Improved tools for cutting rock drilling

Abstract: The present invention relates to a rock bit insert of cemented carbide for cutting rock drilling. The insert (1) is provided with one or more bodies (3) or layers of diamond or cBN produced at high pressure and high temperature in the diamond or cBN stable area. The body ef cemented carbide has a multi-structure containing eta-phase (6) surrounded by a surface zone (4,5) of cemented carbide free of eta-phase and having a low content of cobalt in the surface (4) and a higher content of cobalt next to the eta-phase zone (5).

Description: The present invention concerns the field of drill bits and inserts therefor. More particularly the invention relates to drill bit inserts for cutting rock (EP-A-356097). The inserts comprise cemented carbide provided with bodies and/or layers of diamond and/or cubic boron nitride (cBN). BACKGROUND OF THE INVENTION There are three main groups of rock drilling methods: percussive, rotary crushing and cutting. In percussive and rotary crushing rock drilling the bit buttons are working as rock crushing tools as opposed to cutting, where the inserts work rather as shearing elements. A rock bit generally consists of a body of steel which is provided with a number of inserts comprising cemented carbide. Many different types of such rock bits exist having different shapes of the body of steel and of the inserts of cemented carbide as well as different numbers and grades of the inserts. For percussive and rotary crushing rock drilling the inserts generally have a rounded shape, often of a cylinder with a rounded top surface generally referred to as a button. For shearing rock the inserts are provided with an edge acting as a cutter. There already exists a number of different high pressure-high temperature sintered cutters provided with polycrystalline diamond layers. These high wear resistant cutter tools are mainly used for oil drilling. The technique when producing such polycrystalline diamond tools using high pressure-high temperature (HP/HT) has been described in a number of patents, e.g.: US Patent No 2,941,248: "High temperature high pressure apparatus". US Patent No 3,141,746: "Diamond compact abrasive": High pressure bonded body having more than 50 vol% diamond and a metal binder:Co,Ni,Ti,Cr,Mn,Ta etc. These patents disclose the use of a pressure and a temperature where diamond is the stable phase. In some later patents: e.g. US Patent Nos 4,764,434 and 4,766,040 high pressure-high temperature sintered polycrystalline diamond tools are described. In the first patent the diamond layer is bonded to a support body having a complex, non-plane geometry by means of a thin layer of a refractory material applied by PVD or CVD technique. In the second patent temperature resistant abrasive polycrystalline diamond bodies are described having different additions of binder metals at different distances from the working surface. A recent development in this field is the use of one or more continuous layers of polycrystalline diamond on the top surface of the cemented carbide button. US Patent 4,811,801 discloses rock bit buttons including such a polycrystalline diamond surface on top of the cemented carbide buttons having a Young's modulus of elasticity between 80 and 102 x 10⁶ p.s.i., a coefficient of thermal expansion between 2,5 and 3,4 x 10⁻⁶ °C⁻¹,a hardness between 88,1 and 91,1 HRA and a coercivity between 85 and 160 Oe. Another development is disclosed in US Patent 4,592,433 including a cutting blank for use on a drill bit comprising a substrate of a hard material having a cutting surface with strips of polycrystalline diamond dispersed in grooves, arranged in various patterns. US Patent 4,784,023 discloses a cutting element comprising a stud and a composite bonded thereto. The composite comprises a substrate formed of cemented carbide and a diamond layer bonded to the substrate. The interface between the diamond layer and the substrate is defined by alternating ridges of diamond and cemented carbide which are mutually interlocked. The top surface of the diamond body is continuous-and covering the whole insert. The sides of the diamond body are not in direct contact with any cemented carbide. European patent application 0312281 discloses a tool insert comprising a body of cemented carbide with a layer of polycrystalline diamond and between the layer and the cemented carbide a number of recesses filled with abrasive compact material extending into the supporting body of cemented carbide. Another development in this field is the use of cemented carbide bodies having different structures in different distances from the surface. US Patent 4,743,515 discloses rock bit buttons of cemented, carbide containing eta-phase surrounded by a surface zone of cemented carbide free of eta-phase and having a low content of cobalt in the surface and a higher content of cobalt closer to the eta-phase zone. US Patent 4,820,482 discloses rock bit buttons of cemented carbide having a content of binder phase in the surface that is lower and in the center higher than the nominal content. In the center there is a zone having a uniform content of binder phase. The tungsten carbide grain size is uniform throughout the body. OBJECT OF THE INVENTION The object of the invention is to provide a drill bit cutter of cemented carbide with bodies and/or layers of diamond and/or cBN with high and uniform compression of the diamond or cBN by sintering at high pressure and high temperature in the diamond or cBN stable area. It is a further object of the invention to make it possible to maximize the effect of diamond or cBN on the resistance to cracking, chipping and wear. SUMMARY OF THE INVENTION According to the present invention there is provided a drill bit insert for cutting rock comprising a body of cemented carbide according to US Patent 4,743,515 provided with one or more bodies and/or a layer of diamond and/or cBN and produced at high pressure and high temperature. The cutter above can be adapted to different types of rocks by changing the material properties and geometries of the cemented carbide and/or the diamond or cBN, especially hardness, elasticity and thermal expansion, giving different wear resistance and impact strength of the bits. Hammer impact tests of inserts of the type described in US Patent 4,784,023 with a substrate of cemented carbide and a diamond layer bonded to the substrate (FIG.1) revealed a tendency of chipping off part of the diamond layer after a number of blows. When using a cemented carbine body having a multi-structure according to US Patent 4,743,515 with a diamond layer (FIG.2) it was surprisingly found that the chipping off tendency of the diamond layer considerably decreased compared to the corresponding geometry and composition without the multi-structure carbide (FIG.1). A similar improvement was achieved for inserts having a layer of cBN and comparing cemented carbide bodies with and without a multi-structure according to US Patent 4,743,515. The explanation of this effect,is that the increase of the resistance against chipping, might give a favourable stress pattern caused by the difference between the thermal expansion of the diamond layer and the cemented carbide body, giving the layer a high and uniform compressive prestress. BRIEF DESCRIPTION OF THE DRAWINGS 1 = cemented carbide insert 2 = steel body 3 = diamond or cBN body 4 - cemented carbide : Co poor zone 5 = cemented carbide : Co rich zone 6 = cemented carbide : eta-phase containing core FIG.1 shows a prior art cemented carbide insert having a layer of polycrystalline diamond. FIG.2 shows a cemented carbide insert according to the invention having the same type of layer of diamond as in FIG.1 but with the cemented carbide containing eta-phase surrounded by a surface zone of cemented carbide free of eta-phase. FIG.3-30 show various embodiments of cemented carbide according to the invention, i.e. provided with different bodies of diamond or cBN in the surface. The inserts according to FIG.5-30 can also be provided with at least one layer of diamond and/or cBN partly or completely covering the insert. The core of the cemented carbide insert is in all cases containing eta-phase surrounded by a surface zone of cemented carbide free of eta-phase. DETAILED DESCRIPTION OF THE INVENTION. The rock cutter according to the present invention is provided with one or more bodies and/or a coating of one or more layers of diamond and/or cBN. The coating can have different shapes such as a completely covering layer on top of the insert of cemented carbide or strips of different shapes and patterns on top of the cemented carbide insert. Each strip includes a working face exposed at the surface of the cemented carbide insert. The strips may extend toward a peripheral edge of the insert and may terminate short of such edge or extend all the way thereto. The strips may be non-intersecting or could be interconnected such as at their ends to form an undulating pattern, or chevrons for example. An outer curvilinear strip may interconnect outer ends of other strips to form an extended cutting edge for use in softer formation. The strips may comprise two sets of strips, with each set extending toward a different section of the peripheral edge; the strips of one set may be spaced from the strips of the other set by a central region of the cutting surface. The bodies of diamond and/or cBN may be placed regularly or irregularly on the top of the insert. Different sizes and shapes of the bodies may be mixed. Other modifications, too, are obvious to those skilled in the art. The diamond or cBN may be thermally stable or thermally unstable. The diamond and/or cBN can be sinterd in place in grooves, for example. The grooves may have a depth in the range from 0,2-3,5 mm and a width in the range of from 0,2-4,0 mm. The grooves may include undercut portions to promote stability of the diamond or cBN strips. The cutting insert is preferably brazed to a holder, such as a cemented carbide stud, and the stud is preferably press-fit into a drill-bit. However, brazing is often sufficient. The diamond or cBN bodies or layers shall be adapted to the type of rock and drilling method by varying the grain size of the diamond or cBN feed stock and the amount of binder metal. The grain size of the diamond or cBN shall be 3-500 micrometer, preferably 10-150 micrometer. The diamond or cBN may be only one nominal grain size or consist of a mixture of sizes, such as 80 w/o of 40 micrometer and 20 w/o of 10 micrometer. Different types of catalyst metals can be used such as Co,Ni,Mo,Ti,Zr,W,Si,Ta,Fe,Cr,Al,Mg,Cu etc. or alloys between them. The amount of catalyst metal shall be 1-40 vol.%, preferably 3-20 vol.%. In addition other hard materials, preferably less than 50 vol.%, can be added such as : diamond, cBN, B₄C, TiB₂, SiC, ZrC, WC, TiN, ZrB, ZrN, TiC, (Ta,Nb)C, Cr-carbides, AlN, Si₃N₄, AlB₂.etc. as well as whiskers of B₄C, SiC, TiN, Si₃N₄, etc. (See US Patent 4,766,040). The bodies of diamond or cBN may have different levels of catalyst metal at different distances from the working surface according to US Patent 4,766,040. The cemented carbide grade shall be chosen with respect to type of rock and drilling methods. It is important to chose a grade which has a suitable wear resistance compared to that of the diamond or cBN body or coating. The catalyst phase content shall be 3-35 weight %, preferably 5-25 weight % for cutting rock drilling cutters and the grain size of the cemented carbide at least 1 micrometer, preferably 2-6 micrometer. The cemented carbide insert shall have a core containing eta-phase. The size of this core shall be 10-95%, preferably 30-65% of the total amount of cemented carbide in the insert. The core should contain at least 2% by volume, preferably at least 10% by volume of eta-phase but at most 60% by volume, preferably at the most 35% by volume. In the zone free of eta-phase the content of binder phase, i.e. in general the content of cobalt,shall in the surface be 0,1-0,9, preferably 0,2-0,7 of the nominal content of binder phase and the binder phase content shall increase in the direction towards the core up to a maximum of at least 1,2, preferably 1,4-2,5 of the nominal content of binder phase. The width of the zone poor of binder phase shall be 0,2-0,8, preferably 0,3-0,7 of the width of the zone free of eta-phase, but at least 0,4 mm and preferably at least 0,8 mm in width. The bodies of polycrystalline diamond may extend a shorter or longer distance into the cemented carbide body and the diamond or cBN body can be in contact with all three described zones, preferably in contact only with the cobalt poor zone. In one embodiment the diamond or cBN bodies consist of prefabricated and sintered bodies in which the catalyst metal has been extracted by acids. The bodies or layers are attached by the HP/HT technique. The HP/HT technique give a favourable stress distribution and a better thermal stability because of the absence of binder metal in the diamond or cBN. The cemented carbide inserts are manufacturated by powder metallurgical methods according to US Patent 4,743,515. The holes for the diamond or cBN bodies are preferably made before sintering either in a separate operation or by compacting in a specially designed tool. After sintering of the cemented carbide the mixture of diamond or cBN powder, catalyst metal and other ingredients are put in the holes or on the surface of the cemented carbide body, enclosed in thin foils and sintered at high pressure, more than 3,5 GPa, preferably at 6-7 GPa and at a temperature of more than 1100°C, preferably 1700°C for 1-30 minutes, preferably about 3 minutes. The content of binder metal in the diamond or cBN body or layer may be controlled either by previously coating the insert with a thin layer of e.g. TiN by CVD- or PVD-methods or by using thin foils such as Mo as disclosed in US Patent 4,764,434. After high-pressure sintering the insert is blasted and ground to final shape and dimension. EXAMPLE 1 DIAMOND A hammer impact test was made using a modified Charpy pendulum of diamond inserts according to FIG.2 with and FIG.1 without eta-phase core. The diamond layer had a thickness of 0.7 mm. The total height of the inserts was 3,5 mm and the diameter 13,3 mm. The hammer was released from a certain height and the chipping was observed after each blow. The number of blows before chipping was taken as the measure of the shock resistance. RESULTS Number of blows before chipping Insert without eta-phase core (FIG.1) 5 Insert according to the invention (FIG.2) 8 EXAMPLE 2 cBN Example 1 was repeated but with a cBN instead of a diamond coating with the difference that the hammer was released from another height. RESULTS Number of blows before chipping Insert without eta-phase core (FIG.1) 7 Insert according to the invention (FIG.2) 9

Claims: Cemented carbide insert (1) for rock drilling by cutting having bodies (3) and/or one or more layers (3) of diamond and/or cBN bonded at high pressure and high temperature, at which the insert has a multi-phase structure with a core (6) containing eta-phase surrounded by a surface zone (4,5) free of eta-phase. Insert according to claim 1, characterized in that the binder phase content in a zone (5) close to the eta-phase containing core (6) is higher than the nominal binder phase content. Insert according to any of the preceding claims, characterized in that the binder phase content in the surface (4) of said insert is 0.1-0.9 of the nominal binder phase content, wherein the grain size of the hard phase, i.e diamond or cBN, is 80 vol-% of 40 micrometer and 20 vol-% of 10 micrometer material.

Inventors: DENNIS MAHLON, FISCHER UDO, HILLERT LARS, WALDENSTROEM MATS, DENNIS, MAHLON, FISCHER, UDO, HILLERT, LARS, WALDENSTROEM, MATS,, Waldenström, Mats,
Applicants: DIAMANT BOART STRATABIT SA, SANDVIK AB, DIAMANT BOART STRATABIT S.A., SANDVIK AKTIEBOLAG
Application year: 1991
Main classification: E21B10
IPC codes: E21B10, C22C29