JP2009006413A - Ti based cermet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Ti based cermet suitable for a cutting tool having high chipping resistance and wear resistance. <P>SOLUTION: This Ti based cermet 1 contains at least one kind of Co and Ni, one or more kinds of carbide, nitride and carbon nitride of one or more kinds of group 4, 5 and 6 metals in the periodic table made mainly of Ti, and Re. In the Ti based cermet 1, a hard phase 2 composed mainly of one or more kinds of the carbide, nitride and carbon nitride, and composed of a black first hard phase 2a and a light gray second hard phase 2b in a photograph of arbitrary cross section by a scanning electron microscope (SEM), and a binder phase 3 composed mainly of at least one kind of Co and Ni are observed. In the Ti based cermet 1, a surface region 5 having 0.5 to 5 μm in thickness and ≥80 area% of an area ratio S<SB>1s</SB>of the first hard phase 2a exists on the surface. A thermal expansion coefficient of the Ti based cermet 1 can be reduced and heat resistance can be enhanced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a Ti-based cermet, and more particularly to a Ti-based cermet suitable for a cutting tool having improved thermal shock resistance at a cutting edge.

  Currently, as a member that requires wear resistance, slidability, and fracture resistance, such as cutting tools, wear-resistant members, sliding members, cemented carbides mainly composed of WC, Ti-based cermets mainly composed of Ti, etc. Sintered alloys are widely used. For these sintered alloys, new compositions are being developed to improve their performance.

  Above all, Ti-based cermet has the problem of low resistance to thermal shock due to its low thermal conductivity and 1.3 times larger thermal expansion coefficient than cemented carbide. There was a problem such as sudden breakage in cutting at.

  Thus, for example, Patent Document 1 discloses that by changing the concentration distribution of Ti, W and the binder phase on the surface of the Ti-based cermet, it is possible to perform highly reliable cutting even under severe thermal shock cutting conditions. ing.

On the other hand, various studies have been made on the composition of Ti-based cermets. For example, in Patent Document 2, a superhard alloy (cermet) is produced using titanium carbonitride powder whose surface is coated with rhenium (Re) metal as a raw material powder. It is disclosed that even if the cermet is fired at a higher temperature, grain growth of the sintered body structure is suppressed and its mechanical properties (hardness, strength, toughness, etc.) are improved.
JP-A-6-228702 Japanese Patent Laid-Open No. 10-45414

  However, the method of improving the thermal shock performance by changing the concentration distribution of Ti, W and the binder phase on the surface of the Ti-based cermet as in the above-mentioned Patent Document 1 has a limit in improvement, and further improvement in characteristics is required. It was.

  In addition, in the method of simply adding Re metal into the cermet to make the cermet structure finer as in Patent Document 2, although the mechanical properties of the material itself such as hardness and strength are improved, the thermal properties of the cermet The properties were not improved and the weakness of being vulnerable to thermal shock remained.

  Therefore, the cutting tool of the present invention is for solving the above-mentioned problems, and its purpose is to increase the thermal shock resistance of a Ti-based cermet having poor thermal shock resistance.

The Ti-based cermet of the present invention is at least one of Co and Ni, and one or more of carbides, nitrides and carbonitrides of Periodic Tables 4, 5, and 6 metals mainly composed of Ti In addition, it contains Re and is mainly composed of one or more of the carbides, nitrides, and carbonitrides. In a scanning electron microscope (SEM) photograph of an arbitrary cross section, the black first hard phase and grayish white A hard phase composed of the second hard phase and at least one binder phase of mainly Co and Ni are observed, and the surface area of the first hard phase occupies in the hard phase with a thickness of 0.5 to 5 μm. A surface region having a ratio S _1s of 80 area% or more exists.

  Here, in the above configuration, the Re content is desirably 1 to 10% by mass, and it is desirable that the Re is dissolved in the binder phase at a ratio of 5 to 50% by mass.

Moreover, it is desirable that the average linear thermal expansion coefficient in 40-500 degreeC is 9.0x10 < ^-6 > / degrees C or less.

  According to the Ti-based cermet of the present invention, a surface region containing Re and having an area ratio of the black first hard phase in the hard phase in the region of the cermet surface having a thickness of 1 to 5 μm is 80 area% or more. By being present, the thermal expansion coefficient of the Ti-based cermet can be reduced and a compressive stress can be generated on the surface of the cermet. As a result, the thermal shock characteristics of the Ti-based cermet can be dramatically improved.

  Here, the content of Re is preferably 1 to 10% by mass from the viewpoint of improving wear resistance while reducing the thermal expansion coefficient, and in particular, Re is 5 to 50% by mass in the binder phase. % Is desirable in that the coefficient of thermal expansion can be reduced.

In order to increase the thermal shock resistance of the Ti-based cermet, it is desirable to control the average linear thermal expansion coefficient at 40 to 500 ° C. of the Ti-based cermet to 9.0 × 10 ⁻⁶ / ° C. or less.

  An example of the Ti-based cermet of the present invention will be described on the basis of a scanning electron microscope (SEM) photograph of a cross-sectional main part including the surface region of the cermet 1 of FIG.

  A Ti-based cermet (hereinafter simply abbreviated as cermet) 1 in FIG. 1 is at least one of Co and Ni, and one or more carbides of Group 4, 5, and 6 metals in the periodic table mainly containing Ti. , One or more of nitride and carbonitride, and Re.

And as shown in FIG. 1, the cermet 1 consists of the hard phase 2 which consists of the black 1st hard phase 2a and the gray-white 2nd hard phase 2b, and the at least 1 sort (s) of binding phase 3 of Co and Ni mainly, A major feature of the surface of the cermet 1 is that the surface region 5 having a thickness of 0.5 to 5 μm and an area ratio S _1s of the first hard phase 2a of 80% by area or more is present. As the expansion coefficient decreases and the resistance to impact on the surface of the cermet 1 increases, the thermal shock resistance of the cermet 1 increases.

That is, if Re is not contained in the cermet 1, the thermal expansion coefficient in the cermet 1 cannot be reduced. For example, when the cermet 1 is used as a cutting tool or the like, the cutting edge portion of the cermet 1 has a cutting heat. When the temperature becomes high, the thermal conductivity of the cermet 1 is poor, and the temperature difference between the cutting edge portion and the other portions becomes large. As a result, since only the cutting edge portion is significantly expanded, stress concentration is increased in the vicinity of the cutting edge, and the thermal shock performance of the cermet 1 is deteriorated. Moreover, when the said surface area | region does not exist in the surface of the cermet 1, the impact resistance in the surface of the cermet 1 cannot be improved, but the thermal shock property of the cermet 1 becomes inadequate. On the other hand, when the thickness of the surface region 5 exceeds 5 μm, the thermal shock resistance decreases due to the stress concentration on the surface of the cermet 1. A desirable thickness of the surface region 5 is 0.8 to 3 μm. The area ratio A _s of the first hard phase 2a in the surface region 5 is desirable in that an optimal stress applying it is 85 to 97 area percent of the surface of the cermet 1.

  Further, in the scanning electron microscope (SEM) photograph of the cross-sectional structure of the cermet 1 shown in FIG. 1, the first hard phase 2a is observed as black particles, and the second hard phase 2b is grayish white particles or a white core. Are observed as particles having a cored structure in which a grayish white peripheral portion exists in the periphery. The grayish white color may appear to be a color tone close to white or may be a color tone close to gray depending on the conditions of photography. Here, the first hard phase 2a is black particles made of TiCN, but may contain Co or Ni. Moreover, you may have the cored structure in which the gray-white 2nd hard phase 2b existed in the outer periphery of the 1st hard phase 2a. On the other hand, the binder phase 3 is observed as a white region.

  Here, the content of Re is preferably 1 to 10% by mass in terms of increasing the wear resistance while reducing the thermal expansion coefficient. A particularly desirable range of the Re content is 3 to 7% by mass. The Re is preferably dissolved in the binder phase 3 at a rate of 5 to 50% by mass in terms of reducing the thermal expansion coefficient. A desirable range of the amount of Re dissolved in the binder phase 3 is 20 to 40% by mass.

Further, as shown in a scanning electron microscope (SEM) photograph in the cross section near the surface of the cermet 1 shown in FIG. 1, the average particle diameter d _1s of the first hard phase 2a is 0.05 to 1.0 μm, particularly It is desirable that it is 0.2-0.8 micrometer. A ratio of the binder phase 3 in the surface region 5, it is 1.5 to 3.0 in a ratio _(c s / c _i) for the content ratio of the binder phase 3 in the interior, the heat at the surface of the cermet 1 It is desirable in that the impact resistance can be enhanced and the thermal shock resistance can be enhanced by causing an appropriate stress on the surface of the cermet 1. Thereby, the internal stress on the surface of the cermet 1 can be increased to further increase the resistance to impact.

Further, when the cross-sectional structure inside the cermet 1 is observed, the average particle size of the second hard phase 2b is larger than the average particle size of the first hard phase 2a, and preferably the average of the first hard phase 2a inside. the particle size as _{a i,} when the average particle diameter of the second hard phase 2b was _{b i,} a ratio between _{a i} and _{b i (b i / a i} ) that is 2 to 8, the second hard The phase 2b is desirable in that the thermal conductivity of the cermet 1 is improved by effectively contributing to heat propagation, and the thermal shock resistance of the cermet 1 is improved. A desirable range of the ratio (b _i / a _i ) between a _i and b _i is 3.5 to 7 in that the fracture resistance of the cermet 1 can be maintained.

  In addition, the measurement of the particle size of the hard phase 2 in this invention is measured according to the measuring method of the average particle size of the cemented carbide prescribed | regulated to CIS-019D-2005. At this time, in the case where the hard phase 2 has a cored structure, the particle diameter is measured by taking the core and the outer edge of the peripheral part including the peripheral part as one hard phase. Moreover, when observing the cross-sectional structure inside the cermet 1 in this invention, it observes in the area | region whose depth from the surface of the cermet 1 is 1000 micrometers or more.

Moreover, in the cross-sectional structure about the inside of the cermet 1, the average area of the second hard phase 2b is larger than the average area of the first hard phase 2a, and preferably the first hard phase 2a occupies the entire hard phase 2 inside. the average area and _{a i,} when the average area of the second hard phase 2b account was _{B i,} the ratio of _{a i} and _{B i (B i / a i} ) is to be 1.5 to 5, the The two hard phases 2b are desirable in that the thermal conductivity of the cermet 1 is improved by effectively contributing to heat propagation, and the thermal shock resistance of the cermet 1 is improved.

Further, immediately below the surface region 5 of the cermet 1 as shown in FIG. 1, the average area of the first hard phase 2a to the whole hard phase 2 is occupied and A _m, an average area of the second hard phase 2b occupied and B _m When the cermet 1 has an intermediate region 6 in which the ratio of A _m to B _m (B _m / A _m ) is larger than the ratio of A _i to B _i (B _i / A _i ), It is desirable for improving the thermal shock resistance of the cermet 1 by increasing the thermal conductivity in the vicinity of the surface. A particularly desirable range of the ratio (B _m / A _m ) is 3 to 10, and a desirable range of the ratio (B _m / A _m ) / ratio (B _i / A _i ) is 1.2 to 2.3.

In the intermediate region 6, when the average particle size of the second hard phase 2b in the intermediate region 6 is b _m , the ratio (b _m / b _i) with the average particle size b _i of the second hard phase 2b inside. ) Is 1.1 to 2, particularly 1.1 to 1.5, the second hard phase 2b in the surface region 5 effectively contributes to heat propagation, and the thermal conductivity of the cermet 1 is improved. No. 1 is desirable in that the thermal shock resistance is improved. The intermediate region 6 is preferably 30 to 300 μm thick, more preferably 50 to 150 μm in order to increase the thermal conductivity near the surface of the cermet 1 and improve the thermal shock resistance of the cermet 1. Further, when the average particle diameter of the first hard phase 2a in the intermediate region 6 was _{a m,} the ratio between the average particle size _{a i} of the first hard phase 2a in the interior _(a m / _{a i)} is 1.0 to 1.2 is desirable in terms of improving the fracture resistance in the surface region 8.

  In addition, the total content ratio of the nitrides or carbonitrides of Group 4, 5, and 6 metals in the periodic table mainly containing Ti that forms the hard phase 2 contained in the cermet 1 is 70 to 96% by mass. It is desirable that it is 85-96 mass% especially from the point of improvement of abrasion resistance. On the other hand, the content ratio of the binder phase 3 is preferably 4 to 30% by mass, particularly 4 to 15% by mass, and this makes the cermet 1 have an excellent balance of hardness and toughness. Moreover, as the binder phase 3, it is desirable to contain 65% by mass or more of Co with respect to the total amount of the iron group metal in order to improve the thermal shock resistance of the cutting tool. In order to maintain good sinterability of the cermet 1 so that the burned surface of the cermet 1 becomes a smooth surface, Ni is 5 to 50% by mass, particularly 10 to 10% with respect to the total amount of the iron group metal. It is desirable to make it contain in the ratio of 35 mass%.

Moreover, in order to improve the thermal shock resistance of the cermet 1, it is desirable that the average linear thermal expansion coefficient of the cermet 1 at 40 to 500 ° C. is 9.0 × 10 ⁻⁶ / ° C. or less. And such a structure | tissue structure can be produced by baking on the predetermined baking conditions shown below while adding Re component in a raw material, when manufacturing the cermet 1. FIG.

(Production method)
Next, an example of the manufacturing method of the cermet mentioned above is demonstrated.

  First, TiCN powder having an average particle size of 0.1 to 2 μm, desirably 0.2 to 1.2 μm, metal Re powder having an average particle size of 5 to 50 μm, and other metal carbide powders, nitride powders or A mixed powder obtained by mixing any one of carbonitride powders with Co powder or Ni powder is prepared.

  And a binder is added to this mixed powder, and it shape | molds in a predetermined shape by well-known shaping | molding methods, such as press molding, extrusion molding, and injection molding.

Next, according to this invention, the cermet of the predetermined structure | tissue mentioned above can be produced by baking on the following conditions. As firing conditions, for example, (a) up to 1275 ° C., in particular, the temperature range of 1050 to 1275 ° C. is raised at a rate of temperature increase of 5 to 15 ° C./min, and then (b) the temperature range of 1275 to 1375 ° C. The temperature is increased at a temperature increase rate of 0.1 to 3 ° C./min, and (c) the temperature range from 1375 ° C. to the firing temperature of 1450 to 1600 ° C. is increased at a temperature increase rate of 4 to 15 ° C./min. . At this time, in the temperature raising steps (b) and (c), the firing atmosphere is filled with 30 to 2000 Pa of one or more inert gases of nitrogen (N ₂ ), argon (Ar), and helium (He). Then, (d) after maintaining for a predetermined time at the firing temperature which is the highest temperature in the temperature raising step (c), (e) firing in a firing pattern that is cooled in the inert gas atmosphere.

  Then, if desired, a coating layer is formed on the surface of the cermet 1. A physical vapor deposition (PVD) method such as an ion plating method or a sputtering method can be suitably applied as the coating layer forming method.

TiCN powder having an average particle diameter (d ₅₀ value) of 0.6 μm, WC powder having an average particle diameter of 1.1 μm, TiN powder having an average particle diameter of 1.5 μm, TaC powder having an average particle diameter of 2 μm as measured by the microtrack method, NbC powder with an average particle size of 1.5 μm, MoC powder with an average particle size of 1.5 μm, ZrC powder with an average particle size of 1.8 μm, VC powder with an average particle size of 1.0 μm, Ni powder with an average particle size of 2.4 μm, Then, isopropyl alcohol (IPA) was added to the mixed powder prepared by adjusting the ratio of the Co powder having an average particle diameter of 1.9 μm and the metal Re powder having an average particle diameter of 10 μm as shown in Table 1 using a stainless steel ball mill and a carbide ball. After wet mixing, adding 3% by weight of paraffin, mixing, press-molding into a throw-away tip tool shape of CNMG120408 at 200 MPa, (a) 1 from room temperature to 1275 ° C (B) The temperature was raised from 1275 ° C. to 1375 ° C. at 0.5 ° C./minute, (c) after the temperature was raised to the firing temperature shown in Table 1 at 5 ° C./minute, (d ) Baked in 800 Pa of nitrogen at the firing temperature and firing holding time shown in Table 1, and (e) cooled, sample No. 1 to 9 cermet throwaway chips were obtained. The firing atmosphere in the steps (b), (c) and (e) is shown in Table 1.

  The obtained cermet was observed with a scanning electron microscope (SEM), and image analysis was performed in a region of 8 μm × 8 μm using a commercially available image analysis software for each of the surface and the interior at a 10000 × magnification. And the presence of the intermediate region and the surface region were confirmed by observing the existence state of the hard phase and the structure of the inside and the surface. And the average particle diameter in these area | regions was measured, and these ratios were computed. The results are shown in Table 2 or Table 3.

  Moreover, the composition of the metal element in the binder phase for each sample was measured by the following method. First, the sintered body (cermet) was put in a cemented carbide mortar and pulverized so that there was no residue in a mesh-passed state with # 40 mesh, and 0.2 g of this powder was added to 50 ml of hydrochloric acid (1 + 1) in 50 ml. After elution with heating at 1 ° C. for 1 hour, the volume was adjusted to 100 ml with hydrochloric acid (1 + 1). The metal elements contained in the elution solution were calculated by ICP analysis, and the Re content ratio in the total amount of metals contained in the elution solution was determined. The results are shown in Table 2.

  Further, a thermal expansion curve from 40 ° C. to 1000 ° C. as shown in FIG. 2 was taken, and an average linear thermal expansion coefficient was calculated at each temperature of 100 ° C. to 100 ° C. The thermal expansion coefficient was measured in accordance with JIS R3102. However, when a test piece having the dimensions specified in JIS R3102 cannot be prepared as a measurement object, the measurement is determined as the dimension of the part whose length is to be measured. A rectangular parallelepiped or a cylinder was cut out from the object to be measured so that the difference from the measured dimension was small, and both end faces of the part whose length was to be measured were made parallel by polishing and used as test pieces. 2 is a sample No. of Tables 1-3. The change of the thermal expansion coefficient of 3, 6, and 8 is shown. The values at 500 ° C. (average thermal expansion coefficient at 40 to 500 ° C.) are shown in Table 3.

  Next, using the obtained cermet cutting tool, cutting tests (abrasion resistance evaluation test and fracture resistance evaluation test) were performed under the following cutting conditions. The results are shown in Table 3.

(Abrasion resistance evaluation test)
Work material: SCM435
Cutting speed: 200 m / min
Feed: 0.20mm / rev
Cutting depth: 1.0mm
Cutting condition: wet (use water-soluble cutting fluid)
Evaluation method: Time until the wear amount reaches 0.2 mm (fracture resistance evaluation test)
Work material: SCM440H
Cutting speed: 150 m / min
Feed: 0.20mm / rev
Cutting depth: 1.5mm
Cutting condition: Dry evaluation method: Number of impacts until breakage

  From Tables 1-3, sample No. which does not contain Re. In No. 8, the thermal expansion coefficient increased, the thermal shock resistance was poor, and it was lost early. Sample No. having no surface area is also shown. 10 and the sample No. whose surface region thickness exceeds 5 μm. 9 also had poor fracture resistance due to a decrease in thermal shock resistance.

  On the other hand, sample no. In Nos. 1 to 7, all exhibited excellent wear resistance and good thermal shock resistance, resulting in a long tool life.

Sample No. 1 prepared in Example 1 was used. A cermet having a shape of 3 cutting tool was processed with a diamond grindstone, and a coating layer was formed by an arc ion plating method. Specifically, the substrate was set in an arc ion plating apparatus and heated to 500 ° C., and then a coating layer of Ti _0.4 Al _0.5 Nb _0.1 N was formed. The film forming conditions were a mixed gas of nitrogen gas and argon gas in an atmosphere having a total pressure of 2.5 Pa, an arc current of 100 A, a bias voltage of 50 V, and a heating temperature of 500 ° C. In addition, the layer thickness of the coating layer was 1.0 μm.

  A cutting test was performed under the same cutting conditions as in Example 1 using the obtained cutting tool. As a result, the time until the wear amount reached 0.2 mm after the start of cutting was 70 minutes, and the number of impacts was 49000 times, indicating good cutting performance.

It is an example of the cermet of this invention, and is a cross-sectional structure | tissue photograph about the principal part containing the surface. It is a graph which shows the change of the average linear thermal expansion coefficient with respect to Re content about the cermet of this invention (sample No. 3, 6, 8 of Example 1).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cermet 2 Hard phase 2a 1st hard phase 2b 2nd hard phase 3 Bonding phase 5 Surface area 6 Middle area

Claims (4)

Contains at least one of Co and Ni, one or more of carbides, nitrides and carbonitrides of Group 4, 5, and 6 metals of the periodic table mainly containing Ti, and Re. , Mainly composed of one or more of the carbides, nitrides and carbonitrides, and composed of a black first hard phase and an off-white second hard phase in a scanning electron microscope (SEM) photograph of an arbitrary cross section And at least one binder phase of Co and Ni is observed, and the area ratio S _1s of the first hard phase in the hard phase having a thickness of 0.5 to 5 μm is 80 area% or more on the surface. Ti-based cermet characterized by the presence of a surface region of The Ti-based cermet according to claim 1, wherein the Re content is 1 to 10% by mass. The Ti-based cermet according to claim 1 or 2, wherein the Re is solid-solved in the binder phase at a ratio of 5 to 50 mass%. 4. The Ti-based cermet according to claim 1, wherein an average linear thermal expansion coefficient at 40 to 500 ° C. is 9.0 × 10 ⁻⁶ / ° C. or less.