JP4716855B2 - Sialon cutting tool and tool equipped therewith - Google Patents

Description

  The present invention relates to a sialon cutting tool and a tool including the same, and more particularly to a sialon cutting tool having excellent wear resistance and a tool including the same.

  Sialon is recognized as a material having high hardness compared to silicon nitride and high strength in a temperature range from room temperature to high temperature and high chemical stability. Therefore, it is often used as a structural material for hot steel rolling guide rolls and dies, aluminum die-casting, mechanical sleeves, etc. that require heat resistance and chemical reactivity resistance. Furthermore, since it was recognized that abrasion resistance was good, it came to be considered that it could be used for cutting tools and bearings. However, in reality, Sialon cutting tools are only used for rough cutting of difficult-to-cut heat-resistant alloys, etc., and the wear resistance of the insert edge that affects the surface roughness and dimensional accuracy of the work material It was not considered much.

  In recent years, for the purpose of improving the fuel efficiency of automobiles, weight reduction of automobile members mainly made of FC materials has become a major issue. Against this background, demands for thinner and lighter automobile members are increasing, and high-precision machining is required for roughing and wrinkling.

  For rough machining of these FC materials, silicon nitride cutting tools have been used in the past, but silicon nitride itself is a covalent material, and it tends to decompose into silicon and nitrogen at high temperatures during high-speed machining. Was a drawback. The decomposition reaction proceeds faster when silicon nitride comes into contact with iron or carbon, which are the main components of the FC material, at high cutting pressure during cutting. The cutting edge is worn and damaged by the decomposition of silicon nitride at the cutting edge of the insert. When the cutting edge wears, the surface roughness and dimensional accuracy of the work material deteriorate, and finally the tool becomes unusable and the tool life is reached.

  The inventors of the present invention have made extensive studies on the mechanism by which the blade edge wears due to damage caused by these chemical reactions, and as described above, without degrading the mechanical wear resistance of silicon nitride, the FC material and the tool material It has been found that suppressing chemical reactions is important for extending tool life.

  By the way, it is known that (a) in order to suppress a chemical reaction between a work material and a tool material, the tool material is coated with a hard layer made of a titanium compound or an aluminum compound having low reactivity with iron. For example, Patent Document 1 discloses an example in which an FC material is cut by coating a titanium compound such as titanium nitride or titanium carbide with an aluminum compound such as alumina. Furthermore, an invention is disclosed in which titanium nitride is added to silicon nitride and ordinary cast iron is cut.

  (b) In order to suppress the chemical reactivity between the work material and the tool base material itself, there is also a method for suppressing the chemical reactivity of the tool base material itself by adding titanium nitride or alumina to the tool base material. Are known. Titanium nitride in this case is present in the structure as dispersed particles, and is intended to improve the chemical reactivity resistance of the tool substrate. In addition, alumina dissolves in silicon nitride particles to form sialon particles, and attempts to improve the chemical reaction resistance of the silicon nitride particles themselves. Such a method is disclosed in Patent Document 2.

  (c) In order to improve the high temperature characteristics of a cutting tool, a method is known in which the grain phase is crystallized to reduce the glass phase and improve the wear resistance. The tool base material containing melilite is disclosed in Patent Documents 3 and 4.

Japanese Patent No. 3107168 JP 2005-231928 A Japanese Patent No. 3266200 Japanese Patent No. 3437380

  According to the study by the present inventors, the following matters have been found. In the technique (a) described above, the wear due to the chemical reaction between the work material and the cutting tool substrate is suppressed by the effect of providing the coating layer, but the heat of the silicon nitride substrate and titanium nitride or alumina during coating is suppressed. Due to the difference in expansion coefficient, a tensile residual stress is generated in the coating layer, and the cutting edge of the insert may be damaged using the coating layer as a starting point of fracture, thereby reducing the tool life.

  In the technique (b), the addition of titanium nitride reduces the thermal shock resistance due to the difference in thermal expansion coefficient between titanium nitride and silicon nitride particles, and the sialonization due to the addition of an aluminum compound reduces the hardness of the particles themselves. The tool life during high-temperature cutting may be reduced due to a decrease in mechanical wear resistance and a decrease in strength. In addition, thermal shock resistance may be reduced due to a decrease in thermal conductivity due to excessive sialonization.

  In the technique (c), particularly when the base material is silicon nitride, chemical wear proceeds due to high chemical reactivity, and the effect of suppressing mechanical wear, that is, boundary wear, is small due to the formation of melilite. turn into.

  The present invention has been made in view of these problems.For example, chemical wear caused by a chemical reaction between a work material and a tool blade edge and abrasive mechanical wear can be reduced without deteriorating the characteristics of the tool base. An object of the present invention is to provide a sialon cutting tool with improved tool life.

As means for solving the problems,
Claim 1 includes a sialon phase composed of α-sialon and β-sialon, and a rare earth element derived from a sintering aid, and expressed by Si _6-Z Al _Z O _Z N _8-Z Z value of 0.2 ≦ Z ≦ 0.7, part or all of the grain boundary phase is a melilite phase, and the melilite phase is 0 in the maximum X-ray intensity ratio with respect to the content of β-sialon. The sialon firing is contained at a ratio of 3 or more and 1.0 or less, the α ratio indicating the ratio of the α-sialon phase in the sialon phase is 10% or more and 40% or less, and even if the Vickers hardness at room temperature is small, it is 16 GPa. A sialon cutting tool characterized in that it is formed of a knot.
Claim 2 is the sialon cutting tool according to claim 1, wherein the sialon cutting tool is for cutting cast iron.
A third aspect of the present invention is a tool comprising the sialon cutting tool according to the first or second aspect and a holder for holding the sialon cutting tool.

  According to the present invention, for example, a sialon cutting tool that has improved tool life by reducing chemical wear due to a chemical reaction between the work material and the tool edge and abrasive mechanical wear without degrading the characteristics of the tool base. Can be provided.

  The sialon cutting tool of the present invention is formed of a sialon sintered body having a sialon phase composed of β-sialon and α-sialon as a main phase.

In general, sialon is formed by adding a sintering aid or the like to a raw material powder containing constituent elements such as Si, Al, O, N such as silicon nitride, alumina, aluminum nitride, and silica as raw materials. Usually, sialon particles include β-sialon represented by a composition formula Si _6-Z Al _Z O _Z N _8-Z (0 <Z ≦ 4.2), and a composition formula Mx (Si, Al) ₁₂ (O, N) ₁₆ (0 <X ≦ 2, M represents an element that enters and dissolves, such as Mg, Ca, Sc, Y, Dy, Er, Yb, and Lu). It is mixed. Since β-sialon has a structure in which needle-like structures are entangled like silicon nitride, it has high toughness. Since α-sialon has an equiaxed particle shape, it has low toughness compared to β-sialon. , Has the feature of high hardness.

  The grain boundary phase between sialon particles includes a glass phase and a crystal phase. The sintering aid is liquid phased together with silicon nitride and a silica component contained as an impurity in silicon nitride during sintering, and contributes to generation of sialon particles, rearrangement of sialon particles, grain growth, and densification. It solidifies upon cooling to produce a grain boundary phase at the sialon grain boundary as a glass phase or a crystalline phase. In order to improve the heat resistance, toughness and hardness of the sialon sintered body, the sialon cutting tool suitable among the sialon cutting tools according to the present invention is usually a rare earth element used as a sintering aid, preferably Contains at least one element selected from the group consisting of Sc, Y, Dy, Yb, and Lu in the sialon sintered body in an amount of 1 to 7% by mass in terms of oxide.

  The mass% of oxide content of the specific rare earth element in the sialon sintered body is not the composition contained in the sintered body, assuming that the sintering raw material powder will be a sintered body without excess or deficiency. It can be determined from the composition at the time of preparing the substrate.

Z value of _{Si 6-Z Al Z O Z} N β- sialon represented by _8-Z in sialon sintered body to form a sialon cutting tool made of the present invention is 0.2 to 0.7. A sialon sintered body in which the Z value of β-sialon is in this range is less susceptible to chemical reaction with the work material than sialon cutting tools compared to silicon nitride, and is less susceptible to strength reduction due to sialonization. There is little decrease in conductivity. That is, if it is less than 0.2, the effect of suppressing the chemical reaction between the sialon cutting tool and the work material is not sufficient, and if it is more than 0.7, the strength of the sialon cutting tool is significantly reduced. As a method for measuring this Z value, from the difference between the a-axis lattice constant of β-sialon in the sialon sintered body measured by X-ray diffraction measurement and the a-axis lattice constant of β-silicon nitride (7.60442Å). Calculation is performed by a normal method (refer to Patent Document 5 for the calculation method).

Special table 2004-527434

In the sialon sintered body forming the sialon cutting tool according to the present invention, part or all of the grain boundary phase is the melilite phase. A suitable melilite in the present invention can be represented by Si ₃ Re ₂ O ₃ N ₄ (where Re represents a rare earth element). The content of the melilite phase in the sialon sintered body is 0.2 to 1.0 in terms of the maximum X-ray intensity ratio. When the melilite phase is contained in the sialon sintered body within the above range, the residual glass in the sialon sintered body is extremely reduced, and a sialon cutting tool having excellent wear resistance and high temperature characteristics is realized. Further, if the content of the melilite phase exceeds 1.0 in terms of the maximum X-ray intensity ratio, the oxidation resistance of the sialon sintered body is lowered, so that the cutting tool made of sialon is inferior in chemical wear resistance. End up.

  In the sialon cutting tool according to the present invention, the α ratio indicating the ratio of α-sialon in the sialon particles is 10% or more and 40% or less. It is preferable that a part of the sialon particles is α-sialon to form a sintered body for insert. α-sialon is a solid solution of the specific rare earth element derived from the specific rare earth oxide added as a sintering aid at the time of production in the particles, reducing the amount of crystal phase or glass phase of the sialon grain boundary, Mechanical wear damage can be suppressed. If the α-sialon is not sufficiently generated and the element derived from the rare earth oxide is not sufficiently solid-solved in the α-sialon particle, a large amount of the element remains at the grain boundary, resulting in a sintered body having a large thermal expansion coefficient. Sufficient thermal shock resistance cannot be obtained. The α rate, which is the ratio of α-sialon in the sialon, is determined by the β-sialon (101) plane intensity in β-ray diffraction, the (210) plane peak intensity in β2, and the (102) plane peak in α-sialon in X-ray diffraction. When the intensity is α1 and the (210) plane peak intensity is α2, it is calculated by the formula {(α1 + α2) / (β1 + β2 + α1 + α2)} × 100. When the α ratio is less than 10%, a large number of grain boundary layers remain and the wear resistance and thermal shock resistance are not sufficient. On the other hand, when the α ratio exceeds 40%, the number of equiaxed α-sialon particles having low toughness is increased, so that the fracture resistance is inferior.

  The hardness of the sialon sintered body in the sialon cutting tool of the present invention is 16 GPa or more in terms of Vickers hardness at room temperature. Vickers hardness can be measured according to JIS Z 2244, and in the present invention, it is measured using a commercially available Vickers hardness meter under conditions of room temperature, load of 30 kgf, and holding time of 30 seconds. A sialon cutting tool formed of a sialon sintered body having a Vickers hardness of 16 GPa or more has good wear resistance. If the Vickers hardness is smaller than the above value, the hardness is insufficient and the wear resistance is sufficient. There will be no sialon cutting tool.

  The tool of the present invention has the sialon cutting tool of the present invention and a holder for mounting the cutting tool as a throw-away tip, and is used as a high-performance tool. In particular, the cutting tool and tool made of sialon according to the present invention has a small tool edge wear amount and a low chipping rate when machining not only ordinary cast iron but also difficult-to-cut materials such as ductile cast iron and heat-resistant alloy at high speed. Long life. Even if it is used as a rough cutting tool, it has excellent wear resistance of the tool edge that affects the surface roughness and dimensional accuracy of the work material, and cutting with good surface roughness and dimensional accuracy can be continued for a long time. The tool of the present invention is a cutting tool in a broad sense, and refers to all tools that perform turning, milling, and the like.

A preferred method for producing the sialon cutting tool of the present invention will be described below. Y ₂ O ₃ powder and Dy ₂ O ₃ powder, which are rare earth element oxide powders, using a powder containing an element constituting sialon such as Si ₃ N ₄ powder, Al ₂ O ₃ powder, and AlN powder as a sintering aid. A mixture obtained by mixing with Er ₂ O ₃ powder, Yb ₂ O ₃ powder, Lu ₂ O ₃ powder or the like is used as a raw material powder. As the raw material powder, a powder having an average particle size of 10 μm or less, preferably 5 μm or less, more preferably 3 μm or less is used. The ratio of these raw material powders may be determined in consideration of the composition of the insert after sintering. Usually, the Si ₃ N ₄ powder is 95 to 50% by mass, the Al ₂ O ₃ powder is 0.5 to 20% by mass, the AlN powder is 0 to 40% by mass, and the sintering aid is 1 to 7% by mass. That's fine. 1 to 300 h prepared raw material powder mixing and pulverizing machine such as a ball mill, for example, Si ₃ powder such as ethanol using a Si ₃ N ₄ pot having a N ₄ balls by adding liquid which does not substantially dissolve Mix to produce a slurry. At this time, when the particle size of the raw material powder is large, the pulverization time is lengthened to ensure sufficient pulverization.

  When there are coarse particles in the slurry, the slurry may be removed by sieving the slurry with a sieve of about 200 to 500 mesh. An organic binder such as micro wax is added to the prepared raw material powder in an amount of 1 to 30% by mass with respect to the raw material powder, and granulated and dried by spray drying or the like. The obtained granulated powder is pressed into a desired shape assuming the shape of the sintered body after firing. For molding, injection molding, extrusion molding, cast molding, or the like can be applied. After molding, the molded body is degreased. Usually, degreasing is performed in an inert gas atmosphere such as nitrogen in a heating apparatus. Degreasing is completed in about 30 to 120 minutes at 400 to 800 ° C. The degreased shaped body is sintered at 1500 to 1900 ° C, preferably 1650 to 1800 ° C. Sintering is preferably performed in two stages, and primary sintering is performed in a sheath formed of silicon carbide, boron nitride, silicon nitride, or the like up to 1650-1800 ° C. in a nitrogen or Ar atmosphere of 1-9 atm. What is necessary is just to heat up and hold | maintain for 1 to 5 hours. Secondary sintering may be performed by hot isostatic pressing (HIP). For example, it heats at 1650-1800 degreeC for 1 to 5 hours in 100-5000 atmospheres nitrogen atmosphere.

  The sintered body thus obtained is further heat-treated to produce a melilite phase in the sintered body. The heat treatment is performed by heating at 1500 to 1700 ° C. for 60 to 240 minutes in a nitrogen atmosphere containing carbon. The carbon contained in the nitrogen atmosphere may be carbon derived from carbon powder that embeds the sintered body to be heat-treated, and carbon such as hydrocarbons such as methane and carbon dioxide gas mixed in the nitrogen atmosphere at the time of heat treatment. Carbon derived from the contained gas may be used. Thus, the sialon sintered body containing the melilite phase in the present invention is obtained. This sialon sintered body can be polished into a shape as an insert as shown in FIGS. 1 and 3 to obtain the sialon cutting tool of the present invention. In order to use a tool, the throw-away tip may be mounted on a normal holder as shown in FIGS.

(1) Preparation of insert α-Si ₃ N ₄ powder having an average particle diameter of 1.0 μm or less, Y ₂ O ₃ powder, Dy ₂ O ₃ powder, Er ₂ having an average particle diameter of 1.0 μm or less as a sintering aid O ₃ powder, Yb ₂ O ₃ powder, Lu ₂ O ₃ powder, further Al ₂ O ₃ powder, and AlN powder were blended in the proportions shown in Table 1 to prepare the raw material powder. did. Next, the raw material powder of each inner wall by using the Si ₃ N ₄ made of pods and Si ₃ N ₄ balls, was added to ethanol and mixed for 96 hours to prepare a slurry. Coarse particles were removed from this slurry with a 325-mesh sieve, and 5.0% by mass of a microwax organic binder dissolved in ethanol was added, followed by spray drying to produce granules. The obtained granule was press-molded into the shape of an SNGN120408 insert according to the ISO standard shown in FIG. 1, and then degreased in a heating apparatus at 600 ° C. for 60 minutes in a nitrogen atmosphere. The primary sintering of the degreased compact was set in a silicon nitride sheath, and in the set state, the temperature was raised to 1700 to 1800 ° C. in a nitrogen atmosphere of 1 to 9 atm and held for 120 minutes. Finally, secondary sintering was performed by hot isostatic pressing (HIP). In the secondary sintering, a secondary sintered body was obtained by heating at 1700 ° C. for 180 minutes in a nitrogen atmosphere of 1000 atm.

  This secondary sintered body was heat-treated. The heat treatment was performed at 1500 to 1700 ° C. for 120 minutes in a nitrogen atmosphere containing carbon. The carbon source is carbon powder, which is used by embedding a secondary sintered body.

The thus-obtained sialon sintered body was polished and adjusted to the shape of SNGN120408 according to the ISO standard to obtain an insert for a cutting tool. Table 1 shows the compositions and properties of the inserts of Examples , Reference Examples and Comparative Examples together with the results of cutting performance evaluation. As a simple calculation method, the composition of the sialon sintered body was expressed in mass% with respect to each element at the time of preparing the sintered raw material powder based on the composition of the compound such as oxide or nitride.

(2) Measurement of insert The density of the obtained sialon sintered body was measured by the Archimedes method, and the theoretical density ratio was calculated by dividing by the theoretical density. The samples of all examples and reference examples had a sufficiently high theoretical density ratio, and the micropores were not left in the sintered body and were densified.

  The measurement and calculation of the Z value and the measurement and calculation of the α rate were obtained by the method as described above.

(3) Evaluation of cutting performance (a) Cutting distance Cutting was performed under the following cutting conditions using the SNGN120408 type insert (Chamfer 0.1 mm) in Examples , Reference Examples and Comparative Examples. It was expressed as a cutting distance when the maximum VB wear amount (VBGmax) of the front flank reached 0.3 mm after cutting.
(Processing conditions)
・ Cover cut material: FC200 (Normal cast iron, no cast skin)
・ Shape: Outer diameter 300mm x Inner diameter 50mm x Thickness 30mm
・ Cutting speed: 500 m / min
・ Feeding speed: 0.3mm / blade ・ Incision depth: 0.3mm
Cutting oil: Dry type (b) Boundary wear amount Cutting was performed under the following cutting conditions using the SNGN120408 type insert (Chamfer 0.05 mm) in Examples , Reference Examples and Comparative Examples. The maximum flank wear amount was measured and used as the boundary wear amount (unit: mm).
(Processing conditions)
Work material: FC200 (ordinary cast iron, cast sand remains on both sides)
・ Shape: Outer diameter 300mm x Inner diameter 150mm x Thickness 100mm
・ Cutting speed: 300m / min
・ Feeding speed: 0.2mm / blade ・ Incision depth: 1.5mm
・ Cutting oil: Dry type

As shown in Table 1, it can be seen that the cutting inserts according to Examples and Reference Examples of the present invention have little damage to the tool edge, have a long cutting length, and are excellent in boundary wear resistance. In contrast, the comparative example is inferior in cutting length or boundary wear.

FIG. 1 is a perspective view of the throw-away tip of the present invention. FIG. 2 is an example of a cutting tool for outside diameter processing in which the throw-away tip of the present invention is mounted on a holder. FIG. 3 is a perspective view of another example of the throw-away tip of the present invention. FIG. 4 is a front view showing chamfering of the throw-away tip of FIG. FIG. 5 is a plan view of a cutting tool in which a throw-away tip is mounted on a milling cutter holder.

Explanation of symbols

1: Throw-away tip 2: Holder for outer diameter processing 3: Presser foot 4: Cutting edge 5: Chamfered portion of throw-away tip 6: Holder for milling cutter 7: Holder for milling cutter 8: Cartridge 9 for throw-away tip mounting : Wedge for throwaway tip mounting

Claims (3)

A Z-value of a β-sialon phase comprising a sialon phase composed of α-sialon and β-sialon and a rare earth element derived from a sintering aid and represented by Si _6-Z Al _Z O _Z N _8-Z is 0. 2 ≦ Z ≦ 0.7, and part or all of the grain boundary phase is a melilite phase, and the melilite phase has a maximum X-ray intensity ratio of 0.3 or more with respect to the content of β-sialon. It is contained at a ratio of 0 or less, and the α ratio indicating the ratio of the α-sialon phase in the sialon phase is 10% or more and 40% or less, and is formed of a sialon sintered body having a Vickers hardness at room temperature of 16 GPa. A sialon cutting tool characterized by comprising   The sialon cutting tool according to claim 1, wherein the sialon cutting tool is for cutting cast iron.   A tool comprising the sialon cutting tool according to claim 1 or 2 and a holder for holding the sialon cutting tool.

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