Abstract:
This invention is related to a powder of a transition metal dissolved tungsten alloy carbide which comprises a transition metal element forcibly dissolved as a solid solution which represented by Formula [1] of M-W—C wherein M is one or more of Co, Fe, Ni and Mn and its tungsten alloy carbide diffused cemented carbide. The diffused cemented carbide is compatible with the conventional tungsten carbide diffused cemented carbide and comprises a binder metal and a tungsten alloy carbide which is provided with a solid solution phase of at least one transition metal element selected from the group consisting of cobalt, iron, nickel and manganese, included in a tungsten carbide skeleton, which exhibits a peak derived from a bcc tungsten phase in an X-ray diffraction diagram.

Description:
TECHNICAL FIELD  
       [0001]    The present invention relates to a transition metal included tungsten carbide, tungsten carbide diffused cemented carbide and a process for producing the same. 
       BACKGROUND ART  
       [0002]    Tungsten has a high melting point and modulus of elasticity and is useful as a filament material or a raw material for tungsten carbide (WC). However, the price of tungsten is showing a tendency to increase sharply in accordance with a rapid increase in the domestic demand of China, since the raw material thereof is present only in China. In order to develop materials capable of conserving tungsten resources, there is a need to replace a portion of tungsten with a transition metal element. 
         [0003]    However, it is difficult to prepare tungsten parts by melt-casting due to the high melting point thereof. Further, in spite of using powder metallurgy for imparting a form to the powder material, there is a problem in that alloying effect is not performed in a blended elemental method of a tungsten powder and a transition metal element. In addition, an atomization method is difficult to be applied to the tungsten for preparing an alloy powder. 
         [0004]    Meanwhile, it has been known a conventional method for preparing a tungsten alloy powder by co-precipitating a metal salt or metal hydroxide (Japanese Patent Publication 1 and 2). 
         [0005]    [Japanese Patent Publication 1] PCT International Patent Publication No. 2002-527626 
         [0006]    [Patent Publication 2]: U.S. Pat. No. 4,913,731 
       SUMMARY OF INVENTION  
     Technical Problem to be Solved 
       [0007]    However, in the preparation methods disclosed in Patent Publication 1 and 2, due to the operation of “co-precipitation”, a resulting alloy powder comes to contain a phase of a transition metal element, in addition to a tungsten phase and a tungsten phase alloyed with a transition metal element, it shows that alloying is not sufficiently performed. 
         [0008]    On the other hand, a cemented carbide made of tungsten carbide (WC) having a quite high toughness and alloying with cobalt (Co) is useful for cutting tools and molds, so a lot of cemented carbide is necessary to automobile and electric industries. However, due to mal-distribution of tungsten in China and rapid increasing domestic demand in China, tungsten material cost is escalating. Therefore, we should cut down the used amount of tungsten and cemented carbide demand necessary for the industries should be self-contained in order to sustain industry activity in Japan. 
         [0009]    To solve the problem, an object of the present invention is to provide a novel tungsten carbide necessary for a cemented carbide material by using a tungsten alloy powder and also to provide a cemented carbide. 
       Solution to Problem 
       [0010]    As a result of a variety of extensive and intensive studies to accomplish the object, the present inventors discovered that when tungsten ions and ions of transition metal are homogenized at an ionic level in an aqueous solution, subjected to drying by distillation or spray-drying, thermal decomposition and then hydrogen thermal reduction to obtain a tungsten powder. The tungsten alloy powder in which a transition metal element is thoroughly compulsorily dissolved as a solid solution can be prepared, and it has been found that the tungsten alloy powder can be used for an altemate new tungsten carbide and an alternate new cemented carbide, thus accomplished the present invention. 
         [0011]    That is, the present invention provides a tungsten alloy carbide powder represented by Formula [1] which is carbonized from a tungsten alloy powder with a transition metal dissolved therein as a solid solution represented by Formula [2] in which at least one transition metal element selected from the group consisting of cobalt, iron, manganese and nickel is dissolved in a tungsten grating and a peak derived from a bcc tungsten phase appears in an X-ray diffraction diagram. 
         [0000]      M-W—C   Formula [1]:
 
         [0012]    wherein M represents one or more selected from Co, Fe, Mn and Ni. 
         [0000]      M-W   Formula [2]:
 
         [0013]    wherein M represents one or more selected from Co, Fe, Mn and Ni. 
         [0014]    The tungsten alloy powder represented by Formula [2] comprises: a transition metal selected from the group consisting of cobalt, iron, nickel and manganese is dissolved in tungsten grating and a peak derived from a bcc tungsten phase appears in an X-ray diffraction diagram which means that any transition metal and any its metal compounds do not exist in the grain boundary of tungsten. Therefore, the inventive tungsten alloy powder can be used as an alternative of the ordinary tungsten. Herein, when the amount of transition metal is less than 0.3% of tungsten alloy powder, we have not any advantage of natural resource saving. On the other hand, when the amount of transition metal is more than 20.8 wt % of tungsten alloy powder, we have precipitation phenomenon of the second phase in the grain boundary of tungsten and the transition metal is not dissolved as a solid solution in the tungsten grating. In the tungsten alloy powder, cobalt can be located in a position of tungsten grating and acts as a substitute of tungsten Nickel is cheaper than Cobalt and acts in a same manner of cobalt. Iron and Manganese are cheaper elements and improve the strength of tungsten alloy powder in a same manner. 
         [0015]    The transition metal can be dissolved in the tungsten up to the same mole of tungsten. Among them, cobalt and iron are more preferable. In case of cobalt, it is preferable that cobalt of 40 to 10 mole % can be dissolved in 60 to 90 mole % of tungsten. In case of the other transition metals, the same ratio can be applicable. 
         [0016]    A part of cobalt can be substituted by one or more elements selected from the group consisting of iron, nickel and manganese, to obtain a complex transition metal dissolved tungsten alloy powder. 
         [0017]    The present invention transition metal included tungsten carbide represented by the Formula [1] can be exemplified by Co—W—C/WC. In this case, a preferred composition is Co: 0.3-19.7 wt %, W: 75.3-93.6 wt %, C:4.9-6.2 wt % and a solid solution phase of Co—W—C is included therein, in which all or a part of cobalt can be substituted by one or more selected from the group consisting of iron, manganese and nickel. In case of Co substituted by Fe, it is exemplified by Fe—W—C/WC. In this case, a preferred composition is Fe: 0.3-19.7 wt %, W: 75.3-93.6 wt %, C: 4.9-6.2 wt % and a solid solution phase of Fe—W—C is included therein, in which all or a part of iron can be substituted by one or more selected from the group consisting of cobalt, manganese and nickel. Among them, Fe—Mn—W—C (Fe partially substituted by manganese) is preferable. In case of Co substituted by Ni, it is exemplified by Ni—W—C/WC. In this case, a preferred composition is Ni: 0.3-19.7 wt %, W: 75.3-93.6 wt %, C: 4.9-6.2 wt % and a solid solution phase of Ni—W—C is included therein, in which a part of nickel can be substituted by one or more selected from the group consisting of iron, cobalt, and manganese. In case of Co substituted by Mn, it is exemplified by Mn—W—C/WC. In this case, a preferred composition is Mn: 0.3-19.7 wt %, W: 75.3-93.6 wt %, C: 4.9-6.2 wt % and a solid solution phase of Mn—W—C is included therein, in which a part of manganese can be substituted by one or more selected from the group consisting of cobalt, iron and nickel. 
         [0018]    An another object of the invention is provided a tungsten carbide diffused cemented carbide by a process of sintering the above transition metal included tungsten carbide with the transition metal. That is, it is to provide a tungsten carbide diffused cemented carbide by sinter a tungsten alloy carbide powder represented by Formula [1] which is carbonized from a tungsten alloy powder with a transition metal dissolved therein as a solid solution represented by Formula [2] in which at least one transition metal element selected from the group consisting of cobalt, iron, manganese and nickel is dissolved in a tungsten grating and a peak derived from a bcc tungsten phase appears in an X-ray diffraction diagram. 
         [0000]      M-W—C   Formula [1]:
 
         [0019]    wherein M represents one or more selected from Co, Fe, Mn and Ni. 
         [0000]      M-W   Formula [2]:
 
         [0020]    wherein M represents one or more selected from Co, Fe, Mn and Ni. 
         [0021]    Among them, a tungsten carbide diffused cemented carbide can be exemplified by combination of: Co—W—C as transition metal included tungsten carbide and Co as a combined transition metal; Fe—W—C as transition metal included tungsten carbide and Co as a combined transition metal; Ni—W—C as transition metal included tungsten carbide and Co as a combined transition metal; Mn—W—C as transition metal included tungsten carbide and Co as a combined transition metal. In the above cases, cobalt used in the transition metal included tungsten carbide and the combined transition metal can be totally or partially substituted by one or more elements selected from the group consisting of nickel, iron and manganese. 
       Advantageous Effects 
       [0022]    The tungsten alloy carbide obtained by the present invention maintains a WC-structure (skeleton) and contains a transition metal element dissolved as a solid solution in a tungsten grating, so that the tungsten alloy carbide can provide a novel tungsten carbide diffused cemented carbide having substantially the same properties as those made of the conventional tungsten carbide. 
         [0023]    According to the present invention, there can be provided a tungsten carbide diffused cemented carbide made of Co—W—C as a transition metal included tungsten carbide and Co as a transition metal powder, a preferred composition of which is Co: 1.2-31.7 wt %, W: 64.0-92.7 t %, C: 4.2-6.1 wt %. In this case, cobalt of Co—W—C can be partially substituted by one or more elements selected from the group consisting of iron, nickel and manganese, by which there is provided the other preferred composition of Co: 0.2-12.0 wt %, Fe: 0.3-19.7 wt %, W: 64.0-92.7 wt %, C: 4.2-6.1 wt % in case of Fe—W—C as a transition metal included tungsten carbide and Co as a transition metal powder; Co: 0.9-12.0 wt %, Ni: 0.3-19.7 wt %, W: 64.0-92.7 wt %, C: 4.2-6.1 wt % in case of Ni—W—C as a transition metal included tungsten carbide and Co as a transition metal powder; Co: 0.9-12.0 wt %, Mn: 0.3-19.7 wt %, W: 64.0-92.7 wt %, C: 4.2-6.1 wt % in case of Mn—W—C as a transition metal included tungsten carbide and Co as a transition metal powder. The transition metal Co powder can be totally or partially substituted by one or more selected from the group consisting of Ni, Fe and Mn, each of the substituted compositions resulting in the same effect in case of Co. 
         [0024]    The transition metal included tungsten carbide represented by Formula [1] can be produced by 1) mixing an aqueous solution containing tungsten ions with an aqueous solution containing at least ions of one transition metal selected from the group consisting of cobalt, iron, manganese and nickel, wherein the mixing is performed such that the tungsten ions are 60 mol % or more and the transition metal ions are 40 mol % or less, drying the mixed aqueous solution by distillation or spraying, thermally decomposing the resulting solid, followed by hydrogen thermal reduction, to prepare a transition metal-dissolved tungsten alloy powder represented by Formula [2], 2) carbonizing the resulting oxide powder or transition metal-dissolved tungsten alloy powder by heating with graphite to be mixed or gas-carburizing. 
         [0025]    In the present invention, preferably, the aqueous solution containing tungsten ions is an ammonium paratungstate aqueous solution (5(NH 4 ) 2 O.12WO 3 .5H 2 O). The aqueous solution containing ions at least one transition metal selected from the group consisting of cobalt, iron, manganese and nickel is a transition metal complex salt aqueous solution. Examples of useful transition metal complex salts include acetates (Fe(OH)(C 2 H 3 OO) 2 , Co(C 2 H 3 O 3 ) 2 .4H 2 O, Mn(CH 3 COO) 2 .4H 2 O, and Ni(C 2 H 3 O 3 ) 2 . xH 2 O), which are soluble in water, do not produceharmful materials and low in environmental load. In addition, use of transition metal sulfates of iron, nickel and cobalt can be exemplified by such as CoSO 4 .7H 2 O, FeSO 4 .7H 2 O, and NiSO 4 .6H 2 O which are effective in realizing circulation society. 
         [0026]    Generally, in an electrolytic refining process of copper, the transition metals of iron, nickel and cobalt are concentrated in sulfate in an electrolyte. Accordingly, waste liquid produced during the electrolytic refining of copper may be used as a raw material of the tungsten alloy powder of the present invention and the sulfate produced during drying by distillation or spray-drying may be efficiently used as a by-product. 
         [0027]    The tungsten alloy carbon diffused cemented carbide obtained from the present invention can be produced from the present invention tungsten alloy carbide by 1) mixing an aqueous solution containing tungsten ions with an aqueous solution containing at least ions of one transition metal selected from the group consisting of cobalt, iron, manganese and nickel, wherein the mixing is performed such that the tungsten ions are 60 mol % or more and the transition metal ions are 40 mol % or less, drying the mixed aqueous solution by distillation or spraying, thermally decomposing the resulting solid, followed by hydrogen thermal reduction, to prepare a transition metal-dissolved tungsten alloy powder represented by Formula [2], 2) carbonizing the resulting oxide powder or transition metal-dissolved tungsten alloy powder by heating it with graphite to be mixed or gas-carburizing, to obtain a transition metal dissolved tungsten carbide and 3) sintering the resulting tungsten carbide with a transition metal powder. 
       DESCRIPTION OF EMBODIMENTS  
       [0028]    Hereinafter, the present invention will be described with reference to representative examples. However, it will be apparent to those skilled in the art from Examples that the other tungsten carbide can be produced and the other tungsten carbide can be used with a transition metal powder to produce any other tungsten carbide diffused cemented carbide. 
       Preparation 1 
       [0029]    A conventional material (No.1), materials of the present invention (Nos. 2 to 8, Nos. 11 to 14) and Comparative materials (Nos. 9 and 10) were prepared to have the chemical components (mol %) shown in Table 1, and the possibility of a compulsive solid solution and the existence of precipitation of the second phase were confirmed by X-ray diffraction and EPMA. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Chemical component (mol %) and formation of compulsive solid solution 
               
             
          
           
               
                 No 
                 Fe 
                 Co 
                 Mn 
                 Ni 
                 W 
                 Note 
               
               
                   
               
             
          
           
               
                 1 
                 — 
                 20 
                 — 
                 — 
                 Bal 
                 Conventional 
                 Powder mixing 
                 Second phase (Co) 
               
               
                   
                   
                   
                   
                   
                   
                 material 
                   
                 precipitation 
               
               
                 2 
                 — 
                 10 
                 — 
                 — 
                 Bal 
                 Material of the 
                 Solution method 
                 Compulsive solid 
               
               
                   
                   
                   
                   
                   
                   
                 present invention 
                   
                 solution 
               
               
                 3 
                 — 
                 20 
                 — 
                 — 
                 Bal 
                 Material of the 
                 Solution method 
                 Compulsive solid 
               
               
                   
                   
                   
                   
                   
                   
                 present invention 
                   
                 solution 
               
               
                 4 
                 — 
                 30 
                 — 
                 — 
                 Bal 
                 Material of the 
                 Solution method 
                 Compulsive solid 
               
               
                   
                   
                   
                   
                   
                   
                 present invention 
                   
                 solution 
               
               
                 5 
                 — 
                 40 
                 — 
                 — 
                 Bal 
                 Material of the 
                 Solution method 
                 Compulsive solid 
               
               
                   
                   
                   
                   
                   
                   
                 present invention 
                   
                 solution 
               
               
                 6 
                 10 
                 10 
                 — 
                 — 
                 Bal 
                 Material of the 
                 Solution method 
                 Compulsive solid 
               
               
                   
                   
                   
                   
                   
                   
                 present invention 
                   
                 solution 
               
               
                 7 
                 — 
                 10 
                 — 
                 10 
                 Bal 
                 Material of the 
                 Solution method 
                 Compulsive solid 
               
               
                   
                   
                   
                   
                   
                   
                 present invention 
                   
                 solution 
               
               
                 8 
                 5 
                 10 
                 — 
                    1.85 
                 Bal 
                 Material of the 
                 Solution method 
                 Compulsive solid 
               
               
                   
                   
                   
                   
                   
                   
                 present invention 
                   
                 solution 
               
               
                 9 
                 — 
                 90 
                 — 
                 — 
                 Bal 
                 Comparative 
                 Solution method 
                 2(Co 3 W) phase 
               
               
                   
                   
                   
                   
                   
                   
                 material 
                   
                 precipitation 
               
               
                 10 
                 — 
                 50 
                 — 
                 — 
                 Bal 
                 Comparative 
                 Solution method 
                 2(Co 7 W 6 ) phase 
               
               
                   
                   
                   
                   
                   
                   
                 material 
                   
                 precipitation 
               
               
                 11 
                 0.1 
                 19.9 
                 — 
                 — 
                 Bal 
                 Material of the 
                 Solution method 
                 Compulsive solid 
               
               
                   
                   
                   
                   
                   
                   
                 present invention 
                   
                 solution 
               
               
                 12 
                 5.0 
                 15.0 
                 — 
                 — 
                 Bal 
                 Material of the 
                 Solution method 
                 Compulsive solid 
               
               
                   
                   
                   
                   
                   
                   
                 present invention 
                   
                 solution 
               
               
                 13 
                 20 
                 — 
                 — 
                 — 
                 Bal 
                 Material of the 
                 Solution method 
                 Compulsive solid 
               
               
                   
                   
                   
                   
                   
                   
                 present invention 
                   
                 solution 
               
               
                 14 
                 17.4 
                 — 
                 2.4 
                 — 
                 Bal 
                 Material of the 
                 Solution method 
                 Compulsive solid 
               
               
                   
                   
                   
                   
                   
                   
                 present invention 
                   
                 solution 
               
               
                   
               
             
          
         
       
     
         [0030]    In Table 1, the term “solution method” is a process of the present invention which includes mixing an aqueous solution of transition metal acetate (Co(C 2 H 3 O 3 ) 2 .4H 2 O, Fe(OH)(C 2 H 3 OO) 2 , Mn(CH 3 COO) 2 .4H 2 O and/or Ni(C 2 H 3 O 3 ) 2 . xH 2 O) with an aqueous solution of ammonium paratungstate (5(NH 4 ) 2 O.12WO 3 .5H 2 O), subjecting the mixture to drying by distillation (or spray drying), thermally decomposing the resulting solid into an oxide under an atmosphere at 823 K, and subjecting the resulting product to hydrogen thermal reduction under a hydrogen gas at 1073 K for 1 h to obtain a tungsten alloy powder. 
         [0031]    Sample No. 1 is a conventional material obtained using a blended elemental method, as a conventional powder metallurgy method, including weighing and mixing 7.42% by weight of a pure cobalt powder and the balance of a pure tungsten powder to make the chemical composition of Table 1, followed by compression molding at a pressure of 2 ton/cm 2 , and maintaining for 1 h under a hydrogen gas at 1073 K. A pure cobalt phase remained as the second phase and alloying with tungsten was not performed. 
         [0032]    Sample No. 2 is a material of the present invention obtained by a solution method. An aqueous solution of transition metal acetate (Co(C 2 H 3 O 3 ) 2 .4H 2 O) was mixed with ammonium paratungstate. In the X-ray diffraction diagram of the resulting alloy powder, only a peak derived from a bcc W phase appeared and a W alloy powder was obtained in which Co was homogenously compulsorily dissolved as a solid solution. 
         [0033]    Sample No. 3 is a material of the present invention obtained by a solution method. An aqueous solution of a transition metal acetate Co(C 2 H 3 O 3 ) 2 .4H 2 O was mixed with ammonium paratungstate to make the composition 80 mol % W-20 mol % Co. In the X-ray diffraction diagram of the resulting alloy powder, only a peak derived from a bcc W phase appeared and a W alloy powder was obtained in which Co was homogenously compulsorily dissolved as a solid solution. The equilibrium phases of this composition at a hydrogen thermal reduction temperature of 1073 K were a W phase and a Co 7 W 6  phase. First, it was confirmed that, when cobalt ions and tungsten ions in an aqueous solution were made homogeneous at an ion level by the solution method, cobalt was captured in a tungsten grating even after the hydrogen thermal reduction and equilibrium phase of Co 7 W 6  could not be formed. That is, it was discovered that, when a solution method is applied, an alloy powder compulsorily dissolved as a solid solution in a non-equilibrium state can be prepared. 
         [0034]    Samples No. 4 and No. 5 are materials of the present invention obtained by a solution method. It was confirmed that a W alloy powder in which Co was homogenously compulsorily dissolved in a non-equilibrium state to make a composition of 60 mol % W-40 mol % Co could be obtained. When the solution method was applied, compulsorily dissolved alloy powder as a solid solution in a non-equilibrium state could be prepared, without forming an equilibrium phase of Co 7 W 6  to make this composition. 
         [0035]    Sample No. 6 is a material of the present invention obtained by a solution method, in which a Co(C 2 H 3 O 3 ) 2 .4H 2 O aqueous solution is partially substituted by an Fe(OH)(C 2 H 3 OO) 2  aqueous solution. It was discovered that compulsorily dissolved alloy powder as a solid solution could be prepared, although Co was partially substituted by Fe. 
         [0036]    Sample No. 7 is a material of the present invention obtained by a solution method, in which a Co(C 2 H 3 O 3 ) 2 .4H 2 O aqueous solution is partially substituted by an aqueous solution of Ni(C 2 H 3 O 3 ) 2 .xH 2 O. A compulsorily dissolved alloy powder as a solid solution could be prepared, although Co was partially substituted by Ni. 
         [0037]    Sample No. 8 is a material of the present invention obtained by a solution method, in which a Co(C 2 H 3 O 3 ) 2 .4H 2 O aqueous solution is partially substituted by an aqueous solution of Fe(OH) (C 2 H 3 OO) 2  and Ni(C 2 H 3 O 3 ) 2 .xH 2 O. A compulsorily dissolved alloy powder as a solid solution could be prepared, although Co was partially substituted by Fe and Ni. 
         [0038]    Sample No. 9 is a Comparative material obtained by the solution method. In this composition of 10 mol % W-90 mol % Co, an equilibrium phase of Co 3 W was finally precipitated as a second phase. Accordingly, when the amount of Co is greater, W atoms are readily diffused in a Co lattice in spite of using a solution method and thus a compulsory solid solution could not be prepared. 
         [0039]    Sample No. 10 is a Comparative material obtained by a solution method. In this composition of 50 mol % W-50 mol % Co, the equilibrium phase of Co7W 6  was finally precipitated as the second phase. Accordingly, W atoms were also diffused in this composition, and a compulsory solid solution could not be thus prepared. 
         [0040]    Sample No. 11 is a material of the present invention obtained by a solution method, in which a Co(C 2 H 3 O 3 ) 2 .4H 2 O aqueous solution was partially substituted by an Fe(OH)(C 2 H 3 OO) 2  aqueous solution. Sample No. 11 is a compulsorily dissolved alloy powder as a solid solution in which Co was partially substituted by a small amount of Fe. 
         [0041]    Sample No. 12 is a material of the present invention obtained by a solution method, in which a Co(C 2 H 3 O 3 ) 2 .4H 2 O aqueous solution was partially substituted by an Fe(OH)(C 2 H 3 OO) 2  aqueous solution. A compulsorily dissolved alloy powder as a solution solid could be prepared, although an Ni(C 2 H 3 O 3 ) 2 .xH 2 O aqueous solution shown in Sample No.8 was not added. 
         [0042]    Sample No. 13 is a material of the present invention obtained by a solution method, in which a Co(C 2 H 3 O 3 ) 2 .4H 2 O aqueous solution was entirely substituted by an Fe(OH)(C 2 H 3 OO) 2  aqueous solution. A compulsorily dissolved alloy powder as a solid solution could be prepared, although Co was entirely substituted by Fe. 
         [0043]    Sample No. 14 is a material of the present invention obtained by a solution method, in which a Co(C 2 H 3 O 3 ) 2 .4H 2 O aqueous solution was entirely substituted by an Fe(OH)(C 2 H 3 OO) 2  aqueous solution and a Mn(CH 3 COO) 2 .4H 2 O aqueous solution. A compulsorily dissolved alloy powder as a solid solution could be prepared, although Co was entirely substituted by Fe and Mn. 
       EXAMPLE 1  
       [0044]    A conventional material (No. 21), materials of the present invention (Nos. 22 to 27, and Nos. 30 to 33) and Comparative materials (Nos. 28 and 29) having chemical components (wt %) shown in Table 2 were prepared and the possibility of a compulsive solid solution and the existence of precipitation of the second phase were confirmed by X-ray diffraction and EPMA. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Chemical components of tungsten carbide (wt %) and formation 
               
               
                 of metal phase or second carbide phase in the carbide 
               
             
          
           
               
                 No 
                 Fe 
                 Co 
                 Mn 
                 Ni 
                 W 
                 C 
                 Note 
               
               
                   
               
             
          
           
               
                 21 
                 — 
                 — 
                   
                 — 
                 Bal 
                 6.13 
                 Conventional 
                 X 
               
               
                   
                   
                   
                   
                   
                   
                   
                 material 
               
               
                 22 
                 — 
                 1.20 
                   
                 — 
                 Bal 
                 6.10 
                 Material of the 
                 ◯ 
               
               
                   
                   
                   
                   
                   
                   
                   
                 present invention 
               
               
                 23 
                 — 
                 7.00 
                   
                 — 
                 Bal 
                 5.70 
                 Material of the 
                 ◯ 
               
               
                   
                   
                   
                   
                   
                   
                   
                 present invention 
               
               
                 24 
                 — 
                 16.71 
                   
                 — 
                 Bal 
                 5.11 
                 Material of the 
                 ◯ 
               
               
                   
                   
                   
                   
                   
                   
                   
                 present invention 
               
               
                 25 
                 — 
                 19.70 
                   
                 — 
                 Bal 
                 4.20 
                 Material of the 
                 ◯ 
               
               
                   
                   
                   
                   
                   
                   
                   
                 present invention 
               
               
                 26 
                 3.32 
                 3.50 
                   
                 — 
                 Bal 
                 5.91 
                 Material of the 
                 ◯ 
               
               
                   
                   
                   
                   
                   
                   
                   
                 present invention 
               
               
                 27 
                 — 
                 3.50 
                   
                 3.48 
                 Bal 
                 5.91 
                 Material of the 
                 ◯ 
               
               
                   
                   
                   
                   
                   
                   
                   
                 present invention 
               
               
                 28 
                 — 
                 19.76 
                   
                 — 
                 Bal 
                 4.19 
                 Comparative 
                 X 
               
               
                   
                   
                   
                   
                   
                   
                   
                 material 
               
               
                 29 
                 — 
                 0.29 
                   
                 — 
                 Bal 
                 6.12 
                 Comparative 
                 X 
               
               
                   
                   
                   
                   
                   
                   
                   
                 material 
               
               
                 30 
                  0.033 
                 6.96 
                 — 
                 — 
                 Bal 
                 5.70 
                 Material of the 
               
               
                   
                   
                   
                   
                   
                   
                   
                 present invention 
               
               
                 31 
                 1.66 
                 5.25 
                 — 
                 — 
                 Bal 
                 5.71 
                 Material of the 
                 ◯ 
               
               
                   
                   
                   
                   
                   
                   
                   
                 present invention 
               
               
                 32 
                 6.65 
                 — 
                 — 
                 — 
                 Bal 
                 5.72 
                 Material of the 
                 ◯ 
               
               
                   
                   
                   
                   
                   
                   
                   
                 present invention 
               
               
                 33 
                 5.79 
                 — 
                 0.79 
                 — 
                 Bal 
                 5.73 
                 Material of the 
                 ◯ 
               
               
                   
                   
                   
                   
                   
                   
                   
                 present invention 
               
               
                   
               
               
                 Metal phase is formed in carbide: ◯ 
               
               
                 Metal phase is not formed in carbide: X 
               
             
          
         
       
     
         [0045]    The materials of the present invention of Nos. 22 to 27 shown in Table 2 were prepared by adding graphite to a tungsten alloy powder in which a transition metal was compulsorily dissolved as a solid solution by a solution method, followed by mixing. That is, a tungsten alloy powder in which a transition metal element was compulsorily dissolved as a solid solution was prepared, by 1) mixing an aqueous solution of transition metal acetate selected from the group consisting of Co(C 2 H 3 O 3 ) 2 .4H 2 O, Fe(OH)(C 2 H 3 OO) 2 , Mn(CH 3 COO) 2 .4H 2 O and/or Ni(C 2 H 3 O 3 ) 2 .xH 2 O) with an aqueous solution of ammonium paratungstate (5(NH 4 ) 2 O.12WO 3 .5H 2 O), drying by distillation (or spray drying), thermally decomposing the resulting solid with oxide under an atmosphere at 823 K, and performing hydrogen thermal reduction for 1 h under a hydrogen gas at 1073 K. 
         [0046]    Then, 2) this tungsten alloy powder was mixed with graphite and was allowed to stand in Ar at 1473 K for 1 h to prepare tungsten carbide. 
         [0047]    Sample No. 21 was WC carbide obtained by mixing WO 3  with graphite and carbonizing at 1473 K for 1 h in accordance with a conventional powder metallurgy method. A metal phase was not present in the WC skeleton. 
         [0048]    Sample No. 22 to Sample No. 27 are materials of the present invention obtained by 1) a solution method and 2) carbonization. A specific structure in which a metal phase is present in the WC skeleton was obtained. This metal phase contributes to resource saving of tungsten and the improvement of mechanical properties of carbide. It was confirmed that the content of metal phase increases in accordance in the order of Sample No. 22, No. 23, No. 24, No. 25, No. 26 and No. 27. 
         [0049]    Sample No. 26 and Sample No. 27 are carbides in which metal phase cobalt present therein is substituted by iron, iron-manganese and nickel, respectively, to reduce the cost. 
         [0050]    Samples Nos. 28 and 29 are Comparative materials obtained by a solution method and carbonization. When the amount of cobalt is greater than that of tungsten as in Sample No. 29, tungsten is diffused in the cobalt in the process of preparing the tungsten alloy powder, to produce an equilibrium phase of Co 3 W or Co 7 W 6 . As a result, when this alloy powder is carbonized, the metal phase surrounds the carbide and the metal phase cannot be thus present in the carbide. 
         [0051]    The materials of the present invention of Nos. 30 and 31 shown in Table 2 were prepared by adding graphite to a tungsten alloy powder in which a transition metal is compulsorily dissolved as a solid solution by a solution method, followed by mixing. That is, in the same manner as in Sample 26, a tungsten alloy powder in which a transition metal element is compulsorily dissolved as a solid solution was prepared, by mixing an aqueous transition metal acetate solution (Co(C 2 H 3 O 3 ) 2 .4H 2 O) and an aqueous solution of Fe(OH)(C 2 H 3 OO) 2  with an aqueous solution of ammonium paratungstate (5(NH 4 ) 2 O.12WO 3 .5H 2 O), drying by distillation (or spray drying), thermally decomposing the resulting solid into an oxide under an atmosphere at 823 K, and performing hydrogen thermal reduction for 1 h under hydrogen gas at 1073 K. Then, this tungsten alloy powder was mixed with graphite and was allowed to stand in Ar at 1473 K for 1 h to prepare tungsten carbide. A specific structure in which a Co—Fe solid solution phase is present in the WC skeleton was obtained. 
         [0052]    The materials of the present invention of Nos. 32 and 33 shown in Table 2 were prepared by adding graphite to a tungsten alloy powder in which Fe and Mn were compulsorily dissolved as a solid solution by a solution method, followed by mixing. That is, the tungsten alloy powder in which a transition metal element is compulsorily dissolved as a solid solution was prepared, by mixing an aqueous solution of (Fe(OH)(C 2 H 3 OO) 2 ) and an aqueous solution of Mn(CH 3 COO) 2 .4H 2 O with an aqueous solution of ammonium paratungstate (5(NH 4 ) 2 O.12WO 3 .5H 2 O), drying by distillation (or spray drying), thermally decomposing the resulting solid into an oxide under an atmosphere at 823 K, and performing hydrogen thermal reduction for 1 h under hydrogen gas at 1073 K. Then, this tungsten alloy powder was mixed with graphite and was allowed to stand in Ar at 1473 K for 1 h to prepare tungsten carbide. When Co is entirely substituted by Fe or Fe and Mn, WC containing a Fe metal or Fe—Mn solid solution could be obtained. 
         [0053]      FIG. 1  shows EPMA observation results of the material of the present invention of Sample No. 23. As can be seen from the X-ray image of W and C corresponding to the SEM image, the structure of WC was formed. In addition, it was found from the X-ray image of Co that a metal phase was formed in the structure of WC. That is, 
         [0054]    (a) is an SEM image. A white part represents a WC skeleton and a black part represents a domain composed of a Co metal. The Co domain is inevitably grown when sintered at 1623 K at 3.6 ks, but is maintained at 3 mm or less. 
         [0055]    (b) represents an X-ray image of W and shows formation of the WC skeleton. 
         [0056]    (c) represents an X-ray image of Co and shows formation of the Co domain in a WC skeleton. 
         [0057]    (d) represents an X-ray image of C and shows formation of the WC skeleton. 
         [0058]    This formation of metal phase is effective in reducing the amount of tungsten used and improves mechanical properties. Accordingly, a cemented carbide, in which this novel WC carbide is dispersed, is suitable as an abrasion resistance material. 
       EXAMPLE 2 
       [0059]    The cemented carbide may be prepared by sintering tungsten carbide of the present invention with a Co powder in accordance with a known preparation method.  FIG. 2  shows an EPMA image of a cemented carbide, experimentally prepared by adding 5% by weight of bonded Co to the material of the present invention of Sample No. 33 and sintering at 1623 K at 3.6 ks. It can be seen that, in the cemented carbide, a Fe—Mn solid solution is formed in the WC skeleton and a bonded Co is partially distributed in this Fe—Mn solid solution during sintering. The Vickers hardness was an extremely high hardness of Hv1945. Further, it could be observed that a tip of a Vickers hardness test indentation did not crack and exhibited excellent toughness. That is, 
         [0060]    (a) is an SEM image. A white part is a WC skeleton and a black part is a domain composed of a Fe—Mn solid solution. When sintered, the metal domain inevitably grows, but is maintained at 1 mm or less. This SEM image exhibits an indentation of a Vickers hardness test. The Vickers hardness was an extremely high hardness of Hv1945. Further, it can be seen that a tip of a Vickers hardness test indentation did not crack and exhibited excellent toughness. 
         [0061]    (b) represents an X-ray image of W and shows formation of the WC skeleton. In addition, a part of W is distributed in the Fe—Mn solid solution domain. 
         [0062]    (c) represents formation of the Fe—Mn solid solution domain, which is an X-ray image of Fe. 
         [0063]    (d) is an X-ray image of Co. The bonded Co is partially distributed in the Fe—Mn solid solution domain during sintering. 
         [0064]    (e) represents an X-ray image of C and shows formation of a WC skeleton. 
         [0065]    (f) represents an X-ray image of Mn and shows formation of a Fe—Mn solid solution domain. 
         [0066]    The reason why the WC carbide including a metal domain exhibits a high hardness is that in the present invention, the WC skeleton successfully creates a micro structure which constrains deformation of the metal domain. 
       INDUSTRIAL APPLICABILITY  
       [0067]    As apparent from the foregoing, the alloy powder of the present invention contains a transition metal element homogenously compulsorily dissolved as a solid solution in a tungsten grating. Accordingly, the tungsten alloy powder may be widely used, as an alloy powder in which a portion of the tungsten is substituted by a transition metal element, for resource saving of tungsten such as tungsten carbide materials used for cemented carbides. 
         [0068]    Accordingly, the inventive a transition metal included tungsten carbide can be used to make a new cemented carbide sintered with a combined phase Co in a substitute of the conventional cemented carbide. The inventive tungsten carbide phase including metal phase has a property of toughness as itself, resulting in improved mechanical property of carbide diffused cemented carbide, which provides a long life mold materials. Furthermore, a tungsten carbide sintered body including a metal phase can be also suitable for a new cemented carbide. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS 
       [0069]    The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
         [0070]      FIG. 1  is an image illustrating EPMA observation results of tungsten carbide including a metal phase, for the material of the present invention of Sample No. 23. (a) is an SEM image in which a white part represents a WC skeleton and a black part represents a domain composed of a Co metal. (b) represents an X-ray image of W and shows formation of a WC skeleton. (c) represents an X-ray image of Co and shows formation of a Co domain in a WC skeleton. (d) represents an X-ray image of C and shows formation of a WC skeleton. 
         [0071]      FIG. 2  is an image illustrating EPMA observation results of tungsten carbide including a metal phase, for the material of the present invention of Sample No. 33:(a) is an SEM image in which a white part is a WC skeleton and a black part is a domain composed of a Fe—Mn solid solution.
   (b) represents an X-ray image of W and shows formation of a WC skeleton.   (c) represents an X-ray image of Fe and shows formation of a Fe—Mn solid solution domain.   (d) is an X-ray image of Co in which the bonded Co is partially distributed in the Fe—Mn solid solution domain during sintering.   (e) represents an X-ray image of C and shows formation of a WC skeleton.   (f) represents an X-ray image of Mn and shows formation of a Fe—Mn solid solution domain.