U.S. patent number RE37,127 [Application Number 09/137,254] was granted by the patent office on 2001-04-10 for hardfacing composition for earth-boring bits.
This patent grant is currently assigned to Baker Hughes Incorporated. Invention is credited to Ronald L. Jones, Alan J. Massey, James L. Overstreet, Kevin W. Schader, Danny E. Scott.
United States Patent |
RE37,127 |
Schader , et al. |
April 10, 2001 |
**Please see images for:
( Certificate of Correction ) ( Reexamination Certificate
) ** |
Hardfacing composition for earth-boring bits
Abstract
A hardfacing composition comprises at least 60% by weight of
hard metal granules including a quantity of sintered carbide
pellets and a quantity of cast carbide pellets. The cast and
sintered carbides are selected from the group of carbides
consisting of chromium, molybdenum, niobium, tantalum, titanium,
tungsten, and vanadium carbides and alloys and mixtures thereof.
The balance of the hardfacing composition is matrix metal with
traces of flux or deoxidizer, and alloying elements. All
percentages given are pre-application ratios.
Inventors: |
Schader; Kevin W. (Spring,
TX), Overstreet; James L. (Webster, TX), Massey; Alan
J. (Houston, TX), Jones; Ronald L. (Cleveland, TX),
Scott; Danny E. (Montgomery, TX) |
Assignee: |
Baker Hughes Incorporated
(Houston, TX)
|
Family
ID: |
23344277 |
Appl.
No.: |
09/137,254 |
Filed: |
August 19, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
343005 |
Nov 21, 1994 |
05663512 |
Sep 2, 1997 |
|
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Current U.S.
Class: |
75/239; 75/240;
75/242 |
Current CPC
Class: |
B22F
1/0003 (20130101); B23K 35/327 (20130101); C22C
1/051 (20130101); C22C 29/08 (20130101); E21B
10/50 (20130101); C23C 30/005 (20130101); B22F
1/0096 (20130101); B22F 9/04 (20130101); C22C
33/02 (20130101); C23C 4/10 (20130101); B22F
1/0096 (20130101); C22C 29/08 (20130101); B22F
1/0003 (20130101); C22C 29/08 (20130101); C22C
33/02 (20130101); B22F 2999/00 (20130101); B22F
2999/00 (20130101); C22C 29/06 (20130101); B22F
1/0048 (20130101); B22F 3/10 (20130101); B22F
2999/00 (20130101); B22F 1/0003 (20130101); B22F
9/082 (20130101); B22F 9/04 (20130101) |
Current International
Class: |
C22C
1/05 (20060101); B23K 35/32 (20060101); B23K
35/24 (20060101); C23C 4/10 (20060101); E21B
10/46 (20060101); E21B 10/50 (20060101); C22C
029/00 () |
Field of
Search: |
;75/239,240,242,246
;428/557 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1070039 |
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May 1967 |
|
GB |
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2104101A |
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Mar 1982 |
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GB |
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Other References
British Search Report dated Jan. 24, 1996..
|
Primary Examiner: Mai; Ngoclan
Attorney, Agent or Firm: Felsman, Bradley, Vaden, Gunter
& Dillon, L.L.P. Bradley; James E.
Claims
We claim:
1. An improved, wear-resistant hardfacing composition comprising
the following materials in pre-application ratios:
at least 60% by weight of the composition being granules including
a quantity of sintered carbide pellets and a quantity of cast
carbide pellets, the cast and sintered carbides being selected from
one of the group of carbides consisting of chromium, molybdenum,
niobium, tantalum, titanium, tungsten, and vanadium carbides and
alloys and mixtures thereof;
the balance of the hardfacing composition being matrix metal.
2. The improved hardfacing composition according to claim 1 wherein
the quantity of sintered carbide pellets is about 65.5% by weight
of the granules and the quantity of cast carbide pellets is about
15% by weight of the granules, and the granules further comprise
about 15% by weight crushed sintered carbide particles.
3. The improved hardfacing composition according to claim 1 wherein
the sintered carbide pellets range in size between about 16 and
about 30 mesh.
4. The improved hardfacing composition according to claim 2 wherein
the crushed sintered carbide particles range in size between about
20 mesh and about 30 mesh.
5. The improved hardfacing composition according to claim 1 wherein
the cast carbide pellets range in size between about 40 mesh and
about 80 mesh.
6. The improved hardfacing composition according to claim 1 wherein
the matrix metal is selected from the group consisting of nickel,
iron, cobalt and alloys and mixtures thereof and a portion of the
matrix material is in the form of a tube containing the
granules.
7. The improved hardfacing composition according to claim 1 wherein
the matrix metal is low-carbon steel alloyed with niobium.
8. An improved earth-boring bit hardfacing composition comprising,
in pre-application ratios:
about 41-49% by weight spherical sintered carbide pellets;
about 8-12.8% by weight spherical cast carbide pellets;
about 8-12.8% by weight crushed sintered carbide particles; and
a balance of the composition matrix metal.
9. The improved hardfacing composition according to claim 8 wherein
the spherical sintered carbide pellets range in size between about
16 mesh and about 30 mesh.
10. The improved hardfacing composition according to claim 8
wherein the crushed sintered carbide particles range in size
between about 20 mesh and about 30 mesh.
11. The improved hardfacing composition according to claim 8
wherein the spherical cast carbide pellets range in size between
about 40 mesh and about 80 mesh.
12. The improved hardfacing composition according to claim 8
wherein the particulate carbide materials are selected from one of
the group of carbides consisting of chromium, molybdenum, niobium,
tantalum, titanium, tungsten, and vanadium carbides and alloys and
mixtures thereof.
13. The improved hardfacing according to claim 8 wherein the matrix
metal is low-carbon steel alloyed with niobium.
14. An improved earth-boring bit hardfacing composition comprising,
in pre-application ratios:
about 41-49% by weight spherical sintered tungsten carbide
pellets;
about 8-12.8% by weight spherical cast tungsten carbide
pellets;
about 8-12.8% by weight crushed sintered tungsten carbide
particles; and
a balance of the composition matrix metal in the form of a tube
containing the cast and sintered carbide particles and pellets.
15. The improved hardfacing composition according to claim 14
wherein the spherical sintered carbide pellets range in size
between about 16 mesh and about 30 mesh.
16. The improved hardfacing composition according to claim 14
wherein the crushed sintered carbide particles range in size
between about 20 mesh and about 30 mesh.
17. The improved hardfacing composition according to claim 14
wherein the spherical cast carbide pellets range in size between
about 40 mesh and about 80 mesh.
18. The improved hardfacing according to claim 14 wherein the
matrix metal is low-carbon steel alloyed with niobium..Iadd.
19. An improved, wear-resistant hardfacing composition comprising
the following materials in pre-application ratios:
a quantity of sintered carbide pellets and a quantity of cast
carbide pellets, the cast and sintered carbides being selected from
one of the group of carbides consisting of chromium, molybdenum,
niobium, tantalum, titanium, tungsten and vanadium carbides and
alloys and mixtures thereof;
the balance of the hardfacing composition being matrix metal.
.Iaddend..Iadd.
20. The improved hardfacing composition according to claim 19
wherein in pre-application ratios the quantity of sintered carbide
pellets is about 65.5% by weight of the granules and the quantity
of cast carbide pellets is about 15% by weight of the granules, and
the granules further comprises about 15% by weight crushed sintered
carbide particles. .Iaddend..Iadd.
21. The improved hardfacing composition according to claim 19
wherein the sintered carbide pellets range in size between about 16
to about 30 mesh. .Iaddend..Iadd.
22. The improved hardfacing composition according to claim 20
wherein the crushed sintered carbide particles range in size
between about 20 mesh and about 30 mesh. .Iaddend..Iadd.
23. The improved hardfacing composition according to claim 19
wherein the cast carbide pellets range in size between about 40
mesh and about 80 mesh. .Iaddend..Iadd.
24. The improved hardfacing composition according to claim 19
wherein the matrix metal is selected from the group consisting of
nickel, iron, cobalt and alloys and mixtures thereof and a portion
of the matrix material is in the form of a tube containing the
granules. .Iaddend..Iadd.
25. The improved hardfacing composition according to claim 19
wherein the matrix metal is low-carbon steel alloyed with niobium.
.Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the composition of hardfacing
materials applied to surfaces subjected to abrasive wear to
increase their wear resistance. More particularly, the present
invention relates to hardfacing compositions applied to one or more
surfaces of an earth-boring bit of the rolling cutter variety.
2. Background Information
It is a long-standing practice in the design and manufacture of
earth-boring bits to apply wear-resistant hardfacing materials to
the surfaces of such bits that are subjected to abrasive wear
during drilling operations. In earth-boring bits of the rolling
cutter variety, these surfaces include the teeth of bits of the
milled or steel tooth variety, the gage surfaces of the rolling
cutters, and the shirttails of the bit legs comprising the bit
body.
In the past, these hardfacing compositions generally comprise
carbides of the elements of Groups IVB, VB, and VIB in a matrix
metal of iron, cobalt, or nickel and alloys and mixtures thereof.
The hardfacing is applied by melting the matrix and a portion of
the surface to which the hardfacing is applied with an oxyacetylene
or atomic hydrogen torch. The carbide particles give the hardfacing
material hardness and wear resistance, while the matrix metal lends
the hardfacing fracture toughness. A hardfacing composition must
strike an adequate balance between wear resistance (hardness) and
fracture toughness. A hardfacing composition that is extremely hard
and wear-resistant may lack fracture toughness, causing the
hardfacing to crack and flake prematurely. Conversely, a hardfacing
with adequate fracture toughness, but inadequate hardness and wear
resistance, is eroded prematurely and fails to serve its
purpose.
Many factors affect the suitability of a hardfacing composition for
a particular application. These factors include the chemical
composition and physical structure of the carbides employed in the
composition, the chemical composition and microstructure of the
matrix metal or alloy, and the relative proportions of the carbide
materials to one another and to the matrix metal or alloy.
One early advance in hardfacing compositions for use in
earth-boring bits is disclosed in commonly assigned U.S. Pat. No.
3,800,891, Apr. 2, 1974 to White et al. This patent discloses a
hardfacing composition comprising sintered tungsten carbide in an
alloy steel matrix. Sintered tungsten carbide comprises grains or
particles of tungsten carbide sintered with and held together by a
binder of non-carbide material, such as cobalt. The sintered
tungsten carbide possesses greater fracture toughness than the more
conventional cast tungsten carbide, such that the resulting
hardfacing composition possesses good fracture toughness without
sacrificing hardness and wear resistance.
U.S. Pat. No. 4,836,307, Jun. 6, 1989 to Keshavan et al., discloses
a hardfacing composition employing particles of cemented or
sintered tungsten carbide and relatively small particles of single
crystal monotungsten carbide, sometimes referred to as
"macrocrystalline " tungsten carbide, in a mild steel matrix. This
composition purports to possess the advantages of sintered tungsten
carbide, as disclosed in U.S. Pat. No. 3,800,891, with the
advantages of single crystal monotungsten carbide, which is harder
than the cemented or sintered tungsten carbide, yet is less brittle
than the alternative cast carbide.
U.S. Pat. No. 5,089,182, Feb. 18, 1992, to Findeisen, et al.
discloses a method of manufacturing cast carbide pellets that are
generally spherical in shape and have improved mechanical and
metallurgical properties over prior-art carbide pellets. These cast
pellets are not truly spherical, but are sufficiently symmetrical
that residual stresses in the pellets are minimized. Also, the
generally spherical shape of these pellets eliminates corners,
sharp edges, and angular projections, which are present in
conventional crushed particles, that increase residual stresses in
the particles and tend to melt as the hardfacing composition is
applied to the surface.
A need exists, therefore, for a hardfacing composition having a
near-optimal balance between wear-resistance and toughness and that
incorporates the properties of several types of carbide
materials.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide an
improved hardfacing for use in earth-boring bits and other
applications having a need for good wear resistance in combination
with good fracture toughness.
This and other objects of the present invention are accomplished by
providing a hardfacing composition comprising at least 60% by
weight of hard metal granules including a quantity of sintered
carbide pellets and a quantity of cast carbide pellets. The cast
and sintered carbides are selected from the group of carbides
consisting of chromium, molybdenum, niobium, tantalum, titanium,
tungsten, and vanadium carbides and alloys and mixtures thereof.
The balance of the hardfacing composition is matrix metal with
traces of flux or deoxidizer, and alloying elements. All
percentages given are pre-application ratios.
According to the preferred embodiment of the present invention, the
carbide materials are provided in granular form with the balance of
the material being matrix metal. The granules comprise about 67-71%
by weight of the composition. The sintered carbide pellets comprise
about 62.5 to 68.5% by weight of the granules and the cast carbide
pellets comprise 12-18% by weight of the granules. Crushed sintered
carbide particles comprise about 12-18% by weight of the granules.
The sintered carbide pellets range in size between about 16 mesh
and 30 mesh and the cast carbide pellets range in size between
about 40 mesh and about 80 mesh. The crushed sintered carbide
particles range in size between about 20 mesh and about 30
mesh.
According to the preferred embodiment of the present invention, the
matrix metal is low-carbon steel alloyed with niobium and is
present in the form of a tube containing the granules.
Other objects, features and advantages of the present invention
will become apparent with reference to the detailed description,
which follows.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an earth-boring bit of the type
contemplated by the present invention.
FIG. 2 is a photomicrograph of a section of the applied hardfacing
composition according to the present invention.
FIG. 3 is a photograph of a worn tooth of an earth-boring bit as
shown in FIG. 1, illustrating the wear characteristics of the
applied hardfacing composition according to the present
invention.
FIG. 4 is a photomicrograph of the surface of worn applied
hardfacing composition according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, and specifically to FIG. 1, an
earth-boring bit 11 of the type contemplated by the present
invention is illustrated. Earth-boring bit 11 includes a bit body,
which is threaded at its upper extent 15 for connection onto a
drillstring. Each leg of bit body 13 is provided with a lubricant
compensator 17, a preferred embodiment of which is disclosed in
commonly assigned U.S. Pat. No. 4,727,942, Mar. 1, 1988 to Galle et
al. At least one nozzle 19 is provided in bit body 13 to discharge
drilling fluid from the interior of the drillstring to cool and
lubricate bit 11 and to carry away cuttings generated during
drilling. Three cutters 21, 23 (one of which is obscured from view
in the perspective of FIG. 1) are rotatably mounted on cantilevered
bearing shafts depending from bit body 13. A plurality of cutting
elements 25 are formed on each cutter 21, 23. According to the
preferred embodiment of the present invention, cutting elements 25
are milled or steel teeth formed from the material of cutters 21,
23.
Conventionally, wear-resistant hardfacing may be applied over
cutting elements or teeth 25 to increase their wear-resistance.
Hardfacing may also be applied to the shirttail (portion above the
cutters 21, 23) of each bit leg forming the bit body 13. Hardfacing
may also be applied to the outermost or gage surfaces of cutters
21, 23. These are exemplary surfaces of bit 11 that are subjected
to abrasive wear during drilling operation. Hardfacing generally
may be applied to any surface of bit 11 that is subjected to
abrasive wear.
An improved hardfacing composition that is particularly suitable
for application to earth-boring bits 11 is composed of a quantity
of sintered carbide pellets in combination with a quantity of cast
carbide pellets in a metal matrix. The term "pellet" is used to
mean particles of carbide that are generally spherical in
configuration. Pellets are not true spheres, but lack the corners,
sharp edges, and angular projections commonly found in crushed and
other non-spherical carbide grains or particles. These surface
irregularities cause the particles to possess residual stresses and
may melt during application of the hardfacing composition,
degrading the properties of the hardfacing. Generally spherical
pellets are believed to have reduced levels of residual stresses
and generally do not possess irregularities that are believed to
melt during application.
The sintered carbide pellets comprise crystals or particles of
tungsten carbide sintered together with a binder, usually cobalt,
into the generally spherical pellet configuration. The cast carbide
pellets are tungsten carbide grains or particles melted and cast,
under controlled conditions, in a generally spherical
configuration. The preferred method for manufacturing cast tungsten
carbide pellets is disclosed in U.S. Pat. No. 5,089,182, Feb. 18,
1992 to Findeisen et al.
The enhanced fracture toughness of the sintered carbide pellets,
together with the hardness and strength of the cast carbide
pellets, results in a hardfacing composition having improved
wear-resistance and fracture toughness over hardfacing compositions
employing crushed carbide particles, sintered pellets or particles,
or macrocrystalline or single crystal monotungsten carbide, and
combinations thereof.
Tungsten carbide is the preferred carbide for the hardfacing
composition according to the present invention. However, cast and
sintered pellets of chromium, molybdenum, niobium, tantalum,
titanium, and vanadium carbides would be suitable.
According to the preferred embodiment of the present invention, the
improved hardfacing composition includes the following materials,
in pre-application ratios:
about 41-49% by weight sintered tungsten carbide pellets;
8-12.8% by weight cast tungsten carbide pellets; and
8-12.8% by weight crushed sintered tungsten carbide particles;
a balance of the composition being matrix metal.
According to the preferred embodiment of the present invention, the
carbide pellets and particles are in the form of a granular filler
in a tube rod of matrix metal. To achieve the above-referenced
pre-application ratios, the granular filler comprises 67-71% by
weight of the finished tube rod. The granules then comprise the
following pre-application ratios:
about 62.5-68.5% by weight sintered tungsten carbide pellets;
about 12-18% by weight spherical cast tungsten carbide; and
about 12-18% by weight crushed sintered tungsten carbide.
Also present in the tube rod with the granules is about 2-4% by
weight silicomanganese, about 0.4-0.6% by weight niobium and about
0.36% by weight resinox as flux, alloying element, and deoxidizer
and binder, respectively. The tube rod carrying the granules is
circular in cross-section and is formed of low-carbon steel and has
an outer diameter of 0.125 inch, a wall thickness of 0.013 inch,
and a length of about 28-30 inches. This tube rod thus comprises
29-33% by weight of the tube rod and granular filler. Preferably,
the sintered carbide pellets range in size from ASTM 16 mesh to
ASTM 30 mesh. The cast carbide pellets range in size from about
ASTM 40 mesh to about ASTM 80 mesh. The crushed sintered carbide
ranges in size from about ASTM 20 mesh to about ASTM 30 mesh.
FIG. 2 is a photomicrograph of a polished and etched section of the
hardfacing composition set forth above as applied to a tooth 25 of
an earth-boring bit 11. As can be seen, the larger sintered
tungsten carbide pellets (gray) comprise the bulk of the hardfacing
composition. The interstices or gaps between the larger sintered
carbide pellets are filled by the spherical cast carbide pellets
(dark gray to black). The larger spherical tungsten carbide
pellets, by virtue of their size and larger presence in the
composition, expose the largest surface area to abrasive wear. The
smaller spherical cast carbide pellets fill the gaps or interstices
between the larger sintered pellets, preventing the erosion of
matrix metal from between the spherical sintered carbide pellets,
thus prolonging the retention of the sintered carbide pellets in
the hardfacing. The irregularly shaped crushed sintered carbide
particles fill gaps in the matrix metal not otherwise occupied by
the spherical sintered carbide pellets and are thought to aid in
the weldability of the composition.
FIG. 3 is a photograph of a worn steel tooth of an earth-boring bit
having hardfacing according to the present invention applied
thereto. FIG. 4 is a photomicrograph of a surface of a worn steel
tooth bit having the hardfacing composition according to the
present invention applied thereto. As can be seen, and as was
described with reference to FIG. 2, the larger spherical sintered
tungsten carbide pellets bear the bulk of the abrasive wear and can
be seen to be worn. The smaller spherical cast carbide pellets,
having greater hardness and abrasion resistance than the sintered
carbide pellets, can be seen between the pellets and are far less
worn and stand above the matrix metal. The combination of the
larger, tougher spherical sintered carbide pellets with the
smaller, harder spherical cast carbide pellets yields a hardfacing
composition having improved wear and strength characteristics over
conventional hardfacings employing sintered tungsten carbide,
crushed cast tungsten carbide, or macrocrystalline tungsten
carbide, or combinations thereof.
Following are examples of hardfacing compositions prepared and
applied according to the present invention.
EXAMPLE
The following quantities and sizes of granular carbide materials
were provided:
Spherical sintered tungsten carbide pellets comprising tungsten
carbide particles or grains sintered with a 6% by weight cobalt
binder and provided by Kennametal, Inc. of Fallon, Nev., in the
following sizes and percentages by weight:
ASTM Mesh Size Range Mean +16 0-5% 3% -16/+20 40-50% 47% -20/+30
40-50% 47% -30 0-5% 3%
Crushed sintered tungsten carbide, also provided by Kennametal,
Inc., in the following sizes and percentages by weight:
ASTM Mesh Size Range Mean +20 0-5% 3% -20/+30 90-100% 94% -30 0-5%
3%
Spherical cast carbide pellets, manufactured by WOKA
Schweisstechnik GmbH, of Willich, Germany, in the following sizes
and percentages by weight:
ASTM Mesh Size Range Mean +40 0-5% 3% -40/+60 90-100 94% -60 0-5%
4%
The carbide granules were blended, by tumbling in a barrel mill,
together with 4% by weight silicomanganese, 0.5% by weight niobium
and 0.36% by weight resinox. After the initial blending, alcohol
was added and the granules reblended to "wet" the granular filler,
followed by a drying step.
Annealed, cold-finished, low-carbon steel strip was cleaned and fed
into a conventional tube-forming machine. The granular filler
mixture was fed into the machine to fill the tubes. The tubes then
were cut to 28-30" lengths and the ends of the tube crimped sealed.
The finished tube rod then was baked in an atmosphere of air at
300.degree.-350.degree. F. for a minimum of one hour to insure
complete drying of the granular filler. The resulting tube rods
comprises 68% by weight of the granular filler and 32% by weight of
the tube matrix metal.
A portion of one of the tube rods, prepared as set forth above, was
melted to form a sample of the applied hardfacing composition
according to the present invention. The sample was weighed and
placed in contact with a steel wheel 6.5 inch in diameter and 0.5
inch wide. A force resulting from a 10 kg weight was applied to the
sample and the wheel and sample were immersed in a slurry of 30
grit aluminum oxide suspended in deionized water. The wheel was
rotated at 100 rpm for 500 revolutions. The test apparatus was
similar to that prescribed by the ASTM B611 testing procedure.
Generally, the aluminum oxide slurry is rubbed between the wheel
and sample, resulting in erosion of the sample. After the test, the
sample is weighed to obtain an indication of the quantity of sample
material eroded during the test. The amount of material eroded
during the test is a relative indication of the wear resistance of
the sample material. This test was repeated four times.
The laboratory test results for the samples of the hardfacing
composition according to the present invention showed an average of
12% less material eroded and thus a 12% improvement in wear
resistance over hardfacing compositions previously tested that did
not include the spherical cast carbide pellets in combination with
the spherical sintered carbide pellets.
A tube rod of hardfacing composition prepared as set forth above
was applied by welding to selected teeth of a Hughes Christensen
97/8 inch ATJ-1S bit similar to that depicted in FIG. 1. Other
teeth on the same bit were hardfaced with a hardfacing composition
comprising only sintered spherical tungsten carbide pellets in a
matrix metal. The hardfacing composition was applied by welding
with an oxyacetylene torch, wherein the tube rod matrix metal was
melted, along with a portion of the underlying tooth steel, and the
resulting applied hardfacing was air cooled. Oxyacetylene welding
is preferred to atomic hydrogen welding because the increased
temperatures of the atomic hydrogen welding process, unless
carefully controlled, melt the matrix metal and tooth steel too
quickly, permitting the dense, spherical sintered and cast pellets
to "sink" into the tooth steel and away from the surface of the
hardfacing. This bit was run in a well in Grimes County, Texas.
After 40 hours, the bit drilled 3,392 feet. The bit performance was
rated good and comparison revealed that the bit outperformed, in
turns of cost-per-foot, the average of the best bits run in offset
wells over similar intervals and pulled with a similar dull
condition.
The teeth with the hardfacing composition according to the present
invention were less worn than the other teeth.
The teeth of another Hughes Christensen 97/8 inch ATJ-1S bit were
hardfaced with the composition as set forth above. The bit was run
in another well in Grimes County, Texas. After 48.6 hours, the bit
drilled 3,273 feet. The bit performance was rated good and the dull
condition was much better than that of the best bits run in offset
wells over similar intervals, although it did not top their
performance in terms of cost-per-foot. The teeth with the
hardfacing composition according to the present invention were less
worn than the other teeth.
The teeth of a Hughes Christensen 77/8 inch ATJ-1 bit were
hardfaced with the composition as set forth above. The bit was run
in a well in Carbon County, Wyo. After 55.5 hours, the bit drilled
3,551 feet and was pulled with a better dull condition than the
bits run in offset wells over similar intervals. The teeth with the
hardfacing composition according to the present invention were less
worn than the other teeth.
The teeth of another Hughes Christensen 77/8 inch ATJ-1 were
hardfaced with the composition as set forth above. The bit was run
in another well in Carbon County, Wyoming. After 42.5 hours, the
bit drilled 2,844 feet and was pulled with a better dull condition
that the bits run in offset wells over similar intervals. The teeth
with the hardfacing composition according to the present invention
were less worn than the other teeth.
The laboratory wear resistance testing, combined with the
experimental results obtained from bits in the field, indicate that
the hardfacing composition according to the present invention is a
marked improvement over conventional hardfacing compositions. This
improvement is believed to be the result of the combination of the
spherical sintered and cast tungsten carbide pellets, which yield a
hardfacing composition having a good balance between hardness and
fracture toughness.
The invention has been described with reference to specific
examples and preferred embodiments thereof. It is thus not limited,
but is susceptible to variation and modification without departing
from the scope and spirit of the invention.
* * * * *