JPS644989B2 - - 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). This invention relates to a method for manufacturing a sintered body for cutting tools that is suitable for use in fields that require particularly low thermal wear properties (heat resistance and wear resistance), such as high-speed cutting of hardened steel. . [Prior Art] Recently, in the field of metal processing, there has been rapid progress in increasing the speed of cutting cast iron and switching from grinding to cutting of high-hardness steels such as die steel and high-speed steel. Crystalline boron nitride (hereinafter referred to as CBN) does not react with iron, has a hardness second only to diamond, and has high thermal conductivity, so CBN-containing sintered bodies are suitable as cutting tools for these materials. It has started to attract attention. Titanium carbide (hereinafter referred to as TiC), carbonitride (hereinafter referred to as TiCN) and nitride (hereinafter referred to as TiN)
) has high hardness and welding resistance, so CBN and the bonding components TiC, TiCN and
A CBN-containing sintered body is produced by ultra-high pressure sintering of a green compact of a blended composition consisting of one or more types of TiN alone or in a stacked state with other green compacts or sintered bodies. It has been proposed as a cutting tool for 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
80, and on the other hand, none of the conventional CBN-containing sintered bodies described above has both sufficient toughness and wear resistance. When cutting with a cutting tool made of a CBN-containing sintered body, 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, causing the cutting edge to deteriorate. The defects become noticeable and become unusable. For example, when turning die steel (Rockwell C hardness: 62 or higher), the conventional CBN
Cutting tools made of sintered compacts lack heat resistance and wear resistance, so they are used at cutting speeds of 100 m/min or less, and currently cannot withstand use at higher speeds. Therefore, an object of the present invention is to use cutting tools made of high-hardness steels such as high-hardness cast iron, die steel, and high-speed steel (especially high-hardness steels) that have both extremely excellent toughness and wear resistance properties. It is an object of the present invention to provide a method for manufacturing a sintered body for a cutting tool, which is suitable for use in fields where heat resistance and wear resistance are particularly required, such as high-speed cutting. [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 CBN particles falling off when used as a cutting tool. (b) 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 an adverse effect on the properties of the sintered body, such as a decrease in toughness and wear resistance. (d) Dititanium aluminum carbide, which is a type of Al compound Ti ₂ AlC) or titanium aluminum carbonitride (hereinafter referred to as Ti 2 AlC) or titanium 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. When Ti ₂ AlC or Ti ₂ AlCN, which has these characteristics, is used as a sintering aid and sintered with CBN under ultra-high pressure, wrap-around occurs, and a layered reaction occurs at the interface between CBN and TiC or TiCN produced by decomposition. Although these sintering aids are also a type of Al compound, there is no Al content within this reaction area, and the Al content is outside the reaction area. of
Because it is uniformly distributed within TiC or TiCN and no AlN formation is observed, a sufficient sintering promotion effect can be obtained, and the properties of the sintered body (specifically, toughness and wear resistance) are also improved. (e) The above Ti ₂ AlC or Ti ₂ AlCN is also effective as a sintering aid for TiC, TiCN or TiN, respectively, and when sintering each of the above materials, Ti ₂ AlC
Alternatively, when Ti ₂ AlCN is added, the sinterability is significantly improved, and the decomposed TiC or TiCN exhibits a uniform finely dispersed structure in the sintered body. , these are also collectively referred to as titanium carbon/nitride), and the above-mentioned 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 between the particles and one or more particles of the titanium carbon/nitride blended with the CBN particles. Prevents direct contact with particles and decomposes TiC
Alternatively, it is possible to form a reaction region where no Al content exists at the interface between TiCN and CBN particles, and also improve the sinterability of the blended titanium carbon/nitride. To strengthen the bond between carbon/nitride particles and a binder phase, and improve the toughness and wear resistance 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: 18 to 69%, selected from the group consisting of Ti ₂ AlC and Ti ₂ AlCN. A composition having a composition (by weight) consisting of one or two types of powder: 4 to 30% and CBN powder: the remainder (however, less than 23 to 63%) is mixed and press-molded. A sintered body for a cutting tool, which is made into a green compact and then sintered under ultra-high pressure either alone or in a state where it is stacked with another green compact or a sintered body. 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, 3/7
It is preferable that it is larger than . () Blend composition (i) Titanium carbon/nitride These components provide the resulting sintered body with welding resistance and thermal abrasion prevention effects (heat resistance and
It produces the effect of imparting wear resistance), but
If the blending amount is less than 18% by weight, the desired welding resistance cannot be obtained, and welding (chemical reaction at high temperatures with the workpiece material) tends to occur on the cutting edge during cutting tools, resulting in chipping and wear of the cutting tool. It becomes more likely to occur. On the other hand, 69% by weight
If it exceeds this, the high hardness that is one of the characteristics of CBN-based sintered bodies or CBN-containing sintered bodies cannot be obtained, and the relative proportion of the sintering aid will also decrease, resulting in poor durability. Since both abrasion resistance and toughness are insufficient, the blending amount is increased from 18 to 69.
It was determined as weight%. (ii) Ti ₂ AlC, Ti ₂ AlCN As mentioned in the findings (f), 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), and these components are
When used with CBN and titanium carbon/nitride,
The TiC or TiCN produced by decomposition wraps around between the CBN particles and the blended titanium carbon/nitride particles, preventing direct contact between the CBN particles and the blended titanium carbon/nitride particles. Forming a reaction region with no Al content at the interface between TiCN and CBN particles,
It also improves the sinterability of the blended titanium carbon/nitride, which strengthens the bond between the CBN particles, the binder phase, and the blended titanium carbon/nitride particles, and the resulting sintered It has the effect of improving the toughness of the compact and also improving the wear resistance by preventing particles from falling off. However, if the amount is less than 4% by weight, no improvement in interfacial strength, toughness or wear resistance will be observed, while if it exceeds 30% by weight, the hardness and wear resistance of cutting tools will be reduced. Since this results in a significant decrease in the amount of carbon dioxide, the blending amount was determined to be 4 to 30% by weight. (iii) CBN CBN is an essential component for obtaining extremely excellent wear resistance and chipping resistance. However, if the content is less than 23% by weight, the toughness and wear resistance will be insufficient;
In this case, the relative content of carbon and nitride in titanium decreases, making it impossible to obtain the desired adhesion resistance, and especially wear resistance during high-speed cutting of high-hardness steel where the cutting tool edge tends to become hot. Since it reduces the amount of 23 to 63
It was set as less than %. In the sintered body obtained by
CBN content is about 30-70% by volume. () 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 10 ^-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 compact may be used alone or with other compacts or sintered compacts (for example, cemented carbide, cermet, alumina). Pressure: 1 when stacked with powder body or sintered body before sintering such as base ceramics, silicon nitride base ceramics, etc.
~7GPa, temperature: 1000~1800℃, holding time: 5
The 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. Because Ti ₂ AlC or Ti ₂ AlCN
When used with CBN, as mentioned above,
It is characterized by forming a reaction region where no Al content exists at the interface with CBN grains. This phenomenon is similar to other
This phenomenon is not observed in Al compounds, and this makes it difficult for reverse transformation from CBN to hexagonal boron nitride to occur, so even under relatively low pressure, the property can be satisfied with almost no hexagonal boron nitride. A CBN group or a CBN-containing sintered body having the following properties can be obtained. [Example] Example 1 As raw material powder, CBN powder with an average particle size of 2 μm,
1 μm TiC, TiC _0.5 N _0.5 and Ti ₂ AlC powder,
A 0.1 μm TiN powder and a 3 μm Ti ₂ AlC _0.6 N _0.4 powder were prepared, mixed to the composition shown in Table 1, mixed in a ball mill for 20 hours, and then press-molded at a pressure of 2 t/cm ² . A compacted powder body (thickness: 1.5 mm) and a sintered body of cemented carbide (WC-10%Co) (thickness: 2.0 mm)
With the powder compact superimposed on top, the powder is held in a known belt-type ultra-high pressure device under the sintering conditions listed in Table 1 for 10 minutes, and then cooled and depressurized.
Sintered bodies 1 to 17 of the present invention were manufactured. For comparison, a composition containing only CBN and TiC was prepared without using Ti ₂ AlC or Ti ₂ AlC _0.6 N _0.4 .
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, CBN in the CBN group in the laminate or in the CBN-containing sintered body part was removed.
The content, microvitkers hardness, and fracture toughness values were measured and the results are shown in Table 1. Furthermore, after grinding and polishing, we processed the cutting tool into a cutting tool tip with the shape of SPP432, and conducted cutting tests under the following high cutting speed conditions to determine the cutting life.

【table】

[Table] (* indicates that it is out of the blended composition component or blended composition range of this invention.)
(Time until flank wear width reaches 0.15mm)
was measured and the results are shown in Table 1. <Cutting test conditions> Work material: SKD11 (Rockwell C hardness: 62) Cutting speed: 180 m/min Depth of cut: 0.2 mm Feed: 0.1 mm/rev Note that SKD11 is a type of alloy tool steel,
It is high hardness steel. Example 2 In the sintered bodies No. 1 to 17 of the present invention in Example 1, the thickness of the green compact was 3 mm, and the green compacts were sintered at ultra-high pressure alone (i.e., without stacking the cemented carbide sintered bodies). Except for the above, they were manufactured in the same manner, each was processed into a cutting tool edge having the same shape as in Example 1, and the same cutting test was conducted, and almost the same cutting life values were obtained for each. <Effects of the Invention> As can be seen from Table 1 and Example 2, the CBN-based or CBN-containing sintered body obtained by the production method of the present invention has better hardness, fracture toughness, and cutting resistance than conventional sintered bodies. It is excellent in all aspects of cutting life when used as a tool, and is also superior in terms of cutting life compared to the comparative sintered body. In addition, in contrast, the comparative sintered body is inferior in at least one of the hardness and fracture toughness values. Therefore, the sintered body obtained by the production method of the present invention has excellent toughness, hardness, and wear resistance, and is particularly suitable for high-speed cutting of high-hardness steel, etc., where the temperature of the cutting edge is high. Suitable for use as cutting tools in fields that require heat and wear resistance.

[Brief explanation of drawings]

Figure 1 shows a part of a sintered body (Ti ₂ AlCN) to show the effect of Ti ₂ AlCN (in this case, C/N = 6/4), which is a sintering aid used in the manufacturing method of the present invention. Near the interface between the bonded phase obtained by decomposition and CBN)
It is a microstructure photograph taken by a metallurgical microscope.

Claims (1)

[Scope of Claims] 1. One or more powders selected from the group consisting of titanium carbides, nitrides and carbonitrides: 18 to 69%, from the group consisting of dititanium aluminum carbides and dititanium aluminum carbonitrides. Mixing a composition having a composition (wt%) consisting of one or two selected powders: 4 to 30%, cubic boron nitride powder: the remainder (however, less than 23 to 63%), For use in a cutting tool, which is formed by press forming into a green compact, and then sintered under ultra-high pressure, either alone or in a stacked state with other green compacts or sintered bodies. Manufacturing method of sintered body.