JP2006152409A - Cemented carbide for die and die - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cemented carbide for a die having high wear resistance, and in which a deterioration layer by wire electric discharge machining is made thin as possible, and whose chipping resistance is high. <P>SOLUTION: The cemented carbide is composed of a bonding phase, and a hard phase with inevitable impurities. The bonding phase is composed of Co in, by weight, 6 to 20% to the cemented carbide, Cr in 3 to 15% to the total content with Co, V in 2.5 to 5.0%, and Mo in 1.0 to 5.0%. Then, the hard phase is composed of fine particles and WC of coarse particles, the ratio of the fine particles with a mean particle diameter of 0.3 to 0.6 μm is 60 to 90% of the hard phase, and the ratio of the coarse particles with a mean particle diameter of 0.8 to 2.5 μm is 10 to 40% of the hard phase. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a cemented carbide and a mold for a mold excellent in corrosion resistance, wear resistance, and fracture resistance. In particular, the present invention relates to a cemented carbide having a low affinity with a copper-based metal and suitable for punching a copper-based metal or the like.

  Cemented carbides are (1) harder and harder to wear than tool steel and die steel, (2) less elastic and plastic deformation, (3) excellent heat dissipation characteristics, (4) low coefficient of thermal expansion It is highly evaluated as a mold material that has many features such as

  Wire electrical discharge machining is widely used for the manufacture of cemented carbide molds. At that time, water may be used as a working fluid, and the cemented carbide for the mold is required to have corrosion resistance. In addition, since it is used as a mold, the cemented carbide is required to have high wear resistance and fracture resistance.

  For such a cemented carbide mold, the techniques described in Patent Documents 1 to 4 are known.

  Patent Document 1 discloses a cemented carbide alloy that satisfies both good corrosion resistance during electric discharge machining, good wear resistance when using a mold, and fracture resistance at the same time. In this technology, the corrosion resistance is enhanced by the addition of Cr and Ni. Further, the WC particles are used by mixing fine particles and coarse particles within an average particle diameter of 0.8 to 3 μm, thereby improving the fracture resistance.

  Patent Document 2 discloses a cemented carbide alloy that simultaneously exhibits excellent corrosion resistance and chipping resistance to water-soluble lubricants. In this technology, the amount of V and Cr added to (Co + Ni) is limited to precipitate the carbide phase of V and Cr to improve the corrosion resistance, and the average particle diameter of WC is set to more than 0.7 μm and less than 6 μm. Chipping is improved.

  Patent Document 3 discloses a cemented carbide that extends the life of a mold used for stamping a workpiece of copper or a copper-based alloy. When copper or copper alloy is used as the work material, the high affinity between Co and copper in the cemented carbide, so the mutual diffusion between the cemented carbide and the copper or copper alloy due to the friction generated during punching Occurs. As a result, the action of the binder phase that holds WC that affects the hardness of the cemented carbide becomes fragile, and the WC particles fall off the cemented carbide. Therefore, in this technique, Ni—Co is used as a binder phase, the content of Ni having low affinity with copper is specified, and the reaction between copper and the binder phase is minimized. Furthermore, by using fine WC particles of 0.5 μm or less, stress concentration is relaxed as a uniform fine structure, and WC particles are prevented from falling off the cemented carbide.

  Patent Document 4 discloses a cemented carbide mold part that is excellent in impact resistance, wear resistance, and bending strength, and is particularly suitable for a punching die. This technology ensures impact resistance and wear resistance by setting the average particle size of WC to 2.5 to 4.5 μm. Further, the impact resistance is maintained by limiting the content of fine WC particles having a particle size of less than 1 μm, and the bending strength is maintained by limiting the content of coarse WC particles having a particle size of more than 6 μm.

JP 2003-155538 A JP-A-8-337837 JP-A-6-287675 JP 11-124649 A

  However, any of the above cemented carbides is still insufficient with respect to having corrosion resistance, wear resistance, and fracture resistance.

  Conventional mold production relies on hand finishing by skilled workers with a high degree of skill as the final finish after machining cemented carbide by machining or wire electrical discharge machining. On the other hand, a manufacturing technique that eliminates grinding and polishing for finishing the processed surface is required due to the rapid increase in accuracy of recent wire electrical discharge machining and the request for shortening the delivery time from the mold user. However, a cemented carbide having sufficient corrosion resistance, wear resistance, and fracture resistance has not been obtained even if grinding and polishing by hand finishing are omitted.

  For example, all of the techniques described in Patent Documents 1, 2, and 4 use WC having a large particle diameter of more than 0.7 μm. When the particle size of the WC of the cemented carbide is large, the fracture resistance (chipping resistance) and impact resistance are improved, but the wear resistance is inferior. In particular, there is a problem that wear due to reaction with the workpiece tends to occur, and it is difficult to keep the corners of precision molds sharp.

  On the other hand, the technique described in Patent Document 3 suppresses mutual diffusion of copper and a binder phase when stamping copper or a copper-based alloy by adding Ni, Cr, V, or the like. However, fine particles having a particle size of 0.5 μm or less are used as the WC particles, and the wear resistance is excellent, but the fracture resistance is not sufficient.

  The present invention has been made in view of the above circumstances, and its main purpose is high wear resistance and corrosion resistance. Further, when wire electric discharge machining is performed, it is excellent in chipping resistance of the machined surface. It is to provide a hard alloy.

  Another object of the present invention is to provide a mold having excellent wear resistance, corrosion resistance, and fracture resistance.

  The present invention achieves the above object by adding a predetermined amount of Cr, V, and Mo to the binder phase and mixing and using predetermined fine particles and coarse particles in the hard phase.

  As a result of investigating the problems of the conventional cemented carbide in order to develop a cemented carbide that meets the new requirements, the present inventors have obtained the following knowledge.

(1) In a conventional cemented carbide, there is an altered layer having a certain thickness on the cut surface of the wire electric discharge machining.
(2) The altered layer is (A) a corrosion layer caused by electrochemical corrosion, (B) an embrittlement layer containing fine cracks, and (C) copper contained in the cut wire diffuses into the cemented carbide. The diffusion layer formed mainly is the main one.
(3) Fine cracks in the deteriorated layer gradually develop with use of the mold and cause chipping.
(4) When a copper-based material is punched with a metal mold, copper and Co, which is a binder phase, diffuse to each other and WC, which is a hard phase, easily falls off.

  Based on the above findings, the present invention has been completed as a result of various studies aimed at achieving both wear resistance and fracture resistance and suppressing the generation of a deteriorated layer as much as possible.

  That is, the cemented carbide for the mold of the present invention is a cemented carbide composed of a binder phase, a hard phase, and inevitable impurities. The binder phase is 6 to 20% by weight Co (hereinafter referred to as%) with respect to the cemented carbide, 3 to 15% Cr with respect to the total amount of Co, 2.5 to 5.0% V, and 1.0 to 5.0. % Of Mo. The hard phase is composed of fine particles and coarse particles of WC, fine particles having an average particle size of 0.3 to 0.6 μm are 60 to 90% of the hard phase, and coarse particles having an average particle size of 0.8 to 2.5 μm are hard. It is characterized by 10-40% of the phase.

  By adding a certain amount of Cr, V, and Mo to the binder phase, corrosion resistance, suppression of hard phase particle growth, suppression of reaction with the work material is achieved, and predetermined fine particles and coarse particles are added to the hard phase. By using a mixture, it is possible to achieve both wear resistance and fracture resistance.

  6-20% by weight of Co is used for the binder phase of the alloy of the present invention. If the amount of Co is less than 6%, the bending strength and fracture toughness value are lowered, which is not preferable. On the other hand, if it exceeds 20%, the hardness decreases, and therefore the wear resistance decreases. The amount of the binder phase can balance the bending strength, fracture toughness value, wear resistance and corrosion resistance.

  Cr has an effect of improving corrosion resistance, and if it is less than 3% with respect to the total amount of Co, sufficient corrosion resistance cannot be obtained. On the other hand, if it exceeds 15%, the bending strength is lowered and the fracture resistance is inferior. Addition of Cr can be expected to improve the corrosion resistance of the acid machining fluid used in the wire electric discharge machining fluid. The more preferable content of Cr is 5 to 12% with respect to the total amount of Co. Thereby, corrosion resistance, bending strength, and fracture resistance are more preferable ranges.

  V has a function of suppressing WC grain growth. Therefore, it can suppress that the hard phase of a fine particle grows at the time of sintering, and becomes a coarse particle. If it is less than 2.5% of the total amount of Co, the effect of suppressing grain growth of WC cannot be obtained. On the other hand, if it exceeds 5.0%, the bending strength is reduced due to precipitation of a carbide phase containing V, such being undesirable. A more preferable content of V is 3 to 4% with respect to the total amount of Co. Thereby, it becomes a more preferable range in which the balance between the grain growth inhibiting effect of WC and the bending strength is balanced.

  Mo has low wettability with respect to Cu, and when contained in an appropriate amount, the reaction with the workpiece can be suppressed. Mo has a function of suppressing copper diffusion, and if it is less than 1.0% with respect to the total amount of Co, the effect of suppressing reaction with the workpiece cannot be obtained. On the other hand, if it exceeds 5.0%, the bending strength is lowered, which is not preferable. A more preferable content of Mo is 1.5 to 3.0% with respect to the total amount of Co. Thereby, the reactivity with Cu is suppressed and the bending strength becomes a more preferable range.

  On the other hand, the hard phase uses both fine particles and coarse particles as WC particles. By using fine particles, the wear resistance of the cemented carbide can be improved, and by using coarse particles, the resistance to the progress of cracks in the cemented carbide can be increased, and the fracture resistance and toughness can be improved. In particular, when a die is produced by wire electric discharge machining of the cemented carbide of the present invention, fine cracks occur on the machined surface, but coarse particles can suppress the development of fine cracks when the die is used. .

  The crack suppression mechanism is estimated as follows. FIG. 1 is an explanatory view showing the progress of cracks in a cemented carbide. In this figure, the cemented carbide is composed of WC fine particles 1, coarse particles 2 and a binder phase 3. As for the form of cracks, cracks in the bonded phase 4 that propagate only in the bonded phase 4, cracks 5 in the WC that propagate in the WC particles and the bonded phase, bonded phases that pass through the interface between the bonded phase and WC- It can be classified as WC grain boundary crack 6. When the particle size of WC is small, cracks pass through the binder phase-WC grain boundary or bypass the WC particles. Therefore, any of cracks in the binder phase crack 4, the WC crack 5, and the binder phase-WC grain boundary crack 6 is likely to occur. On the other hand, when the grain size of WC is large, the cracks in the binder phase 4 and the binder phase-WC grain boundary cracks 6 that are going to propagate hit the coarse WC particles, and the WC cracks 5 are not generated. Since the particles are large, the crack growth is stopped. As a result, it is considered that the fracture resistance can be improved.

  To achieve both the above-mentioned wear resistance and fracture resistance, specifically, fine particles having an average particle size of 0.3 to 0.6 μm are 60 to 90% of the hard phase and coarse particles having an average particle size of 0.8 to 2.5 μm. A hard phase containing 10 to 40% of the hard phase is used.

  Such fine particles contribute to improvement of wear resistance and strength of the cemented carbide. In addition, since the particle spacing can be reduced to reduce the thickness of the binder phase, mutual diffusion between the workpiece and the binder phase can also be suppressed. Furthermore, since the particle size is small, the edge of the mold can be processed more sharply when processed into a mold.

  If the average particle size of the fine particles is smaller than 0.3 μm, the fracture toughness value is lowered, so that cracks are likely to develop at the time of mold production, and chipping resistance at the time of mold use is also unfavorable. On the other hand, if it exceeds 0.6 μm, the hardness decreases and the wear resistance is poor.

  On the other hand, coarse particles contribute to the prevention of crack propagation during mold manufacture and mold use. If the particle size of the coarse particles is smaller than 0.8 μm, the fracture toughness value becomes low, and a sufficient crack growth preventing effect cannot be obtained. On the other hand, if it is larger than 2.5 μm, the hardness is inferior and the wear resistance is inferior, and the gap between the particles is increased and the thickness of the binder phase is increased, so that the effect of suppressing reaction with the workpiece cannot be obtained. Furthermore, when manufacturing the mold, particularly when performing precision machining, it becomes difficult to sharpen the edge of the mold, and precise dimensional accuracy cannot be obtained.

  The composition ratio of the fine particles and coarse particles described above indicates that if the fine particles are larger than 90% and the coarse particles are smaller than 10%, the fracture toughness value is lowered and the crack growth resistance suppressing effect cannot be obtained, and chipping resistance is not obtained. It is not preferable because of poor properties. On the other hand, if the number of fine particles is less than 60% and the number of coarse particles is more than 40%, the hardness decreases and wear resistance cannot be obtained, which is not preferable.

  Hereinafter, more preferable ranges of the present invention will be described in detail.

  In the cemented carbide of the present invention, a part of Co in the binder phase may be replaced with Ni. The Ni content is up to an amount equal to the Co content. Ni is an element having higher corrosion resistance than Co and has higher corrosion resistance. In addition, Ni has a good compatibility with Cr, and it is effective to contain Ni in the above specified amount in order to dissolve more Cr. As described above, Cr also has a function of improving the corrosion resistance. However, the addition of Cr increases the corrosion resistance especially against acids. If Ni is larger than the amount of Co with respect to the total amount of Co and Ni, the bending strength is lowered, which is not preferable.

  When a part of Co is replaced with Ni, the “total amount of Co” which is a reference for the content of Cr, V, and Mo is also replaced with “total amount of Co and Ni”. That is, Cr, V, and Mo may be contained in amounts of 3 to 15%, 2.5 to 5.0%, and 1.0 to 5.0%, respectively, with respect to the total amount of Co and Ni.

  More preferable hard phase particle size and composition ratio are such that fine particles having an average particle size of 0.4 to 0.6 μm are 70 to 85% of the hard phase, and coarse particles having an average particle size of 1.0 to 2.0 μm are 15 to 30%. This is because the effect of mixing coarse particles and fine particles is better exhibited by this configuration.

  On the other hand, a more preferable binder phase amount is 8 to 14% with respect to the cemented carbide. It can be a cemented carbide having both superior wear resistance and fracture resistance.

  Moreover, this invention metal mold | die consists of said invention cemented carbide alloy, and is finish-processed by wire electric discharge machining, It is characterized by the above-mentioned. It has already been mentioned that wire electric discharge machining is used when making molds. However, the cemented carbide of the present invention has a good balance of corrosion resistance, wear resistance, and fracture resistance, so it is finished by wire electric discharge machining. Used as a mold.

  In particular, a mold composed of the cemented carbide of the present invention can be used as a mold as it is after being finished by wire electric discharge machining. Since the cemented carbide of the present invention is excellent in corrosion resistance and crack growth suppressing properties, the deteriorated layer can be thinned to the micron order. Therefore, it can be used as a mold without removing the corrosive layer by wire electric discharge machining fluid, which has been done manually by skilled workers, and removing the brittle layer including fine cracks by wire electric discharge machining. Can do.

  Copper or copper alloy can be considered as a suitable processing object of this metal mold | die. More specifically, a tie bar cut punch is constituted by the alloy of the present invention and used for lead processing of a semiconductor element. Since the alloy of the present invention is excellent in resistance to copper, even if it is used in a mold for processing copper or a copper alloy, the binder phase can be prevented from reacting with copper to form a deteriorated layer, resulting in a long life. Can be used as a mold.

The cemented carbide of the present invention can exhibit the following effects.
(1) By adding appropriate amounts of Cr, V, and Mo, it is possible to achieve mainly corrosion resistance, suppression of grain growth, and suppression of reaction with the workpiece.
(2) By using a mixture of predetermined fine particles and coarse particles in the hard phase, both wear resistance and fracture resistance can be achieved.

Moreover, this invention metal mold | die can have the following effects.
(1) By using the cemented carbide of the present invention, it is possible to obtain a mold having a balanced balance of corrosion resistance, wear resistance, and fracture resistance.
(2) By using a binder phase having low reactivity with the workpiece and a hard phase containing fine particles, a mold having sharp corners can be obtained.
(3) Since the deteriorated layer is extremely small, it can be used as a mold while being subjected to wire electric discharge machining.

  Embodiments of the present invention will be described below.

  WC powder with various average particle size and Co powder with average particle size of 1.3μm, Ni powder with average particle size of 3μm, Cr powder with average particle size of 7μm, VC powder with average particle size of 1.6μm and average particle size of 0.9μm Mo powder was prepared. These powders were weighed so as to have the composition shown in Table 1, and charged together with cemented carbide balls into an attritor, mixed and pulverized to prepare raw material powders. In Table 1, the Co and Ni columns show the proportion of Co and Ni in the starting material in weight percent. Further, the contents of Cr, V and Mo are shown by weight% with respect to “Co + Ni”. When Ni is not included, it is shown as a percentage of Co. In addition, since a part of what was added with VC powder was dissolved in Co + Ni as the metal component V and exhibited the effect of addition, Table 1 shows the content by the value of V / (Co + Ni). .

  The adjusted raw material powder was pressure-molded to produce a powder compact, which was sintered by holding it at 1400 ° C. in a vacuum for 1 hour. Furthermore, it was kept at 1320 ° C. for 1 hour in an argon gas of 98 MPa and subjected to HIP treatment to obtain the present inventions of sample numbers 1-1 to 1-5 and comparative examples 2-1 to 2-7. The obtained sintered body was ground and finished to 12.5 × 12.5 × 4 mm.

  The hardness, bending strength, fracture toughness value, and acid corrosion layer thickness of the obtained sintered body were measured, and the results are shown in Table 2. In this, the corrosion layer was measured as follows. 12.5 × 12.5mm surface of sintered body was lapped with diamond paste # 3000, immersed in PH3.5 solution and immersed at 60 ° C for 36 hours ("PH3.5" in Table 2), and PH5.5 A solution ("PH5.5" in Table 2) was prepared by dipping in the solution and holding at 40 ° C for 59 hours. As the machining fluid used for wire electric discharge machining, a highly acidic one having a pH of 3.5 to 5.5 is used, and the corrosion resistance was examined under the above conditions. The thickness of the corrosion layer from the 12.5 × 12.5 mm lapping surface of the sample thus obtained was measured. Specifically, the wrapping surface was cut with a surface having a certain angle, the cut surface was lapped, and the thickness of the corrosion layer was measured with a microscope.

  Further, the specimen for measuring the bending strength shown in Table 2 was a size of 4 × 5 × 25 mm obtained by grinding each side surface of the sintered body. FIG. 2 is a front view for explaining a method for measuring the bending strength. Supporting round bars 13 are installed at predetermined intervals, and the bending test piece 10 is placed thereon. Next, the bending force was measured by applying pressure until the bending test piece 10 was broken by the presser 14 disposed on the bending test piece 10. In FIG. 2, 11 indicates a wire electric discharge machining surface and 12 indicates a grinding surface. In this embodiment, both 11 and 12 are grinding surfaces. The hardness and fracture toughness values were measured by a conventionally known method.

  Sample Nos. 1-1 to 1-5 and 2-6, in which appropriate amounts of Cr and V are added with WC powder having an average particle size of 0.5 μm, maintain high levels of hardness and bending strength. However, when looking at the thickness of the corrosion layer of PH3.5, sample numbers 1-1 to 1-5 of the present invention are as thin as 4.5 to 8.3 μm and high in corrosion resistance, whereas sample number 2-6 is PH5 Up to .5, it was not inferior to the sample of the present invention, but it was clearly found that the corrosion resistance was inferior at PH 3.5.

  Next, the relationship between the conditions of wire electric discharge machining and the thickness of the altered layer was examined. A plurality of 4 × 5 × 25 mm ground samples were prepared under the same conditions as Sample Nos. 1-3, 2-3, and 2-6 of Example 1. Next, a surface of 5 × 25 mm was machined by 10 μm or more by wire electric discharge machining by the method shown in FIG. 3 to be described later, the influence of the ground surface was removed, and the influence of only wire electric discharge machining was left on the surface.

  FIG. 3 is an explanatory diagram of a machining method by wire electric discharge machining. The bending test piece was horizontally and vertically placed with the upper right corner of the bending test piece 10 as the origin, the -X axis direction was the longitudinal direction of the bending test piece, and the -Y axis direction was the thickness direction. The electric discharge machining wire 20 was set in the Z-axis direction at the upper right of the origin, that is, X = 0.5 mm and Y = 0.01 mm on the coordinates. Move the bending test specimen 10 and the wire 20 relatively in the -X-axis direction, wire-discharge machining the bending test specimen over the entire length, and then move it in the -Y-axis direction to the position where the sample is cut. Then, it was moved in the X-axis direction and wire EDM was performed. Such a process was repeated to remove the grinding effect from the surface of the bending test specimen, leaving only the influence of wire electric discharge machining.

  The wire electric discharge machining was performed under the four conditions described in Table 3. Since the conditions of wire electric discharge machining are complicated, the machining conditions are shown in Table 4 by the surface roughness of the machined work material. Specifically, FS3 power supply for fine finishing was used for processing condition 1, and FM power supply for fine finishing was used for processing condition 2. For processing conditions 3 and 4, an FS4 power source capable of microfabrication was used. In processing condition 4, the applied voltage was lower than in processing condition 3, and processing was performed under conditions that resulted in further fine finishing.

  Next, the thickness of the deteriorated layer by wire electric discharge machining was measured by the method shown below. First, the bending strength of the sample ground on the whole surface is measured. Next, one of the 5 × 25 mm surfaces of the sample was subjected to wire electric discharge machining, the surface was ground at a constant thickness, and the bending strength was measured by the method shown in FIG. 2 each time. At this time, the measurement was performed such that the influence of the processed surface was reflected in the strength with the wire electric discharge processed surface facing down. Then, the graph shown in FIG. 4 was prepared, and the grinding amount when the bending force equivalent to the bending force of the sample ground on the whole surface was obtained was calculated and listed in Table 3.

  FIG. 4 is a graph showing the grinding amount on the horizontal axis and the bending force on the vertical axis, and the bending force 30 of the entire ground sample is indicated by a dotted line. Then, the bending strength 31 when the wire-discharge processed surface is ground to remove the deteriorated layer is measured and written on the graph. This operation was repeated, and when the bending strength was the same as the bending strength 30 of the whole ground sample, it was judged that the deteriorated layer was completely removed, and this was defined as the thickness of the deteriorated layer. In the case of the graph shown in FIG. 4, the thickness of the altered layer can be about 6 μm.

  As is clear from the processing conditions 3 and 4 in Table 3, when the electric discharge machining is performed on the cemented carbide of the present invention under the processing conditions such that the surface roughness is 1 μm or less, the thickness of the surface damaged layer becomes about 1 μm. . If the thickness of the deteriorated layer is suppressed to such a thickness, the surface subjected to wire electric discharge machining can be used as it is as a mold surface without grinding. However, the thickness of the deteriorated layer of the conventional cemented carbide does not become smaller than 2 μm even if wire electric discharge machining is performed under the condition that the surface roughness is reduced. Therefore, the wire electric discharge machining surface cannot be a finished surface.

  Using the same material as Sample Nos. 1-3, 2-3, and 2-6 of Example 1, a tie bar cutting punch for a resin-sealed lead frame was manufactured. At this time, the tip of the punch was subjected to wire electric discharge machining using water as a machining liquid. Table 4 shows the amount of wear of the punch when a resin-encapsulated lead frame was shot with 100,000 shots and 1 million shots using a wire-discharge-processed die. The lead frame was a copper alloy containing 99% or more of copper.

  Sample No. 2-3 was so worn that 1 million shots could not be made. The hard phase of Sample No. 2-3 is only coarse particles and does not contain fine WC particles. For this reason, it is inferior in wear resistance, and is prone to wear due to reaction with the workpiece. The hard phase of Sample No. 2-6, on the contrary, has only fine particles and no coarse particles, so it has high wear resistance but is inferior in chipping resistance, resulting in 20 μm wear. Sample Nos. 1 to 3 of the present invention had only 10 μm of wear even after 1 million shots, and had excellent wear resistance.

  Next, the affinity between copper and cemented carbide was examined. Specifically, two samples were produced, in which a 99.9% pure copper plate was sandwiched between polished cemented carbides. Each of these was held in air at 900 ° C. for 30 minutes and in vacuum at 900 ° C. for 10 hours to examine the diffusion of copper into the cemented carbide. Next, the sample was taken out, the cemented carbide was cut, the cross section was polished, and the thickness of the diffusion layer formed by the reaction between the cemented carbide binder phase and copper was measured. This measurement was performed by SEM observation of the cross section. Table 5 shows the measurement results.

  It can be seen that the diffusion layer of Sample 1-1 of the present invention is much thinner than Sample No. 2-6, which is a comparative example, in the air or in vacuum. Therefore, it can be said that the cemented carbide of the present invention has low reactivity with copper and low affinity with cut wires.

  Since the cemented carbide of the present invention has high chipping resistance and high wear resistance, it is expected to be used as a stamping die for machine parts and copper alloys in addition to ordinary dies. In particular, it can be suitably used for parts that require corrosion resistance, mold parts that are finished by electrical discharge machining, machine parts, and the like.

The cemented carbide of the present invention is a schematic cross-sectional view for explaining that the structure has a structure in which cracks hardly develop. It is a front view explaining the measuring method of a bending strength. It is explanatory drawing of the processing method by wire electric discharge machining. It is a graph which shows the relationship between grinding amount and bending strength.

Explanation of symbols

1 WC fine particles 2 WC coarse particles
3 Bond phase 4 Crack in bond phase
5 Cracks in WC 6 Bonded phase-WC grain boundary cracks
10 Folding specimen 11 Wire EDM surface
12 Grinding surface 13 Support round bar
14 Presser
20 wires
30 Folding force of whole surface grinding sample
31 Folding force when the altered layer is removed

Claims (6)

A cemented carbide alloy for molds composed of a binder phase, a hard phase and inevitable impurities,
The binder phase is
6 to 20% by weight (hereinafter referred to as%) of Co with the cemented carbide,
Consists of 3 to 15% Cr, 2.5 to 5.0% V, and 1.0 to 5.0% Mo with respect to the total amount of Co,
The hard phase is
Consists of WC of fine particles and coarse particles,
Ultra-die for molds characterized in that fine particles with an average particle size of 0.3-0.6 μm are 60-90% of the hard phase and coarse particles with an average particle size of 0.8-2.5 μm are 10-40% of the hard phase Hard alloy. A portion of Co in the binder phase is replaced with Ni;
The Ni content is up to an amount equal to the Co amount,
The cemented carbide for mold according to claim 1, wherein Cr, V, and Mo are contained in amounts of 3 to 15%, 2.5 to 5.0%, and 1.0 to 5.0%, respectively, based on the total amount of Co and Ni. alloy.   The hard phase is characterized in that fine particles having an average particle diameter of 0.4 to 0.6 μm are 70 to 85% of the hard phase, and coarse particles having an average particle diameter of 1.0 to 2.0 μm are 15 to 30% of the hard phase. The cemented carbide for molds according to claim 1 or 2.   The cemented carbide for molds according to any one of claims 1 to 3, wherein the amount of the binder phase is 8 to 14% with respect to the cemented carbide.   A mold comprising the cemented carbide for a mold according to any one of claims 1 to 4, and being finished by wire electric discharge machining.   6. The mold according to claim 5, wherein the workpiece of the mold is copper or a copper alloy.

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