Classifications

• • 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
  • B22F7/00—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression
  • B22F7/06—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite workpieces or articles from parts, e.g. to form tipped tools
  • B22F7/08—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite workpieces or articles from parts, e.g. to form tipped tools with one or more parts not made from powder
• • 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
  • 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
  • C22C1/053—Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor with in situ formation of hard compounds
  • C22C1/055—Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor with in situ formation of hard compounds using carbon
• • 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
  • C22C1/053—Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor with in situ formation of hard compounds
  • C22C1/056—Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor with in situ formation of hard compounds using gas
• • 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
  • C22C1/10—Alloys containing non-metals
  • C22C1/1094—Alloys containing non-metals comprising an after-treatment
• • 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
  • C22C29/005—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides comprising a particular metallic binder
• • 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
  • C22C29/08—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 based on tungsten carbide
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21C—MINING OR QUARRYING
  • E21C35/00—Details of, or accessories for, machines for slitting or completely freeing the mineral from the seam, not provided for in groups E21C25/00 - E21C33/00, E21C37/00 or E21C39/00
  • E21C35/18—Mining picks; Holders therefor
  • E21C35/19—Means for fixing picks or holders
• • 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
  • B22F5/00—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product
  • B22F2005/001—Cutting tools, earth boring or grinding tool other than table ware
• • 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
  • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy

Definitions

• the present invention relates to a method of producing a tool for cutting, drilling or crushing of solid material, said tool comprising a cemented carbide body attached to a steel holder, wherein said method comprises the steps of providing said cemented carbide body by; providing a powder mixture, compacting said powder mixture into a compact, sintering the compact into said cemented carbide body, and attaching the compact to said steel holder.
• the present invention also relates to a tool produced in accordance with the principles of the method of the present invention.
• Tools for cutting, drilling or crushing of solid material often comprise a cemented carbide body attached to a steel holder.
• the joint between the cemented carbide body and the steel holder may be a braze joint between a base surface of the cemented carbide body and the steel holder.
• the braze joint may be accomplished by means of a brazing process in which a solder, typically comprised by Nickel-Copper- Manganese alloy, is positioned between the base surface of the cemented carbide body and a surface of the steel holder, and in which the solder is melted and then forced to diffuse into the cemented carbide body and into the steel by means of inductive heating thereof.
• convective heating in an oven may be applied.
• the brazing process may be performed in an inert gas atmosphere, or a fluxing means may be applied onto the cemented carbide body.
• the cobalt in the cemented carbide body plays a vital role in the sense that is responsible for the generation of heat through the induction of an eddy current therein.
• a too low content of cobalt will result in a low wettability of the cemented carbide by the solder, and therefore a poor bonding between the cemented carbide and the steel.
• Cemented carbide bodies with low cobalt contents are therefore generally considered as unsuitable for joining by means of brazing, especially when using inductive brazing which is the most suitable brazing method to use when producing tools for cutting or drilling minerals or rock.
• attachment by means of clamping or similar mechanical joining is considered to be the only reasonable option.
• the object of the invention is achieved by means of a method of producing a tool for cutting, drilling or crushing of solid material, said tool comprising a cemented carbide body attached to a steel holder, wherein said method comprises the steps of -providing said cemented carbide body by;
• said compound and said grain growth promoting element is of a type that will diffuse into the compact in connection to sintering of the latter and thereby will induce a generation of a cobalt content gradient in the sintered compact, with an increasing cobalt content in a direction away from a surface onto which said compound and said grain growth promoting element has been applied,
• cemented carbide body having a low mean cobalt content and/or a low cobalt content in the tip that is active in cutting, crushing etc. at the same time the cemented carbide body has a base region having more a sufficiently high cobalt content to enable strong braze joints to steel.
• the cobalt content at said base surface of the cemented carbide body being cobalt content level (B) becomes > 5.0 wt , or > 5.5 wt , or > 6.0 wt .
• the ratio cobalt content level (B) to cobalt content level (A) is >1.12, or >1.14, or >1.16, or >1.2.
• the ratio cobalt content level (B) to cobalt content level (A) is ⁇ 1.5, or ⁇ 1.4.
• said tip region of the cemented carbide body has a mean cobalt content, being cobalt content level (C), of ⁇ 4.5 wt , or ⁇ 4.0 wt , or ⁇ 3.5 wt , or ⁇ 3.0 wt .
• C cobalt content level
• the extent of the tip region into the body is suitably defined as starting at the surface and going about 2 mm down into the cemented carbide body.
• the ratio cobalt content level (B) to cobalt content level (C) is >1.2, or >1.3, or >1.4.
• the cobalt content of the cemented carbide body, being cobalt content level (A), is ⁇ about 5.0 wt . According to one embodiment, the cobalt content of the cemented carbide body, being cobalt content level (A), is ⁇ about 4.5 wt%.
• said compact comprises top and lateral surfaces and said base surface, and said compound and said grain growth promoting element is applied to at least 50% of the total area of the top and lateral surfaces.
• the degree of coverage of the applied compound and grain growth promoting element, and the amount thereof applied, is decisive for the generation of the required cobalt gradient in the cemented carbide body.
• said compact comprises top and lateral surfaces and said base surface, and said compound and said grain growth promoting element is applied to at least 70% of the total area of the top and lateral surfaces.
• said compact comprises top and lateral surfaces and said base surface, and said compound and said grain growth promoting element is applied to at least 80% of the total area of the top and lateral surfaces.
• said compact comprises top and lateral surfaces and said base surface, and wherein the distance between the top surface and the base surface, which is opposed to the top surface, is less than 25 mm, preferably less than 15 mm, and more preferably less than 10 mm, and wherein said compound and said grain growth promoting element are applied onto at least a part of said top surface. Thanks to a sufficiently low distance between top and base surfaces, sufficiently high cobalt content can be obtained in the base surface due to the generated cobalt gradient.
• said compact comprises top and lateral surfaces and, in a zone of the lateral surface or surfaces neighbouring the base surface, the lateral surface or surfaces are excluded from the application of said compound and said grain growth promoting element. Thereby, the generation of a cobalt-depleted zone in the transition region between lateral surfaces and base surface is avoided.
• said compact has a generally knob-like shape, has a generally circular bottom surface with a diameter d, and has a height h, wherein 0.5 ⁇ h/d ⁇ 2, and said bottom surface defines said base surface.
• said compact has a generally plate-like shape, has width w, a height h and a thickness t, and wherein 0.2 ⁇ h/w ⁇ 2, t ⁇ w, 2mm ⁇ t ⁇ 20mm, and, said base surface is a large side of said compact, and said tip region includes at least a part of an opposite large side thereof.
• the element that has a grain growth inhibiting effect on WC is any of chromium, vanadium, tantalum or niobium, preferably chromium or vanadium, most preferably chromium.
• the grain refiner compound is suitably selected from the group of carbides, mixed carbides, carbonitrides or nitrides of vanadium, chromium, tantalum and niobium.
• the grain refiner compound is a carbide or nitride of chromium or vanadium, such as Cr 3 C 2 , Cr 23 C 6 , Cr 7 C 3 , Cr 2 N, CrN or VC, most preferably carbides of chromium, such as Cr 3 C 2 , Cr 23 C 6 , or Cr 7 C 3 .
• said compound is applied onto the compact in an amount of more than 0.5 mg/cm 2 , preferably more than 2.5 mg/cm 2 , preferably more than 3.0 mg/cm 2.
• said compound is applied onto the compact in an amount of not more than 10.0 mg/cm 2 , preferably not more than 7.0 mg/cm 2 , preferably not more than 6.0 mg/cm .
• the above-mentioned limits are generally applicable for the different compounds mentioned above and particularly applicable for Cr 3 C 2 . Too high levels of said compound may result in the unwanted generation of brittle phases.
• said grain growth promoting element is carbon in the form of graphite.
• the carbon provided onto the surface of the compact may be in the form of deposited carbon from a carburizing atmosphere, amorphous carbon, which is present in e.g. soot and carbon black, or graphite.
• the carbon is in the form of soot or graphite.
• the weight ratio of grain refiner compound, to grain growth promoter is suitably from about 0.05 to about 50, preferably from about 0.1 to about 25, more preferably from about 0.2 to about 15, even more preferably from about 0.3 to about 12, most preferably from about 0.5 to about 8.
• the weight ratio Cr 3 C 2 /C may preferably be from about 1 to about 14, preferably from about 1.5 to about 6.
• said grain growth element is applied onto the compact in an amount of more than 0.2 mg/cm 2 , preferably more than 0.5 mg/cm 2 , preferably more than 1.0 mg/cm .
• said grain growth-promoting element is applied onto the compact in an amount of not more than 3.0 mg/cm , preferably not more than 2.5 mg/cm .
• the above-mentioned limits are particularly applicable when said grain growth promoting element is carbon. Too high levels of carbon may result in an unwanted generation of a carbon shell on the sintered compact and negative effects on the sintering process.
• the grain refiner compound and/or grain growth promoter may be provided by application in the form of a separate or combined liquid dispersion or slurry to the compact.
• the liquid phase is suitably water, an alcohol or a polymer such as polyethylene glycol.
• the grain refiner compound and grain growth promoter may alternatively be provided by application in the form of solid substances to the compact, preferably powder.
• the application of the grain refiner compound and grain growth promoter onto the compact is suitably made by applying the grain refiner compound and grain growth promoter onto the compact by, dipping, spraying, painting, or application onto the compact in any other way.
• the grain growth promoter is carbon, it may alternatively be provided onto the compact from a carburizing atmosphere.
• the carburizing atmosphere suitably comprises one or more of carbon monoxide or a C1-C4 alkane, i.e. methane, ethane, propane or butane.
• the carburizing is suitably conducted at a temperature of from about 1200 to about 1550°C.
• the method comprises providing the grain refiner compound and grain growth promoter on the surface of a compact by combining the grain refiner compound and the grain growth promoter with a WC-based starting material powder which is then pressed into a compact.
• the provision of the grain refiner compound and grain growth promoting element on the surface of the compact is suitably made by introducing the grain refiner compound and the grain growth promoter into a pressing mould prior to the introduction of a WC-based starting material powder followed by pressing.
• the grain refiner compound and grain growth promoter is suitably introduced into the pressing mould as a dispersion or slurry.
• the liquid phase in which the grain refiner compound is dispersed or dissolved is suitably water, an alcohol or a polymer such as polyethylene glycol.
• one or both of the grain refiner compound and the grain growth promoter is introduced into the pressing mould as a solid substance.
• the compact presents an open porosity and said compound and said grain growth promoting element is provided as powder in slurry which is applied onto the compact, and the powder particle size of said compound and said grain growth promoting element is small enough to enable said powder thereof to be introduced into pores of the compact by capillary forces generated by said pores.
• Open porosity may be referred to as continuous porosity, typical for a not yet fully dense material.
• the grain refiner is diffused away from the surface or surfaces provided with the grain refiner compound, thereby suitably forming a zone with an in average decreasing content of grain refiner when going deeper into the body.
• a zone is also suitably formed during sintering with an in average increasing content of binder when going deeper into the body.
• the sintering temperature is suitably from about 1000°C to about 1700°C, preferably from about 1200°C to about 1600°C, most preferably from about 1300°C to about 1550°C.
• the sintering time is suitably from about 15 minutes to about 5 hours, preferably from about 30 minutes to about 2 hours.
• said brazing is inductive brazing.
• the braze joint may be accomplished by means of a brazing process in which a solder, typically comprised by Nickel-Copper-Manganese alloy, is positioned between the base surface of the cemented carbide body and a surface of the steel holder, and in which the solder is forced to diffuse into the cemented carbide body and into the steel by means of inductive heating thereof.
• a solder typically comprised by Nickel-Copper-Manganese alloy
• the object of the invention is also achieved by means of a tool for cutting, drilling or crushing of solid material, wherein
• said tool comprises a cemented carbide body attached to a steel holder by a braze joint located between a base surface of the cemented carbide body and the steel holder,
• said cemented carbide body comprises a hard phase mainly comprised by tungsten carbide, WC, and a binder consisting of cobalt, wherein the cobalt content of the cemented carbide body is at a cobalt content level (A) and is ⁇ about 5.5 wt , and wherein,
• the cemented carbide body presents a cobalt content gradient therein, wherein the cobalt content increases from a tip region towards said base surface to a cobalt content level (B) and is at least 4.5 wt at said base surface, the ratio cobalt content level (B) to cobalt content level (A) is >1.09.
• the cobalt content at said base surface of the cemented carbide body being cobalt content level (B) is at least 5.0 wt , or at least 5.5 wt , or at least 6 wt% .
• the ratio cobalt content level (B) to cobalt content level (A) is >1.12, or >1.14, or >1.16, or >1.2.
• the ratio cobalt content level (B) to cobalt content level (A) is ⁇ 1.5, or ⁇ 1.4.
• said tip region of the cemented carbide body has a mean cobalt content, being cobalt content level (C), of ⁇ 4.5 wt , or ⁇ 4.0 wt , or ⁇ 3.5 wt%, or ⁇ 3.0 wt%.
• C cobalt content level
• the extent of the tip region into the body is suitably defined as starting at the surface and going about 2 mm down into the cemented carbide body.
• the ratio cobalt content level (B) to cobalt content level (C) is >1.2, or >1.3, or >1.4.
• the cobalt content of the cemented carbide body is ⁇ about 5.0 wt%.
• the cobalt content of the cemented carbide body is ⁇ about 4.5 wt%.
• the Co content gradient and the Co content at the base surface of the cemented carbide body are suitably determined by using the hardness, cobalt concentration and tungsten grain size equation (Eq. 1) by Roebuck et al, "A national measurement good practice guide" No. 20, Mechanical Tests
• HV5 888-9.9 Co+[(229+532exp((6- Co)/6.7))]/dWC0.5
• the WC grain size dWC is first calculated using equation 1 on HV5 hardness data from a reference sample with the same mean Co content. Then HV5 measurements on a sample having a Co content gradient are done by making numerous indentations on a cross sectional cut. As an example, if the cemented carbide body has a thickness of 12 mm one could program the hardness tester to make indentations at 0.3, 0.8, 1.3, 1.8, 2.3, 2.8, 3.3, 3.8, 4.3, 4.8, 5.3 and 5.8 mm distance to the edge on a cross sectional cut. The distance between the indentations can for example be set to 0.5 mm. From the results a HV5 iso lines map is provided. The HV5 hardness iso lines map can then be transformed into a Co content iso lines map by using equation 1.
• the mean Co content for the whole, or part, of the cemented carbide body is suitably determined by chemical analysis.
• said element that has a grain growth inhibiting effect on WC is any of chromium, vanadium, tantalum or niobium, preferably chromium or vanadium, most preferably chromium.
• the grain refiner compound is suitably selected from the group of carbides, mixed carbides, carbonitrides or nitrides of vanadium, chromium, tantalum and niobium.
• the grain refiner compound is a carbide or nitride of chromium or vanadium, such as Cr 3 C 2 , Cr 23 C6, Cr 7 C 3 , Cr 2 N, CrN or VC, most preferably carbides of chromium, such as Cr 3 C 2 , Cr 23 C 6 , or Cr 7 C 3 .
• said element that has a grain growth promoting effect on WC is carbon.
• the cemented carbide body can be coated with one or more layers according to known procedures in the art.
• layers of TiN, TiCN, TiC, and/or oxides of aluminum may be provided onto the cemented carbide body.
• the base surface, aimed for attachment by means of brazing may not be provided with such coating.
• the braze joint has been accomplished by means of inductive brazing.
• the braze joint may be accomplished by means of a brazing process in which a solder, typically comprised by Nickel-Copper-Manganese alloy, is positioned between the base surface of the cemented carbide body and a surface of the steel holder, and in which the solder is forced to diffuse into the cemented carbide body and into the steel by means of inductive heating thereof.
• the cemented carbide body is a cemented carbide tool body.
• the cemented carbide body is a body for a mining tool, such as a rock drilling tool or a mineral cutting tool, or for an oil and gas drilling tool.
• the cemented carbide body is a coldforming tool, such as a tool for forming thread, beverage cans, bolts and nails.
• said cemented carbide body comprises top and lateral surfaces and said base surface, and wherein the distance between the top surface and the base surface, which is opposed to the top surface, is less than 21.2 mm, preferably less than 12.5 mm, and more preferably less than 8.3 mm, wherein the cemented carbide body presents a cobalt content gradient therein in a direction from said top surface towards said base surface as a result of the presence of said grain growth promoting element and said grain growth inhibiting element in the region of said top surface. All measures correspond to the previously mentioned measures of a compact adjusted with regard to the fact that the dimensions of the compact are about 1.2 times larger than the corresponding measures of the sintered compact, i.e. the cemented carbide body.
• the geometry of the body is typically ballistic, spherical or conical shaped, but also chisel shaped and other geometries are suitable in the present invention.
• said compact has a generally knoblike shape (including ballistic, semi- spherical or conical shape), has a generally circular bottom surface with a diameter h, and has a height h, wherein 0.5 ⁇ h/d ⁇ 2, and said bottom surface defines said base surface.
• said compact has a generally plate-like shape, has width w, a height h and a thickness t, and wherein 0.2 ⁇ h/w ⁇ 2, t ⁇ w, 1.7mm ⁇ t ⁇ 17mm, and, said base surface is a large side of said compact, and said tip region includes at least a part of an opposite large side thereof. All measures correspond to the previously mentioned measures of a compact adjusted with regard to the fact that the dimensions of the compact are about 1.2 times larger than the corresponding measures of the sintered compact, i.e. the cemented carbide body.
• the present invention further relates to the use of the cemented carbide tool body in rock drilling or mineral cutting operations.
• Fig. 1 is a perspective view of an embodiment of a tool according to the invention
• Fig. 2 is a perspective view of a compact according to the invention before application of a coating thereon
• Fig. 3 shows the application of a coating of a grain-growth inhibiting compound and a grain growth promoting element onto an outer surface of the compact shown in fig. 2,
• Fig. 4 is a side view of the coated compact
• Fig. 5 is a cross-section of a part of the tool shown in fig. 1, presenting a body formed by the compact shown in figs. 2-4 after sintering thereof and connected to a holder by means of brazing
• Fig. 6 is a perspective view of another embodiment of a compact before application of a coating thereon
• Fig. 7 shows the application of a coating of a grain-growth inhibiting compound and a grain growth promoting element onto an outer surface of the compact shown in fig. 6,
• Fig. 8 shows the coated compact of fig. 7
• Fig. 9 shows a part of another embodiment of a tool provided with a body formed the compact shown in figs. 6-8 after sintering thereof and connection to a holder by means of brazing
• Fig. 10 is a perspective view of one embodiment of a coated compact
• Fig. 11 is a perspective view of another embodiment of a coated compact
• Fig. 12 is an ISO-line representation of a cross-section of a body formed by a sintered compact having a cylindrical geometry and a coating of a suspension of chromium carbide and free carbon, showing measured hardness for a cemented carbide body having a mean Co-content of 5.0 wt ,
• Fig. 13 is an ISO-line representation of a cross-section of a body formed by a sintered compact having a cylindrical geometry and a coating of a suspension of chromium carbide and free carbon, showing calculated Co-content respectively for a cemented carbide body having a mean Co-content of 5.0 wt ,
• Fig. 14 is an ISO-line representation of a cross-section of a body formed by a sintered compact having geometry and a coating of a suspension of chromium carbide and free carbon, as shown in figs. 3-5, showing measured hardness and calculated Co-content respectively for a cemented carbide body having a mean Co- content of 10 wt ,
• Fig. 15 is an ISO-line representation of a cross-section of a cemented carbide body formed by a sintered compact having geometry and a coating of a suspension of chromium carbide and free carbon as shown in fig. 11, showing measured hardness and calculated Co-content respectively for a cemented carbide body having a mean Co-content of 6.0 wt
• Fig. 16 is an ISO-line representation corresponding to the one shown in fig. 15, but for a cemented carbide body having an mean Co-content of 8 wt , and
• Fig. 17 is an ISO-line representation of a cross section of a body formed by a sintered compact having geometry and coating of a suspension of chromium carbide and free carbon as shown in fig. 10, showing measured hardness and calculated Co-content respectively for a cemented carbide body having a mean Co-content of 8 wt .
• Fig. 1 shows an embodiment of a tool 1 according to the invention, comprising a cemented carbide body 2 and a holder 3.
• the cemented carbide body 1 is connected to the holder 3 by means of brazing.
• the tool 1 shown in fig. 1 is an example of a so called MGT-tool designed for mining and graveling applications (MGT: Mineral and Grounds Tools).
• MGT Mineral and Grounds Tools
• the invention is not limited to such tools but could be applied to all kind of tools comprising a cemented carbide body attached to a steel holder by means of brazing.
• the body 2 shown in fig. 1 is produced by means of a process in which a powder mixture is compacted into a compact which is then sintered to the body 2.
• the process includes selection of a suitable powder mixture composition including tungsten carbide and cobalt, compaction thereof to a suitable compact geometry, and treatment of the compact in order to affect the grain size of the tungsten carbide in connection to the subsequent sintering, and to induce a cobalt gradient therein, wherein in the cobalt content increases towards a surface of the sintered body that could preferably be used as a surface which is attached to a steel holder by means of brazing.
• a compact produced in accordance with the teaching is shown in fig. 2 and indicated with reference number 4.
• a process step in which the compact 4 is provided with a coating comprising an element that has a grain growth inhibiting effect on tungsten carbide and an element that has a grain growth inhibiting effect on tungsten carbide is shown in fig. 3.
• the invention thus includes a method of producing a tool 1 for cutting, drilling or crushing of solid material, said tool comprising a cemented carbide body 2 attached to a steel holder 3, wherein said method comprises the steps of providing said cemented carbide body 2 by; providing a powder mixture, compacting said powder mixture into a compact 4 comprising a hard phase mainly comprised by tungsten carbide, WC, and a binder consisting of cobalt, wherein the cobalt content of the compact 4 is equal to or lower than about 5.5 wt , providing a compound comprising a carbide or a nitride formed by carbon or nitrogen and an element that has a grain growth inhibiting effect on tungsten carbide, and providing an element that has a grain growth promoting effect on WC, and applying said compound and said grain growth promoting element onto at least a tip region 5 of said compact 4, wherein said tip region 5 will form a tip region 6 of the cemented carbide body 2 aimed for engagement with material to be cut, drilled into, turned or crushed
• the compact 4 provided with said compound and said grain growth promoting element is then sintered into said cemented carbide body 2 such that the cobalt content at said base surface 8 becomes equal to or higher than 4.5 wt as a result of said induced generation of a cobalt content gradient, the ratio cobalt content cobalt content of the compact to cobalt content level at the base surface 8 becomes >1.09, and said base surface 8 of the cemented carbide body 2 is attached to the steel holder 3 by means of brazing.
• brazing would not be conceived for a body having such a low mean content of cobalt, but due to a surprisingly strong effect of said compound and said grain growth promoting element, the cobalt content at the base surface 8 of the body 2 is surprisingly high and therefore enables brazing as a means of attaching the body to the steel holder 3.
• bodies with a very low mean content of cobalt can be attached to a steel holder by means of brazing.
• the mean cobalt content may be below 5 wt or even below 4.5 wt .
• the compact 4 as presented in figs. 2-4, as well as the body 2 formed therefrom, is cylindrical with a conical tip. It may be generally defined as knob-shaped.
• the generally circular base surface 7 of the compact 4, and thus the base surface 8 of the body 2 is formed by a bottom surface thereof located opposite to the tip region 5, 6 of the compact 4 and body 2 respectively.
• the base surface 7 of the compact 4 and the base surface 8 of the body 2 are generally flat, but could have some other geometry if necessitated by the design of the steel holder 3 or because of other design-related or function-related reasons.
• slurry 9 comprising said compound, said grain growth promoting element and a solvent, suitably water, an alcohol or a polymer such as polyethylene glycol, is provided in a can 10, and the compact 4 is dipped into the slurry 9, as shown in fig. 3.
• the compact 4 has an open porosity, and the particles of said compound and said grain growth promoting element in the slurry 9 are of such size that particles of said compound and said grain growth promoting element will be introduced into pores of the compact 4 by capillary forces generated by said pores.
• a solvent suitably water, an alcohol or a polymer such as polyethylene glycol
• said compound consists of particles of Cr 3 C 2 and said grain growth promoting element consists of carbon in the form of soot.
• said grain growth promoting element consists of carbon in the form of soot.
• the amount of said compound and said grain growth promoting element adopted by the compact 4 should be above a predetermined level in relation to the mass of the compact 4.
• a primary reason for introducing said compound and said grain growth promoting element in the compact may be to control the grain size of the tungsten carbide during the subsequent sintering of the compact 4 in order to obtain a body presenting a tip surface having higher hardness due to lower binder content (and slightly larger tungsten carbide grains) and a more ductile region below said surface having higher binder content.
• this may be determining for the amount of added compound and grain growth promoting element and the displacing effect thereof on cobalt.
• the shape of the compact 4 in particular the height is designed with regard thereto.
• the height h of the compact 4 should be less than 25 mm, preferably less than 20 mm, preferably less than 15 mm, and more preferably less than 10 mm.
• a too high cylindrical compact will result in insufficiently high cobalt content at the base surface thereof. Referring to fig. 4, for a cylindrical compact having a height h and a generally circular base surface with a diameter d, 0.5 ⁇ h/d ⁇ 2.
• the mass of compact into which cobalt is displaced from the region in which said compound and grain growth promoting element is added should be delimited such that a significant cobalt gradient is achieved and remarkably increased cobalt content is obtained at said base surface.
• the porosity of the compact may be in the region of 50%, whereby the measures of the non-sintered compact 4 are about 1.2 times the measures of the sintered compact, i.e. the cemented carbide body 2.
• said compound and grain growth promoting element may also be applied onto lateral surfaces 11 of the compact 4.
• said compound and grain growth promoting element may have a negative effect on the cobalt content of the base surface 7 in the region of said edge 12 or transition region. Therefore, it is preferred that, in a zone 11 ' of the lateral surface or surfaces 11 neighbouring the base surface 7, the lateral surface or surfaces 11 are excluded from the application of said compound and said grain growth promoting element.
• Figs. 2-4 show the presence of such a zone.
• said compound and said grain growth promoting element should be applied to at least 50%, preferably at least 70%, and most preferably to at least 80% of the total area of the top and lateral surfaces.
• the tip region 5 defines a rounded or conical top surface 5.
• Fig. 6 shows an alternative embodiment of a compact 13, wherein said compact 13 has a generally plate-like shape, has a width w, a height h and a thickness t, and wherein 0.2 ⁇ h/w ⁇ 2, t ⁇ w, 2mm ⁇ t ⁇ 20mm, and, said base surface 14 is a large side of said compact, and said tip region 16 includes at least a part of an opposite large side 15 thereof.
• Fig. 7 shows an alternative approach of where to apply said compound and grain growth element onto the compact 13.
• the tip region 16 of the compact 13 which will form a tip region of the cemented carbide body aimed for engagement with material to be cut, drilled into, turned or crushed by means of said tool, is provided with said compound and grain growth promoting element.
• Application is achieved by means of dipping of the compact 13 into a can filled with slurry corresponding to the can 10 and slurry 9 shown in fig. 3.
• the application may be more or less concentrated to the tip region 16.
• Fig. 10 shows an example in which a is approximately 45°, and only an edge region defining said tip region 16 is provided with said compound and grain growth promoting element.
• Fig. 11 shows an alternative embodiment in which the whole large side 15 opposite said based surface 14 has been provided with said compound and grain growth promoting element by using a dipping angle a of approximately 0°. Parts of the lateral sides 17, from the large side 15 and a distance x towards the base surface 14 of the compact 13 has been provided with said compound and grain growth promoting element.
• the compact 13 has lateral surfaces 18 neighbouring the base surface 14. A zone 18' of the lateral surface or surfaces neighbouring the base surface 14, is excluded from the application of said compound and said grain growth promoting element.
• Fig. 9 shows a body 19 formed by means of sintering of a compact 13 provided with said compound and grain growth promoting element in accordance with the principles disclosed in figs. 7 and 8.
• a base surface 20, corresponding to the base surface 14 of the compact 13 is attached to a steel holder 21 by means of brazing.
• an end region of the body 19 opposite to the end at which the tip region is located may be attached to steel holder 21 by means of brazing.
• the body 19 and the steel holder 21 together define a tool 22.
• the tip region of the body is indicated with 23.
• the design of the compact will have an impact on the possibility of obtaining sufficiently high cobalt content at the base surface 20 of the body 19.
• the mass of compact into which cobalt is displaced should be delimited. Accordingly, for a compact with the design presented in fig. 6, 2 mm ⁇ t ⁇ 20 mm.
• the lower the mean cobalt content in the compact the more important it becomes that the thickness thereof is relatively low in order to reduce the mass of compact into which cobalt displaced from regions in which said compound and grain growth promoting element are applied is low, such that a high level of cobalt (equal to or higher than 6 wt%) is obtained at the base surface 20.
• t is less than 20 mm, preferably less than 15 mm, and more preferably less than 10 mm, wherein said compound and said grain growth promoting element are applied onto at least a part of said top surface (here large side 15), preferably on the whole top surface.
• the porosity of the compact may be in the region of 50%, whereby the measures of the non-sintered compact are about 1.2 times the measures of the sintered compact, i.e. the cemented carbide body.
• the following examples should be regarded as supporting the general inventive concept of providing a sufficiently high cobalt content at the base surface of a sintered compact, including for different shapes of the cemented carbide body, such that the latter may be attached to a steel holder by means of brazing, preferably inductive brazing.
• the powder used in the test samples was granulated by spray drying, had a mixture of tungsten carbide, cobalt binder and polymer binder having a carbon balance in such way that no eta phase is found after sintering without green body surface treatment with grain growth promoters and grain growth inhibitors and in the same time having a carbon balance that is compensated for the carbon absorbed from the treatment.
• Hardness measurement was done using a programmable hardness tester, KB30S by KB Pruftechnik GmbH. Untreated samples were used as references.
• HV5 888-9.9 Co+[(229+532exp((6- Co)/6.7))]/d WC a5 (Equation 1).
• n*2*6*8+n*6*6 415 mm (treated part of the body approximated with a cylinder with radius r and height h). Note that effective surface area (the true surface area due to roughness of the surface) is not considered.
• the sintered samples were cut along their cylindrical center line and then ground and polished before the HV5 measurement.
• the amount of C and Cr 3 C 2 is roughly 5 mg and 30 mg respectively and hence the specific treatment would be 0.012 mg/mm 2 and 0.072 mg/mm 2 C and Cr 3 C 2 respectively.
• Figure 13 shows that the cobalt concentration difference between the zone closest to the treated surface and zone most distant from the treated surface is about 1.8 wt%.
• the amount of C and Cr 3 C 2 is roughly 12 mg and 60 mg respectively and hence the specific treatment would be 0.012 mg/mm 2 and 0.061 mg/mm 2 C and Cr 3 C 2 respectively.
• Figure 14 shows that the cobalt concentration difference between the zone closest to the treated surface and zone most distant from the treated surface is about 2.2 wt%.
• the planar treated or dipped sample of the 6% Co grade shows that the HV5 is highest at the treated side and lowest at the opposite side, see figure 15.
• the calculation of the Co distribution shows that the difference in cobalt concentration between treated surface and opposite surface is about 1.8%.
• the planar treated or dipped sample of the 8% Co grade shows that the HV5 is highest at the treated side and lowest at the opposite side, see figure 16.
• the calculation of the Co distribution shows that the difference in cobalt concentration between treated surface and opposite surface is about 2.2%.
• Table 4 shows a summary of the found differences in cobalt concentration (iso-lines maps) between zones closest and most far away from the treated surface.
• Example 1 (table 2) and Example 2 (table 3). It is therefore appropriate to use the hardness, cobalt concentration and tungsten grain size equation by Roebuck et al. for determining cobalt content.
• Example 6 (brazing of 5% sample onto steel)
• Example 1 Samples of Example 1 were brazed onto steel plates 20 mm in diameter and 5 mm in thickness made of EN 42CrMo4. Before brazing the steel plates where shot blasted with steel grains. Afterwards the plates where cleaned in an ultrasound cleaner in an ethanol solvent. The cemented carbide samples were grit blasted with SiC grit and also afterwards cleaned in an ultrasound cleaner in an ethanol solvent.
• the used braze material was also cleaned in an ultrasound cleaner in an ethanol solvent.
• Inductive brazing under ambient conditions was used.
• the brazing unit consisted of two 20kW generators, but just one was used due to the reason that just one coil (single coil) was necessary to heat the assembly.
• the frequency was adjusted to between 70 and 450kHz according to resonance frequency which guarantees fast heating.
• the assembly was heated up to 950°C (temperature measured by two pyrometers). After around 15 s the braze melted. After about 10 s the assembly was let to cool down in air to room temperature.
• the braze joint was satisfactory strong.

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• 2016
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