TUNGSTEN CARBIDE-BASED CEMENTED HARD MATERIAL

Abstract

A tungsten-carbide-based hard material includes the following components: tungsten carbide with an average particle size of 0.1-1.3 μm; 1.0-5.0 wt. % (Co+Ni), with a ratio of Co/(Co+Ni) in wt. % of 0.4≤Co/(Co+Ni)≤0.95; 0.1-1.0 wt. % Cr, with a ratio of Cr to (Co+Ni) in wt. % of 0.05 Cr/(Co+Ni) 0.20; 0.01-0.3 wt. % Mo; and 0.02-0.45 wt. % Me, where Me represents one or more elements from the group Ta, Nb, Hf and Ti, preferably Ta and/or Nb; and wherein 0.01≤Me/(Co+Ni)≤0.13.

Claims

1-14. (canceled)

15. A tungsten carbide-based cemented hard material, comprising: tungsten carbide having an average particle size of 0.1-1.3 μm; 1.0-5.0% by weight of (Co+Ni), with a ratio of Co to (Co+Ni) in % by weight of 0.4≤Co/(Co+Ni)≤0.95; 0.1-1.0% by weight of Cr, with a ratio of Cr to (Co+Ni) in % by weight of 0.05≤Cr/(Co+Ni)≤0.20; 0.01-0.3% by weight of Mo; and 0.02-0.45% by weight of Me, where Me is one or more elements selected from the group consisting of Ta, Nb, Hf and Ti; and 0.01 Me/(Co+Ni)≤0.13.

16. The tungsten carbide-based material according to claim 15, wherein Me is at least one of Ta or Nb.

17. The tungsten carbide-based material according to claim 15, wherein the tungsten carbide has an average particle size of 0.1-0.8 μm.

18. The tungsten carbide-based material according to claim 17, wherein the tungsten carbide has an average particle size of 0.2-0.5 μm.

19. The tungsten carbide-based material according to claim 15, wherein 0.6≤Co/(Co+Ni)≤0.9.

20. The tungsten carbide-based material according to claim 15, wherein 0.05≤Cr/(Co+Ni)≤0.15.

21. The tungsten carbide-based material according to claim 15, wherein a ratio of Mo to Cr in % by weight is Mo/Cr<0.5.

22. The tungsten carbide-based material according to claim 21, wherein the ratio Mo/Cr<0.4.

23. The tungsten carbide-based material according to claim 15, wherein 0.02 Me/(Co+Ni)≤0.08.

24. The tungsten carbide-based material according to claim 15, wherein a ratio of Me to Cr in % by weight is Me/Cr<0.65.

25. The tungsten carbide-based material according to claim 15, having a hardness HV10 in a range given by the equation:
HV10=2550−100.Math.% by weight of (Co+Ni)±150.

26. The tungsten carbide-based material according to claim 15, having a fracture toughness K.sub.IC in MPa.Math.m.sup.1/2 in a range
K.sub.IC=6.8+(⅓).Math.% by weight of (Co+Ni)±0.5.

27. The tungsten carbide-based material according to claim 15, having a transverse rupture strength TRS in MPa in a range:
TRS=2150+(2500/6).Math.% by weight of (Co+Ni)±500.

28. A woodworking tool, comprising a working region made of a tungsten carbide-based cemented hard material according to claim 15.

29. A forming tool, comprising a working region made of a tungsten carbide-based cemented hard material according to claim 15.

30. The forming tool according to claim 29, configured as a tool for cold forming.

31. The forming tool according to claim 30, being a drawing die for wire production or a deep-drawing tool.

Description

[0020] Further advantages and useful aspects of the invention may be derived from the following description of working examples with reference to the accompanying figures.

[0021] The figures show:

[0022] FIG. 1: a schematic depiction of a woodworking tool having a working region composed of a cemented hard material according to one illustrative embodiment;

[0023] FIG. 2: an enlarged schematic depiction of a detail II of FIG. 1;

[0024] FIG. 3: a schematic depiction of a forming tool having a working region composed of a cemented hard material according to another illustrative embodiment;

[0025] FIG. 4: a schematic plan of the forming tool of FIG. 3;

[0026] FIG. 5: a schematic cross-sectional view of the forming tool of FIG. 3;

[0027] FIG. 6: an optical micrograph of a cemented hard material as per comparative example 1;

[0028] FIG. 7: an optical micrograph of a cemented hard material as per Example 1;

[0029] FIG. 8: an optical micrograph of a cemented hard material as per Example 2;

[0030] FIG. 9: an optical micrograph of a cemented hard material as per Example 3; and

[0031] FIG. 10: an optical micrograph of a cemented hard material as per Example 4.

ILLUSTRATIVE EMBODIMENT

[0032] An illustrative embodiment of the tungsten carbide-based cemented hard material will firstly be described in general terms below.

[0033] The cemented hard material has a specific composition which will be described in more detail below.

[0034] The cemented hard material consists predominantly of tungsten carbide having an average particle size in the range 0.1-1.3 μm. The average particle size can preferably be in the range 0.1-0.8 μm. The average particle size is particularly preferably in the range 0.2-0.5 μm.

[0035] The proportion of tungsten carbide in the cemented hard material can be, in particular, from 92 to 98.5% by weight. The cemented hard material additionally comprises a ductile metallic binder. In the illustrative embodiment, the metallic binder consists predominantly of Co (cobalt) and Ni (nickel), with the ratio in per cent by weight of Co to the sum of Co and Ni being in the range from 0.4 to 0.95. The ratio is preferably in the range from 0.6 to 0.9; i.e. the proportion of Co in the metallic binder is preferably greater than the proportion of Ni in the metallic binder.

[0036] The tungsten carbide-based cemented hard material further comprises from 0.1 to 1% by weight of Cr, with the ratio of Cr to the sum of Co and Ni in per cent by weight being selected so that 0.05≤Cr/(Co+Ni)≤0.20. When the Cr content is kept within this range, the desired grain-refining effect is achieved and chromium-containing mixed carbide precipitates can be largely avoided. Preference is given to: 0.05≤Cr/(Co+Ni)≤0.15. In this case, chromium-containing mixed carbide precipitates can be avoided particularly reliably without the production parameters in the powder-metallurgical production process having to be kept within narrow tolerance ranges.

[0037] The cemented hard material of the illustrative embodiment also additionally comprises 0.01-0.3% by weight of Mo. The Mo content is preferably set so that it is significantly lower than the Cr content, preferably less than half the Cr content, particularly preferably less than 40% of the Cr content.

[0038] According to the invention, the cemented hard material further comprises one or more elements from the group consisting of Ta, Nb, Hf and Ti, with the total proportion in the cemented hard material being in the range from 0.02 to 0.45 per cent by weight. The ratio of the total proportion of Ta, Nb, Hf and Ti to the total proportion of Co and Ni is in the range from 0.01 to 0.13. The ratio can particularly preferably be in the range from 0.02 to 0.08. The cemented hard material can preferably comprise only Ta and/or Nb from the group consisting of Ta, Nb, Hf and Ti, which two elements have a particularly positive effect on the physical properties of the cemented hard material. The total proportion of the further elements of the group consisting of Ta, Nb, Hf and Ti in the cemented hard material can preferably be significantly smaller than the proportion of Cr in the cemented hard material, in particular less than 65% of the Cr content. Optionally, the cemented hard material can comprise additionally up to maximum 0.2% by weight vanadium, preferably up to maximum 0.15% by weight.

[0039] The cemented hard material as per the illustrative embodiment was produced powder-metallurgically using WC powder having a particle size (FSSS, Fisher sieve sizes) of 0.5 μm; Co powder having an FSSS particle size of 0.9 μm, Ni powder having an FSSS particle size of 2.5 μm, Cr.sub.3C.sub.2 powder having an FSSS particle size of 1.5 μm; Mo.sub.2C powder having an FSSS particle size of 1.35 μmm; NbC powder having an FSSS particle size of 1.2 μm, TaC powder having an FSSS particle size of 0.9 μm and (Ta, Nb)C powder (more precisely: (Ta.sub.0.6, Nb.sub.0.4)C powder) having an FSSS particle size of 1.2 μm. Production was carried out by mixing of the respective starting powders with a solvent in a ball mill or an attritor and subsequent spray drying in the customary way. The resulting granular material was pressed and brought to the desired shape and was subsequently sintered in a conventional way in order to obtain the cemented hard material. Drawing dies for steel wire as working region for a forming tool and saw teeth as working region for a woodworking tool in the form of a circular saw were manufactured from the cemented hard material. The determination of the average grain size of the tungsten carbide grains in the cemented hard material was carried out by the “equivalent circle diameter (ECD)” method from EBSD (electron backscatter diffraction) images. This method is described, for example, in “Development of a quantitative method for grain size measurement using EBSD”; Master of Science Thesis, Stockholm 2012, by Frederik Josefsson.

[0040] A first illustrative embodiment of a woodworking tool 100 having a working region 10 made of the tungsten carbide-based cemented hard material as has been described above is depicted in FIG. 1 and FIG. 2.

[0041] In the illustrative embodiment specifically depicted, the woodworking tool 100 is a circular saw blade which has a plurality of saw teeth which each form a working region 10 which engages with the wood to be worked. The working region 10 composed of the cemented hard material in the form of the saw tooth is in each case metallurgically bonded, e.g. via a solder joint, to the main element 11 of the circular saw blade, which can, for example, be made of steel in the conventional way.

[0042] Although a circular saw blade is depicted by way of example as woodworking tool in FIG. 1 and FIG. 2, the tungsten carbide-based cemented hard material can also be used as working region on other woodworking tools.

[0043] An illustrative embodiment of a forming tool 200 having a working region 20 made of the tungsten carbide-based cemented hard material as has been described above is depicted in FIG. 3 to FIG. 5.

[0044] In the illustrative embodiment specifically depicted in FIG. 3 to FIG. 5, the forming tool 200 is a tool for cold forming, in particular a drawing die for wire production, and the working region 20 is a draw plate which comes into direct contact with the material to be worked, e.g. steel wire. The working region 20 composed of ii the cemented hard material is accommodated in a housing 21 which can, for example, be made of steel.

EXAMPLES

Comparative Example 1

[0045] As comparative example, a tungsten carbide-based cemented hard material was produced by the powder-metallurgical process indicated above using the following composition: 2.25% by weight of Co; 0.75% by weight of Ni; 0.35% by weight of Cr (corresponds to 0.4% by weight of Cr.sub.3C.sub.2 as starting material); 0.047% by weight of Mo (corresponds to 0.05% by weight of Mo.sub.2C as starting material), balance WC and unavoidable impurities. The proportion of WC is thus about 96.55% by weight. An optical micrograph of the microstructure of this cemented hard material is shown in FIG. 6.

[0046] In the production process, the carbon balance was set so that the resulting cemented hard material is at least substantially free of η phase, i.e. of undesirable (W.sub.x, Co.sub.y).sub.zC mixed phases, and substantially free of carbon precipitates. In this context, substantially free of η phase means that from 0 to not more than 0.5% by volume of η phase is present.

[0047] The average grain size of the tungsten carbide grains was in the range 0.2-0.5 μm. A Vickers hardness HV10 of 2140, a fracture toughness K.sub.IC of 7.8 MPa.Math.m.sup.1/2 and a transverse rupture strength of 3200 MPa were measured.

Example 1

[0048] A tungsten carbide-based cemented hard material was produced by the above-described powder-metallurgical production process using the following composition: 2.7% by weight of Co; 0.9% by weight of Ni; 0.45% by weight of Cr (corresponds to 0.52% by weight of Cr.sub.3C.sub.2 as starting material); 0.047% by weight of Mo (corresponds to 0.05% by weight of Mo.sub.2C as starting material) and 0.094% by weight of Ta (corresponds to 0.1% by weight of TaC as starting material), balance WC and unavoidable impurities. The proportion of WC was thus about 95.73% by weight. The content of Co+Ni was 3.6% by weight, with a Co/(Co+Ni) ratio of 0.75. The Cr/(Co+Ni) ratio was 0.125. The Me/(Co+Ni) ratio was 0.026; with Me=Ta in this Example 1. An optical micrograph of the microstructure of the cemented hard material is shown in FIG. 7.

[0049] In this example, too, the carbon balance was set in the production process so that the resulting cemented hard material is at least substantially free of η phase, i.e. of undesirable (W.sub.x, Co.sub.y).sub.zC mixed phases, and substantially free of carbon precipitates.

[0050] The average grain size of the tungsten carbide grains in the cemented hard material was in the range from 0.2 to 0.5 μm. The Vickers hardness HV10 was (in accordance with ISO 3878:1991) determined and was 2145. The fracture toughness K.sub.IC was also determined as described above and was 8.0 MPa.Math.m.sup.1/2. The determination of the transverse rupture strength by the method indicated above gave 3650 MPa.

[0051] It can thus be seen that the tungsten carbide-based cemented hard material of Example 1 has both a higher fracture toughness K.sub.IC and a higher transverse rupture strength compared to the cemented hard material of Comparative Example 1 at a comparable hardness HV10.

Example 2

[0052] A tungsten carbide-based cemented hard material was produced by the above-described powder-metallurgical production process using the following composition: 3.15% by weight of Co; 1.05% by weight of Ni; 0.83% by weight of Cr (corresponds to 0.96% by weight of Cr.sub.3C.sub.2 as starting material); 0.132% by weight of Mo (corresponds to 0.14% by weight of Mo.sub.2C as starting material) and 0.188% by weight of Ta (corresponds to 0.2% by weight of TaC as starting material), balance WC and unavoidable impurities. The proportion of WC was thus about 94.50% by weight. The content of Co+Ni was 4.2% by weight, with a Co/(Co+Ni) ratio of 0.75. The Cr/(Co+Ni) ratio was 0.198. The Me/(Co+Ni) ratio was 0.045; with Me=Ta in this Example 2 as well. An optical micrograph of the cemented hard material is shown in FIG. 8.

[0053] In this example, too, the carbon balance was set so that the cemented hard material was substantially free of ƒ phase and free of carbon precipitates.

[0054] The average grain size of the tungsten carbide grains was in the range 0.2-0.5 μm. A Vickers hardness HV10 of 2180, a fracture toughness K.sub.IC of 8.1 MPa.Math.m.sup.1/2 and a transverse rupture strength of 3800 MPa were measured.

[0055] It can thus be seen that the cemented hard material of Example 2 has both a higher fracture toughness K.sub.IC and a higher transverse rupture strength compared to comparative example 1 at a higher hardness HV10.

Example 3

[0056] A tungsten carbide-based cemented hard material was produced by the above-described power-metallurgical production process using the following composition: 2.7% by weight of Co; 0.9% by weight of Ni; 0.45% by weight of Cr (corresponds to 0.52% by weight of Cr.sub.3C.sub.2 as starting material); 0.094% by weight of Mo (corresponds to 0.1% by weight of Mo.sub.2C as starting material) and 0.177% by weight of Nb (corresponds to 0.2% by weight of NbC as starting material), balance WC and unavoidable impurities. The proportion of WC was thus about 95.58% by weight. In this example 3, Me was thus Nb. An optical micrograph of the cemented hard material is shown in FIG. 9.

[0057] In this example, too, the carbon balance was set so that the cemented hard material was substantially free of η phase and free of carbon precipitates.

[0058] The average grain size of the tungsten carbide grains was in the range 0.2-0.5 μm. A Vickers hardness HV10=2235, a fracture toughness K.sub.IC of 7.9 MPa.Math.m.sup.1/2 and a transverse rupture strength of 3600 MPa were measured.

[0059] It can thus be seen that the cemented hard material of Example 3 has both a higher fracture toughness K.sub.IC and a higher transverse rupture strength compared to comparative example 1 at a significantly higher hardness HV10.

Example 4

[0060] A tungsten carbide-based cemented hard material was produced by the above-described powder-metallurgical reduction process using the following composition: 2.7% by weight of Co; 0.9% by weight of Ni; 0.45% by weight of Cr (corresponds to 0.52% by weight of Cr.sub.3C.sub.2 as starting material); 0.094% by weight of Mo (corresponds to 0.10% by weight of Mo.sub.2C as starting material), 0.113% by weight of Ta (corresponds to 0.2% by weight of (Ta, Nb)C as starting material) and 0.071% by weight of Nb (corresponds to 0.2% by weight of (Ta, Nb)C as starting material), balance WC and unavoidable impurities. The proportion of WC was thus about 95.58% by weight. The content of Co+Ni was 3.6% by weight, with a Co/(Co+Ni) ratio of 0.75. The Cr/(Co+Ni) ratio was 0.125. The Me/(Co+Ni) ratio was 0.051; with Me=Ta+Nb in this Example 4. An optical micrograph of the microstructure of this cemented hard material is shown in FIG. 10.

[0061] In this example, too, the carbon balance was set so that the cemented hard material was substantially free of η phase and free of carbon precipitates.

[0062] The average grain size of the tungsten carbide grains in the cemented hard material was in the range from 0.2 to 0.5 μm. The Vickers hardness HV10 was (in accordance with ISO 3878:1991) determined and was 2220. The fracture toughness K.sub.IC was also determined as described above and was 7.9 MPa.Math.m.sup.1/2. The determination of the transverse rupture strength by the method indicated above gave 3500 MPa.

[0063] It can thus be seen that the cemented hard material of Example 4 has both a higher fracture toughness K.sub.IC and a higher transverse rupture strength compared to comparative example 1 at a significantly higher hardness HV10.