JPS62170451A - Sintered hard alloy - Google Patents

Abstract

PURPOSE:To improve the hardness and rupture toughness of a hard sintered alloy consisting of a hard phase of the carbide, nitride or carbonitride of a group IVa, Va or VIa metal of the periodic table and a binding phase of an iron group metal by controlling the average grain sizes of coarse grains and fine grains forming the hard phase. CONSTITUTION:A hard sintered alloy is composed of a hard phase of one or more kinds of compounds selected among the carbides, nitrides and carbonitrides of the group IVa, Va and VIa metals of the periodic table, 5-30wt% binding phase of an iron group metal and inevitable impurities. The hard phase is composed of a group of coarse grains and a group of fine grains, the ratio in average grain size between the groups is regulated to 1:>=3 and a structure of 0.25-0.9mum average thickness is provided to the binding phase. Thus, >=1,000 Vickers hardness (Hv) and >=10 rupture toughness (Kic) are obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to sintered hard alloys such as cemented carbide and cermet with improved breakage resistance for use in cutting tools and wear-resistant tools.

[Prior art]

Cemented carbide and cermet are widely used in the machining field as cutting tools and wear-resistant tools, but the processing conditions are becoming stricter year by year, and the demands on these hard sintered alloys are becoming more and more advanced. It is becoming difficult to respond by improving properties such as rupture strength. Therefore, these 1iil
! Efforts have been made to make various improvements in the combination of hard phase components and bonding metal phases in quality sintered alloys.

Among the uses of this hard alloy, micro-feed tools such as end mills and micro drills have a phenomenon in which micro-chipping occurs during use, which causes welding and shortens the life of the tool. This is because minute cracks start due to heat generation 9 and mechanical stress during cutting.

In order to delay the occurrence of this crack as much as possible, and so that the tool as a whole can withstand breakage even if a crack occurs, improvements have been made such as making the entire hard phase atomized and increasing the composition ratio of the binder phase. However, an alloy that can prevent both the breakage resistance of the entire tool and the propagation of microcracks has not yet been found.

(Problems to be Solved by the Invention) The present invention delays the occurrence of microcracks that occur in tool alloys as described above, and improves the overall abrasive resistance (breakage resistance) against tool breakage even if cracks occur. It is an attempt to coerce them.

In the case of WC-Co alloys, the smaller the thickness of the Co phase (bonding phase), which has lower strength, the less cracks will occur.

On the other hand, the difficulty of crack propagation is due to the high energy required for crack propagation, that is, within the Co phase>inside the WC grains, or wc-wc
The order is interface>WC-Co interface. When +c (fracture toughness) is used as a substitute characteristic to indicate the crack propagation resistance, as qualitatively shown in FIG. 2, the fracture toughness usually decreases as the hardness increases.

In this case, high hardness is comparable to finer particle size of the hard particles.

The present invention aims to improve fracture toughness and improve welding resistance, toughness, and heat resistance even with the same amount of binder phase and the same hardness. That is, the alloy properties are intended to be improved in the direction of B from A in FIG.

[Means for Solving the Problems] The present invention provides a hard phase that is one or more types of carbides, nitrides, and 3 carbonitrides of metals in group N a + V a r VT a of the periodic table; In a hard alloy consisting of one or more metal binder phases and unavoidable impurities, hardness and fracture toughness are improved by controlling the average particle size of the coarse and fine particles of the hard phase. It is something.

In the above, the hard phase refers to WC, TiC, and TiN.

MoC, CRtCs, TaC, TaNbC, TaN,
NbN, etc., and the ferrous metals are Fe, Ni, Go,
Its amount is 5-30% by weight of the total alloy.

The average particle size of the coarse particles in the hard phase and the size of the fine particles are 1:3: fine: coarse, or coarse: fine.
It is necessary that the above difference be made, and that the amount of coarse particles and the amount of fine particles be in a weight ratio of 1:1 to 1:3.

By controlling the dispersion state of the hard phase particles in this way, the mean free path of the binder phase is controlled, and as a result, when the alloy hardness Visokers hardness (Hv) is 1100 or more, the fracture toughness (Kic unit M N / m 3/2 ) is 10
A hard alloy with the above breakage resistance can be obtained. That is, the structure of the alloy of the present invention can be schematically expressed as shown in FIG.
Hard phase coarse particle group 1 and hard phase fine particle group 2 in binder phase 3
are dispersed, the occurrence of cracks is delayed by the presence of the fine particles, and the cracks 4 that have occurred are prevented from propagating by the coarse and fine particles.

In the case of the WC-Co system, which is a typical composition of cemented carbide, those that satisfy the above conditions have a lower fracture toughness than conventional cemented carbide containing only uniform fine grained WC, even with the same amount of -Co. Significantly improved.

Also, TiC, TaC, TaNbC, TaN, TiN,
In the case of the composite hard phase cemented carbide containing T1CN etc. Such characteristic improvements can be completely achieved.

If the particle size of the hard phase differs by less than 1:3, no improvement in fracture toughness will be observed compared to conventional hard alloys having a uniform fine-grained hard phase. That is, the effect of suppressing crack generation is small. Further, if the weight ratio of the coarse particles to the fine particles is other than 1:1 to 1:3 (fine:coarse) or coarse:fine (1:1 to 1:3), the effect of suppressing crack propagation will be small, and the refracting strength will tend to decrease.

This will be explained below using examples.

Example I WC powder and Co powder were mixed and the amount of Co was varied by 7 to 16%. Two types of WC'lt 1 degree were used to create an alloy with different particle size distribution as a hard phase. The hardness and Hv fracture toughness (CK IC) were measured and the results shown in Table 1 were obtained.

An end mill (φ5.02 blades) was made from these alloys, and the cutting speed V =
60m/min, A d = 5+no+ Rd
Table 1 also shows the results of dry cutting under the conditions of -1 mm and feed f = 0.05 mm/blade.

Example 2 A cemented carbide consisting of a hard phase consisting of WC-TiC-TaC and 10% Co was prepared with different hard particle sizes in the hard phase, and the Visocurs hardness and fracture toughness were measured. Table 2 shows the results. It is as follows.

Table 2 [Effects of the Invention] The alloy of the present invention has less cracking during processing, and as a result has improved welding resistance, and can be used as a cutting tool (throw-away tip, end mill) for materials that easily weld, such as austenitic stainless steel. The lifespan of has been improved.

Also, due to improved breakage resistance, the performance as a small diameter end mill or a micro drill for printed circuit boards has also been improved.

It has also been found that the cutting properties of the alloy of the present invention can be further improved by 1 when coated with wear-resistant coating by CVD or PV.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing the microscopic structure of the alloy of the present invention, and FIG. 2 is a comparative diagram showing the relationship between the hardness and fracture toughness of the alloy of the present invention and a conventional hard alloy. -A-1 Figure 2 Figure 11 Hard Maro (Hv)

Claims (3)

[Claims] (1) A binder phase with a weight ratio of 5 to 30% consisting of one or more hard phases of carbides, nitrides, and carbonitrides of metals in groups IVa, Va, and VIa of the periodic table and iron group metals, and unavoidable impurities. In a hard sintered alloy, the hard phase is composed of a coarse particle group and a fine particle group, the average particle size of the two differs by 1:3 or more, and the average thickness of the binder phase is 0.25 μ to 0.9 μ. Yes, Vickers hardness (Hv) is 1000 or more,
A sintered hard alloy having a fracture toughness (K_i_c) of 10 or more. (2) A sintered hard alloy according to claim 1, wherein the fine hard phase particles are 0.5μ or more and the coarse hard phase particles are 3μ or more. (3) A sintered hard alloy according to claim 1, wherein the hard phase is WC and the binder phase is Co.