Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/05—Mixtures of metal powder with non-metallic powder
  • C22C1/051—Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor
  • C22C1/053—Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor with in situ formation of hard compounds
  • C22C1/055—Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor with in situ formation of hard compounds using carbon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
  • C22C29/02—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides
  • C22C29/06—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds
  • C22C29/08—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds based on tungsten carbide

Definitions

• This invention relates to a hard alloy having excellent hardness, toughness, wear resistance, fracture resistance, plastic deformation resistance and thermal cracking resistance, in which plate-crystalline tungsten carbide (hereinafter abbreviated to "platy WC”) is crystallized, specifically to a platy WC-containing hard alloy suitable as cutting tools such as an insert, a drill and an end mill, a base material of a coating super hard tool, plastic working tools such as a drawing mold, a die mold and a forging mold and shearing tools such as a punching mold and a slitter, a composition for forming platy WC and a process for preparing the platy WC-containing hard alloy.
• platy WC plate-crystalline tungsten carbide
• hardness i.e, wear resistance and strength and toughness, i.e., fracture resistance of a hard alloy
• hardness i.e, wear resistance and strength and toughness, i.e., fracture resistance of a hard alloy
• toughness i.e., fracture resistance of a hard alloy
• a particle size of WC, a Co content and an addition amount of other carbide so that the hard alloy has been widely used for various purposes.
• there is a problem of antinomy tendency that if wear resistance is heightened, fracture resistance is lowered, while if fracture resistance is heightened, wear resistance is lowered.
• a means obtained by paying attention to anisotropy of mechanical characteristics due to crystal faces of WC specifically, for example, a means relating to a hard alloy in which platy WC exists, which platy WC has a shape represented by a triangle plate or a hexagonal plate and has a (001) face preferentially grown in the direction of the (001) face since the (001) face of WC crystal shows the highest hardness and the direction of a (100) face shows the highest elastic modulus, or a process for preparing the same.
• the growing rate of the (001) crystal face of WC is low, all of the a axis length, c axis length and c/a ratio of the WC crystal are small and the ratio of platy WC contained is low, whereby there is a problem that all of various characteristics of the hard alloy, particularly hardness, wear resistance, strength, toughness and fracture resistance cannot be improved.
• the preparation processes there are problems that it is difficult to control a particle size, it is difficult to heighten the ratio of platy WC contained, said processes can be applied only to a hard alloy in which compositional components are limited, and preparation cost is high.
• the present invention has solved the problems as described above, and an object of the present invention is to provide a platy WC-containing hard alloy exhibiting a synergistic effect by high hardness, high toughness and high strength that hardness is high, wear resistance is excellent, toughness is high and also fracture resistance is excellent, which cannot be considered in a conventional hard alloy, and achieving a long lifetime by heightening all of the growing rate of a WC (001) crystal face, the a axis length, c axis length and c/a ratio of WC (001) crystal and the ratio of platy WC crystal contained, and to provide a process for preparing the same, by which platy WC can be easily incorporated into a hard alloy by sintering under heating mixed powder of platy WC-forming powder comprising composite carbide containing an iron group metal, W and C or a precursor thereof and carbon powder.
• the present inventors have studied for many years in order to improve strength, toughness and fracture resistance of a hard alloy without lowering hardness and wear resistance thereof, and consequently found that such an object can be achieved by heightening all of the growing rate of a WC (001) crystal face, the a axis length, c axis length and c/a ratio of WC (001) crystal and the ratio of platy WC crystal contained.
• a hard alloy by adding carbon powder to composite carbide comprising an iron group metal, W and C or powder of a precursor which forms this composite carbide during heating and then heating the mixture, platy WC satisfying the characteristics described above can be easily formed by reaction and crystallization, to accomplish the present invention.
• the platy WC-containing hard alloy of the present invention is a hard alloy which comprises 4 to 40 % by volume of a binder phase containing at least one of iron group metals (cobalt (Co), nickel (Ni) and iron (Fe)) as a main component; and the balance of a hard phase comprising tungsten carbide, or tungsten carbide containing 50 % by volume or less of a compound with a cubic structure selected from at least one of carbide and nitride of the 4a (titanium (Ti), zirconium (Zr) and hafnium (Hf)), 5a (vanadium (V), niobium (Nb) and tantalum (Ta)) or 6a (chromium (Cr), molybdenum (Mo) and tungsten (W)) group element of the periodic table and mutual solid solutions thereof, and inevitable impurities, wherein when peak intensities at a (001) face and a (101) face in X-ray d
• the binder phase of the platy WC-containing hard alloy of the present invention there may be specifically mentioned, for example, Co, Ni, Fe, and alloys such as Co-Ni, Co-W, Ni-Cr and Fe-Ni-Cr. If the amount of the binder phase is less than 4 % by volume, sintering becomes difficult so that cavities remain in an inner portion, or the rate of forming platy WC crystal is lowered so that strength and hardness are lowered remarkably. On the other hand, if the amount exceeds 40 % by volume, the amount of WC including plate crystal is relatively decreased so that hardness and wear resistance are lowered remarkably.
• the compound with a cubic structure in the platy WC-containing hard alloy of the present invention there may be specifically mentioned, for example, TaC, NbC, V 4 C 3 , VC, (W,Ti)C, (W,Ti,Ta)C, TiN, ZrN, (W,Ti)(C,N) and (W,Nb,Zr)CN. If the amount of the compound with a cubic structure exceeds 50 % by volume, the amount of WC including platy WC is relatively decreased so that hardness and toughness are lowered remarkably.
• the platy WC-containing hard alloy comprises 4 to 40 % by volume of the binder phase containing at least one of iron group metals (Co, Ni and Fe) as a main component; and the balance of WC, wherein when peak intensities at a (001) face and a (101) face in X-ray diffraction using Cu-K ⁇ rays are represented by h(001) and h(101), respectively, said WC satisfies h(001)/h(101) ⁇ 0.50. If the peak intensity ratio of h(001)/h(101) is less than 0.50, the growing rate of the WC (001) crystal face showing the highest hardness is low, whereby improvement of hardness is small.
• the peak intensity ratio of h(001)/h(101) is preferably 0.55 or more, particularly preferably 0.60 or more.
• the platy WC-containing hard alloy has a feature that the WC crystal has an a axis length of 0.2907 nm or more and a c axis length of 0.2840 nm or more. If the a axis length is less than 0.2907 nm or the c axis length is less than 0.2840 nm, inner distortion of a WC crystal lattice is small, whereby an effect of increasing hardness is small.
• the platy WC-containing hard alloy of the present invention has a feature that the ratio of the c axis length to the a axis length of the crystalline axis, i.e., the c/a ratio is particularly preferably 0.9770 or more.
• the platy WC-containing hard alloy has a feature that the (001) face of the WC crystal is oriented in parallel to a pressurized face in a molding step to exhibit orientation property. That is, when the peak intensities at the (001) face and the (101) face of the WC crystal by X-ray diffractometry of a face p parallel to said pressurized face and a face h perpendicular thereto are represented by p(001), p(101), h(001) and h(101), respectively, p(001)/p(101) > 1.2 x h(001)/h(101) is satisfied.
• the orientation rate of the WC (001) face in a specific direction is decreased to lower anisotropy of hardness, which is not suitably used for exhibiting properties by improving hardness in a specific direction or face.
• platy WC-containing hard alloy In the platy WC-containing hard alloy described above, it is preferred that 20 % by volume or more of platy WC having a ratio of the maximum length to the minimum length of a WC particle in a sectional structure of the WC particle being 3.0 or more is contained, whereby all of various characteristics such as hardness, wear resistance, strength, toughness and fracture resistance are improved. It is particularly preferred depending on the case that the average particle size of WC is 0.5 ⁇ m or less.
• Platy WC in the sectional structure of the hard alloy is contained preferably in an amount of 40 % by volume or more, particularly preferably 50 % by volume or more.
• the composition for forming platy WC to be used for preparing the platy WC-containing hard alloy of the present invention comprises composite carbide containing 60 to 90 % by weight of W, 0.5 to 3.0 % by weight of carbon and the balance of at least one of iron group metals, whereby a hard alloy having a high content of platy WC can be obtained.
• composite carbide there may be specifically mentioned, for example, Co 3 W 9 C 4 , Co 2 W 4 C, Co 3 W 3 C, Co 6 W 6 C, Ni 2 W 4 C, Fe 2 W 4 C, Fe 3 W 3 C, Fe 4 W 2 C and mutual solid solutions thereof.
• the process for preparing the platy WC-containing hard alloy of the present invention comprises molding mixed powder of platy WC-forming powder comprising composite carbide comprising an iron group metal, W and C and/or a precursor thereof, carbon powder and, if necessary, cubic compound-forming powder, and then sintering the molded compact under heating at 1,200 to 1,600 °C under vacuum or non-oxidizing atmosphere.
• the process of the present invention is carried out under the same conditions as in a conventional process for preparing a hard alloy, for example, for a sintering-maintaining time of 30 to 90 minutes under atmosphere of a non-oxidizing gas such as an inert gas or hydrogen gas under reduced pressure, normal pressure or pressurization.
• the composite carbide in the process for preparing the platy WC-containing hard alloy of the present invention is the same as the composite carbide described above. Further, there may be mentioned those in which 20 % by weight or less of the 4a, 5a or 6a group metal (excluding W) of the periodic table is dissolved in the above composite carbide such as Co 3 (W,Ti) 9 C 4 , Co 2 (W,V) 4 C, Co 3 (W,Ta) 3 C, (Ni,Cr) 2 W 4 C and (Fe,Mo) 3 W 3 C.
• the dissolved 4a, 5a or 6a group metal is preferred in some cases since it has an action of controlling the size, shape and distribution of crystallized platy WC particles simultaneously with forming carbide by sintering under heating.
• the precursor of the composite carbide in the process for preparing the platy WC-containing hard alloy of the present invention there may be specifically mentioned a W alloy containing an iron group metal, a mixture of W and/or W 2 C and an iron group metal and a mixture of WC, oxide of the 4a, 5a or 6a group metal of the periodic table and an iron group metal.
• powder of an alloy of W-10 % by weight of Co mixed powder of W 2 C-10 % by weight of Co, mixed powder of WC-10 % by weight of TiO 2 -10 % by weight of Co and mixed powder of W-10 % by weight of WC-2 % by weight of Cr 2 O 3 -10 % by weight of Ni, each of which reacts with a part of carbon powder added during sintering under heating to form the above composite carbide.
• the carbon source compound in the process for preparing the platy WC-containing hard alloy of the present invention there may be specifically mentioned graphite, thermal carbon, petroleum pitch and a thermosetting resin.
• graphite Particularly when powder of the precursor of the above composite carbide is used, it is preferred to use graphite having an average particle size of 2 to 20 ⁇ m since formation of platy WC is accelerated to increase hardness and toughness.
• the amount of carbon may be any amount so long as it is an amount sufficient for reducing residual oxygen in mixed powder by sintering under heating and capable of forming a platy WC with a W component, and also it is such an amount that the composite carbide does not remain or free carbon is not precipitated in the hard alloy obtained by sintering.
• the cubic compound-forming powder to be added there may be specifically mentioned, for example, TaC, NbC, V 4 C 3 , VC, TiC, (W,Ti)C, (W,Ti,Ta)C, TiN, ZrN and Ti(CN).
• the sintering under heating in the process for preparing the platy WC-containing hard alloy of the present invention includes a first stage of forming composite carbide represented by M 3-X N 3+X C (where M represents an iron group metal and 0 ⁇ x ⁇ 1) and a second stage of forming platy WC from said composite carbide since formation of platy WC is accelerated to increase hardness and toughness.
• W alloy powder and/or metal W powder is/are contained as the above precursor since the WC (001) face in the hard alloy obtained is oriented in a specific direction to improve anisotropy of hardness. That is, the flat faces of the W alloy powder and/or metal W powder which are made flat by mixing and pulverization are oriented in parallel to a pressurized face in the molding step so that the (001) face of WC formed by sintering under heating is oriented in parallel to the pressurized face.
• the platy WC-containing hard alloy of the present invention has an action of improving hardness, strength, toughness and fracture resistance of an alloy simultaneously by the growing rate of a WC (001) crystal face, the a axis length, c axis length and c/a ratio of WC (001) crystal and the ratio of platy WC crystal contained, and the process for preparing the same has an action of forming platy WC and a binder phase by reacting composite carbide comprising an iron group metal, W and C with carbon.
• the respective powders of commercially available W having average particle sizes of 0.5 ⁇ m, 1.5 ⁇ m and 3.2 ⁇ m shown as "W/F”, “W/M” and “W/L", respectively, in the following tables
• carbon black with a size of 0.02 ⁇ m shown as “C” in the tables
• Co, Ni, Fe, Cr, Cr 3 C 2 and TaH 2 with a size of 1 to 2 ⁇ m were weighed in accordance with the formulation compositions shown in Table 1 and charged into pots made of stainless steel together with an acetone solvent and balls made of a hard alloy.
• the powders were mixed and pulverized for 24 hours and then dried to prepare mixed powders.
• composition powders P(1) to P(6) of the present invention and precursors P(7) and P(8) for preparing composition powders of the present invention were charged into graphite crucibles and heated under vacuum where atmospheric pressure was about 10 Pa for 1 hour under at temperatures shown in Table 1 to prepare composition powders P(1) to P(6) of the present invention and precursors P(7) and P(8) for preparing composition powders of the present invention. After these powders were fixed by X-ray diffraction, compositions and components were quantitated by the internal addition method. The results are shown in Table 1.
• composition powders in Table 1 and the respective powders of the above W, C, Co, Ni, Fe, Cr and Cr 3 C 2 , commercially available WC having average particle sizes of 0.5 ⁇ m, 1.5 ⁇ m and 3.2 ⁇ m (shown as “WC/F”, “WC/M” and “WC/L”, respectively, in the tables), W 2 C with a size of 1.4 ⁇ m, graphite with a size of 6.0 ⁇ m (shown as “G” in the tables), WO 3 with a size of 0.4 ⁇ m, TiO 2 with a size of 0.03 ⁇ m and a (W,Ti,Ta)C solid solution (WC/TiC/TaC 50/20/30 in terms of weight ratio, shown as "WTT” in the tables) with a size of 1.5 ⁇ m were weighed in accordance with the formulation compositions shown in Table 2 and charged into pots made of stainless steel together with an acetone solvent and balls made of a hard alloy.
• the powders were mixed and pulverized for 48 hours and then dried to prepare mixed powders.
• the mixed powders were charged into metal molds and pressurized under a pressure of 2 ton/cm 2 to prepare green compact molds each having a size of about 5.5 x 9.5 x 29 mm.
• the green compact molds were placed on sheets comprising alumina and carbon fiber, heated under vacuum where atmospheric pressure was about 10 Pa and maintained for 1 hour at temperatures shown in Table 2 to obtain hard alloys of Present samples 1 to 17 and Comparative samples 1 to 17.
• the hard alloy samples thus obtained were subjected to wet grinding processing using #230 diamond grinding stone to prepare samples each having a size of 4.0 x 8.0 x 25.0 mm.
• Each flexural strength (strength resistant to bending) was measured (by a method corresponding to Japanese Industrial Standard B4104 which is similar to ISO 242, 2804).
• Vickers hardness and a fracture toughness value K1c were measured with a load of 198 N (by the so-called IM method in which measurement is carried out by measuring length of cracks formed from an edge of dent by using a Vickers hardness tester).
• a structure photograph of the face subjected to lapping was taken by an electron microscope.
• the average particle size of WC and the volume ratio of platy WC having a ratio of the maximum size to the minimum size of 3.0 or more to the whole WC were determined. Further, the ratio of the peak intensity at the (001) face of WC to the peak intensity at the (101) face of WC in X-ray diffraction using Cu-K ⁇ rays, and the lattice constant (a axis length, c axis length) and c/a ratio of the WC crystal were measured. The results are shown in Table 3.
• Formulation composition (% by weight) Sintering temperature (°C) Synthetic composition (% by weight) Present sample 1 96.8P(1)-3.2C 1,400 85.5WC-14.5Co Present sample 2 96.0P(2)-1.0Cr 3 C 2 -3.0C 1,380 78.5WC-21.5(Co-Cr) Present sample 3 97.1P(3)-2.9C 1,420 84.5WC-15.5(Ni-Cr) Present sample 4 96.8P(4)-3.2C 1,380 66.5WC-33.5Co Present sample 5 96.7P(5)-3.3C 1,360 64WC-36Fe Present sample 6 94.4P(7)-5.6G 1,400 84.5WC-15.5Co Present sample 7 94.8P(8)-5.2G 1,420 82WC-18(Ni-Cr) Present sample 8 67.1W 2 C-30.0P(1)-2.9C 1,480 95.5WC-4.5Co Present sample 9 59.2W 2 C-30.0W/M-7.0Co-3.8G 1,420 88.5WC-11.5Co Present sample 10 81.0WC/M-10.0WO 3 -6.8Co-2.2Gr 1,420
• Green compact molds of Present samples 1, 6, 7, 9, 10, 11, 15 and 16 and Comparative samples 1, 6, 7, 9, 10 and 13 used in Example 1 were heated by the same method and under the same conditions as in Example 1, maintained at the respective temperatures of 950 °C and 1,100 °C for 5 minutes, cooled and then taken out.
• approximate compositions thereof were determined by the internal addition method by X-ray diffraction. The results are shown in Table 4. Table 4 Sample No.
• the hard alloy samples thus obtained were subjected to wet grinding processing using #230 diamond grinding stone, and one face of the upper and lower faces (shown as “p face” in Table 5) and one face the side faces (shown as “h face” in Table 5) of the samples were subjected to lapping with 1 ⁇ m of diamond paste.
• the peak intensity ratio of the (001) face to the (101) face of the WC crystal by X-ray diffraction was measured. Further, as to the respective peak intensity ratios obtained, the ratio of the p face to the h face was calculated. The results are shown in Table 5.
• Peak intensity ratio Face ratio of peak intensity p/h p face h face Present sample 6 0.74 0.42 1.76 Present sample 7 0.80 0.49 1.63 Present sample 9 0.67 0.44 1.52 Present sample 15 0.75 0.51 1.47 Comparative sample 6 0.31 0.32 0.96 Comparative sample 7 0.36 0.33 1.09 Comparative sample 9 0.33 0.33 1.00 Comparative sample 13 0.30 0.29 1.03
• the platy WC-containing hard alloys of the present invention exhibit flexural strength, hardness and fracture toughness all of which are higher than those of the comparative hard alloys comprising the same components.
• the surfaces of the chips were coated successively with 1.0 ⁇ m of TiN, 5.0 ⁇ m of TiCN, 2.0 ⁇ m of TiC, 2.0 ⁇ m of Al 2 O 3 and 1.0 ⁇ m TiN (total coating thickness: 11 ⁇ m).
• an intermittent lathe turning test was conducted by using steel under the following conditions to measure a life time until a blade tip was broken or a flank wear amount became 0.35 mm. The results are shown in Table 6.
• the hard alloy containing platy WC of the present invention has remarkably excellent effects that it has a Vickers hardness of 500 or more at HV20 and a fracture toughness K1c of 0.5 MPa ⁇ m 1/2 or more as compared with a conventional hard alloy having the same composition and particle size, and the process for preparing the same has effects that a hard alloy having a high content of platy WC and a controlled particle size can be prepared easily and inexpensively.
• the effect of the hard alloy containing platy WC of the present invention can be expected when a covered hard alloy is prepared by covering the surface of the hard alloy of the present invention with a hard film comprising a single layer or a multilayer of at least one of carbide, nitride, oxycarbide and oxynitride of the 4a (Ti, Zr and Hf), 5a (V, Nb and Ta) or 6a (W, Mo and Cr) group element of the periodic table, oxide and nitride of Al and mutual solid solutions thereof, diamond, diamond-like carbon, cubic boronitride and hard boronitride.
• a hard film comprising a single layer or a multilayer of at least one of carbide, nitride, oxycarbide and oxynitride of the 4a (Ti, Zr and Hf), 5a (V, Nb and Ta) or 6a (W, Mo and Cr) group element of the periodic table, oxide and nitride of Al and mutual solid solutions thereof

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• 1995
  • 1995-08-23 EP EP19950113238 patent/EP0759480B1/fr not_active Expired - Lifetime
  • 1995-08-23 DE DE1995625248 patent/DE69525248T2/de not_active Expired - Lifetime

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