JPS63255305A - Composite material for cutting tool - Google Patents

Abstract

PURPOSE:To obtain a composite material for a cutting tool having superior toughness and wear resistance by forming an intermediate layer on the outside of high toughness steel as a central material and further forming a sintered hard alloy layer having high wear resistance by vapor phase synthesis and sintering. CONSTITUTION:An intermediate layer of a prescribed thickness such as a Ti layer is deposited on the outside of high toughness steel such as high-speed steel as a central material. A sintered hard alloy layer consisting of the carbide, nitride or carbonitride of one or more of the groups IVa, Va and VIa metals and an iron family metal is then formed on the intermediate layer by vapor phase synthesis and sintering to obtain a composite material for a cutting tool. The thickness of the sintered hard alloy layer is preferably regulated to 1-10% of the thickness or diameter of the tool. The intermediate layer may be made of Cr, Hf, Ti or Mo. Since the performance and reliability of the cutting tool are considerably improved by the composite material, working efficiency can be increased by changing the service conditions of the tool, that is, by increasing cutting speed of feed speed.

Description

[Detailed description of the invention] [Industrial application field] This invention is applicable to cutting tools, cutters, drills, end mills,
This invention relates to composite materials for cutting tools used in hobs, taps, etc.

[Conventional technology]

High-speed tool steel (hereinafter referred to as high-speed steel) is the most commonly used constituent material for cutting tools such as those mentioned above.
It is a steel type that contains O, W, ■, etc., and has higher wear resistance than ordinary steel by precipitating carbides of these components through heat treatment.

The next most commonly used material is cemented carbide, which is made by sintering WC with CO. This steel has a larger amount of carbide (WC) than high-speed steel, has significantly improved wear resistance, and has less hardness loss at high temperatures, so it can be used for high-speed cutting. but,
In terms of toughness, it is not as tough as high-speed steel, so its use has been limited until now.

Therefore, various improvements have been made to bridge the gap between high-speed steel and cemented carbide.

First, improvements from high speed steel include powdered high speed steel and coated high speed steel. The former powdered high-speed steel is produced by atomizing a high-speed steel alloy powder with an increased content of alloy components such as Crs Mo and Wlv, and sintering it by hot isostatic pressing or the like. In the conventional melting method, the alloying components are increased (which inevitably causes the carbide particles to become coarser, resulting in a significant decrease in toughness.
There was a problem that grinding was difficult, but the powder method made it possible to finely disperse these carbides, and succeeded in increasing wear resistance while maintaining toughness and improving grindability. There is.

Next, coated high speed steel is made by coating the surface of conventional high speed steel with hard ceramics such as TiC5TiN to a thickness of several μm to over 10 μm using a PVD method, etc. This hard ceramic improves wear resistance. .

On the other hand, as an improvement from cemented carbide, there is an example in which the WC particles are made extremely fine (1 μm or less) to improve the strength of the alloy and improve its reliability.

In addition, as a method that combines the advantages of both the toughness of high-speed steel and the wear resistance of cemented carbide, a central shaft is made of high-speed steel, a cemented carbide cylinder is fitted on the outside of the shaft, and the two are joined together (for example, by "shrink fit"). ”) has also been proposed.

[Problem that the invention seeks to solve]

Among the above-mentioned conventional techniques, high-speed steel made by melting has poor heat resistance and wear resistance, and when the cutting speed is increased, the temperature of the cutting edge increases, causing the cutting edge to deform and become unusable. The same is true for powdered high-speed steel, and although a slight improvement in performance has been recognized, it is not a fundamental solution.Also, coated steel is certainly effective in improving wear resistance, but coated steel The thickness of the layer is from several μm to several tens of micrometers, and when the temperature of the cutting edge increases, it deforms and becomes unusable, and this tendency becomes even more pronounced as the coating layer wears out. In this way, high-speed steel (various types) is basically an iron-based alloy, so it can be heated in a temperature range above the tempering temperature (usually 600℃).
(considered to be the above) is of no use, and therefore, even if an attempt is made to improve machining efficiency by increasing the cutting temperature or feed, there will naturally be a limit.

Next, although cemented carbide has strength comparable to that of high-speed steel (transverse rupture strength of about 500 kg/fi"), it is still a brittle material with a large amount of carbides. However, the cutting edge could suddenly chip or break at the root, resulting in poor reliability and making it difficult to adapt to unmanned machining.

In addition, although high-speed steel and cemented carbide are bonded together, although their toughness is improved compared to cemented carbide, they sometimes crack at the joint, resulting in insufficient performance.

The purpose of this invention is to solve the above problems and achieve both toughness and excellent wear resistance.

[Means for solving problems]

The tool material of this invention uses steel with high toughness in the center,
It is a composite material in which a highly wear-resistant cemented carbide is formed on the outside by vapor phase synthesis and sintering, with an intermediate layer sandwiched between the central steel and the outer cemented carbide layer. It is.

Note that the thickness of the cemented carbide layer is 1 of the total thickness or diameter of the tool.
% or more and 10% or less.

Further, this cemented carbide layer is composed of one or more carbides, nitrides, or carbonitrides of fVa, Va, and Via group metals and an iron group metal, and its desirable composition is WC: 5 to 5.
95% by weight, 80-95% by weight of carbides, nitrides, or carbonitrides of IVa, Va, and Via group metals other than the wc group, and 3-40% by weight of iron group metals.

A more preferable composition can be obtained if the composition of this layer is rich in iron metals near the interface with steel, and gradually decreases in iron group metals toward the surface.

In addition, the intermediate layer is preferably formed of a material whose coefficient of thermal expansion is smaller than that of the central steel and larger than that of the outer cemented carbide.The reasons for these points will be described later.

The central steel is used to improve the toughness of the entire tool, ensuring its resistance to stresses such as tension, compression, bending, and shearing that are applied to the tool. Therefore, although a high-strength steel is desired, considering the case where the outer cemented carbide layer wears out, conventionally used high-speed steel (made by ingot or powder metallurgy) is most preferable.

The outer cemented carbide layer is intended to provide heat resistance and wear resistance, and is made of carbides of rVa, ■a, and ■a group metals synthesized in a vapor phase, and a steel layer mainly made of iron group metals. It is made by depositing it on and sintering it. The first reason for using vapor-phase synthesized carbides and nitrides is that ultrafine particles can be obtained.

It is known that the strength of cemented carbide depends on the inherent defects, such as bores, coarse grained WC,
Binder (CO) pools, etc. have been reported. However, if these defects become the same size as the WC grain size in the alloy, no further improvement in strength can be expected.

Therefore, ultrafine-grained cemented carbide with a smaller WC grain size has been developed, but even in that case, the WC grain size is 0.5 μm.
The extent is the limit. However, according to the gas phase method, 0.1μ
Ultrafine particles with a diameter of 100 m or less can be obtained relatively easily, and the particle size after sintering can be kept small, resulting in a dramatic improvement in the strength of the alloy.

Additionally, since it is an ultra-fine particle, it has the advantage of improving edge sharpness. That is, when forming the cutting part of a drill, end mill, etc.
Since the edge portion becomes thinner, if there are coarse particles, chipping may occur at that portion and the cutting edge may be damaged, but with ultra-fine particles, such problems do not occur.

Furthermore, by using ultrafine particles, sinterability is improved and sintering at low temperatures becomes possible.

The second reason for using vapor phase synthesis is that it can be easily mixed with the bound metal particles. Conventional cemented carbide production follows a process of ball-milling carbides, nitrides, and bonding metals together in a solvent, then pressing, and sintering; insufficient mixing can result in non-uniform alloys. There was a problem. On the other hand, carbide and nitride particles synthesized in the vapor phase can be mixed with iron group metal particles as the binding metal in the vapor phase. A characteristic of mixing in the gas phase is that the mean free path is large relative to the particle size, and a homogeneous mixture is quickly formed. Therefore, in the vapor phase synthesis method, it is possible to form a uniform mixture in a short time, and the properties of the alloy are also stable.

The third reason for using gas phase synthesis is that the composition can be easily controlled. In other words, by controlling the synthesis rate or the transportation rate of raw materials, the ratio of carbides, nitrides, and iron group metals can be changed arbitrarily and continuously, and as a result, the composition of cemented carbide can be changed to This makes it possible to change continuously from the interface with the surface to the surface.

In the previous section, it was stated that it is desirable for the composition of cemented carbide to be rich in iron group metals at the interface with steel, and to decrease toward the surface, because the properties of the cemented carbide on the mesh side are Because it approaches steel, the difference in thermal expansion coefficient becomes smaller and the thermal stress at the interface due to the difference is alleviated.On the other hand, on the surface side, the wear resistance increases due to the reduction of iron group metals. According to the method, such composition control can be easily carried out, and the degree of freedom in alloy design is significantly increased.

Since the cemented carbide layer of the tool material of this invention is formed by the above-mentioned vapor phase synthesis, its properties are further improved compared to cemented carbide obtained by general manufacturing methods.

Next, there is the intermediate layer, whose main purpose is to alleviate thermal stress due to the difference in thermal expansion coefficient between the steel and cemented carbide after sintering, and secondly, to join the steel and cemented carbide. In addition to making the alloy stronger, it also works to prevent the alloy components of both from diffusing and deteriorating their properties. The reason why it is desirable that the material constituting the intermediate layer has a coefficient of thermal expansion between that of steel and that of the outer cemented carbide is that the main purpose of this intermediate layer is to alleviate heating stress.

The coefficient of thermal expansion is approximately 12X for high-speed steel (SKH57).
10-'/'j:, approximately 5 Xl0-'/' for cemented carbide
It is C. Considering this, suitable intermediate layers include Cr5HE, Tr, Mo, Nb, Pd5Pt, R
o, Rh, Ru, Sb, S i, Tas Ti.

V s Z r −A l * Os , M o S
i z , T i C, , Ti0. ,That,Y
, O,, UO*, Zr0t, mullite, spinel, etc., but the material of the intermediate layer referred to in the present invention is not limited to the above-mentioned examples, and the intermediate layer may be made of multiple layers instead of a single one. Naturally, this is also included within the scope of the present invention.

Next, the reason why the thickness of the cemented carbide layer is desirably 1 to 10% relative to the overall thickness or diameter of the tool is because if it is less than 1%, satisfactory heat resistance and wear resistance cannot be obtained. %, the toughness will be significantly reduced.

In addition, the cemented carbide includes WC: 5 to 95% by weight, carbides, nitrides, and carbonitrides of other IVa, Va, and VIa group metals: 80 to 95% by weight, and iron group metals: 3 to 40% by weight. The reason why the composition is desirable is that this composition can bring out the maximum effect. That is, WC contributes to improving the heat resistance and wear resistance of the alloy, but if the content is less than 5% by weight, the above two properties cannot be sufficiently enhanced, while if it exceeds 95% by weight, the toughness decreases. do. (2) Carbides, nitrides, and carbonitrides of a, Va, and VTa group metals have the effect of further increasing the heat resistance and wear resistance of the alloy, but if the content exceeds 95% by weight, the toughness still decreases. Further, iron group metals improve the toughness of the alloy, but if it is less than 3%, the effect is weak, and if it exceeds 40%, the wear resistance deteriorates.

Examples of this invention are listed below.

[Example 1] Using a high-speed tool steel end mill (SKH56, 2-flute, blade diameter 9.0ss), place it into the cemented carbide layer generation cylinder N1 shown in the attached diagram, and first generate Ti particles. device 2 to T
A Ti layer as an intermediate layer was deposited on the surface of the end mill with a thickness of 2 lums by introducing a particle flow of 2 lums.
The C gas phase synthesizer 3 and the CO fine particle generator 4 were operated, and the WC ultrafine particles and the CO fine particles were mixed and deposited on the end mill. At this time, WC-Co mixed layers with various thicknesses were created by varying the deposition time. Then, the obtained end mill was placed in a sintering furnace, vacuum sintered at a temperature of 1300° C., and then ground into a predetermined tool shape.

The ratio of the thickness of the cemented carbide part of the prototype to the machining diameter is shown in Table 1.This sample was subjected to a wear resistance test and a cutting test. The test conditions are as follows.

Test 1 (wear resistance test) Workpiece material 5KDII Cutting speed 30m/sin Table feed 50B/sin Depth of cut 100 Cutting style Groove cutting life standard 0.4 during peripheral blade wear Test 2 (breakage test) Workpiece material 5soc Cutting speed 49m/ sin Table feed 200n/win ~ Depth of cut 10mm Cutting style Groove cutting life standard Table feed when breakage The test results are also listed in Table 1. For comparison, end mills made of high speed steel, powdered high speed steel, coated high speed steel, and cemented carbide were also tested under the same conditions, and the results are also shown in Table 1.

[Example 2] After depositing 5 μm of PT as an intermediate layer on the surface of a round bar of Alloy 1) (S CM435) with a diameter of 5 mm, cemented carbide layers with controlled compositions of various types were deposited, and then sintering was performed. The composite was then fabricated into a drill. The thickness of the cemented carbide layer was 0.25 m.

This drill was subjected to a cutting test under the conditions shown below. The composition and test results of each alloy are listed in Table 2.

Work material 545C Cutting speed 40m/+ll1n Feed 0.2/rev Hole depth 35 (penetration) Work material vibration frequency 2Hz Work material vibration amplitude 1) Life standard Machining size until breakage or hole diameter defect Table 2 [Effects] As mentioned above, the cutting tool material of the present invention has steel in the center and a cemented carbide layer made by vapor phase synthesis and firing on the outside. Furthermore, by arranging an intermediate layer between the central steel and the outer cemented carbide layer, we are able to combine the strong acidity of steel with the excellent wear resistance of cemented carbide. The performance and reliability of the cutting tool are dramatically improved because the characteristics such as the following are stably maintained.
It is possible to increase machining efficiency by increasing the cutting speed and feed rate, and it is also possible to support long-term unattended operation of the processing machine.

[Brief explanation of the drawing]

The attached drawing is a diagram showing a schematic configuration of an example of an apparatus used for manufacturing the tool material of the present invention. 1...Cemented carbide layer generating device, 2...T
i particle generation device, 3...WCC machine synthesis device 4
...Co particle generator, 5 ... Furnace body, 6 ... Heater, 7 ... Power supply for heater, 8.8' ...・Particle introduction tube, 9...
Ti raw material, 10...Electron gun for evaporation, 1)...
... CO raw material, 12 ... Evaporation power source, 13.
...transport pipe, 14...raw material for carbide and nitride generation, 15...power supply for arc discharge

Claims (5)

[Claims] (1) IVa, Va synthesized in a vapor phase on the outside of the central steel
, a cemented carbide layer consisting of one or more carbides, nitrogen substances, or carbonitrides of Group VIa metals and an iron group metal is provided by firing, and further, the steel in the center and the cemented carbide layer on the outside are provided. Composite material for cutting tools consisting of an intermediate layer sandwiched between. (2) The composite material for a cutting tool according to claim (1), wherein the thickness of the cemented carbide layer is 1% or more and 10% or less of the thickness or diameter of the entire tool. (3) The composition of the cemented carbide is WC: 5 to 95% by weight,
Claim (1) characterized in that carbides, nitrides, or carbonitrides of group VIa, Va, and VIa metals other than WC: 0 to 95% by weight, and iron group metals: 3 to 40%. Or the composite material for cutting tools according to item (2). (4) Claims (1) to (3) characterized in that the intermediate layer is formed of a material whose coefficient of thermal expansion is smaller than that of the central steel and larger than that of the outer cemented carbide. Composite material for cutting tools according to any of paragraphs. (5) The cemented carbide layer is rich in iron group metals near the interface with the steel, and iron group metals decrease toward the surface. (4) Composite material for cutting tools according to any one of items.