Classifications

• • 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
• • 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

Definitions

• the present invention relates to a hard alloy to be used for cutting tools, wear resistant tools, corrosion resistant and wear resistant parts, etc., and particularly to a hard alloy in which characteristics such as hardness, toughness, strength, wear resistance, fracture resistance, plastic deformation resistance, thermal crack resistance, antioxidation property, corrosion resistance, etc., by adding specific element(s) to crystal of hexagonal tungsten carbide which is a primary hard phase as a solid solution, and to a W-based composite carbide powder which becomes a starting material thereof.
• a hard alloy produced by mixing, in addition to WC and Co, other powder of carbides such as TiC, TaC, VC, Cr 3 C 2 , etc., subjecting to molding under pressure, and sintering under heating has been used for various kinds of uses such as cutting tools, wear resistant tools and parts. Also, by adjusting grain size of WC, a Co amount, a kind and amount of a carbide to be added, and the like, alloy characteristics such as hardness, strength, toughness, heat resistance, oxidation resistance, corrosion resistance, etc. required for the respective uses are obtained.
• TiC is added to steel cutting tools in which wear due to a reaction or welding becomes a problem
• TaC and/or ZrC is/are added to hot-working mold or steel cutting tools in which plastic deformation at high temperatures becomes a problem
• VC and/or Cr 3 C 2 is/are added to a drill to which hardness and strength are required as a grain growth inhibitor of WC
• Cr 3 C 2 and/or Mo 2 C is/are added to wear resistant parts in which corrosion becomes a problem.
• Japanese Provisional Patent Publication No. 7-54001 there is disclosed a preparation method of fine complex carbide powder for preparation of a tungsten carbide-based hard alloy in which mixed powder comprising tungsten oxide, cobalt oxide, carbon, and further carbides of V, Cr, Ta and/or Nb each having an average particle diameter of about 1 ⁇ m or lower is subjected to reduction treatment and carbonization treatment both at'700 to 1200°C.
• powder comprising a transition metal carbide and Group VIII metal and a process for preparing the same, which comprises heating a precursor mixed powder which becomes a metal selected from iron, cobalt and nickel and a transition metal carbide of a metal selected from tungsten, titanium, tantalum, molybdenum, zirconium, hafnium, vanadium, niobium and chromium at 1173 to 1773K (900 to 1500°C).
• a precursor mixed powder which becomes a metal selected from iron, cobalt and nickel and a transition metal carbide of a metal selected from tungsten, titanium, tantalum, molybdenum, zirconium, hafnium, vanadium, niobium and chromium at 1173 to 1773K (900 to 1500°C).
• a complex carbide containing a tungsten carbide obtained by heating a mixed powder comprising tungsten oxide and chromium oxide or metallic chromium in hydrogen atmosphere at 700 to 1100°C to obtain a solid solution or a intermetallic compound, mixing carbon powder thereto, and carbonizing in hydrogen and vacuum at a temperature of 1300 to 1700°C, and 0.5 to 2.0% by weight of metal chromium based on the amount of the tungsten carbide, and a process for preparing the same.
• transition metal or its carbide is uniformly and finely dispersed, so that when they are used as a hard alloy, characteristics such as hardness, strength, toughness, etc. can be improved but a heating temperature is low so that an amount of the transition metal dissolved in tungsten carbide is extremely little, whereby there is no improvement in characteristics of the tungsten carbide itself.
• a heating temperature is low so that an amount of the transition metal dissolved in tungsten carbide is extremely little, whereby there is no improvement in characteristics of the tungsten carbide itself.
• This is to subject a (W, Mo)C solid solution which has conventionally been well known to nitriding synthesis by heating to 500 to 2000°C in a nitrogen atmosphere at a pressure of 10 atm or higher.
• the (W, Mo)(CN) powder disclosed in this publication has a wide range of an amount of Mo as a solid solution and when it is employed for a hard alloy, an effect of making particles fine by the nitrogen can be expected.
• an amount of Mo to be dissolved as a solid solution is large, there are problems that decreases in hardness, strength, wear resistance, plastic deformation property and oxidation resistance are remarkable.
• Hei.11-6025 there are disclosed a hard alloy comprising 3 to 25% by weight of Co and Ni in total, 10 to 30% by weight of Cr in terms of chromium carbide based on the amount of Co and Ni, and the reminder being tungsten carbide and inevitable impurities, a coated alloy using the hard alloy as a matrix and coated cutting tools.
• a Cr content, a Co/Ni ratio and grain size of WC are limited to optimum ranges when they are used as cutting tools, and Cr is dissolved in a metal binder phase, but is not dissolved in WC as a solid solution, so that there is a problem that an effect of Cr added cannot sufficiently be shown.
• an iron-based hard alloy comprising a binder phase which comprises Fe containing 0.35 to 3.0% by weight of C, 3.0 to 30.0% by weight of Mn, and 3.0 to 25.0% by weight of Cr.
• a hard alloy using titanium compound powder as a starting material which powder has a coated film on the surface thereof, comprising at least one substance selected from the group consisting of Groups 4a, 5a, 6a metal except for titanium, their carbide, nitride and carbonitride, and rhenium metal and iridium metal.
• the hard alloys containing Mn or Re metal disclosed in these publications are to improve strength, toughness, corrosion resistance, heat resistance, etc. of the hard alloy by adding these metals as a solid solution to a metal binder phase, but these metals are not dissolved in WC, so that an effect of adding Mn or Re is little and if an amount of these metals to be added is large, the metal binder phase becomes brittle whereby there are problems that strength and toughness are lowered.
• the present invention is to solve the above-mentioned problems, and specifically, an object of the present invention is to provide a hard alloy in which contradicting alloy characteristics of the hard alloy are simultaneously improved by dissolving specific element(s) such as Ti, Zr, V, Ta, Cr, Mn, etc. into crystalline of WC as a solid solution whereby hardness, toughness, oxidation resistance, corrosion resistance, etc. of the WC itself are improved, and to provide W-based composite carbide powder which becomes a starting material of the hard alloy.
• specific element(s) such as Ti, Zr, V, Ta, Cr, Mn, etc.
• the present inventors have studied to improve contradicting characteristics of hard alloy at the same time for a long period of time, and as a result, they have found that to improve characteristics of WC itself is effective, various characteristics of the alloy can be improved when specific element(s) is/are dissolved in the crystal of WC, metals belonging to Group IVB (Ti, Zr, Hf), VB (V, Nb, Ta) or VIB (Cr, Mo) of the Periodic Table (except for W), and Mn and Re are the most effective as the specific element(s), and WC dissolved the specific element(s) therein can be obtained by subjecting a mixed powder of W, C and an oxide of the specific element(s) to heat treatment, whereby they have accomplished the present invention.
• specific element(s) is/are dissolved in the crystal of WC
• the hard alloy of the present invention comprises 5 to 50% by volume of a metallic binder phase comprising at least one element selected from cobalt, nickel and iron as a main component, 0 to 40% by volume of a cubic crystal compound comprising at least one compound selected from a carbide, nitride and mutual solid solution of a metal of Group IVB (Ti, Zr, Hf), VB (V, Nb, Ta), VIB (Cr, Mo) of the Periodic Table, and the reminder being hexagonal tungsten carbide and inevitable impurities, wherein at least one specific element(s) selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, manganese and rhenium is dissolved in the crystal of the hexagonal tungsten carbide as a solid solution in an amount of 0.1 to 3.0% by weight based on the amount of the tungsten carbide.
• a metallic binder phase comprising at least one element
• the hexagonal tungsten carbide in the hard alloy of the present invention is a material in which at least one of the specific element(s) selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, Mn and Re is dissolved in the crystal of WC as a solid solution.
• An amount of the specific element(s) to be dissolved in WC as a solid solution is defined to be 0.1 to 3.0% by weight, since if it is added in an amount of less than 0.1% by weight, improved effects in hardness, toughness, oxidation resistance, corrosion resistance, etc. are little, whereas Ti, Zr, Hf, V, Nb or Ta is extremely difficult to be dissolved in WC in an amount exceeding 3.0% by weight, and even when Cr, Mo, Mn or Re can be dissolved in WC in an amount exceeding 3.0% by weight, it accompanies with lowering in hardness or oxidation resistance, or formation of brittle sub-carbide material.
• the amount is preferably 0.3 to 2% by weight.
• the specific element(s) dissolved in WC crystal has slightly different characteristics to be provided to the hard alloy depending on the kind thereof.
• Ti, Zr, Hf and V improve hardness, wear resistance, welding resistance, oxidation resistance, etc.
• Nb and Ta improve toughness, fracture resistance, heat resistance, etc.
• Cr improves toughness, oxidation resistance and corrosion resistance
• Mo, Mn and Re improve hardness, toughness, heat resistance, etc.
• the specific element(s) is/are at least one selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium and tantalum, and a content of a cubic crystal compound mentioned hereinbelow is 1% by volume or less, since strength and toughness are particularly high.
• the specific element(s) is chromium, and 0.1 to 10% by weight of chromium is contained based on the total amount of the hard alloy, since chromium is also dissolved in the metal binder phase as a solid solution, so that improved effects of hardness, toughness, heat resistance, corrosion resistance, oxidation resistance, etc. are more remarkable.
• the specific element(s) is/are manganese and/or rhenium, and 0.1 to 10% by weight of manganese and/or rhenium is/are contained in the total amount of the hard alloy, since it is/they are also dissolved in the binder phase, whereby improved effects of hardness, toughness, heat resistance, etc. are more remarkable.
• the metal binder phase of the hard alloy according to the present invention comprises an alloy containing iron group metal (Fe, Co, Ni) as a main component and 30% by weight or less of W is dissolved therein. More specifically, the binder phase may be mentioned, for example, Co-W alloy, CoRe alloy, Co-W-Cr alloy, Ni-Mo alloy, Ni-Cr-W alloy, Co-Ni-Cr-W alloy, Fe-Ni-W alloy, Fe-Mo-Cr alloy, Fe-Mn alloy, and the like.
• An amount of the metal binder phase is defined to be 5 to 50% by volume, since if it is less than 5% by volume, micro pores are remained in the alloy, so that hardness, strength, toughness or fracture resistance is lowered, while if it exceeds 50% by volume, hardness or wear resistance is lowered.
• the cubic crystal compound which is an optional component of the hard alloy according to the present invention may be specifically mentioned, for example, VC, NbC, TaC, (W,Ti)C, (W, Zr) C, (W, Ti, Ta) C, (W, Ti, Re) C, TiN, ZrN, HfN, (W,Ti,Ta)-(C,N), (W,Ti,Mo)(C,N), and the like.
• the hard alloy of the present invention may contain Cr 7 C 3 , Mo 2 C, etc. which do not belong to the cubic crystal compound with a small amount. If the content of the cubic crystal compound in the hard alloy exceeds 40% by volume, an amount of WC to which the specific element(s) is/are dissolved is relatively lowered, so that an improved effect thereof becomes a little.
• the W-based composite carbide powder of the present invention comprises complex carbide powder which contains tungsten, carbon, and at least one specific element(s) selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, manganese and rhenium, wherein said complex carbide powder contains 80% by volume or more of hexagonal tungsten carbide, and 0.1 to 3.0% by weight of the specific element(s)is/are dissolved in the crystals of the hexagonal tungsten carbide.
• An amount of the specific element(s) to be dissolved in the W-based composite carbide powder of the present invention is defined to be 0.1 to 3.0% by weight, since if it is less than 0.1% by weight, improved effects on the WC itself such as hardness, toughness, oxidation resistance, corrosion resistance, etc. are low, and it is difficult to dissolve the specific element(s) in an amount exceeding 3.0% by weight in the WC crystal.
• the complex carbide of the present invention is represented by the chemical formula, it is a material of (W 1-x ,M x )C y wherein x and y satisfy the relationship of 0.002 ⁇ x ⁇ 0.06 and 0.95 ⁇ y ⁇ 1.00 since the specific element(s) is/are substituted for the W atom in the WC crystal, and taken into the hexagonal crystal lattice.
• M represents at least one of the specific elements.
• the W-based composite carbide powder of the present invention comprises WC in which the specific element(s) is/are dissolved as a main component, and a cubic crystal compound into which W is dissolved, and W 2 C, Cr 3 C 2 , Mo 2 C or the like into which the specific element(s) is dissolved. If an amount of the WC in which the specific element(s) is/are dissolved is less than 80% by volume, improved effects on hardness, toughness, oxidation resistance, corrosion resistance, etc. due to the specific element(s) dissolved in WC are little in the hard alloy to be produced by using the present products.
• the cubic crystal compound which may be contained in the complex carbide powder comprises W, carbon and/or nitrogen, and at least one selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium and tantalum. Specific compositions thereof may be mentioned (W 0.6 Ti 0.4 )C 0.8 , (W 0.06 Zr 0.95 )C 0.75 , (W 0.45 V 0.55 )C 0.9 , (W 0.65 Ta 0.35 )C 0.9 , (W 0.5 Ti 0.5 )(C 0.9 N 0.1 ) 0.95 , (W 0.5 Ti 0.3 Ta 0.2 )C 0.9 , and the like.
• These cubic crystal compounds are formed when the specific element(s) is/are added exceeding a limit of an amount capable of being dissolved, and to show added effects of the specific element(s) at the highest level, the presence of the cubic crystal compound is sometimes preferred.
• an amount thereof becomes 20% by volume or more, it becomes difficult to adjust a ratio of the composition for producing the hard alloy, and in particular, a problem of lowering in strength of the hard alloy arises.
• W 2 C is likely formed when the content of carbon is lower, when the powder is subjected to heat treatment at higher temperatures, when the specific element(s) is Cr or Mo, or the like, but to enlarge an amount of the element(s) to be dissolved, W 2 C is rather preferably contained in an amount of up to 5% by volume.
• the WC crystal to which the specific element(s) is/are dissolved has a lattice constant of a axis of a hexagonal crystal lattice of 0.2910 nm or longer and/or a lattice constant of c axis of the same of 0.2840 nm or longer, since dissolution of the specific element(s) in the WC crystal is complete and uniform whereby improved effects of the various kinds of characteristics become maximum.
• the hard alloy of the present invention can be produced by the conventionally employed powder metallurgy method when the W-based composite carbide powder of the present invention is used as a starting material.
• the W-based composite carbide powder can be obtained, for example, by heating a mixed powder of WC and TiH 2 , a mixed powder of W, TiN and carbon, a mixed powder of WO 3 , TiO 2 and carbon and the like in a non-oxidative atmosphere or a combined atmosphere of reducing and carburizing atmospheres at high temperatures.
• powder with a much amount of dissolution as well as a uniform dissolution degree and uniform grain size distribution can be produced.
• the W-based composite carbide powder of the present invention can be produced by subjecting a mixed powder comprising W powder, carbon powder and oxide powder of the specific element(s) each having a grain size of 1 ⁇ m or less to heat treatment at 1500 to 2000°C or so in an inert gas atmosphere or under vacuum.
• a mixed powder comprising W powder, carbon powder and oxide powder of the specific element(s) each having a grain size of 1 ⁇ m or less
• the heat treatment temperature is higher, an amount of the specific element(s) dissolved in the powder increases but the WC crystals become coarse to cause abnormal grain growth.
• Cr or Mn which has a higher vapor pressure is used as the specific element(s)
• the hexagonal tungsten carbide into which the specific element(s) is/are dissolved, which is in the W-based composite carbide powder used as a starting material has functions of improving hardness, toughness, heat resistance, corrosion resistance, oxidation resistance, etc. of the tungsten carbide itself, and the improved characteristics have functions of improving alloy characteristics or practical characteristics.
• a formulated carbon amount was adjusted by addition of C or W, so that the alloy became medium carbon alloy (center of a range of a sound phase which does not precipitate free carbon or Co 3 W 3 C, Ni 2 W 4 C) after sintering. Then, these powders were filled in a mold, and green compacts having a size of 5.5 x 9.5 x 29 mm were produced with a pressure of 196 MPa, placed on a sheet comprising alumina and carbon fiber and heated by inserting into a vacuum atmosphere furnace.
• the atmosphere was made vacuum of about 20 Pa, and thereafter, heating was carried out in the atmosphere shown in Table 4, and sintering was carried out at 1400°C for 1.0 hour to obtain hard alloys of Present products 1 to 14 and Comparative products 1 to 14.
• Present product and Comparative product with the same number were so formulated that the components of the hard alloy and grain size of WC are substantially the same.
• the resulting hard alloy sample piece was subjected to wet polishing processing with a 230 mesh diamond whetstone to produce a sample with a size of 4.0 x 8.0 x 25.0 mm, and transverse-rupture strength (hereinafter abbreviated to as "TRS") was measured by the JIS method. Also, one surface of the same sample was subjected to lap processing with a diamond past having an average particle size of 0.3 ⁇ m, hardness and fracture toughness value K1C (IM method) were measured under a load of 196N using a Vickers indenter.
• TRS transverse-rupture strength

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• 2003
  • 2003-10-23 EP EP03024424A patent/EP1420076A1/de not_active Withdrawn
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