JP5134217B2 - Sintered hard material and mold using the same - Google Patents

Description

  The present invention relates to a sintered hard material suitable for mold materials for molding high-precision optical elements such as lenses, prisms, and gratings used in optical equipment, or mold materials for injection molding such as metals, plastics, and composite materials. .

  Highly reliable as a method for obtaining the final product shape when manufacturing optical elements such as optical pickup lenses used in CDs, DVDs, digital cameras, mobile phones, etc. and glass hard disks used in computer hard disk substrates. In recent years, press molding at high temperatures that does not require complicated and precise mechanical processing has been adopted in order to realize high performance and low cost.

  The mold material used in this high-temperature press molding is required to have excellent mirror surface workability, as well as properties such as high-temperature hardness, high thermal conductivity, and low coefficient of thermal expansion. Sintered hard materials such as hard alloys and ceramics are used.

  For example, Patent Document 1 discloses that 3 to 10 mass% of cobalt is used as a cemented carbide for hot isostatic pressing suitable for an optical element molding die whose surface after processing forms a mirror surface having an Rmax of 0.05 μm or less. Including a WC-based cemented carbide is disclosed.

  However, as the accuracy of the optical lens increases, the surface of the molding part of the optical element molding die needs to be further improved. At present, the surface of the lens molding part after processing is Rmax 0.01 μm. It is essential to obtain the following mirror surface.

  On the other hand, a WC-based cemented carbide containing 1% by mass or more of an iron group metal such as Fe, Co, or Ni as a binder phase has a large hardness difference between the WC phase and the iron group metal phase, so that a desired surface accuracy is obtained by machining. It has become difficult. For this reason, even in the past, a cemented carbide material only comprising a carbide phase, which does not include an iron group metal phase having a large hardness difference from the carbide phase, a so-called binderless cemented carbide material is used as a material for precision molding dies. 2 and 3.

  In the sintered hard materials shown in Patent Documents 2 and 3, the surface of the molded lens part after processing can be finished to a mirror surface with a Rmax of 0.01 μm or less relatively easily, but the second phase is compared with the WC phase. As a result, it contains a relatively large amount of composite carbide having a high hardness and a brittle NaCl-type crystal structure. Therefore, there is a difference in local processing performance such as sub-micron order or nano-order. Was an obstacle to further pursuing.

  In addition, the second phase of the sintered hard material disclosed in Patent Documents 2 and 3 can have a non-stoichiometric composition, so that the composite carbide of iron group metal and W can be controlled by controlling the amount of carbon in the material. Among them, it was an indispensable phase because crystallization of the η phase (hereinafter referred to as an abnormal phase) can be prevented relatively easily.

On the other hand, in the sintered hard material shown in Patent Document 4, the inevitable impurity components such as Fe, Co, and Ni that are constituent elements of the abnormal phase are suppressed to a very small amount of 0.02 to 0.10% by weight. Since it is considered that phase crystallization can be prevented, it is no longer necessary to include the aforementioned second phase in the material. Then, the sintered hard material shown in Patent Document 4, a range of WC and _W 2 in the tungsten carbide _C ratio of _{X W} 2 _C X / a (WC ₊ W 2 _{C X)} 0.01 to 0.15 By doing so, the hardness is improved.

  Certainly, according to the sintered hard material shown in Patent Document 4, the hardness is improved. However, the fracture toughness of the sintered hard material shown in Patent Document 4 is lower than that of the sintered hard material shown in Patent Documents 2 and 3. Therefore, it is considered that there is a higher possibility of causing chipping and chipping of the edge portion in machining and handling than the sintered hard material disclosed in Patent Documents 2 and 3.

The reason why the fracture toughness of the sintered hard material shown in Patent Document 4 is lower than that of the sintered hard material shown in Patent Documents 2 and 3 is considered to be because the iron group metal which is an impurity component is reduced. That is, the amount of iron group metal at the WC / WC interface, WC / W ₂ C _X interface or W ₂ C _X / W ₂ C _X interface of the sintered hard material shown in Patent Document 4 is shown in Patent Documents 2 and 3. Between these interfaces because the amount of iron group metal at the WC / WC interface, WC / W ₂ C _X interface or W ₂ C _X / W ₂ C _X interface of sintered hard material It seems that the bond strength of was weakened.
Japanese Examined Patent Publication No. 62-51211 Japanese Patent Laid-Open No. 2-120244 Japanese Patent Laid-Open No. 10-7425 Japanese Patent Laid-Open No. 9-25535

  The problem to be solved in the present invention is that a sintered hard material mainly composed of a tungsten carbide phase has no structural defects such as pores or abnormal phases, has high hardness, has a high Young's modulus, and has a thermal expansion. In addition to the characteristics of having a small coefficient and excellent machined surface accuracy and surface roughness, it is to provide excellent fracture toughness.

The sintered hard material of the present invention has (W, M1) ₂ C _X as the second phase in addition to the WC phase as the first phase in the tungsten carbide phase.
The fracture toughness of the tungsten carbide phase is improved by crystallizing (0.8 ≦ X <1.0). Where (W, M1) ₂ C _X
(0.8 ≦ X <1.0) means that W1 is a transition metal element other than W in the groups 4a, 5a, and 6a of the periodic table (one or more of Cr, V, and Nb). ₂ C _X (0.8 ≦ X <1.0) is a solid solution.

  In this sintered hard material, the WC phase is excellent in hardness, strength, processed surface roughness, etc., but by making the average particle diameter 0.5 μm or less, the structure becomes finer, thereby the hardness and mirror surface. Workability can be further improved. On the other hand, hardness and specular workability tend to decrease due to an increase in average particle diameter. In particular, when the average particle diameter exceeds 0.5 μm, the hardness and specular workability are drastically decreased. Therefore, in the present invention, the average particle diameter of the tungsten carbide phase is preferably 0.5 μm or less.

  However, since fracture toughness generally tends to decrease as the structure becomes finer, particularly when the average particle diameter is 1 μm or less, there is a high risk of causing chipping or chipping during processing and handling.

In contrast, X ranges 0.8 ≦ X <1.0 in (W, _M1) 2 _{C X} is, WC, etc. and holds the same manner hexagonal crystal structure, thus NaCl-type crystal structure Compared with many other carbides, it has a large plastic deformability. Therefore, fracture toughness can be improved by crystallizing this (W, M1) ₂ C _X in tungsten carbide. Further, it is conceivable that the role of strengthening dispersion is also achieved by dispersing the (W, M1) ₂ C _X particles in the WC phase.

The (W, _M1) for the crystallization of _{2 C X, (W, M1} ) 2 C X of (-1-11) The integrated peak intensity of X-ray diffraction of the surface ∫I ((W, _{M1) 2} ) Dθ, and when the integrated peak intensity of X-ray diffraction on the (101) plane of WC is expressed as ∫I (WC) dθ, the integrated peak intensity ratio ∫I ((W, M1) ₂ C _X ) dθ If / I (WC) dθ is less than 0.5%, the amount of (W, M1) ₂ C _X phase is small and the contribution to fracture toughness improvement is small. On the other hand, if it exceeds 10.0%, the contribution to fracture toughness improvement is not clear, but the sinterability is lowered and a dense material cannot be obtained, so that it can be applied to the technical field of the present invention. Can not. From the above, in tungsten carbide, the ratio of X in the range of X ≦ 0.8 <X <1.0 (W, M1) ₂ C _X is 0.5% to 10.0% in the integrated peak intensity ratio. To be in the range.

Regarding the integrated peak intensity of X-ray diffraction, the main diffraction peaks of WC are the (101) plane and the (100) plane, and the diffraction peak of the (100) plane of WC is (W, M1) ₂ C. _Since the diffraction angle with the diffraction peak of the (110) plane of _X is close and overlaps with each other, the diffraction peak of the (101) plane of WC was selected as the main diffraction peak of WC. Further, (W, _M1) has been denoted the (-1-11) plane of the main diffraction peak as a diffraction peak of _{2 C X, (W, M1} ) 2 C X (0.8 ≦ X <1.0 ), For example, for W _5.08 C ₁₂ , the main diffraction peak is the (111) plane, but the (111) plane and the (−1-11) plane are the same {111} crystal system. Equivalent.

Furthermore, the diffraction peak of (W, M1) ₂ C _X (0.8 ≦ X <1.0) described so far is basically W ₂ C _X (0.8 ≦ X <1.0). However, the diffraction peak has a slight width and is shifted slightly higher than the diffraction peak position of W ₂ C _X (0.8 ≦ X <1.0). This is because the value of X has a non-stoichiometric value, and one or more transition metal elements other than W in groups 4a, 5a, and 6a of the periodic table are dissolved in the lattice. It is considered that However, the shift amount is very small and is about 0.1 degree (2θ / degree) or less.

In the sintered hard material of the present invention, the value of X in (W, M1) ₂ C _X (0.8 ≦ X <1.0) is (−1− of (W, M1) ₂ C _X. 11) The integral peak intensity ratio ∫I ((W, M1) ₂ C _X ) dθ / ∫I (WC) dθ of X-ray diffraction between the (101) plane and the (101) plane of WC is 0.5% to 10.0. In the range of%, as the intensity ratio increases, the diffraction peak of (W, M1) ₂ C _X having a value of X = 0.84 approaches and the shift amount from the theoretical value of the diffraction peak is small. Become. This is probably because (W, M1) ₂ C _X exists stably at a value of X = 0.84, and has a value of X = 0.84 as the amount of carbon in the material decreases ( This is probably because the phase amount of W, M1) ₂ C _X increases.

On the other hand, as shown in the sintered hard material of Patent Document 4, W ₂ C _X having an X range of 1.0 ≦ X <2.0 is originally in the alloy carbon range where W ₂ C _X is crystallized. Although its existence is confirmed in the high carbon region, even if W ₂ C _X having this X range of 1.0 ≦ X <2.0 is present in the sintered hard material, its abundance is very high. Therefore, the improvement effect of fracture toughness cannot be confirmed, and even if confirmed, it is very small.

Here, in W ₂ C _X (0.8 ≦ X <1.0), transition metals other than W in the groups 4a, 5a and 6a of the periodic table (one or more of Cr, V and Nb) ) Is dissolved, that is, (W, M1) ₂ C _X
The presence of M1 atoms in (0.8 ≦ X <1.0) affects the diffusion of each element and suppresses the coarsening of (W, M1) ₂ C _X particles. W ₂ C _X
(W, M1) ₂ C _X is present as (W, M1) ₂ C _X
It is considered that the (0.8 ≦ X <1.0) phase can be present in tungsten carbide more stably because the lattice strain is reduced. _Thus, rather than as _{W 2 C X (W, M1} ) 2 C X
It is considered that the effect of improving the fracture toughness is more stably exhibited when it is present as, and the effect as dispersed particles as dispersion strengthening is also more exhibited.

On the other hand, the sinterability is improved by the presence of iron group metals such as Fe, Co and Ni as impurity components, and the interface between WC / WC, WC / W ₂ C _X or W ₂ C _X / W ₂ C _X is improved. Although the bonding strength is increased, in the sintered hard material mainly composed of the tungsten carbide phase as in the present invention, due to the presence of these iron group metals, a composite carbide of W and iron group metal called η phase is formed. Mechanical strength deteriorates due to crystallization. However, if the content in the sintered hard material is extremely small such as less than 0.05% by mass, for example, as shown in the following reference, the iron group metal and W can be easily controlled by controlling the carbon content in the material. It is considered that this composite carbide can be crystallized as a hexagonal crystal structure such as a κ phase, which can prevent deterioration of mechanical properties. Therefore, the content of one or more of the impurity components Fe, Co, and Ni is preferably suppressed to less than 0.05% by mass.

(Reference) Schwarzkopf and R.W. Kieffer,
CEMENTED CARBIDES, The McCillan Company, New York, U.S.A. S. A. , P. p. 74-101, (1960).

  According to the sintered hard material of the present invention, there are very few systematic defects such as pores and abnormal phases, high hardness, high Young's modulus, low thermal expansion coefficient, and good mirror surface accuracy. In addition to obtaining the characteristics such as, it is possible to obtain excellent fracture toughness. Accordingly, the same machining as that of the conventional material can be performed, and the possibility of chipping and chipping of the edge portion is reduced in machining and handling thereof, and the lifetime can be extended.

  The best mode for carrying out the present invention will be described below based on examples.

As the raw material powder of the sintered hard material of the present invention, WC powder having an average particle diameter of 0.5 μm is used, and further, Cr ₂ C _{3 having} an average particle diameter of 1.4 μm, VC of 1.7 μm, and 1.1 μm, respectively. NbC was blended. The raw material powder blended with these is mixed in a carbide ball mill or resin ball mill in a methanol solvent, and after temporary press molding at 10 MPa, hot press sintering at 1700 ° C. to 2100 ° C. and 0.5 to 2 hours in a vacuum atmosphere ( After performing HP), HIP treatment of 1 to 2 hours was performed at 1500 ° C. in an Ar atmosphere, and finished to the final shape by grinding. Here, the (W, M1) ₂ C _X phase amount was adjusted by adjusting the carbon content in the material. That is, it was adjusted by adding graphite carbon or tungsten powder. And the surface roughness (Rmax) after processing of the sintered hard material obtained, the fracture toughness value (K _C ), and the integrated peak intensity ratio of (W, M1) ₂ C _X and WC (∫I ( (W, M1) ₂ C _X ) dθ / ∫I (WC) dθ) was determined, and the results are shown in Table 1 (described as HP + HIP in the production column). Here, the sample Nos. The mark with * is an example of the present invention, and the others are comparative examples. FIG. 1 shows the relationship between the fracture toughness value (K _C ) and the integrated peak intensity ratio for the examples of the present invention.

The surface roughness (Rmax) was measured using a contact type tally step manufactured by Taylor Hobson. Fracture toughness value (K _C
), A diamond indenter was applied for 5 seconds at a load of 30 kg with a Vickers hardness tester, and was calculated from the diagonal length and crack length of the resulting indentation using the following Evans formula. In addition, the average particle diameter of tungsten carbide was confirmed to be 0.5 μm or less for at least the examples from the observation of the fracture surface using a scanning electron microscope (SEM). About the amount of iron group impurities, the amount was calculated | required by the ICP emission analysis, and it confirmed that Fe, Co, and Ni total amount was less than 0.05 mass% .

_{(K C φ / Ha) =} 0.15k (c / a) -3/2 ( formula Evans)
However, Ha: Vickers hardness, E: Young's modulus, a: Indentation radius, c: Crack radius, φ = 3, k = 3.

As shown in Table 1, the integrated peak intensity ratio (∫I ((W, M1) ₂ C _X ) dθ / ∫I (WC) dθ) of (W, M1) ₂ C _X and WC is within the scope of the present invention. A comparative example of 0.5% or less, that is, sample No. For 1, 2, 13, 25, and 26, the fracture toughness value is as low as 4.0 or less. On the other hand, for the examples in which the integrated peak intensity ratio is within the range of the present invention, the measurement value of the fracture toughness value is improved to approximately 4.0 or more, although it includes some measurement error. Moreover, also about the surface roughness after a process, all the Examples of this invention are confirmed that Rmax is 7 nm or less. Sample No. No. 24 is a comparative example using a WC powder having an average particle diameter of 1.0 μm as a raw material powder, and has the same composition and an integrated peak intensity ratio of (W, M1) ₂ C _X and WC (∫I ((W, M1 ) ₂ C _X ) Sample No. _{2 in which} dθ / θI (WC) dθ) is comparable. Although the fracture toughness value is larger than 25, the surface roughness is deteriorated. This is because the average particle diameter of WC after sintering was 1.1 μm, which was larger than other samples.

In addition, as shown in FIG. 1, the sintered hard material of the present invention is (W, M1) ₂ C _X although there is a slight difference in the degree of effect from the added M1 element.
It is confirmed that the fracture toughness value (K _C ) increases as (0.8 ≦ X <1.0) increases.

  The example which applied the pulse electric current sintering (PCS) manufacturing method to this invention is demonstrated. In addition, about the result of this application example, it described together in Table 1 (it describes as PCS + HIP in the manufacturing method column).

In this example, only the sintering process and its conditions are different from the HP manufacturing method. That is, the raw material powder was mixed with a ball mill of a methanol solvent, temporarily press-molded at 10 MPa, pressed at 20 to 40 MPa in a vacuum atmosphere, and subjected to PCS sintering at 1400 ° C. to 1600 ° C. and 10 min to 60 min. A 1-2 hour HIP treatment was performed at 1500 ° C. in an Ar atmosphere and finished to the final shape by grinding. And the processing surface roughness (Rmax) of the obtained sintered hard material, fracture toughness value (K _C ), and the integrated peak intensity ratio of (W, M1) ₂ C _X and WC (∫I ((W M1) ₂ C _X ) dθ / ∫I (WC) dθ).

As shown in Table 1, even when the PCS manufacturing method is used, the integrated peak intensity ratio of (W, M1) ₂ C _X and WC (∫I ((W, M1) ₂ C _X ) dθ / ∫I ( WC) dθ) is within the scope of the present invention, it is confirmed that the fracture toughness value is 4.0 or more. Furthermore, with respect to the processed surface roughness, Rmax is 6 nm or less, which indicates that it is further superior to the HP manufacturing method.

  An example in which the sintered hard material of the present invention is applied to a lens molding die of a glass lens high-temperature molding apparatus will be described.

  A glass lens was press-molded with a lens molding die manufactured using the sintered hard material shown in Examples and Comparative Examples of the present invention shown in Table 1, and changes in the surface roughness of the glass lens were investigated.

  In a glass lens press molding test, spherical optical lens material glass is placed in the upper and lower mold cavities of a lens molding die, nitrogen with an oxygen concentration of 50 ppm is introduced through a gas inlet pipe, The mold was heated to 500 ° C. Further, after being held at a molding pressure of 2 MPa for 3 minutes, it was cooled to room temperature.

Table 2 shows the surface roughness of the obtained glass lens. From the table, the surface roughness of the glass lens molded using the example of the present invention is almost the same value as the surface roughness of the sintered hard material of the present invention shown in Table 1, respectively. It was confirmed that chipping and chipping are less likely to occur during machining into a molding die and handling during lens molding.

  The sintered hard material of the present invention has excellent mirror surface workability, wear resistance, erosion wear resistance, etc., so it can be used for molding high-precision optical elements such as lenses, prisms, and gratings used in optical equipment. In addition to ultra-precision molding dies and peripheral devices, mechanical seal rings, heat-resistant sliding members such as shaft sleeve slide bearings, injection molding molds for metals, plastics, composite materials, etc., and vacuum chucks for electronic component manufacturing equipment It can also be applied as a material.

The fracture toughness value (K _C ) of the sintered hard material of the present invention is shown.

Claims (5)

WC and second phase (W, M1) ₂ C _X
(0.8 ≦ X <1.0) containing tungsten carbide phase,
This (W, M1) ₂ C _X
(0.8 ≦ X <1.0) is a solid solution of M1, which is one or more of Cr, V, and Nb , in W ₂ C _X (0.8 ≦ X <1.0) And
This (W, M1) ₂ C _X
The integrated peak intensity of X-ray diffraction of the (−1-11) plane of (0.8 ≦ X <1.0) is expressed as ∫I ((W, M1) ₂ C _X ) dθ, and the (101) plane of WC When the integrated peak intensity of X-ray diffraction of is expressed as ∫I (WC) dθ, the integrated peak intensity ratio ∫I ((W, M1) ₂ C _X
) Dθ / ∫I (WC) dθ is Ri range der 0.5% to 10.0%,
And the sintered hard material whose content of 1 type, or 2 or more types is less than 0.05 mass% among Fe, Co, and Ni . The sintered hard material according to claim 1, wherein the M1 is two or three of Cr, V, and Nb. The sintered hard material according to claim 1 or 2 , wherein an average particle diameter of the tungsten carbide phase is 0.5 µm or less. A mold for high-precision optical element molding or injection molding , which is formed of the sintered hard material according to any one of claims 1 to 3 . The mold according to claim 4, wherein the high-precision optical element is a lens, a prism, or a grating .

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