JP2001247369A - Cutting tool and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide both a cutting tool composed of a silicon nitride sintered compact capable of exhibiting high abrasion resistance and defective resistance especially in high-speed cutting of a cast iron and to provide a method for producing the same. SOLUTION: Both TiC and TiN are added to a sintered compact and TiN is made to preferentially exist on the surface of the sintered compact. A raw material molding containing TiC is heated and retained in a nitrogen gas atmosphere at a temperature lower than a fixed baking temperature and baked at the fixed baking temperature for >=10 hours to prepare the sintered compact.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cutting tool comprising a silicon nitride sintered body having excellent chipping resistance and wear resistance, and a method for producing the same. The present invention relates to the manufacturing method.

[0002]

2. Description of the Related Art Silicon nitride sintered bodies used as cutting tools include alumina sintered bodies, alumina sintered bodies obtained by adding zirconia, titanium carbide, etc. to alumina, and various types of sintering aids to silicon nitride. There is a silicon nitride sintered body to which an agent is added. Among them, the silicon nitride sintered body has the highest toughness among ceramics, and is particularly often used as a cutting tool.

[0003]

In order to improve productivity in various cutting fields, demands for heavy cutting such as high-speed machining and high feed machining are increasing, and the use conditions of cutting tools are increasing year by year. Feeding is progressing. For this reason,
Cutting tools are required to have even higher wear resistance and chipping resistance.

[0004] However, the cutting tool made of the conventional silicon nitride sintered body as described above, when cutting high-speed, high-feed cutting of cast iron, specifically, at a speed of 800 m / min or more and a feed of 0.1 mm.
When the cutting was performed under the condition of 7 mm / rev (mm / tooth) or more, the cutting edge became extremely high temperature, so that sufficient wear resistance and chipping resistance could not be exhibited. As a result, the above-mentioned conventional cutting tool is liable to cause chipping, chipping, abnormal wear, and the like of the cutting edge, and has a short life.

[0005] Accordingly, the present invention provides a cutting tool made of a silicon nitride sintered body which can exhibit high wear resistance and chipping resistance especially for high-speed cutting of cast iron, and a method of manufacturing the same. It is the purpose.

[0006]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and have found that TiC and Ti
It has been found that the cutting tool can exhibit high wear resistance and fracture resistance by including both N in the sintered body and preferentially presenting TiN on the surface of the sintered body.

Further, the present inventors heat and hold a raw material compact containing TiC in a nitrogen gas atmosphere at a temperature lower than a predetermined firing temperature, and then perform firing at the predetermined firing temperature for 10 hours or more. As a result, it has been found that such a sintered body can be produced, and the present invention has been completed.

More specifically, the cutting tool according to the first aspect of the present invention is characterized in that 10 to 68.5 mol% of silicon nitride, 30 to 80 mol% of Ti compound in the form of at least carbide and nitride, and Al a cutting tool using silicon nitride sintered body having a 1.5 to 10 mol% in terms of al ₂ O _3,
The sintered body is characterized in that TiN is preferentially present on the surface of the sintered body.

In such a cutting tool, a large amount of residual stress is generated on the surface portion, and the toughness and hardness are enhanced. That is, TiN having a large coefficient of thermal expansion generates a residual stress in the surface portion in the process of heating and cooling during firing, and the residual stress increases the toughness and hardness of this portion. On the other hand, in the case where TiN is uniformly dispersed and contained in the sintered body or the case where TiN is preferentially present in the inside rather than the surface portion, such improvement in toughness and hardness cannot be obtained. Further, since TiN having excellent toughness and reaction resistance is preferentially present in the surface portion, both abrasion resistance and fracture resistance are further enhanced.

Further, since the sintered body contains TiC having a low coefficient of thermal expansion together with TiN, fracture resistance at a high temperature is improved.

That is, according to the first aspect of the present invention, the wear resistance of the cutting tool is improved by coexisting TiC and TiN as Ti compounds and preferentially allowing TiN to be present on the surface of the sintered body. , Fracture resistance and thermal shock resistance are enhanced.

Further, as a method of manufacturing such a cutting tool,
The third aspect of the present invention is to provide the silicon nitride of 10 to 68.5 mol%.
And at least 30 to 80 mol% of a Ti compound in the form of a carbide and 1.5 to 10 mol% of Al in terms of Al ₂ O ₃ , which are mixed and pulverized, and the mixture is pulverized. Is molded into a predetermined shape, heated and held at a temperature lower than a predetermined firing temperature in a nitrogen gas atmosphere, and then fired at a predetermined firing temperature for 10 hours or more, so that the surface portion of the sintered body is The Ti carbide is preferentially changed to a Ti nitride.

In this manufacturing method, the nitrogen in the firing atmosphere permeates from the surface of the molded body to the inside until the heated body is kept at a temperature lower than the predetermined baking temperature because the molded body has a low density. However, at this stage, the reaction between TiC and nitrogen hardly occurs.

[0014] On the other hand, although the mechanism is not clear, firing at a predetermined firing temperature at a temperature higher than heating and holding results in:
Nitrogen penetrating inside reacts with TiC.

At this time, a reaction from carbide to nitride takes place. As a result, TiC is changed to TiN. By firing at this predetermined temperature for 10 hours or more, the TiN
Formation proceeds to the desired depth.

The surface of the cutting tool is polished as necessary to adjust the sintered body to a predetermined size. Therefore, if the TiN formation is too shallow, no TiN will remain on the surface of the sintered body after polishing. Therefore, T
It is important that the iN formation proceeds to the desired depth.

[0017]

Embodiments of the present invention will be described below.

The silicon nitride sintered body constituting the cutting tool according to the present invention has a silicon nitride content of 10 to 68.5 mol% and a Ti compound in the form of at least carbide and nitride of 30 to 8%.
0 mol%, and 1.5 to 10 mol% of Al in terms of Al ₂ O ₃
It is a composition which has. These compositions are compositions after sintering as a silicon nitride sintered body.

Of these, silicon nitride constitutes a hard phase as hard particles. As the silicon nitride powder used in the present invention, a reduction nitridation method, α-type produced by a direct nitridation method, etc.
Any of the β type may be used, and a powder having a BET specific surface area of 5 m ² / g or more and an impurity oxygen amount of 0.7 to 2% by weight is suitable. When the content of silicon nitride is less than 10 mol%, the sinterability is reduced, and a dense sintered body cannot be obtained, so that the characteristics as a cutting tool cannot be satisfied. On the other hand, the content is 68.5 mol%.
If it is larger than this, the effect of improving the wear resistance and chipping resistance of the cutting tool is small.

In the present invention, the Ti compound such as TiC or TiN is dispersed as hard particles between silicon nitride particles, and has the effect of improving the hardness, reaction resistance and toughness of the sintered body. Furthermore, the cutting tool of the present invention is characterized in that TiC having a low coefficient of thermal expansion and excellent thermal shock resistance and TiN having excellent wear resistance, fracture resistance and reaction resistance coexist as a Ti compound, and It is preferentially present on the surface.

The Ti compound containing TiC and TiN is 3
If it is less than 0 mol%, the effect of improving the wear resistance and fracture resistance of the cutting tool is small, while if it is more than 80 mol%, the sinterability is reduced and a dense sintered body cannot be obtained, so that the cutting tool cannot be used. Cannot be satisfied. It is particularly preferable that the content of the Ti compound is 35 to 75 mol%.

Further, if the surface portion is at least about 750 μm from the surface of the sintered body base material for improving the toughness of the cutting tool, the effect of improving wear resistance and chipping resistance is remarkable. On the other hand, when the layer thickness is thinner than this level, the effect of improving wear resistance and fracture resistance tends to be insignificant. In the cutting tool of the present invention, T
It is desirable that the iN amount is larger than the TiC amount. These T
It is preferable to compare the abundance ratio of iN and TiC with the peak intensity obtained by X-ray diffraction measurement using CuKα radiation. Specifically, for the sintered body constituting the cutting tool, the X-ray diffraction peak of TiN on the surface of the sintered body [(111)
Plane], the peak intensity of TiN in: IN: TiC
When the X-ray diffraction peak of is IC :, it is preferable that IN> IC. In this case, since the TiN concentration on the surface of the sintered body is high, abrasion resistance and chipping resistance tend to be improved. On the other hand, when IN <IC, abrasion resistance,
There is a tendency that the improvement in fracture resistance is hardly seen.

The presence of TiC or TiN can also be performed by observing the structure with a metallographic microscope. Silicon nitride, TiC, and TiN, which are hard particles, have distinctly different light and darkness in the above microstructure observation, and it is easy to confirm their existence. Therefore, the presence of TiC or TiN at a desired depth can be confirmed by polishing the surface of the sintered body in the depth direction and observing the structure on the exposed surface.

Next, the Al is added as a sintering aid in the form of Al ₂ O ₃ . The sintering aid reduces voids in the sintered body,
It has the effect of reducing the particle size. Al is 1.
If the amount is less than 5 mol%, the sinterability is low, and a dense silicon nitride sintered body cannot be obtained when a Ti compound is added. On the other hand, if it is more than 10 mol%, the thermal shock resistance and the reaction resistance of the sintered body are deteriorated, and the performance as a cutting tool is inferior.

In the cutting tool of the present invention, an oxide of a Group 3a element (RE) may be added together with Al as a sintering aid. Examples of Group 3a elements of the periodic table used in the present invention include Y, Sc, Yb, Er, Dy, Ho, and Lu. Among them, Er, Yb, and Lu are particularly used when used as a cutting tool. Is good.

When the element of Group 3a of the periodic table is contained, if it is more than 10 mol% in terms of oxide relative to the silicon nitride, the hardness of the sintered body is reduced and the wear resistance as a cutting tool is deteriorated. I do. If the content of Group 3a element in the periodic table is less than 1 mol% with respect to silicon nitride, a dense body cannot be obtained and the chipping resistance of the cutting tool decreases.

These sintering aids such as Al ₂ O ₃ and oxides of Group 3a element (RE) are included in the grain boundary phase of the sintered body.
The grain boundary phase may be amorphous, but is preferably crystallized. Apatite, Y
It is desirable that the main component be at least one of AM, wollastonite, disilicate, and monosilicate.

Next, a method for manufacturing such a cutting tool will be described.

First, a powder of a Group 3a element (RE) oxide of the periodic table as an additional component is added to silicon nitride powder;
Al ₂ O ₃ powder is added and mixed with a ball mill or the like.

The mixture mixed as described above is formed into an arbitrary shape by desired molding means, for example, a die press, a cold isostatic press, an extrusion molding, a casting molding, an injection molding and the like.

Next, the molded body is put into a firing furnace,
After heating and holding at a temperature lower than a predetermined firing temperature in a nitrogen gas atmosphere, firing is performed for 10 hours or more at a predetermined firing temperature, so that Ti
C is preferentially changed to TiN.

In the production method of the present invention, the sintering temperature is 1700 to 2000 ° C., although it varies depending on the starting composition and the size of the molded product, and the heating and holding temperature is 1600 to 1800 ° C. Is preferred.
In particular, the firing temperature is preferably in the range of 1770 ° C to 1780 ° C, and the heating and holding temperature is preferably in the range of 1650 ° to 1760 ° C.

When the heating and holding temperature is lower than 1600 ° C., the production of TiN as a reaction product tends to be difficult. On the other hand, when the heating holding temperature exceeds 1800 ° C., the densification of the sintered body proceeds rapidly, and as a result, TiN tends to be hardly generated.

When the calcination temperature is lower than 1700 ° C., the amount of TiN produced tends to decrease.
If the temperature is higher than 000 ° C., abnormal crystal growth may occur, or silicon nitride may be decomposed and the surface may be roughened.

The temperature difference between the heating and holding and the firing is 1
A temperature difference range from 0 ° C to 200 ° C is preferred. When this temperature difference is less than 10 °, TiN tends to be hardly generated. Also, when the temperature difference exceeds 200 ° C., TiN tends to be hardly generated.

It is preferable that the heating and holding are performed for 4 to 8 hours and the firing is performed for 10 to 18 hours. If the heating holding time is less than 4 hours, TiN tends to be hardly generated. On the other hand, if the heating holding time exceeds 8 hours, the effect of improving wear resistance and fracture resistance tends to decrease. If the baking time is less than 10 hours, it tends to be difficult to densify, and it is difficult to generate TiN. On the other hand, if the firing time exceeds 18 hours, the effect of improving wear resistance and chipping resistance tends to decrease.

As a firing method, it is sufficient that silicon nitride is not decomposed, and normal pressure firing, nitrogen gas pressurization firing at 2 atm or more of nitrogen gas, hot press firing method and the like are used. In addition, after these heat holding and firing, 1000
It can be further densified by hot isostatic firing under a pressure of at least atmospheric pressure. In particular, firing in a non-oxidizing atmosphere containing nitrogen gas at 2 atm or more is desirable.

After firing, in order to adjust the sintered body to a predetermined size of the cutting tool, the surface is polished to remove a thickness of about several hundred μm as necessary.

Further, in the cutting tool of the present invention, the surface of the sintered body may include a hard layer made of at least one selected from carbides, nitrides, carbonitrides, and Al ₂ O _{3 of} Groups 4a, 5a and 6a of the periodic table. May be coated.

The carbides, nitrides, carbonitrides and Al ₂ O ₃ belonging to groups 4a, 5a and 6a of the periodic table have a high hardness and an excellent reaction resistance with the work material. Can be improved. It is desirable to use a CVD method and a PVD method to form the surface coating layer.

In the case of a cutting tool having the hard layer, it is difficult to measure the maximum peak intensity of TiN and TiC in the X-ray diffraction strictly on the surface of the sintered body.
This means that even when working carefully when removing the hard layer,
This is because the surface of the sintered body is usually removed by about several to several tens of μm. Therefore, the measurement of the X-ray diffraction in the case where the hard layer is provided indicates that the surface of the original sintered body is several to several times.
Even if it is removed by about 10 μm or more, it may be performed on the surface after the removal.

[0042]

EXAMPLE An α-type silicon nitride powder (BE) was used as a raw material powder.
T specific surface area 10 m ² / g, impurity oxygen content 1.0 wt%)
And a sintering aid using an oxide of an element belonging to Group 3a of the Periodic Table shown in Table 1, Al ₂ O ₃ , and a Ti compound. A binder for molding was added thereto and mixed using a silicon nitride ball, and CNGN160412 was applied under a pressure of ² ton / cm ^2.
Then, press molding was performed to the tool shape of SNGN120408. Further, cold isostatic pressing was performed at a pressure of 3 ton / cm ² to obtain a molded body.

The molded body was placed in a firing furnace, and was heated and held at a nitrogen gas pressure of 5 atm and fired at a predetermined temperature at a nitrogen gas pressure of 10 atm at the temperature and time shown in Table 1, and the results are shown in Table 1. Sample No. 1 to 23 sintered bodies were obtained.

[0044]

[Table 1]

Subsequently, the surface of these sintered bodies was about 250 μm
Was subjected to a polishing treatment to obtain a final tool shape as a cutting tool.

The obtained cutting tool was subjected to ICP emission spectroscopic analysis to determine Si, a Group 3a element (RE) of the periodic table,
The amounts of Al and Ti are determined, and Si is regarded as Si ₃ N ₄ and RE
Is RE ₂ O ₃ , Al is Al ₂ O ₃ , Ti is T
The composition ratio was determined by converting it into carbide, nitride and carbonitride of i. The X-ray diffraction peak was measured using CuKα radiation.

Further, the surface structure of the cutting tool was observed with a metallographic microscope, 750 μm was polished, and the structure was observed with a metallographic microscope.

FIG. 1 shows the sample No. of the product of the present invention shown in Table 1. Sample No. 1 and Comparative Example 18 sintered body surface (2
4 is a graph of the X-ray diffraction peak (after polishing removal of 50 μm). As shown in the figure, in both samples, α-type silicon nitride was changed to β-type silicon nitride.

Further, the sample No. of the product of the present invention was used. 1 is
The maximum peak intensity of TiN is more than three times greater than the maximum peak intensity of TiC. Therefore, TiN
The concentration is several times higher than the TiC concentration. All other examples of the present invention (samples Nos. 2 to 9) had similar results.

Further, according to the structure observation by the metallographic microscope, the products of the present invention (samples Nos. 1 to 9) showed that the TiN was obtained at both the surface of the cutting tool and at a depth of 750 μm from the surface.
Could be confirmed. In addition, the existence ratio of TiN particles was clearly higher on the surface.

On the other hand, Sample No. 18
Has a peak of TiC, but a peak of TiN cannot be clearly distinguished. As for the peak of TiN, there is only a possibility that a very small peak exists at a portion indicated by a dotted line A in the figure. In such a sintered body, it cannot be said that TiN exists preferentially on the surface. Among other comparative examples, No. 17,
19 to 21 had similar results.

Further, the sample Nos. 17 ~
In No. 21, almost no TiN was confirmed on the surface in the structure observation with the metal microscope. On the other hand, 750
At a depth of μm, the presence of TiC particles could not be confirmed at all.

The sample No. Comparative Example No. 22 was prepared by adding only TiN as a Ti compound and containing TiN in a substantially uniform dispersion state throughout the sintered body. In Comparative Example 23, only TiN was added as a Ti compound, and the entire sintered body contained TiN and TiC in a substantially uniformly dispersed state. That is, in these two comparative examples, TiN was contained in the sintered body as a whole in a substantially uniformly dispersed state.

Sample No. shown in Table 1 For 1 to 23,
As a cutting test for evaluating abrasion resistance using a CNGN160412 tool shape, a gray cast iron material was dry-turned under the following cutting conditions, and a wear width after cutting for 20 minutes was measured. The results are shown in Table 1 above. Work material FC250 Cutting speed 800m / min Feed 0.7mm / rev Depth of cut 3.0mm In addition, as a cutting test for evaluating fracture resistance, S
Using a sample having the shape of NGN120408, a test for processing a spheroidal graphite cast iron material by face milling under the following conditions was performed. Work material FCD450 (cubic shape of 125 × 300 mm) Cutting speed 800 m / min Feeding 0.7 mm / tooth Cutting depth 3.0 mm The cutting time up to chipping in this test is also shown in Table 1 described above.

As shown in Table 1, the sample No. of the product of the present invention was used. Each of 1 to 9 has a wear width of 0.2, which is generally judged to have good wear resistance in a cutting test.
It was less than 0 mm, and no defect occurred even after 20 minutes. The reason why the product of the present invention exhibited good wear resistance and chipping resistance as described above is considered to be as follows.

The product of the present invention is made of Ti having a large coefficient of thermal expansion.
N generates a residual stress in the surface portion in the process of heating and cooling during firing, and the residual stress increases the toughness and hardness of this portion. In addition, T which is excellent in toughness and reaction resistance
Since iN is preferentially present in the surface portion, both abrasion resistance and fracture resistance are further enhanced. Further, the example product of the present invention contains TiC having a low coefficient of thermal expansion together with TiN, whereby the fracture resistance at high temperatures is enhanced.

On the other hand, the samples No. 10-2 of the comparative example
In No. 3, the wear width was larger than the wear width of 0.20 mm, and further, chipping occurred within 20 minutes, and the tool life was shortened.

Of the comparative examples, sample no. The compositions of Nos. 10 to 16 are out of the range of the present invention, so that at least one of abrasion resistance and fracture resistance is not good. This shows that the composition range of the present invention is important.

In addition, the sample No. of the comparative example was no. 17-21 are
As described above, almost no TiN is formed on the surface of the sintered body, and TiN is not predominantly present on the surface of the sintered body. That is, almost all Ti compounds contained in the sintered body are TiC. as a result,
At least one of wear resistance and fracture resistance is not good. From this, it is understood that it is important that both the TiN and TiC are contained in the sintered body and that the TiN is preferentially present on the surface portion of the sintered body.

Among them, the sample No. of the comparative example. In No. 18, the heating holding temperature and the sintering temperature were the same as 1700 ° C. As a result, almost no TiN was formed on the surface of the sintered body, and neither the wear resistance nor the chipping resistance was good. From this,
In the manufacturing process of the cutting tool of the present invention, it is understood that it is important to raise the temperature of the firing performed after the heating and holding with respect to the heating and holding temperature.

The sample No. of the comparative example was used. In No. 19, the firing time was less than 10 hours (9 hours). As a result, almost no TiN was formed on the surface of the sintered body, and neither the wear resistance nor the chipping resistance was good. This indicates that it is important to perform firing for 10 hours or more in the manufacturing process of the cutting tool of the present invention.

Next, the sample No. of the comparative example was used. Samples Nos. 22 and 23 contained TiN in a substantially uniformly dispersed state throughout the sintered body. As a result, both the fracture resistance and the wear resistance were not good. That is, even if TiN is contained in the entire sintered body, when TiN is not preferentially present on the surface portion of the sintered body, the fracture resistance and the wear resistance are not improved. This indicates that it is important that TiN preferentially exists on the surface of the sintered body.

[0063]

As described in detail above, the cutting tool of the present invention has excellent wear resistance, chipping resistance and thermal shock resistance in high-speed cutting of cast iron, and can extend the life of the tool.

[Brief description of the drawings]

FIG. 1 shows a sample No. which is an example of the present invention. 1 and Comparative Example No. 18 is a graph of the X-ray diffraction peak on the surface of the sintered body No. 18 (after polishing and removal of 250 μm).

[Explanation of symbols]

 A Location where a TiN peak may be present.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C04B 35/64 C04B 35/58 102T 35/64 DF Term (Reference) 3C046 FF33 FF40 FF42 4G001 BA03 BA08 BA09 BA25 BA32 BA73 BB03 BB08 BB09 BB25 BB32 BB38 BC12 BC13 BC52 BC57 BD12 BD18 BE11 BE35

Claims (4)

[Claims] (1) a silicon nitride of 10 to 68.5 mol% and a Ti compound in the form of at least carbide and nitride of 30 to
A cutting tool using a silicon nitride sintered body having 80 mol% and 1.5 to 10 mol% of Al in terms of Al ₂ O ₃ , wherein the sintered body is made of TiN and a surface portion of the sintered body. Cutting tool characterized by being preferentially present in the cutting tool. 2. In X-ray diffraction using Cu Kα ray,
The cutting tool according to claim 1, wherein the maximum peak intensity of TiN on the surface of the silicon nitride sintered body is larger than the maximum peak intensity of TiC. 3. A silicon nitride of 10 to 68.5 mol% and a Ti compound in the form of at least 30 to 80 mol% of carbide.
And a composition for a silicon nitride sintered body containing 1.5 to 10 mol% of Al in terms of Al ₂ O ₃ , mixed and pulverized, and the mixture is formed into a predetermined shape, and the mixture is formed in a nitrogen gas atmosphere. A method for manufacturing a cutting tool, comprising a step of heating and holding at a temperature lower than a firing temperature and then firing at a predetermined firing temperature for 10 hours or more. 4. The method according to claim 3, wherein the sintering temperature is 1700 to 2000 ° C., and the heating and holding temperature is 1600 to 1800 ° C.