Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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 suitable
for use in highly abrasive environments.
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.
Many wear-resistant alloys have been developed for use
in such tools and for other uses demanding an alloy 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 manufacture, it is frequently impor-
tant that the wear-resistant alloy be substantially
unimpaired by heat treatment. For example, a convenient
method of joining a metal part composed of a 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 hea~-treat the steel to strengthen
it. Many alloys are adversely affected by such heat
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treatment, and either cannot be used under these circum-
stances, or the steel cannot be treated to harden.
Frequently, also, known wear-resistant alloys are
unsuitable for use with tools which are subjected to
frequency shocks, since, typically, these wear-resistant
hard alloys are brittle, and readily break under shock
treatment.
Accordingly, it is an object of this invention to
provide a specially treated inexpensive wear-resistant
alloy comprised of readily available elements.
It is another object of this invention to provide a
method of producing a highly wear-resistant alloy.
Brief Summary of the Invention
According to one aspect of the invention there is
provided a wear-resistant alloy in the form of cast
spheroidal particles, said alloy comprising:
chromium - about 25 to about 61% by weight
boron - about 6 to about 12% by weight
Iron - balance
According to another aspect of the invention there i-s
provided a method of improving the hardness character-
istics of an alloy comprising:
chromium - about 25 to about 61% by weight
boron - about 6 to about 12% by weight
Iron - balance;
the method comprising the steps of producing cast
spheroidal particles of the alloy by streaming the molten
alloy onto a hard surface thus breaking up the molten
alloy into droplets and thereater rapidly quenching and
solidifying the molten alloy with a quench liquid while
still in the droplet configuration.
Other aspects of the invention disclosed herein are
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claimed in our co-pending patent application Serial No.
224,726 filed on April 16, 1975, of which the present
application is a division.
As used herein the terms "composite" or "composite
alloy" means an alloy material wherein two or more metal-
lurgically 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 homo-
geneous mixture thereof. This alloys mixture is thensubjected 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.
The resulting "composite" alloy, although in a
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single mass, contains both the original alloys in dis-
tinctly 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 Description of the Drawings
Fig. 1 is a photomicrograph of alloy particles
of this invention embedded in an alloy matrix. (magnifi-
cation - 50X).
Fig. 2 is another photomicrograph of alloy
particles of this invention embedded in an alloy matrix
(magnification - lOOX).
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, expecially spheroids.
These spheroidal particles may be "brazed" together or
alternately incorporated into a composite alloy that com-
prises the spheroidal particles in a strong ductile alloy
matrix. These composite alloys and tools reinforced therewith
are claimed in Canadian patent application Serial No.
224,600 filed on April 15, 1975, entitled "Composite Wear-
Resistant Alloy, and Tools from Same", and assigned to the
same assignee as this application.
The wear-resistant alloy portion of the invention
-is essentially an iron-chromium based alloy with boron therein.
More particularly, the alloy of the invention sub-
stantially comprises boron, chromium and iron in the following
amounts per cent by weight:
~1
r-4
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.
Boron - about 6.0 to about 12~
Chromium - about 25 to about 61%
Iron - balance
This combination of elements, in the portions indic-
ated, gives a complex mixture of iron and chromium borides
having extremely high hardness values, typically from about
1200 to about 1600 kg/mm 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 in not really the case with
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the alloy Or t~le invention. ~ is lilcely that this c n be
attributed to the high percentageso~ iron in the alloy,
which forms an iron phase to give the necessary ductllity
to the alloy composition.
An alloy, quite similar to the above-notéd compos-
ition, is also useful as the wear-reslstant component in the
invention. Specifically boron, chromium, iron and carbon in
the ranges:
Boron 6.o to about 12
Chromium 61 to about 70%
Carbon 0.05 to about 2
Iron balance
e~libits extreme hardness when processed iIl~O SilOt
2S described below.
This can be effectively accomplished by a method
comprising pouring the molten alloy mixture onto a surface
of material, such as graphite, at ambient temperatures, and
which is positioned over a contalner of llquld coolant.
Preferably, the molten mixture is poured in a stream ~rom a
suitable height (about 4 to 5 reet) above the cool surface.
Conveniently, the liquid coolant may be water, or other
suitable liquid. The llquid coolant is arranged to a depth
surficient to assure complete solidification Or the alloy
particles before they reach the bottom Or the quenching
liquidO
On striking the cold surrace, th~ mo~ten mixture
explodes into thousands Or spheroidal particles Or various
sizes, which immediately fall into the container Or cool~nt
where they cool and solidify very rapidly.
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High alloy compositions formed by this method exhibit
properties of high strength and high hardness, with concom-
itantly high resistance to wear. The extreme hardness and
strength of these alloy particles are thought to be at least
in part due to the surface tension set up in the particles as
they form into spheroids after contacting the cold surface.
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 con-
ventional methods. For example, in one test, solid slugs havingan 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/mm
(500 gm. load). Similarly sized particles of the same compo-
sition produced by the exploding method described above were
found to have Knoop hardness of about 1400 Kg/mm (500 gm. load).
In a similar test utilizing an alloy composition of
40% Cr, 10 ~ and 50 Fe, the particles produced by breaking up
a solid casting had a Knoop hardness of 1200 to 1300 Kg/mm
(500 gm. load), whereas the exploded particles had a Knoop
hardness of 1500 to 1600 Kg/mm (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 Rg/mm (100 gm.
load).
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After solidification, the spheroidal alloy particles
are removed from the liquid coolant. They are then most
advantageously plated with a protective metal, particularly
when the particles are to be subsequently brazed with a matrix
alloy to form a desired composite alloy. This metal plating
serves to protect the alloy from oxidation during storage and
further serves to retard to some extent bonding of the particles
with the substrate during brazing, thereby preventing alloy
diffusion into this substrate. Diffusion tends to erode the
hard spheroids and further degrades the desiréd crystalline
structure of the shot particles, at least in the peripheral
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 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 matrix alloy during the sintering or brazing
step in production of composite alloys.
The spheroidal alloy particles may be formed, with or
without plating by compacting, into a homogenous block of the
desired shape. Also, the particles may either be cast
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- in place in the desired location, or may be cast separately,
and then bonded in position. In addition, the alloy particles
may be incorporated into a matrix of another material. While
generally, greater hardness and strength results from a body
comprised solely of the spheroidal alloy particles, 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 is
desirable if greater shock absorption capacity is desired.
Figures 1 and 2 of the drawing are photomicrographs
of the composite alloy of the invention. They clearly show the
spheroidal wear-resistant alloy particles. Figure 1 shows
spheroidal particles that have a composition of 35% Cr, 10.9% B,
remainder iron. The thin nickel plate surrounding the wear-
resistant sphere is also apparent. Figure 2 is also a photo-
micrograph of a specimen of composite alloy. The spheroidal
particle was analyzed at 50% Cr, 10.9% B and the remainder Fe.
The spheroidal particle was also nickel plated.
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 (Trade Mark), electrolytic chromium and ferrD boron melted
in an induction furnace at 2600-2700F. The resultant composition
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 tank filled with
water. 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.
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The process above resulted in cast spheroidal partlcles comprised
principally Or borides with a ICnoop Hardness Number o~ 1400 and
above. These particles were then electrolytically cleaned and
then coated with a nickcl pla~c to rctard sur~ace ox~dation and
improve matrix alloy bonding.
