US20210230729A1 - Method of strengthening binder metal phase of sintered body - Google Patents

Method of strengthening binder metal phase of sintered body Download PDF

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Publication number
US20210230729A1
US20210230729A1 US17/001,351 US202017001351A US2021230729A1 US 20210230729 A1 US20210230729 A1 US 20210230729A1 US 202017001351 A US202017001351 A US 202017001351A US 2021230729 A1 US2021230729 A1 US 2021230729A1
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particles
hardness
ejection
sintered body
binder metal
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Yoshio Miyasaka
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Fuji Kihan Co Ltd
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Fuji Kihan Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/24—After-treatment of workpieces or articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/12—Both compacting and sintering
    • B22F3/16—Both compacting and sintering in successive or repeated steps
    • B22F3/164—Partial deformation or calibration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
    • B24C1/00—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods
    • B24C1/10—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods for compacting surfaces, e.g. shot-peening
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/04—Making non-ferrous alloys by powder metallurgy
    • C22C1/05—Mixtures of metal powder with non-metallic powder
    • C22C1/051—Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C26/00—Alloys containing diamond or cubic or wurtzitic boron nitride, fullerenes or carbon nanotubes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
    • C22C29/02—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides
    • C22C29/06—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/12—Both compacting and sintering
    • B22F3/16—Both compacting and sintering in successive or repeated steps
    • B22F3/164—Partial deformation or calibration
    • B22F2003/166—Surface calibration, blasting, burnishing, sizing, coining
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
    • C21D7/04—Modifying the physical properties of iron or steel by deformation by cold working of the surface
    • C21D7/06—Modifying the physical properties of iron or steel by deformation by cold working of the surface by shot-peening or the like
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon

Definitions

  • the present invention relates to a method for strengthening a phase of a binder metal (referred to as a “binder metal phase” in the present invention) in a sintered body in which hard particles of a carbide, oxide, nitride, boride, silicide, or the like are sintered together with a binder metal such as Fe, Ni, or Co, such as in a cemented carbide, a cermet, or cBN.
  • a binder metal phase such as Fe, Ni, or Co
  • the cemented carbide is configured by fine particles (normal particles of cemented carbide have a particle diameter of a few ⁇ m, and ultrafine particles of cemented carbide have a particle diameter of from about 0.5 ⁇ m to about 0.8 ⁇ m) of a carbide (WC, TiC, TaC) of a metal such as tungsten (W), titanium (Ti), Tantalum (Ta) sintered together using as a binder a metal such as iron (Fe), nickel (Ni), or cobalt (Co).
  • cemented carbide sometimes refers to only WC—Co based alloys configured from particles of tungsten carbide (WC) sintered together using a cobalt (Co) binder.
  • cemented carbides are materials have remarkable hardness, in a hardness range of from 1000 HV to 1800 HV, and excellent wear resistance, and are accordingly employed as the material for tools, machine components, and the like where wear resistance is demanded, such as cutting tools.
  • cemented carbides have high hardness, they have the disadvantage of being brittle, and brittle fracture is liable to occur. This means that, for example, cracks, nicks, and the like are liable to occur at the cutting-edge of cutting tools made from cemented carbide. This reduces productivity due to the need to either replace cutting tools partway through a job when such cracks or nicks have occurred, or to perform a regrinding operation or the like to regenerate the cutting tools cutting-edge.
  • the mechanical characteristics, such as hardness and toughness, of cemented carbides are known to vary according to the particle diameter of the hard particles and the addition amount of the binder metal.
  • the particle diameter of the hard particles and the addition amount of the binder metal should be changed to obtain a cemented carbide having the targeted hardness and toughness.
  • the relationships of hardness and toughness against the particle diameter of the hard particles are relationships in which the hardness of the cemented carbide increases but the toughness decreases as the average particle diameter of the hard particles decreases, and conversely the fracture toughness increases but the hardness decreases as the average particle diameter of the hard particles increases.
  • the relationships of hardness and toughness against the addition amount of binder metal are relationships in which the hardness of the cemented carbide increases but the toughness decreases as the addition amount of the binder metal is decreased, and the toughness of the cemented carbide increases but the hardness decreases as the addition amount of the binder metal is increased.
  • the hardness and toughness of the cemented carbide accordingly have conflicting relationships in that increasing one causes a decrease in the other. This means that a cemented carbide possessing the two conflicting properties of having excellent toughness while also having high hardness and is accordingly difficult to obtain by adjusting the particle diameter of the hard particles and adjusting the addition amount of the binder metal.
  • Proposed methods to improve toughness without reducing the hardness of cemented carbides accordingly include, for example: a method of coating a surface of a base body made from a cemented carbide with a hard coating layer including a toughened zone of excellent toughness (see abstract of Japanese Patent KOKAI (LOPI) No. 2000-246509 (JP2000-246509A); and a method to raise the fracture toughness of only a surface portion while maintaining the overall hardness of a cemented carbide, which is achieved by providing a surface layer of a toughness that has been raised by increasing the WC particle diameter and/or increasing the Co concentration at the surface of a cemented carbide (see abstract of Japanese Patent KOHYO (LOPI) No. 2004-514790 (JP2004-514790A)).
  • the inventors of the present invention have proposed an instantaneous heat treatment method for a metal article directed toward forming micro-structures, dimples, and the like on a surface by shot peening.
  • substantially spherical shaped shot having a higher hardness than the base material hardness of a workpiece and including three or more different approximate ranges of grain size lying in a range of from 100 grit to 800 grit (average particle diameter: 20 ⁇ m to 149 ⁇ m), are mixed together and a mixed fluid of the shot combined with compressed air is ejected intermittently, at from 0.1 seconds to 1 second and intervals of from 0.5 seconds to 5 seconds, onto the workpiece.
  • This ejection is performed at an ejection pressure of from 0.3 MPa to 0.6 MPa, at an ejection velocity of from 100 m/s to 200 m/s, and with an ejection distance of 100 mm to 250 mm, so as to form numerous random fine indentations having substantially circular bottom faces and a diameter of from 0.1 ⁇ m to 5 ⁇ m on the surface of the workpiece (claim 1 of Japanese Patent KOKAI (LOPI) No. 2012-135864 (JP2012-135864A)).
  • LOPI Japanese Patent KOKAI
  • JP2012-135864A Japanese Patent KOKAI No. 2012-135864
  • a “carbide” is employed as the workpiece (see Table 11-1 in Japanese Patent KOKAI (LOPI) No. 2012-135864 (JP2012-135864A)).
  • this method requires an operation to form the hard coating layer provided with the toughened zone on the surface of the cemented carbide using a method such as physical vapor deposition (PVD), chemical vapor deposition (CVD), or the like. Forming the hard coating film in this manner requires extensive investment in equipment etc., such as the need for a costly vacuum deposition system.
  • PVD physical vapor deposition
  • CVD chemical vapor deposition
  • the reason high toughness is achieved in this method is that a hard coating film is formed on the surface, and not because the toughness is increased of the cemented carbide itself, which means that the toughness is lost if the hard coating film detaches.
  • JP2004-514790A a configuration such as that described in Japanese Patent KOHYO (LOPI) No. 2004-514790 (JP2004-514790A), in which a surface layer of high toughness is provided on a cemented carbide by increasing the WC particle diameter and/or increasing the Co concentration, enables the toughness to be raised locally for only a surface layer portion without lowering the hardness within the cemented carbide.
  • a surface layer having increased WC particle diameter and/or increased Co concentration in this manner has a hardness that is decreased as a result of increasing the toughness.
  • the wear resistance thereof is accordingly decreased (see FIG. 1 and FIG. 2 ), and wear readily occurs when employed in an application in which direct contact or sliding occurs against other members.
  • the inventors have considered whether the occurrence of brittle fracture such as cracks or nicks can be suppressed if the binder metal phase can be strengthened at least in the vicinity of the surface of a cemented carbide 1 .
  • the cemented carbide 1 has a structure in which hard particles 10 , such as WC, are bonded together by a binder metal phase 20 , such as Co, having a higher ductility than that of the hard particles 10 .
  • the hard particles 10 therein have extremely high hardness, for example 1780 HV for WC, 3200 HV for TiC, and 1800 HV for TaC, and hardly deform. Any plastic deformation occurring when an external force is imparted to the cemented carbide 1 can accordingly be logically inferred to have occurred mainly in the portion where the binder metal phase 20 , such as the Co, is present. This provides support as to why the overall toughness (deformability) of the cemented carbide 1 is raised by increasing the addition amount of the binder metal (see FIG. 2 ).
  • the deformation of the cemented carbide 1 is thought to mainly occur in the binder metal phase 20 portion, and brittle fracture, such as cracks or nicks occurring in the cemented carbide 1 , is thought to be generated by cracking of the binder metal phase 20 due to strain accompanying deformation, which grows as more strain is imparted, and which eventually leads to fracturing occurring.
  • the binder metal phase 20 portion of the cemented carbide 1 could be strengthened, and in particular the binder metal phase 20 in the vicinity of the surface of the workpiece where fractures tend to originate could be strengthened, then this should enable the ability to withstand brittle fracture such as cracks or nicks, namely the fracture toughness, to be raised.
  • strengthening the binder metal phase 20 is thought to contribute to making brittle fracture less liable to occur and to raising the toughness of a sintered body, not only for the cemented carbide 1 , but also for sintered bodies in general having a similar structure of the hard particles 10 bonded together with the binder metal phase 20 , such as a cermet, cBN, or the like.
  • Japanese Patent KOKAI (LOPI) No. 2012-135864 JP2012-135864A discloses an instantaneous heat treatment method performed by ejecting beads made from high-speed steel (HSS) onto a treatment subject for an Example of a draw punch made from cemented carbide (Table 11-1 of Japanese Patent KOKAI (LOPI) No. 2012-135864 (JP2012-135864A)).
  • Japanese Patent KOKAI (LOPI) No. 2012-135864 JP2012-135864A
  • JP2012-135864A Japanese Patent KOKAI No. 2012-135864
  • JP2012-135864A Japanese Patent KOKAI No. 2012-135864
  • JP2012-135864A includes the advantageous effects of increasing hardness by micronization of the surface structure using the instantaneous heat treatment method, and preventing seizing and the like by dimples formed thereby functioning as oil reservoirs.
  • Wear resistance is also a reference to “wear resistance” being increased, however there is no reference whatsoever to raising the ability to withstand nicking and cracking such as chipping, called “brittle fracture”, namely no reference whatsoever to increasing toughness.
  • the present invention is directed towards solving the disadvantages in a sintered body such as a cemented carbide mentioned above of low fracture toughness, and proposes a method to strengthen the binder metal phase 20 in the vicinity of the surface of the sintered body 1 using a comparatively simple method.
  • An object of the present invention is to make brittle fracture less liable to occur (to impart toughness) while maintaining the characteristic high hardness of sintered bodies, such as cemented carbides, cermets, and cBN.
  • the method of strengthening a binder metal phase 20 of a sintered body 1 comprises:
  • a sintered body 1 such as cemented carbide that includes hard particles 10 such as tungsten carbide (WC) and a binder metal phase 20 such as cobalt (Co) bonding the hard particles 10 together, by ejecting the spherical shaped ejection particles 30 together with a compressed gas at an ejection pressure of from 0.2 MPa to 0.6 MPa or at an ejection velocity of from 80 m/s to 200 m/s and the spherical ejection particles 30 having a hardness that is not less than the hardness of the binder metal phase 20 and that is a hardness of not more than 1000 HV and being particles of from 100 grit to 800 grit (having an average particle diameter of from 20 ⁇ m to 149 ⁇ m).
  • a sintered body 1 such as cemented carbide that includes hard particles 10 such as tungsten carbide (WC) and a binder metal phase 20 such as cobalt (Co) bonding the hard particles 10 together, by ejecting the sp
  • a sintered body 1 employed as a treatment subject is a sintered body 1 having a hard coating film (not illustrated in the drawings) coated on at least a portion of surface at a thickness of not more than 5 ⁇ m, and the ejection particles 30 may be ejected against the sintered body 1 at the portion of the surface coated with the hard coating film.
  • the ejection particles 30 may be any of metal particles, ceramic particles, or a mixture of metal particles and ceramic particles, and a hardness of the ceramic particles employed is preferably not more than 800 HV.
  • the sintered body 1 is configured by the hard particles 10 made from WC, TiC, or TaC, and by the binder metal phase 20 such as a Co phase bonding between the hard particles 10 (see FIG. 3 ).
  • the hard particles 10 such as WC (1780 HV), TiC (3200 HV), or TaC (1800 HV), have higher hardness than the ejection particles 30 , which have a hardness of not more than 1000 HV.
  • the ejection particles 30 having a hardness not less than the hardness of the binder metal phase 20 impact the surface of the sintered body 1 serving as the workpiece, as illustrated in FIG. 4B , although there is no deformation of the hard particles 10 in the sintered body 1 , the binder metal phase 20 present between the hard particles 10 undergoes plastic deformation and moves the hard particles 10 , causing the surface of the sintered body 1 to deform.
  • Plastic deformation resulting from such impact and the instantaneous temperature rise and cooling (instantaneous heat treatment) occurring at the impact sites micronizes the structure of the binder metal phase 20 in the vicinity of the surface of the sintered body 1 , causes a change to a dense structure, and also imparts compressive residual stress thereto. This results in strengthening.
  • the method of the present invention enables the binder metal phase 20 in the vicinity of the surface of the sintered body 1 to be strengthened, and enables good prevention of the occurrence of brittle fracture such as cracks or nicks in the sintered body 1 , which arise from cracking and breaking occurring at the grain boundaries of the hard particles 10 .
  • Strengthening the binder metal phase 20 in this manner may be similarly performed in cases in which a hard coating film (not illustrated in the drawings) of 5 ⁇ m or less is formed on the surface of the sintered body 1 , enabling the binder metal phase 20 of the sintered body below the hard coating film to be strengthened even after the hard coating film has been formed on the surface of the sintered body 1 .
  • the cohesion strength of the hard coating film can be increased and detachment made less liable to occur by strengthening the binder metal phase 20 in this manner.
  • the micronization and densification occurring in the structure of the binder metal phase 20 , and the compressive residual stress that has been imparted thereto by the ejection of the ejection particles 30 might be lost by heating the sintered body 1 .
  • film forming of the hard coating film by a method involving heating the sintered body 1 is not able to be performed after the binder metal phase 20 has been strengthened by ejecting the ejection particles 30 .
  • the sintered body 1 after film forming a hard coating film in this manner can be employed as the treatment subject, and so this does not provide a limitation to the method of forming the hard coating film.
  • metal particles, ceramic particles, and a mixture of both metal particles and ceramic particles may all be employed as the ejection particles 30 .
  • making the hardness of such ceramic particles not more than 800 HV enables the toughness to be increased more certainly.
  • FIG. 1 is a graph to explain relationships of hardness and toughness of a cemented carbide against particle diameter of hard particles therein;
  • FIG. 2 is a graph to explain relationships of hardness and toughness of a cemented carbide against addition amount of binder metal therein;
  • FIG. 3 is a schematic diagram to explain a structure of a sintered body (a WC—Co based cemented carbide).
  • FIG. 4 is an explanatory diagram of states of deformation arising when ejection particles have impacted a workpiece of higher hardness than the ejection particles
  • FIG. 4A is for a general workpiece other than a sintered body
  • FIG. 4B is for a sintered body workpiece including a binder metal phase having a hardness not more than the hardness of the ejection particles.
  • a sintered body configured by the hard particles 10 sintered together with a binder metal is employed as a treatment subject.
  • the hard particles 10 are not limited to being a single type of hard particle, and plural types of hard particle may be mixed together and employed therefor.
  • the binder metal is also not limited to being a single type of metal, and an alloy may be employed therefor.
  • Examples of such a sintered body 1 include a cemented carbide, a cermet, and cBN. All of these have a structure such as that schematically illustrated in FIG. 3 in which the hard particles 10 are bonded together by the binder metal phase 20 .
  • the “cemented carbide” of the sintered body 1 is configured by the hard particles 10 made from a carbide (WC, TiC, TaC) of a metal such as tungsten (W), titanium (Ti), Tantalum (Ta) sintered together with a binder of a metal such as iron (Fe), nickel (Ni), or cobalt (Co).
  • cemented carbide sometimes refers to only a WC—Co based alloy of particles of tungsten carbide (WC) sintered together using a binder of cobalt (Co).
  • the present invention is not limited to a WC—Co based alloy, and a cemented carbide containing any of the above carbide particles may be employed as the treatment subject.
  • such WC—Co based alloys encompass, in addition to a WC—Co alloy, alloys containing carbide particles other than WC, such as a WC—TiC—Co alloy, a WC—TiC—TaC(NbC)—Co alloy, or a WC—TaC(NbC)—Co alloy.
  • the binder metal is not limited to being a single metal such as Fe, Ni, or Co, and another metal such as an alloy of these metals may also be employed.
  • the “cermet” of the sintered body 1 is a sintered body configured by the hard particles 10 of a ceramic such as a carbide, oxide, nitride, boride, or silicide, bonded together with a binder metal, and within a wide definition may include the cemented carbides listed above.
  • cermets examples include a TiC—Mo—Ni cermet, and also a TiC based cermet with the addition of TiN, TaN thereto, an A 1 2 O 3 —Cr cermet, and the like. Any of these may be employed as the treatment subject of the present invention.
  • the “cBN” of the sintered body is a sintered body of hard (fine) particles 10 of cubic boron nitride of which hexagonal boron nitride is modified by ultrahigh pressure and high temperature, that is sintered using a binder metal such as Co.
  • the sintered body 1 may be employed in various forms and applications, such as in cutting tools such as a milling cutter or drill, shaping tools such as a wire drawing die or a centering tool, wear resistant components such as a roller, gage or dot pin of a printer, a corrosion-resistant tool in a mining application such as a rock cutter or coal cutter, as well as a mold or the like. These may variously be employed as the treatment subject, irrespective of form and application thereof.
  • a sintered body may be attached to a portion of the tool or component, such as in a cutting tool or the like in which, for example, a sintered body is attached as the cutting-edge portion alone by brazing.
  • the treatment subject may be a sintered body in which the surface of the sintered body serving as the treatment subject has a hard coating film (ceramic coating film) of, for example, TiN, TiCN, TiAlN, DLC, TiCrN, CrN, or the like formed thereon at a film thickness of not more than 5 ⁇ m by physical vapor deposition (PVD) or chemical vapor deposition (CVD).
  • a hard coating film ceramic coating film of, for example, TiN, TiCN, TiAlN, DLC, TiCrN, CrN, or the like formed thereon at a film thickness of not more than 5 ⁇ m by physical vapor deposition (PVD) or chemical vapor deposition (CVD).
  • Dry ejection of the ejection particles 30 together with compressed gas is performed on the surface of the sintered body 1 serving as the above treatment subject.
  • the material employed for the ejection particles 30 there is no particular limitation to the material employed for the ejection particles 30 as long as the material lies within the hardness range described below.
  • the ejection particles 30 being made from a metal, those made from a ceramic (including glass) may also be employed.
  • ejection particles 30 made from a single type of material but also ejection particles 30 made from a mixture of plural materials may also be employed.
  • the objective of ejecting the ejection particles 30 is to perform micronization and densification of the structure by plastically deforming the binder metal phase 20 , and to impart compressive residual stress and the like thereto, i.e. the objective thereof is to obtain the advantageous effects of what is referred to as “shot peening”, and so spherical shaped (spherical shaped particles) are employed therefor.
  • spherical shaped in the present invention need not refer strictly to a “sphere”, and includes a wide range of non-angular rounded shapes, such as spheroid shapes or barrel shapes.
  • Such spherical shaped ejection particles 30 may be obtained by an atomizing method for metal based materials, and may be obtained by crushing and then melting for ceramic based materials.
  • the hardness of the ejection particles 30 employed is a hardness not less than the hardness of the binder metal phase 20 and ejection particles of not more than 1000 HV are employed. Moreover, when the ejection particles 30 are ceramic particles, then preferably those of not more than 800 HV are employed therefor.
  • the respective melting points for Co, Mo, Ni that may be employed as the binder metal are 1495° C., 2625° C., 1455° C.
  • Sintering is performed at a high temperature in the vicinity of the melting point of the binder metal, and a hardness of the binder metal phase 20 after sintering is from 500 HV to 800 HV (for example, about 500 HV for Ni, and about from 700 HV to 800 HV for Co).
  • alumina-silica beads (792 HV), HSS beads (1000 HV), or the like are for example suitably employed as the ejection particles 30 .
  • alumina-silica beads (792 HV), HSS beads (1000 HV), or the like are for example suitably employed as the ejection particles 30 .
  • preferably glass beads (565 HV) are employed as the ejection particles 30 .
  • the hardness of the binder metal phase 20 is not known, for example, trials are performed, in which plural types of ejection particles 30 of different hardness of not more than 1000 HV are actually ejected against the surface of the sintered body 1 .
  • the ejection particles 30 capable of rendering a matt (or satin) finish on the surface of the sintered body 1 in such trials may then be employed as ejection particles 30 having a hardness not less than that of the binder metal phase 20 .
  • ejection particles 30 having a hardness of not more than 1000 HV are employed, sometimes considerable damage is inflicted on the surface of the sintered body 1 and the toughness thereof is actually lowered when ceramic based (including glass) ejection particles 30 with a hardness exceeding 800 HV thus toughness are lowered.
  • ejection particles 30 having a hardness of not more than 800 HV are preferably employed for ceramic based ejection particles 30 .
  • the ejection particles 30 employed have a particle diameter in the range of from 100 grit to 800 grit for grain size distributions as defined by JIS R 6001(1987) (an average particle diameter of from 20 ⁇ m to 149 ⁇ m). As long as the particle diameter falls within this grain size range, a mixture of plural types of ejection particles 30 of different particle diameter may be employed.
  • the method for ejecting such ejection particles 30 against the sintered body 1 which is the workpiece may employ various known dry type blasting treatment apparatuses capable of ejecting particles, and an air blasting treatment apparatus is preferably employed therefor because this enables comparatively easy adjustment of ejection velocity and ejection pressure.
  • Such air blasting treatment apparatuses include direct pressure type, gravity suction type, and other types of blasting treatment apparatus. Any of these types of blasting treatment apparatus may be employed, and the type thereof is not particularly limited as long as the blasting treatment apparatus has the performance capable of ejecting the ejection particles at an ejection pressure of from 0.2 MPa to 0.6 MPa, or at an ejection velocity of from 80 m/sec to 200 m/sec.
  • a sintered body 1 having a structure in which the hard particles 10 are bonded together by the binder metal phase 20 for example a WC—Co cemented carbide
  • the hardness of the WC particles configuring the hard particles 10 is a high hardness of 1780 HV
  • the hardness of the Co phase configuring the binder metal phase 20 is about 700 HV, giving a combined overall hardness of about 1450 HV.
  • the hardness of the ejection particles 30 of not more than 1000 HV is a hardness lower than the overall hardness of the sintered body 1 (hardness of the WC—Co based cemented carbide: 1450 HV) and lower than the hardness of the hard particles 10 (hardness of the WC particles: 1780 HV), the hardness of the ejection particles 30 is not less than the hardness of the binder metal phase 20 (hardness of the Co phase: 700 HV).
  • the average particle diameter of the hard particles in the sintered body 1 is generally a few ⁇ m or so, and for fine hard particles is from about 0.5 ⁇ m to about 0.8 ⁇ m, and this is sufficiently smaller than the particle diameter of the ejection particles 30 at from 100 grit to 800 grit (an average particle diameter of from 20 ⁇ m to 149 ⁇ m).
  • the hard particles 30 when the ejection particles 30 are caused to impact the surface of the sintered body 1 , as illustrated in FIG. 4B , even though no deformation can be achieved of the hard particles 10 having a higher hardness than the ejection particles 30 , the hard particles can be moved by deforming the binder metal phase 20 , and this is thought to deform the surface of the sintered body 1 so as to enable processing to a slight matt finish.
  • the binder metal phase 20 is thought to be strengthened by being imparted with compressive residual stress that suppresses the generation and growth of cracks.
  • Such strengthening of the binder metal phase 20 is not only obtained in cases in which the ejection particles 30 are caused to directly impact the surface of the sintered body 1 , and is also obtained in cases in which the ejection particles 30 are caused to impact a sintered body 1 having a hard coating film (not illustrated in the drawings) such as a ceramic coating film or the like coated on a surface thereof, by impacting from above the hard coating film.
  • a hard coating film such as a ceramic coating film or the like coated on a surface thereof
  • Ejection particles were ejected under the conditions listed in Table 1 below against a cold forging punch (diameter 20 mm, length 150 mm) made from a WC—Co cemented carbide (1450 HV).
  • the hardness of the Co phase that is the binder metal phase is approximately 700 HV.
  • Example 1 Example 2 Blasting Device Gravity Type Gravity Type Gravity Type Gravity Type Ejection Material HSS (SKII) Glass FeCrB particles Hardness Approximately 534 HV Approximately 1000 HV 1200 HV Average particle Approximately Approximately Approximately diameter 40 ⁇ m 40 ⁇ m 40 ⁇ m Shape Substantially Substantially Substantially spherical shaped spherical shaped spherical shaped Ejection Pressure 0.6 MPa 0.6 MPa 0.6 MPa conditions Nozzle 9 mm diameter - 9 mm diameter - 9 mm diameter - 9 mm diameter - diameter long long long long long Ejection 100 mm to 100 mm to 100 mm to distance 150 mm 150 mm 150 mm Ejection Approximately Approximately Approximately Approximately duration 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds 30
  • Example 1 and Comparative Examples 1 and 2 The state of the surface of cold forging punches was observed with the naked eye after ejection of the ejection particles and on an un-processed cold forging punch.
  • Each of the cold forging punches of Example 1 and Comparative Examples 1 and 2 was employed to perform repeated cold forging (punching 20 mm diameter holes), and the number of cycles (shot number) at the time when chipping (nicking) occurred in the respective cold forging punch was employed to evaluate the lifespan of the cold forging punch.
  • Test Example 1 The test results of Test Example 1 are illustrated in Table 2 below.
  • Example 1 employing ejection particles of 1000 HV which is a higher hardness than the hardness of the Co phase (approximately 700 HV), deformation was induced of the surface of the treatment subject to give a slight matt finish, and a lifespan of three times the untreated case was achieved.
  • the ejection particles made from HSS employed in Example 1 had a hardness of approximately 1000 HV and a lower hardness than the hardness of the cemented carbide (1450 HV) of the material configuring the cold forging punch serving as the treatment subject.
  • deformation occurring at the time of impact of the ejection particles would occur at the ejection particle side having lower hardness, and as a result hardly any plastic deformation would be induced on the treatment subject side (see FIG. 4A ).
  • the advantageous effects of micronization and densification of the surface structure of the workpiece, imparting of compressive residual stress, and the like would accordingly not be obtained.
  • the sintered body 1 serving as the treatment subject in the present invention has a structure in which the WC particles 10 of high hardness, i.e. 1780 HV, are bonded together with the Co phase 20 having a lower hardness of approximately 700 HV.
  • the WC particles 10 of high hardness i.e. 1780 HV
  • the Co phase 20 having a lower hardness of approximately 700 HV.
  • Comparative Example 2 employing the ejection particles having a hardness of 1200 HV i.e. a lower hardness than the sintered body 1 but a higher hardness than the Co phase, plastic deformation can be induced in the Co phase. This could be confirmed in the test results illustrated in Table 2 by a change of the surface of the sintered body to a matt finish.
  • ejection particles having a hardness of not less than the hardness of the binder metal phase (Co phase) need to be employed as the ejection particles in order to increase the toughness of the sintered body (cemented carbide), and that ejection particles having a lower hardness than 1200 HV, and more specifically preferably employed ejection particles have a hardness of not more than 1000 HV such as those confirmed to strengthen the Co phase in Example 1.
  • Ejection particles were ejected under the conditions listed in Table 3 below against a header processing die (outer diameter 50 mm, inner diameter 15 mm, height 30 mm) made from a WC—Co cemented carbide (1150 HV).
  • the hardness of the Co phase that is the binder metal phase is approximately 700 HV.
  • the state of the surface of the header processing die was observed with the naked eye after ejection of the ejection particles 30 .
  • An un-processed header processing die, and the header processing die treated under the above conditions were each employed to perform repeated header processing (cold heading) of SCM435, and the number of cycles (shot number) at the time when damage occurred on the inner peripheral face of the die was employed to evaluate the lifespan of the respective header processing die.
  • Test Example 2 The test results of Test Example 2 are illustrated in Table 4 below.
  • Example 2 employing ejection particles having a hardness of 1000 HV, which is a higher hardness than the hardness of the Co phase (approximately 700 HV), plastic deformation was induced of the surface of the treatment subject to give a slight matt finish. The lifespan was also able to be extended to three times that of the untreated case.
  • Employing the ejection particles within the hardness range stipulated by the present invention was confirmed to be effective in increasing the toughness of the sintered body.
  • Ejection particles were ejected under the conditions listed in Table 5 below against a drill (5 mm diameter) made from a WC—TiC—TaC—Co cemented carbide (91.5HRA (1600 HV)).
  • the hardness of the Co phase that is the binder metal phase is approximately 700 HV.
  • Example 3 Blasting Device Fine powder Fine powder suction type suction type Ejection particles Material Alumina-silica Zirconia-Silica Hardness 792 HV Approximately (Approximately 1000 HV 800 HV) Average particle Approximately ⁇ 50 ⁇ m diameter 38 ⁇ m Shape Substantially Substantially spherical shaped spherical shaped Ejection Pressure 0.4 MPa 0.6 MPa conditions Nozzle 7 mm diameter - 7 mm diameter - diameter long long Ejection 100 mm to 100 mm to distance 150 mm 150 mm Ejection Approximately Approximately duration 20 seconds 20 seconds 20 seconds
  • FCD400 ductile cast iron
  • ejection particles made from a ceramic preferably employed ejection particles have a hardness of not more than 792 HV (approximately 800 HV) such as those for which the advantageous effect of strengthening the binder metal phase (Co phase) is confirmed in the Example.
  • Ejection particles were ejected under the conditions listed in Table 6 below against a diamond shaped insert made from a TiCN—NbC—Ni cermet (93HRA (1900 HV)) for turning the inner diameter of a cylinder made from SUS304.
  • the hardness of the Ni phase that is the binder metal phase is approximately 500 HV.
  • Example 4 The state of the surface of the insert was observed with the naked eye after ejection of the ejection particles under the conditions of Example 4.
  • An un-processed insert and the insert of Example 4 were each employed to turn the inner diameter of cylinders made from SUS304.
  • the surface of the cutting-edge portions of the untreated insert was smooth, and the cutting-edges of the insert after treatment under the treatment conditions of Example 4 was a slight matt finish. This confirmed that ejection of the ejection particles enables plastic deformation to be induced in the cutting-edge surfaces of the insert.
  • the finish on the inner diameter finished surface was better on cylinders machined using the insert of Example 4 than on cylinders machined using the untreated insert.
  • Ejection particles were ejected under the conditions listed in Table 7 below against a diamond shaped cutting insert made from a WC—TiC—TaC—Co cemented carbide (91.5HRA (1600 HV)) that had been coated with a TiC film at a film thickness of approximately 3 ⁇ m using a CVD method.
  • the hardness of the Co phase that is the binder metal phase is approximately 700 HV.
  • Compressive residual stress values were measured in the vicinity of the surface of an untreated insert and an insert on to which ejection particles had been ejected under the conditions of Example 5. Each of the insert was also employed to machine a shaft made from SCM440.
  • Example 5 even with the TiC coating film formed to a film thickness of 3 ⁇ m, compressive residual stress was confirmed to be imparted to at least a depth of 5 ⁇ m in the base material below (a total depth of 8 ⁇ m when the 3 ⁇ m thickness of the hard coating film is included).
  • the logical inference therefrom is that if the hard coating film formed on the surface had a film thickness of up to about 5 ⁇ m, then compressive residual stress can be imparted at least to a depth of about 3 ⁇ m from the base material surface (a total depth of 8 ⁇ m when the 5 ⁇ m thickness of the hard coating film is included), and the binder metal phase in the vicinity of the surface of the sintered body can be strengthened.
  • Ejection particles were ejected under the conditions listed in Table 9 below against a diamond shaped cutting insert made from cBN (4700 HV) configured from cubic crystals of boron nitride sintered together with a Co binder.
  • the hardness of the Co phase binder is higher than in a carbide tool, and the hardness of the Co phase in the cBN of the present Test Example is approximately 800 HV.
  • Such a difference is thought to be due to the cBN being sintered under ultrahigh pressure as described above, making the hardness of the Co phase, at about 800 HV, about 100 HV higher than in a cemented carbide such that sufficient plastic deformation could not be imparted to the Co phase by alumina-silica beads of 792 HV. This is thought to result in not being able to achieve strengthening through work hardening from micronization of the crystal structure and imparting compressive residual stress.

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US20090297835A1 (en) * 2004-12-14 2009-12-03 Sumitomo Electric Hardmetal Corp. Coated cutting tool
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