Hard alloy and W-based composite carbide powder used as starting material

Abstract

There is disclosed a hard alloy which 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, VB or VIB of the Periodic Table, and the reminder being hexagonal tungsten carbide and inevitable impurities,

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] 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.

[0003] 2. Prior Art

[0004] A hard alloy produced by mixing, in addition to WC and Co, other powder of carbides such as TiC, TaC, VC, Cr3C2, 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. With regard to the other carbides to be added, for example, 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 Cr3C2 is/are added to a drill to which hardness and strength are required as a grain growth inhibitor of WC, and Cr3C2 and/or Mo2C is/are added to wear resistant parts in which corrosion becomes a problem.

[0005] However, when one of the alloy characteristics is improved by adding another carbides, there is a problem of antinomy wherein the other alloy characteristics is lowered. For example, when TiC, TaC, ZrC or VC is added, strength or toughness is markedly lowered even when an amount thereof to be added is a little. Also, Cr3C2 improves corrosion resistance or oxidation resistance of a binder phase, but WC causes alkali corrosion or preferential oxidation, so that its effect cannot sufficiently be revealed.

[0006] As a measure of the above problems, it has been proposed powder (for example, Japanese Provisional Patent Publication No. Hei. 7-54001, Japanese PCT Provisional Patent Publication No. 2000-512688, Japanese Provisional Patent Publications No. Hei. 10-212165 and No. Hei. 11-236221) for manufacture of a hard alloy to which other carbides are contained in WC powder, or a hard alloy (for example, Japanese Provisional Patent Publications No. Hei. 10-298698, Hei. 11-6025, 2001-81526 and Hei. 10-45414) to which other metals such as Cr, Mn, Re, etc. have been added. The former is intended to prevent from lowering in strength, toughness, etc., while maintaining added effects of the other carbides by dispersing the fine other carbides uniformly, and the latter is intended to strengthen a binder phase by alloying other metals.

[0007] Among the prior art references which relate to powder for producing a hard alloy containing other carbides, in 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 μm or lower is subjected to reduction treatment and carbonization treatment both at 700 to 1200° C. In Japanese PCT Provisional Patent Publication No. 2000-512688, there are disclosed 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.). In Japanese Provisional Patent Publication No. 10-212165, there are disclosed 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.

[0008] In complex carbide powders comprising tungsten carbide and transition metal, transition metal carbide, iron-group metal and the like described in these references, 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. Thus, there is a problem that an antinomy problem possessed by the hard alloy cannot be solved.

[0009] Also, in Japanese Provisional Patent Publication No. Hei. 11-236221, there is disclosed a complex carbonitride material comprising high melting point metals represented by the formula: (M1m, M2n)(CxNy) wherein M1 and M2 are each metal element having a high melting point different from each other among Nb, Mo, Ta and W, m+n=1, 0.0<m<1, x+y≈1, x≦0.99 and y≧0.01, particularly to (W, Mo) (CN). 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. However, when 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.

[0010] Among the prior art references relating to hard alloys to which other metal(s) is/are added, in Japanese Provisional Patent Publication No. Hei. 10-298698, there is disclosed a hard alloy comprising 3 to 25% by weight of Co and Ni, 0.1 to 3% by weight of chromium carbide based on the amount of Co and Ni, and the reminder being tungsten carbide and inevitable impurities, and in Japanese Provisional Patent Publication No. 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.

[0011] In these chromium-containing hard alloys disclosed in both of the publications, 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.

[0012] Also, in Japanese Provisional Patent Publication No. 2001-81526, there is disclosed 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. In Japanese Provisional Patent Publication No. Hei. 10-45414, there is disclosed 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.

[0013] 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.

[0014] 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.

SUMMARY OF THE INVENTION

[0015] 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.

[0016] That is, 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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] 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. More specifically, there may be mentioned (W,Ti)C, (W,Zr)C, (W,V)C, (W,Ta)C, (W,Cr)C, (W,Mo)C, (W,Re)C, (W,Ti,Mo)C, (W,Zr,Cr)C, (W,V,Cr)C, (W,Nb,Mn)C and (W,Ta,Re)C, which are a complex carbide having the same hexagonal structure as that of WC. 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.

[0018] Here, the specific element(s) dissolved in WC crystal has slightly different characteristics to be provided to the hard alloy depending on the kind thereof. For example, 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, and Mo, Mn and Re improve hardness, toughness, heat resistance, etc.

[0019] In the hard alloy of the present invention, it is preferred that 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. Also, it is preferred that 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. Moreover, it is preferred that 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.

[0020] 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, Co—Re 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.

[0021] 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. Here, the hard alloy of the present invention may contain Cr7C3, Mo2C, 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.

[0022] For preparing the hard alloy of the present invention, it is necessary to use powder in which the specific element(s) has/have previously been dissolved in the WC crystal as a starting material. That is, 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.

[0023] 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. Here, when the complex carbide of the present invention is represented by the chemical formula, it is a material of (W1−x, Mx)Cy 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. Provided that M represents at least one of the specific elements.

[0024] 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 W2C, Cr3C2, Mo2C 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.

[0025] Here, 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 (W0.6Ti0.4)C0.8, (W0.06Zr0.95) C0.75, (W0.45V0.55) C0.9, (W0.65Ta0.35) C0.9, (W0.5Ti0.5) (C0.9N0.1)0.95, (W0.5Ti0.3Ta0.2)C0.9, 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. However, if 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. Also, W2C 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, W2C is rather preferably contained in an amount of up to 5% by volume.

[0026] In the W-based composite carbide powder of the present invention, it is preferred that 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.

[0027] 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. On the other hand, the W-based composite carbide powder can be obtained, for example, by heating a mixed powder of WC and TiH2, a mixed powder of W, TiN and carbon, a mixed powder of WO3, TiO2 and carbon and the like in a non-oxidative atmosphere or a combined atmosphere of reducing and carburizing atmospheres at high temperatures. Also, when it is produced by the following method and conditions, powder with a much amount of dissolution as well as a uniform dissolution degree and uniform grain size distribution can be produced. That is, 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 μm or less to heat treatment at 1500 to 2000° C. or so in an inert gas atmosphere or under vacuum. When 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. Also, when Cr or Mn which has a higher vapor pressure is used as the specific element(s), it is necessary to carry out the procedure at a low temperature treatment in which an inert gas is introduced and dissipation thereof shall be prevented.

[0028] In the hard alloy of the present invention, 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.

EXAMPLE 1

[0029] By using each powder of commercially available W having an average particle size of 0.5 μm, carbon black (hereinafter referred to as “C”) having an average particle size of 0.02 μm, TiO2, ZrO2, HfO2, V2O5, Nb2O5, Ta2O5, Cr2O3, MoO3 and MnO2 each having an average particle size of 0.05 to 0.2 μm, metal Re having an average particle size of 1.0 μm, and WC (hereinafter referred to as “WC/F”) having an average particle size of 0.5 μm, TiC having an average particle size of 1.2 μm, Mo having an average particle size of 1.1 μm, WC (hereinafter referred to as “WC/C”) having an average particle size of 3.5 μm, each powder was weighed with a formulation shown in Table 1, placed in a pot made of stainless steel with an acetone solvent and balls made of a hard alloy, mixed and pulverized for 24 hours and then dried to obtain respective mixed powders. Then, these mixed powders were each filled in a carbon crusible, and heated after inserting into a vacuum furnace. Heating was carried out under about 20 Pa vacuum until 1200° C., and heating thereafter was carried out under atmosphere and a temperature shown in Table 1 maintaining for 1.0 hour to obtain products of the present invention (present products): PA to PR and Comparative product: complex carbide powders of CA to CH. Provided that Comparative product: CH is not subjected to mixing and heat treatments.

TABLE 1
			Heated	Results of
Sample	Composition	Heated	temperature	X-ray
No.	(% by weight)	atmosphere	(° C.)	diffractmetry
Present
products
PA	93.6W—6.2C—0.2TiO2	Vacuum	1800	WC + W2C
		about 10 Pa
PB	93.0W—6.3C—0.7TiO2	Vacuum	1800	WC
		about 10 Pa
PC	91.3W—6.7C—2.0TiO2	Vacuum	1900	WC + (W, Ti)
		about 10 Pa		C + W2C
PD	88.7W—7.3C—4.0TiO2	Vacuum	2000	WC + (W, Ti)
		about 10 Pa		C + W2C
PE	92.7W—6.3C—1.0ZrO2	Vacuum	1900	WC + W2C
		about 10 Pa
PF	92.8W—6.2C—1.0HfO2	Vacuum	2000	WC + W2C
		about 10 Pa
PG	92.5W—6.5C—1.0V2O5	Vacuum	1800	WC
		about 10 Pa
PH	92.6W—6.4C—1.0Nb2O5	Vacuum	1900	WC + W2C
		about 10 Pa
PI	92.7W—6.3C—1.0Ta2O5	Vacuum	1900	WC + W2C
		about 10 Pa
PJ	89.0W—7.0C—	Vacuum	2000	WC + (W, Ta,
	2.0Ta2O5—2.0TiO2	about 10 Pa		Ti) C + W2C
PK	91.4W—6.6C—2.0Cr2O3	0.1 MPa Ar	1800	WC + W2C
PL	92.6W—6.4C—1.0Cr2O3	0.1 MPa Ar	1850	WC
PM	90.9W—6.6C—	0.1 MPa Ar	1900	WC +
	2.0Cr2O3—0.5Ta2O5			(W, Cr)2C
PN	88.9W—7.1C—4.0MoO3	Vacuum	1800	WC + W2C
		about 10 Pa
PO	92.0W—6.5C—1.5MnO2	10 kPa Ar	1500	WC +
				(W, Mn)2C
PP	91.8W—6.6C—	10 kPa Ar	1550	WC
	1.0MnO2—0.5Ta2O5
PQ	92.8W—6.2C—1.0Re	Vacuum	1800	WC
		about 10 Pa
PR	91.1W—6.3C—2.0Re—	0.1 MPa Ar	1800	WC
	0.6Cr2O3
Comparative
products
CA	93.8W—6.2C	Vacuum	1700	WC
		about 10 Pa
CB	100.0WC/F	Vacuum	1600	WC + W2C
		about 10 Pa
CC	93.7W—6.2C—0.1TiO2	Vacuum	1750	WC
		about 10 Pa
CD	99.8WC/F—0.2TiC	Vacuum	1800	WC + (W, Ti)
		about 10 Pa		C + W2C
CE	81.2W—8.8C—	Vacuum	1900	(W, Ti) C +
	10.0TiO2	about 10 Pa		WC + W2C
CF	88.0W—7.0C—5.0Cr2O3	0.1 MPa Ar	1800	WC +
				(W, Cr)2C
CG	89.0W—6.0C—5.0Mo	Vacuum	1800	WC + W2C
		about 10 Pa
CH	100.0WC/C	—	—	WC

[0030] Complex carbide powders of the thus obtained Present products PA to PR and Comparative products CA to CH were crushed and pulverized, and passed through a sieve of 100 mesh to prepare sample powders for evaluation. With regard to these samples, X-ray diffraction analysis (tube: Cu, tube voltage; 50 kV, tube current; 250 mA) was carried out 10 and components in the powder were identified. The results are also shown in Table 1.

[0031] Next, to the respective sample powders was added 30% by weight of cupper powder (commercially available electrolytic copper powder: 2.5 μm) and the mixture was mixed by using a mortar, and after molding by a mold with a pressure of 2 ton/cm2, these samples were heated and sintered under vacuum at 1150° C. for 20 minutes to obtain sample alloys for analyses. Then, these sample alloys were polished by diamond whetstone and subjected to lap processing with a diamond paste having an average particle size of 1 μm, and then, applied to observation and analyses by an electric field radiation type scanning electron microscope.

[0032] First, presence and distribution of WC and particles other than WC (W2C, cubic crystal compound, etc.) were confirmed by compositional image contrast and element mapping. With regard to WC and cubic crystal compound, compositional analyses were carried out by focusing electronic beam to the center potion of a particle having a relatively large size. Also, a content (% by volume) of the respective particles constituting the respective sample powders was obtained by photographs and an image treatment device. These results are shown in Table 2. Moreover, average particle sizes of WC, W2C and cubic crystal compounds were obtained. The results are shown in Table 3.

	TABLE 2
	Amount of	Composition of powder
	dissolved	(% by volume)
Sample	element in WC			Cubic crystal
No.	(% by weight)	WC	W2C	compound
Present
products
PA	0.12Ti	99.0	1.0	O
PB	0.42Ti	100.0	0	0
PC	0.82Ti	93.2	2.6	4.2(W0.6Ti0.4)C
PD	0.87Ti	80.3	3.4	16.3(W0.6Ti0.4)C
PE	0.73Zr	98.4	1.6	0
PF	0.85Hf	97.1	2.9	0
PG	0.57V	100.0	0	0
PH	0.70Nb	98.0	2.0	0
PI	0.82Ta	99.0	1.0	0
PJ	0.80Ta + 0.54Ti	86.8	3.2	10.0(W0.6Ta0.2Ti0.2)C
PK	1.37Cr	97.6	2.4	0
PL	0.60Cr	100.0	0	0
PM	1.00Cr + 0.42Ta	99.0	1.0	0
PN	2.73Mo	96.0	4.0	0
PO	0.87Mn	98.7	1.3	0
PP	0.62Mn + 0.37Ta	100.0	0	0
PQ	1.00Re	100.0	0	0
PR	1.75Re + 0.35Cr	100.0	0	0
Comparative
products
CA	0	100.0	0	0
CB	0	97.9	2.1	0
CC	0.06Ti	100.0	0	0
CD	0.08Ti	98.7	0.4	0.9(W0.6Ti0.4)C
CE	0.85Ti	39.9	10.4	49.7(W0.6Ti0.4)C
CF	3.22Cr	92.6	7.4	0
CG	5.00Mo	90.9	9.1	0
CR	0	100.0	0	0

[0033]

	TABLE 3
	Average particle size
	(μm)
			Cubic	Lattice constants
Sample			system	(nm)
No.	WC	W2C	compound	a axis	c axis
Present
products
PA	3.1	0.8	—	0.2913	0.2845
PB	2.5	0.6	—	0.2911	0.2844
PC	2.7	0.9	0.9	0.2917	0.2851
PD	3.6	1.3	2.4	0.2915	0.2850
PE	3.0	0.8	—	0.2914	0.2849
PF	7.3	2.0	—	0.2913	0.2846
PG	1.2	0.5	—	0.2911	0.2841
PH	1.8	0.7	—	0.2912	0.2847
PI	2.7	0.8	—	0.2916	0.2850
PJ	3.5	1.1	2.2	0.2919	0.2852
PK	3.1	2.2	—	0.2911	0.2847
PL	2.0	—	—	0.2914	0.2847
PM	2.4	1.5	—	0.2912	0.2844
PN	2.4	2.9	—	0.2915	0.2849
PO	2.5	1.8	—	0.2911	0.2850
PP	2.4	—	—	0.2919	0.2841
PQ	3.4	—	—	0.2914	0.2852
PR	1.7	—	—	0.2919	0.2847
Comparative
products
CA	3.1	0.8	—	0.2905	0.2837
CB	1.3	0.9	—	0.2907	0.2835
CC	2.9	0.8	—	0.2909	0.2841
CD	3.2	1.7	1.4	0.2908	0.2839
CE	2.8	0.8	1.8	0.2917	0.2852
CF	2.2	2.4	—	0.2902	0.2831
CG	3.2	1.4	—	0.2909	0.2855
CH	3.5	1.1	—	0.2906	0.2837

[0034] Next, an interplanar spacing and a lattice spacing were calculated from the position of a peak of WC (2θ=30 to 120°) which was measured by the above-mentioned X-ray diffraction conditions, and lattice constants were obtained with respect to each of a axis and c axis by an extrapolation method. The results are also shown in Table 3.

EXAMPLE 2

[0035] By using complex carbide powders PA, PB, PE, PG, PH, PI, PJ, PK, PL, PM, PO, PP, PQ and PR as well as CA, CB, CD and CH obtained in Example 1, respective powders of W, C and metal Re used in Example 1, and commercially available Co having an average particle size of 1.0 μm, Ni with 1.2 μm, Fe with 1.0 μm, metal Mn with 3.5 μm, and TiC, ZrC, VC, NbC, TaC and Cr3C2 each having 1.0 to 1.5 μm, these powders were weighed with a composition shown in Table 4, inserted in a pot made of stainless with an acetone solvent and balls made of hard alloy and pulverized and crushed for 48 hours, and then, dried to obtain respective mixed powders. Here, 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 Co3W3C, Ni2W4C) after sintering. Then, these powders were filled in a mold, and green compacts having a size of 5.5×9.5×29 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. Up to 1200° C., 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. Incidentally, 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.

TABLE 4
	Composition	Sintering
Sample No.	(% by weight)	atmosphere
Present	1	93.0PA—7.0Co	Vacuum about 10 Pa
Products	2	93.0PB—7.0Co	Vacuum about 10 Pa
	3	92.92E—0.1C—7.0Co	Vacuum about 10 Pa
	4	93.0PG—7.0Co	Vacuum about 10 Pa
	5	92.9PH—0.1C—7.0Co	Vacuum about 10 Pa
	6	93.0PI—7.0Co	Vacuum about 10 Pa
	7	92.8PJ—0.2C—7.0Co	Vacuum about 10 Pa
	8	92.5PK—0.5Cr3C2—7.0Co	1 kPa Ar
	9	92.0PL—8.0Co	1 kPa Ar
	10	91.9PM—0.1C—8.0Co	1 kPa Ar
	11	90.0PO—2.0W—8.0Ni	10 kPa Ar
	12	89.0PP—3.0W—8.0Ni	10 kPa Ar
	13	92.0PQ—8.0Co	Vacuum about 10 Pa
	14	91.8PR—0.2C—8.0Ee	1 kPa Ar
Comparative	1	93.0CD—7.0Co	Vacuum about 10 Pa
products	2	62.5CA—30.0CB—0.5TiC—7.0Co	Vacuum about 10 Pa
	3	92.2CA—0.8ZrC—7.0Co	Vacuum about 10 Pa
	4	92.2CB—0.1C—0.7VC—7.0Co	Vacuum about 10 Pa
	5	22.1CA—70.0CB—0.1C—0.8NbC—	Vacuum about 10 Pa
		7.0Co
	6	82.2CA—10.0CB—0.8TaC—7.0Co	Vacuum about 10 Pa
	7	90.0CH—1.GTaC—1.4TiC—7.0Co	Vacuum about 10 Pa
	8	91.0CA—2.0Cr3C2—7.0Co	1 kPa Ar
	9	31.3CA—60.0CB—0.7Cr3C2—8.0Co	1 kPa Ar
	10	47.9CA—40.0CB—2.2W—0.4TaC—	1 kPa Ar
		1.5Cr3C2—8.0Co
	11	58.1CA—30.0CB—3.0W—0.9Mn—	10 kPa Ar
		8.0Ni
	12	48.0CA—40.0CB—CB—3.0W—0.4TaC—	10 kPa Ar
		0.6Mn—8.0Ni
	13	91.1CH—0.9Re—8.0Co	Vacuum about 10 Pa
	14	19.44CA—60.0CB—0.3C—0.5Cr3C2—	1 kPa Ar
		1.8Re—8.0Fe

[0036] 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 4.0×8.0×25.0 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 μm, hardness and fracture toughness value K1C (IM method) were measured under a load of 196N using a Vickers indenter. Moreover, micro-structural photograph was taken by an electron microscope with regard to the lap surface of the respective samples, an average particle size of WC and contents of the binder phase and the cubic crystal compound were obtained by using an image treatment device. These results are shown in Table 5.

TABLE 5
					Amount
					of
			Fracture	Particle	binder	Amount of
			toughness	size	phase	cubic crystal
Sample	TRS	Hardness	value	of WC	(% by	compound
No.	(MPa)	(HV)	(MPa · m½)	(μm)	volume)	(% by volume)
Present
products
1	3160	1640	11.6	3.1	11.8	0
2	3050	1670	10.8	2.5	11.5	0.6(W,Ti)C
3	2850	1660	11.3	3.0	11.6	0.2(Zr,W)C
4	2770	1790	8.9	1.2	11.6	0.3VC
5	3210	1710	10.7	1.8	11.6	0.2NbC
6	3140	1650	11.1	2.7	11.7	0.1TaC
7	2540	1680	10.0	3.4	11.1	4.7(W,Ti,Ta)C
8	2910	1630	11.2	3.0	12.6	0
9	2790	1650	10.5	1.9	13.6	0
10	2780	1570	11.2	2.2	14.7	0
11	2840	1610	10.9	2.3	13.7	0
12	2920	1620	10.5	2.1	13.6	0
13	2750	1620	10.6	3.2	13.5	0
14	2790	1630	12.5	2.4	13.7	0
Comparative
products
1	2530	1620	11.3	3.2	11.7	0.8(W,Ti)C
2	2310	1640	10.5	2.5	11.5	2.9(W,Ti)C
3	2420	1610	11.1	3.1	11.7	1.7(Zr,W)C
4	2490	1770	8.8	1.2	11.6	1.9VC
5	2170	1690	10.2	1.7	11.7	1.5NbC
6	1980	1630	10.8	2.8	11.8	0.8TaC
7	2410	1630	9.8	3.3	11.0	9.4(W,Ti,Ta)C
8	2760	1590	10.9	3.0	15.1	0
9	2650	1620	10.2	2.0	14.5	0
10	2610	1530	10.7	2.5	15.8	0.5TaC
11	2730	1590	10.5	2.3	15.0	0
12	2840	1610	10.1	2.1	13.8	0.4TaC
13	2750	1610	10.2	3.1	13.9	0
14	2380	1600	12.0	2.3	14.7	0

[0037] The hard alloys produced by the W-based composite carbide powder of the present invention are improved in all of hardness, strength, toughness, etc., as compared with the hard alloy using the conventional high purity WC, when the composition and the WC grain size are made almost the same, and for example, in the hard alloy to which a small amount of TiC or TaC is added, there is a remarkable effect that strength is highly improved.

Claims

1. A hard alloy which 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, VB or VIB 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.

2. The hard alloy according to claim 1, wherein the specific element(s) is at least one selected from the group consisting of titanium, zirconium, hafnium and vanadium.

3. The hard alloy according to claim 1, wherein the specific element(s) is at least one selected from the group consisting of niobium and tantalum.

4. The hard alloy according to claim 1, wherein the specific element(s) is chromium.

5. The hard alloy according to claim 1, wherein the specific element(s) is at least one selected from the group consisting of molybdenum, manganese and rhenium.

6. The hard alloy according to claim 1, wherein the specific element(s) is at least one selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium and tantalum, and the cubic crystal compound is contained in an amount of 1% by volume or less.

7. The hard alloy according to claim 1, wherein the specific element(s) is chromium, and chromium is contained in an amount of 0.1 to 10% by weight based on the total amount of the hard alloy.

8. The hard alloy according to claim 1, wherein the specific element(s) is at least one of manganese and rhenium, and the at least one of manganese and rhenium is contained in an amount of 0.1 to 10% by weight based on the total amount of the hard alloy.

9. A tungsten-based complex carbide powder which comprises a complex carbide powder containing 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 the complex carbide powder contains 80% by volume or more of hexagonal tungsten carbide, and the specific element(s) is dissolved in the crystal of the hexagonal tungsten carbide in an amount of 0.1 to 3.0% by weight.

10. The tungsten-based complex carbide powder according to claim 9, wherein the powder contains particles of a cubic crystal compound comprising tungsten, at least one of carbon and nitrogen, and at least one selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium and tantalum in an amount of less than 20% by volume.

11. The tungsten-based complex carbide powder according to claim 9, wherein the crystal of the hexagonal tungsten carbide has at least one of a lattice constant of a axis of 0.2910 nm or longer and a lattice constant of c axis of 0.2840 nm or longer.