JP2008069420A - Cemented carbide and coated cemented carbide, and manufacturing methods therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cemented carbide of which the cutting performance is improved by increasing the effect of addition of ZrC and Cr<SB>3</SB>C<SB>2</SB>by reduction of oxygen content and also to provide a manufacturing method therefor. <P>SOLUTION: The cemented carbide comprises a binder phase containing at least either of cobalt and nickel and chromium, a zirconium-containing cubic compound and tungsten carbide and has 0.01 to 0.1 wt.% oxygen content. The method for manufacturing the cemented carbide is characterized in that, in a process for raising the temperature of a powder mixture, the powder mixture is held in a nitrogen atmosphere of 1 kPa to 1 MPa at a prescribed temperature ranging from 1,000 to 1,250°C. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cemented carbide, a coated cemented carbide excellent in strength, toughness, and plastic deformation resistance, and a method for producing them.

In order to improve cutting performance, cemented carbides for cutting tools represented by WC- (W, Ti, Ta) C-Co system have been tried to add ZrC, Cr ₃ C ₂ , nitrogen and the like. ZrC improves plastic deformation resistance and enables high-speed cutting, and Cr ₃ C ₂ dissolves in Co as a binder phase to improve hardness and toughness. On the other hand, a cemented carbide containing nitrogen with TiN or the like improves the dispersibility and thermal conductivity of the (W, Ti, Ta) C phase and improves the life in intermittent cutting.

As a prior art of a cemented carbide to which Zr and Cr are added, there is a cemented carbide to which both ZrC and Cr ₃ C ₂ are added (for example, see Patent Documents 1 and 2). These cemented carbides plastic deformation resistance improved and Cr ₃ C ₂ added by hardness by ZrC added, albeit those aimed at improving the toughness and oxidation resistance, ZrC and Cr ₃ C ₂ are both oxidized Since it is easy and difficult to reduce by carbon, there is a problem that the amount of oxygen in the cemented carbide increases and the strength and toughness are remarkably lowered due to the residual ZrO ₂ and Cr ₂ O ₃ and the generation of burrows.

Further, as a conventional technique for reducing the amount of oxygen in the cemented carbide, there is a cemented carbide in which both the amount of oxygen and the amount of nitrogen are reduced (see, for example, Patent Document 3). This cemented carbide contains oxygen: 0.001 to 0.200% by weight and nitrogen: 0.001 to 0.200% by weight. As a manufacturing method thereof, a sintering atmosphere is used in the sintering process. Partial pressure: A hydrogen flow of 10 Torr or more and a vacuum of 1 × 10 ⁻² Torr or less are alternately repeated. When the method of repeating the hydrogen flow and vacuum in the sintering process is applied to the manufacture of cemented carbide with addition of ZrC and Cr ₃ C ₂ , the reduction reaction by hydrogen hardly occurs. There is a problem that it is difficult to improve thermal shock resistance and toughness due to nitrogen content.

JP-A-6-158214 JP 2003-113437 A Japanese Patent Laid-Open No. 4-29349

  The present invention solves the above-described problems. Specifically, by reducing oxygen, the effect of adding zirconium and chromium is maximized, and the cutting performance is greatly improved. An object is to provide a hard alloy and a coated cemented carbide.

  The present inventor has been studying the improvement of the characteristics and cutting performance of a cemented carbide containing both zirconium and chromium. The performance is improved as the amount of oxygen in the alloy is reduced, and nitrogen is added to the alloy. When it is contained, the performance is further improved, and in order to achieve these, the knowledge that it should be maintained in a nitrogen atmosphere when it reaches a predetermined temperature during the temperature rise in the manufacturing method of the cemented carbide is obtained. The invention has been completed.

  That is, the cemented carbide of the present invention comprises a binder phase containing at least one of cobalt and nickel and chromium, a cubic compound containing zirconium, and tungsten carbide, and the amount of oxygen in the entire cemented carbide. The content is 0.01 to 0.1% by weight.

  The binder phase in the cemented carbide of the present invention is an alloy containing at least one of cobalt and nickel as a main component and chromium. Here, in this invention, the binder phase which has at least 1 sort (s) of cobalt and nickel as a main component means the binder phase which contains 60 weight% or more of cobalt and nickel with respect to the whole binder phase. If the amount of chromium contained in the binder phase is less than 3% by weight, improvement in toughness due to solid solution strengthening in the binder phase and improvement in adhesion to the coating when the hard film is coated are insufficient. If the content exceeds 20% by weight, the chromium carbide content increases and the strength decreases rapidly, so 3-20% by weight is preferred. In addition, W may be dissolved in the bonded phase in an amount of 1 to 20% by weight based on the entire bonded phase, and at least one of Mo, V, Ti, Ta, Zr, and Nb is based on the entire bonded phase. It may be dissolved in 5% by weight or less. Specific examples of the binder phase include Co-Cr, Ni-Cr, Co-Cr-W, Ni-Cr-W, Co-Ni-Cr-W, and Co-Ni-Mo-Cr-W. it can.

  In addition, if the amount of the binder phase is less than 3% by weight, the strength and toughness are low, and conversely, if the amount exceeds 15% by weight, the hardness is remarkably lowered, so the amount of binder phase is in the range of 3 to 15% by weight. preferable.

  The cubic compound in the cemented carbide of the present invention is composed of carbonitrides of Group 4a, 5a, and 6a elements of the periodic table containing at least zirconium. Specifically, (Zr, Ti, W) (C , N), (Zr, Nb, W) (C, N), (Zr, Ti, Ta, W) (C, N), (Zr, Hf, V, W) (C, N) and these and Zr Mention may be made of mixtures with (C, N), (Zr, W) (C, N). Zirconium carbide added as a raw material powder is nitrided by heating in a nitrogen atmosphere, and with sintering, solid solution of W, Ti, Ta, Nb, etc. forms cubic carbonitride.

  If the amount of zirconium contained in the cubic compound is less than 5% by weight relative to the total amount of the cubic compound, the effect of improving the plastic deformation resistance is small. Therefore, the range of 5 to 50% by weight is preferable. Further, the amount of the cubic compound is inferior in wear resistance if it is less than 3% by weight relative to the entire cemented carbide, and conversely, if it exceeds 15% by weight, the strength, toughness and fracture resistance are markedly reduced. Therefore, the range of 3 to 15% by weight is preferable. Among them, the amount of the cubic compound is more preferably 5 to 10% by weight because the balance between wear resistance and fracture resistance is good.

  The cubic compound in the cemented carbide of the present invention has a half-value width of 0.5 ° or more at the peak of the (200) plane of X-ray diffraction of 0.5 ° or more. Since the difference in content is large, the toughness becomes higher, and conversely, if it exceeds 1.0 °, the Zr content becomes non-uniform and has a double peak. This is preferable. In particular, it is preferable that the amount of nitrogen is increased from the inside of the alloy toward the surface of the alloy because fracture cracks propagate around the cubic compound particles and become high toughness.

  When the amount of oxygen contained in the cemented carbide of the present invention is less than 0.01% by weight with respect to the entire cemented carbide, it is difficult to manufacture, and conversely, when it exceeds 0.1% by weight, Since the cubic compound in which oxygen is preferentially dissolved is weakened and the strength and toughness are remarkably lowered, the content is determined to be 0.01 to 0.1% by weight. Also, if the amount of nitrogen contained in the entire cemented carbide is 0.1 to 0.3% by weight, the dispersibility and thermal conductivity of the cubic compound are improved and the thermal shock resistance is improved. preferable.

The coated cemented carbide of the present invention in which the surface of the cemented carbide of the present invention is coated with a hard film is preferable because it exhibits excellent wear resistance. The coated cemented carbide of the present invention is excellent in adhesion between the substrate and the hard film. As the hard film, at least one of periodic table 4a, 5a, 6a group elements, Al, Si carbides, nitrides, oxides and their mutual solid solutions is preferable. Specifically, TiC, TiN, TiCN, TiAlN, Al ₂ O _{3 and the} like can be mentioned.

  The cemented carbide of the present invention includes at least one of cobalt and nickel, at least one of chromium metals, carbides and nitrides, zirconium carbide, and elements of groups 4a, 5a and 6a in the periodic table excluding zirconium. A predetermined temperature of 1000 to 1250 ° C. in the process of raising the temperature in a vacuum or an inert gas atmosphere after press-molding a mixed powder composed of at least one of these carbides and their mutual solid solution and tungsten carbide Can be produced by holding in a nitrogen atmosphere of 1 kPa to 1 MPa.

Generally, cemented carbide mixed powder to which WC, Co, TiC, TaC or the like is added contains 0.3 to 1% by weight of oxygen, but when vacuum sintered, it is contained in carbides such as WC, TiC, and TaC. The amount of oxygen in the alloy is reduced to 0.1 to 0.5% by weight by the reduced free carbon. However, when the amount of ZrC or Cr ₃ C ₂ added is increased, it is difficult to reduce the oxygen content. The reason for this is that ZrC and Cr ₂ C ₃ are preferentially oxidized to ZrO ₂ and Cr ₂ O ₃ by the CO ₂ gas generated at 500 to 1000 ° C. during the temperature rise, and these oxides are thermodynamically. This is because the carbon is not easily reduced even when heated to a higher temperature because of its stability. In addition, the reduction reaction of these oxides with hydrogen gas is thermodynamically difficult. However, nitridation reduction with nitrogen gas is thermodynamically possible.

This nitriding reduction is expressed by 2ZrO ₂ + 4C + N ₂ → 2ZrN + 4CO, and is reacted by introducing nitrogen gas in a temperature range from 1000 ° C. or higher to 1250 ° C. at which the densification of the molded body (molded mixed powder) becomes rapid. For example, the temperature is raised in vacuum up to 1150 ° C., 0.1 MPa of nitrogen gas is introduced at 1150 ° C. and held for 30 minutes, and then the temperature is raised again to raise the temperature and sinter.

  That is, the method for producing a cemented carbide according to the present invention excludes at least one powder of cobalt and nickel, at least one powder of chromium metal, carbide, and nitride, zirconium carbide powder, and zirconium. A step of obtaining a mixed powder composed of a carbide of the periodic table 4a, 5a, 6a group element and at least one powder of these solid solutions and a tungsten carbide powder, and pressing the mixed powder to form a compact. A step of obtaining, a step of heating the molded body in a vacuum or an inert gas atmosphere, a step of holding the molded body in a nitrogen atmosphere of 1 kPa to 1 MPa at a predetermined temperature of 1000 to 1250 ° C., and a molded body of 1000 to 1250 ° C. It is characterized by going through the steps of raising the temperature from a predetermined temperature to the sintering temperature, sintering the molded body at the sintering temperature, and cooling the obtained sintered body. That.

  In the method for producing a cemented carbide according to the present invention, the nitrogen gas partial pressure in the step of maintaining in a nitrogen atmosphere is slow when the reaction rate of nitriding reduction is less than 1 kPa, and conversely, if it exceeds 1 MPa, the production cost increases. Therefore, since it is not a good measure in production, the pressure is set to 1 kPa to 1 MPa. Further, it is preferable to perform evacuation temporarily during holding in a nitrogen atmosphere because CO of the reaction product gas is quickly discharged and efficient deoxidation is possible. When the temperature maintained in the nitrogen atmosphere is less than 1000 ° C., the nitriding reduction reaction hardly occurs. Conversely, when the temperature exceeds 1250 ° C., the nitrogen content becomes excessive due to nitriding, and the molded body shrinks, so that it is near the surface. Since the difference in the nitrogen content from the inside becomes significant, the temperature was set to 1000 to 1250 ° C.

  When the surface of the cemented carbide of the present invention is coated with a hard film using a conventional CVD method or PVD method, the coated cemented carbide of the present invention can be obtained.

  Since the cemented carbide of the present invention contains Zr and Cr and contains a small amount of oxygen, it is excellent in plastic deformation resistance, strength, toughness and the like. Since the coated cemented carbide using the cemented carbide of the present invention as a base material has excellent adhesion to a hard film and excellent wear resistance, the tool life is improved compared to conventional coated cemented carbide.

Commercially available WC with an average particle size of 4.5 μm, ZrC with an average particle size of 1.5 μm, (W, Ti) C with an average particle size of 1.1 μm (WC / TiC = 70/30 by weight), average particle size 1.2 μm TiN, TaC with an average particle size of 1.0 μm, NbC with an average particle size of 1.3 μm, VC with an average particle size of 2.7 μm, Co with an average particle size of 1.0 μm, Ni with an average particle size of 1.7 μm , Cr ₃ C _{2 having} an average particle diameter of 2.7 μm, Mo ₂ C having an average particle diameter of 1.3 μm, and Cr ₂ N having an average particle diameter of 3.3 μm were weighed into the composition shown in Table 1. The mixture was inserted into a stainless steel pot together with an acetone solvent and a cemented carbide ball, mixed and ground for 48 hours, and then dried to obtain a mixed powder. Then, these mixed powders were filled in a mold, a molded body of 5.5 × 9.5 × 29 mm was produced with a pressure of 196 MPa, and placed on a carbon plate coated with carbon black powder. Then, it inserts in a sintering furnace and goes through each process of temperature rising, the process in nitrogen, temperature rising, sintering, and cooling, The test piece made from the cemented carbide of this invention products 1-7 and comparative products 1-6 Got. Table 2 shows the details of atmosphere and temperature in each process of applied temperature rise, treatment in nitrogen, sintering, and cooling. Table 1 shows the condition number, sintering temperature and holding time during sintering. Also written.

注）昇温速度を１０℃／ｍｉｎとした。

Note) The heating rate was 10 ° C./min.

With respect to the test pieces of the present invention products 1 to 7 and comparative products 1 to 6 thus obtained, the contents of tungsten carbide, cubic compound and binder phase were calculated from the composition shown in Table 1. Note that the content of the cubic compound is the total amount of ZrC, (W, Ti) C, TiN, TaC, NbC, VC, and Mo ₂ C, and the content of the binder phase is Co, Ni, Cr ₃ C ₂ , Cr ₂ Total amount with Cr in N. Further, a sample that was wet ground with a # 230 diamond wheel and then lapped with a 1 μm diamond paste was analyzed by EPMA analysis using a field emission scanning electron microscope and included in the amount of Zr contained in the cubic compound and the binder phase. The amount of Cr produced was measured. The above results are shown in Table 3.

  The test pieces of the present invention products 1 to 7 and comparative products 1 to 6 were wet-grinded with a # 230 diamond grindstone, and formed into a 4.0 × 8.0 × 25.0 mm shape. Was measured. Further, one surface of the sample was lapped with 1 μm diamond paste, and then the load using a Vickers indenter: hardness at 196 N and fracture toughness value: K1c (IF method) were measured. These results are shown in Table 4.

  Also, for each one of the test pieces, the entire surface was polished to a depth of 0.2 mm with a # 230 diamond grindstone and ground to # 100 or less in a cemented carbide mortar, and an oxygen / nitrogen analyzer was used. Then, each content of oxygen and nitrogen was measured. The results are also shown in Table 4.

  Further, X-ray diffraction using a Cu target was performed on each of the lapped specimens, and the half width at the peak of the (200) plane of the cubic compound phase was measured. The results are also shown in Table 4.

  In Table 4, the inventive product 2 and the comparative product 2 using the same mixed powder, and the inventive product 5 and the comparative product 5 are compared, and the inventive product treated in nitrogen has higher strength and toughness, It can be seen that the amount of oxygen is small.

Using the mixed powders of the present invention products 2, 4, 5, 7 and comparative products 1, 2, 4, 5 obtained in Example 1, respectively, with a chip die with a breaker of SNMG120408 according to ISO standard A cutting tip material was obtained by press molding and sintering under the same conditions as in Example 1. The upper and lower support surfaces are ground with a # 270 diamond grindstone (however, the blade tip and breaker surface are sintered), and then the blade tip is polished with a nylon brush containing # 320 silicon carbide abrasive grains. Round honing with a radius of 0.1 mm was applied. Next, CVD co after washing - inserted into Teingu apparatus, heating H _2, HCl, Ar, a mixed gas such as _{N 2, TiCl 4, CH 3} CN, CO 2, AlCl 3 to 900 to 1050 ° C. From the cemented carbide substrate surface, TiN having an average thickness of 1.0 μm, columnar crystal TiCN having an average thickness of 6.0 μm, TiC having an average thickness of 1.0 μm, and an average thickness of 3. A coated cemented carbide tool was prepared by coating a hard film with an average thickness of 12 μm in total of 0 μm Al ₂ O ₃ and TiN having an average thickness of 1.0 μm.

  Using three of each of the coated cemented carbide tools thus obtained, the conditions of work material: S48C (with four grooves), cutting speed: 250 m / min, depth of cut: 2.0 mm, feed: 0.25 mm / rev A dry intermittent turning test was conducted to determine the average life time until the chipping of the cutting edge, the damage to the cutting edge, and the average flank wear width became 0.30 mm. The results are shown in Table 5.

  As shown in Table 5, the comparative product has a life due to wear accompanied by plastic deformation and film peeling, whereas the product of the present invention has a long life due to normal wear.

Claims (9)

  A cemented carbide comprising a binder phase containing at least one of cobalt and nickel and chromium, a cubic compound containing zirconium, and tungsten carbide, and having an oxygen content of 0.01 to 0.1% by weight.   The cemented carbide according to claim 1, wherein the cemented phase is 3 to 15% by weight, the cubic compound is 3 to 15% by weight, and the balance is tungsten carbide.   The cemented carbide according to claim 1 or 2, wherein the binder phase contains 3 to 20% by weight of chromium with respect to the whole binder phase.   The cemented carbide according to any one of claims 1 to 3, wherein the cubic compound contains 5 to 50 wt% of zirconium with respect to the entire cubic compound.   The cemented carbide according to any one of claims 1 to 4, wherein the cubic compound has a half-value width of 0.5 to 1.0 at the peak of the (200) plane of the X-ray diffraction peak.   The cemented carbide according to any one of claims 1 to 5, wherein the amount of nitrogen contained in the cemented carbide is 0.1 to 0.3% by weight.   A coated cemented carbide obtained by coating the surface of the cemented carbide according to any one of claims 1 to 6 with a hard film.   At least one powder of cobalt and nickel, at least one powder of chromium metal, carbide, nitride, zirconium carbide powder, carbides of elements of group 4a, 5a, 6a of periodic table excluding zirconium, and A step of obtaining a mixed powder composed of at least one of these mutual solid solutions and a tungsten carbide powder, a step of pressing the mixed powder to obtain a compact, and the compact in a vacuum or an inert gas atmosphere The step of raising the temperature of the molded body, the step of holding the molded body in a nitrogen atmosphere of 1 kPa to 1 MPa at a predetermined temperature of 1000 to 1250 ° C., the step of heating the molded body from the predetermined temperature to the sintering temperature, and sintering the molded body The manufacturing method of the cemented carbide which passes through each process of the process sintered at temperature, and the process of cooling the obtained sintered compact.   The manufacturing method of the coated cemented carbide which coat | covers a film on the surface of the cemented carbide obtained with the manufacturing method of Claim 8.