JP2005054258A - Fine-grained cemented carbide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fine-grained cemented carbide material which is used for a small-diameter tool, has a sufficient inhibitory effect against grain growth, a sufficiently high hardness by inhibiting grain growth in a WC hard dispersed phase and a high strength at a grain boundary and is excellent in heat resistance, defect resistance and chipping resistance. <P>SOLUTION: The fine-grained cemented carbide has a metallic composition comprising, by mass, 2-13% Co and/or Ni, 0.1-3% at least one selected from Cr, V, Ta, Nb, Zr, Hf and Mo, provided that at least 0.1-1.8% Cr is contained, and the balance being W and unavoidable impurities. The hard dispersed phase essentially comprises WC and has an average particle size of ≤0.8 μm, and Cr oxide with a size of ≤100 nm is present in the hard dispersed phase. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a so-called fine cemented carbide comprising particles mainly composed of tungsten carbide having an average particle diameter of 0.8 μm or less, which is used for a small diameter tool having a blade diameter of 0.3 mm or less, particularly a small diameter drill.

A fine cemented carbide containing a WC hard dispersed phase having an average particle diameter of 1 μm or less is widely used in small diameter end mills, small diameter drills, various shearing blades and the like because of its high hardness and toughness. In recent years, as the number of finely processed products has increased, the diameter of end mills and drills has been rapidly reduced, and the average particle size of fine-grained alloys has become smaller and higher in hardness and toughness. Therefore, in order to suppress grain growth of the WC hard dispersed phase during sintering, metals such as V, Cr, Ta or their compounds (carbides, nitrides, carbonitrides, etc.) are used as grain growth inhibitors for WC. It has been proposed. As specific examples of these, Patent Documents 1 to 6 are disclosed.
In Patent Document 1, by adding V and Cr in combination, a large amount of V or Cr is not added so that a third phase that causes a reduction in the toughness of the alloy is generated, and in a 100 MPa Ar atmosphere after vacuum sintering. By performing the HIP treatment, a cemented carbide having V and Cr dissolved in the binder phase and essentially consisting of two phases, ie, a WC phase and a binder phase, and having an average WC grain size of 0.7 μm or less is obtained. It is disclosed.
In Patent Document 2, two types of V and Cr are added, pressure sintering is performed at 5.9 MPa after vacuum atmosphere sintering, and quenching is performed, whereby WC is a thin layer of precipitated composite carbide of V, W, and Cr. A cemented carbide with higher strength is disclosed by coating and eliminating the precipitation of (V, W, Cr) C in the binder phase.
In Patent Document 3, pressure sintering is performed at 4.9 to 14.7 MPa after vacuum atmosphere sintering, and rapid cooling is performed at 50 to 100 ° C./min, whereby V, W, and Cr are contained in a binder phase mainly composed of Co. A cemented carbide having a much higher strength is disclosed by finely dispersing and dispersing a hard dispersed phase composed of the precipitated composite carbide of WC and coating WC with a thin layer of the precipitated composite carbide of V, W and Cr. .
In Patent Document 4, three types of V, Cr, and TaC or (Ta, Nb) C are added, and after vacuum sintering, HIP treatment is performed at 100 MPa in an Ar atmosphere to obtain (Ta, W) C or a certain amount or less. A cemented carbide having an average particle diameter of WC of 0.6 μm or less and improved welding resistance is disclosed by precipitating a solid solution (Ta, Nb, W) C in the alloy.
Patent Document 5 describes the addition of V, Cr, Ta, pressure sintering at 5.9 MPa after vacuum atmosphere sintering, and a WC hard dispersion phase having an average particle size of 0.6 μm or less is dispersed. Disclosed is a cemented carbide that disperses solid solution particles of carbides or carbonitrides such as V, Cr, Ta, etc. in the base of the hard alloy, and prevents the decrease in the toughness of the alloy by making the maximum particle size 3 μm or less. ing.
Patent Document 6 describes a Co-based alloy containing W and C, which are constituents of a dispersed phase, further comprising a binder phase with a Co-based alloy containing V and Cr, and the remaining dispersed phase having a particle size of 100 nm in the substrate. A cemented carbide in which ultrafine particles are dispersed and distributed is disclosed.
In the prior arts disclosed in Patent Documents 1 to 6, V, Cr, and Ta are added, all of which consist of two phases, a WC phase and a binder phase, or a thin layer in which WC is made of carbide. Or a precipitate phase or a hard dispersed phase is included, and the effect when an oxide is contained has not been studied. On the other hand, as mentioned earlier, drilling work with small diameter drills has become faster and more efficient with the rapid increase in density and cost of printed circuit boards and other circuits, and frictional heat between the drill and the work material has been increased. As a result, the temperature applied to the drill itself increases, and there is a demand for a fine grain alloy for small diameter tools having higher hardness and toughness at high temperatures. For this reason, the realization of the fine grain alloy for small diameter tools excellent in heat resistance, high hardness, and high toughness is desired.

Japanese Patent No. 1539991 JP-A-11-350061 Japanese Patent No. 3291562 Japanese Patent No. 1487479 JP-A-6-81072 Japanese Patent No. 3214385

  The problem to be solved by the present invention is that it has a sufficient grain suppression effect and can sufficiently suppress the grain growth of the WC hard dispersion phase, so that the hardness is high, and the strength of the grain boundary is high. The object is to provide a fine cemented carbide material for small diameter tools having excellent chipping and chipping resistance.

  The present invention is one or two of Cr, V, Ta, Nb, Zr, Hf and Mo containing 2 to 13% by mass and Co and / or Ni and containing at least 0.1 to 1.8% of Cr. The hard dispersed phase mainly composed of WC has a metal composition consisting of 0.1 to 3% of the seed or more, the remainder being W and inevitable impurities, and the hard dispersed phase is mainly 0.8 μm or less. Is a fine cemented carbide characterized in that Cr oxide having a size of 100 nm or less is present. By adopting this configuration, since the elements contained in the alloy have a sufficient grain suppression effect, the grain growth of the WC hard dispersed phase is sufficiently suppressed, the hardness is high, and the strength of the grain boundary is high, It is possible to provide a fine cemented carbide material for small diameter tools having excellent heat resistance, chipping resistance and chipping resistance.

  By adding Cr and the like, the grain growth of the WC hard dispersed phase can be sufficiently suppressed, and a high-hardness fine cemented carbide alloy material having an average particle size of 0.8 μm or less can be realized. Moreover, in the hard phase mainly composed of WC. Furthermore, the strength of the grain boundary is increased by precipitating a Cr oxide having a size of 100 nm or less, and high toughness can be realized. As a result, it is possible to provide a fine cemented carbide material for small diameter tools with excellent wear resistance, chipping resistance, and chipping resistance even when cutting speed is increased at high speed and high efficiency. it can. For example, when a small-diameter drill for drilling a printed circuit board is produced using the fine cemented carbide material of the present invention, a small-diameter drill capable of drilling with high speed, high efficiency and high accuracy can be realized.

The present invention uses Cr ₃ C ₂ -containing WC powder prepared by solid solution and / or diffusion of Cr such as Cr, CrC, Cr ₂ O ₃ in the powder production stage, and Cr, V, Ta, Nb, Zr In addition, a predetermined amount of one or more of Hf and Mo is added to prepare a fine cemented carbide material, the average particle size is 0.8 μm or less, and the sintering conditions are devised, and 1.3 to After holding at a predetermined temperature within a range of 1330 to 1480 degrees for 0.5 to 2 hours in a vacuum atmosphere of 13.2 Pa, the atmosphere is changed to a pressurized atmosphere of pressure: 4.9 to 14.7 MPa, and this pressurized atmosphere For 15 to 60 minutes, after so-called sinter HIP treatment, Cr oxide having a size of 100 nm or less is precipitated in the hard phase by rapidly cooling to 1200 ° C. at a cooling rate of 50 to 100 degrees / min. It is possible to add Cr, etc. WC while suppressing sufficiently the grain growth of the hard dispersed phase, and a simultaneously high toughness and fracture resistance can be realized an excellent fine cemented carbide chipping resistance by. By precipitating a Cr oxide having a size of 100 nm or less in the hard dispersed phase, the strength of the interface between the WC hard dispersed phase and the binder phase or the interface of the WC hard dispersed phase is increased, and the toughness is high. In addition, it is possible to realize a fine cemented carbide material for small diameter tools having excellent hardness and toughness. This is because fine Cr oxide is precipitated between the WC hard dispersed phase and the binder phase, or at the interface between the WC hard dispersed phase, so that the oxygen concentration is moderately controlled and the strength of the interface is increased. It is considered that toughness and heat resistance are increased. In order to allow Cr oxide having a size of 100 nm or less to exist in the hard dispersed phase, it is effective to use WC powder to which Cr is added in the raw material powder production stage as a raw material and to rapidly cool after sintering HIP. Regardless of the fact, the presence of a Cr oxide having a size of 100 nm or less in the hard dispersed phase increases the strength of the interface between the WC hard dispersed phase and the binder phase or the interface of the WC hard dispersed phase. Is important. The presence of Cr oxide having a size of 100 nm or less in the WC hard dispersed phase means that a fine cemented carbide alloy is observed at 125 k times with a transmission electron microscope (hereinafter referred to as TEM), and a TEM apparatus is used. This can be confirmed by analyzing the composition with an attached energy dispersive X-ray analyzer (hereinafter referred to as EDX). When the microstructure of the fine cemented carbide of the present invention is observed at a magnification of 125 k by TEM, the proportion of Cr oxide having a size of 100 nm or less in the hard dispersed phase is 1 to 5 in 50 views. Therefore, further excellent toughness can be obtained.

  Next, the reason for the numerical limitation will be described. When the Cr content of the entire alloy is less than 0.1%, the growth of the WC hard dispersion phase proceeds during sintering, and the average particle size exceeds 0.8 μm, resulting in the disadvantage that wear resistance and toughness are reduced. On the other hand, if it exceeds 1.8%, the Cr content in the binder phase is excessively increased, resulting in a drawback that the toughness is lowered. Therefore, the Cr content is 0.1 to 1.8%. In addition, when one or more of Cr, V, Ta, Nb, Zr, Hf, and Mo is less than 0.1%, the growth of the WC hard dispersed phase proceeds during sintering and wear resistance is increased. When the toughness is lowered and the heat resistance is lowered, the disadvantage is that if it exceeds 3%, the precipitation of the additive compound is increased and the toughness is lowered. Therefore, Cr is essential, and the content of one or more of Cr, V, Ta, Nb, Zr, Hf, and Mo is 0.1 to 3%. In addition, when the average particle size of the hard dispersed phase mainly composed of WC exceeds 0.8 μm, the hardness and toughness of the fine-grain cemented carbide are greatly reduced, and the wear resistance and fracture resistance are insufficient. Therefore, the average particle size of the hard dispersed phase made of WC is set to 0.8 μm or less.

As the raw material powder, a WC powder containing Cr ₃ C ₂ and having an average particle diameter of 0.8 μm prepared by dissolving and / or diffusing Cr in the powder production stage was used. The amount of Cr ₃ C ₂ contained in the WC powder is six types of 0.1, 0.3, 0.5, 0.7, 0.9, and 1.1%. Also, Cr ₃ C ₂ powder with an average particle size of 1.5 μm, VC powder with 0.9 μm, TaC powder with 1.2 μm, NbC powder with 2 μm, ZrC powder with 2.3 μm, 1.5 μm HfC powder, 1.5 μm Mo ₂ C powder and Co powder were prepared, these raw material powders were blended into a predetermined composition, mixed for 12 hours with an attritor, dried under reduced pressure, and then added with wax and solvent. After mixing for 1 hour, long shaped bodies having a diameter of 2.5 mm were prepared by an extrusion molding machine, and after dewaxing these long shaped bodies, in a vacuum atmosphere of 1.3 to 13.2 Pa, After holding at a predetermined temperature within a range of 1330 to 1480 ° C. for 0.5 to 2 hours, the atmosphere is changed to a pressurized atmosphere of pressure: 4.9 to 14.7 MPa, and after holding in this pressurized atmosphere for 15 to 60 minutes, Up to 1200 ° C, 50-100 ° C / min By cooling rapidly at a cooling rate, a long sintered material having a diameter of 2 mm made of a fine cemented carbide was produced. The Cr ₃ C ₂ powder having an average particle size of 1.5 μm was used when the Cr ₃ C ₂ amount was insufficient with the Cr-containing WC powder alone. The composition of the long sintered material was quantitatively analyzed with a fluorescent X-ray apparatus, and the contents of W, Co, Cr, V, Ta, Nb, Zr, Hf and Mo were measured. The average crystal grain size was determined by mirror-polishing the cross section of the sintered material, then clarifying the grain boundaries by etching with Murakami's reagent for 0.5 minutes and aqua regia for 0.5 minutes, and then using a scanning electron microscope (Hereinafter referred to as SEM), an image taken at a magnification of 10 k was enlarged and copied, and this was calculated by analyzing it with an image analyzer. Further, whether or not the fine cemented carbide material is mainly composed of a binder phase composed of Co and a hard dispersed phase, and Cr oxide having a size of 100 nm or less exists in the hard dispersed phase, is determined by TEM. The field of view was observed 50 times, and evaluation was performed by measuring the composition of each region by EDX. Table 1 summarizes the composition of the present invention material and the average particle diameter of the hard phase mainly composed of WC and the number of fields of view in which Cr oxide having a size of 100 nm or less was observed in the hard dispersed phase. It was. As an example of observation of Cr oxide, FIG. 1 shows a TEM image of Cr oxide observed in Example 10 of the present invention. The results of EDX analysis of the fine particles were, by mass, Cr: 71.8%, O: 4.2%, W: 20.1%, Co: 3.9%. In addition, for the purpose of comparison, the furnace is cooled at a cooling rate of about 10 ° C./min after holding the sintering condition at a predetermined temperature in the range of 1350 to 1480 ° C. for 1.5 hours in a vacuum atmosphere of 6.6 Pa. Thus, a comparative example was prepared. Table 1 shows the characteristics of the comparative example evaluated under the same conditions as the examples of the present invention. Although all of the comparative examples were mainly composed of a binder phase made of Co and a hard dispersed phase, fine particles having a Co component of about 50% were found when observed with a TEM at 125k magnification, but Cr oxidation of 100 nm or less was observed. Nothing was found.

  Three long blades each having a shank diameter of 2.0 mm and a cutting edge diameter of 0.1 mm were produced using the long sintered material produced from the inventive examples and comparative examples. Using this, two glass epoxy plates with high-Tg (Tg is the glass transition temperature) 0.2mm-thick double-sided Cu were stacked on the condition of a rotational speed of 250,000 / min and a feed of 0.01mm / rev. A drilling test was conducted. This condition is a cutting condition where the cutting edge temperature tends to be higher at a higher speed. The smaller of the number of holes drilled until 5% wear occurred on the outer diameter of the outer peripheral blade or the number of holes drilled until breakage was measured, and the average of the three holes was defined as the average drilling life. Table 1 also shows the results of measuring the average drilling life of each small-diameter drill produced from the inventive examples and the comparative examples.

  From the results shown in Table 1, each of Inventive Examples 1 to 18 had at least one visual field in 50 visual fields and a Cr oxide having a size of 100 nm or smaller in the hard dispersed phase, whereas In Comparative Examples 19 to 36, no visual field was observed. Comparing the drilling life of the small diameter drills produced using the inventive examples 1 to 18 and the comparative examples 19 to 36, the present invention was found to have almost the same composition and the particle size of the WC hard dispersed phase. The small diameter drill produced using the example is 1.5 times or more superior to the comparative example. For example, the drilling life of Comparative Example 33 is 1080 holes, while Inventive Example 15 is 1650 holes, 1.53 times better than the Comparative Example. Further, in the present invention example, a Cr oxide having a size of 100 nm or less was observed in 6 out of 50 views in the hard dispersed phase, despite the same Co amount and WC hard dispersed phase particle size. The drilling life of Invention Example 13 is 1700 holes, whereas the drilling life of Invention Example 12 observed only in 5 out of 50 fields is 2580 holes, which is 1.5 times better. I understood.

FIG. 1 shows a photograph obtained by TEM observation of the alloy structure of the example of the present invention at a magnification of 500 k.

Explanation of symbols

  1: Cr oxide

Claims (1)

One or more of Cr, V, Ta, Nb, Zr, Hf, and Mo containing Co and / or Ni in an amount of 2 to 13% and at least Cr in an amount of 0.1 to 1.8% are 0% by mass. 0.1 to 3%, the balance is W and inevitable impurities, and the hard dispersed phase mainly composed of WC has an average particle size of 0.8 μm or less, and the hard dispersed phase has a size of A fine-grain cemented carbide comprising Cr oxide of 100 nm or less.