Note: Descriptions are shown in the official language in which they were submitted.
; 1062Sl~
Background of the Invention
This invention relates to a wear-resistant or abrasive
resistant alloy, and method of producing this alloy. The
invention particularly relates to such an alloy and com-
posite thereof especially suitable for use with ground-
engaging tools.
Ground-engaging tools such as ripper tips, bucket
teeth and cutting edges for various types of earth-working
machines are all subject to accelerated wear during
working of the machines due to continual contact of these
parts with rock, sand and earth. It is therefore
desirable that these tools be comprised of a highly
wear-resistant material, e.g., U.S. Patents 1,493,191;
3,275,426 and 3,334,996 and further, that such material be
relatively inexpensive to thereby minimize the cost when
replacement inevitably becomes necessary; note, for
instance, British Patent 1,338,140.
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106Z51V
Many wear-resistant alloys have been developed for
use in such tools and for other uses demanding an al-loy of high
abrasive resistance. Many such alloys, however, are composed
of materials which are not readily available, or are expensive,
or both. One such example is tungsten carbide which has
excellent wear-resistant properties, but which is relatively
expensive. Additionally, particularly in the case of tool
manufactLre, it is frequently important that the wear-resistant
alloy be substantially unimpaired by heat treatment. For example,
a convenient metllod of joining a metal part composed of wear-
resistant alloy to a steel ground-engaging tool is by brazing;
this process, however, usually weakens the steel of the tool,
making it necessary to heat-treat the steel to strengthen it.
Many alloys are adversely affected by such heat treatment, and
either cannot be used under these circumstances, or the steel
cannot be treated to harden. Frequently, also, known wear-
resistant alloys are unsuitable for use with tools which are
subjected to frequent shocks, since, typically, these wear-
resistant hard alloys are brittle, and readily break under shock
treatment.
It is an object of this invention to provide a highly
wear-resistant composite alloy which can be heat-treated under
conditions employed in hardening steel without being adversely
affected.
It is an additional object of this invention to provide
a wear-resistant composite alloy which is especially suitable for
use with ground-engaging tools.
It is yet another object of this invention to provide
a wear-resistant shock-resistant composite alloy.
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Brief Summary of the Invention
According to the invention there is provided a g-round-
engaging tool having increased resistance to wear
including a contact section for engaging the ground and at
least a portion of said section reinforced with a wear-
resistant composite alloy, said wear-resistant alloy
comprising cast spheroidal particles of a first alloy
embedded in a matrix of a second alloy.
Other aspects of the invention disclosed herein are
claimed in patent application Serial No. 224,600 filed on
April 15, 1975 of which the present application is a
.
dlvlslon.
The spheroidal wear-resistant alloy component of the
composite alloy is claimed in U.S. Patent No. 3,970,445
issued on July 20, 1976 entitled "Wear-Resistant Alloy,
and Method of Making Same", which is assigned to the same
assignee as this application.
As used herein the terms "composite" or "composite
alloy" means an alloy material wherein two or more
metallurgically distinct alloys are first prepared
physically separate one from the other. These separate
alloys are then physically mixed together, generally in
the "dry" state, and at ambient temperatures to produce an
homogeneous mixture thereof. This alloys mixture is then
subjected to heat processing wherein a temperature is
achieved sufficiently high to cause at least one of the
alloys to experience "melting" or at least incipient
"melting" and to thereby "braze" the mixture into a single
physical mass. It should be understood that at least one
of the alloy components remains essentially physically
unchanged during the "brazing" step.
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The ~esulting "composite" alloy, although in a single
mass, contains both the original alloys in distinctly
segregated portions within the mass, and both alloys
continue to exhibit their individual metallurgical pro-
perties on an individual basis, although the "composite"
alloy, as a whole, exhibits its separate and individual
metallurgical and physical properties as well.
Brief Descri~tion of the Drawinqs
Fig. 1 is a photomicrograph of alloy particles of this
invention embedded in an alloy matrix, to form a composite
alloy. (magnification - 50X).
Fig. 2 is another photomicrograph of alloy particles
of this invention embedded in an alloy matrix, to form a
composite alloy. (magnification - lOOX).
Fig. 3 is a schematic cross-sectional view of a
ground-engaging tool tip wherein the composite alloy is
incorporated to prolong tool life.
Detailed Description of the Invention
The invention comprises a wear-resistant alloy
comprised of relatively low cost, readily available
elements, that are alloyed and then processed to yield
extremely hard wear-resistant particles, especially
spheroids. These spheroidal particles are in turn
incorporated into a composite alloy that comprises the
spheroidal particles in a strong ductile alloy matrix.
The wear-resistant alloy portion of the invention is
essentially an iron-chromium based alloy which boron
therein.
More particularly, the alloy of the invention sub-
stantially comprises boron, chromium and iron, preferablyin the following amounts in per cent by weight:
`` 10625110
Boron about 6.0 to about 12%
Chromium about 25 to about 61%
Iron balance
This combination of elements, in the portions
indicated, gives a complex mixture of iron and chromium
borides having extremely high hardness values, typically
from about 1200 to about 1600 kg/mm2 Knoop (or above
about 70 on the Rockwell "C" hardness scale). Although it
would normally be expected that the high percentages of
boron and chromium defined by the above ranges would
result in an extremely brittle alloy composition, this is
not really the case with the alloy of the invention. It
is likely that this can be attributed to the high per-
centage of iron in the alloy, which forms an iron phase to
give the necessary ductility to the alloy composition.
An alloy, quite similar to the above-noted com-
position, is also useful as the wear-resistant component
in the invention. Specifically boron, chromium, iron and
carbon in the ranges:
Boron 6.0 to about 12%
Chromium 61 to about 70%
Carbon 0.05 to about 2%
Iron balance
exhibits extreme hardness when processed into shot as
described below.
This can be effectively accomplished by a method
comprising pouring the molten alloy mixture onto a surface
of material, such as grahite, at ambient temperatures, and
which is positioned over a container of liquid coolant.
Preferably, the molten mixture is poured into a stream
from a suitable height (about 4 to 5 feet) above the cool
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surface. Conveniently, the liquid coolant may be water,
or other suitable liquid. The liquid coolant is arranged
to a depth sufficient to assure complete solidification of
the alloy particles before they reach the bottom of the
quenching liquid.
On striking the cold surface, the molten mixture
explodes into thousands of spheroidal particles of various
sizes, which immediately fall into the container of
coolant where they cool and solidify very rapidly.
High alloy compositions formed by this method exhibit
properties of high strength and high hardness, with con-
commitant high resistance to wear. The extreme hardness
and strength of these alloy particles are thought to be at
least in part due to the fine microstructure set up in the
particles as they are chilled into spheres by rapid
cooling.
The relative hardness of the alloy particles produced
by the above method has been compared by tests with
similarly-sized alloy particles of the same chemistry
produced by conventional methods. For example, in one
test, solid slugs having an alloy composition of 25% Cr,
8.8% B, and 66.2% Fe were broken up and screened to give
particles of 10 to 20 mesh, which were found to have a
Knoop hardness of about 1100 Kg/mm2 (500 gm. load).
Similarly sized particles of the same composition produced
by the exploding method described above were found to have
Knoop hardness of about 1400 Kg/mm2 (500 gm. load).
In a similar test utilizing an alloy composition of
40% Cr, 10 B and 50 Fe, the particles produced by breaking
up a solid casting had a Knoop hardness of 1200 to 1300
Kg/mm2 (500 gm. load), whereas the exploded particles
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had a Knoop hardness of 1500 to 1600 Kg/mm2 (500 gm.
load).
Even harder spheroidal particles have been produced
from the alloy compositions including up to 2% carbon in
addition to the boron, chromium and iron. One composition
of about 62.5% Cr, 9% B, 1.8% C and Fe remainder produces
a eutectic metallurgical structure of chromium borides and
iron carbides. Alloys in this range of composition have
yielded shot with a hardness range of 1700-2000 Knoop
Kg/mm2 (100 gm. load).
After solidification, the spheroidal alloy particles
are removed from the liquid coolant. They are then most
advantageously plated with a protective metal, partic-
ularly when the particles are to be subsequently brazed
with a matrix alloy to form the desired composite. This
metal plating serves to protect the alloy from oxidation
during storage and further serves to prevent the loss of
particle elements to the braze by erosion and diffusion.
Diffusion and erosion tend to degrade the desired crystal-
line structure of the shot particles, at least in theperipheral portions thereof. Suitably, the alloy
particles are plated with nickel, although other metals
which will provide the desired protection, such as copper
or chromium, can be used.
The plating may be a conventional electro-plating
method. The spheroidal particles are placed in a
container such as a barrel with openings therein covered
with fine mesh screens to retain the small particles
within the container. The container is then submerged in
a metallic plating solution, e.g., Ni and rotated therein
while electric current is applied. The plating solution
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can flow freely through the rotating barrel to reach all
the particles therein. A metal coating of about 0.001 to
about 0.003 inches is sufficient to retard oxidation and
to minimize erosion by the matrix alloy during the
sintering or brazing step in production of the composite
alloy.
It is frequently advantageous to provide a composite
body of alloy particles and matrix material; for example,
a composite alloy of spheroidal particles and strong,
ductile matrix material yields a composite alloy of great
usefulness.
Although the matrix material is chosen according to
the properties desired in the finished product, and can be
one of a number of commercially available alloys, several
matrix materials have been found to be particularly
suitable for use when the product is to be used with
ground-engaging tools. Two of the exemplary materials
have the following composition:
(Percent
ElementsI(AMI[TRADE MARR]930) by II(AMI[TRADE MARR]790)
Weight) _ _
Carbon 0.07 0.03
Silicon 7.0 3.50
Copper 5.0
Manganese 23.0
Boron - 1.50
Iron - 1.25
Nickel (Balance) 65.0 (approx) 94.0 (approx)
It should be understood that the above are merely
examples of satisfactory matrix alloys. Other alloys are
suitable so long as they are tough and ductile and do not
strongly erode
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106Z510
the wear-resistant alloy particles during brazing or sintering
of the composite.
The composite alloy materials comprising the spheroidal
alloy particles and matrix material are mixed together in a dry
or solid form by any conventional method which insures a uniform
mixture. For example, the matrix material, usually in the
powdered form and spheroidal alloy particles may be arranged in
successive layers and vibrated during mixing. After mixing, the
materials are then permanently joined by a conventional brazing
or sintering process, for example, in a vacuum furnace.
Figures 1 and 2 of the drawing are photomicrographs of
the composite allov of the invention. They clearly show the
spheroidal wear-resistant alloy particles embedded in the matrix
material. Figure 1 shows spheroidal particles that have a com-
position of 35~ Cr, 10.9% B, remainder iron, surrounded by a
matrix alloy of 0.03~C, 3.5% Si, 1.5% B, 1.25% Fe and about 94%
Ni. The thin nickel plate surrounding the wear-resistant speroid
is also apparent. Figure 2 is also a photomicrograph of a
specimen of composite alloy. The spheroidal particle was
20 analyzed at 50% Cr, 10.9% B and the remainder Fe. The matrix
was the same alloy as shown in Figure 1. The spheroidal particle
was also nickel plated.
The alloy particles in the composite alloy material
should be sufficiently closely spaced to block wear paths when
abrasive wear occurs in the composite alloy material. The
abrasive wear generally starts as a small groove or slot and
proceed through the composite material in the path of
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least resistance, i.e., through the matrix material since it is
the weaker of the two components. However, after the wear path
has progressed a short distance, it will encounter a hard alloy
particle, and will be stopped or retarded. Thus, sufficient
alloy particles should be present in the composite material to
stop wear paths before significant damage has occurred through
abrasion to the matrix material. Generally, as high a percentage
as possible of alloy particles should be incorporated into the
matrix material.
It has been found that optimal wear resistance and
shock absorption for ground-engaging tool parts is typically
obtained when the composite alloy material comprises about 55-70%
alloy particles and about 30-45% matrix material, by volume.
When the matrix material is either AMI 790 or 930 noted above,
about 60~ hard alloy to about 40~ matrix, by volume, appears to
yield the composite alloy with optimum properties. Preferably,
the alloy particles selected for incorporation into the matrix
material have a size of about 10 to about 40 mesh.
The composite alloy may be formed, most suitably, by
mixing the hard alloy spheroids with the matrix alloy in a
ceramic or graphite mold in the desired shape. After brazing in
a vacuum furnace, the block of composite alloy is cooled to room
temperature to yield the desired product. In the composite
alloy block, the hard spheroidal alloy particles are permanently
bound by the matrix alloy to form the composite.
The composite alloy may be joined to a substrate,
e.g., tool surface by any appropriate method. If the substrate
is a conventional steel ground-engaging tool, the composite
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106Z510
material may be appropriately joined to this substrate by
brazing. This will ordinarily weaken the steel of the substrate
but the steel can then be subjected to a conventional heat-
treatment to harden without adversely affecting the composite
alloy material.
Figure 3 of the drawing illustrates a typical
applicatlGn of the wear-resistant composite alloy to a tool tip
or edge.! More specifically, a ground-engaging tool 10 is shown
having wear-resistant insert 11 situated posteriorly of front
surface 12 of tool 10. An arrow indicates the normal direction
of blade movement. Although a blade of elongate configuration,
such as a cutting edge of a motor grader blade is illustrated
as ground-engaging tool 10, it is to be understood that this
embodiment, including the posterior location of insert 11, is
similarly applicable to other ground-engaging tools such as
ripper tips, bucket teeth and the like. Obviously, wear-
resistant insert 11 should be relatively situated with respect
to the bottom surface of the specific ground-engaging tool in
the same manner as insert 11 is situated with respect to bottom
surface 13 and front surface 12 of cutting edge 10.
The cutting edge 10 of Fig. 3 is shown attached to a
portion of a motorgrader cutting edge support or mold board 14.
The cutting edge 10 is removably secured to board 14 by, for
example, a plurality of plow bolt and nut assemblies 16. The
distal portion 17 of cutting edge 10 is of substantially lesser
thickness than the proximal portion 18 of cutting edge 10. Wear
resistant insert 11 is secured as by brazing, or the like, to
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distal portion 17, thereby providing a substantially uniform
cross-sectional area over most of cutting edge 10.
The thinner distal portion 17 of cutting edge lO may
conveniently be formed by machining an original cutting edge 10
of substantially uniform thickness to the desired shape.
Variations of the shape of distal portion 17 illustrated in Fig.
3 may be alternatively employed if desired. Insert 11 may be
secured to distal portion 17 of cutting edge 10 by brazing or
other convenient method. If the material of insert 11 is amen-
able, it is desirable to reheat steel ground-engaging tools
after brazing to restore the metallurgical properties of the
tools.
The composite alloy material of this invention exhibits
a substantially higher wear resistance than do ordinary pro-
duction steels; for example, a ripper tip wear test specimen of
alloy particles in AMI 930 matrix material showed increases in
wear life of 400% to 650~ over the wear life of a 4340 steel
standard specimen having a hardness of Rockwell "C" 45-50.
In another test, cast blocks of the composite alloy
material (~I 930 matrix) secured in the cutting edge of a
ground-engaging tool showed an increase in wear life of 700% to
2000% (depending on test severity) as compared to a standard
steel cutting edge. The long wear life of the alloys of this
invention and the relatively low cost of the raw materials
gives a desirably low "cost/wear life" ratio for these alloys.
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1062510
The following Example is provided as an illustration
of the method and composition of this invention.
Example
Hard particles were made from a mixture of Armco Ingot
Iron, electrolytic chromium and ferro-boron melted in an
induction furnace to as high as 3700F. The resultant com-
position of the wear resisting alloy was iron 66%, chromium 25%,
and boron 9%. The molten alloy was dropped about 3 feet onto
a slanted graphite plate located just above a water filled tank.
As the molten alloy stream struck the graphite plate, it was
broken into various size particles. When it entered the water,
the alloy solidified forming spheroidal particles. By screening,
the spheres between 10 and 30 mesh were selected from the hard
particles (the size of hard particles in the matrix for optimum
wear resistance was found to be approximately in a range of 6
to 40 mesh). The process above resulted in cast spheroidal
particles comprised principally of borides with a Knoop Hardness
Number of 1400 and above. These particles were then electro-
lytically cleaned and then coated with a nickel plate to retard
surface oxidation and to prevent particle erosion in the braze.
The spheroidal particles were then mixed with matrix alloy. The
matrix alloy (AMI 930) had the following chemical composition -
carbon 0.07%, silicon 7%, copper 5%, manganese 23~, and nickel
65%. The hard particles and the matrix powder were thoroughly
mixed and then tamped into the cavity of a graphite mold. In
the next step the mixture was then sintered in a vacuum furnace
at 1650-1800F. The resultant heterogenous composite insert
was by volume 55-70% iron-chromium borides and 45-30% matrix.
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Finally, the composite alloy insert was brazed onto a ground-
engaging tool surface. For this purpose the insert was attached
to the tool with ~I 930 alloy and brazing was accomplished at
1650-1800~F.
Upon testing, composite alloy ripper tips gave a 4Q0
to 650% increase in wear life when compared to a 4340 steel
standard tip (Re 45-50).
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