JPS5815082A - Manufacture of silicon nitride tip for cutting tool - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a silicon nitride tip for a cutting tool, which has excellent wear resistance and impact resistance, and improved cutting performance.

In recent years, in order to enable high-speed cutting of steel, cast iron, etc., there has been a great deal of interest in improving the performance of cutting tools, and various developments have been attempted.

Conventionally, such i-cutting tools are generally required to have wear resistance and oxidation resistance, so alumina, which has excellent properties, has been used. However, although alumina has the above-mentioned excellent properties, it is resistant to thermal shock. poor mechanical properties at high temperatures,
Conventional cutting speed turning is 800m, which is required in recent years.
In high-speed cutting over 7 m, it is extremely difficult to perform stable cutting.

Therefore, in recent years, the use of silicon nitride (hereinafter abbreviated as Si3N4) sintered bodies, which have high heat resistance and high temperature strength, has been studied and disclosed in JP-A-55-85481 and JP-A-55-47276.
Specific examples have been proposed in publications such as No. That is, in the former case, Aj? zO3, Al0
At least one coating thin film of N is formed to improve wear resistance and impact resistance, and the latter is made of Y2031. Metal oxides selected from ZrO2 and MgO are mixed and heated under a pressure of 850 to 455 kg/d.
After hot compacting at 1700 to 1750°C for 3 to 8.5 hours, the hot compacted body was heated at 100°C/h without applying pressure.
The tool life is improved by cooling at an average cooling rate of r.

However, although the former method forms a coating thin film, it relies solely on chemical or physical vapor deposition methods, and the bonding is insufficient, and the thin film peels off during high-speed cutting accompanied by high temperatures. The disadvantage is that it causes difficulties in cutting life and cutting efficiency, and does not take full advantage of the characteristics of the base material and thin film.Also, although there is no risk of peeling as mentioned above, the latter is difficult because the compressed body is made to be substantially free of pores. It is difficult to improve the wear resistance and impact resistance, but there are limits.
I cannot say that I am fully satisfied yet.

Thus, the present invention deals with the above-mentioned actual situation and aims to provide a silicon nitride chip that has a reliable sealing process, no fear of peeling, and has better cutting properties. A mixed powder obtained by adding a sintering aid to silicon powder is pre-shaped and sintered to form a pre-sintered body, and then the surface of the pre-sintered body is coated with ceramic using an appropriate vapor deposition method, and then the ceramic coating is applied. Nitriding for cutting tools, which involves hot isostatic pressing a pre-sintered body in a nitrogen gas atmosphere at a pressure of 500 to 2000 atm and a temperature of 1500 to 2000°C for 5 minutes or more to form a tip for a cutting tool. Its feature is a method of manufacturing silicon chips.

Of course, the use of hot isostatic press treatment (hereinafter referred to as HIP treatment) in producing cutting tools is not new, and the applicant has already proposed several methods.

However, the known HIP process actually uses Ar gas as a pressure medium and does not use nitrogen gas as a pressure medium as in the present invention.

However, recently, attention has been focused on HIP processing using N2 gas as a pressure medium, and when ceramics including Si3N4 were processed, it was discovered that it has various advantages.

That is, several types of pre-sintered bodies of 5j3N4 were made, the HIP conditions were constant at a pressure of 100 Mpa and a constant treatment time of 60 minutes, the treatment temperature was changed to 1700°C and 1900°C, and Ar gas and N2 gas were used as pressure media. We conducted measurements of density and weight changes, microstructural observations, and three-point bending tests at room temperature using Ar-HIP. For materials, the density may increase or decrease, but
In the case of N2-HIP material, the density before and after I(IP treatment hardly changes), and on the other hand, the density of Ar-HIP material slightly decreases in the area of 89/d and above soil, whereas the density of N2-HIP material
In P materials, there is a tendency for N to increase.
The density improvement effect of 2-HIP is slightly greater at 1900°C than 1700°C HIP treatment, and although the degree of improvement is slightly different for all pre-sintered bodies, N2-HIP improves density better. It was found to be effective.

Also, when observing the sample surface after HIP, N'2-HI
While the P material turned slightly grayish-white, the Ar-HIP material clearly turned greenish-gray, and as a result of investigation by X-ray diffraction, a strong diffraction peak of SiC was observed. This A
The cause of SiC generation in r-HIP material is Si3N4→
8 This is thought to be the result of Si produced by the decomposition of Si3N4 shown in the reaction of Si + 2N2, reacting with CO gas mainly generated from the graphite heater of the HIP furnace or the graphite crucible; It was found that the effect was extremely small, and the effect was only grayish white. Next, we cut a cross-section of the HIP material and observed the structure after polishing. Visual observation revealed that the surface of the Ar-HIP material was whiter than the inside, but... 'h −H
On the contrary, it was observed that the IP material turned black. Further observation using a microscope revealed that the surface of the Ar-HIP material was dotted with pores in the high-density pre-sintered body, but the surface and internal holes were found in the N2-HIP material. No obvious difference was seen between them. Possible explanations for this phenomenon include the fact that the temperature rises at the surface of the sample is faster than that at the inside, so the liquid phase tends to concentrate on the surface, and that it is due to the internal pressure of N2 gas generated by the decomposition of Si3N. When observing only the □ densification in the Ar-HIP material, it is recognized that the density of the sample as a whole decreases due to HIP treatment, although densification is progressing in some parts, whereas in the N2-HIP material, the density is extremely high. It was observed that the number of pores was small and corresponded well to the case of the above-mentioned density.

Furthermore, regarding the bending strength, there is a relatively wide variation in the case of Ar-HIP material (although the improvement effect of HIp treatment is not necessarily clear, the bending strength of N2-HIP material is approximately equal to the density). Although it is on the same level as hot-pressed material, there is relatively little variation in strength in the high-density region, and the strength of N2-HIP material is comparable to that of Ar-HIP material.
N2-HIP is better than P material in all respects.
It has been shown that processing strength can be improved. In this way, when performing HIP treatment on a Si3N4 pre-sintered body, N2 gas is preferable to Ar as the pressure medium during HIP treatment.
It can be seen that it is superior to gas. Moreover, N2-gas is extremely easy to obtain compared to Ar-gas, and the fact that it is economically and industrially advantageous cannot be overlooked.Thus, the present invention performs the HIP treatment in a nitrogen gas atmosphere as described above. This is an essential requirement.

Hereinafter, specific embodiments of the method of the present invention will be described in detail.

First, in the first step of manufacturing the silicon nitride chip of the present invention, 51 gN
After adding a sintering aid to the a powder, the mixed powder is molded into a predetermined shape. In this case, known Y2O3 powder, Al2O3 powder, MgO powder, etc. are used as the additive auxiliary agent, and usually any of them or a mixture thereof is used to form the Si3
It is added in an amount of 5 to 15% by weight based on the N4 powder.

On the other hand, various well-known molding methods such as injection molding, extraction molding, mold press molding, and isostatic pressing can be used to mold the mixed powder, and a molded product having the desired shape can be used. In this case, it does not necessarily have to be a completed chip shape.

After the first stage of molding is completed, the molded body is then subjected to preliminary sintering. This preliminary sintering is performed prior to the subsequent sintering, in this case the HIP treatment, and in consideration of the later-described coating and sintering by the HIP treatment, it is preferable to set the relative density to 80%.

As the preliminary sintering method, any known sintering method such as N2 gas atmosphere sintering method or hot press sintering method can be used as appropriate.

In addition, in the above-mentioned preliminary sintering, as mentioned above, the relative density is 8.
Since it has a relatively low density of 0% or more, sintering is relatively simple and even complex shapes can be easily obtained.

The presintered body thus obtained is then subjected to a ceramic coating step, which is one of the characteristics of the method of the present invention, to form a ceramic coating layer on its surface. This coating is performed by a suitable vapor deposition method such as a normal chemical vapor deposition method (CRD method) or a physical vapor deposition method (PVD method), and the ceramic to be coated is Aj? z
Various ceramics such as Oa, AnON, and TiC can be used, and among them, TiC or TiN is the most effective in terms of high strength and improved wear resistance.

Although the thickness of the coating layer is not necessarily specified, it is preferably 20 μm or less because if it is too thick, the properties of 5iaN4 will not be utilized and it will be easy to peel off during cutting.

This coating completely seals the pores on the surface of the pre-sintered body, enables high density through subsequent HIP treatment, and plays a major role in improving wear resistance as a cutting tool.

The pre-sintered body coated as described above is then subjected to HIP treatment as secondary sintering.
It is required to take advantage of the effects of the treatment and conduct it under an N2 gas atmosphere.

In this case, the conditions for the HIP treatment were selected from the viewpoint of achieving high density and suppressing the Si3N40 decomposition reaction, and the pressure was 500 to 2000 atm and the temperature was 15
A preferable temperature range is 00 to 2000°C.

Normally, if the pressure is less than 50 ton pressure, the time required for HIP treatment will be longer and it will be difficult to achieve high density.If the pressure is too high, the pressure will increase even if it is good in terms of suppressing the decomposition reaction and increasing the density. It is not practical because it takes a long time and increases the size of the IP device.

On the other hand, if the HIP temperature is too low, the sintering rate will be slow, and if it is too high, the decomposition reaction of 5isN4 tends to increase, so it is preferable to carry out the treatment within the above range.

However, the HIP temperature is of course related to other conditions such as pressure, and must be below the decomposition temperature of Si3N4, but this decomposition temperature also increases as the HIP pressure increases.
Therefore, it is preferable to carry out the reaction at a temperature that is at least about 100°C lower than the decomposition temperature at the HIP pressure.

In the sintered body treated in this manner, the coating material is firmly bonded to the base material Si3N4 by HIP, and the gap existing between the two completely disappears, resulting in a chip material with excellent wear resistance.

This chip material is then molded into a predetermined cutting tool chip and removably attached to the tool body using a clamp mechanism or the like. It is a good idea to use the eight corners in sequence, so that if they wear out, use other corners.

As described above, the method of the present invention involves forming a mixed powder of Si3N4 powder with a sintering aid added, pre-sintering it, and then coating the surface of the pre-sintered body with ceramic such as TiC or TiN. Then, since the method is to make a Si3N4 chip by performing HIP treatment, Ti
Ceramic coating layer such as C, TiN is Si3
Formed on the surface of a base material made of N4, it has a remarkable effect on improving wear resistance, and the base material Si3N has a high density and high thermal shock resistance, making it excellent for high-speed cutting. It is possible to provide a chip that exhibits and exhibits excellent performance.

Moreover, in the above-mentioned method of the present invention, the ceramic of the coating layer and the Si3N4 base material are bonded by HIP processing, which is different from conventional coatings. Not only can the cutting life be increased while making full use of the coating, but also the coating completes the sealing treatment of the pre-sintered body, making it possible to achieve high density through HIP treatment and improving cutting performance. This method, together with its superiority over that of Ar gas, exhibits a remarkable effect suitable for the current high-speed manufacturing method for cutting chips, and is a method that can be expected to have great practicality and usefulness.

Hereinafter, the method of the present invention will be further specifically explained with reference to Examples.

Example 1 Y2O3 powder 6 was added as a sintering aid to commercially available Si3N4 powder.
%, Al t O3 powder 2%, and MgO powder 3% were added and mixed, and this mixed powder was cold-formed in a 500 mm mill, and then N! Preliminary sintering was performed in gas at 1600° C. for 1100 minutes to produce a pre-sintered body with a relative density of 97%. next,
The surface of this pre-sintered body was coated with TiN and TiC to a thickness of about 5 μm each by physical vapor deposition.

Next, the pre-sintered body on which these coating layers were formed was subjected to HIP treatment under the HIP treatment conditions shown in Table 1.
A 5iaN4 sintered body was produced. Furthermore, for comparison, the 5isNa sintered body without the coating layer and the preliminary sintered body with the coating layer were subjected to HI in an Ar gas atmosphere.
A 5isN4 sintered body was prepared by P treatment. Regarding these 5iaN4 sintered bodies, 1. Work material: Cast iron (FC2
5) Cutting speed: 100m/sm Feed rate: 0.3fl/rev
A cutting test was conducted under the following conditions: depth of cut: 2.01111 tool shape: 5NGN 482, and the results shown in Table 1 were obtained.

The cutting performance was evaluated based on the cutting time at which the flank wear width of the tool was 0.3M.

As is clear from Table 1, TiN or TiC is coated and then H is applied under specified conditions in an N2 gas atmosphere.
The cutting performance of the tool subjected to IP treatment by the method of the present invention is as follows:
Regardless of the method of the present invention, the results were extremely good compared to tools subjected to HIP treatment in an Ar gas atmosphere, and the cutting performance improvement effect of the coating was remarkable. In addition, tools subjected to HIP treatment in an Ar gas atmosphere (test! 'h2,
L8) is a tool without a coating layer (test calm 7)
Yoshi also has low cutting performance, but this is due to the base material Si3N4.
This is thought to be due to incomplete adhesion between the film and the coating layer.

Example 2 Commercially available Si3N powder and Y2O3 powder 6 as a sintering aid
%, 3% Al2O3 powder, and 1% MgO powder were added and mixed, and this mixed powder was used in the same manner as in Example 1 to produce a preliminary sintered body having a relative density of 86%.

The surface of this pre-sintered body was coated with TiC or TiN to a thickness of 8 μm each by chemical vapor deposition.
When HIP treatment was carried out in the same manner as above and a cutting test was conducted on these Si3N4 sintered pieces, the results shown in Table 2 were obtained.

(7:7) (1) From the results in Table 2 above, HIP is performed under N2 gas atmosphere.
The cutting performance of the tool treated by the method of the present invention is significantly superior to that of the tool treated by the HIP treatment in an Ar gas atmosphere that is not treated by the method of the present invention, and shows the same tendency as shown in Table 1. was clearly observed.

Patent applicant: Kobe Steel, Ltd.

Claims (1)

[Claims] 1. After molding and pre-sintering a mixed powder of silicon nitride powder and adding an energizing agent, and then coating the surface of this pre-sintered body with ceramic using an appropriate vapor deposition method, The ceramic coating layer forming pre-sintered body was heated under a nitrogen gas atmosphere at a pressure of 500 to 2000 atm, lIl&x56
Manufacturing method 1 of a silicon nitride chip for a cutting tool, characterized in that the silicon nitride chip is formed into a cutting tool chip by performing hot isostatic pressing treatment for 5 minutes or more under conditions of o ~ 2ooo ° C. 2. Relative of pre-sintered body A method 8 for producing a silicon nitride tip for a cutting tool according to claim 1, wherein the density is 80% or more, and claim 1 or 8, wherein the ceramic to be coated is titanium carbide or titanium nitride. Silicon nitride for cutting tools≠Production method 4 for cutting tools according to claim 2, wherein the coating layer has a thickness of 20μ or less Silicon nitride chips for cutting tools according to claim 1, 2 or 3 Manufacturing method