WO1999039075A1

WO1999039075A1 - Rotary cone drill bit having a ball plug weld with hardfacing

Info

Publication number: WO1999039075A1
Application number: PCT/US1999/002114
Authority: WO
Inventors: Frank A. Lada; Michael S. Beaton
Original assignee: Dresser Industries, Inc.
Priority date: 1998-01-30
Filing date: 1999-01-29
Publication date: 1999-08-05

Abstract

A rotary cone drill bit for forming a borehole having a bit body with an upper portion adapted for connection to a drill string. A number of support arms extending from the bit body with each support arm having an exterior surface with an opening extending therethrough. A number of cutter cone assemblies equal to the number of support arms with each cutter cone assembly rotatably mounted on a respective support arm and projecting generally downwardly and inwardly from the respective support arm. A ball retainer passageway extending from the opening in the exterior surface of each support arm to allow installing ball bearings through the opening and the ball retainer passageway to rotatably mount each cutter cone assembly on its respective support arm. A ball retainer plug disposed within the ball retainer passageway to maintain engagement of the ball bearing with the respective cutter cone assembly and support arm. A layer of hardfacing material disposed within the opening adjacent to one end of the ball retainer plug to form a fluid barrier between the exterior of each support arm and the respective ball retainer passageway. For other applications a layer of alloy steel and a layer of hardfacing material may be used to form the fluid barrier between the ball retainer passageway and the exterior surface of the support arm.

Description

ROTARY CONE DRILL BIT HAVING A BALL PLUG WELD WITH HARDFACING

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to a rotary cone drill bit and more particularly to a drill bit having support arms with a ball plug weld formed at least in part with a layer of hardfacing material.

BACKGROUND OF THE INVENTION

Various types of rotary drill bits or rock bits may be used to form a borehole in the earth. Examples of such rock bits include roller cone drill bits or rotary cone drill bits used in drilling oil and gas wells. A typical roller cone drill bit includes a bit body with an upper portion adapted for connection to a drill string. A plurality of support arms, typically three, depend from the lower portion of the bit body with each support arm having a spindle or journal protruding radially inward and downward with respect to a projected axis of rotation of the bit body.

Conventional roller cone drill bits are typically constructed in three segments. The segments may be positioned together longitudinally with a welding groove between each segment.- The segments may then be welded with each other using conventional techniques to form the bit body. Each segment also includes an associated support arm extending from the bit body. An enlarged cavity or passageway is typically formed in the bit body to receive drilling fluids from the drill string. U.S. Patent 4,054,772 entitled Positioning System for Rock Bi t Welding, shows a method and apparatus for constructing a three cone rotary rock bit from three individual segments.

A cutter cone assembly is generally rotatably mounted on each spindle or journal. Various types of bearings and/or bearing surfaces may be disposed between the exterior of each spindle and the interior of a cavity formed in the associated cutter cone assembly to receive the respective spindle. In a sealed roller cone drill bit, a lubricant under pressure is forced into a space between the exterior surface of the spindle and the interior surface of the cavity to cool and protect the bearings and/or bearing surfaces. A lubricant reservoir is used to compensate for any partial loss of lubricant and to balance internal lubricant pressure with external hydrostatic pressure during downhole drilling operations. The lubricant may comprise, for example, a calcium complex grease. Additionally, solids, such as molybdenum disulfide, may be added to the lubricant to increase the load carrying capacity of the bearings and/or bearing surfaces.

The bearings and bearing surfaces in a typical rotary cone drill bit are heavily loaded during downhole drilling operations. During such drilling operations, the drill bit is rotated in a borehole which causes the associate cutter cone assemblies to rotate on respective spindles. The drill bit typically operates at a low speed with heavy weight applied to the bit which also produces a high load on the associated bearings. Many rotary cone drill bits include one or more elastomeric seals which may be damaged by exposure to high temperatures created by excessive friction due to such heavy loads. The resulting seal failure often allows water, drilling fluids, and other debris from the drilling operation to penetrate the space between the cavity in the cutter cone assembly and the associated spindle which increases wear on the bearings and/or bearing surfaces to the point the cutter cone assemblies may be lost in the borehole.

One or more nozzles may be formed on the underside of the bit body adjacent to the support arms. The nozzles are typically positioned to direct drilling fluid passing downwardly from the drill string through the bit body toward the bottom of the borehole being formed. Drilling fluid is generally provided by the drill string to perform several functions including washing away material removed from the bottom of the borehole, cleaning the cutter cone assemblies, and carrying the cuttings radially outward and then upward within an annulus defined between the exterior of the bit body and the wall of the borehole. U.S. Patent 4,056,153 entitled Rotary Rock Bi t wi th

Mul tiple Row Coverage for Very Hard Formations, and U.S. Patent 4,280,571 entitled Rock Bi t, show examples of conventional rotary cone bits with cutter cone assemblies mounted on a spindle projecting from a support arm. Typically, ball bearings are inserted through an opening or hole in an exterior surface of each support arm and a ball retainer passageway extending therefrom to rotatably secure each cutter cone assembly on its respective spindle. A ball retainer plug is then inserted into the ball retainer passageway. Finally, a ball plug weld is typically formed in the opening to secure the ball retainer plug within the ball retainer passageway.

Attempts have been made to place a compact or insert into the hole or opening in the exterior surface of a support arm to seal the ball retainer and retain the ball plug and the ball bearings within the support arm. Placing an insert or compact into the hole has a tendency to damage or crack portions of the support arm adjacent to the hole which results in compromising the fluid integrity of the associated lubrication system.

Hardfacing of metal surfaces and substrates is a technique used to minimize or prevent erosion and abrasion of the metal surface or substrate. Hardfacing can be generally defined as applying a layer of hard, abrasion resistant material to a less resistant surface or substrate by plating, welding, spraying or other well known deposition techniques. Hardfacing is used to extend the service life of drill bits and other downhole tools used in the oil and gas industry. Tungsten carbide and its various alloys are sometimes used as hardfacing materials to protect drill bits and other downhole tools associated with drilling and producing oil and gas wells. Hardfacing is typically a mixture of a hard, wear-resistant material embedded in a matrix deposit which is preferably fused with the surface of a substrate by forming metallurgical type bonds to ensure uniform adherence of the hardfacing to the substrate.

A wide variety of hardfacing materials have been satisfactorily used on drill bits and other downhole tools. A frequently used hardfacing includes sintered tungsten carbide particles in an alloy steel matrix deposit. Other forms of tungsten carbide particles may include grains of monotungsten carbide, ditungsten carbide and/or macrocrystalline tungsten carbide. Satisfactory binders may include materials such as cobalt, iron, nickel, alloys of iron and other metallic alloys. For some applications loose hardfacing material is generally placed in a hollow tube or welding rod and applied to the substrate using various welding techniques. This technique of applying hardfacing is sometimes referred to as "tube rod welding." Tungsten carbide/cobalt hardfacing applied with tube rods has been highly successful in extending the service life of drill bits and other downhole tools.

As a result of the welding process, a matrix deposit including both steel alloy melted from the substrate surface and steel alloy provided by the welding rod or hollow tube is formed with the hardfacing. Various alloys of cobalt, nickel and/or steel may be used as part of the binder for the matrix deposit. Other heavy metal carbides and nitrides, in addition to tungsten carbide, have been used to form hardfacing.

SUMMARY OF THE INVENTION

In accordance with teachings of the present invention, disadvantages and problems associated with rotary cone drill bits having ball plug welds have been substantially reduced or eliminated. In one aspect of the present invention, a rotary cone drill bit is provided with support arms having a layer of hardfacing material which forms at least a portion of a ball plug weld associated with each support arm. A ball plug weld formed in accordance with teachings of the present invention will maintain and preserve integrity of the lubrication system associated with each support arm by reducing or preventing generation of leak paths through the ball plug weld or adjacent portions of the associated support arm.

Premature drill bit failure is known to occur because of fluid leak paths developing in the vicinity of conventional ball plug welds through abrasion, erosion and/or of relatively soft weld material used to provide ball plug welds in the support arms of a typical rotary cone drill bit. The present invention will prolong the downhole life of a rotary cone drill bit by reducing or eliminating ball plug weld failures due to abrasion, erosion and/or wear. A layer of hardfacing material formed as part of each ball plug weld in accordance with teachings of the present invention generally prolongs the downhole life of the associated rotary cone drill bit.

Technical advantages of the present invention include the ability to use any hardfacing material capable of producing a fluid tight seal to form all or portions of a ball plug weld which will prevent abrasion, erosion and wear of the associated support arm and maintain fluid tight integrity of the associated lubrication system. Such hardfacing materials may be applied in accordance with teachings of the present invention by any appropriate hardfacing process, such as plasma, GMAW, GTAW, SMAW, OFW, OFSW, HVOF or other suitable process for applying hardfacing material to a substrate.

For some applications, a ball plug weld may be formed in accordance with teachings of the present invention only from hardfacing material. For other applications, a ball plug weld may be formed in accordance with teachings of the present invention with one or more layers of mild steel alloy welding material and one or more layers of hardfacing material. The depth or thickness of the ball plug weld will depend upon the configuration of the support arm, ball retainer passageway and ball plug disposed therein. For relatively deep or thick ball plug welds, a layer of mild steel welding material may be used to form a fluid tight seal between the ball passageway and the exterior of the associated support arm. A wide variety of welding materials may be satisfactory to form this first, fluid tight layer within the ball passageway. Any welding material capable of producing an adequate fluid tight seal is acceptable for use in accordance with teachings of the present invention. A layer of corrosion and erosion resistant hardfacing materials may then be disposed on the layer of mild steel alloy. The mild steel alloy layer and the layer of hardfacing material may be applied using a wide variety of welding techniques. A ball plug weld may be formed using authentic manganese steel, diamond deposits, tungsten carbide deposits, cobalt based deposits, nickel based deposits, iron based deposits, or other suitable materials or combinations. Covering a ball plug hole with a layer of hardfacing in accordance with teachings of the present invention may be most effective during drilling of horizontal and directional well bores which result in increased side loading of the associated drill bit and support arms. Premature drill bit failure due to increased abrasion, erosion, and/or wear of the support arms may occur under such conditions. Tungsten carbide inserts may be included as part of each support arm adjacent to the ball plug hole to further enhance abrasion, erosion and/or wear resistance.

Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and its advantages, reference is now made to the following brief description, taken in conjunction with the accompanying drawings and detailed description, wherein like reference numerals represent like parts, in which:

FIGURE 1 is a schematic drawing showing an isometric view of a rotary cone drill bit formed in accordance with teachings of the present invention; FIGURE 2 is a schematic drawing in section with portions broken away showing one embodiment of a support arm and cutter cone assembly formed in accordance with teachings of the present invention; and FIGURE 3 is an enlarged drawing in section with portions broken away of the support arm of FIGURE 2 showing a ball plug weld incorporating an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiments of the present invention and its advantages are best understood by referring now in more detail to FIGURES 1-3 of the drawings, in which like numerals refer to like parts. FIGURES 1 through 3 illustrate various aspects of a rotary cone drill bit, indicated generally at 10, of the type used in drilling a borehole in the earth. Drill bit 10 may also be referred to as a "roller cone rock bit" or "rotary rock bit." With rotary cone drill bit 10, cutting action occurs as cone-shaped cutters, indicated generally at 12, are rolled around the bottom of the borehole (not shown) by the rotation of a drill string (not shown) attached to bit 10. Cutter cone assemblies 12 may also be referred to as "rotary cone cutters" or "roller cone cutters." Each cutter cone assembly 12 will rotate on respective journal or spindle 14 with associated bearings 16 disposed therebetween. It should be understood that the teachings of the present invention are not limited to rotary cone drill bits as shown in FIGURES 1 and 2. Rotary cone drill bit 10 comprises an enlarged bit body 18 having a tapered, externally spread upper portion 20 that is adapted to be secured to the lower end of the drill string. Depending from body 18 are three support arms 22 (two visible in FIGURE 1) . Each arm support 22 include cutter cone assembly 12 rotatably mounted on one end. As shown in FIGURE 2, each support arm 22 includes a journal 14 formed integral to the support arm 22. Journals 14 are preferably angled downwardly and inwardly with respect to bit body 18 and exterior surface 24 of the associated support arm 22 so that as bit 10 is rotated, cutter cone assemblies 12 engage the bottom of the borehole (not expressly shown) . For some applications, journals 14 may also be tilted at an angle of zero to three or four degrees in the direction of rotation of bit 10.

Cutter cone assemblies 12 each may include pressed inserts 26 on the gage surface and protruding inserts 28 or milled teeth, both of which scrape and gouge against the sides and bottom of the borehole under the down-hole force supplied through the drill string. The formation of borehole debris thus created is carried away from the bottom of the borehole by a drilling fluid flowing from nozzles 30 adjacent to lower portion 32 of bit body 18. The drilling fluid then flows upwardly toward the surface through an annulus (not shown) formed between drill bit 10 and the side wall (not shown) of the borehole. Each of the three cutter cones assemblies 12 is generally constructed and mounted on its associated journal 14 in a substantially identical manner. Accordingly, only one support arm 22 and cutter cone assembly 12 is described in detail. It should be understood that such description also applies to the other support arms 22 and cutter cones assemblies 12.

FIGURE 2 is a cross-sectional view of a support arm, indicated generally at 22, of FIGURE 1. Cutter cone assembly 12 has a generally cylindrical internal cavity 34 for receiving journal 14. Bearings 16 are pressed in cutter cone assembly 12 such that cutter cone assembly 12 may rotate about journal 14. An elastomer seal 36 is located at the mouth of internal cavity 34 to provide a 10

fluid seal between internal cavity 34 and journal 14. Elastomer seal 36 may be formed from various elastomeric materials that will form a fluid-tight seal. This provides a sealed-bearing assembly for each cutter cone assembly 12 mounted on journal 14. The present invention may be satisfactorily used with a wide variety of cutter cone assemblies having fluid seal and bearing systems other than those shown in FIGURES 1 and 2.

Cutter cone assembly 12 is retained on journal 14 by a plurality of ball bearings 42 inserted through opening 40 in exterior surface 24 of support arm 22 and ball passageway 44 in journal 14. Ball bearings 42 reside in an annular array within cooperatively associated ball races 46 and 48 in journal 14 and cutter cone assembly 12, respectively. Once inserted, ball bearings 42 prevent the disengagement of cutter cone assembly 12 from journal 14. Ball passageway 44 is subsequently plugged by inserting ball plug 50 into ball passageway 44. Ball plug 50 includes a necked down or reduced diameter intermediate portion 54. As discussed later, ball plug weld 120 is preferably formed within each opening 40 to provide a fluid barrier between respective ball passageway 44 and the exterior of support arm 22. Ball plug weld 120 also retains ball plug 50 within the respective ball passageway 44.

Drill bit 10 includes a lubricant cavity 56 that is open to the outside surface of drill bit 10 (not shown in FIGURE 1) . Lubricant cavity 56 houses a main lubricant reservoir. The main lubricant reservoir includes a generally cylindrical lubricant container 58 disposed within lubricant cavity 56. Lubricant container 58 has a closed end 60 with lubricant opening 62, disposed therein. The opposite open end of lubricant container 58 has a flanged shoulder 64 supporting a flexible resilient 11

diaphragm 66 that closes lubricant container 58. A cap 68 covers diaphragm 66 and defines a chamber 70 facing diaphragm 66 to provide a volume into which diaphragm 66 can expand. Cap 68, diaphragm 66 and lubricant container 58 are retained within lubricant cavity 56 by a snap ring 72. Cap 68 also includes an opening 74 for placing the outer face of diaphragm 66 in fluid communication with external fluids surrounding roller cone rock bit 10. The volume between diaphragm 66 and lubricant container 58 may be filled with a suitable lubricant to define a source of lubricant for bearing 16 and ball bearings 42 of drill bit 10.

Lubricant passage 76 extends through support arm 22 to place lubricant cavity 56 in fluid communication with ball passageway 44. Lubricant passage 76 may be drilled from an end of lubricant cavity 56 generally adjacent lubricant opening 62 and lubricant container 58. Ball passageway 44 is placed in fluid communication with internal cavity 34 by conduit 78. Upon assembly of drill bit 10, lubricant passage 76, lubricant container 58, lubricant cavity 56, the available space in the ball passageway 44, conduit 78 and the available space in internal cavity 34 are filled with lubricant through an opening 80 in arm 22. Opening 80 is subsequently sealed after lubricant filling. The pressure of the external fluids outside drill bit

10 may be transmitted to the lubricant in lubricant container 58 through diaphragm 66. The flexing of diaphragm 66 maintains the lubricant at a pressure generally equal to the pressure of the external fluids outside roller cone rock bit 10. This pressure is transmitted through lubricant passage 76, ball passageway 44, conduit 78 and internal cavity 34 to the inward face of elastomer seal 36 exposing elastomer seal 36 to an internal 12

pressure from the lubricant generally equal to the pressure of the external fluids.

For some applications, ball plug weld 120 may be formed from multiple layers of material. For the embodiment shown in FIGURE 2, ball plug weld 120 preferably includes first layer 122 and second layer 124. For this embodiment, first layer 122 is preferably formed from mild steel alloys similar to the steel alloys used to form support arm 22. The material used to form first layer 122 is preferably selected to form a grease tight, or fluid tight barrier within opening 40 of ball passageway 44. Ball plug weld 120, and in particular, first layer 122 also serve to secure and retain ball plug 50 within ball passageway 44. The particular material used to form first layer 122 is selected to provide better sealing capacity. The mild steel weld of first layer 122 provides ductility to resist micro-cracking to maintain the integrity of the fluid seal. Accordingly, the material often exhibits very low wear resistance, sometimes lower than the tempered, mild steel used to form the associated support arm 22 in which ball plug 50 is secured.

In the absence of second layer 124, first layer 122 may be subject to excessive wear. This may jeopardize the fluid tight seal provided by first layer 122 which may allow lubricant to escape. Alternatively, this may allow drilling fluids from the borehole to invade the lubrication system and deteriorate the bearings and elastomeric seals. This could lead to failure of the seal and/or bearings. In an extreme case the ball plug may become disengaged and eject from ball passageway 44, and ball bearing 42 could be compromised. As a result of the present invention, ball plug welds no longer rely entirely on soft, or mild steel alloys to form the entire ball plug weld. 13

Referring to FIGURES 1-3, ball plug welds 120 and 220 of the present invention incorporate wear resistant hardfacing material at layers 124 and 224, respectively, to prevent the erosion of ball plug weld 120. Cracks within first layer 122 will have a tendency to propagate through the mild steel. When hardfacing is placed on top of the mild steel of first layer 122, small cracks or fissures may terminate either before the hardfacing or terminate at the hardfacing. The interface between first layer 122 and second layer 124 prevents block crack propagation, helps maintain the integrity of the seal system of the lubricant, and prevents weld fluids from migrating into the lubrication system.

For purposes of the present application, the term "hardfacing" is used to refer to a layer of material applied to a substrate to protect the substrate from abrasion, erosion and/or wear. Various binders such as cobalt, nickel, copper, iron and alloys thereof may be used to form the matrix or binder portion of the deposit. Various metal alloys, ceramic alloys and cermets such as metal borides, metal carbides, metal oxides and metal nitrides may be included as part of the matrix deposit in accordance with the teachings of the present invention. Some of the more beneficial metal alloys, ceramic alloys and cermets will be discussed later in more detail. Hardfacing may also be referred to as a "matrix deposit."

Layers 124 and 224 may be formed from various types of hardfacing material in accordance with teachings of the present invention. These materials include, but are not limited to hard ceramic particles and/or hard particles formed from superabrasive and superhard materials commonly found as phases in the boron-carbon-nitrogen-silicon family of compounds and alloys. Additional examples of materials that may be satisfactorily used to provide hard particles 14

for hardfacing layers 124 and 224 in accordance with teachings of the present invention include diamonds, silicon nitride (Si₃N₄), silicon carbide (SiC), boron carbide (B„C) in addition to cubic boron nitride (CBN) . Various materials including boron, carbon, copper, nickel, iron, cobalt, carbides, nitrides, borides, suicides and oxides of tungsten, niobium, vanadium, molybdenum, titanium, tantalum, hafnium, yttrium, zirconium, chromium, and mixtures and alloys thereof may also be used to form hardfacing layers 124 and 224. For example, metal borides, metal carbides, metal oxides and metal nitrides or other superhard and superabrasive materials may be used to form all or a portion of hardfacing layers 124 and 224. An alloy called colminoy 88, which is a very easily weldable material available in wire form, may also be used to form at least a portion of second layer 124.

For purposes of the present application, the term "tungsten carbide" includes monotungsten carbide (WC) , ditungsten carbide (W₂C) , macrocrystalline tungsten carbide and cemented or sintered tungsten carbide. Sintered tungsten carbide is typically made from a mixture of tungsten carbide and cobalt powders by pressing the powder mixture to form a green compact. Various cobalt alloy powders may also be included. Depending upon the intended application for hardfacing layers 124 and 224, various types of tungsten carbide may be used to form all or a portion of hardfacing layers 124 and 224. An important feature of the present invention includes the ability to select the type of material which will form each portion of ball plug weld 120 and 220 to provide the desired abrasion, wear, and erosion resistance and a fluid tight seal in an efficient, cost-effective, reliable manner. 15

Embodiments of the present invention may include 3/32 to 1/8 inch thick deposits of hardfacing material to form at least of portion of plug weld 120 or 220. When greater thicknesses are required, it may be advantageous to provide a first layer of a more ductile welding material, similar to first layer 122. For the embodiment shown in FIGURE 3, ball plug weld 220 includes only layer 224. For this embodiment, layer 224 may be formed from the same types of hardfacing materials which form second layer 124 of ball plug weld 120.

A hardfacing layer 23 may also be applied to support arm 22 as illustrated in FIGURE 1. The hardfacing material used to form hardfacing layer 23 may be similar to those available for second layer 124. During fabrication and assembly of drill bit 10, hardfacing layer 23 may be applied contemporaneously with second layer 124.

The present invention may be satisfactorily used with a drill bit having a one piece or unitary bit body (not expressly shown) . Examples of such drill bits and their associated bit body, support arms and cutter cone assemblies are shown in U.S. Patent 5,439,067 entitled Rock Bi t Wi th Enhanced Fl uid Return Area, and U.S. Patent 5,439,068 entitled Modular Rotary Drill Bi t . These patents provide additional information concerning the manufacture and assembly of unitary bit bodies, support arms and cutter cone assemblies which are satisfactory for use with the present invention.

Welding techniques suitable for use within the teachings of the present invention include, but are not limited to Gas Metal Arc Welding (GMAW) , TIG, Gas Tungsten Arc Welding (GTAW) or "helium arc welding", Shielded Metal Arc Welding (SMAW) or "stick electro welding", Oxy Fuel Welding (OFW) , Oxy Fuel Spot Welding (OFSW) and High Velocity Oxy Fuel (HVOF) . 16

EXPERIMENTAL TEST RESULTS: Six ball plug weld specimens were received; all were seal welded with standard procedure GMAW process with E70S wire. Subsequently, all were capped with austenitic manganese filler, 3 using GMAW, 3 using GTAW. The six specimens were sectioned into four quarters. All sections were free of cracks.

Although the present invention has been described by several embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompasses such changes and modifications as fall within the scope of the present appended claims.

Claims

WHAT IS CLAIMED IS:

1. A ball plug weld for sealing a ball retainer passageway of a rotary cone drill bit, wherein the ball plug weld is formed at least in part by a layer of hardfacing material.

2. The ball plug weld of Claim 1, wherein the layer of hardfacing material is formed at least in part from materials selected from the group consisting of boron, carbon, copper, nickel, iron, cobalt, carbides, nitrides, borides, suicides and oxides of tungsten, niobium, vanadium, molybdenum, titanium, tantalum, hafnium, yttrium, zirconium, chromium, and mixtures thereof.

3. The ball plug weld of Claim 1, wherein the layer of hardfacing material is formed at least in part from materials selected from the group consisting of metal borides, metal carbides, metal oxides and metal nitrides.

4. The ball plug weld of Claim 1, wherein the layer of hardfacing comprises a matrix portion with a plurality of hard particles disposed therein.

5. The ball plug weld of Claim 4, wherein the matrix portion is selected from the group consisting of cobalt, nickel, copper, iron, colminoy 88, cobalt alloy, nickel alloy, copper alloy and iron alloy.

6. The ball plug weld of Claim 4, wherein the matrix portion is selected from the group consisting of metal alloys, ceramic alloys and cermets.

7. The ball plug weld of Claim 4, wherein the hard particles are selected from the group consisting of diamonds, silicon nitride (Si₃N₄) , silicon carbide (SiC) , boron carbide (B₄C) and cubic boron nitride (CBN) .

8. A rotary cone drill bit for forming a borehole, comprising: a bit body having an upper portion adapted for connection to a drill string for rotation of the drill bit; a number of support arms attached to and extending from the bit body opposite the upper portion, each of the support arms having an inside surface with a respective journal connected thereto; each journal projecting generally downwardly and inwardly with respect to its associated support arm; each of the support arms having a leading edge, a trailing edge, and an exterior surface disposed therebetween; a number of cutter cone assemblies equal to the number of support arms with each cutter cone assembly respectively rotatably mounted on one of the support arms; an opening formed in the exterior surface of each support arm with a ball retainer passageway extending from the opening in the exterior of the support arm whereby ball bearings may be inserted through the opening and the ball retainer passageway to rotatably secure the respective cutter cone assembly on the journal; a ball plug weld disposed within the opening to form a fluid barrier between the ball retainer passageway and the exterior surface of the respective support arm; and a layer of hardfacing material forming at least a portion of each ball plug weld. 20

9. The drill bit of Claim 8, wherein each support arm further comprises: a layer of hardfacing material disposed on the exterior surface of each support arm; and a plurality of inserts disposed in the exterior surface of each support arm.

10. The drill bit of Claim 8, wherein each support arm further comprises: a ball plug disposed within the ball retainer passageway; a layer of weldable material disposed within the ball retainer passageway adjacent to the opening in the exterior of the support arm; and the layer of hardfacing material disposed on the layer of weldable material.

11. The drill bit of Claim 8, wherein the hardfacing material is selected from the group consisting of metal borides, metal carbides, metal oxides and metal nitrides.

12. The drill bit of Claim 8, wherein the hardfacing material is formed at least in part by materials selected from the group consisting of diamonds, silicon nitride (Si₃N₄) , silicon carbide (SiC) , boron carbide (B₄C) and cubic boron nitride (CBN) .

21

13. A method for sealing an opening to a ball retainer passageway in a support arm comprising the steps of: inserting a plurality of ball bearings through the opening and the ball retainer passageway to rotatably secure a cutter cone assembly on a spindle extending from the support arm; inserting a ball plug into the ball retainer passageway; and welding a layer of hardfacing material between the end of the ball plug and the opening at an exterior surface of the support arm to form at least a portion of a fluid barrier between the ball retainer passageway and an exterior surface of the support arm.

14. The method of Claim 13, further comprising the steps of: welding a layer of ductile material between the end of the ball plug and the opening at the exterior surface of the support arm prior to welding the layer of hardfacing material .

15. The method of Claim 13, wherein the layer of hardfacing material is formed at least in part from materials selected from the group consisting of boron, carbon, copper, nickel, iron, cobalt, carbides, nitrides, borides, suicides and oxides of tungsten, niobium, vanadium, molybdenum, titanium, tantalum, hafnium, yttrium, zirconium, chromium, and mixtures thereof.

16. The method of Claim 13, wherein the layer of hardfacing material further comprises a matrix portion and a plurality of hard particles disposed therein. 22

17. The method of Claim 16, wherein the matrix portion is formed at least in part from materials selected from the group consisting of cobalt, nickel, copper, iron, colminoy 88, cobalt alloy, nickel alloy, copper alloy, and iron alloy.

18. The method of Claim 16, wherein the matrix portion is selected from the group consisting of metal alloys, ceramic alloys and cermets.

19. The method of Claim 16, wherein the hard particles are selected from the group consisting of diamonds, silicon nitride (Si₃N₄) , silicon carbide (SiC) , boron carbide (B₄C) and cubic boron nitride (CBN) .