JPS582580B2 - 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 superior properties in terms of cutting properties, in addition to the fact that titanium carbide, which is a raw material, is inexpensive and lightweight.

First, in terms of oxidation resistance, Pieschwarzkopf (P.S.
chwarzkopf: Refractory Har
d Metals. Mac MillanCo. (19
According to 53) P371) et al., the oxidation resistance of TiC-based alloys is much better than that of WC-based alloys.

Such characteristics are extremely desirable as they are less susceptible to deterioration of the tool due to oxidation during high-speed cutting where one 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. (Fukatsu, Yuhara: Journal of the Japan Institute of Metals, 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 wear is extremely suppressed in a TiC-based alloy in which the TiC content is the majority, for example, due to its affinity with the workpiece material.

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 equal 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 workpiece from coming into direct contact with the sharp tip of the cutting edge, thereby reducing stress on the cutting edge. be.

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

Although these two methods have each achieved success 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, and the latter reduces the hardness of the tool, which both promote deformation and narrow the range of use as a tool. many.

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

First, in heavy cutting equivalent to P20 or P30, which has a large depth of cut and feed, the temperature of the cutting edge becomes high, so the TiC-based alloy will significantly deform the cutting edge and will not be able to withstand cutting.

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

Furthermore, 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 flank wear on the cutting edge.

Although the range of use of TiC-based alloys is still limited mainly due to the above two drawbacks, the object of the present invention is to provide an alloy that has improved 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 crystals have excellent strength and plastic deformation resistance at high temperatures, and when other elements are dissolved in TiC, the properties of TiC itself hardly change, and the properties of WC do not change. It is presumed that it cannot have high-temperature strength.

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, and especially when cutting steel, generally speaking, the less WC phase there is, the better the Bl-type crystal phase (compounds with NaCl-type crystal structure). In the present invention, ■a group, Va group,
The smaller the amount of W in a group VIa solid solution (refers to a crystal in which C and N have a NaCl structure), 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 composition of the (Ti.W)C phase (also called MC phase), whose WC content and crystal structure are Bl type, is as follows if the temperature is -5. W
It is impossible to improve the wear resistance of the C phase while keeping the amount of the C phase constant (Ti.W).

By the way, regarding this MC phase, IVa and V are placed at the M position.
A high melting point metal of Group Ia may be substituted, and N may be substituted at the C position.

The present inventors paid attention to this point, carried out intensive research, and by changing the composition of this hard phase, we succeeded in creating an M(C,N) type hard phase of Bl with a low W content and high wear resistance crystal structure. and 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 IVa metal) A (Group VIa metal).

)(CXNY)Z ・・・・・・・・・・・・・・・
・・・・・・・・・・■However, A+C=1, X+Y=
It can be displayed as 1.

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

As a result of examining the relationship between VEC and crystal stability for carbonitride systems of group IVa and VIa metals, the inventors found that although this stability is also affected by the nitrogen partial pressure of the atmosphere, it is the subject of the present invention. It has been found that the crystal is stable when VEC<8.6, but becomes unstable when VEC≧8.6.

Furthermore, if this unstable carbonitride crystal contains W, (MoM'p...Wu)(CXNY)Z
→(Mo', M'p', ......, Wu')
(CX'NY')Z'+(u-u')WC...
It was also found that the following reaction occurred, and WC could be precipitated.

Since a denitrification reaction also occurs along with the above reaction, in order to make this WC remain stable and in large quantities in an alloy, sintering under a high vacuum of 10-4 mmHg or less, where denitrification is severe, is not desirable, and depending on the composition, 10-1Torr to 200T
It is effective to use a stable carbonitride that crystallizes under a nitrogen partial pressure of orr and contains Ti and W as a raw material.

From the above, by selecting the composition of the hard phase so that VEC≧8.6, it is possible to increase the amount of WC phase and reduce the W content in the M(CN) phase.

In order to increase the VEC, the higher the amount of N, the better; however, if it is too small, there is no effect, and if it is too large, the sinterability of the alloy will be inhibited.

Therefore, according to the formula (2), 0.05≦Y≦0.30 is desirable, and among these, 0.10≦Y≦0.25 is the optimum range.

Among the Group VIa 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 IVa elements reduce VEC, so it is preferable to use them in small amounts, but Ti has the advantages of being inexpensive, improving the sinterability of the alloy, and increasing the strength of the hard phase, so the crystal structure is similar to that of B1. The amount of metal elements contained in the type M (C, N) phase cannot be reduced to less than 20 at %.

Moreover, if it exceeds 80 atomic %, the strength will deteriorate.

Zr and Hf also improve wear resistance.

The amount of binder phase is 2 to 33% by weight in the alloy, but if it is less than 2%, the alloy becomes brittle, and if it is more than 33%, the alloy has low heat resistance and cannot be used for practical use.

Next, regarding the story of Z, when 1<Z, free carbon is Z<0.8
5, the η-type embrittlement phase (for example, Co3W3C) precipitates and embrittles the alloy, so 0.85<Z<1 is desirable.

Note that Fe, Co, and Ni are suitable as the binding metal, but as a matter of course, when these metals become the binding phase, they contain constituent elements of the hard phase.

Therefore, the constituent elements of the hard phase are determined in advance by Fe, Co, and Ni.
It is also effective to use it as a bonding metal by alloying or mixing with.

Furthermore, there are problems specific to nitrogen-containing alloys in improving the properties of the bonded metal.

That is, nitrogen may dissolve in the liquid metal during sintering, and this may precipitate as bubbles during cooling after sintering.

This phenomenon embrittles the alloy and must be prevented.

Although it is effective to increase the cooling rate of the alloy, it is particularly desirable to maintain the cooling rate during the process from the sintering temperature to the disappearance of the liquid phase at 20° C./min or more.

It is also effective to maintain the pressure of the atmosphere during cooling higher than the pressure during sintering.

This will be explained in detail below using examples.

Example 1 Titanium nitride 9.6% by weight, titanium carbide 14.1% by weight,
Mix 76.3% by weight of tungsten carbide and heat at 1800℃
After hot pressing for 1 hour, the mixture was pulverized to produce a double carbonitride.

As a result of analysis, the composition of this double carbonitride is (Ti0.75W0.25) (C0.70N0.30)
It was 1.0.

49.4% by weight of this double carbonitride, 40.7% by weight of WC
, 9.8% by weight of Co were measured, acetone was added thereto, and the mixture was wet-mixed using a stainless steel ball mill using a cemented carbide ball.

Add 3% by weight of camphor to this mixed powder at 2t/cm
Embossed with 2.

This stamped body was sintered under a vacuum T 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 (1) was observed under a microscope, two hard phases were observed.

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

A wear resistance test and a toughness test using interrupted cutting were conducted using this alloy.

It is shown in Table 1. ★Composition: 540% by weight WC-19.0%T
iC-18.0%TaC-90%Co ★★Cutting conditions: Work material SCM3■, HS=40, cutting speed 170m/min, depth of cut 1.5mm, feed 0.36
mm/rev, cutting time 10 minutes★★★Cutting conditions: Work material S50C (grooved), cutting speed 150m/min, depth of cut 2.0mm, feed 0.45m
It is clear that the alloy of the present invention is superior in terms of m/rev.

Example 2 A large number of alloys were created according to Example 1.

Table 2 shows the analyzed composition (expressed in mole fraction) and the results of the cutting test.

Claims (1)

[Scope of Claims] 1. A superhard alloy in which the hard phase is bonded by 2 to 33% by weight of an iron group metal in the alloy, in which all components of the hard phase are {(Group IVa metal) A (Group VIa metal) C}(CX
NY)Z, and the IVa group metal is Ti or Ti
Group VIa metals are W or two or three types containing W, and A. C. (A.C. is the mole fraction,
Z is the molar ratio of the non-metal component to the metal component) A+C=1, X+Y=1 0<A<1, 0<C<1 4A+6C+4XZ+5YZ≧8.6 0.05≦Y≦0.30, 0. There is a relationship of 85≦2≦1.00, and these two hard phases exist in the alloy structure: a WC phase with hexagonal type crystals and a carbonitride phase with NaCl type crystals. A superhard alloy characterized in that the carbonitride contains Ti in an amount of 20 to 80 at% of the metal atoms in the carbonitride.