JPH03202404A - Combined hard alloy material - Google Patents

Abstract

PURPOSE:To drastically improve wear resistance while keeping excellent toughness by manufacturing a combined hard alloy material composed of sintered hard alloy in the center part and sintered alloy steel on the outer circumferential part under the specific condition. CONSTITUTION:The sintered hard alloy in the center part has composition composed of 50-95vol% one or more kinds of carbide, nitride, carbo-nitride of IVa, Va, VIa group elements in the periodical table and the balance of iron group metal with inevitable impurities. Further, the sintered alloy steel on the outer circumferential part is constituted of dispersing 15-60vol% first hard phase of TiN particles having <=0.3mum particle diameter and 1-10vol% second hard phase of TiN particles having 1-3mum particle diameter into 30-84vol% alloy steel of bonding phase. Then, this alloy steel is composed of wt.% of 2.5-4.5% Cr, 1.5-5.0% Mo, 2.0-6.0% W, 0.3-1.2% C, 1.5-15% Co, <=0.5% Mn, <=0.5% Si and the balance of Fe with inevitable impurities, and the intermediate part between the center part and outer circumferential part, has the composition, which is varied continuously or stepwise from the composition in the center part to the composition on the outer circumferential part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a composite hard alloy material used as a material for cutting tools and the like.

[Prior Art] High-speed tool steel or cemented carbide is most commonly used as a material for cutting tools and the like.

High-speed tool steels are mainly Cr, Mo, and WSV.

It is an alloy steel containing Co and C as alloy components and having Fe as a matrix. In high-speed tool steel, by adjusting each alloy component, properties suitable for the tool material can be adjusted, and at the same time, the properties can be changed by heat treatment.

- High-speed tool steel for boat fishing has excellent toughness and is therefore used as a material for cutting tools that require high reliability. Manufacturing methods for high-speed tool steel include melt casting,
The atomized powder is subjected to hot isostatic pressing (HIP, Hot
Powder metallurgy methods are widely used, in which the powder is solidified by methods such as 1sostat pressing.

Furthermore, in order to add wear resistance to high-speed tool steel which has excellent toughness as described above, a method has been proposed in which the amount of carbides and nitrides is increased. For example, JP-A-55-583
No. 50 and Japanese Unexamined Patent Publication No. 58-181848 disclose a method of mixing and sintering high-speed tool steel powder with powders such as carbides and nitrides to increase the amount of carbides and nitrides in the matrix. has been proposed as a method to do so. Furthermore, Japanese Patent Publication No. 60-18742 proposes a material in which extremely fine TiN particles are dispersed in a matrix of high-speed tool steel. JP-A-60-2648 and JP-A-61-179845 disclose a high-speed tool steel in which extremely fine TiN particles are dispersed in a matrix;
Tool materials composited with alloy steels such as high-speed tool steels have been proposed.

On the other hand, cemented carbide is an alloy obtained by sintering carbides such as WC, TtC, TaC, and Nbc using Co'pNi as a base. Although this cemented carbide is inferior to high-speed tool steel in terms of toughness, it has excellent high abrasion resistance, making it a tool material that exhibits its characteristics in high-speed cutting. The properties of cemented carbide suitable for use as a tool material can be adjusted by changing its composition, but the properties can also be adjusted by appropriately changing the grain size of its hard phase. Note that cemented carbide can be manufactured by a powder metallurgy method consisting of a series of steps of mixing, pressing, and sintering powder as a raw material.

[Problems to be Solved by the Invention] As described above, although high-speed tool steel has excellent toughness, it has insufficient wear resistance, so it is difficult to use it as a tool material suitable for high-speed cutting.

In order to improve the wear resistance of high speed tool steels, increasing the alloying content and increasing the amount of carbides in the matrix are commonly used.

However, it is not easy to achieve improved wear resistance while maintaining the excellent toughness that characterizes high-speed tool steel.

In other words, by increasing the alloy components, the amount of carbides in high-speed tool steel increases, and the wear resistance increases, but on the other hand,
A rapid decrease in toughness occurs. In particular, when manufactured by the melt casting method, the volume of carbides in high-speed tool steel is at most about 15% by volume, and if more than this amount of carbides is included in the matrix, it cannot be used as a practical tool. Unable to obtain toughness. Further, although the amount of carbides can be increased to some extent by powder metallurgy, the amount of carbides that can be increased is about 30% by volume at most.

By mixing powders such as carbides and nitrides with high-speed tool steel powder,
According to the sintering method, it is theoretically possible to contain any amount of carbide or nitride. However, even in this case, it is inevitable that as the hard phase increases, the toughness will decrease. - When powders with a particle size of several microns are mixed into the film, compression molded, and then sintered, as the amount of hard ceramics such as carbides and nitrides increases, the grain boundaries of the powder of high-speed tool steel increase. carbides and nitrides aggregate in a network. When carbides and nitrides aggregate in this way, the toughness decreases to an unacceptable degree. As a countermeasure to this problem, it is possible to make carbides and nitrides into ultrafine particles on the order of submicrons. However, such ultrafine particles tend to aggregate, and it is not easy to uniformly disperse them. Therefore, it is currently impossible to obtain a structure of high-speed tool steel in which carbides and nitrides are dispersed so as to have desired properties.

Furthermore, since the elastic modulus of high-speed tool steel is smaller than that of cemented carbide, which will be discussed later, deformation during cutting increases.
There was a problem in that it could not be used for applications such as tools that required high accuracy.

On the other hand, unlike high-speed tool steel, cemented carbide has excellent wear resistance but does not have sufficient toughness.

Therefore, cemented carbide is not used as a material for tools that require reliability. As a method of improving the toughness of cemented carbide, a method of making carbides in the hard phase finer has been adopted. However, this method also has its limitations, and the toughness obtained falls far short of that of high-speed tool steel. Usually, the amount of carbide contained in cemented carbide is about 80 to 90% by volume. In order to improve toughness depending on the application, cemented carbide is manufactured with a composition in which the amount of carbide is reduced to about 60% by volume, but the wear resistance rapidly decreases and it cannot be used as a material for cutting tools. .

As mentioned above, high-speed tool steel and cemented carbide used as materials for conventional cutting tools each have drawbacks.
In practice, they can only be used under conditions that do not cause these drawbacks. Therefore, there was a problem that the characteristics of high-speed tool steel or cemented carbide could not be fully exhibited.

Therefore, an object of the present invention is to provide a composite hard alloy material that maintains the excellent toughness characteristic of high-speed tool steel and at the same time has significantly improved wear resistance.

[Means for Solving the Problems] A composite hard alloy material according to the present invention includes a central portion made of a sintered hard alloy, and an outer peripheral portion covering the central portion and made of sintered alloy steel. The sintered hard alloy contains at least 50% by volume and 95% by volume of one or more of carbides, nitrides, and carbonitrides of Na, Va, and VIa group elements of the periodic table, and the remainder is iron group elements. Consists of metals and unavoidable impurities. The sintered alloy steel constituting the outer peripheral portion includes a first hard phase, a second hard phase, and a bonding phase. The first hard phase is 15% by volume or more6 in the outer peripheral portion.
Contains 0% by volume or less, and has a particle size of 0. TiN less than 3μm
Consists of particles. The second hard phase contains 1% by volume or more and 10% by volume or less in the outer peripheral portion, and has a particle size of 1μm or more and 3μm.
It consists of TiN particles with a size of less than m. The binder phase contains 30% by volume or more and 84% by volume or less in the outer peripheral portion, and is made of alloy steel for dispersing and binding the first hard phase and the second hard phase therein. The alloy steel contains 2.5% by weight of Cr.
4.5% by weight or less, Mo 1.5% by weight or more and 5.0% by weight
Weight% or less, W from 2.0% to 60% by weight,
C: 0.63% by weight or more and 1.2% by weight or less, Co: 1.5% by weight
% by weight or more and 15% by weight or less, Mn not more than 0.5% by weight,
It contains 0.5% by weight or less of Si, and the remainder consists of Fe and unavoidable impurities.

The intermediate portion between the center portion and the outer circumferential portion has a composition that changes continuously or stepwise from the composition of the center portion to the composition of the outer circumferential portion. This intermediate part is 100μm or more and 5m
It is preferable to have a thickness of m or less.

Preferably, 50 atomic % or less of Ti in TiN is 2', Hf, V, Nb5Ta, Cr.

It may be substituted with one or more elements selected from the group consisting of Mo, W, Ai, and Si.

Preferably, 50 atomic % or less of N in TiN may be substituted with one or more elements selected from the group consisting of ESC and O.

Furthermore, the thickness of the outer peripheral portion made of sintered alloy steel is 0.0
8 mm or more, and the total thickness of the composite hard alloy material is 0.
It is sufficient if it is 3 or less.

[Function] According to the composite hard alloy material according to the present invention, TiN particles as a hard phase dispersed in the sintered alloy steel constituting the outer peripheral portion have wear resistance that is insufficient in high-speed tool steel alone. enhance TiN has a Vickers hardness of Hv2000k.
g/mm2, - Hv8 of high-speed tool steel for boat fishing.
The hardness is more than twice that of 00 to 1000 kg/mm2. By dispersing this hard TiN, the hardness of the high-speed tool steel becomes HvlO00 kg/mm2 or more, and a significant improvement in wear resistance is achieved. Furthermore, TiN has little reactivity with steel, suppresses adhesive wear during cutting, and improves the surface roughness of the cut surface.

According to the conventional technology for dispersing TiN as a hard phase into high-speed tool steel, the strength of the tool steel sharply decreases as the amount of TiN increases because the TiN particles are large. On the other hand, according to the present invention, the particle size of the TiN particles is reduced to 0.
．． By suppressing the thickness to 3 μm or less, the TiN particles are uniformly and finely dispersed, making it possible to reduce the decrease in strength.

The TiN particles as the basic hard phase need to be finely dispersed as described above. However, by dispersing some TiN particles as a hard phase to have a constant particle size of 1 μm or more, it is possible to suppress the cracks generated in the matrix from propagating, and as a result, Fracture toughness value improves. In addition, due to the presence of TiN particles having a particle size of 1 μm or more,
Squeezing wear is suppressed. If the particle size of such coarse TiN particles is less than 1 μm, the above effects will not be sufficient;
If the thickness exceeds 3 μm, the strength will decrease.

Furthermore, if the amount of coarse TiN particles is less than 1% by volume, the above effects cannot be achieved, and if it exceeds 10% by volume, the strength will drop sharply as described above. In addition, if the particle size is 0. The amount of TiN particles having a diameter of 3 μm or less is suitably 15% by volume or more and 60% by volume or less. If it is less than 15% by volume, the effect of improving wear resistance by dispersing TiN as a hard phase will be small, and if it exceeds 60% by volume, the toughness will decrease slightly.

On the other hand, the binder phase for dispersing and bonding the above-mentioned hard phase therein has a matrix composition close to that of the high-speed tool steel during quenching. Basically, it is most important to create a composition that does not precipitate primary carbides during the quenching process. The toughness provided by high speed tool steels is due to this matrix composition. Also in the present invention, the maximum effect can be obtained by employing this matrix composition. If the alloy components other than Fe are below the specified lower limit, sufficient strength cannot be obtained, and if they exceed the upper limit, the toughness decreases.

The hard phase to be dispersed in the matrix may be mainly composed of TiN, with some of the components of the binder phase matrix dissolved therein. In addition, up to 50 atomic % of Ti in TiN is replaced by Zr, Hf, and V.

N b ST a SCr s M o, W, All,
It is possible to substitute with one or more elements selected from the group consisting of and Si. Similarly, 50 atom% of N in TiN
It is also possible to replace up to one element selected from the group consisting of BSC and O. These substitutions are
It is effective in improving the heat resistance, wear resistance, toughness, etc. of the alloy.

However, substitution exceeding 50 atom % is not preferable because it impairs the properties of TiN.

The sintered alloy steel configured as described above can exhibit satisfactory characteristics as a tool material for cutting tools and the like.

However, by introducing a composite method using the above-mentioned sintered alloy steel as the outer peripheral portion, it is possible to improve the performance of the -layer.

First, by employing a sintered hard alloy, so-called cemented carbide, as the core material, it is possible to significantly improve the rigidity of the tool material as a whole. As a result, the machining accuracy of the tool improves, and the surface roughness of the surface machined by the tool improves.

Since the outer peripheral portion is made of the above-mentioned sintered alloy steel, a cutting tool edge with improved wear resistance can be obtained while maintaining the toughness of high-speed tool steel. Incidentally, coating the surface of the sintered alloy steel with a hard ceramic film brings about good results in further improving the performance. As the material for this film, TiN is preferable, but TiN
C or Ti (CN) may be used, and ALOa may be further coated thereon.

The cemented carbide that makes up the core material and the sintered alloy steel that makes up the outer periphery have quite different characteristic values, such as the coefficient of thermal expansion, so when they are joined together, distortion occurs at the interface, causing cracks. Defects such as cracks and cracks may occur. This problem can be solved to some extent by appropriately selecting the composition so as to reduce the difference in the characteristic values between the two. However, if this is done, it becomes impossible to select a composition that can exhibit the best performance of both. According to the present invention, the above problem is solved by interposing an intermediate phase in which the composition and properties of both are changed continuously or stepwise. Preferably, the thickness of this mesophase is 10
The thickness can be appropriately selected within the range of 0 μm or more and 5 mm or less. If the thickness of the mesophase is less than 100 μm, the effect of intervening the mesophase as described above will not be observed, and if it exceeds 5 mm, the significance of the presence of the mesophase will be diminished.

[Example] FIG. 1 is a sectional view conceptually showing a composite hard alloy material according to the present invention. According to this figure, an outer peripheral portion 1 made of sintered alloy steel and a central portion 2 made of sintered hard alloy
is covered. Between the outer peripheral part 1 and the central part 2,
Intermediate portion 3 whose composition is changed continuously or stepwise
is intervening.

Example 1 The outer periphery of a rod made of cemented carbide was coated by thermal spraying with an alloy phase whose composition was continuously changed from the composition of cemented carbide to the composition of alloy steel, which will be described later. The composition of the cemented carbide is 75% by volume of WC.
, TiC 7.5% by volume, TaC 4.0% by volume, Co
was 13.5% by volume. The cemented carbide rod had a diameter of 4 mm and a length of 200 mm. The thermal spray coating treatment was carried out by sequentially changing the composition of the supplied powder to obtain the desired composition. After the outer periphery of the rod made of cemented carbide that has been spray coated in this way is coated with alloy steel powder having a predetermined composition,
Cold isostatic pressing (CIP, co 1 diso
static preSsing). The composition of the alloy steel powder has an average particle size of 0.2 μ as a hard phase.
35% by volume of TiN particles of m, 10% by volume of VC particles with an average particle size of 0.18 μm, 5% by volume of TiN particles with an average particle size of 2.5 μm, 5% by volume of high-speed tool steel powder as a binder phase.
It was 0% by volume. The powder composition of high-speed tool steel is Cr
was 4.0% by weight, Mo was 3.5% by weight, W was 2.0% by weight, Co was 8.5% by weight, C was 0.5% by weight, and the remainder was Fe and unavoidable impurities.

In this way, a 2 mm thick outer peripheral portion made of alloy steel powder was formed. This molded body was placed in a cylindrical container made of mild steel and heated to a temperature of 500°C while being deaerated.
Vacuum sealed. Thereafter, this molded body was subjected to hot isostatic pressing treatment.

The conditions for the hot isostatic pressing treatment are as follows: At a temperature of 1130°C, the pressure of the A gas used as a pressure medium is 100°C.
It was set to 0 kg/Cm2. A drill with a diameter of 6 mm was prototyped from the sintered body thus obtained. In the cross-sectional structure of this drill, a portion made of cemented carbide with a diameter of 4 mm is located at the center, and a portion made of sintered alloy steel is placed around the outer periphery with an intermediate layer having a thickness of 0.5 mm. 5m
It was surrounded by a thickness of m. Predetermined grooves and cutting edges were molded into the drill.

For comparison, a prototype drill made of sintered alloy steel without cemented carbide in its center was produced. Cutting tests were conducted using prototype drills of the present invention and comparison products, and commercially available drills made of cemented carbide and high-speed tool steel. The cutting conditions were as follows.

Work material: 550C Cutting speed: 50m/min Feed speed: 0.25mm/rev Machining depth: 12mm The results of the cutting test are shown in Table 1.

According to the test results in Table 1, with drills made of cemented carbide, wear is small in the early stages when the number of holes to be machined is small, but as the number of holes to be machined increases, subtle chipping occurs on the cutting edge, and this is the cause. It was observed that wear increased. Furthermore, the comparative product was slightly inferior to the invented product. When comparing the enlargement allowance of the processed hole, the inventive product had an enlargement of about 20 μm, while the comparative product had an enlargement of about 50 μm.

Example 2 Each particle was uniformly distributed so that the hard phase particles having a predetermined structure form were 40% by volume, the TiN particles with an average particle size of 2.3 μm were 10% by volume, and the matrix of high-speed tool steel was 50% by volume. Dispersed alloy steel powder and cemented carbide powder were prepared. The hard phase particles surround the TiN particles (Ti W
It had a structure in which a solid solution of Mo)(CN) was formed surrounding it. The average particle size of these hard phase particles is 0.
The thickness of the solid solution surrounding the TiN particles was 0.02 μm. The composition of the high-speed tool steel constituting the matrix is 3.8% by weight of Cr and 5.8% by weight of Mo.
5% by weight, W 2.5% by weight, CO 10.0% by weight,
C was 0.45% by weight, and the remainder was Fe and unavoidable impurities. The composition of the cemented carbide powder was 85% by volume of WC and 15% by volume of Co.

Alloy steel powder and cemented carbide powder were mixed in the proportions shown in Table 2.

Table 2 On top of the sintered cemented carbide, mixed powder 1, mixed powder 2,
After placing the powder in the order of alloy steel powder, it was pressed and formed. The obtained compact was sintered in an atmosphere with a nitrogen partial pressure of 20 Torr. A round bar was cut out from the composite hard alloy material thus obtained.

A cutting tool having a predetermined shape for an end mill was made from the round bar. A cutting test was conducted using this cutting tool under the following conditions.

Work material: 5US304 stainless steel Cutting speed: 40m/min Feed speed: 0.15mm/1 blade machining width: 2. Omm Machining depth: 10 mm According to the cutting test results, if the end mill made of composite hard alloy material according to the present invention is used, machining is possible without any particular problem, and the deviation of the side surface of the machined groove from the vertical line teeth,
The accuracy was extremely high, at most 0.05 mm. In addition,
For comparison, if an end mill made of cemented carbide is used,
Immediately after machining started, the cutting edge chipped, making cutting impossible. Additionally, if you use an end mill made of high-speed tool steel,
No cutting was possible due to rapid wear.

The compositional analysis results of the joint of the composite hard alloy material obtained in Example 2 are shown in FIG. For comparison, FIG. 3 shows the compositional analysis results when the central part made of cemented carbide and the outer peripheral part made of sintered alloy steel were directly joined without intervening an intermediate layer. In FIG. 2, the thickness of the intermediate layer was approximately 0.8 mm.

[Effects of the Invention] As described above, according to the present invention, it is possible to obtain an alloy material whose wear resistance is improved to a level comparable to that of cemented carbide while maintaining the toughness of high-speed tool steel. can. Furthermore, when used as a cutting tool, it has high rigidity and enables highly accurate cutting. Therefore, the composite hard alloy material of the present invention can be used as a material for cutting tools.
It can contribute to improving cutting efficiency and reliability.

[Brief explanation of drawings]

FIG. 1 is a sectional view conceptually showing a composite hard alloy material according to the present invention. FIG. 2 is a graph showing the compositional analysis results of the joint of the composite hard alloy material obtained in Example 2. FIG. 3 is a graph showing the compositional analysis results of a joint in the case where, as a comparative example, a central part made of cemented carbide and an outer peripheral part made of sintered alloy steel were directly joined without intervening an intermediate layer. 1st

Claims (1)

[Scope of Claims] (1) A central portion made of a sintered hard alloy; and an outer circumference portion covering the central portion and made of sintered alloy steel, wherein the sintered hard alloy is made of periodic table IVa, The sintered alloy contains at least 50% by volume and 95% by volume of one or more of carbides, nitrides, and carbonitrides of Va, Group VIa elements in the central portion, and the remainder consists of iron group metals and unavoidable impurities. The steel has a grain size of 0.
The first hard phase consisting of TiN particles with a particle size of 3 μm or less is 15% by volume or more and 60% by volume or less, and the second hard phase consisting of TiN particles with a particle size of 1 μm or more and 3 μm or less is 1% by volume or more and 10% by volume or less.
% by volume or less, and the first hard phase and the second hard phase.
The alloy steel contains 30% by volume or more and 84% by volume or less of a binder phase made of alloy steel for dispersing and bonding a hard phase of Cr, and the alloy steel contains Cr of 2.5% by weight or more and 4.5% by weight. % by weight or less, Mo from 1.5% by weight to 5.0% by weight, W from 2% to 5.0% by weight.
．． 0% to 6.0% by weight, C 0.3% to 1.2% by weight, Co 1.5% to 15% by weight, Mn 0.5% by weight or less, Si 0.5% by weight
The remainder consists of Fe and unavoidable impurities, and the intermediate portion between the central portion and the outer peripheral portion is
A composite hard alloy material having a composition that changes continuously or stepwise from the composition of the central portion to the composition of the outer peripheral portion. (2) 50 atomic% or less of Ti in the TiN particles is Zr, Hf, V, Nb, Ta, Cr, Mo, W, A
The composite hard alloy material according to claim 1, wherein the composite hard alloy material is substituted with one or more elements selected from the group consisting of L and Si. (3) The composite hard alloy according to claim 1 or 2, wherein 50 atomic % or less of N in the TiN particles is replaced with one or more elements selected from the group consisting of B, C, and O. Material. (4) The thickness of the outer peripheral portion is 0.08 mm.
or more, and 0.3 of the total thickness of the composite hard alloy material
The composite hard alloy material according to any one of claims 1 to 3, which is as follows. (5) The composite hard alloy material according to any one of claims 1 to 4, wherein the thickness of the intermediate portion is 100 μm or more and 5 mm or less.