METHOD OF PRODUCING A TOOL FOR CUTTING, DRILLING OR CRUSHING OF SOLID MATERIAL, AND SUCH A TOOL

Abstract

A tool for cutting, drilling or crushing of solid material, wherein the tool includes 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. The cemented carbide body has a hard phase mainly of tungsten carbide, WC, and a binder consisting of cobalt, wherein the cobalt content of the cemented carbide body is equal to or lower than about 5.5 wt %. The cemented carbide body has a cobalt content gradient therein wherein the cobalt content increases towards the base surface and is at least 4.5 wt % at the base surface. The ratio of the cobalt content at the base surface to the cobalt content of the cemented carbide is 1.09. A method for producing the tool is also presented.

Claims

1. A method of producing a tool for cutting, drilling or crushing of solid material, said tool including a cemented carbide body attached to a steel holder, wherein said method comprises the steps of: providing a cemented carbide body by providing a powder mixture, compacting said powder mixture into a compact having a hard phase of tungsten carbide, WC, and a binder of cobalt, wherein the cobalt content of the compact is at a first cobalt content level and is about 5.5 wt %; providing a compound including 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; applying said compound and said grain growth promoting element onto at least a tip region of said compact, wherein said tip region will form a tip region of the cemented carbide body arranged for engagement with material to be cut, drilled into or crushed by said tool, and keeping a base surface of the compact, which will form a base surface of the cemented carbide body that will be attached to said steel holder, free from said compound and grain growth promoting element, wherein 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; sintering the compact provided with said compound and said grain growth promoting element into said cemented carbide body, the cobalt content at said base surface being a second cobalt content level that is 4.5 wt % as a result of said induced generation of a cobalt content gradient, wherein the ratio of the second cobalt content level to the first cobalt content level is 1.09; and attaching said base surface of the cemented carbide body to the steel holder by brazing.

2. The method according to claim 1, wherein the second cobalt content at said base surface is 5.0 wt %.

3. The method according to claim 1, wherein the second cobalt content at said base surface is 6.0 wt %.

4. The method according to claim 1, wherein the ratio of the second cobalt content level to the first cobalt content level is 1.14.

5. The method according to claim 1, wherein said tip region of the cemented carbide body has a mean cobalt content, being a third cobalt content level of 4.5 wt %.

6. The method according to claim 5, wherein the ratio of the second cobalt content level to the third cobalt content level is 1.2.

7. The method according to claim 1, wherein the first cobalt content level is about 5.0 wt %.

8. The method according to claim 1, wherein said compact includes top and lateral surfaces and said base surface, and that said compound and said grain growth promoting element is applied to at least 50% of the total area of the top and lateral surfaces.

9. The method according to claim 1, wherein said compact includes top and lateral surfaces and wherein, 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.

10. The method according to claim 1, wherein said compact includes top and lateral surfaces and said base surface, and wherein a distance between the top surface and the base surface, which is opposed to the top surface, is less than 25 mm, and wherein said compound and said grain growth promoting element are applied onto at least a part of said top surface.

11. The method according to claim 1, wherein, in said compound, the element that has a grain growth inhibiting effect on WC is any of chromium, vanadium, tantalum or niobium and said grain growth promoting element is carbon in the form of graphite.

12. A tool for cutting, drilling or crushing of solid material, comprising: 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 having a hard phase of tungsten carbide, WC, and a binder consisting of cobalt, wherein the cobalt content of the cemented carbide body is at a first cobalt content level and is equal to or lower than about 5.5 wt %, and wherein, the cemented carbide body has a cobalt content gradient therein wherein the cobalt content increases from a tip region towards said base surface, the base surface having a second cobalt content level that is at least 4.5 wt %, wherein the second ratio cobalt content level to first cobalt content level is 1.09.

13. The tool according to claim 12, wherein the second cobalt content level is at least 5.0 wt % at said base surface of the cemented carbide body.

14. The tool according to claim 12, wherein the second cobalt content level is at least 6 wt % at said base surface of the cemented carbide body.

15. The tool according to claim 12, wherein the ratio second cobalt content level to first cobalt content level is 1.14.

16. The tool according to claim 12, wherein said tip region of the cemented carbide body has a mean cobalt content having a third cobalt content level of 4.5 wt %.

17. The tool according to claim 16, wherein the ratio of the second cobalt content level to the third cobalt content level is 1.2.

18. The tool according to claim 12, wherein the cobalt content of the cemented carbide body, being the first cobalt content level, is about 5.0 wt %.

19. The tool according to claim 12, wherein said cemented carbide body 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.

20. The tool according to claim 12, wherein said cemented carbide body 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, 1.7 mm<t<17 mm, and, said base surface being a large side of said body, and wherein said tip region includes at least a part of an opposite large side thereof.

21. The tool according claim 12, wherein at least in the tip region thereof, the cemented carbide body has an outer surface zone having an elevated WC mean grain size as a result of an elevated content of an element that has a grain growth promoting effect on WC, and a second zone below said outer surface zone, wherein, in said second zone, the WC mean grain size is smaller than in said outer surface zone as a result of an elevated content therein of an element that has a grain growth inhibiting effect on WC, and wherein the cemented carbide body has the cobalt content gradient therein as a result of the presence of said grain growth promoting element and said grain growth inhibiting element therein.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Embodiments of the invention will be presented more in detail with reference to the annexed drawing, on which;

[0068] FIG. 1 is a perspective view of an embodiment of a tool according to the invention,

[0069] FIG. 2 is a perspective view of a compact according to the invention before application of a coating thereon,

[0070] 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,

[0071] FIG. 4 is a side view of the coated compact,

[0072] 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,

[0073] FIG. 6 is a perspective view of another embodiment of a compact before application of a coating thereon,

[0074] 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,

[0075] FIG. 8 shows the coated compact of FIG. 7,

[0076] 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,

[0077] FIG. 10 is a perspective view of one embodiment of a coated compact,

[0078] FIG. 11 is a perspective view of another embodiment of a coated compact,

[0079] 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 %,

[0080] 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 %,

[0081] 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 %,

[0082] 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 %,

[0083] 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

[0084] 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 %.

DETAILED DESCRIPTION OF THE INVENTION

[0085] 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.

[0086] 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). However, 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.

[0087] 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.

[0088] 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 by means of said tool 1, and keeping a base surface 7 of the compact 4, which will form a base surface 8 of the cemented carbide body 2 that will be attached to said steel holder 3, free from said compound and grain growth promoting element, wherein said compound and said grain growth promoting element is of a type that will diffuse into the compact 4 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. 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. Normally, 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. With this technique of controlling the cobalt content of the base surface of the body, bodies with a very low mean content of cobalt can be attached to a steel holder by means of brazing. Depending on the design of the compact and how much of said compound and grain growth promoting element that is adopted by the compact, the mean cobalt content may be below 5 wt % or even below 4.5 wt %.

[0089] 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.

[0090] In order to apply said compound and said grain growth promoting element, 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. Other principles of application of said compound are possible, and have been mentioned in the foregoing summary of the invention.

[0091] In the exemplifying embodiment, said compound consists of particles of Cr.sub.3C.sub.2 and said grain growth promoting element consists of carbon in the form of soot. As previously mentioned, other alternatives are feasible within the scope of the invention.

[0092] In order to achieve sufficient cobalt gradient, and as a result thereof a sufficiently high cobalt content at the base surface 8 of the body 2 to enable attachment of the latter to a steel holder 3 by means of brazing, 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. However, 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. Thus, this may be determining for the amount of added compound and grain growth promoting element and the displacing effect thereof on cobalt. Accordingly, in order to promote sufficiently high cobalt content at the base surface 8 of the body 2, 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. In other words, 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.

[0093] In order to further promote the generation of high cobalt content at the base surface, said compound and grain growth promoting element may also be applied onto lateral surfaces 11 of the compact 4. However, if applied all the way to the edge 12 or transition region between lateral surfaces 11 and base surface 7, 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.

[0094] When said compact comprises top and lateral surfaces 11 and said base surface 7, 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. In the case of a knob-like body like the one shown in FIG. 2, the tip region 5 defines a rounded or conical top surface 5.

[0095] 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, 2 mm<t<20 mm, 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.

[0096] 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. Depending on the dipping angle of the compact into the slurry, wherein is the angle between the large side of the compact opposite to said base surface, 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 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. In this context it should be emphasized that other application principles than dipping into slurry are of course conceivable for the application of said compound and grain growth promoting element. However, dipping into slurry has been found a relatively reliable and relatively uncomplicated way of application and is therefor, for the moment being, suggested as preferred application method.

[0097] 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. Also 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.

[0098] As previously discussed regarding the cylindrical compact and body presented in FIGS. 1-5, 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. Therefore, 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.

EXAMPLES

[0099] In the following, examples that prove the unexpectedly strong effect of the application of a compound according to the invention and a grain growth promoting element according to the invention on the cobalt gradient in a sintered compact comprising tungsten carbide and cobalt are presented. Though the mean cobalt content in some of the test samples are higher than the mean cobalt content according to the claimed invention, these examples give a very clear vision of what cobalt content levels that could be expected at a base surface for sintered compacts with a mean cobalt content as suggested by the invention. Accordingly, 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.

Powder

[0100] 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.

Sintering

[0101] The sintering was done under normal production sintering conditions for hardmetals.

Hardness Measurement

[0102] Hardness measurement was done using a programmable hardness tester, KB30S by KB Prftechnik GmbH. Untreated samples were used as references.

Estimation of the Cobalt Concentration

[0103] An estimation of the cobalt concentration was done using the known equation by Roebuck et al.sup.[1] that relates hardness with weight % Co and tungsten carbide grain size, d.sub.WC. The untreated reference samples were used to evaluate the tungsten carbide grain size by using the known % Co and measured hardness. Finally, the weight % Co was back calculated from the measured hardness values of the treated samples.

HV5=8889.9% Co+[(229+532exp((6% Co)/6.7))]/d.sub.WC.sup.0.5(Equation 1).

[0104] One important approximation with this method is using a constant tungsten carbide grain size. The carbide grain size is affected by the treatment in a zone below the treated surface to about 2-3 mm below the treated surface. However, the calculation of % Co is used to see the amount of cobalt far away from the surface that was treated. Another approximation was to neglect the residual stresses both from sample preparation and variation in thermal expansion.

[0105] Each reference sample used for establishing d.sub.WC was measured ten times on HV5. Results are presented in table 1.

TABLE-US-00001 TABLE 1 Grade HV5 (std-dev.) d.sub.WC (m) Eq. 1 5% Co 1502 (12) 1.6 10% Co 1088 (7) 3.0 6% Co 1383 (6) 1.9 8% Co 1199 (15) 2.6

Example 1 (Cylindrical Sample)

[0106] Green bodies, compacts, were powder pressed to 50% porosity into 12 mm diameter cylindrical bodies (pellets) having a total height of 12 mm.

[0107] The treatment was done by coating the body from the top all the way down to (about 8 mm) below the top with a suspension holding chromium carbide and free carbon. This corresponds to about a projected surface area 2rh+r.sup.2=*2*6*8+*6*6=415 mm.sup.2 (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.

[0108] The sintered samples were cut along their cylindrical center line and then ground and polished before the HV5 measurement.

[0109] A few bodies were chemically analyzed on chromium and cobalt. Prior analyzing, the bodies were cut in a top piece defined by a cut at 2.3 mm below the top and a bottom piece defined by a cut at 1.5 mm above the bottom. The analyzing methods are Co % XRF:H12 and Cr % XRF:HM12. Results are presented in table 2.

TABLE-US-00002 TABLE 2 (5.0% Co-grade) Position Co % Cr % Top 4.17 0.33 Bottom 5.71 <0.10

[0110] From the chemical results it is indeed seen a higher Co concentration in the bottom.

[0111] The HV5 data and the estimation of the cobalt concentration are reproduced in FIGS. 12 and 13. The results agree well with chemical analysis above. It is therefore appropriate to use the hardness, cobalt concentration and tungsten grain size equation by Roebuck et al. The difference is partly affected by that the chemical analysis gives an average cobalt content of the whole piece analysed while the hardness method by Roebuck et al. gives cobalt content maps over the whole body.

[0112] The amount of C and Cr.sub.3C.sub.2 is roughly 5 mg and 30 mg respectively and hence the specific treatment would be 0.012 mg/mm.sup.2 and 0.072 mg/mm.sup.2 C and Cr.sub.3C.sub.2 respectively.

[0113] FIG. 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 %.

Example 2 (Cylindrical Sample with Cone)

[0114] Green bodies, compacts, were powder pressed to 50% porosity into 19 mm diameter cylindrical bodies with a conical tip having a total height of 25 mm.

[0115] The treatment was done by coating the body from the tip all the way down to 20 mm below the tip with a suspension holding chromium carbide and free carbon. This corresponds to about a projected surface area r(S+2h)=*9.5*(14.2+2*9.4)=985 mm.sup.2 (treated part of the body approximated with a cone with radius r and side S and a cylinder with radius r and height h). Note that effective surface area is not considered.

[0116] A few bodies were chemically analyzed on chromium and cobalt. Prior analyzing, the bodies were cut in a top piece defined by a cut at 6.5 mm below the tip and a bottom piece defined by a cut at 3 mm above the bottom. The analyzing methods are Co % XRF:H12 and Cr % XRF:HM12. Results are presented in table 3.

TABLE-US-00003 TABLE 3 (10% Co-grade) Position Co % Cr % Top 9.27 0.14 Bottom 10.90 0.06

[0117] From the chemical results it is indeed seen a higher Co concentration in the bottom. The sintered samples were cut along their cylindrical center line and then ground and polished before the HV5 measurement. The HV5 data and the estimation of the cobalt concentration are reproduced in FIG. 14. The results agree well with chemical analysis above. It is therefore appropriate to use the hardness, cobalt concentration and tungsten grain size equation by Roebuck et al. The difference is partly affected by that the chemical analysis gives an average cobalt content of the whole piece analyzed while the hardness method by Roebuck et al. gives cobalt content maps over the whole body.

[0118] The amount of C and Cr.sub.3C.sub.2 is roughly 12 mg and 60 mg respectively and hence the specific treatment would be 0.012 mg/mm.sup.2 and 0.061 mg/mm.sup.2 C and Cr.sub.3C.sub.2 respectively.

[0119] FIG. 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 %.

Examples 3-5 (Rectangular Samples)

[0120] Green bodies, compacts, were powder pressed to 50% porosity into 15156 mm rectangular samples. The green bodies were dipped according to the drawing showed by FIG. 7. Sintering was done with standard production sintering furnaces. The samples were cut after sintering followed by grinding, polishing and HV5 measurement.

Example 3 (6% Co)

[0121] Treatment was done on the projective surface area about 1*15*4+15*15=285 mm.sup.2. The added amount of C and Cr.sub.3C.sub.2 is 2.8 mg and 14.0 mg respectively and hence the specific treatment is 0.010 mg/mm.sup.2 and 0.049 mg/mm.sup.2 respectively.

[0122] 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 FIG. 15. The calculation of the Co distribution shows that the difference in cobalt concentration between treated surface and opposite surface is about 1.8%.

Example 4 (8% Co)

[0123] Treatment was done on the projective surface area about 1*15*4+15*15=285 mm.sup.2. The amount of C and Cr.sub.3C.sub.2 is 3.0 mg and 15.1 mg respectively and hence the specific treatment is 0.011 mg/mm.sup.2 and 0.053 mg/mm.sup.2 respectively.

[0124] 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 FIG. 16. The calculation of the Co distribution shows that the difference in cobalt concentration between treated surface and opposite surface is about 2.2%.

Example 5 (8% Co)

[0125] Treatment was done on the projective surface area about) 15*1.3*(1/cos 60+1/sin 60+1.3.sup.2/sin 120=63 mm.sup.2. The amount of C and Cr.sub.3C.sub.2 is 0.6 mg and 3.2 mg respectively and hence the specific treatment is 0.010 mg/mm.sup.2 and 0.051 mg/mm.sup.2 respectively.

[0126] The edge treated or dipped sample of the 8% Co grade shows that the HV5 is highest at the treated edge and lowest at the opposite side, see FIG. 17. The calculation of the Co distribution shows that the difference in cobalt concentration between treated surface and opposite surface is about 2.3%.

Summary of Iso-Lines Maps from Examples 1-5:

[0127] 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.

TABLE-US-00004 TABLE 4 5.0% Co 10.0% Co 6.0% Co 8.0% Co 8.0% Co (ex. 1) (ex. 2) (ex. 3) (ex. 4) (ex. 5) Averaged % Co 1.7 2.2 1.8 2.2 2.3 difference

[0128] The results agree well with chemical analysis for samples of 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)

[0129] 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.

[0130] The used braze material was also cleaned in an ultrasound cleaner in an ethanol solvent.

[0131] Braze material used: High Temp 548 (55% Cu, 6% Ni, 35% Zn, 4% Mn) with solidus temp. 880 C. and liquidus temp. 920 C.

[0132] Flux used: Superior 609

[0133] Assembling procedure: Cover braze shim with flux. Put shim on steel and cemented carbide-disc on top. Cover with flux.

[0134] Inductive brazing under ambient conditions was used. The brazing unit consisted of two 20 kW 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 450 kHz 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.

[0135] The braze joint was satisfactory strong.

REFERENCES

[0136] Ref [1]. A national measurement good practice guide, No 20, Mechanical tests for hardmetals, B Roebuck, M Gee, E G Bennet and R Morell, National Physical Laboratory. 1999.