JPS5814498B2 - super hard alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sintered hard alloy containing Ti and W that has significantly improved cutting properties.

Compared to WC-based alloys, titanium carbide-based alloys have a variety of excellent properties in terms of cutting characteristics, in addition to the characteristics that titanium carbide, which is a raw material, is inexpensive and lightweight.

First of all, it has oxidation resistance.
．． Ref ra
ctory Hard Metals, Mac Mi
llan Co. (1953) P371) et al.
The oxidation resistance of IC-based alloys is much better than that of WC-based alloys.

This characteristic is extremely desirable because it makes the tool less susceptible to deterioration due to oxidation during high-speed cutting where the tool is exposed to high temperatures.

The second concern is chemical affinity for metals.

On the tool surface exposed to high temperatures during cutting, chemical reactions such as diffusion and welding occur between the workpiece and the tool surface, and this accelerates tool wear as reported by Fukatsu et al. 29 (1965), 582) and others.

According to the results of these studies, it has also been found that TiC has an extremely low affinity for iron compared to WC.

This is a P series alloy for steel cutting that has been created empirically.
The wear resistance of this series of alloys is that of TiC.
This proves that it is significantly superior to alloys that do not contain .

Therefore, it is a natural consequence that a TiC-based alloy, in which TiCi is the majority, can suppress wear to an extremely low level due to its affinity with the workpiece material, for example.

TiC-based alloys with excellent properties as described above have attracted attention as future tools, and various alloys have been proposed, but their range of use is still limited.

The first reason is that it has poor toughness and is prone to chipping.

For example, it is known from experience that TiC-based alloys are more likely to chip than conventional WC-based alloys when used in places where they are subjected to impact forces such as interrupted cutting, or when machine tools have low rigidity. .

Additionally, the edge of the chip may be damaged due to curling of chips during cutting, which also indicates the brittleness of the TiC-based alloy.

One way to prevent this kind of brittleness is to round or chamfer the cutting edge of the tool to prevent the work material from directly hitting the sharp tip of the cutting edge, thereby reducing stress on the cutting edge. .

Another method is to increase the amount of bonded metal to improve the toughness of the alloy.

Although these two methods have achieved results in their respective fields, they cannot be said to be effective in all cases, related to the second reason for the limited use of TiC-based alloys, which will be discussed next. .

The second reason why the use of TiC-based alloys is limited is that the cutting edge deforms significantly under high temperature and high pressure.

Of the two methods for preventing brittleness mentioned above, the former causes a rise in the temperature of the cutting edge, while the latter reduces the hardness of the tool, which both promote deformation and narrow the range of use as a tool. There are many things.

More specifically, the deformation of the cutting edge limits the range of use of TiC-based alloys.

First, in heavy cutting equivalent to P20 and P30, which have large depths of cut and feed, the temperature of the cutting edge becomes high, so in Tic-based alloys, the cutting edge deforms significantly and cannot withstand cutting.

This is probably the main reason why TiC-based alloys are used only for light cutting.

Further, when cutting high-hardness materials, the temperature at the cutting edge increases significantly, so TiC-based alloys are also unsuitable in this case, and this is also a factor that limits the range of use of this alloy.

In addition, there are cases where the underlying cause of a chipped edge that appears to have nothing to do with the deformation of the cutting edge is the deformation of the cutting edge.

For example, TiC-based alloys are prone to chipping during high-speed, high-feed interrupted cutting, but this is due to the softening of the cutting edge.
It is thought that this is because the strength decreases and this leads to defects.

Furthermore, TiC-based alloys are said to be unsuitable for cutting cast iron, and this is also related to the deformation of the cutting edge.

It is well known that when cutting cast iron, the cutting mechanism is different from when cutting steel, and discontinuous chips are produced.

Therefore, in this case, the contact surface is shorter than in the case of steel cutting, and concentrated force is applied to the cutting edge.

In the case of cast iron, since graphite is used, it is a type of interrupted cutting, and in this case, instead of deforming the cutting edge, the softened part is removed, resulting in increased blank wear on the cutting edge.

The range of use of TiC-based alloys is still limited due to the two main drawbacks mentioned above, but the present invention
It is an object of the present invention to provide an alloy that is improved in these drawbacks.

The essential difference between conventional TiC-based alloys and WC-based alloys is WC.
This is thought to be due to the difference in properties between the crystal and the TiC crystal.

For example, it is a well-known fact that WC crystal has excellent strength and plastic deformation resistance at high temperatures, and Ti
In a method in which other elements are dissolved in C, the properties of TiC itself hardly change, and it seems that it is not possible to provide the high-temperature strength that WC has.

Therefore, in order to impart strength and plastic deformation resistance equivalent to those of a WC-based alloy to a Ti-based alloy, it is considered that it is an essential condition that the WC phase remains in the alloy.

By the way, when considering wear resistance, which is another important property of alloys, in general, the less WC phase there is, the better the crystal structure is B1 type (NaC), especially when cutting steel.
The smaller the amount of W in the hard phase (MC phase) of type I), the less the reaction between W and steel and the better the wear resistance of the alloy.

Of course, if we consider only the Ti-W-C system, the (Ti.W)C phase (
If the temperature is constant, the composition of the MC phase will be almost uniquely determined as a function of the W content (as the variation due to the C value is negligible near the stoichiometric value), and the composition of the WC phase will be constant as a function of the W content. It is impossible to improve the wear resistance of the (Ti.W) C phase.

By the way, regarding this MC phase, there is IVaVa at the M position.
A high melting point metal of Group VIa may be substituted, and N may be substituted at the C position.

The present inventors paid attention to this point, conducted intensive research, and by changing the composition of this hard phase, the crystal structure with low W content and high wear resistance was created with the M(C,N) type hard phase of B1. W.C.
We have discovered a method to improve the wear resistance of the alloy without impairing its toughness by coexisting with the phase.

The theoretical basis of the present invention will be described below.

As one index for considering the stability of the hard phase, the number of outer shell electrons (Valence Electron Concent
(hereinafter abbreviated as VEC).

The molecular formula of the hard phase contained in the alloy that is the object of the present invention is generally {(Group 3 metal) A (Group Va metal) B (Group 18 metal J
E a) (CXNY)Z ・・・・・・・・・・・・
...■However, it can be expressed as A+B+C=1, X0Y=1.

Therefore, as is well known, the VEC is VBC=4・A+5・B+6・C+4XZ+5YZ...
...It is calculated as ■.

Group IV metals include Ti, two or three metals containing Ti, and Group V metals.
Group A metals are one or more types, Group Vla metals are W or two or three types containing W, A, B, C, X, and Y are mole fractions, and Z is a nonmetal relative to the metal component. molar ratio of components,
0<A<1. There is a relationship 0<B<1.0<C<1.

The inventors investigated the relationship between VEC and crystal stability for carbonitride systems of group 3, va, and group metals, and found that vE
It has been found that the crystal is stable when C×D (D is a relation to the partial pressure of nitrogen in the atmosphere), but becomes unstable when vEC≧D.

Furthermore, if this unstable carbonitride crystal contains W, (Mo, M..., wU) (
CxNY ) Z → (Mo/, M, /,...
, WU') (CX'NY')z Cow (U-IJ') WC・
It was also found that the following reaction occurred and WC could be precipitated.

The reason for the restriction on Z is described below.

If Z is 0.85 or less, the WC and Fe group bond metal will react and a brittle phase will precipitate, which is impractical, and Z cannot be greater than 1 in normal sintering.

From the above, by selecting the composition of the hard phase so that VEC≧D, the amount of WC phase can be increased, and W in the M(C,N) phase can be increased.
The content can be reduced.

The value of D becomes smaller as the nitrogen partial pressure of the atmosphere increases, and this is thought to be because carbonitrides become relatively more stable as the nitrogen partial pressure increases.

Therefore, theoretically, it is possible to make the value of D extremely low by increasing the nitrogen partial pressure, but increasing the nitrogen partial pressure too much will inhibit the sinterability of the alloy, so in practice, the transformation partial pressure is 50m
It is below iHP.

Although the value of D also varies depending on the composition and homogeneity of the hard phase of the B1 crystal, it was experimentally confirmed that D≧8.6 within the scope of the present invention.

If an alloy having such a composition is sintered so that nitrogen does not escape, a WC phase and a double carbonitride phase will be present in the alloy.

Naturally, the composition of the alloy also has the following restrictions.

In order to increase the VEC, it is better to have a larger amount of N, but if it is too small, there is no effect, and if it is too large, the sinterability of the alloy will be inhibited.

Accordingly, according to the equation (2), 0.05≦Y≦0.50 is desirable, and among these, 0.10≦Y≦0.40 is the optimum range.

X is from 0.50 to 0.95, and if it is less than 0.5, sinterability will be impaired, and if it is more than 0.95, the WC phase will not exist.

(2) Of the Group 3 elements, W is an essential element from the purpose of the present invention, which is an alloy having WC crystals.

Since Mo improves the sinterability of the alloy of the present invention, adding 2% by weight or more of the entire alloy further improves the toughness of the alloy.

However, if it exceeds 60% by weight, wear resistance deteriorates.

Addition of Cr improves the corrosion resistance of the alloy. Group V elements increase the VEC and also improve the wear resistance and toughness of the alloy, so adding more than 2% by weight of the entire alloy will already improve the properties of the alloy, but adding more than 70% by weight will reduce the raw material. It is not practical because it is expensive.

Most preferably it is 5% to 50% by weight.

■Group 3 elements reduce VEC, so a small amount is desirable from the viewpoint of WC precipitation, but Ti has the advantages of being inexpensive, improving the sinterability of the alloy, and increasing the strength of the B1 crystal phase. Therefore, M(
The amount of metal elements contained in the C, N) phase cannot be reduced to less than 20 atomic percent.

However, when Ti exceeds 80 atomic %, heat resistance decreases. Zr improves wear resistance but slightly decreases wear resistance.

Hf also improves wear resistance. The amount of the binder phase made of Fe group metal is 0.01 by weight of the total amount of the B1 crystal phase and the WC phase.
If it is less than 0.5 times, the alloy will become brittle, and if it is too much, for example, 0.5 times or more, the alloy will have low heat resistance and cannot be put to practical use.

Such alloys have characteristics such as excellent wear resistance and heat cracking resistance.

The gist of the present invention is to further improve the wear resistance of the present alloy.

As can be seen from equation (①), if A, B, C, and Z are constant, Y
The higher the value (N amount), the higher the VEC.

Now, considering the case where the VEC of the nitrogen-containing alloy is slightly higher than D, a WC phase exists in this alloy.

If some nitrogen is replaced with carbon to lower the VEC to below D, the WC phase in the alloy disappears.

By the way, when it comes to alloys whose composition is almost constant, W
The absence of C phase improves the wear resistance of the alloy.

However, the toughness of the alloy decreases. Therefore, B1 crystal phase and W
If an alloy consisting of a C phase and a binder metal phase that binds these phases is made without the WC phase only on the surface, the alloy will have excellent wear resistance without sacrificing properties.

As can be easily inferred from the above facts, the method involves selecting an alloy composition containing nitrogen so that its VEC is slightly higher than D, and then reheating it during or after sintering to reduce nitrogen on the surface. It is sufficient to set the VEC of the surface to D or less so that only the surface has a composition free of WC phase.

In order to reduce nitrogen on the surface by reheating during or after sintering, the atmosphere may be evacuated or carburized.

We have described the case where VEC is slightly higher than D, but even if the initial composition is V E C >> D, the amount of WC on the surface is reduced by reducing the nitrogen on the surface, so the wear resistance of the surface is improved. and has the same effect as above.

In addition to the above-mentioned effects, reducing surface nitrogen also has the following effects.

In particular, when processing in a vacuum, surface nitrogen dissipates and even if we consider the diffusion of C from inside, Z decreases as Y decreases.
will also decrease.

Therefore, the decrease in nitrogen is caused by Suzuki et al. (Suzuki, Hayashi: Trans.
．． Japan Inst. Metals, 7, (196
6) 99; Dan (1967) 253; Dan ( 1 9 6
8) 77; Suzuki, Yamamoto: Inst. J. Pow
Der Met. 3 (1967) 17)
C-TiC-Co, WC-TaC-C
o, WC-Ti has the same effect as the reduction of C in the iC-TaC-Co system, and the bonded phase (Co or/and Ni)
When the solid solution amount of W is increased and further decreased, η phase (Co3W3C) is precipitated on the surface.

When a large amount of W is contained in the binder phase, the binder phase is hardened and the wear resistance of the alloy is improved.

Precipitation of a small amount of η phase is also effective in improving the wear resistance of the alloy.

Examples are shown below.

Example 1 96% by weight of titanium nitride, 14.1% by weight of titanium carbide, 3% by weight of 76% by weight of tungsten carbide were mixed, hot pressed at 1800° C. for 1 hour, and then crushed to produce a composite carbonitride.

Analysis result The composition of this composite carbonitride is (TiO.75W
0.25) (C0.70 N0.30).

The X-ray diffraction results revealed that it had a Bl type crystal structure.

The above composite carbonitride 49.4% by weight Ta0.75Nb0,
25C19. 1% by weight, WC21.7% by weight, Co9
．． 8% by weight was weighed out, acetone was added, and the mixture was wet-mixed using a stainless steel ball mill using carbide balls.

Add 3% by weight of camphor to this mixed powder, and add 2t/c
Embossed with m2.

This stamped body was sintered under a vacuum of 10-3 mmHg up to 1200°C, at a sintering temperature of 1380°C from 1200°C, and under a nitrogen partial pressure of 1 Torr until the end of sintering.

When the obtained alloy A was observed under a microscope, it was found that the hard phase was 2
Recognized.

These were a Bl type hard phase and a WC phase.

Separately, an alloy having the same composition was sintered in a vacuum up to 1380° C. while flowing a CH4-H2 mixture at a pressure of ITorr at the sintering temperature.

Only a Bl type hard phase and a Co phase were observed on the surface of the obtained alloy B.

The interior consisted of a WC phase, a Bl type hard phase, and a Co phase.

Wear resistance tests and toughness tests using interrupted cutting were conducted using this alloy.

The results are shown in Table 1 along with comparative alloys.

It will be clear that the alloy according to the invention is extremely superior.

The composition of carbide PIO in the table is in weight%: 51% WC122%
TiC, 18% TaC, 9% Co, TiC-Mo
-The composition of the Ni-based cermet is 80% TiC, 1% by weight.
0% Mo2C, 10% Ni.

Example 2 (Ti0.75W0.25) (
CO,7N0.3)1 was created.

This composite carbonitride contained 58.0% by weight of TaO. 75NbO
．． 25C 27.0% by weight, WC 3.9% by weight, Ni 3.
5% by weight and 7.6% by weight of Co were weighed out, and a stamped body was prepared in the same manner as in Example 1.
MP was vacuum sintered.

The surface 30μ of the obtained alloy contains a Bl type hard phase and a Co
The inner part was a WC phase, a Bl-type hard phase, and a Co phase.

The lattice constant of the Co phase on the surface was 4.565 Å, and the lattice constant of the portion where WC was precipitated was 4.550 Å, and it was confirmed that the amount of W in the Co phase was greater on the surface than in the interior.

Using this alloy, a wear resistance test and a toughness test by interrupted cutting were conducted under the same conditions as in Table 1.

As a result, the surface wear of the present alloy was 0.04 mm, the crater wear was 0.02 mm, and the interrupted cutting test result was 1000.
I was able to cut through the cycle without chipping.

Claims (1)

[Claims] 1. The hard phase structurally contains a WC phase, W and Ti,
The crystal structure consists of a phase of B 1 (NaCl type crystal), and the molecular formula of the entire composition of the hard phase is generally {(Group ■a metal) A (Group Va metal) B (Group Via metal) c) (CxNy)z [However, Group IVa metals include Ti or two types containing Ti, T
Ti is 20 to 80 atomic weight ratio for three types including i, Group Va metal is 2 to 70 weight ratio for one or more types, Group Vla metal is W or 2 types containing W, and 3 types containing W. When MO is included, Mo is 2 to 60% by weight, A, B, C,
X, Y are the mole fractions of each element, Z is the mole fraction of nonmetallic elements to metal elements, A+B+C=1, X+Y=1,0
<A<1, O<B<1, O<C<1, 0.5
0≦X≦0.9 5 , 0.0 5≦Y≦0.5 0
, 0.8 5≦Z≦1.0 0 , 4A+5 B
+6C + 4 A super hard alloy that is characterized by being hardened.