JPS6246511B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ceramic material containing Si ₃ N ₄ as a main component and used as a cutting tool.

The main materials for cutting tools are cemented carbide mainly composed of WC, cermets mainly composed of TiC, and ceramics mainly composed of Al ₂ O ₃ . to
Coating tools that coat TiC and Al ₂ O ₃ are being developed. On the other hand, due to the shortage of W resources and Co resources, research is underway to develop alloys that can replace WC-Co alloys as a so-called W-saving approach. Ceramics containing silicon nitride or silicon carbide as a main component are seen as promising candidates. The reason for this is that these compounds have a low coefficient of thermal expansion and good high-temperature oxidation resistance, which reduces the increase in cutting edge temperature during high-speed cutting (1000
It is thought that it can withstand temperatures of around 30°F (°C), and its toughness at high temperatures is much better than that of Al ₂ O ₃ ceramics. However, cutting tools containing Si ₃ N ₄ and SiC as main components are not yet commercially available.

This is because when steel is cut using a sintered body containing Si ₃ N ₄ as the main component, abnormal wear occurs on the rake face side of the tool cutting edge in a short period of time, causing the cutting edge to break. As a countermeasure to this, if a coating film such as Al ₂ O ₃ is applied to the surface of the Si ₃ N ₄ tool, the wear will become normal and it will
The research conducted by the present inventors has revealed that Si ₃ N ₄ exhibits exactly the same performance as TiC-TiN cermet tools, and is actually more advantageous on the high-speed cutting side.

Generally, sintered bodies of Si ₃ N ₄ are made of Y ₂ O ₃ , MgO, Al ₂ O ₃ ,
It is sintered with oxides such as ZrO ₂ to form spinel with SiO ₂ to increase the density of the sintered body. Since sintering with oxides reduces the strength at high temperatures, it is necessary to reduce the amount of additives as much as possible, and many studies have been conducted on this topic. However, as the amount of additives decreases, the strength of the Si ₃ N ₄ grain boundaries decreases.
This decrease in grain boundary strength is caused by Si ₃ N ₄ along with chips during cutting.
This seems to cause abnormal wear of the cutting edge because the particles are carried away.

The present inventors have found that the strength at high temperatures does not decrease, and
As a result of investigating various binders that firmly fix Si ₃ N ₄ particles, we found that silicides of group a, a, and a
It was found that it is most suitable for sintering Si ₃ N ₄ .

TiSi ₂ (melting point mp=
1540℃), ZrSi ₂ (mp=1520℃), group a silicides include VSi ₂ (mp=1600℃), NbSi ₂ (mp
= 1950°C), TaSi ₂ (mp = 2400°C), CrSi ₂ (mp = 1570°C), MoSi ₂ (m.
p=1870°C), WSi ₂ (mp=2650°C), etc.

Of these, MoSi ₂ is suitable for Si ₃ N ₄ sintered bodies for cutting tools. The sintering temperature of Si ₃ N ₄ is 1600°C to 1900°C, and preferably 1700°C to 1850°C. 1850℃
In this case, changes such as transformation of Si ₃ N ₄ from α to β, decomposition of Si ₃ N ₄ , and denitrification occur. At this time, if MoSi ₂ etc. coexists as a binder, the decomposed Si becomes MoSi ₂
The sintering progresses rapidly due to the absorption in the material.

If MoSi ₂ is less than 1% by weight, it has no effect on improving sinterability, and if it exceeds 20% by weight, it deteriorates the high-temperature properties.

It has been found that sintering with this silicide improves the wetting of the grain boundaries of the sintered body, thereby significantly reducing wear during cutting.

In carrying out this method, up to 5% by weight of MgO, Y ₂ O ₃ , Al ₂ O ₃ may be added as a sintering accelerator.
When these sintering accelerators exceed 5% by weight, the high temperature properties deteriorate. Further, it is desirable that the Si ₃ N ₄ raw material powder used contains 70% by weight or more of the α phase; if the α phase is less than 70% by weight, the sinterability is poor and it is difficult to obtain a high-strength sintered body in the end.

Example 1 MoSi ₂ powder was added to 89% by weight of α-type Si ₃ N ₄ powder.
A mixed powder containing 10% by weight and 1% by weight of MgO was pressure-molded at a pressure of 5 tons/cm ² to form a tool edge shape of SNG432. This molded body was buried in Si ₃ N ₄ powder and sintered in a vacuum furnace consisting of a carbon heating element. The sintering conditions were as follows: the pressure was adjusted to 500 Torr in a reduced-pressure nitrogen atmosphere, and the temperature was maintained at 1750° C. for 2 hours. The obtained sintered body had a specific gravity of 98% or more of the theoretical specific gravity. A carbon steel cutting test was conducted using the sintered body as a cutting tip of SNG432.
The carbon steel used had a hardness of approximately HB200 and a C content of approximately 0.5% by weight, and was cut at a cutting speed of 200 m/min, depth of cut of 1.5 mm, and feed rate of 0.3 mm/rotation.
The tool life time was measured.

The tool of the present invention has a wear amount of V _B = 0.2 mm over a life of 20 minutes.
It was hot. On the other hand, the conventional Si ₃ N ₄ consisting of Si ₃ N ₄ - Y ₂ O ₃
After 10 seconds of cutting, the KT of the tool began to wear abnormally, making it unusable.

Claims (1)

[Claims] 1 MoSi ₂ 1 to 20% by weight, the balance being α phase 70% by weight
A sintered body for Si ₃ N ₄ cutting tools made of Si ₃ N ₄ containing the above. 2 MoSi ₂ 1-20% by weight, Y ₂ O ₃ , MgO, ZrO ₂ 1
A sintered body of Si ₃ N ₄ for a cutting tool, which is made of Si ₃ N ₄ containing 5% by weight or less of seeds or more, and the balance containing 70% by weight or more of α phase.