JPS644988B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] This invention has both extremely excellent toughness and wear resistance, and is suitable for cutting tools made of high-hardness steel such as high-hardness cast iron, die steel, and high-speed steel (especially high-hardness steel). The present invention relates to a method for manufacturing a cubic boron nitride (hereinafter referred to as CBN)-based sintered body suitable for use in cutting tools in fields that require particularly high toughness, such as high-load cutting of hard cast iron. [Prior art] Recently, in the field of metal processing, there has been a rapid increase in the speed of cutting cast iron, and a rapid switch from grinding to cutting of high-hardness steels such as die steel and high-speed steel. does not react with iron,
CBN-based sintered bodies are attracting attention as cutting tools for these materials because they have a hardness second only to diamond and high thermal conductivity.
And titanium carbide (hereinafter referred to as TiC),
Carbonitrides (hereinafter referred to as TiCN) and nitrides (hereinafter referred to as TiN) have high hardness and welding resistance, so CBN and TiC, which can be said to be a bonding component,
Ultra-high-pressure sintering of a green compact of a blended composition consisting of one or more of TiCN and TiN, either alone or in a stacked state with other green compacts or sintered bodies.
CBN-based sintered bodies have been proposed as cutting tools for cast iron and high-hardness steel. [Problems to be solved by the invention] However, in general, high-hardness steels such as die steel and high-speed steel often have a high hardness with a Rockwell C hardness of 50 or more in a heat-treated state.
In chilled cast iron, which is a high-hardness cast iron, the shore hardness is
It has a high hardness of about 70 to 80. On the other hand, the conventional CBN-based sintered body does not have sufficient toughness and wear resistance. When cutting with conventional CBN-based sintered cutting tools, as the cutting speed increases, the depth of cut increases, and the feed rate increases, the load applied to the cutting edge during lathe machining becomes extremely large. , the cutting edge becomes noticeably damaged and worn out, making it unusable. For example, when turning chilled cast iron, when the depth of cut and feed rate become high, the conventional CBN-based sintered body described above lacks toughness and is prone to chipping. Specifically, chilled cast iron with a shore hardness of 70 When cutting with a workpiece material at a high cutting speed of 80 m/min and a depth of cut of 1.0 mm, even if the feed is as small as less than 0.1 mm, chips will occur at the cutting edge. Therefore, at present, the above-mentioned conventional cutting tools made of CBN-based sintered bodies are used only for cutting with small depths of cut and small feed. Therefore, an object of the present invention is to provide a cutting tool made of high-hardness steel such as high-hardness cast iron, die steel, and high-speed steel (particularly, high-hardness cast iron) that has both extremely excellent toughness and wear resistance properties. (Cutting tools for fields that require particularly toughness, such as high-load cutting with high cutting depth and high feed conditions)
It is an object of the present invention to provide a method for manufacturing a CBN-based sintered body for cutting tools suitable for use in. [Means for solving the problem] As a result of various studies and considerations, the present inventors have found that
We obtained the knowledge described below. (b) When CBN and TiN alone are sintered under ultra-high pressure, TiN is softer than CBN, so it deforms plastically and wraps around the CBN interface, but no reaction occurs between the two, so the interface is strong. As a result, the toughness will not be sufficiently improved, and the wear resistance will be poor due to the CBN particles falling off when used as a cutting tool. (2) Sintering CBN and TiC alone or TiCN alone under ultra-high pressure (c) In order to form a liquid phase and cause a reaction, Al, which is conventionally known as a sintering aid for CBN, is used.
Intermetallic compounds of Al, such as TiAl ₃
If TiB or TiAl is used, a reaction occurs during ultra-high pressure sintering, but a large amount of AlN is also produced in addition to TiB ₂ .
Therefore, a sufficient sintering promotion effect cannot be obtained, and at the same time, it has a negative effect on the properties of the sintered body (toughness, wear resistance, etc.); (c) dititanium aluminum carbide, which is a type of Al compound; (hereinafter referred to as Ti ₂ AlC) or dititanium aluminum carbonitride (hereinafter referred to as Ti 2 AlC)
When used alone, Ti ₂ AlCN) gradually decomposes at temperatures above 1300°C, producing TiC or TiCN, respectively. Using Ti ₂ AlC or Ti ₂ AlC with these characteristics as a sintering aid,
When sintered with CBN under ultra-high pressure, CBN may wrap around the CBN interface and decompose with CBN.
A layered reaction region is formed at the interface with TiC or TiCN (see Figure 1), and these sintering aids are also
Despite being a type of Al compound, there is no Al content within this reaction region, and the Al content is uniformly distributed within TiC or TiCN outside the reaction area, and no formation of AlN is observed. (d) The Ti ₂ AlC or Ti ₂ AlCN mentioned above should be TiC, TiCN or TiCN, respectively. It is also effective as a sintering aid for TiN, and when sintering each of the above materials, Ti ₂ AlC
Alternatively, when Ti ₂ AlCN is added, the sinterability is significantly improved, and TiC or TiCN produced by decomposition exhibits a uniform finely dispersed structure in the sintered body. (e) CBN, TiC, TiCN and TiN ( Hereinafter, these are also collectively referred to as titanium carbon/nitride), and the above-mentioned sintering aids are used as sintering aids.
When Ti ₂ AlC or Ti ₂ AlCN is used, Ti ₂ AlC
Alternatively, TiC or TiCN produced by the decomposition of Ti ₂ AlCN gets around between the CBN particles and one or more particles of the titanium carbon/nitride blended with the CBN particles, and the titanium carbon/nitride blended with the CBN particles. This prevents direct contact with the nitride particles and prevents Al from forming at the interface between the decomposed TiC or TiCN and CBN particles.
It forms a reaction region where no particles exist, and also improves the sinterability of the blended titanium carbon/nitride, thereby creating a bond between the CBN particles and the binder phase and between the titanium carbon/nitride particles and the binder phase. To strengthen the sintered body and improve the toughness of the obtained sintered body. This invention was invented based on the above knowledge, and includes one or more powders selected from the group consisting of TiC, TiN and TiCN: 5 to 31%, selected from the group consisting of Ti ₂ AlC and Ti ₂ AlCN. A composition (by weight) consisting of one or two types of powder: 1 to 23%, and CBN powder: the remainder (63 to 93%) is mixed, press-molded, and compressed. A CBN-based sintered body for a cutting tool, which is made into a powder and then sintered under high ultra-pressure, either alone or in a state where it is stacked with other green bodies or sintered bodies. It is a manufacturing method. The configuration of this invention will be explained below. () Raw materials Titanium carbon/nitride powder, Ti ₂ AlC powder,
The average particle size of both the Ti ₂ AlCN powder and the CBN powder is preferably 10 μm or less. And the C/N of Ti ₂ AlCN which is the raw material powder
(atomic ratio) can be any numerical value, but
In order to increase the hardness of the obtained sintered body, 3/
It is preferably greater than 7. () Blend composition (i) Titanium carbon/nitride Each of these components has the effect of imparting heat resistance and welding resistance to the resulting sintered body, but if the blending amount is less than 5% by weight, the desired When the resulting sintered body is used as a cutting tool, welding tends to occur on the cutting edge (due to chemical reaction at high temperatures with the work material of the cutting tool). As a result, chipping and wear of the cutting edge are likely to occur. On the other hand, if it exceeds 31% by weight, the high hardness that is one of the characteristics of CBN-based sintered bodies cannot be obtained, or sufficient interfacial strength cannot be obtained due to a decrease in the relative proportion of the sintering aid. As a result, the wear resistance or toughness would be insufficient, so the blending ratio was set at 5 to 31% by weight. (ii) Ti ₂ AlC, Ti ₂ AlCN As mentioned in Findings (e), these components are sintering aids and cause a decomposition reaction during ultra-high pressure sintering to produce TiC or TiCN. (When used with CBN, some TiB ₂ is also formed).
When used with CBN and titanium carbon/nitride,
The decomposed TiC or TiCN gets around between the CBN particles and the blended titanium carbon/nitride particles, and directly prevents and decomposes the titanium carbon/nitride particles blended with the CBN particles.
Al at the interface between TiC or TiCN and CBN particles
It also improves the sinterability of the blended titanium carbon/nitride, thereby creating a bond between the CBN particles, the binder phase, and the blended titanium carbon/nitride particles. It has the effect of strengthening the bond and improving the toughness of the obtained sintered body. However, if the blending ratio is less than 1% by weight, the above-mentioned toughness improvement effect will not be observed, while if it exceeds 23% by weight, the wear resistance will be significantly reduced. It was determined that (iii) CBN CBN can be said to be an essential component for obtaining extremely excellent wear resistance and chipping resistance. However, if the blending ratio is less than 63% by weight, the toughness will be insufficient in high-load cutting for reasons that are unclear, and this is particularly unfavorable for cutting in this field where toughness is required. On the other hand, if the amount exceeds 93% by weight, the sinterability will be significantly deteriorated, and the CBN particles will easily fall off, reducing the wear resistance of the resulting sintered body. Ratio 63~
It was set at 93% by weight. The CBN content in the obtained sintered body is approximately 70.
The capacity is about 95%. () Mixing/molding/sintering process Next, the composition having the above-mentioned composition is
For example, after mixing in a ball mill to form a mixed powder, this mixed powder is press-molded at a pressure of 0.5 to 5.0 t/cm ² to form a compact, and this compact can be used as it is or pre-treated for ultra-high pressure sintering. as 0 ^-2 ~
800 to 10 ^-4 torr in vacuum or inert gas
After pre-sintering at a temperature of 1200°C to increase its strength, the green compact or pre-sintered body is
or other compacts or sintered bodies (e.g. cemented carbide, cermet, alumina-based ceramics,
Pressure: 4 when stacked on a green compact or sintered body (pre-sintered powder body or sintered body such as silicon nitride-based ceramic)
~7GPa, temperature: 1400~1800℃, holding time: 5
The CBN-based sintered body of the present invention is produced by sintering under conditions of ~120 minutes. The pressure and temperature during ultra-high pressure sintering do not necessarily have to be within the stable range of CBN, and such ultra-high pressure and high temperature are not necessarily required. This is because, as described above, when Ti ₂ AlC or Ti ₂ AlCN is used together with CBN, a reaction region where no Al content is present is formed at the interface with the CBN grains. This phenomenon is not observed in other Al compounds, and this makes it difficult for CBN to undergo reverse transformation into hexagonal boron nitride.
Even under relatively low pressure, a CBN-based sintered body containing almost no hexagonal boron nitride and having satisfactory properties can be obtained. [Example] Example As the principle powder, CBN powder with an average particle size of 2 μm,
1 μm TiC _0.5 N _0.5 powder, TiN powder, and Ti ₂ AlC _0.6
N _0.4 powder, 0.1 μm TiC powder, 3 μm Ti ₂ AlC
After preparing the powder and blending it into the composition shown in Table 1,
Mixed in a ball mill for 2 hours, then press-molded at a pressure of 2t/cm ² to form a green compact.
After holding at 800°C for 30 minutes in a vacuum of 10 ^-3 torr, holding for 10 minutes under the sintering conditions listed in Table 1 using a belt-type ultra-high pressure device, the sintered bodies 1 to 1 of the present invention were prepared by cooling and removing the pressure. 17 were manufactured. For comparison, a blended composition of _{only CBN} and _TiC , _a blended composition of CBN and
Blend composition of TiC _0.5 N _0.5 only or CBN and TiN
Conventional sintered bodies 1 to 3 using a blended composition of
Comparison of conventional sintered bodies 4 to 5 using conventionally known TiAl ₃ or Al as a sintering aid instead of Ti ₂ AlC or Ti ₂ AlC _0.6 N _0.4 , and whose blending composition is outside the blending composition range of the present invention. Sintered bodies 1 to 12 were produced in the same manner. After polishing these sintered bodies of the present invention, comparative sintered bodies, and conventional sintered bodies, the CBN content, fracture toughness value, and Vickers hardness of each sintered body were measured, and the results are shown in Table 1. Indicated. Next, these sintered bodies were ground and polished to obtain a cutting edge for a cutting tool. Using this cutting edge, the work material is chilled cast iron with shore hardness of 70, cutting speed: 80 m/min, depth of cut: 1.0 mm, feed rate is 0.05 mm/rev., then 0.1 to 0.7 0.1mm from the smallest within the range of mm/rev.
Cutting was performed for 5 minutes at each feed rate, and the feed rate at which chipping first occurred was investigated. The results are shown in Table 1. [Effects of the Invention] As shown in Table 1, the sintered body of the present invention has better fracture toughness, hardness, and feed rate that can be used as the cutting edge of a cutting tool without causing chipping, compared to the conventional sintered body. It is excellent in all aspects, especially in terms of fracture toughness and usable feed rate.
Moreover, the sintered body of the present invention is superior to the comparative sintered body in terms of the feed rate that can be used as the cutting edge of a cutting tool without causing chipping. In addition, the comparative sintered body, on the other hand, is inferior to the sintered body of the present invention in either fracture toughness or hardness, and cannot satisfy both properties at the same time. Incidentally, in the case of cutting tools made of CBN-based sintered bodies, it is 0.3
mm/rev. or more can be considered a high feed condition.

【table】

【table】

[Table] Therefore, the production method obtained by the production method of this invention
CBN-based sintered bodies are particularly useful as cutting tools in fields where toughness is particularly required, such as high-cut, high-feed, high-load cutting of high-hardness cast iron.

[Brief explanation of the drawing]

Figure 1 shows a sintered body (CBN and Ti ₂ AlCN held at a pressure of 4 GPa and a temperature of 1400°C for 10 minutes) to demonstrate the effect of Ti ₂ AlCN, a sintering aid used in the manufacturing method of this invention. A part of the structure (the binder phase obtained by decomposing Ti ₂ AlCN)
This is a micrograph showing the area near the interface with CBN.

Claims (1)

[Scope of Claims] 1. One or more powders selected from the group consisting of titanium carbides, nitrides and carbonitrides: 5 to 31%, from the group consisting of dititanium aluminum carbides and dititanium aluminum carbonitrides. One or two selected powders: 1 to 23%, cubic boron nitride powder: remaining (63 to 93%)
A composition having a compounding composition (the above, weight %) is mixed, press-molded to form a green compact, and then this green compact is stacked alone or with other green compacts or sintered bodies. 1. A method for producing a cubic boron nitride-based sintered body for a cutting tool, the method comprising sintering the cubic boron nitride-based sintered body under ultra-high pressure.