JPS6235994B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention disperses hard particles in a sintered body mainly composed of silicon nitride or silicon nitride solid solution (hereinafter referred to as Si ₃ N ₄ ) to increase toughness and wear resistance. The present invention relates to a high-strength sintered body and a method for manufacturing the same. [Prior art and its problems] In recent years, in the industry that cuts steel, cast iron, etc.
High-speed cutting at speeds of 300 m/min or more is becoming commonplace. In such a high-speed cutting region, a white tool made of an aluminum oxide (Al ₂ O ₃ )-based sintered body and an Al ₂ O ₃
-A typical cutting tool is a black tool made of TiC (titanium carbide) composite sintered body. Both of these cutting tools must be made of high-strength sintered bodies that are tough and have high wear resistance. Of these, aluminum oxide (hereinafter referred to as
The sintered body (referred to as Al ₂ O ₃ ) has excellent oxidation resistance, low reactivity with molten iron, and is a cutting tool material that exhibits excellent cutting properties for steel and cast iron. However, this
Al ₂ O ₃ sintered bodies (alumina ceramics) have drawbacks in chipping resistance and chipping resistance due to the brittleness peculiar to ceramics, and many attempts have been made to improve these. Among them, the so-called black tool, which is made by adding 20 to 40% by weight of TiC to Al ₂ O ₃ , is the most commonly used ceramic cutting tool at present, as it has improved to some extent the drawbacks of Al ₂ O ₃ -based cutting tools. There is.
However, even this black tool is still insufficient for interrupted cutting such as milling, and furthermore, no tool has been found that has sufficient thermal shock resistance to enable cold water cutting. In view of the current situation, consideration has been given to constructing cutting tools using Si ₃ N ₄ based sintered bodies, which have even better thermal shock resistance than Al ₂ O ₃ based cutting tools. However, although this Si ₃ N ₄ -based sintered body has great toughness, its reactivity with molten iron is extremely high compared to Al ₂ O ₃ -based sintered body, so it is not suitable for cutting tools used for high-speed cutting of steel and cast iron. In this case, due to the high temperature at the boundary between the tool and the workpiece, it reacts with the locally melted surface of the workpiece, resulting in wear that is 3 to 5 times that of Al ₂ O ₃ based cutting tools. Si ₃ N ₄ based sintered bodies have not been put to practical use especially as cutting tool materials. [Means for solving the problems] The present invention was developed in view of the above-mentioned circumstances, and combines the excellent properties such as toughness and thermal shock resistance of silicon nitride sintered body with the alumina sintered body. Non-reactivity with molten iron,
As a result of research to combine properties such as wear resistance, improvements were made by suppressing the reaction between silicon nitride and alumina during firing and allowing alumina to exist as hard particles independently from silicon nitride crystal particles. I found out that. The present invention will be explained in detail below. According to the present invention, it is important that aluminum oxide (alumina) crystal particles are present in the sintered body mainly composed of silicon nitride, independently of other structures such as silicon nitride crystal particles. It has been known that alumina is an excellent sintering aid for silicon nitride. Normally, when a mixture of silicon nitride powder and alumina powder or a compact thereof is exposed to a high temperature atmosphere of 1500℃ or higher, alumina dissolves in silicon nitride and reactants such as Si-Al-O-N are generated. Alternatively, aluminosilicate glass is generated between silicon nitride crystal particles by reacting with SiO ₂ that inevitably exists on the surface of the silicon nitride powder. Conventionally, when alumina is used as a sintering aid, the main idea is to allow all of the added alumina to exist as a reactant such as Si-Al-O-N or aluminosilicate glass without remaining as alumina. be. The present invention differs from such a concept, and is aimed at minimizing the reaction of the added alumina powder with silicon nitride or silica, and actively allowing the alumina powder to remain as it is. Specifically, the manufacturing method is as follows: aluminum oxide (alumina) as raw material powder is over 30% by weight and 80% by weight or less, silicon nitride powder is 20% by weight, 70% by weight or less.
After the mixed powder blended at a ratio of less than % by weight is molded into a predetermined shape, it is fired. Firing is from 1550
For example, hot press firing, non-pressure firing, or gas pressure firing is performed at a temperature of 1800° C. in a non-oxidizing atmosphere such as nitrogen or argon. As the firing progresses, a reaction with silicon nitride or SiO ₂ progresses from the surface of the added alumina powder particles. However, in the present invention, by stopping the firing before the reaction is completed, unreacted particles can be removed. This is intended to allow alumina to remain as hard particles. Further, the remaining amount of alumina is determined by the balance between firing temperature and firing time. That is,
When the firing temperature is high, alumina can remain by setting the firing time short. The preferable firing time is 5 to 180 minutes so that the remaining amount becomes a predetermined amount. If the firing time is less than 5 minutes, sintering will be insufficient and the strength will decrease.
If the time exceeds 1 minute, all the alumina will react and no remaining alumina will be formed. Furthermore, the reason why the amount of aluminum oxide added to the raw material powder was limited to the above-mentioned range is that if the amount of aluminum oxide is less than 30% by weight, it will react with silicon nitride or silica to form hard particles of alumina into the sintered body. This is because it is difficult to make it exist in a proportion of 50% by weight, and if it exceeds 80% by weight, the thermal shock resistance and high strength, which are the characteristics of silicon nitride, cannot be obtained. The sintered body thus obtained contains aluminum in an amount of more than 30% by weight and less than 80% by weight in terms of oxide.
It contains silicon at a ratio of 20% by weight, less than 70% by weight in terms of nitride, of which the remaining amount as alumina is smaller than the total amount from the viewpoint of performance as a cutting tool, as is clear from the examples described later. against 10
The content is preferably from 50% by weight. That is, if the amount of residual alumina is less than 10% by weight, the effect of the present invention is insufficient, the amount of wear is large, and the strength and height are low. On the other hand, if it exceeds 50% by weight, wear resistance improves but strength decreases. This alumina exists as hard particles that are independent of other structures such as silicon nitride crystal particles, and its particle size depends on the particle size of the raw material powder. The particle size is not particularly limited as long as the particle size is . Furthermore, according to the present invention, it is desirable to add other components for the purpose of improving the strength of the sintered body. Other components used include AlN,
In addition to MgO, rare earth oxides such as Y ₂ O ₃ can be used. The preferred blending amount of these is 1 AlN.
MgO is 1 to 8% by weight, and rare earth oxides are 1 to 8% by weight. If the amount of any of these additives is exceeded, the strength tends to deteriorate. The invention will now be explained with the following examples. Example: Si ₃ N ₄ powder with an average particle size of 0.65μ as raw material powder,
Using the same 2.4 μ α-Al ₂ O ₃ powder, the composition was prepared as shown in Table 1, and 200 c.c. of methanol and 650 g of
24 sealed in a 500c.c. poly container with Si ₃ N ₄ balls
The mixture was mixed and ground in a vibrating mill for hours. Next, the powder obtained by dry granulation was filled into a graphite mold and heated at 1650℃ and 350℃.
Samples A to E were prepared by hot press firing at Kg/cm ² for 20 minutes. The residual amount of α-Al ₂ O ₃ in samples A to E for each composition ratio, bending strength,
The hardness and amount of wear when subjected to cutting were measured and shown in Table 1. Note that the remaining amount of Al ₂ O ₃ in the sintered body is α−
It was analyzed as Al ₂ O ₃ by X-ray diffraction method. The conditions under which the cutting test was carried out were as follows: using a test sample of SNGN432 (Japanese Super Tool Association standard) chamfer 0.2, cast iron (FC25) as the cut material, cutting conditions: speed 300 m/min, feed 0.25 mm, depth of cut 0.2
mm, and after cutting for 1 minute, the amount of wear on the flank was measured. In addition, the bending strength was determined by sample shape 3×
Measurements were made using 3-point bending on a 3 x 15 mm span of 10 mm.

[Table] According to Table 1, the raw material composition is 10 to 80% by weight.
_In samples mixed _{with Al 2} O ₃ powder _of The abrasive effect is insufficient, and bending strength tends to decrease when it exceeds 50% by weight, and when it exceeds 10% by weight.
It was found that those with a residual Al ₂ O ₃ content of 50% by weight were superior in terms of flank wear amount, bending strength, hardness, etc. Example Using Si ₃ N ₄ powder with an average of 0.65μ and Al ₂ O ₃ powder with an average diameter of 2.4μ as raw material powder, the Si ₃ N ₄ powder was fixed at 60% by weight and Al ₂ O ₃ was fixed at 40% by weight. Samples were prepared in the same manner as Example 1, then the hot pressing conditions were changed.
(a) to (g) were created. In addition, as an additive, AIN with an average particle size of 2.0 μ
(aluminum nitride) powder, also 0.5μ MgO
Powder, also using 1.0 μ of Y ₂ O _3, was mixed to the composition ratio shown in Table 2, and then 200 c.c. of methanol and 650 c.c.
The mixture was sealed in a 500 c.c. polyethylene container with ₄ g of Si ₃ N balls, and mixed and pulverized in a vibrating mill for 24 hours. After dry granulation,
The obtained powder was hot press fired using a graphite mold at 350 kg/cm ² under the conditions listed in Table 2.

〔Effect of the invention〕

As described above in detail, the sintered body for cutting tools of the present invention improves the toughness of the silicon nitride sintered body by making aluminum oxide exist as hard particles in the sintered body mainly composed of silicon nitride. It is possible to improve wear resistance while maintaining strength, and also to improve reactivity with molten iron, thereby making it possible to use it for high-speed cutting of steel and cast iron.

Claims (1)

[Scope of Claims] 1. A sintered body for a cutting tool consisting mainly of silicon nitride and aluminum oxide, characterized in that aluminum oxide is present as hard particles in the sintered body in a proportion of 10 to 50% by weight. A sintered body for cutting tools. 2 Aluminum oxide powder exceeds 30% by weight, 80
Weight% or less, silicon nitride powder is 20% by weight, 70% by weight
After molding the mixed powder in a proportion of less than
A method for producing a sintered body for a cutting tool, characterized in that aluminum oxide remains as hard particles at a ratio of 10 to 50% by weight by firing for 180 minutes.