JPH0375485B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for producing titanium carbonitride with uniform grains and fine particles with little deviation from a desired composition when producing titanium carbonitride that is a raw material for cutting tools such as cemented carbide and cermet. Prior art and its problems Methods for producing titanium carbonitride can be roughly divided into the following three methods. A method of heat-treating a mixture of titanium carbide powder and titanium nitride powder at high temperatures (referred to as method A), a method of heat-treating a mixture of titanium metal powder and carbon powder under a nitrogen atmosphere (referred to as method B), and titanium oxide powder A method of heat-treating a mixture of carbon powder and carbon powder in a nitrogen atmosphere (Method C
). First, method A has the advantage that it is easy to control the ratio of carbon and nitrogen in titanium carbonitride, but in order to achieve a sufficient solid solution of titanium carbide and titanium nitride, a high temperature of 2000℃ or higher is usually required. Under such high temperatures, the particles become coarser, and at the same time, sintering progresses between the particles, resulting in solidification, making it difficult to grind as a post-process. If an attempt is made to process at a low temperature to avoid this, it will take a long time to complete the solid solution, which is impractical. Furthermore, using titanium carbide or titanium nitride that has been carbonized and nitrided as a raw material is wasteful in terms of energy, resulting in an increase in cost. Next, regarding method B, in order to obtain fine powder, the starting material, titanium metal powder, must also be fine-grained, which increases the surface area, which causes the problem that the amount of residual oxygen in the powder increases. be.
In addition, metal titanium powder generally has an angular shape, and the resulting powder also retains this shape.
Requires pulverization before use. Finally, method C can use fine particles of 1 μm or less for both titanium oxide and carbon powder as starting materials, and the resulting powder not only has a similar fineness, but also saves energy and costs. There are advantages. Despite this, the reason why this method has not been put to practical use is because it uses oxides as starting materials, oxygen tends to remain in the resulting powder, and the added carbon powder does not completely dissolve in solid solution, leaving it as free carbon. There is a big reason why they remain. A method to solve this problem has also been proposed (Japanese Patent Application Laid-Open No. 58-213617
(No.), heating is performed at 1,700 to 2,000℃ to remove residual oxygen, so some grain growth is unavoidable, and carbonitrides with a high proportion of nitrogen cannot be produced in principle (described later). be. Another problem was that it was difficult to control the ratio of carbon and nitrogen in the resulting carbonitride. Means for Solving the Problems In order to solve the above problems and obtain titanium carbonitride with uniform grains and fine particles with little deviation from the desired composition, it is necessary to control not only the temperature but also the nitrogen partial pressure. I thought it might be necessary. When producing titanium carbonitride, titanium carbide is stable at high temperatures, but titanium nitride decomposes into metallic titanium and nitrogen at high temperatures, so nitrogen separates during heat treatment during production, resulting in a change in the desired carbon to nitrogen ratio. The ratio of nonmetallic elements to titanium (Z value)
It tends to become a powder with low The pressure at which this decomposition occurs (equilibrium nitrogen partial pressure) can be uniquely determined by determining the composition and temperature of the carbonitride. Based on this fact, the present inventors mixed titanium oxide powder and carbon powder at a predetermined ratio and controlled the temperature and nitrogen partial pressure to achieve a Z value of 1 at the desired ratio of carbon and nitrogen. It has been found that it is possible to obtain titanium carbonitride powder similar to the above. The present invention has been made based on the above findings, and in producing titanium carbonitride powder, titanium oxide powder and the amount necessary to reduce the titanium oxide and carbonize it to titanium carbonitride with a desired composition. 1600K~ after adding carbon powder and mixing well
By heating at a temperature of 1900K while flowing nitrogen at a nitrogen partial pressure that satisfies log PN ₂ = ⁻⁴ This method is characterized in that titanium carbide powder with uniform grains and fine particles is obtained with little deviation from the desired composition. As can be seen from the above calculation formula, a powder with a high nitrogen content can be obtained even at the same nitrogen partial pressure by processing at a low temperature. However, this is a conclusion derived from equilibrium theory, and when considering industrial production, it is also necessary to consider reaction kinetics. According to experiments conducted by the present inventors, it has been found that at temperatures below 1600 K, it takes more than 100 hours to complete the reaction, which is not practical. In addition, at 1900K or higher, the reaction rate increases, but it is not particularly advantageous, and on the contrary, sintering and coarsening of the powder occur, complicating the post-treatment process. Also, from the point of view of energy conservation, high temperatures of 1900K or higher are disadvantageous. From these points, the temperature range was set at 1600-1900K. Next, regarding the nitrogen partial pressure, once the composition and temperature are determined, the equilibrium nitrogen partial pressure is determined. However, this is often calculated from thermodynamic data;
There are few examples of measuring true partial pressure. Therefore, in carrying out the present invention, it is not necessarily accurate to strictly apply the determined equilibrium nitrogen partial pressure, and reduction and carbonitriding are performed under a nitrogen partial pressure that has a certain allowable range. That is appropriate. This is the reason why the nitrogen partial pressure is set within a certain range. If it is higher than this nitrogen partial pressure, nitriding progresses and the composition deviates from the desired composition, and free carbon tends to come out. If it is lower than this nitrogen partial pressure, nitriding does not progress sufficiently and oxygen tends to remain, which is undesirable. . Examples will be explained below. Example 1 To produce titanium carbonitride with a molar ratio of TiC and TiN of 1:9, 76.0% titanium oxide powder and carbon powder were used.
This powder after dry mixing to a proportion of 24.0% diameter
Granulated into a cylindrical shape of 1.5 mm and 10 to 15 mm long, 1600K
Carbonitriding was carried out at a temperature of ~1800K for 1 hour. At that time, production was carried out using both the method according to the present invention in which N ₂ is flowed while maintaining the nitrogen partial pressure at the equilibrium nitrogen partial pressure of Ti (C _0.1 N _0.9 ) at the relevant temperature, and the conventional method in which the nitrogen partial pressure is maintained at 1 atm. I went. The analysis results, particle size and calculated composition of the powder produced are shown in Table 1.

[Table] Example 2 To produce titanium carbonitride with a molar ratio of TiC and TiN of 3:7, titanium oxide powder 74.3%; carbon powder
After dry mixing to a proportion of 25.7%, this powder is
Granulate into a cylindrical shape with a length of 1.5 mm and 10 to 15 mm.
Carbonitriding was carried out at a temperature of 1900K for 1 hour. At that time, production was performed using both the method of the present invention in which N ₂ is flowed while maintaining the nitrogen partial pressure at the equilibrium nitrogen partial pressure of Ti (C _0.3 N _0.7 ) at the relevant temperature, and the conventional method in which N ₂ is flowed at 1 atmosphere. I went there. The analytical results and particle size of the powder produced and the calculated composition are shown in Table 2.

[Table] Example 3 To produce titanium carbonitride with a molar ratio of TiC and TiN of 5:5, titanium oxide powder 72.7% carbon powder
This powder after dry mixing to a proportion of 27.3% diameter
Granulate into a cylindrical shape with a length of 1.5 mm and 10 to 15 mm, and
Carbonitriding was carried out at a temperature of 2000K for 1 hour. that time,
Production was carried out using both the method of the present invention in which N ₂ is flowed while maintaining the nitrogen partial pressure at the equilibrium nitrogen partial pressure of Ti (C _0.5 N _0.5 ) at the relevant temperature, and the conventional method in which N ₂ is flowed at 1 atmosphere. . Table 3 shows the analysis results, particle size and calculated composition of the powder produced.

[Table] Example 4 To produce titanium carbonitride with a molar ratio of TiC and TiN of 8:2, 70.4% titanium oxide powder and carbon powder were used.
After dry mixing to a proportion of 29.6%, this powder is
Granulated into cylindrical shapes of 1.5mm and 10-15mm long, 1800~
Carbonitriding was carried out at a temperature of 2000K for 1 hour. At that time, production was carried out using both the method according to the present invention, in which N ₂ is flowed while maintaining the nitrogen partial pressure at the equilibrium nitrogen partial pressure of Ti (C _0.8 N _0.2 ) at the relevant temperature, and the conventional method, in which N ₂ is flowed at 1 atm. I went. Table 4 shows the analysis results and particle sizes of the powders produced, as well as the calculated compositions.

[Table] Effects of the Invention As described above, by the method of the present invention, titanium carbonitride with uniform grains and fine particles having a desired composition can be obtained.

Claims (1)

[Claims] 1. Add titanium oxide powder and carbon powder in an amount necessary to reduce the titanium oxide powder and carbonize it to titanium carbonitride with the desired composition, mix thoroughly, and then heat at 1600 to 1900K. At a temperature of (1327℃ to 1627℃) log PN ₂ = -4X-1.6×10 ⁴・1/T+Y (10≦Y≦11) where PN ₂ : nitrogen partial pressure (atm) C+N) T: A method for producing titanium carbonitride powder, which is characterized by heating while flowing nitrogen at a nitrogen partial pressure that satisfies the absolute temperature (K) to perform reduction and carbonitriding.