JPH059386B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical field] The present invention relates to a high-hardness silicon nitride sintered body suitable for cutting tools and wear-resistant tools, and in particular, by incorporating a crystal phase consisting of α-type trigonal crystals, it can be used as a heat-resistant alloy or a super heat-resistant alloy. The present invention also relates to a silicon nitride sintered body suitable for cutting tools such as steel. [Background technology] Conventionally, silicon nitride has a trigonal α _- type (low-temperature type) and a hexagonal β-type (high-temperature type) crystal structure _. ,
A sintered body obtained by adding a sintering aid such as Y ₂ O ₃ or MgO is sintered at a high temperature of 1500° C. or higher, so it becomes a high-temperature hexagonal crystal structure. A Si-Al-O-N crystal in which Al and O elements are dissolved or penetrated into silicon nitride is generally called sialon, and especially Si ₆ -
A crystal expressed by the formula zAlzN ₈ −zOz was published in Japanese Patent Application Laid-open No. 1983
-508, which is also called β-Sialon because it has a high-temperature crystal structure, whereas the crystal represented by the _formula Mx (Si, Al) ₁₂ (O, N) It was explained in detail by S. Hampshire et al. [Nature, 274, 880-82 (1978)], and is also called α-sialon because it has a low-temperature crystal structure. Sintered bodies mainly made of silicon nitride with a trigonal crystal structure have not been researched and developed as much as those with a hexagonal crystal structure, and are particularly used in tool parts such as cutting tools and wear-resistant tools. is a silicon nitride sintered body with a hexagonal crystal structure. This silicon nitride sintered body with a hexagonal crystal structure exhibits good cutting performance when the workpiece material is cast iron when used as a cutting tool, but it can be used in workpiece materials other than cast iron, especially heat-resistant alloys. When cutting hard materials with high breaking strength such as super heat-resistant alloys and steel,
Compared to Al ₂ O ₃ ceramics, it has extremely poor wear resistance or chipping occurs on the cutting edge, which limits its use as a cutting tool to a very narrow range. [Object of the Invention] The present invention solves the problems of the conventional silicon nitride sintered body as described above. Specifically, the present invention solves the problems of the conventional silicon nitride sintered body as described above. carbides, nitrides, borides of group 4a, 5a and 6a metals,
By the presence of a dispersed phase of at least one of silicides, oxides or mutual solid solutions thereof,
A silicon nitride sintered body with high hardness and high toughness that has excellent wear resistance, chipping resistance, and thermal shock resistance, especially when used as a cutting tool, even when the work material is various steels, heat-resistant alloys, and non-ferrous metals. The purpose is to provide. [Disclosure of the Invention] Silicon nitride sintered bodies with a trigonal crystal structure tend to have inferior toughness at room temperature compared to silicon nitride sintered bodies with a hexagonal crystal structure, but the hardness decreases less at high temperatures; The deformation mechanism of the silicon nitride sintered body with a crystal structure is only plastic deformation due to dislocation slip and does not involve deformation due to dislocation creep or diffusion creep, so it has excellent toughness at high temperatures. On the other hand, silicon nitride sintered bodies with a hexagonal crystal structure have slightly lower hardness at room temperature than silicon nitride sintered bodies with a trigonal crystal structure, but they have a smaller coefficient of thermal expansion and higher thermal conductivity, so they are more heat resistant. Excellent impact resistance. The present invention is based on the abrasion resistance, chipping resistance, and thermal shock resistance that have been completed as a result of pursuing to maximize the respective advantages of silicon nitride with a trigonal crystal structure and silicon nitride with a hexagonal structure as described above. This silicon nitride sintered body is an excellent silicon nitride sintered body for tools, and exhibits excellent performance especially when cutting various types of steel. That is, the silicon nitride sintered body for tools of the present invention contains the crystal structure modifier 1 of one or more nitrides and/or oxynitrides of metals from groups 1a, 2a, 3a, 3b, and 4b of the periodic table. ~35% by volume and periodic table 4a, 5a,
Group 6a metal carbides, nitrides, borides, silicides,
A sintered body consisting of 1 to 40% by volume of at least one type of dispersed phase in an oxide or a mutual solid solution thereof, the balance being silicon nitride, and inevitable impurities, and meeting the requirements of periodic table 1a, 2a, 3a, 3b, 4b. A hard phase formed by silicon nitride and one or more nitrides and/or oxynitride crystal structure modifiers of group metals is 25
It is a sintered body containing more than % by volume of trigonal structure as a crystalline phase. The hard phase mainly composed of silicon nitride formed by this crystal structure modifier and silicon nitride has a composition of (Sia, Mb) ₂₄ (Ox, Ny) ₃₂
(However, Si is silicon, M is Li of group 1a of the periodic table,
Na, K, Rb, Cs2a group Be, Mg, Ca, Sr, Ba,
Sc, Y of Ra3a group, B, Al of lanthanoid 3b group,
It represents at least one of Ga, In, Tl, and Ge of group 4b, O represents oxygen, and N represents nitrogen. a and b
represent the molar ratio of Si and M, respectively, x and y
represent the molar ratio of oxygen and nitrogen, respectively, a+b=1, a>0, b>0, x+y=1, x≧
It is 0. ) is the trigonal structure crystal phase that can be expressed as 25
It contains more than % by volume. Among these, in the case of a sintered body in which all of the hard phases mainly composed of silicon nitride are crystal phases with a trigonal structure, for example, when used as a cutting tool, the cutting edge or the In some cases, chipping or chipping may occur on the cutting edge due to thermal cracking, which is undesirable. Therefore, in order to increase hardness, toughness, and thermal shock resistance at high temperatures, the hard phase mainly composed of silicon nitride, which is formed by a crystal structure modifier and silicon nitride, has a trigonal structure crystal phase of 35 to It is desirable that the content is 95% by volume. The silicon nitride sintered body for tools of the present invention has a trigonal crystal structure crystal phase and a hexagonal structure crystal phase consisting of a crystal structure modifier and silicon nitride, and carbides of groups 4a, 5a, and 6a of the periodic table. A sintered body consisting of a dispersed phase of at least one of nitrides, borides, silicides, oxides, or mutual solid solutions thereof, in which the trigonal structure crystal phase is mainly the It contributes to hardness and plastic deformation resistance at high temperatures, increasing wear resistance and creep deformation resistance, and the hexagonal crystal structure mainly contributes to improving toughness and increasing fracture resistance. The dispersed phase mixed in the trigonal crystal structure consisting of the modifier and silicon nitride further increases the hardness of the sintered body and increases its thermal conductivity and electrical conductivity, resulting in excellent wear resistance. This results in a sintered body with excellent fracture resistance and thermal shock resistance, resulting in a sintered body for tools that can cut steel and heat-resistant alloys with high breaking strength. Although the hard phase formed by the crystal structure modifier and silicon nitride present in the sintered body of the present invention mainly consists of a trigonal crystal structure crystal phase and a hexagonal crystal structure crystal phase, depending on the manufacturing conditions or Depending on the type and amount of the crystal structure modifier, nitrogen-containing crystalline silicates [e.g. (Si, M) ⁵ (N,
O) ₇ etc.] may be included. The silicon nitride sintered body for tools of the present invention has a temperature increase rate, sintering temperature, or N ₂ partial pressure (PN ₂ ) in the sintering process.
Although it is possible to prevent the transformation from low-temperature trigonal crystals to high-temperature hexagonal crystals and control the content of trigonal structure crystals to some extent by controlling the K, Rb, Cs, Be of group 2a metal, Mg, Ca, Sr, Ba, Ra, group 3a metal
Sc, Y, lanthanoids, group 3b metal B, Al,
Blend component ratio of silicon nitride and crystal structure modifier consisting of at least one of nitrides, oxynitrides, or mutual solid solutions of Ga, In, Tl, and Ge of group 4b metals, and silicon nitride as a starting material The content of the trigonal crystal phase in the sintered body can be controlled by the crystal structure of the sintered body. When increasing the content of the trigonal crystal structure crystal phase in the sintered body, the silicon nitride powder used as the starting material has a high content of trigonal α-silicon nitride, for example, an α ratio of 50% or more. It is desirable to use particles whose average particle size is
It is desirable to use powder with an average particle diameter of 10 μm or less, preferably 2 μm or less, from the viewpoint of improving the strength of the sintered body. In addition, if silicon nitride powder containing amorphous silicon nitride with an α rate of 50% or more is used as a starting material, sintering will be promoted due to the fine powder, but depending on the manufacturing method of silicon nitride powder, it may contain a large amount of oxygen. Particular attention must be paid to the oxygen content because this oxygen content reduces the formation of trigonal crystals during the sintering process. Such silicon nitride powder contains trace amounts of impurities such as Al and Fe,
Oxygen is adsorbed on the surface of silicon nitride powder, forming SiO or
SiO ₂ may be formed, and this SiO or
SiO ₂ is effective in accelerating sintering and densification, but on the other hand, too much of it will reduce the formation of trigonal structure crystals, so use as high a purity as possible, for example 1.2 volume % or less of SiO or SiO ₂ -containing silicon nitride powder. It is preferable to use In addition, the starting raw material powder used in addition to the silicon nitride powder should be as fine as possible to ensure uniform dispersion in the mixed powder and sinterability.
Powder with a diameter of 3 μm or less is desirable. These starting powders may be stoichiometric or non-stoichiometric compounds, in particular carbides of metals from groups 4a, 5a and 6a of the periodic table;
If the starting material powder of at least one of nitrides, borides, silicides, oxides, or mutual solid solutions thereof is a non-stoichiometric compound, the sintering process is performed while adsorbing gases generated during the sintering process. It is effective in promoting sintering and densification. The method for manufacturing a silicon nitride sintered body for tools of the present invention includes:
Conventional powder metallurgy methods are available. For example, to mix and grind powder, a predetermined amount of starting material powder is placed in a container made of stainless steel, ceramics, or stainless steel lined with cemented carbide or rubber, together with Si ₃ N ₄ ceramic balls, ZrO ₂ ceramic balls, or superalloy balls. It can be mixed and pulverized in a dry method or wet method in which an organic solvent such as hexane, alcohol, benzene, or acetone is added. The molding and sintering of this mixed powder is carried out by filling a carbon or graphite sintering mold with the mixed powder and then directly sintering the mold under high-frequency pressure using a hot press, sintering under current pressure, or sintering under pressure using _N2 atmospheric gas. A molded body formed by sintering or molding a mixed powder by rubber pressing, extrusion molding, or a molded body, or a molded body formed by pre-sintering this molded body at a temperature lower than the sintering temperature and then machining it. Ordinary sintering (including pressureless sintering) in a vacuum or non-oxidizing atmosphere, or sintering while pressurizing with atmospheric gas, or further 1
The sintered material can be subjected to hot isostatic pressing (HIP) to promote densification and improve the strength of the sintered material. Although the sintering temperature varies depending on the type of starting material powder, the blended components, or the above manufacturing conditions, a dense sintered body with a relative density of approximately 100% can be obtained at a temperature of 1500 to 1900°C. Among these manufacturing conditions,
Impurities mixed into the sintered body are often mixed in during the mixing and crushing process, and the types of impurities include iron group metals and carbides, nitrides, and carbonitrides of metals in groups 4a, 5a, and 6a of the periodic table. Among these, if iron group metals are mixed as impurities, it is desirable to reduce the amount to 1% by volume or less, as this may cause a decrease in the strength of the sintered body, and depending on the application, the manufacturing conditions may need to be carefully selected. Therefore, it is necessary to reduce the impurity of iron group metal to 0.3% by volume or less. Here, the reason for limiting the numerical values of the silicon nitride sintered body for tools of the present invention will be described. Regarding crystal structure modifiers: If the crystal structure modifier consisting of one or more nitrides and/or oxynitrides of metals from Groups 1a, 2a, 3a, 3b, and 4b of the periodic table is less than 1% by volume, silicon nitride will not be used. The trigonal crystal phase in the main crystal is 25% by volume.
Although the crystal structure modifier has the effect of promoting sintering, if it is less than 1% by volume, the sinterability is poor and it is difficult to form a dense sintered body. On the other hand, if the crystal structure modifier exceeds 35% by volume, the hardness of the sintered body decreases and plastic deformation tends to occur, and wear resistance deteriorates. %. In particular, from the viewpoint of the effect of promoting sintering and the wear resistance and plastic deformation resistance of the sintered body, the crystal structure modifier is
Volume % is preferred. In terms of the strength of the sintered body, the type of crystal structure modifier is Group 2a of the periodic table.
Be, Mg, Ca, Sr, Ba, Ra, Sc which is group 3a,
Y, lanthanoids (rare earths), B, which is group 3b;
It is desirable that the crystal structure modifier contains at least 50% by volume of at least one of nitrides, oxynitrides, or mutual solid solutions of Al, Ga, In, and Tl metals. About dispersed phases Carbides, nitrides of metals from groups 4a, 5a, and 6a of the periodic table,
1% by volume of a dispersed phase consisting of at least one of borides, silicides, oxides, or mutual solid solutions thereof
If the sintered body is used as a cutting tool for recreational machining of steel materials, the damage caused by wear and thermal shock may increase, and the sintered body may not be used for electric discharge machining. This makes it difficult to process. On the other hand, if the amount of the dispersed phase exceeds 40% by volume, the sinterability tends to deteriorate and the toughness of the sintered body tends to decrease. For this purpose, the amount of the dispersed phase was determined to be 1 to 40% by volume. The content of the dispersed phase is preferably 10 to 20% by volume from the viewpoint of wear resistance, thermal shock resistance, and chipping resistance. About crystals with trigonal structure If the trigonal crystal phase in the hard phase formed by the crystal structure modifier and silicon nitride is less than 25% by volume, the hexagonal crystal phase becomes relatively large and sintering As the hardness of the compact decreases, the plastic deformation resistance also decreases. For this purpose, the trigonal structure crystal phase in the hard phase formed by the crystal structure modifier and silicon nitride was determined to be 25% by volume or more. [Representative mode for carrying out the invention] Example 1 Si ₃ N ₄ (α rate 90%) with an average particle size of 1 μm and amorphous 35
% containing Si ₃ N ₄ (α rate 60%) and an average particle size of 6 μm.
Using Si ₃ N ₄ (α ratio 79%) and various powders with an average particle size of 1 to 3 μm, each sample was blended as shown in Table 1, and each of the blended samples was mixed with WC-based cemented carbide in a hexane solvent. The mixture and balls were mixed and ground in a urethane-lined container. After removing the solvent from the obtained mixed powder by evaporation, it was filled into a carbon mold coated with BN powder, and after purging the inside of the furnace with N ₂ gas, the molding pressure was 100 to 400 Kg/cm ² and the temperature was 1700 to 1850 °C. Pressure sintering was performed with a holding time of 50 to 90 minutes. Table 2 shows various properties of the obtained sintered body.

【table】

【table】

[Industrial applicability]

From the results of the above examples, the silicon nitride sintered body for tools of the present invention has high hardness and excellent thermal shock resistance and plastic deformation resistance, so it is expensive for steel cutting.
It has been confirmed that the sintered body has wear resistance and fracture resistance comparable to that of CBN-based sintered bodies, and can also be used for difficult-to-cut materials that are prone to fractures caused by crimping and separation damage in tools. did it. From this, cutting tools such as scissors, slitters, cutting blades, cutlery, balls, etc.
Taking advantage of the corrosion resistance of Si ₃ N ₄ , we can manufacture mechanical parts jigs such _as guide bushes, rolls, and gauges, as well as wear-resistant and corrosion-resistant parts such as valves, mechanical seals, chemical industry-related parts, _etc. Utilizing its lubricity, it can be used for bearing parts, various wear-resistant tools such as molds that require mold releasability, turning tools for various work materials, milling tools, and pressure-resistant, wear-resistant, and chipping-resistant tools. Due to its excellent properties, the sintered body of the present invention can be used as various cutting tools, typified by drilling tools such as end mills, reamers, and drills. Furthermore, due to its light weight and excellent thermal conductivity, it is an industrially useful sintered body that may be applied to structural materials that require heat resistance, such as engine parts and turbine parts.

Claims (1)

[Scope of Claims] 1. 1 to 35% by volume of a crystal structure modifier of one or more nitrides and/or oxynitrides of metals from groups 1a, 2a, 3a, 3b, and 4b of the periodic table and the periodic table. Tables 4a, 5a,
Group 6a metal carbides, nitrides, borides, silicides,
A sintered body consisting of 1 to 40% by volume of a dispersed phase of at least one of oxides or a mutual solid solution thereof, the balance silicon nitride, and unavoidable impurities, and which is composed of the crystal structure modifier and the silicon nitride. 1. A silicon nitride sintered body for tools, characterized in that the hard phase formed by this process contains 25% by volume or more of a crystallizing agent having a trigonal structure. 2. Claim 1, characterized in that the hard phase formed by the crystal structure modifier and the silicon nitride is contained as a crystal phase with a trigonal structure in an amount of 35 to 95% by volume. Silicon nitride sintered body for tools. 3 The crystal structure modifier mentioned above is 2a, 3a, 3b of the periodic table.
Claim 1 or 2, characterized in that the material is mainly composed of at least one of group metal nitrides, oxynitrides, or mutual solid solutions thereof.
A silicon nitride sintered body for tools as described in .