JP2533872B2 - Composite material for cutting tools - Google Patents

Description

TECHNICAL FIELD The present invention relates to a composite material for a cutting tool used for a cutting tool, a cutter, a drill, an end mill, a hob, a tap, and the like.

[Conventional technology]

High speed tool steel (hereinafter abbreviated as high speed steel) has been most frequently used as a constituent material of the cutting tool as described above. This is an alloying component in steel such as Cr, Mo,
It is a steel type that contains W, V, etc., and has carbides of these components that are extruded by heat treatment to have higher wear resistance than ordinary steel.

The next most frequently used material is cemented carbide obtained by sintering WC with Co. Compared with high-speed steel, it has a larger amount of carbide (WC), has significantly improved wear resistance, and has less hardness reduction at high temperatures, so it can be used for high-speed cutting. However, in terms of toughness, it falls short of that of high-speed steel, and its application area has been limited so far.

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

First, as an improvement over HSS steel, powder HSS steel and coated HSS steel are mentioned. The former powdered high-speed steel is produced by atomizing the alloy powder of high-speed steel with an increased content of Cr, Mo, W, V, etc., which is an alloying component, and sintering it by hot isostatic pressing. is there. In the conventional melting method, coarsening of carbide particles is unavoidable when the alloy component is increased, and therefore, there is a problem that the toughness is remarkably reduced and grinding becomes difficult. It is possible to disperse finely, and it has succeeded in improving wear resistance and grindability while maintaining toughness. Next, the coated high-speed steel is a conventional high-speed steel coated with hard ceramics such as TiC and TiN to a thickness of several μm to several tens of μm by the PVD method, etc., and this hard ceramics improves wear resistance. ing.

On the other hand, as an improvement from the 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 enhance the 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 axis is made of high-speed steel and a cemented carbide tube is fitted on the outside of the central axis to bond the two (for example, "shrink fit"). Technology is also proposed.

[Problems to be solved by the invention]

Among the above-mentioned conventional technologies, high-speed steel manufactured by the melting method is
It has poor heat resistance and wear resistance, and when the cutting speed is increased, the cutting edge temperature rises and the cutting edge becomes deformed, making it unusable. this is,
The same applies to the powdered high-speed steel, and although some performance improvement is recognized, it has not been a fundamental solution. Also,
Coated steel is certainly effective in improving wear resistance, but the thickness of the coating layer is from several μm to several tens of μm.
When the temperature of the cutting edge rises, it also deforms and becomes unusable, and when the coating layer is consumed, this tendency becomes more remarkable. In this way, high-speed steels (various types) are basically iron-based alloys, so they cannot be used in the temperature range above the tempering temperature (usually considered to be 600 ° C or higher), so the cutting temperature and feed rate must be increased for processing. Even if you try to improve efficiency,
There are limits naturally.

Next, with cemented carbide, the strength is about the same as HSS hardness (with a transverse rupture strength of about 500 kg / mm ² ).
There is no change that it is a brittle material with a large amount of carbide, and the cutting edge may suddenly chip off or break from the root,
The reliability was poor and it was difficult to deal with unmanned processing.

Moreover, although the toughness of the high-speed steel and cemented carbide joined was improved compared to the cemented carbide, the joint sometimes cracked, and the performance was not sufficiently satisfactory.

It is an object of the present invention to solve the above problems and achieve both toughness and excellent wear resistance.

[Means for solving problems]

The tool material of the present invention is a composite material in which high-toughness steel is used in the center part, and a cemented carbide with high wear resistance is formed on the outside by vapor phase synthesis and firing. An intermediate layer is sandwiched between the hard alloy layer and the hard alloy layer.

The thickness of the cemented carbide layer is preferably 1% or more and 10% or less of the thickness or diameter of the entire tool.

The cemented carbide layer is composed of one or more carbides, nitrides or carbonitrides of group IVa, Va, and VIa metals and an iron group metal, and the desirable composition is WC. : 5 to 95% by weight, carbides, nitrides or carbonitrides of group IVa, Va, and VIa metals other than WC: 0 to 95% by weight, iron group metals: 3 to 40% by weight. The composition of this layer is more rich in iron metal in the vicinity of the interface with the steel, and a structure in which the iron group metal gradually decreases from the surface toward the surface can be more preferable.

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

The steel at the center is for improving the toughness of the entire tool, and this steel ensures resistance to stress such as tension, compression, bending, and shear acting on the tool. Therefore, in consideration of the case where high strength steel is desired but the outer cemented carbide layer is worn away, conventionally used high-speed steel (melt or powder metallurgy) is most preferable.

The outer cemented carbide layer is for obtaining heat resistance and wear resistance, and the layer is made of vapor-synthesized IVa, Va, and VIa group metal carbides and iron group metal-based steels. It is made by depositing it on top and sintering it. The reason why vapor-phase synthesized carbides and nitrides are used is that ultrafine particles can be obtained.
It is known that the strength of cemented carbide depends on internal defects, and as the defects, pores (voids), coarse grains WC, binder (Co) pool, etc. have been reported. As the size of these defects decreases, the strength of the alloy increases,
If this defect has the same size as the WC grain size in the alloy, further improvement in strength cannot be expected. Therefore, ultra-fine grained cemented carbide with a reduced WC grain size has been developed.
The particle size of WC is limited to about 0.5 μm. However, according to the vapor phase method, ultrafine particles of 0.1 μm or less can be obtained relatively easily, the grain size after sintering can be suppressed to a small value, and the strength of the alloy can be dramatically improved.

Further, since they are ultrafine particles, there is also an advantage that the blade sharpness is improved. That is, when forming a blade portion of a drill, end mill, etc., since the edge portion becomes thin, if there are coarse particles, chipping may occur at that portion and the blade edge may be lost, but if it is ultrafine particles, No such problem occurs.

Furthermore, by using ultrafine particles, the sinterability is improved and it becomes possible to sinter at a low temperature.

The second reason for using vapor phase synthesis is that it can be easily mixed with particles of a bound metal. Conventional manufacturing of cemented carbide follows the process of ball-milling carbide, nitride and bond metal together in a solvent, then pressing and sintering. There was a problem of becoming. On the other hand, the vapor-phase synthesized carbide and nitride particles can be mixed in the vapor phase with the iron group metal particles as the binding metal. The feature of mixing in the gas phase is that the mean free path is large with respect to the size of the particles, and a uniform mixture is quickly formed. Therefore, in the vapor phase synthesis method, a uniform mixture can be formed in a short time, and the alloy characteristics are stable.

The third reason for using gas phase synthesis is that the composition can be easily controlled. That is, the ratio of carbides, nitrides and iron group metals can be changed arbitrarily and continuously by controlling the synthesis rate or the transport rate of raw materials. As a result, the steel composition centered on the cemented carbide is used. It becomes possible to change continuously from the interface with and toward the surface. In the preceding paragraph, the composition of the cemented carbide is rich in the iron group metal at the interface with the steel, and it is desirable that the iron group metal decreases as it goes to the surface. As it approaches steel, the difference in the coefficient of thermal expansion becomes smaller, and the thermal stress at the interface due to the difference is relaxed. On the other hand, on the surface side, wear resistance increases due to the decrease in the iron group metal.
According to the gas phase synthesis, such composition control can be easily performed, and the degree of freedom in synthesis design is significantly increased.

Since the cemented carbide layer of the tool material of the present invention is formed by the above-mentioned vapor phase synthesis, the characteristics are further improved as compared with the cemented carbide obtained by a general manufacturing method.

Next, regarding the intermediate layer, this is mainly aimed at relaxing thermal stress due to the difference in thermal expansion coefficient between the steel and cemented carbide after sintering, and secondarily, the joining of steel and cemented carbide. And strengthens the alloy, and prevents the alloy components of both from diffusing and deteriorating the characteristics. The reason why the constituent material of the intermediate layer preferably has a coefficient of thermal expansion between that of steel and the cemented carbide on the outside is that the main purpose of this intermediate layer is to alleviate the heating stress.

The thermal expansion coefficient of high-speed steel (SKH57) is about 12 × 10 ^-6 /
℃, about 5 × 10 ^-6 / ℃ for cemented carbide. Considering this, as a suitable intermediate layer, Cr, Hf, Tr, Mo,
Nb, Pd, Pt, Ro, Rh, Ru, Sb, Si, Ta, Ti, V, Zr, Al
₂ O ₃ , MoSi ₂ , TiC, TiO ₂ , ThO ₂ , Y ₂ O ₃ , UO ₂ , ZrO _{2 and} other mullite, spinel, etc. are mentioned, but the material of the intermediate layer in the present invention is the above-mentioned examples. Not limited. In addition, it is naturally included in the scope of the present invention that the intermediate layer is not a single layer but a multilayer.

Next, the thickness of the cemented carbide layer is preferably 1 to 10% in terms of the ratio to the thickness or diameter of the entire tool. The reason is that if it is 1% or less, satisfactory heat resistance and wear resistance cannot be obtained. This is because if it exceeds%, the toughness is significantly reduced.

Cemented carbide has a WC of 5 to 95% by weight, other than IV
Carbides, nitrides, and carbonitrides of a, Va, and VIa metals: 0 to 95
The composition of wt% and iron group metal: 3 to 40 wt% is preferable because this composition can bring out the maximum effect.
That is, WC contributes to the improvement of heat resistance and wear resistance of the alloy, but if the content of WC is 5% by weight or less, the above two properties cannot be sufficiently enhanced, while if it exceeds 95% by weight, the toughness decreases. To do. Carbides, nitrides, and carbonitrides of group IVa, Va, and VIa 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 also decreases. . Further, the iron group metal enhances the toughness of the alloy, but if the content is 3% or less, the effect is small, and if it exceeds 40%, the wear resistance deteriorates.

 Examples of the present invention will be given below.

[Example 1] End mill made of high-speed tool steel (SKH56, 2-flute, blade diameter
9.0 mm) E was put into the cemented carbide layer generator 1 shown in the attached drawing, and a Ti particle flow was first introduced from the Ti particle generator 2 to form a Ti layer as an intermediate layer on the surface of the end mill. 20
It was deposited to a thickness of μm. After that, WC vapor phase synthesizer 3
Then, the Co fine particle generator 4 was operated, and the WC ultrafine particles and the Co fine particles were mixed and deposited on the end mill. At this time, the WC-Co mixed layer having various thicknesses was formed by changing the deposition time. Then, insert the obtained end mill into a sintering furnace,
After performing vacuum sintering at a temperature of 00 ° C., it was ground into a predetermined tool shape.

Table 1 shows the ratio of the thickness of the cemented carbide part of the prototype to the working diameter. Next, this sample was subjected to an abrasion resistance test and a cutting test. The test conditions are as follows.

Test 1 (Abrasion resistance test) Work material SKD11 Cutting speed 30m / min Table feed 50mm / min Cutting depth 10mm Cutting style Groove cutting life standard Peripheral blade wear width 0.4mm Test 2 (Fracture test) Work material S50C Cutting speed 40m / min Table Feed 200mm / min ~ depth of cut 10mm Cutting method Groove cutting life standard Table feed when breakage This test result is also shown in Table 1. For comparison, high-speed steel, powdered high-speed steel, coated high-speed steel, and cemented carbide end mills 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 on the surface of a round bar of alloy steel (SCM435) having a diameter of 5 mm, a cemented carbide layer controlled to various compositions was deposited, followed by sintering, and then ,
This composite was processed into a drill. The thickness of the cemented carbide layer is 0.
It was 25 mm.

This drill was subjected to a cutting test under the following conditions.
Table 2 shows the composition of each alloy and the test results.

Work Material S45C Cutting Speed 40m / min Feed 0.2mm / rev Hole Depth 35mm (Through) Work Material Vibration Frequency 2Hz Work Material Vibration Amplitude 1mm Life Standard Number of Holes drilled until breakage or defective hole diameter [Example 3] Throw-away tip SNG432 (SKH5) made of high-speed tool steel
7) Deposit 5 μm of Ti layer as an intermediate layer on the surface of (chip thickness 4.76 mm), then deposit a cemented carbide layer controlled to various compositions as shown in Table 3, then 1280
Sintering was performed at ° C. This chip was subjected to a cutting test under the following conditions. The results are also shown in Table 3.

Work Material: SCM435 4 Groove Material Cutting Speed: 120m / min Feed: 0.25mm / rev. Depth of Cut: 1.5mm Tool Holder: FN11R-44A Life Standard: 5min Flank Wear Width V _B (mm) After Cutting Missing time [Effect] As described above, the cutting tool material of the present invention has steel in the center, and a cemented carbide layer formed by vapor phase synthesis and firing on the outside thereof, and further, By arranging an intermediate layer between the steel and the outer cemented carbide layer, it has both the toughness of steel and the excellent wear resistance of cemented carbide. Since it is designed to be stably maintained, the performance and reliability of the cutting tool will be dramatically improved, and for that purpose, the operating conditions of the tool, that is, the cutting speed and feed rate should be increased to improve the efficiency. It is also possible to obtain the effect that it becomes possible to cope with the unmanned operation of the processing machine for a long time.

[Brief description of drawings]

The attached drawing is a diagram showing a schematic configuration of an example of an apparatus used for producing the tool material of the present invention. 1 ... Cemented carbide layer generator, 2 ... Ti particle generator, 3
...... WC phase synthesizer, 4 Co particle generator, 5
Furnace body, 6 ... Heater, 7 ... Heater power supply, 8, 8 '...
… Particle introduction tube, 9 …… Ti raw material, 10 …… Evaporation electron gun,
11 …… Co raw material, 12 …… Evaporation power supply, 13 …… Transport pipe, 14…
… Raw materials for producing carbides and nitrides, 15… Power source for arc discharge

Claims (5)

(57) [Claims] 1. A vapor-phase synthesized IV is formed on the outside of the steel in the center.
a, V a, VI a group 1 metal or 2 or more types of carbide, nitrogen or carbonitride, and a cemented carbide layer made of an iron group metal are provided by firing; A composite material for cutting tools that has an intermediate layer sandwiched between it and a cemented carbide layer. 2. The cutting tool composite material according to claim 1, wherein the cemented carbide layer has a thickness of 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,
Carbide, nitride or carbonitride of a group IVa, Va, or VIa metal other than WC: 0 to 95% by weight, iron group metal: 3 to 40%. The composite material for a cutting tool according to item 1) or (2). 4. The intermediate layer is formed of a material having a coefficient of thermal expansion smaller than that of the steel at the center and larger than that of the cemented carbide on the outside. The composite material for a cutting tool according to any one of 3). 5. The cemented carbide layer is rich in an iron group metal in the vicinity of the interface with steel, and the iron group metal decreases as it reaches the surface. Through the composite material for a cutting tool according to any one of (4).