Ti, Ta / Nb) CS phase is also precipitated on the surface of the carbide substrate, and as a result, the wear resistance of the carbide substrate is reduced, or the (Ti, Ta / Nb) CS precipitation phase. Is agglomerated and coarsened and, conversely, becomes a starting point for crack generation, the S content (average composition) was determined to be 0.02 to 0.2 mass%.

(B) Tissue on the surface side of the cemented carbide substrate, tissue on the inner side The surface side of the cemented carbide substrate, that is, the surface side from a predetermined width within a range of 10 to 50 μm from the surface of the cemented carbide substrate is substantially Consists of a first hard layer and a binder phase to ensure wear resistance, without the presence of a second hard phase or (Ti, Ta / Nb) CS phase that would reduce wear resistance, Similarly, the content of the S component that lowers the wear resistance must be less than 0.02% by mass.
On the other hand, the inner side from the predetermined width within the range of 10 to 50 μm from the surface of the carbide substrate is formed by the first hard layer, the second hard phase, the (Ti, Ta / Nb) CS precipitated phase and the binder phase. While maintaining the prescribed wear resistance, maintain the prescribed high-temperature strength, and also suppress the propagation of cracks generated by high-speed intermittent heavy cutting by the (Ti, Ta / Nb) CS precipitate phase. Therefore, chipping resistance and chipping resistance are improved.
As described above, the surface-side structure state and the internal-side structure state of the cemented carbide substrate are mainly composed of carbon containing 1.5% by mass or more of S in the production of the cemented carbide substrate by sintering. It can be obtained by placing a sintered body on a floor plate coated with the paste of No. 1 and sintering it, and controlling the cooling rate to 1200 ° C. after sintering to 1.5 to 3 ° C./min.

(C) Hard coating layer formed by vapor deposition on the surface of the cemented carbide substrate On the surface of the cemented carbide substrate, the fracture resistance and wear resistance of the WC-based cemented carbide cutting tool in high-speed intermittent heavy cutting are improved. Hard coating layer is vapor-deposited so that excellent tool characteristics can be exhibited over the period of use, but for the kind and formation method of hard coating layer, various well-known materials and methods are used. It can be used and is not particularly limited.
For example, a Ti compound layer composed of one or more of Ti carbide layer, nitride layer, carbonitride layer, carbonate layer, nitride oxide layer, and carbonitride oxide layer is used as the lower layer. In this case, when the total thickness of the hard coating layer is 3 μm or less, excellent wear resistance cannot be exhibited. Further, if the total layer thickness exceeds 25 μm, chipping and defects are likely to occur. Therefore, the total layer thickness of the hard coating layer is preferably 3 to 25 μm.

  In the coated carbide tool of the present invention, the dendritic (Ti, Ta / Nb) CS precipitation phase present on the inner side of the cemented carbide substrate constituting the same suppresses the propagation of cracks generated during cutting. In addition, the surface side of the cemented carbide substrate has no (Ti, Ta / Nb) CS precipitated phase and has an S content of less than 0.02% by mass, and thus has excellent wear resistance. Furthermore, since the hard coating layer itself formed by vapor deposition on the carbide substrate has excellent wear resistance, it is accompanied by high heat generation, and a large mechanical load and thermal shock are repeatedly applied to the cutting edge. Even when used in high-speed intermittent heavy cutting, it exhibits excellent wear resistance as well as excellent fracture resistance.

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

Co powder, TiC powder, TaC powder, NbC powder, and WC 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 in the composition shown in Table 1. The mixture was wet mixed in a ball mill for 24 hours, dried, and pressed into a green compact at a pressure of 98 MPa. This green compact was dissolved in carbon powder containing 2.1% by mass of S in methanol to give a paste. Placed on the coated base plate, the following sintering conditions, that is,
(A) The temperature is raised from room temperature to a predetermined sintering temperature in the range of 1350 to 1550 ° C. in a vacuum atmosphere of 100 Pa or less at 2 ° C./min. The temperature is increased at a rate of
(B) Holding at the sintering temperature for 1.5 hours in a vacuum atmosphere of 100 Pa or less,
(C) Slow cooling from the sintering temperature to 1200 ° C. at a rate of 2 ° C./min.
Sintering is performed under the conditions consisting of the steps (a) to (c) above, and an ISO standard / CNMG120408 chip shape having the average composition shown in Table 2 is applied, and the cutting edge portion is subjected to a honing process of R: 0.07 mm. The cemented carbide substrates 1 to 10 of the present invention were produced.

  In addition, for comparison purposes, the green compact having the composition shown in Table 1 was placed on a base plate not containing S, and the cooling rate of the sintering condition (c) was rapidly cooled to 5 ° C./min or more. Except for the above, comparative carbide substrates 1 to 10 having the average composition shown in Table 3 were produced under substantially the same conditions as in the above examples.

  With respect to the obtained cemented carbide substrates 1 to 10 and comparative cemented carbide substrates 1 to 10 obtained as a result, the inside of the cemented carbide substrate constituting this, the precipitation state of carbon sulfide on the surface side, the surface side of the cemented carbide substrate The presence or absence of the second hard phase and the S content were measured with an energy dispersive X-ray analyzer (EDS), and the measurement results are shown in Tables 2 and 3, respectively.

  Next, each of the superhard substrates 1 to 10 of the present invention and the comparative superhard substrates 1 to 10 were charged into a normal chemical vapor deposition apparatus. Table 4 (l-TiCN in Table 4 is disclosed in JP-A-6-8010). Table 5 shows the conditions for forming a TiCN layer having a vertically grown crystal structure described in the publication No., and the other conditions for forming a normal granular crystal structure. The coated carbide tools 1 to 10 of the present invention and the comparative coated carbide tools 1 to 10 were produced by vapor-depositing a hard coating layer composed of a Ti compound layer and an Al oxide layer having the target layer thicknesses shown.

Next, for the above-described coated carbide tools 1 to 10 and comparative coated carbide tools 1 to 10 above, all of them are screwed to the tip of the tool steel tool with a fixing jig,
Work material: JIS · SCM440 lengthwise equidistant 4 vertical grooved round bar,
Cutting speed: 300 m / min,
Cutting depth: 2.0 mm,
Feed: 0.8 mm / rev,
Cutting time: 5 minutes,
Dry high-speed intermittent high-feed cutting test of alloy steel under the following conditions (referred to as cutting condition A) (normal cutting speed and feed are 150 m / min and 0.3 mm / rev, respectively)
Work material: JIS / S20C lengthwise equidistant round bars with 4 vertical grooves,
Cutting speed: 400 m / min,
Cutting depth: 6.0 mm,
Feed: 0.4 mm / rev,
Cutting time: 5 minutes,
Of carbon steel under the above conditions (referred to as cutting conditions B), high-speed intermittent high-cut cutting test (normal cutting speed and cutting are 200 m / min and 3.0 mm, respectively),
Work material: JIS / FC300 lengthwise equidistant 4 bars with vertical grooves,
Cutting speed: 400 m / min,
Cutting depth: 3.0 mm,
Feed: 0.4 mm / rev,
Cutting time: 5 minutes,
Cast iron dry high-speed intermittent high-feed / high-cut cutting test under normal conditions (referred to as cutting condition C) (normal cutting speed, feed and cutting are 200 m / min, 0.2 mm / rev, 1.5 mm, respectively) ,
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 2, 3, and 6, the coated carbide tools 1 to 10 of the present invention are observed in a section of the cemented carbide substrate constituting the same, and in particular, a predetermined range of 10 to 50 μm from the surface. The (Ti, Ta / Nb) CS precipitate phase is precipitated in a dendritic shape on the inner side from the width (FIG. 1), and the second hard side on the surface side from a predetermined width within a range of 10 to 50 μm from the surface. Phase and (Ti, Ta / Nb) CS precipitate phase, and the S content is less than 0.02% of the zone (FIG. 2). Even in high-speed intermittent heavy machining with mechanical loads and thermal shocks, it exhibits excellent wear resistance and excellent fracture resistance, whereas the comparative coated carbide tools 1 to 10 constitute this. Dendritic structure (Ti, which prevents the propagation of cracks to the inner side of the cemented carbide substrate Since there is no Ta / Nb) CS precipitate phase (FIG. 3), it is apparent that the service life is reached in a relatively short time due to the occurrence of defects and chipping.

  As described above, the coated carbide tool of the present invention has high heat generation as well as cutting under normal conditions such as various steels and cast iron, and is repeatedly subjected to a large mechanical load on the cutting edge. -It exhibits excellent wear resistance and excellent fracture resistance even in high-speed intermittent heavy cutting that is subject to thermal shock, and can fully satisfy the labor saving and energy saving of cutting work and further cost reduction.

It is a metallographic photograph (etching solution: Murakami reagent, magnification: 1000 times) showing a distribution state of dendritic (Ti, Ta / Nb) CS precipitation phase on the inside of the carbide substrate of the coated carbide tool of the present invention. Metal structure photograph showing that dendritic (Ti, Ta / Nb) CS precipitation phase and second hard phase do not exist on the surface of the carbide substrate of the coated carbide tool of the present invention (etching solution: Murakami reagent, magnification: 1000 times). It is a metal structure photograph (etching liquid: Mr. Murakami reagent, magnification: 1000 times) showing the inside of the carbide substrate of the comparative coated carbide tool.

Claims (1)

(A) In mass%,
Co: 5-12%
S: 0.02-0.2%
And in carbide equivalent value,
TiC: 1-5%
One or two of TaC and NbC: 1 to 5%,
WC: The rest
In a surface-coated WC-based cemented carbide cutting tool in which a hard coating layer is vapor-deposited on the surface of a WC-based cemented carbide substrate composed of a sintered body having an average composition consisting of:
(B) When observed in a cross section, the inner side from the predetermined width within the range of 10 to 50 μm from the surface of the substrate is
A first hard phase comprising WC;
A second hard phase composed of either or both of a composite carbide solid solution and a composite carbonitride solid solution containing Ti and Ta and / or Nb and W as main metal components;
A dendritic carbon sulfide precipitation phase containing Ti as a metal component, further containing either or both of Ta and Nb, and containing C and S as non-metal components combined with the metal component;
It consists of a sintered body consisting of a binder phase and inevitable impurities,
(C) The surface side from the predetermined width within the range of 10 to 50 μm from the substrate surface is
A sintered body composed of the first hard phase and the binder phase and having an S content of less than 0.02% by mass, wherein the second hard phase and the dendritic carbon sulfide precipitation phase do not exist. Consist of
A surface-coated WC-based cemented carbide cutting tool with excellent fracture resistance characterized by

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