JP2008196041A - Cemented carbide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cemented carbide having high strength and reduced in the variation of the strength. <P>SOLUTION: The cemented carbide has a composition comprising, by weight, 0.0001 to 0.002% Al, 0.0001 to 0.002% Ca, 0.0002 to 0.005% rare earth elements, one or two kinds selected from Co and Ni by 3 to 20%, the group 4a, 5a, 6a elements in the Periodic Table excluding W by 0.2 to 2%, 5 to 6% C (carbon) and ≤0.2% N (nitrogen), and the balance W with inevitable impurities. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cemented carbide suitable for drills, end mills, die punches, and the like, and more particularly to a cemented carbide suitable for a printed circuit board drill.

  Small-diameter drills used for drilling printed circuit boards use fine cemented carbides with wear resistance and breakage resistance. Although improvement of wear resistance can be achieved by atomization of WC, in order to improve breakage resistance, systematic defects such as coarse WC, Co ingots, and foreign materials that cause fracture must be removed as much as possible. Don't be. In particular, it is difficult to reduce the inevitable impurities that are the generation source of foreign substances because they are mixed from raw materials and manufacturing processes.

  As a conventional technique in which the type and amount of inevitable impurities in a sintered alloy are controlled, there is a sintered alloy in which Ca is 100 ppm or less and S is 50 ppm or less (see, for example, Patent Document 1). Although this sintered alloy has reduced CaS generated during sintering to prevent a decrease in strength, it is difficult to reduce Ca to 5 ppm or less, particularly when Al is contained as an inevitable impurity. There is a problem that the strength is significantly reduced.

  Further, as a conventional technique of a cemented carbide containing a rare earth element, a rare earth element such as Ce, Y arbitrarily added up to 2% (for example, refer to Patent Document 2), or 0.01% by volume. There are those in which oxides such as Mg, Al, and rare earth elements are dispersed in a WC crystal (see, for example, Patent Document 3). These cemented carbides are intended to improve hardness and toughness by dispersing rare earth oxides or the like in the binder phase or WC crystal. There is a problem that high strength cannot be achieved.

Japanese Patent Laid-Open No. 60-258446 JP-A-10-121182 Japanese Patent Laid-Open No. 11-124650

  Drills for drilling printed circuit boards are required to improve the strength of cemented carbide, which is a drill material, and to reduce variations in strength in order to cope with the reduction in diameter, difficulty in processing the substrate, and high feed processing. The present invention solves the above-described problems. Specifically, high strength is achieved by adding a trace amount of rare earth elements to a cemented carbide containing at least Al and Ca as inevitable impurities. The purpose is to provide a cemented carbide to achieve.

  The present inventor investigated the structural defects of the conventional fine cemented carbide, and found that most of the oxide aggregates were mainly composed of Al and Ca, and Al and Ca were mixed from the raw materials. In order to prevent coarsening of aggregates of these oxides, it is only necessary to add a trace amount of rare earth elements, and rare earth elements form a complex oxide with Al and Ca to form fine oxides. In addition, the inventors have obtained the knowledge that the uniform dispersion and, as a result, the strength of the cemented carbide can be improved and the variation in strength can be reduced, and the present invention has been completed.

  That is, the cemented carbide of the present invention has Al: 0.0001 to 0.002 wt%, Ca: 0.0001 to 0.002 wt%, and at least one of rare earth elements: 0.0002 to 0 0.005% by weight, one or two of Co and Ni: 3 to 20% by weight, periodic table 4a, 5a and 6a elements excluding W: 0.2 to 2% by weight, and C (carbon) : 5 to 6% by weight, N (nitrogen): 0.2% by weight or less, and the remainder consists of W and inevitable impurities.

  The cemented carbide of the present invention has a complex oxide phase, a metal-bonded phase, a cubic compound phase, and a WC phase when the addition amount of group elements 4a, 5a, and 6a in the periodic table excluding W is large. In the case where the structure is composed of inevitable impurities and the addition amount of the elements of the periodic table 4a, 5a, 6a excluding W is small, the composite oxide phase, the metal bonded phase, the WC phase, It becomes a structure composed of inevitable impurities.

  Al and Ca contained in the cemented carbide of the present invention are unavoidable impurities contained in WC, Co, and Ni powders as main raw materials. It is difficult to make the Al content and Ca content less than 0.0001% by weight from the raw material production process and cost, and conversely, if the content exceeds 0.002% by weight, it becomes a systematic defect. Since the composite oxide aggregates increase and become coarser, the strength is significantly reduced. Therefore, the Al content and the Ca content were determined to be 0.0001 to 0.002% by weight, respectively.

  The rare earth element in the present invention indicates at least one of Sc, Y and lanthanides (elements having atomic numbers 57 to 71). The rare earth element contained in the cemented carbide of the present invention is positively added in the manufacturing process of the cemented carbide. If the rare earth element content is less than 0.0002% by weight, the effect of preventing the coarsening of the composite oxide and the effect of uniformly dispersing the composite oxide are small, so that the strength is not sufficiently improved. If the amount exceeds 005% by weight, the added rare earth element forms a coarse rare earth oxide and becomes a systematic defect, thereby reducing the strength. Therefore, the rare earth element content is determined to be 0.0002 to 0.005% by weight. It was. Among the rare earth elements, at least one of La, Ce, Nd, Gd, and Tb is more preferable. This is because a composite oxide formed from these rare earth oxides and oxides of Al and Ca has a high melting point and is difficult to aggregate or grow in cemented carbide.

Al, Ca and rare earth elements contained in the cemented carbide of the present invention mainly form a composite oxide phase. Specific examples of the composite oxide phase include (Al, Ca, Y) ₂ O ₃ , (Al, Ca, Ce) ₂ O ₃ , (Al, Ca, La, Sm) ₂ O _{3 and the} like. . Further, when a large amount of S is contained in the cemented carbide as an inevitable impurity, an oxysulfide such as (Al, Ca, Ce) ₂ O ₂ S, (Al, Ca, Y) (O, S) _{X is} used. There may be.

Here, the relationship between the total content of Al and Ca and the amount of rare earth element added is preferably close to 1: 1 in terms of atomic ratio. Al ₂ O ₃ and CaO which are oxides of Al and Ca contained are oxides of added rare earth elements (for example, Y ₂ O ₃ , La ₂ O ₃ , Ce ₂ O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O _3, etc.) to form a complex oxide. When the atomic ratio is 1: 1, a higher melting point and thermodynamically stable composite oxide is formed, so that it is difficult to cause grain growth and aggregation during sintering of the cemented carbide.

  One or two of Co and Ni contained in the cemented carbide of the present invention forms a metal bonded phase. Specific examples of the metallic binder phase include a Co—W alloy, a Co—Cr—W alloy, a Co—Ni—W—Cr alloy, and a Ni—Mo—Cr solid solution of 20 wt% or less of W, Cr, Mo and the like. Mention may be made of alloys such as alloys. Among them, a Co—Cr—W alloy in which 5 to 20 wt% of Cr is solid-solved with respect to the entire metal binder phase is preferable because strength and toughness are improved. When the content of one or two of Co and Ni is less than 3% by weight, the strength and toughness are low, and thus the chip tends to be broken. Conversely, when the content exceeds 20% by weight, the hardness and wear resistance are reduced. In order to increase elastic deformation and plastic deformation, the content of one or two of Co and Ni was determined to be 3 to 20% by weight.

In the cemented carbide of the present invention, when the content of at least one of the elements in the periodic table 4a, 5a, 6a excluding W is less than 0.2% by weight with respect to the entire cemented carbide, sintering causes WC causes abnormal grain growth, which decreases the strength because it becomes a structural defect. Conversely, when it exceeds 2% by weight, the cubic compound phase and the dispersed phase such as Cr ₇ C ₃ and Mo ₂ C increase. Strength decreases. Therefore, the content of at least one of the periodic table 4a, 5a, and 6a elements excluding W is defined as 0.2 to 2% by weight. When the content of Ti, Zr, Hf, V, Nb, Ta is large, a cubic compound is formed. Specific examples of the cubic compound include VC, NbC, TaC, ZrN, V (C, N), (V, W) C, (V, W, Cr) C, (W, Ti, Ta) C, ( Nb, Zr, W) (C, N) and the like. Among them, the addition of V is preferable because the effect of suppressing the grain growth of WC is large, and the addition of Zr is preferable because a cubic compound is uniformly dispersed and a fine high-strength cemented carbide is obtained.

W and C contained in the cemented carbide of the present invention mainly form WC. The optimum amount of C greatly varies depending on the alloy composition, and it is necessary to adjust the amount of C so that free carbon or Co ₃ W ₃ C does not precipitate in the cemented carbide. N forms a cubic compound together with part of C, but does not exceed 0.2% by weight in the composition range of the present invention. Here, if the average particle size of the WC phase is less than 0.1 μm, it is very difficult to produce, and conversely, if it exceeds 1 μm, the strength and strength decrease, so the average particle size of the WC phase is The range of 0.1-1 micrometer is preferable.

  Although the cemented carbide of the present invention can be produced by ordinary powder metallurgy, the rare earth element can be finely and uniformly added by dissolving it in a solvent such as water or an organic solvent in the form of nitrate or oxalate. It is preferable because it can be dispersed in the water.

  In the cemented carbide of the present invention, the added rare earth element forms a composite oxide together with Al and Ca which are inevitable impurities. The produced complex oxide is less likely to aggregate during sintering and less likely to grow. Since the complex oxide dispersed finely and uniformly does not become a systematic defect, the strength of the cemented carbide is improved and the effect of reducing the variation in strength is obtained.

  The cemented carbide of the present invention has an effect that the strength is improved by about 15% and the variation in strength is reduced to about ½ compared to the conventional cemented carbide.

  Two types of commercially available WC powder (abbreviated as WC / A and WC / B), two types of Co powder (abbreviated as Co / A and Co / B), and Ni powder were prepared. Table 1 shows the average particle diameter of each prepared powder and the contents of Al, Ca, and S contained in each powder.

And each powder of WC / A, WC / B, Co / A, Co / B, Ni described in Table 1, carbon black (denoted as C) having an average particle diameter of 0.05 μm, and average particles Each powder of Cr ₃ C _{2 having} a diameter of 1.2 μm, VC having an average particle diameter of 1.3 μm, ZrN having an average particle diameter of 2.1 μm, TaC having an average particle diameter of 1.0 μm, and Y (NO ₃ ) ₃ .6H ₂ O La (NO ₃ ) ₃ · 6H ₂ O, Ce (NO ₃ ) ₃ · 6H ₂ O, Nd (NO ₃ ) ₃ · 6H ₂ O, Sm (NO ₃ ) ₃ · 6H ₂ O, Eu (NO ₃ ) Table 3 shows nitrate hydrates of ₃ · 6H ₂ O, Gd (NO ₃ ) ₃ · 5H ₂ O, Tb (NO ₃ ) ₃ · 6H ₂ O, Yb (NO ₃ ) ₃ · 3H ₂ O. Weigh to the composition shown, insert into a stainless steel pot with acetone solvent and cemented carbide balls, mix and grind for 48 hours, then heat The solvent to obtain a mixture powder by adding 2 wt% of paraffin wax with drying Te.

＊希土類元素の硝酸塩水和物は、外掛けで添加。

* Nitrate hydrates of rare earth elements are added on the outside.

These mixed powders were filled in a mold, and a green compact of 5.5 × 9.5 × 29 mm was produced with a pressure of 196 MPa, and placed on a carbon plate coated with carbon black powder. Then, it inserted in the continuous sintering furnace which can be vacuum-sintered and a hot isostatic-pressure process (HIP), and heated. Then, after dewaxing, vacuum sintering was performed under the conditions listed in Table 2, followed by HIP treatment (1280 ° C.-60 min, in 30 MPa of Ar), and inventive products 1-9 and comparative products 1-4. A cemented carbide was obtained. Here, by observation of the structure with an optical microscope, it was confirmed that any cemented carbide was a cemented carbide in a healthy phase region containing no free carbon and Co ₃ W ₃ C.

  Each cemented carbide thus obtained was wet-grinded with a # 230 diamond grindstone to obtain a 4.0 × 8.0 × 25.0 mm test piece.

  Next, after one surface of each bending strength test piece was lapped with a 1.0 μm diamond paste, main metal elements were analyzed using a scanning analytical electron microscope. Moreover, it grind | pulverized to # 100 or less with the cemented carbide mortar, and measured each content of C and N using each analyzer of carbon and nitrogen. These results are shown in Table 3.

Furthermore, a predetermined amount of each pulverized powder of the bending strength test piece was completely dissolved in nitrous acid (HF: HNO ₃ = 1: 1). And each solution was analyzed using the emission-spectral-analysis (ICP) apparatus, and content of Al, Ca, and rare earth elements was measured. The results are shown in Table 4. Further, the content of the complex oxide was calculated from the contents of these elements, and the results were also shown in Table 4. However, Al is present in the form of Al ₂ O ₃ , Ca is in the form of CaO, and the rare earth element (abbreviated as RA) is in the form of (RA) ₂ O ₃ .

  From Table 4, the amount of Al and the amount of Ca of the inventive products 1 to 9 are 0.0003 to 0.006% by weight, respectively, and the amount of rare earth elements of the inventive products 1 to 9 is 0.0008 to 0.0045. It turns out that it is weight%.

  Each sintered cemented carbide is wet-grinded with a # 230 diamond grindstone to produce 4.0 × 8.0 × 25.0 mm test pieces, which are used to measure the bending strength according to the JIS method. did. Weibull plots were performed for each of the 20 measured values, and the average value of the bending strength and the Weibull coefficient were obtained. The results are shown in Table 5. In addition, the fracture surface of the test piece after measuring the bending strength was observed with a scanning electron microscope, and the ratio of the test piece in which the origin of fracture became an oxide aggregate was obtained. The piece was subjected to a qualitative analysis of the elements contained in the oxide aggregates. The results are also shown in Table 5.

  Table 5 shows that the present invention product 1 and the comparative product 1 having the same amount of Co are compared with each other in comparison with the comparative product 1 in that the average value of the bending strength and the Weibull coefficient of the present product 1 are higher. . Further, from Table 5, when the inventive products 3-9 having the same amount of Co and the comparative products 2-4 are compared, the bending strength and the Weibull coefficient of the inventive products 3-9 are those of the comparative products 2-4. You can see that it is higher than These indicate that the strength of the product of the present invention is improved and the variation in strength is reduced as compared with the comparative product. Moreover, it can be seen from Table 5 that the product of the present invention has a lower proportion of oxide aggregates in the origin of destruction than the comparative product.

Claims (5)

  Al: 0.0001 to 0.002% by weight; Ca: 0.0001 to 0.002% by weight; Rare earth elements: 0.0002 to 0.005% by weight; one or two of Co and Ni: 3 to 20% by weight, at least one of the periodic table elements 4a, 5a and 6a excluding W: 0.2 to 2% by weight, C (carbon): 5 to 6% by weight, N ( Nitrogen): Cemented carbide comprising 0.2% by weight or less, the balance being W and inevitable impurities.   The cemented carbide according to claim 1, wherein the rare earth element is at least one of La, Ce, Nd, Gd, and Tb.   The cemented carbide according to claim 1 or 2, wherein the cemented carbide is composed of a composite oxide phase, a metal bonded phase, a cubic compound phase, a WC phase, and inevitable impurities.   The cemented carbide according to claim 1 or 2, wherein the cemented carbide is composed of a composite oxide phase, a metal bonded phase, a WC phase, and inevitable impurities.   The cemented carbide according to claim 3 or 4, wherein the WC phase has an average particle size of 0.1 to 1 µm.