JPS593533B2 - hard alloy - Google Patents

Description

[Detailed Description of the Invention] Tungsten, which is used in cemented carbide, exists in only a small amount on the earth, so it is a precious metal and has continued to rise in price in recent years as a so-called strategic material.

Therefore, it has become important to replace tungsten in cemented carbide.

One solution is to use so-called ceramic tools based on alumina or cermet tools based on titanium instead of cemented carbide tools.

However, it is also true that there are many cases in which these methods cannot replace cemented carbide in terms of toughness.

Therefore, the possibility of replacing tungsten carbide in cemented carbide with molybdenum carbide has been investigated.

The present invention relates to the latter.

Tungsten carbide (WC) to molybdenum carbide (MoC)
The biggest problem in the case of substitution is that MoC is unstable and brittle Mo2C is precipitated according to the reaction formula: 2MoC-+Mo2C+C.

As a way to solve this problem, a method has been proposed in which a part of MO in MoC is replaced with W to stabilize it in a simple hexagonal (Mo, W) C phase (Japanese Patent Application Laid-Open No. 51-14
However, according to this method, it is necessary to maintain heating at around 1400° C. for a long time during cooling during production of the raw material (Mo, W)C, which is a major industrial restriction.

The inventors found that the simple hexagonal phase could not be stabilized by not only replacing the metallic elements (-Mo) of M and C with W, but also replacing the non-metallic elements (-〇) with other non-metallic elements. That's what I thought.

As a result, it was found that when part of the carbon is replaced with oxygen and part of the Mo is replaced with W at the same time, a simple hexagonal phase can stably exist even when sintered with a so-called bonding metal whose main component is an iron group metal. Understood.

Furthermore, it was found that in this case, even if a small amount of nitrogen was mixed in, the stability did not change.

More specifically, it has been found that there is an upper limit and a lower limit to the amount of oxygen that exhibits the above effects.

The amount of oxygen is 00.02 to 10.0 in the nonmetallic constituent elements of the hard phase.
A weight ratio is preferable, and if it is less than 0.022% by weight, no effect is observed, and if it is more than 10.0% by weight, it impairs sinterability, which is not preferable.

It has also been found that there are limits to the preferred amount of tungsten in relation to the amount of oxygen.

- Although the details of the reason are unknown, it is thought that the affinity between oxygen and tungsten is inferior to the affinity between oxygen and molybdenum.

Therefore, in order to increase the amount of oxygen, it is preferable to decrease the amount of tungsten, but industrially, the amount of tungsten must be 1 to 90% by weight of the elements constituting the hard phase.

This is because if it is more than 90% by weight, it is impossible to stably contain oxygen, and if it is less than 1% by weight, the simple hexagonal phase lacks stability.

Furthermore, it has been experimentally confirmed that nitrogen coexisting at this time does not have an adverse effect up to 10 times the oxygen content in atomic terms.

It is known that it is advantageous to form a Bl type solid solution in addition to the simple hexagonal phase mainly for cutting tools.

The constituent elements are Ti and zr. Hf, V, Nb, Tat
These are so-called IV a tVa and Via group transition metals such as cr, Mo, and W, and nonmetallic components such as C, N, and O.

It is desirable that the amount of the B1 type solid solution is changed depending on the cutting application, but substitution may be made in the range of 0.1 to 90 volume.

In this case, there is no change in the limitations regarding the amounts of oxygen and tungsten even if the double carbide of tungsten and molybdenum is replaced with a Bl type hard carbide.

Regarding the nitrogen content, it was also found that since IVa and Va group elements easily combine with nitrogen, substitution up to 0.5 times the total of these elements does not have an adverse effect.

Therefore, in this case, the nitrogen content is 1 atomic fraction of the oxygen content.
It should be less than 0 times or 0.5 times the sum of IVa and Va group atoms, whichever is greater.

As for the alloy, it is desirable that the iron group metal has a weight coefficient of 3 to 50% by weight of the composition.

If the weight ratio is 3 or less, it will be too brittle, and if it exceeds 50 weight ratio, the high temperature properties will deteriorate.

In addition, when the iron group metal becomes a bonding phase, rV a tV
It is natural to form a solid solution with Group VIa metals, and Al
The effects of the present invention are not lost by the addition of elements having solid solubility with these, such as Si tcutAg.

Note that the effects of the present invention are essentially the same whether the simple hexagonal phase is one phase or separated into two or more phases.

The method for analyzing oxygen, which plays an important role in the present invention, is as follows.

After crushing the alloy into small pieces of approximately 1 square inch, they were heated at 2500°C in a vacuum.
This is the amount of oxygen detected when dissolved in a Ni bath at the above temperature and the gas generated at this time measured by gas chromatography or infrared absorption method.

Examples will be described below.

Example 1 2μ of MO2C, 7μ of WC powder, carbon powder, and a trace amount of Co as a diffusion aid were added to make the composition of the final carbide (M
oo, 8. A mixture of Wo and 2) C was reacted at 2000° C. for 30 minutes in a hydrogen stream.

When the reaction product was examined using X-rays, two phases of WC and Mo2C were detected.

This was heated to 1400° C. in a furnace in which carbon monoxide gas was continuously supplied, with the furnace internal pressure set to 300 Torr again, and then immediately cooled.

In the X-ray diffraction results of this carbide, the Mo2C peak completely disappeared, and all of the carbides showed a simple hexagonal type crystal form of the WC type.

Adding Co powder to this (Mo(,B W(,2)C),
The composition of the final alloy is (Moo, s Wo, 2) CCo
It was set as 10 weight section.

The mixed powder was stamped, shaped into a predetermined shape, and then sintered.

The sintering conditions were heating to 1000°C under a vacuum of 1O-2 Torr and heating from 1000°C to 1400°C under a reduced pressure of 300 Torr in a carbon monoxide atmosphere.

At the same time, an alloy was prepared in which carbon monoxide was not used in the carbide production process and sintering process, and compared with the method of the present invention.

The contents in the table below are the same as above.

In the method of the present invention, the reaction rate of the (Mo-W)C-Co alloy (=bond carbon in the alloy/theoretical bond carbon) is high, and there are no precipitates when looking at the structure of the alloy.

On the other hand, in the conventional method of reducing oxygen in the alloy, the reaction rate is only 98%, and free carbon is released even though the amount of carbon in the alloy is small.

Mo2C is also found in the tissue.

This is considered to be because the alloy was decomposed into MoC-+Na2C+C during the sintering process.

In the method of the present invention, the reaction rate is high and the alloy structure is normal.

This is probably because oxygen in the alloy prevents MoC from decomposing and also plays a role in stabilizing the simple hexagonal phase.

Example 2 - 60 weight (MOo, 7 Wo, 3) C530
(Tio, 7 Mo□, 3)C by weight and Co by 10 weight were blended and wet mixed in a ball mill.

The mixed powder was heated at 1O-2T to 800℃ in a stamping type vacuum furnace.
Sintered under vacuum of orr, 30 to 800-1400℃
Sintering was completed by heating in a Torr carbon oxide atmosphere and holding at 1400° C. for 1 hour.

At the same time, in order to reduce the amount of oxygen in the alloy, the entire sintering process was
Sintering was also carried out at O-2 Torr or less.

The oxygen content in the alloy was varied using the above two methods, and the differences in properties were investigated in detail.

The analysis results and A-value structure observation results of the obtained alloy are shown in Table 2.
It was like that.

A cutting test was conducted using this, and the results were as follows.

As understood from the above examples, it is clear that the alloy of the present invention has excellent wear resistance and rigid edge deformability.

Example 3 TaC (Moo, 7Wo, 3)C110 by weight and Co by 20 weight were blended and wet mixed in a ball mill.

After stamping the mixed powder, heat it in a vacuum furnace to 600°C at 1O-2.
It was heated under a vacuum of Torr, and heated from 600° C. to 1400° C. under a reduced pressure of 95 Torr in a carbon monoxide atmosphere.

Further, Table 4 shows the results of comparing the alloys obtained by sintering the same embossed body in a vacuum of 10-2 Torr or less with the above-mentioned products of the present invention.

A cutting test was conducted on the alloy of the present invention under the following conditions.

Tool: 5NG432 Holder: FNllR-44 Work material: 5US304 Cutting conditions: V = 80 mAn i n: f = 0
．． 30mm/rev: a=t, S Shochu Machine Machine 2 NC lathe using water-soluble cutting material The alloy of the present invention was cut for 5 minutes and the flank wear was Q, 12
m1n, whereas the conventional alloy had flank wear of 0.42 mm after 2 minutes of machining and became uncuttable.

For comparison, when cutting with commercially available M-30 cemented carbide, the flank wear reached 0.83 after cutting for 5 minutes.

Claims (1)

[Claims] 1. An alloy in which a hard phase is a double carbide of tungsten and molybdenum having a simple hexagonal crystal structure, and this hard phase is bonded by a bonding metal mainly composed of an iron group metal. In a hard alloy in which the simple hexagonal phase is stabilized by substituting carbon in the alloy with oxygen, the amount of oxygen in the nonmetallic constituent elements of the hard phase is 0. .0
2 to 10.0% by weight, and tungsten is 1 to 90% by weight of the hard phase metal constituent elements. 2 In an alloy in which a double carbide of tungsten and molybdenum having a simple hexagonal crystal structure is used as a hard phase, and this hard phase is bonded by a bonding metal mainly composed of an iron group metal, the iron group metal accounts for 3 to 50% of the composition. 0 of the double carbides of tungsten and molybdenum in hard alloys in which the simple hexagonal phase is stabilized by replacing carbon in the alloy with oxygen.
．． 1 to 90% by volume is substituted by Bl-type hard carbide of group IVa, Va, and VIa transition metal atoms, and the oxygen content is 0.02 to 10% by volume in the nonmetallic constituent elements of the hard phase.
0 weight ratio, tungsten is 1 to 1 among the hard phase metal constituent elements
A hard alloy characterized by a weight coefficient of 90.