CA1237122A

CA1237122A - Rock bits having metallurgically bonded cutter inserts

Info

Publication number: CA1237122A
Application number: CA000475943A
Authority: CA
Inventors: William J. Salesky; Karl O. Kuhn
Original assignee: Smith International Inc
Current assignee: Smith International Inc
Priority date: 1984-03-28
Filing date: 1985-03-07
Publication date: 1988-05-24
Also published as: IT8567304A1; IT1184061B; GB8506221D0; IT8567304A0; GB2158101A

Abstract

ABSTRACT OF THE DISCLOSURE

A cladding process is disclosed wherein hard carbide cutter inserts, as well as polycrystalline diamond composites, are metallurgically bonded in-into an interior core of a drag bit body. The cladding is bonded onto the exterior surface of the core of the drag bit by a powder metallurgy process. A thin layer or coat-ing of a suitable metal, preferably nickel, is pro-vided on, for example, the carbide inserts prior to mounting into the core. The coating prevents degra-dation of the carbide through loss of carbon into the core during the powder metallurgy process and accommodates mismatch of thermal expansion between the cutter insert and the core.

Description

~237~

ROCK BITS HAVING METALLURGICALLY BO~DED
_ _ _ ~UTTER INSERTS

BACKGROUND OF THE INVENTION
1. Field of the Invention _ _ The present invention is directed to improvements in the construction of rock bits. More particularly, the present invention is directed to cutter cones of roller cone rock bits and drag bits having metallurgi- ~
cally bonded cutter inserts.

2. Descri tion of the Prior Art P
Roller cone rock bits used for drilling in subter-ranean formations when prospecting for oil, gas orminerals have a main body which is connected to a drill string and a plurality, typically three, of cutter cones rotatably mounted on journals. The journals extend at an angle from the main body of the rock bit.
As the main body of the rock bit is rotated either from the surface through the drill string, or by a down- ¦
hole motor, the cutter cones rotate on their respective journals. During their rotation, teeth provided in the cones come into contact with the subterranean formation and provide the drilling action.
Drag bits (or shear bits), on the other hand, are typically one piece, having no rotating parts. The cut-ting structure may include, for example, diamond chips imbedded in a matrix on the cutting face of the bit, ~237~.2~

synthetic polycrystalline cutters mounted to the face of the bit body, or synthetic polycrystalline discs mounted to tungsten carbide shanks, the shanks being subsequently interference fitted within complementary holes formed in the face of the drag bit body.
As is known, the subterranean environment is often very harsh. Highly abrasive drilling mud is continu-ously circulated from the surface to remove debris of the drilling, and for other puxposes. Furthermore, the subterranean formations are composed of rock with a wide range of compressive strength and abrasiveness.

One type of cutter cone, used for drilling in higher compressive strength (harder) formations, has a plurality of very hard cermet cutting inserts which are typically comprised of tungsten carbide and are mounted in the cone to project outwardly therefrom. Such a rock bit having cutter cones containing tungsten carbide cut-ter inserts is shown, for example, in ~nited States Patent No. 4,358,384 wherein the general mechanical structure of 2~ the rock bit is also described.
The cutter inserts, which typically have a cylindrical base, are usually mounted through an interference fit into matching openings in the cutter cone or in the face at the cutting end of a drag bit. This method, however, of mounting ,~

~371~:

the cutter inserts to the cone and within holes formed in the drag bit face is not entirely satisfactory be-cause the inserts are often dislodged from the cone or the drag bit face by fluid particle erosion of body material, excessive force, repetitive loadings or shocks which unavoidably occur during drilling.
Another problem encountered in the manufacture of rock bits relates to the number of machining and other steps required to fabricate the bit.
~onventional ~it are fabricated in several machin-ing opera~ions which are, generally speaking, laborintensive and expensive.

None of the prior art processes are entirely satisfactory from the standpoint of providing rock bit cutter cones and drag bit bodies with sufficient abil-ity to retain the cutting structure (including insert type cutters) under severe load conditions.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a drag bit body wherein hard cutting inserts are affixed to the face of the drag bit by a metallurgical bond.

It is another object of the present invention to provide a drag bit face with cutting structures in the matrix of the face of the bit wherein inadvertent degradation of cutter inserts is avoided during fabrication of the drag bit.

~23'7~2 It is still another object of the present invention to provide a drag bit body which has a tough resilient core and a hard outer cladding obtained by a powder metallurgy process.
It is yet another object of the present invention to provide a drag bit which the tunysten carbide cutter supports, metallurgically bonded to the drag bit face are joined to polycrystalline diamond blanks in a separate processing operation - the purpose of the diamond blanks being to provide a highly wear resistant rock cutting surface.
These and other objects and advantages are attained by a drag bit body which has a tough shock resistant core, and hard, cutting inserts fitted in cavities or on projections provided in the core or matrix face of the bit. A hard cladding is disposed on the outer surface of the drag bit face, having been metallurgically bonded thereto in a suitable mold by a powder metallurgy process.
In accordance with the present invention there is provided a drag type rock bit comprising:
a drag bit core body forming an interior chamber therein, said core forming a first cutter end and a second pin end, said interior chamber being op~n to said pin end, said core further including on its-exterior surface at said first cutter end, a plurality of cavities;
a plurality of hard cutter inserts, the exterior cavities and the cutter inserts having substantially matching dimensions so that said cutter inserts are accommodated in the cavities without substantial interference; and ~237~22 a cladding disposed on at least the exterior sur~ace of the core, the cladding having been deposited by a powder metallurge technique including a step wherein compacted powder of the cladding is heated to metallurgically bond said powder to the core, the cladding being harder than the core, said cladding partially embedding the cutter inserts and metallurgically bonding said inserts to the core and to the cladding.
Also in accordance with the present invention there is provided a process for making a drag bit type of rock bit having a steel body and a plurality of diamond cutting tips extending from the body at a cutting end thereof, the process comprising the steps of:
depositing a powder composition on an outer surface of the drag bit body;
first, heating and pressing the powder in a mold to metallurgically bond said powder to the drag bit body and thereby to provide an exterior cladding of the body, said cladding substantially conforming to the desired :Einal exterior configuration of the drag bit, and being comprised of a material selected from a group consisting of metals and cermets having a hardness greater than the steel body;
second, heating and pressing in a separate cycle, diamond cutting tips onto said drag bit at a sufficiently low temperature to avoid damage to the diamond cutting tips.
Further to the present invention there is provided a drag bit type of a rock drilling bit used Eor drilling in subterranean formations, the bit comprising:

,~>, -4a-~

.

a core bit body comprising tough shock-resistant mild steel having a first cutting end and a second pin end, said core further comprising an interior chamber formed therein, said second pin end being open to said chamber, and a plurality of cavities disposed on its exterior first cutting end surface a cladding comprising material selected from a group consisting of tool steel and cermets;
a plurality of hard cutter inserts being dimensioned for mounting into the exterior cavities of the first cutting end of said core without substantial interference, the cladding substantially covering the exterior first cutting end surface of the core, partially embedding the cutter inserts and being metallurgically bonded thereto, the cladding having a hardness of at least 50 Rockwell C hardness units and having been deposited on the core by a powc1er metallurgy process including a step of placing a suitable powder on the exterior surface of the core to ~hich the inserts are mounted, and heating the powder to metallurgically bond the powder to the core, the cladding having substantially lO0 percent density, the cutter inserts comprising tungsten-carbide, and further comprising a coating disposed on the inserts, said coating comprising a material which substantially prevents diffusion of carbon from the cutter insert into the core during the powder metallurgy process.
Further to the present invention there is provided a drag bit type of rock bit comprising:
a tough, shock-resistant, solid steel core body, the core body having a first cutter end and a second pin end, said core ~,~

-4b--~;~3~ 2 defining an interior chamber opened to said second pin end of said core body, the core also having means disposed on its first cutter end surface for accepting, through a slip fit, a plurality of cutting inserts;
a plurality of tungsten-carbide cutter insert studs, said insert studs having a diamond cutting element metallurgically bonded to an end of said stud, each of the diamond inserts being mounted into the means disposed on the exterior first cutter end surface of the core;
an exterior cladding disposed on the core partially embedded the diamond cutter inserts, having a hardness of at least 50 Rockwell C units, said cladding having been deposited on the core by a powder metallurgy process including a step wherein a suitable metal powder is heated under high isostatic pressure to metallurgically bond said powder to the core and to metallurgically bond the cutter inserts to the core and cladding;
a means for protecting the diamond cutting elements bonded to said tungsten-carbide stud during said cladding process, and a thin layer of a diffusion-preventing metal disposed ~etween each diamond cutter insert stud and the core, said layer comprising means for preventing diffusion or carbon from the tungsten-carbide insert stud into the core during the step of heating under high isostatic pressure.
Further to the present invention there is provided a process for making a drag bit type of rock bit, said drag bit having a plurality of tungsten-carbide diamond-tipped cutter insert studs, the process comprising the steps of:

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~IL2~7~
depositing a thin layer of a material selected from a group consisting of graphite, copper, copper alloys, silver, silver alloys, cobalt, cobalt alloys, tantalum, tantalLIm alloys, gold, gold alloys, palladium, palladium alloys, platinum, platinum alloys, nickel and nickel alloys on the diamond tipped cutter insert studs;
placing a plurality of the diamond tipped cutter insert studs into cavities formed into an outer surface of a first cutter end of a solid core of a drag bit body, said cavities being dimensioned to accept the diamond tipped cutter insert studs with a slip fit, the diamond tipped cutter insert studs having the thin layer of the material selected from the group consisting of graphite, copper, copper alloys, silver, silver alloys, cobalt, cobalt alloys, tantalum, tantalum alloys, gold~ gold alloys, palladium, pallad:ium alloys, platinum, platinum alloys, nickel and nickel alloys;
depositing a suitable powder composition on the outer surface of the drag bit body;
first, heating and pressing the powder in a suitable mold to metallurgically bond said powder to the drag bit body and thereby to provide an exterior cladding o the body, said cladding having a hardness of at least 50 Rockwell C units, substantially conforming to the desired final exterior configuration of the drag bit, and being comprised of a material selected from a group 5 consisting of metals and cermets, and second, a step comprising means for heating and pressing the powder in said mold sufficiently to bond said diamond insert -4d-~

st~lds to said outer surface of said drag bit body into a two-step process, without destroying the diamond cutting elements metallurgically bonded to said tungsten-carbide studs.
Further to the present invention there is provided a process for making a drag bit type of rock bit, said drag bit having a plurality of diamond tipped tungsten-carbide studded inserts in a cutter end of said drag bit, the process comprising the steps of:
depositing a thin layer of a metallic material on the tungsten-carbide studs minus their diamond cutting tips;
placing a plurality of said coated tungsten-carbide studs into an outer surface of a first cutter end of a solid core of a drag bit body, said cavities being dimensioned to accept the coated tungsten-carbide studs with a slip fit;
depositing a suitable powder composition on the outer surface of the drag bit body;
heating said powder composition between 1900F. and 2300F. in a suitable mold for 4 to 10 hours;
pressing said powder composition during said heating 20 cycle between 15,000 and 30,000 pounds per square inch to consolidate said powder composition on said drag bit body providing an exterior cladding thereon, said cladding having a hardness of at least 50 Rockwell C units, substantially conforming to the desired final exterior configuration of the drag bit, and being comprised of a material selected from a group consisting of metals and cermets; and pressing and heating, in a separate cycle, diamond cutting tips to said coated tungsten-carbide studs, a A -4e-~

~:~37~22 nickel shim is first placed between each of said diamond cutting tips and said tungsten-carbide studs, said heating cycle having temperatures between 1~00E~. (650~C) and 1385F (750C) for 0.5 to 4 hours, said pressiny cycle taking place simultaneously with said heating cycle, said pressing cycle having pressures between 15,000 and 30,000 pounds per square inch to bond said diamond tips to said studs.
Further to the present invention there is provided a process for making a drag bit type of rock bit, said drag bit having a plurality of projection extending from a body of said drag bit at a cutting end of said drag bit, the process comprising the steps of:
depositing a suitabie powder composition on the outer surface of the drag bit body;
heating said powder composition between 1900F. and 2300F. in a suitable mold for 4 to 10 hours;
pressing said powder composition duriny said heating cycle between 15,000 and 30,000 pounds per square inch to consolidate said powder composition on said drag bit bod~
providing an exterior cladding thereon, said cladding having a hardness of at least 50 Rockwell C units, su~stantially conforming to the desired final exterior configuration of the drag bit, and being comprised of a material selected from a group consisting of metals and cermets, and pressing and heating, in a separate cycle, diamond cutting tips to said projections extending from the cutting end of said drag bit, a nickel shim is first placed between each of said projections, said heating cycle having -4f-~

~l237~2 temperatures between 1200F. (650C.~ and 1385F. (750C.) for 0.5 to 4 hours, said pressing cycle taking place simultaneously with said heating cycle, said pressing cycle having pressures between 15,000 and 30,000 pounds per square inch to bond said diamond tips to said studs.
Preferably, metallurgical bonding of the cladding occurs through hot isostatic pressing (~IP or HIPPING). The cutting inserts and/or drag bit studs are also metallurgically bonded to the core and to the cladding as a result of the formation of the cladding through hot isostatic pressing or like powder metalluryy processes.
In order to prevent degradation of the cemented car-~3'7~Z2 bide studs for drag bits into undesirable "eta" phase, by diffusion of carbon from the insert into the underlying core duriny the powder metallurgical bonding process, and to accommodate the mismatch in thermal expansion coeffi-cients between the cutting insert and the ferrous core body, a thin coating of a suitable material is depositedon the inserts prior to placement of the inserts into corresponding cavities in the core. Examples of such material are copper, copper alloys, silver, silver alloys, cobalt, cobalt alloys, tantalum, tantalum alloys, gold, gold alloys, palladium, palladium alloys, platinum, platinum alloys, and nickel or nickel alloys.
Another alternative to prevent degradation of the cutting inserts is to provide an alternative source of carbon, such as a graphite layer, in the vicinity of the cutting inserts.
With regard to drag or shear bits, the preferably mild steel core of the bit body has machined therein a chamber to admit hydraulic fluid ("mud") that is di-rected through one or more nozzles strategically placedin the cutting face of the drag bit body. The interior walls of the chamber may be clad with metal powder or cermet in a manner similar to the powder metallurgi-cal bonding process of the interior bearing surfaces of the rock bit cones. An alternative to simply cladding ~237~

the walls of the nozzles in the drag bit body is to form the nozzles such that the cladding initially fills the nozzle bore which is later machined to the proper diameter. In this alternative, it is preferable that the hardness of the cladding prior to machining be rea-sonably soft, preferably less than 40 Rockwell C.
With regard to drag matrix or shear bits, the fabri-cation cycle is preferably a combination of stud forma-tion and/or bonding in association with the attachment of polycrystalline diamond (PCD) pieces to the studs or projections in the drag or matrix bit face in a second, separate lower temperature/pressure HlPping cycle. The purpose of this second lower temperature/pressure cycle is both to prevent degradation of the PCD, while permit-ting the preferred HIP bond to be established between the PCD and the stud or supporting projection in the bit face.
The features of the present invention c~n be best understood, together with further objects and advantages, from the following description ta~en together with the appended drawings wherein like numerals indicate like parts.

.

~237~2 sRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-sectional view of a typical drag bit body;
Figure 2 is a view of a synthetic polycrystalline disc mounted to a protrusion formed in the powder metal-lurgically formed face of the drag bit;
Figure 3is an alternative embodiment wherein a poly-crystalline disc is bonded to a tungsten carbide stud, the stud being interference fitted or metallurgically bonded within a complementary recess in the face of the drag bit; and Figure 4 is a chart illustrating the preferred fab~
rication cycle to fabricate the drag bit. The first cy-cle is used to form and/or bond the cladding and/or the studs to the drag bit face. The second cycle is used for bonding the polvcrystalline diamond pieces to the studs and/or projection in the bit face.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In conventional drag bit construction, a plurality of tungsten-carbide-cobalt (cermet) cutter inserts or diamond tipped insert studs are interference fitted into corresponding circular holes which are drilled individually in the cutting face of a drag bit. This procedure is not only labour intensive, but provides a drag bit which has, under severe drilling conditions, less than adequate retention of the cutter inserts.

~237~Z%
Referring now specifically to Figure 1, the drag bit core, generally designated as 128, consis-ts of a machined steel forging or body 112. The body is preferably fabri-cated from A.I.S.I. 9315 or A.I.S.I. 4815 steel. However, the body could be forged from a 4000 series mild steel, such as as 4120, 4310, 4320 and 4340. These materials would be interchangeable with 9315 steel. Regardless of the material from which the core is made, the pin end 114 (the end that threadably engages a drillstring) must be protected from the cladding process 134 to facilitate the pin threading operation (not shown).
A nozzle bore 120 may be provided in the head or face end 116 of body 112. The internal surface of the cylinder bore 120 may or may not be clad with the cladding material i34, depending upon the type of hy-draulic nozzle to be secured within the bore.
A preferable alternative to cladding the nozzle bore 120 is to form the drag bit body such that the intended nozzle is completely filled with cladding material after consolidation in such a manner that after consolidation the cladding is sufficiently soft (preferably less than 40 Rockwell C) such that the bore could be readily machined.
The cladding thickness may be varied on the exterior surface 115 of the core body 112 as well as the interior surface 113 that forms internal chamber 118.
The metal or cermet composition comprising the cladding should satisfy the following requirements. It should 7~L22 be capable of being hardened and metallurgically bonded to the underlyin~ core 128 to provide a substantially one hundred percent dense claddinq of a hardness of at least 50 Rockwell C, Many tool steel and cermet compositions satisfy these requirements. For example, commercially available, well-known A.I.S.I. D2, M2, M42 and S2 tool and high-strength steels are suitable for the cladding. An excellent cladding for the present in-vention is the tool steel composition which consists essentially of 2.45 weight percent carbon, 0.5 percent manganese, 0.9 percent silicon, 5.25 percent chromium, , . ~ , .. . . .
9.0 percent vanadium, 1.3 percent molybdenum, 0.07 per-cent sulfur, with the remainder of the composition be-ing iron. This composition is well-known in the metal-lurgical arts under the CPM-lOV designation of the Crucible Metals Division of Colt Industries. Still another excellent cladding material is a proprietary alloy of the above-noted Crucible Metals Division, known under the Development Nun~er 516,892.
Instead of powdered steel compositions, such pow-dered cermets as tungsten-carbide-cobalt (~C-Co), titanium-carbide-nickel-molybdenum (TiC-Ni-Mo), or titanium-carbide-iron alloys (Ferro-TiC alloys) may also be used for the cladding 134.
~5 ~23~

The application of the powdered material of the clad-ding 134 and metallurgical bonding to the underlying core 128 and its subsequent hardening are performed in accordance with well-known powder metallurgy processes and conventional heat treatment practices. Although these well-known processes need not be disclosed here in detail, it is noted that the powder metallurgy pro-cesses suitable for use in the present invention include the use of a ceramic molding process (not shown) which determines the exterior configuration of the drag bit 1~.
Furthermore, the powder metallurgy process involves application of high pressure to compact the powder and heating the powdered cladding in the ceramic mold ~not shown) at a high temperature-but below the melting tem-perature of the powder - to transform the powder into dense metal, or cermet, and to metallurgically bond the same to the underlying core 128. Thus the cladding 134 incorporated in the drag bit 100 of the present invention may be obtained by cold pressing or cold isostatic pressing the powdered layer 134 on the core 1~, followed ~y a step of sintering.
A preferred process for obtaining the hard cladding 134 for the draq bit 100 of the present invention is, however, hot isostatic pressing (HIPping). Details of this process, including the preparatory steps to the actual hot isostatic pressing , _ --10--~3~ 2 of the drag bit 100, are described in United States Patents Nos. 3,-/00,435 and 3,804,575. When the Crucible CPM-lOV powered steel composition is used for the drag bit 100 of the present invention, the hot isostatic pressing step is preferably performed between approximately 1040C to 1200C, for approximately 4 to 10 hours, at approximately 10,500 to 30,000 g/mm2.
An ideal temperature for the pressing cycle is 1175 -- 15~ Centigrade, at a pressure of 10,500 ~ 350 g/mm2 for 8 hours.
With reference to Figures 2 and 3, the protrusions 125 and 138 are formed in the powder metallurgy mold to provide a means to mount, for example, polycrystal-line diamond discs, generally designated as 140 (Fig-ure 2). These discs, as well as the diamond tipped in-sert studs referred to earlier, are fabricated on a tungsten carbide substrate, the diamond layer being composed of a polycrystalline material. The synthetic polycrystalline diamond layer (PCD) is manufactured by the Specialty Material Department of General Electric Company of Worthington, Ohio. The foregoing drill cut-ter blank is known by the trademark name of STRATAPAX
drill blank.
The diamond capped tungsten carbide stud, generally designated as 150, is provided with a complementary non-interference sized hole 145 in protrusion 138 (Fiqure 3) so that the insert 150 may be metallurgically bonded to the cladding 134 on face 116 of core body 112.

~37~2~

In accordance with the presentinvention, a plurality of cavities 145 may be provided in the outer surface of the core 112 to receive, preferably by a slip fit, a plurality of cutter inserts 150. The cavities 145 may be configured as circular apertures, shown on Figure 9, but may also comprise circumferential grooves (not shown) on the exterior surface of the core 112. Furthermore, the cutter inserts 150 may be of other than cylindrical con-figuration. They may be tapered, or may have an annulus comprising a protrusion. Alternatively, the inserts may be tapered and oval in cross section. What is important in this regard is that the cutter inserts 150 are positioned into the cavities 145 without force fitting, or without the need for fitting each individual insert into a precisely matching hole, thereby eliminating significant labor and cost.
The cutter inserts 150 are typically made of hard cermet material. In accordance with usual practice in the art, the cutter inserts comprise tungsten-carbide-cobalt cermet. ~owever, other cermets which have the required hardness and mechanical properties may be used.

Such alternative cermets are tungsten carbide in iron,iron-nickel, and tungsten carbide in iron-nickel-cobalt matrices. In fact, tungsten-carbide-iron based metal cermets often match better the thermal expansion coeffi-cient of the underlying steel core than the tungsten-carbide-cobalt cermets.

~2~ 2 Subsequent to positioning the cutter inserts in-to the cavities, a powdered metal or cermet composition is applied to the exterior surface of the core to eventually become a hard exterior cladding of the drag bit.

Since polycrystalline diamond discs are preferred as a cutting structure for drag or shear bits, two sep-arate hot isostatic pressing cycles may be required as is illustrated in Figure 4. The first high-temperature/
high-pressure cycle consolidates the cladding 134 to the core body 112 and bonds, for example, the tungsten carbide studs 142 (Figure 3) within the cladding mate-rial. When Crucible CPM-lOV powdered steel composition is used during the first HIPping cycle for the drag bit 100 of the present invention, the hot isostatic press-ing step is preferably performed between approximately 1040C to 1200C, for approximately 4 to 10 hours, àt approximately 10,500 to 21,000 g/mm2.
After the hot isostatic pressing step, certain fur-ther heat treatment steps well-known in the art, such as quenching and tempering, may be performed on the drag bit 100. The conditions for quenching and tempering are preferably those recommended by the suppliers of the powdered steel composition which is used for the cladding 134.
Alternatively J for drag bits, once the cladding is consolidated, a sufficiently hard (greater than 50 Rock-well C) and abrasion resistant surface layer may be ob-tained by rapid cooling the bit, thereby requiring no further heat treatment. Such a cooling cycle is typi-cally available in hot isostatic pressing units equipped with a convective cooling device. A cold inert gas flow may also adequately cool the bit.
The second cycle (less temperature and pressure) serves to metallurgically bond the PCD (polycrystalline diamond) disc 140 to the cladding material ~130, Fig-ure 2) or the disc 150 to the tungsten carbide stud 142 (130, Figure 3). In Figures 2 and 3, a nickel shim 131 may be used to bond the PCD discs 140/150 to the pro-trusion 126 or to the tungsten carbide stud body 142, ~Where the nickel shim is used as a diamond bonding agent, the temperature should be between 650 and 750~C, at a pressure between 10,500 to 21,000 g/mm~ for 0.5 to 4 hours. The Dreferred conditions of this bondinq vrocess are 650C at 10,500 g/mm2 for about 2 hours.
Where the PCD discs 140/150 are silver brazed to the protrusion 126 or to the stud body 142, a tem~era-ture of about 350C, at pressures ranging from 10,500 to 21,000 g/mm2 will accomplish the task. It should be emphasized that the process as outlined above will work equally well for both ~he steel projections 126 and the tungsten carbide studs 142.
The drag bit 100, obtained in the above-described manner, has an exterior configuration which corresponds to the final, desired configuration. In other words, ~37~L22 little, if any machining is required on -the exterior of the drag bit 100 obtained in accordance with the presen-t invention.
Uniform thickness of the cladding is illustra-ted in Fig. 1, however, it could well be an advantage to clad the head 116 of drag bit body 112 heavier or thicker than the cladding on the rest of the body for extended performance. The cladding on the head 116 of the drag bit could; for example, be 5mm thick while the rest of the drag bit body 112 (with the exception of the threaded pin end 114) could be 3mm thick. The walls 113, forming chamber 118, could be uniformly clad to the thickness of the drag bit body 112 or the cladding 134 on walls 113 may be thinner than the exterior cladding since the interior of the bit is subjected to less abrasive action than the exterior surfaces of drag bit 100.
A further, very significant advantage is that the cutter inserts 150 and diamond disc 140 are affixed to the core 128 and to the cladding 134 by metallurgical bonds. Experience has shown that, for example, a tungsten-carbide-cobalt insert having an 0.5 inch (12O7mm) diameter and a 0.310 inch (7.87mm) "grip", affixed to a steel body in accordance with the present invention re~uires on the average a pulling force in excess of 9500 kg to dislodge the insert from the steel body. In contrast, conventional interference fitted inserts are dislodged from a steel body by a force of approximately 3,200 to 4,500 kg.
Similarly, for drag bits, the metallurgical bond-ing of the studs and/or projections into the bit face is a substantial advantage over present art. Typi-cally, drag bit studs/cutters interference fitted into holes in the bit face are lost in service through ~Z3~7~22 erosion of the bit face being especially aggressive at the base of the cutters such that a substantial portion of the grip length of the stud/cutter can be eroded away.
The loss of these studs/cutters in service not only de-creases the rate of drilling but introduces highly un-desirable and difficult debris into the well which, if not removed, will damage and/or destroy every bit put into the well afterward. Therefore, the metallurgical bonding of the studs into the bit face will significantly reduce the frequency of stud/cutter loss, thereby increas-ing the overall life of the drag bit as well as decreasing the likelihood of an expensive fishing operation, neces-sary to remove debris from the hole.
The cladding 134 of the cone 10 and the drag bit 100, obtained in accordance with the present invention, is substantially one hundred percent (99.995%) dense and has a surface hardness of at least 50 Rockwell C.
The interior of the drag bit body is internally clad through the powder metallurgy process;

preferably a process that includes the hot isostatic pressing step. The forged mild steel drag bit core body 112 is provided with a machined chamber 118 and a nozzle bore 120. A counterbore 122 may also be machined in the body 112 to accommodate a threaded nozzle body (not shown). Obviously, the cladding 134 resists the abrasive effect of pressurized hydraulic drilling mud during a drilling operation. A "wash-out" of the in-ternal nozzle cavity has been a problem with both roll-~23~2:~

ing cone and drag type rock bits, hence internally cladsurfaces would inhibit this type of catastrophic damage to the cutting tools.
In accordance with still another feature of the improved drag bit lO0 of the present invention, the tungsten-carbide-cobalt cutter inserts has a thin coating or layer 143 of a material which preven-ts diffusion of carbon from the tungsten carbide into the underlying steel core 128 during the high-temperature hot isostatic pressing or sintering process. As is known, such diffusion has a significant driving force because the carbon content of the steel core 128 typically is low. Loss of carbon from the tungsten carbide results in formation of "eta" phase of the tung-sten carbide, which has significantly less desirablemechanical properties than the original tungsten car-bide insert.
It was discovered, in accordance with the present invention, however, that the above-noted diffusion, un-desirable "eta" phase formation and degradation of me-chanical properties of the tungsten carbide inserts 150 may be prevented by providing a layer of copper, copper alloys, silver, silver alloys, cobalt, cobalt alloys, tantalum, tantalum alloys, gold, gold alloys, palladium, palladium alloys, platinum, platinum alloys, and nic.~el or nickel alloys on the cutter inserts ~237~2Z

lS0 before the inserts 150 are incorporated into the core 128.
Alternatively, a layer of graphite (not shown) also prevents degradation because it provides an alternate source of carbon. A layer of graphite is readily placed on or near the insert 150 by, for example, applying a suspension of graphite in a volatile solvent, such as ethanol, on the insert 150. The graphite prevents or reduces diffusion of carbon from the tung-sten carbide because it eliminates the driving forceof the diffusion.
The other metals noted above prevent or reduce dif-fusion of carbon by virtue of the limited solubility of carbon in these metals at the temperatures and pressures which occur during the hot isostatic pressing process.

The metal coatings may be applied to the cutter in-serts lS0 by several methods, such as electroplating, electroless plating, chemical vapor deposition, plasma depositionl and hot dipping. The metal layer or coat-ing 143 on the cutter inserts is pre~erably approxi-mately 25 to 100 microns thick.
The metal layer -143, deposited on the cutter in-sert preferably, should not melt during the hot iso-static pressing or sintering process. It certainly 2~ must not boil during said processes. Nickel or nickel alloys are most preferred materials for the coating or layer 143 used in the present invention.

o -18-~237 31L;~:~

The metal coating 143 on the inserts 150 not only prevents the undesirable "eta" phase formation in the inserts 150, but also provides a transition layer of intermediate thermal expansion coefficient between the tungsten carbide inserts 150 and the surrounding ferrous metal cladding 134 and core 128. In the absence of such a transition layer, the boundary may crack. Nevertheless, as it was noted above, test re-sults in the absence of such a metal coating still show significant improvement over nonmetallurgically bonded inserts with regards to the force required to dislodge the inserts~
A "cemented carbide" is defined as a solid and coherent mass made by pressing and sintering a mixture of powders of one or more of the metallic carbides and a much smaller amount of a metal, such as cobalt, to serve as a binder.

Claims

The embodiments of the invention in which an exclusive property or pivilege is claimed are defined as follows:

1. A drag type rock bit comprising:
a drag bit core body forming an interior cham-ber therein, said core forming a first cutter end and a second pin end, said interior chamber being open to said pin end, said core further including on its exterior sur-face at said first cutter end, a plurality of cavities;
a plurality of hard cutter inserts, the exte-rior cavities and the cutter inserts having substantially matching dimensions so that said cutter inserts are accom-modated in the cavities without substantial interference; and a cladding disposed on at least the exterior sur-face of the core, the cladding having been deposited by a powder metallurgy technique including a step wherein com-pacted powder of the cladding is heated to metallurgically bond said powder to the core, the cladding being harder than the core, said cladding partially em-bedding the cutter inserts and metallurgically bonding said inserts to the core and to the cladding.

2. The drag bit of Claim 1 wherein the core is a solid steel core.

3. The drag bit of Claim 2 wherein the core com-prises mild steel.

4. The drag bit of Claim 3 wherein the material of the core is selected from a group consisting of A.I.S.I.
9315 steel and A.I.S.I. 4815 steel.

5. The drag bit of any one of claims 1 to 3 wherein the cladding has been bonded to the core by a hot isostatic pressing process.

6. The drag bit of Claim 1 further comprising means disposed on the cutter inserts for substantially prevent-ing diffusion of carbon from the cutter inserts into the core and the cladding during the step wherein compacted powder of the cladding is heated to metallurgically bond the same to the core.

7. The drag bit of Claim 6 wherein the means com-prise a layer disposed on the cutter inserts, the mate-rial of which is selected from a group consisting of graphite, copper, copper alloys, silver, silver alloys, cobalt, cobalt alloys, tantalum, tantalum alloys, gold, gold alloys, palladium, palladium alloys, platinum, platinum alloys, nickel, and nickel alloys.

8. The drag bit of Claim 7 wherein the layer con-sists of nickel.

9. 8 The drag bit of Claim wherein the layer is approximately 25 to 100 microns thick.

10. The drag bit of any one of claims 1 to 3, wherein the cutter inserts comprise a cermet of tungsten carbid carbide and cobalt.

11. The drag bit of claim 1 wherein the cladding comprises material selected from a group consisting of tool steel and cermets.

12. The drag bit of Claim 11 wherein the cladding comprises material selected from a group consisting of D2, M2, M42, S2 tool steel, and a tool steel composition consisting essentially of 2.45 percent carbon, 0.5 percent manganese, 0.9 percent silicon, 5.25 percent chromium, 1.3 percent molybdenum, 9.0 percent vanadium, 0.07 percent sulfur and 80.53 percent iron.

13. The drag bit of Claim 12 wherein the cladding comprises material selected from tungsten-carbide-cobalt cermet, titanium-carbide-nickel-molybdenum cermet and titanium-carbide-ferro alloy cermets.

14. The drag bit of Claim 11 wherein the metal of the cladding consists essentially of 2.45 percent carbon, 0.5 percent manganese, 0.9 percent silicon, 5.25 percent chromium, 1.3 percent molybdenum, 9.0 percent vanadium, 0.07 percent sulfur, and 80.53 percent iron.

15. The drag bit of Claim 1, wherein the cutter inserts comprise tungsten-carbide, the cutter inserts further comprising a coating disposed on the inserts, said coating comprising a material which substantially prevents diffusion of carbon from the cutter insert into the core during the powder metallurgy process.

16. The drag bit of Claim 15 wherein the material of the coating is selected from a group consisting of graphite, copper, copper alloys, silver, silver alloys, cobalt, cobalt alloys, tantalum, tantalum alloys, gold, gold alloys, palladium, palladium alloys, platinum, platinum alloys, nickel and nickel alloys.

17. The drag bit of Claim 16 wherein the material of the coating is selected from a group consisting of nickel and nickel alloys.

18. The drag bit of any one of claims 1 to 3, wherein the cladding has substantially 100 percent density.

19. The drag bit of any one of claims 1 to 3, wherein the classing has a hardness of at least 50 Rockwell C.

20. The drag bit of any one of claims 1 to 3, wherein the hard cutter inserts have a diamond cutting element metal-lurgically bonded to the exposed end of the insert.

21. A process for making a drag bit type of rock bit having a steel body and a plurality of diamond cutting tips extending from the body at a cutting end thereof, the process comprising the steps of:
depositiong a powder composition on an outer surface of the drag bit body;

first, heating and pressing the powder in a mold to metallurgically bond said powder to the drag bit body and thereby to provide an exterior cladding of the body, said cladding substantially conforming to the desired final exterior configuration of the drag bit, and being comprised of a material selected from a group consisting of metals and cermets having a hardness greater than the steel body;
second, heating and pressing in a separate cycle, diamond cutting tips onto said drag bit at a sufficiently low temperature to avoid damage to the diamond cutting tips.

22. The process of Claim 21 comprising the steps of forming a plurality of cavities in the drag bit body;
placing a plurality of cemented carbide inserts into such cavities, said cavities being dimensioned to accept the inserts without substantial interference; and metallurgically bonding the powder to the inserts in the first heating and pressing step.

23. The process of Claim 22 further comprising the step of depositing a thin layer of a material selected from a group consisting of graphite, copper, copper alloys, silver, silver alloys, cobalt, cobalt alloys, tantalum, tantalum alloys, gold, gold alloys, palladium, palladium alloys, platinum, platinum alloys, nickel and nickel alloys on the cemented carbide before placing the cemented carbide inserts into the cavities.

24. The process of Claim 23 wherein the step of depositing a thin layer of material on the cemented carbide inserts comprises electroplating.

25. The process of Claim 23 wherein the material of the thin layer is selected from a group consisting of nickel and nickel alloys.

26. The process of Claim 22 wherein the second heating and pressing step comprises placing a nickel shim between each of said diamond cutting tips and said tungsten carbide studs, heating at temperatures between 650°C and 750°C for 0.5 to 4 hours and simultaneously isostatically pressing at pressures between 10,500 and 21,000 g/mm2.

27. The process as set forth in Claim 22 wherein said diamond cutting tips are silver brazed to said tungsten carbide studs at a temperature of about 350°C and a pressure of about 10,500 g/mm2.

28. The process of any one of claims 21 to 23, wherein the first heating and pressing step comprises heating said powder composition between 1040°C and 1260°C in a mold for 4 to 10 hours; and pressing said powder composition during said heating cycle between 10,500 and 321,000 g/mm2 to consolidate said powder composition on said drag bit body.

29. The process of any one of claims 21 to 23 wherein the cladding has a hardness of at least 50 Rockwell C.

30. The process of any one of claims 21 to 23 wherein the powder composition is selected from a group consisting of tunqsten-carbide-cobalt cermet, titanium-carbide-nickel-molybdenum cermet, titanium-carbide-ferro alloy cermet, D2, M2, M42, S2 tool steels and a tool steel composition consisting essentially of 2.45 percent carbon, 0.5 percent manganese, 0.9 percent silicon, 5.25 percent chromium, 9.0 percent vandium, 1.3 percent molybdenum, 0.07 percent sulfur, and 80.53 percent iron.

31. The process of Claim 21 wherein the drag bit has a plurality of projections extending from the drag bit body at a cutting end thereof wherein the second heating and pressing step comprises metallurgically bonding the diamond cutting tips to said projections.

32. The process of Claim 31 wherein a nickel shim is placed between each of said projections and such a diamond cutting tip before heating and pressing.

33. The process of Claim 32 wherein the second heating and pressing step comprises heating the body to a temperature between 650°C and 750°C for 0.5 to 4 hours and simultaneously isostatically pressing at pressures between 10,5000 and 21,000 g/mm2 to bond said diamond tips to said projections.

34. The process as set out in Claim 31 wherein said diamond cutting tips bonded to said projections on said drag bit are heated in a heating cycle to about 650°C for about 2 hours.

35. The process as set forth in Claim 31 wherein said diamond tips bonded to said projections extending from said drag bit are pressed during the heating cycle to a pressure of about 10,500 g/mm2.

36. The process as set forth in Claim 31 wherein the diamond cutting tips are silver brazed to said projections at a temperature of about 350°C at a pressure of about 10,500g/mm2.

37. A drag bit type of a rock drilling bit used for drilling in subterranean formations, the bit comprising:
a core bit body comprising tough shock-resistant mild steel having a first cutting end and a second pin end, said core further comprising an interior chamber formed therein, said second pin end being open to said chamber, and a plurality of cavities disposed on its exterior first cutting end surface;
a cladding comprising material selected from a group consisting of tool steel and cermets;
a plurality of hard cutter inserts being dimensioned for mounting into the exterior cavities of the first cutting end of said core without substantial interference, the cladding substantially covering the exterior first cutting end surface of the core, partially embedding the cutter inserts and being metallurgically bonded thereto, the cladding having a hardness of at least 50 Rockwell C hardness units and having been deposited on the core by a powder metallurgy process including a step of placing a suitable powder on the exterior surface of the core to which the inserts are mounted, and heating the powder to metallurgically bond the powder to the core, the cladding having substantially 100 percent density, the cutter inserts comprising tungsten-carbide, and further comprising a coating disposed on the inserts, said coating comprising a material which substantially prevents diffusion of carbon from the cutter insert into the core during the powder metallurgy process.

38. The cutter inserts of claim 37, wherein the material of the coating is selected from a group consisting of graphite, copper, copper alloys, silver, silver alloys, cobalt, cobalt alloys, tantalum, tantalum alloys, gold, gold alloys, palladium, palladium alloys, platinum, platinum alloys, nickel and nickel alloys.

39. The cutter inserts of claim 38, wherein the material of the coating is selected from a group consisting of nickel and nickel alloys.

40. A drag bit type of rock bit comprising:
a tough, shock-resistant, solid steel core body, the core body having a first cutter end and a second pin end, said core defining an interior chamber opened to said second pin end of said core body, the core also having means disposed on its first cutter end surface for accepting, through a slip fit, a plurality of cutting inserts;
a plurality of tungsten-carbide cutter insert studs, said insert studs having a diamond cutting element metallurgically bonded to an end of said stud, each of the diamond inserts being mounted into the means disposed on the exterior first cutter end surface of the core;
an exterior cladding disposed on the core partially embedded the diamond cutter inserts, having a hardness of at least 50 Rockwell C units, said cladding having been deposited on the core by a powder metallurgy process including a step wherein a suitable metal powder is heated under high isostatic pressure to metallurgically bond said powder to the core and to metallurgically bond the cutter inserts to the core and cladding;
a means for protecting the diamond cutting elements bonded to said tungsten-carbide stud during said cladding process, and a thin layer of a diffusion-preventing metal disposed between each diamond cutter insert stud and the core, said layer comprising means for preventing diffusion of carbon from the tungsten-carbide insert stud into the core during the step of heating under high isostatic pressure.

41. The drag bit of claim 40, wherein the means disposed on the surface of the cone comprise a plurality of apertures.

42. The drag bit of claim 40, wherein the metal of the cladding is a tool steel.

43. The drag bit of claim 42, wherein the metal of the cladding is selected from a group consisting of D2, M2, M42, S2 tool steel, and a tool steel composition consisting essentially of 2.45 percent carbon, 0.5 percent manganese, 0.9 percent silicon, 5.25 percent chromium, 1.3 percent molybdenum, 9.0 percent vanadium, 0.07 percent sulfur, and 80.53 percent iron.

44. The drag bit of claim 43 wherein the metal of the cladding consists essentially of 2.45 percent carbon, 0.5 percent manganese, 0.9 percent silicon, 5.25 percent chromium, 1.3 percent molybdenum, 9.0 percent vanadium, 0.07 percent sulfur, and 80.53 percent iron.

45. The tungsten-carbide studs of the diamond inserts of claim 42, wherein the thin layer of diffusion-preventing metal is selected from a group consisting of copper, copper alloys, silver, silver alloys, cobalt, cobalt alloys, tantalum, tantalum alloys, gold, gold alloys, palladium, palladium alloys, platinum, platinum alloys, nickel and nickel alloys.

46. The tungsten-carbide studs of the diamond inserts of claim 45, wherein the thin layer of diffusion-preventing metal is deposited on the cutter inserts prior to mounting the cutter inserts into the core.

47. The tungsten-carbide studs of the diamond inserts of claim 46, wherein the thin layer of diffusion-preventing metal is selected from a group consisting of nickel and nickel alloys, and wherein said layer is approximately 25 to 100 microns thick.

48. A process for making a drag bit type of rock bit, said drag bit having a plurality of tungsten-carbide diamond-tipped cutter insert studs, the process comprising the steps of:
depositing a thin layer of a material selected from a group consisting of graphite, copper, copper alloys, silver, silver alloys, cobalt, cobalt alloys, tantalum, tantalum alloys, gold, gold alloys, palladium, palladium alloys, platinum, platinum alloys, nickel and nickel alloys on the diamond tipped cutter insert studs;
placing a plurality of the diamond tipped cutter insert studs into cavities formed into an outer surface of a first cutter end of a solid core of a drag bit body, said cavities being dimensioned to accept the diamond tipped cutter insert studs with a slip fit, the diamond tipped cutter insert studs having the thin layer of the material selected from the group consisting of graphite, copper, copper alloys, silver, silver alloys, cobalt, cobalt alloys, tantalum, tantalum alloys, gold, gold alloys, palladium, palladium alloys, platinum, platinum alloys, nickel and nickel alloys;
depositing a suitable powder composition on the outer surface of the drag bit body;
first, heating and pressing the powder in a suitable mold to metallurgically bond said powder to the drag bit body and thereby to provide an exterior cladding of the body, said cladding having a hardness of at least 50 Rockwell C units, substantially conforming to the desired final exterior configuration of the drag bit, and being comprised of a material selected from a group consisting of metals and cermets, and second, a step comprising means for heating and pressing the powder in said mold sufficiently to bond said diamond insert studs to said outer surface of said drag bit body in a two-step process, without destroying the diamond cutting elements metallurgically bonded to said tungsten-carbide studs.

49. The process of claim 48, wherein the step of depositing a thin layer of material on the diamond cutter inserts comprises electroplating.

50. The process of claim 48, wherein the material of the thin layer is selected from a group consisting of nickel and nickel alloys.

51. The process of claim 48, wherein the solid core is a mild steel core.

52. The process of claim 51, wherein the powder composition is selected from a group consisting of tungsten-carbide-cobalt cermet, titanium-carbide-nickel-molybdenum cermet, titanium-carbide-ferro alloy cermet, D2, M2, M42, S2 tool steels, and a tool steel composition consisting essentially of 2.45 percent carbon, 0.5 percent manganese, 0.9 percent silicon, 5.25 percent chromium, 9.0 percent vanadium, 1.3 percent molybdenum, 0.07 percent sulfur, and 80.53 percent iron.

53. A process for making a drag bit type of rock bit, said drag bit having a plurality of diamond tipped tungsten-carbide studded inserts in a cutter end of said drag bit, the process comprising the steps of:
depositing a thin layer of a metallic material on the tungsten-carbide studs minus their diamond cutting tips;
placing a plurality of said coated tungsten-carbide studs into an outer surface of a first cutter end of a solid core of a drag bit body, said cavities being dimensioned to accept the coated tungsten-carbide studs with a slip fit;
depositing a suitable powder composition on the outer surface of the drag bit body;
heating said powder composition between 1900°F. and 2300°F. in a suitable mold for 4 to 10 hours;
pressing said powder composition during said heating cycle between 15,000 and 30,000 pounds per square inch to consolidate said powder composition on said drag bit body providing an exterior cladding thereon, said cladding having a hardness of at least 50 Rockwell C units, substantially conforming to the desired final exterior configuration of the drag bit, and being comprised of a material selected from a group consisting of metals and cermets; and pressing and heating, in a separate cycle, diamond cutting tips to said coated tungsten-carbide studs, a nickel shim is first placed between each of said diamond cutting tips and said tungsten-carbide studs, said heating cycle having temperatures between 1200°F. (650°C) and 1385°F (750° C) for 0.5 to 4 hours, said pressing cycle taking place simultaneously with said heating cycle, said pressing cycle having pressures between 15,000 and 30,000 pounds per square inch to bond said diamond tips to said studs.

54. The process of claim 53, wherein said metallic material deposited on said tungsten-carbide studs is selected from a group consisting of graphite, copper, copper alloys, silver, silver alloys, cobalt, cobalt alloys, tantalum, tantalum alloys, gold, gold alloys, palladium, palladium alloys, platinum, platinum alloys, nickel and nickel alloys.

55. The process of claim 54, wherein the step of depositing a thin layer of material on the tungsten-carbide stud bodies of said diamond cutter inserts comprises electroplating.

56. The process, as set forth in claim 53, wherein the temperature of the heating cycle of the powder composition is about 2150°F.

57. The process, as set forth in claim 53, wherein the pressure utilized to consolidate said powder composition during the heat cycle is about 15,000 pounds per square inch.

58. The process, as set forth in claim 53, wherein the diamond cutting tips are bonded and heated in a separate cycle, said diamond cutting tips are silver brazed to said tungsten-carbide studs at a temperature of about 650°F., the pressing of said diamond tip to said tungsten-carbide stud during the heating cycle is about 15,000 pounds per square inch.

59. A process for making a drag bit type of rock bit, said drag bit having a plurality of projection extending from a body of said drag bit at a cutting end of said drag bit, the process comprising the steps of:
depositing a suitable powder composition on the outer surface of the drag bit body;
heating said powder composition between 1900°F. and 2300°F. in a suitable mold for 4 to 10 hours;
pressing said powder composition during said heating cycle between 15,000 and 30,000 pounds per square inch to consolidate said powder composition on said drag bit body providing an exterior cladding thereon, said cladding having a hardness of at least 50 Rockwell C units, substantially conforming to the desired final exterior configuration of the drag bit, and being comprised of a material selected from a group consisting of metals and cermets, and pressing and heating, in a separate cycle, diamond cutting tips to said projections extending from the cutting end of said drag bit, a nickel shim is first placed between each of said projections, said heating cycle having temperatures between 1200°F. (650°C.) and 1385°F. (750°Co) for 0.5 to 4 hours, said pressing cycle taking place simultaneously with said heating cycle, said pressing cycle having pressures between 15,000 and 30,000 pounds per square inch to bond said diamond tips to said studs.

60. The process, as set forth in claim 59, wherein said diamond cutting tips bonded to said projections on said drag bit are heated on a heating cycle to about 1200°F. for about 2 hours.

61. The process, as set forth in claim 59, wherein said diamond tips bonded to said projections extending from said drag bit are pressed during the heating cycle to a pressure of about 15,000 pounds per square inch.

62. The process, as set forth in claim 59, wherein the diamond cutting tips are silver brazed to said projections at a temperature of about 650°F. at a pressure of about 15,000 pounds per square inch.