JPH06172912A - Tough cemented carbide - Google Patents

Abstract

PURPOSE:To obtain a tough cemented carbide excellent in chipping resistance by specifying a compsn. consisting of Co, TiC, MC (M is Ta or Nb) and WC and the ratio of the number of ungrown WC grains (alpha1 phase) to that of all of WC grains. CONSTITUTION:This cemented carbide consists of 5-15wt.% Co, 3-50wt.% TiC or TiC and MC and the balance WC with inevitable impurities and has a carbide structure in which the ratio of the number of ungrown WC grains (alpha1 phase) to that of all of WC grains is 30-95%. The carbide structure is formed by regulating the carbon content and crushing strength of starting materials, sintering conditions, etc., and controlling the growth of WC grains at the time of sintering.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cemented carbide that exhibits excellent toughness when used in a cutting tool or the like.

[0002]

2. Description of the Related Art WC-based cemented carbide is widely used as a cutting tool material because of its excellent wear resistance.
Among them, the WC-Co alloy has particularly excellent characteristics, but the tool rake face is greatly worn (so-called crater wear) during cutting of steel that produces continuous chips, and the tool life is significantly shortened. Therefore, in order to suppress the crater wear, an alloy to which solid solution carbide containing TiC having excellent oxidation resistance is added is used.

[0003]

However, this WC-
When a solid solution carbide containing TiC (called a β solid solution) is contained in a Co alloy, it is illustrated in page 132, "Cemented Carbide and Sintered Hard", edited by Toshi Suzuki, February 20, 1986, published by Maruzen Co., Ltd. (Shown as Figure 1)
As described above, the transverse rupture strength of cemented carbide, that is, the strength tends to decrease. Therefore, when the alloy of the present system is used under severe conditions of high load such as a drill, a chipping called chipping is likely to occur, and the chipping resistance increases due to the chipping, and the cutting tool may be damaged in some cases. was there. An object of the present invention is to provide a tough cemented carbide having excellent chipping resistance in order to solve the above problems.

[0004]

Cemented carbide is manufactured by a so-called powder metallurgy method in which a predetermined amount of powdered hard carbide and Co are blended, pulverized and mixed, powder compacted and sintered at high temperature. It Since the WC phase, which is the main component of the hard component, is crystallographically hexagonal, crystallization progresses into triangular prisms when the grains grow due to the dissolution and precipitation process through the liquid phase of Co in the sintering step, and the grains become angular. It becomes the shape. Such a grain-grown and angular WC phase is called an α2 phase. On the other hand, the WC phase in which crystallization due to grain growth is suppressed and which maintains a rounded and irregular shape in a pulverized state is called an α1 phase.

The ungrown WC grains (α1 phase) and grain-grown WC grain phases (α2 phase) are geometrical shapes in which the shape of the WC phase grains is mainly composed of straight lines in an alloy structure photograph by an optical microscope or an electron microscope. Shape, that is, a square shape (α2 phase), or a shape that is mainly composed of curves, that is, a rounded shape (α1)
Phase). In general, cemented carbide has a risk of forming voids in the alloy if sintering is insufficient. Therefore, it is necessary to sufficiently sinter, but if sintering is excessive, WC grains will grow. There are more angular α2 phases.

[0006] By the way, FIG. 2 is edited by Keneth JA Brookes, World Directory Hand.
book of HARDMETALS, UK International in 1987
Figure 3.6, shown in Carbide Data, Inc., 4th edition, page 51 (shown as FIG. 2).
And a microstructure photograph showing a typical microstructure of a cemented carbide containing a solid solution carbide containing TiC. The WC phase particles seen here are all angular, and
It is clear that there are two phases. From this, it can be said that conventionally, no attention was paid to the shape of the WC phase particles of the present system alloy, and most of the alloys had many angular α2 phases.

On the other hand, according to the present invention, as a result of various studies focusing on the relationship between the particle shape of the WC phase of the WC-based cemented carbide containing TiC and the alloy characteristics, particularly toughness, the results of WC 2
An alloy with a small α phase and a round WC phase particle shape
This is based on a previously unknown new finding that the toughness is superior to an alloy having many α2 phases and angular WC phase particles.

Therefore, the cemented carbide according to the present invention contains
5% to 15% Co, 3% TiC or TiC and MC
A cemented carbide having a composition of 50% (where M is Ta and / or Nb) with the balance being WC and unavoidable impurities, and an ungrained WC particle phase (α1 phase) with respect to the total number of WC particle phases on the alloy structure. The ratio of the numbers is 30 to 95%, and thus the toughness is excellent, the chipping resistance is excellent even when used in a drill, etc., and no breakage occurs.

In order to control the ratio of the number of ungrained WC phases (α1 phase) to the total number of WC grain phases on the alloy structure to 30 to 95%, it is necessary to suppress WC grain growth during sintering as much as possible. However, as the means, the carbon content in the alloy is made into a low carbon state, the crushing strength of the raw materials is suppressed to reduce the activity of the powder surface after pulverization and mixing, and the sintering condition is set to a low temperature for a short time. Etc., but the alloy of the present invention can be obtained by using these methods alone or in combination.
However, in any case, it is needless to say that a phase harmful to the cemented carbide such as η phase or free carbon should not appear, or the characteristics should not be deteriorated due to unsintering.

Next, the reason why the component composition is limited as described above will be explained. (1) Co If Co is less than 5%, the toughness cannot be secured, and
If it exceeds%, the wear resistance is lowered and it becomes unsuitable for use as a tool for cutting steel. (2) TiC, TaC, NbC If the content is less than 3%, the crater wear resistance necessary for materials such as tools for cutting steel is insufficient and 50%.
This is because the toughness is remarkably deteriorated when the value exceeds. (3) Ratio of the number of α1 phase particles to the total number of WC phase particles When the ratio of the number of α1 phase particles is 30% or less, the toughness is insufficiently improved, and when the ratio is 95% or more, the toughness is still insufficient in the state of insufficient sintering. This is because there will be a shortage.

[0011]

EXAMPLES The contents of the present invention will be described below with reference to examples. (Example 1) As a raw material powder, WC powder having an average particle size of 5 μm, (W, Ti) C solid solution powder of 1.5 μm (however, WC / TiC ratio 70/30), TaC powder, NbC powder and Co powder of 1 μm Were finally blended so as to have the composition shown in Table 1, and were mixed and pulverized by a ball mill using acetone as a solvent, and then the solvent was dried. 1% by weight of paraffin wax is added to this as a molding aid, and dry CIP is applied.
It was formed into a round bar shape by (cold isostatic pressing). The compact was dewaxed, subjected to intermediate sintering at 750 ° C. for 1 hour, then slightly molded, and further vacuum-sintered to obtain a sintered body. Here, the ball mill time, the carbon content of the alloy, the sintering temperature and the sintering time were changed as shown in Table 2, and the ratio of the number of ungrained WC phase particles (α1 phase) was within the range of the present invention. Comparative alloys (Nos. 4 to 6) in which the ratio of the alloy gold (Nos. 1 to 3) α1 phase in Example 1 was different from the present invention were prepared.

[0012]

[Table 1]

[0013]

[Table 2]

The round bar sintered body thus obtained was processed into a drill shape with a diamond grindstone, and then TiCN coating was applied by the PVD method, and a drill hole drilling test shown in Table 3 was conducted. Table 4 shows the WC phase particle shape of the obtained alloy and the result of the drilling test. As an example of the WC phase particle shape,
Electron micrographs of the alloy structure of the present invention alloy (No. 1) and the comparative alloy (No. 4) (magnification: 4000 times) are shown in FIGS. 3 and 4, respectively. In the photograph, the white phase is the WC phase, but in the case of the alloy of the present invention (FIG. 3), the contour of the WC phase has many curves and is rounded, whereas the comparative alloy (FIG. 4) has a linear contour. It is clear that it is geometric and angular. This difference in the shape of the WC phase particles brings about a decisive difference in performance. That is, as shown in Table 4, the drill lives (the number of drilled holes) of the alloys of the present invention are long as 1600 or more, whereas the comparative alloys have a clearly shorter life despite having the same composition.

[0015]

[Table 3]

[0016]

[Table 4]

(Example 2) In order to examine the influence of the component composition, the same raw material powder as that used in Example 1 was used.
Under the composition and manufacturing conditions shown in, alloys (N
o. 7 to 10) and comparative alloys (No. 1) out of the composition range
1 to 13) were prepared and a drilling test was conducted. The manufacturing method and drill drilling test conditions are described in Example 1.
Is the same as. The results are shown in Table 6, and the comparative alloys whose WC phase particle shape is rounded but whose composition range is outside the scope of the present invention have extremely short lives and are suitable for use as a cutting tool or the like targeted by the present invention. Turns out to be unsuitable.

[0018]

[Table 5]

[0019]

[Table 6]

[0020]

As described above, the present invention provides a WC-based cemented carbide WC containing TiC, which has never been neglected.
By controlling the phase particle shape in a rounded state as in the present invention, the toughness is remarkably improved as compared with the conventional alloy, and a stable life can be obtained even when used as a drill for drilling steel. Further, the alloy of the present invention is also suitable for intermittent turning of steel, which requires particularly toughness, and throw-away inserts for milling.

[Brief description of drawings]

FIG. 1 is a graph showing changes in transverse rupture strength when a solid solution carbide containing TiC is added to a WC-based cemented carbide.

FIG. 2 is a typical microstructure photograph of a cemented carbide containing a solid solution carbide containing TiC.

FIG. 3 is an electron micrograph of a cemented carbide according to the present invention.

FIG. 4 is an electron micrograph of a comparative cemented carbide.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hiroaki Murakami 20 Ishigane, Toyama City, Toyama Prefecture Fujikoshi Co., Ltd.

Claims (1)

[Claims] 1. A cemented carbide having a composition of 5 to 15% by weight of Co, 3 to 50% of TiC or TiC and MC (where M is Ta and / or Nb), and the balance WC and unavoidable impurities. In the alloy structure, the ratio of the number of ungrown WC particle phases (α1 phase) to the total number of WC particle phases is 30.
A tough cemented carbide, characterized in that it is ˜95%.