Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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COMPOSITE METAL PRODUCT
TECHNICAL FIELD
The present disclosure relates to a method of
centrifugal casting of a composite metal product, the
finished product typically ranging in mass from 20-5,000
kg, having a host metal matrix, typically a ferrous metal
matrix, and comprising outer surface layer, nominally 1-20
mm thick, of hard, insoluble refractory particles for
enhanced wear resistance.
The present disclosure also relates to centrifugally
cast composite metal products.
In the context of the present disclosure, the term
"refractory particles" is understood to include particles
of high melting point carbides and/or nitrides and/or
borides of any one or more than one of the nine transition
metals titanium, zirconium, hafnium, vanadium, niobium,
tantalum, chromium, molybdenum and tungsten dispersed in a
tough host metal, which acts as a binder phase. Each of
these refractory particles is a particle of a refractory
material and is referred to herein as a "refractory
material". Typically, the host metal is a ferrous metal
alloy. The host metal may also be nickel-based and
cobalt-based superalloys.
In the context of the present disclosure, the term
"insoluble" is understood to mean that, for all intents
and purposes, the refractory material is not soluble in
the host metal at the casting temperatures, typically in a
range 1200 -1600 C for ferrous host metals. There may be
limited solubility. However, the refractory particles are
essentially distinct from the host metal to the extent
that there is negligible partitioning of the elements in
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the refractory material particles to the host metal during
the casting method and in the solidified product.
SUMMARY OF THE DISCLOSURE
In a first aspect, embodiments are disclosed of a
centrifugally cast composite metal product having an axis
of rotational symmetry and a mass of at least 5kg,
typically at least 10 kg, and more typically at least
20kg, and comprising a metal host and insoluble solid
particles of a refractory material in a non-uniform
distribution throughout the host metal, wherein the
particles have a density that is within 30%, typically
within 20%, of the density of the metal host at its
casting temperature.
The composite metal product comprises two distinct
zones throughout the solidified material, namely a zone of
insoluble solid particles of the refractory material and
an at least substantially refractory particle-free region
of the host metal, with the refractory particles being
essentially distinct from the host metal to the extent
that there is negligible partitioning of elements in the
refractory material particles to the host metal at the
casting temperature and in the solidified product.
The feature of the invention of solid particles of
the refractory material that are insoluble in the host
metal at the casting temperature and after solidification
distinguishes the invention from proposals in the prior
art, such as JPS632864, for the addition of ferroalloys
(a) Fe-W, (b) Fe-Mo and (c) Fe-Cr to a host ferrous alloy
that forms respectively (a) tungsten carbide, (b)
molybdenum carbide and (c) chromium carbide which are
soluble to varying degrees in the host metal at the usual
casting temperatures. As a consequence, in these systems,
the volume % of hard, insoluble refractory carbides in the
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microstructure is substantially reduced and the dissolved
tungsten and/or molybdenum and/or chromium may adversely
influence the physical and chemical properties of the host
metal at room temperature by an unknown amount, (e.g.
reduced toughness and a different response to heat
treatment).
In some embodiments, the refractory particles may
have a density that is higher than that of the host metal,
in which case there will be a higher concentration of the
refractory particles towards an exterior surface of the
composite centrifugally cast metal product.
In some embodiments, the refractory particles may
have a density that is lower than that of the host metal,
in which case there will be a higher concentration of the
refractory particles towards an interior surface of the
product.
In some embodiments, the non-uniform distribution of
refractory particles may comprise a first concentration of
refractory particles in an exterior or interior surface
layer of the product that is higher than a second
concentration of refractory particles in another layer in
the product.
In some embodiments, the first concentration of
refractory particles in the exterior surface layer of the
product may be at least 50 vol%, typically at least 60
vol%, typically at least 70 vol%, and more typically 50-
120 vol% higher than the nominal volume percentage of the
refractory material in the product.
In some embodiments, the first concentration of
refractory particles in the exterior surface layer of the
product may be at least 10%, typically at least 20%,
typically less than 40%, and more typically in a range of
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10-40 vol%, of the total volume of the exterior surface
layer.
In some embodiments, the second concentration of
refractory particles in the other layer of the product may
be in a range of 2-4.5 vol%, typically 2-3.5 vol%, of the
total volume of the other layer.
In some embodiments, the exterior or interior surface
layer of the product may extend at least 5%, typically at
least 20%, more typically at least 25% of the radial
thickness of the product from the exterior or interior
surface.
In some embodiments, the exterior or interior surface
layer of the product may extend less than 50%, typically
less than 40%, more typically less than 30%, and more
typically less than 20% of the radial thickness of the
product from the exterior or interior surface.
In some embodiments, the exterior or interior surface
layer of the product may extend at least 10 mm, typically
at least 20 mm, typically less than 50 mm, typically 1-50
mm, and more typically 5-20 mm from the exterior or
interior surface.
In some embodiments, the first concentration of
refractory particles in the exterior surface layer of the
product may be in a range of at least 5 vol%, typically at
least 10 vol%, typically 5-90 vol%, and more typically 10-
vol%, of the total volume of the particles.
In some embodiments, the overall concentration of the
refractory particles in the product may be at least 5
35 vol%, typically at least 10 vol%, and more typically in a
range of 5-50 vol% of the total volume of the product.
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In some embodiments, the overall concentration of the
refractory particles in the product may be in a range of
5-40 vol% of the total volume of the product.
In some embodiments, the overall concentration of the
refractory particles in the product may be in a range of
5-20 vol% of the total volume of the product.
In some embodiments, the refractory particles may be
carbides and/or borides and/or nitrides of one or more
than one transition metal where the particles are a
chemical mixture (as opposed to a physical mixture) of the
carbides and/or borides and/or nitrides of the transition
metals. In other words, in the case of carbides, the
refractory particles may be of the type described as
(411142)C or (N41Nr2 243,)C , where `IA" is a transition metal.
One example that is discussed further herein in
(Nb,Ti,W)C.
The host metal may be any suitable host metal. The
host metal may be a ferrous alloy, such as a stainless
steel or an austenitic manganese steel or a cast iron.
The host metal may be a non-ferrous host metal, such as
titanium or a titanium alloy.
In some embodiments, the host metal may be an alloy
comprising any one of the following alloys:
(a) Hadfield steel for use for example in gyratory
crusher mantles;
(b) 420C stainless steel for use for example in
shaft sleeves in slurry pumps; and
(c) high chromium white cast iron.
As used in some embodiments, the Hadfield steel may
comprise:
1.0 - 1.4 wt% C
0.0 - 1.0 wt% Si,
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- 15 wt%
0.0 - 3.0 wt% Mo,
0.0 - 5.0 wt% Cr,
0.0 - 2.0 wt% Ni,
5 with the remainder being Fe and incidental impurities.
As used in some embodiments, the 420C stainless steel
may comprise:
0.3 - 0.5 wt%. C,
10 0.5 - 1.5 wt% Si,
0.5 - 3.0 wt% Mn,
0.0 - 0.5 wt% Mo,
10 - 14 wt% Cr,
0.0 - 1.0 wt%. Ni,
with the remainder being Fe and incidental impurities.
As used in some embodiments, the high chromium white
cast iron may comprise:
1.5 - 4.0 wt% C,
0.0 - 1.5 wt% Si,
0.5 - 7.0 wt% Mn,
0.0 - 1.0 wt% Mo,
15 - 35 wt% Cr,
0.0 - 1.0 wt% Ni,
with the remainder being Fe and incidental impurities.
The composite metal product may be any product that
is adapted to be centifugally cast and requires high wear
and high toughness properties. Examples of such products
include a gyratory crusher mantle for a primary, secondary
or tertiary crusher, a slurry pump shaft sleeve, rollers
for use in crushers (including large diameter rollers that
are of the order of 1 m in diameter with radial wall
thicknesses in a range of 300-400 mm), and other
components of crushers and pumps.
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In a second aspect, embodiments are disclosed in
which the composite metal product of the first aspect may
be a gyratory crusher mantle for a primary, secondary or
tertiary crusher.
In a third aspect, embodiments are disclosed in which
the composite metal product of the first aspect may be a
slurry pump shaft sleeve.
In a fourth aspect, embodiments are disclosed of a
method of centrifugally casting a composite metal product
having an axis of rotational symmetry and a mass of at
least 5kg, typically at least 10 kg, and more typically at
least 20kg and comprising a host metal and a non-uniform
dispersion of insoluble solid refractory particles of a
refractory material, with the method comprising:
(a) forming a slurry comprising solid particles of
the refractory material dispersed in a liquid host metal,
with the refractory particles comprising 5-50 vol%,
typically 5-40 volsI5, of the total volume of the slurry,
with the refractory particles being insoluble at a casting
temperature, and with the refractory particles having a
density that is within 30%, typically within 20%, of the
density of the metal host at the casting temperature; and
(b) pouring the slurry into a mould for the
composite metal product and centrifugally casting the
product in the mould and obtaining a non-uniform
distribution of insoluble solid refractory particles
throughout the host metal.
In some embodiments, step (a) may comprise forming
the refractory particles in situ in the molten host metal
and dispersing the particles within a molten form of the
host metal.
In some embodiments, step (a) may comprise adding
refractory particles to a molten form of the host metal.
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In some embodiments, steps (a) and (b) may be carried
out under an inert environment, such as in an inert gas
atmosphere.
In some embodiments, step (b) may comprise preparing
the mould by forming an inert environment within the
mould.
In some embodiments, step (b) may comprise rotating
the mould about the axis subsequent to and/or during
pouring the slurry into the mould to cause a concentration
of refractory particles at or near an exterior surface or
at or near an interior surface of the composite metal
product that is higher than the concentration of particles
elsewhere in the product.
In some embodiments, step (b) may comprise rotating
the mould at a 10-120 G-Factor, where G-Factor is the
centrifugal force acting on a rotating body divided by the
gravitational force.
In some embodiments, step (b) may comprise rotating
the mould at a peripheral speed of 2.5-25 m/s.
In some embodiments, step (b) may comprise rotating
the mould for sufficient time to obtain the non-uniform
distribution of solid particles throughout the host metal.
In some embodiments, step (b) may comprise
rotating the mould until the host metal has solidified.
In some embodiments, step (b) may comprise pouring
the slurry into the mould at a casting temperature in a
range of 1200-2000 C, typically in a range of 1350-1650 C.
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In some eMbodiments, the method may comprise
selecting the production parameters to form the slurry in
step (a) that has a required fluidity for processing in
step (b).
The production parameters may comprise any one or
more of the particle size, reactivity, density, and
solubility of the refractory materials, as described in
International patent application PCT/AU2011/000092
(W02011/094800) in the name of the present applicant.
Density and solubility of the refractory materials are
discussed below.
The density of the refractory material of the
particles, compared to the density of the host metal in
the liquid state, is a parameter to consider during the
method of the present disclosure to control the dispersion
of refractory particles in the hot host metal.
The nominal density of a host ferrous liquid metal. at
1400 C is 6.9 grams/cc. When refractory particles in the
form of tungsten carbide (WC) particles, with a density of
15.7 grams/cc at 25 C, are added to a host ferrous metal to
form the slurry, the WC particles will sink to the bottom
of the slurry. When refractory particles in the form of
titanium carbide (TiC) particles, with a density of 4.8
grams/cc at 1400 C, are added to the same host ferrous
metal, the TiC particles will float to the top of the
slurry. Refractory particles in the form of niobium
carbide (NbC), with a density of 7.7 grams/cc at 1400 C,
are fairly close to the density of the host ferrous liquid
metal at 6.9 grams/cc and are less prone to the Above-
described segregation in the liquid host ferrous metal
than TiC or WC.
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TiC, with a density of 4.9 grams/cc at 25 C, is
completely soluble in NbC, which has a density of 7.8
grams/cc at 25 C. Therefore, refractory particles with
densities in the range 4.9-7.8 grams/cc at 25 C can be
obtained by selecting (Nb,Ti)C particles with the required
niobium and titanium contents.
Tungsten carbide (WC), with a density of 15.7
grams/cc at 25 C, is mostly soluble in NbC, TiC and
(Nb,Ti)C. Therefore, refractory particles with densities
in the range 4.8-15.7 grams/cc at 25 C can be obtained by
selecting (Nb,Ti,W)C particles with the required niobium,
titanium and tungsten contents.
All refractory particles, described by the formula
(Nb,Ti,W)C, are insoluble in liquid ferrous host metals at
casting temperatures in the range 1200-1600 C.
Niobium carbide and titanium carbide have similar
crystal structures and are isomorphous.
It is evident from the above that selecting the
required Nb:Ti ratio in a (Nb,Ti)C chemical compound or
the required Nb:Ti:W ratio in a (Nb,Ti,W)C chemical
compound can yield a refractory material with a required
density within 20% of the density of the ferrous host
metal.
The addition of refractory particles that are, for
all intents and purposes, insoluble, (that is, having
minimal solid solubility in a host liquid metal), to
produce a centrifugally cast casting of a composite metal
product in accordance with the method of the present
disclosure, produces a product that displays physical and
chemical properties that are very similar to the host
metal with substantially improved wear resistance due to
the presence of a controlled dispersion of a high volume %
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of hard refractory material particles in the
microstructure of the host metal.
For example, the solubility of a refractory material
in the form of (14b,Ti,W)C in liquid host metals in the
form of (a) liquid Hadfield steel and (b) liquid 420C
stainless steel and (c) liquid high chromium white cast
iron at elevated temperatures is negligible (<0.3 wt%).
The addition of (14b,Ti,W)C with the required densities to
these three host metal alloys, followed by centrifugally
casting a composite metal product and standard heat
treatment procedure for each host metal produces
microstructures in the product comprising a dispersion of
primary niobium-titanium-tungsten carbides in the host
metals which are substantially free of niobium, titanium
and tungsten, that is, there is negligible partitioning of
the transition metals in the refractory material slurry
particles to the liquid host metal.
Consequently, there is a negligible influence of the
particulate refractory materials on the physical
properties (for example, melting point) and chemical
properties (for example, response to heat treatment) of
the host metal.
In addition to the above, in particular the applicant
has found that providing a composite metal product with a
microstructure that includes particles of niobium carbide
and/or particles of a chemical (as opposed to a physical)
mixture of two or more than two of niobium carbide,
titanium carbide, and tungsten carbide dispersed in a
matrix of a host metal considerably improves wear
resistance of the hard metal material without
detrimentally affecting the contribution that other
alloying elements have on other properties of the
composite metal product.
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In addition, and as described above, in particular
the applicant has found that it is possible to adjust the
density of particles of a chemical mixture of two or more
than two of niobium carbide, titanium carbide and tungsten
carbide to a sufficient extent in relation to the density
of a host metal, which forms a matrix of the composite
metal product. This opportunity for density control is an
important finding in relation to centrifugally cast
castings of the hard metal material.
In particular, by virtue of this finding, it is
possible to produce centrifugally cast castings of the
composite metal product with controlled non-uniform
distribution, that is, segregation, of the particles in
parts of the castings. This is important for end-use
applications for castings where it is desirable to have a
concentration of high wear resistant particles near a
surface of a casting of a hard metal material.
In addition, the applicant has found that forming
castings of the composite metal product to include
particles of niobium carbide and/or particles of a
chemical mixture of two or more than two of niobium
carbide, titanium carbide and tungsten carbide in a range
of 5-50 vol%, typically 5-40 vol%, more typically 5-20
vol% of the total volume of the composite metal product,
dispersed in a host metal, which forms a matrix of the
composite metal product, does not have a significant
negative impact on corrosion resistance and toughness of
ferrous material in the host metal. Hence, the present
disclosure makes it possible to achieve high wear
resistance of a composite metal product without a loss of
other desirable material properties,
Accordingly, in a fifth aspect there is provided a
method of centrifugally casting a composite metal product
having an axis of rotational symmetry and a mass of at
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least 5kg and comprising a host metal and a non-uniform
distribution of insoluble solid refractory particles of a
refractory material, the method comprising adding (a)
niobium or (b) two or more than two of niobium and
titanium and tungsten to a melt containing a host metal in
a form that produces solid refractory particles of niobium
carbide that are insoluble at a casting temperature and/or
solid refractory particles of a chemical mixture of two or
more than two of niobium carbide and titanium carbide and
tungsten carbide that are insoluble at the casting
temperature, with the solid refractory particles being in
a range of 5-50 volst, typically 5-40 volsti more typically
5-20 von, of the total volume of the product, and
centrifugally casting the product in a mould and obtaining
a non-uniform distribution of insoluble solid particles
throughout the host metal.
The terms "a chemical mixture of niobium carbide and
titanium carbide" and "niobium/titanium carbide" are
hereinafter understood to be synonyms. In addition, the
term ''chemical mixture" is understood in this context to
mean that the niobium carbides and the titanium carbides
are not present as particles of single metal carbides in
the mixture but are present as particles of
niobium/titanium carbides, (Irb,Ti)C.
The terms "a chemical mixture of niobium carbide and
titanium carbide and tungsten carbide" and
"niobium/titanium/tungsten carbide" are hereinafter
understood to be synonyms. In addition, the term
"chemical mixture" is understood in this context to mean
that the niobium carbides and the titanium carbides and
the tungsten carbides are not present as particles of
single metal carbides in the mixture but are present as
particles of niobium/titanium/tungsten carbides,
(Nb,Ti,W)C.
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Niobium carbide and titanium carbide and tungsten
carbide each have a Vickers hardness around 25 GPa, which
is about 10 GPa above the hardness of chromium carbides
(nominally 15 GPa). Accordingly, composite metal products
having a microstructure containing 5-50 vol%, typically 5-
40 vol%, more typically 5-20 vol%, of niobium carbide
and/or niobium/titanium carbide and/or
niobium/titanium/tungsten carbide have excellent wear
resistance properties. The applicant has recognised that
niobium carbides and titanium carbides and tungsten
carbides and niobium/titanium carbides and
niobium/titanium/tungsten carbides are substantially inert
chemically with respect to other constituents in the
composite metal product so those constituents provide the
product with the properties for which they were selected.
For example, chromium added to cast iron alloys still
produces chromium carbides and provides corrosion
resistance.
The niobium and the titanium and the tungsten may be
added to a melt of the host metal to form the slurry in
any suitable form, bearing in mind the requirement of
forming insoluble solid particles of niobium carbides
and/or niobium/titanium carbides and/or
niobium/titanium/tungsten carbides in the composite metal
product.
For example, the method may comprise adding the
niobium to the melt in the form of ferro-niobium, for
example particles of ferro-niobium. In this situation,
the ferro-niobium dissolves in the melt and the resultant
free niobium and carbon chemically combine to form
insoluble solid niobium carbides in the melt.
The method may also comprise adding the niobium to
the melt as elemental niobium.
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The method may also comprise adding the niobium and
the titanium to the melt as ferro-niobium-titanium.
The method may also comprise adding the niobium and
the titanium and tungsten to the melt as ferro-niobium-
titanium-tungsten.
The method may also comprise adding the niobium to
the melt in the form of particles of niobium carbide.
The method may also comprise adding the niobium and
the titanium to the melt in the form of insoluble solid
particles of niobium/titanium carbides.
The method may also comprise adding the niobium and
the titanium and the tungsten to the melt in the form of
insoluble solid particles of niobium/titanium/tungsten
carbides.
In each of these cases, the solidified metal alloy
may be formed from a slurry of particles of niobium
carbide and/or niobium/titanium/tungsten carbides
suspended in the melt, If the weight fraction of these
carbides in the melt slurry is too high, the flow
properties of the slurry may be adversely affected with
the result that unsound castings of the melt may be
produced.
The insoluble solid particles of niobium/titanium
carbides may be any suitable chemical mixture of a general
formula (Nbõ,Tiy)C.
The insoluble solid particles of
niobium/titanium/tungsten carbides may be any suitable
chemical mixture of a general formula (Nbz,Tiy,WOC. By
way of example, the niobium/titanium /tungsten carbides
may be (Nb0 . 25 TiO 50 ,W15,25)C
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The niobium and/or the titanium and/or the tungsten
may be added to the melt to produce insoluble solid
particles of niobium carbide and/or niobium/titanium
carbides and/or niobium/titanium/tungsten carbides in a
range of 12-33 wt% niobium carbides or niobium/titanium
carbides or niobium/titanium/tungsten carbides of the
total weight of the cast product.
The niobium and/or the titanium and/or the tungsten
may be added to the melt to produce insoluble solid
particles of niobium carbide and/or niobium/titanium
carbides and/or niobium/titanium/tungsten carbides in a
range of 12-25 wt% niobium carbides and niobium/titanium
carbides and niobium/titanium/tungsten carbides of the
total weight of the cast composite metal product.
The quantity of particles of niobium carbide and/or
niobium/titanium carbides and/or niobium/titanium/tungsten
carbide in the microstructure of the solidified hard metal
material may depend on the system.
The applicant is concerned particularly with solid
hard composite metal products that include host metals in
the form of ferrous alloys, such as ferrous alloys
described as high chromium white cast irons, stainless
steels, and austenitic manganese steels (such as Hadfield
steels). For ferrous alloys the quantity of insoluble
solid particles of refractory material in the form of
niobium carbide and/or niobium/titanium carbides and/or
niobium/titanium/tungsten carbides in the final composite
metal product may be in a range of 5-50 vol%, typically 5-
vol%, more typically 5-20 vol%, of the total volume of
the cast composite metal product.
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The particle size of niobium carbide and/or
niobium/titanium carbide and/or niobium/titanium/tungsten
carbide may be in a range of 1 - 150 pm in diameter.
The method may comprise stirring the slurry with an
inert gas or magnetic induction or any other suitable
means in order to disperse particles of niobium carbide
and/or niobium/titanium carbides and/or niobium/
titanium/tungsten carbides in the slurry.
The method may comprise adding particles of niobium
carbide and/or particles of niobium/titanium/tungsten
carbides to the melt of the host ferrous metals under
inert conditions, such as an argon blanket, to reduce the
extent to which niobium carbide and/or niobium/titanium
/tungsten carbide oxidize while being added to the melt.
The method may comprise adding particles of ferro-
niobium and/or ferro-titanium and/or ferro-tungsten and/or
ferro-niobium-titanium-tungsten to the melt under inert
conditions, such as an argon blanket, to reduce the extent
to which niobium and/or titanium and/or tungsten oxidize
while being added to the melt.
In a situation where particles of niobium/titanium
/tungsten carbides are required in the cast composite
metal product, the method may comprise pre-melting ferro-
niobium and ferro-titanium and ferro-tungs ten and/or
ferro-niobium-titanium-tungsten under inert conditions and
forming a liquid phase that is a homogeneous chemical
mixture of iron, niobium and titanium and tungsten and
solidifying this chemical mixture. The chemical mixture
can then be processed as required, for example by crushing
to a required particle size, and then added to the melt
(containing carbon) under inert conditions. The iron,
niobium and titanium and tungsten dissolve in the melt and
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chemically combine with carbon to form niobium/titanium
/tungsten carbides in the melt.
Other aspects, features, and advantages will become
apparent from the following detailed description when
taken in conjunction with the accompanying drawings, which
are a part of this disclosure and which illustrate, by way
of example, principles of inventions disclosed.
BRIEF DESCRIPTION OF THE DRAWINGS
Notwithstanding any other forms which may fall within
the scope of the method and resultant composite metal
product as set forth in the Summary, specific embodiments
of the method and resultant composite metal product will
now be described by way of example and with reference to
the accompanying Figures, of which:
Figure 1 is a diagram that illustrates a typical
centrifugal casting method;
Figure 2 is a SEM image of a section of one of the
samples from centrifugally cast test cylinder "37863" (A.05
host metal + 5 vol.% NbC particles) produced during
experimental work in relation to the invention;
Figure 3 comprises cross-sections of optical images
of samples from centrifugally cast test cylinders "37628",
"37629", "37630", and "37655" CA05 host metal + 5 vol.% NbC
particles) produced during experimental work in relation
to the invention;
Figure 4 is a graph of hardness versus distance from
outer surfaces to inner surfaces of the samples described
in relation to Figure 3;
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Figure 5 comprises optical images of cross-sections
of samples from centrifugally cast test cylinders "37631",
"37632", "37633", and "37636" (h.05 host metal + 12 vol%
NbC particles) produced during experimental work in
relation to the invention;
Figure 6 is a graph of hardness versus distance from
outer surfaces to inner surfaces of the samples described
in relation to Figure 5;
Figure 7 comprises optical images of cross-sections
of samples from centrifugally cast test cylinders "37634"
and"37635" (h05 host metal + 17 vol% NbC particles)
produced during experimental work in relation to the
invention;
Figure 8 is a graph of hardness versus distance from
outer surfaces to inner surfaces of the samples described
in relation to Figure 7;
Figure 9 is an optical image of a cross-section of a
sample of a centrifugally cast test cylinder A352 (C21
host metal -I- 10 vol% NbC particles) produced during
experimental work in relation to the invention;
Figure 10 is an optical image of a cross-section of
the outer layer of the cross-section of the sample shown
in Figure 9 after etching the sample;
Figure 11 is an optical image of a cross-section of a
sample of a centrifugally cast test cylinder A323 cylinder
(A49 host metal 15 vol% NbC particles); and
Figure 12 is a graph of hardness versus distance from
outer surfaces to inner surfaces of sections of the sample
described in relation to Figure 11.
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Figure 13 is a graph of the thickness of the NbC
particle-rich outer layer versus the nominal vol% of NbC
in the total composition of centrifugally cast cylinders
of A05 host metal + NbC particles; and
Figure 14 is a graph of the vol% NbC in the NbC
particle-rich outer layer versus the nominal vol% of NbC
in the total composition of centrifugally cast cylinders
of A05 host metal + NbC particles.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
Figure I was sourced from the internet and
illustrates in diagrammatic form the basic steps in a
centrifugal casting method.
These centrifugal casting steps include forming a
molten melt and pouring the melt into a suitable mould and
rotating the mould about a vertical axis (in the case of
the arrangement shown in the Figure) at a required rate of
rotation to form a cast product.
In alternative arrangements, such as the arrangement
used to carry out the experimental work described below,
the casting mould is positioned horizontally and the mould
is rotated about a horizontal axis.
In the context of the present disclosure, typically
the molten melt comprises a slurry of hard, insoluble
solid refractory particles in a host metal and the cast
product is a composite metal product, typically ranging in
mass from 5 kg to 5,000 kg, having a ferrous metal matrix
(the host metal) and comprises a non-uniform distribution
of hard, insoluble refractory particles in the ferrous
metal matrix, specifically an outer surface layer,
nominally 1-20 mm thick, of hard, insoluble refractory
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particles that provide enhanced wear resistance in the
surface layer.
The actual centrifugal casting conditions may be
selected in any given situation based on the required
characteristics of an actual product to be cast. The
casting conditions include, by way of example, the rate of
rotation of the mould and the rotation time and the
cooling conditions and the conditions in which the casting
is conducted, for example in an inert atmosphere.
Refractory particle property requirements may
include:
= Density greater than or less than the host
ferrous metal.
= Hardness in excess of 15 GPa.
= Diameter less than 500 microns, preferably
less than 50 microns.
= 10-80 vol* refractory particles present in
the hard surface layer.
= 5-50 volls, typically 5-40 vol.*, more
typically 5-40 volst, refractory particles in the
composite metal product.
The composite metal products produced by the
centrifugal casting process of the invention include by
way of example only the following products:
1. Slurry pump shaft sleeves
= Stainless steel cylinders
= Size: ranging from 25-400 mm diameter, 10 -
50 mm wall thickness and 2000 mm long.
= Outer surface layer, 1-10 mm thick,
containing a high concentration of hard, insoluble
refractory particles.
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The prior art comprises hard faced welding a
stainless steel cylinder to obtain approximately 1 mm
thick tungsten carbide surface layer. Hard-faced layers
then require grinding/machining to achieve a smooth
finish.
Centifugally casting a slurry pump shaft sleeve in
accordance with the invention permits the manufacture of a
cylinder approximately 2000 mm long with a required
smooth, hard surface layer in one casting operation. In
addition, the long cylinder can be sectioned to yield a
number of shaft sleeves which range in length from 60 to
300 mm.
2. Outer surface of gyratory crusher mantles
The standard composition of gyratory crusher mantles
is austenitic manganese steel (Hadfield steel). The
initial hardness of Hadfield steel is approximately 200
Brinell (HE) and the surface layer of the steel work
hardens to approximately 550 HE in service while the
interior maintains a lower hardness and extremely high
toughness. The yield strength for Hadfield steel with a
hardness of 200 HB is about 1/3 the tensile strength.
Severe plastic deformation can occur in service before
work hardening to 550 HE occurs. As a result, crusher
mantles wear rapidly and undergo excessive plastic
deformation in the early stages of operation. All previous
attempts to improve the initial hardness and yield
strength of Hadfield steel have invariably resulted in
unacceptable loss in toughness and a high risk of
catastrophic cracking in service.
Centrifugally casting a Hadfield steel crusher mantle
in accordance with the present disclosure and forming an
outer surface layer of insoluble solid refractory carbides
in the casting, while maintaining the original Hadfield
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steel composition in the body of the casting, provides a
more wear-resistant material with minimal loss of
toughness.
3. White cast irons
Centrifugally casting high chromium white cast irons
with refractory particles produces composite metal
products having surface layers containing a high
concentration of refractory particles for improved wear
resistance.
4. Breaker bars, hammer tips, ground engaging tools
Centrifugally casting breaker bars, hammer tips and
ground engaging tools from high chromium white cast irons
with refractory particles produces a surface layer
containing a high concentration of refractory particles
for improved wear resistance.
EXPER/MENTAL WORK
In order to investigate the invention the applicant
has carried out extensive experimental work in relation to
particles of a particular refractory maternal, namely NbC
particles, in different ferrous host metals.
Specifically, the experimental work investigated the
effects of vol.% of NbC particles and wall thickness and
centrifugal forces on the NbC-rich zones in centrifugally
cast products.
In the experimental work fourteen cylinders were
centrifugally cast in a horizontally arranged centrifugal
casting arrangement.
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The fourteen cylindrical shaft sleeves with different
concentrations of NbC particles and a ferrous-based host
metal, as summarised below, were centrifugally cast and
machined and then tested.
= Four A301 cylinders (A05 host metal + 5
vol% NbC particles of the total volume).
= Four A303 cylinders (AOS host metal + 12
vol% NbC particles of the total volume).
= Four A304 cylinders (A05 host metal + 17
vol% NbC particles of the total volume).
= One A352 cylinder (C21 host metal + 10 vol%
NbC particles of the total volume).
= One A323 cylinder (A49 host metal + 15 vol%
NbC particles of the total volume).
A05 is a eutectic high Cr cast iron, C21 is a 420C
stainless steel, and A49 is a hypoeutectic high Cr cast
iron. The nominal compositions of the ADS, C21, and A49
ferrous alloys are as follows, with the amounts of each
element in wt%:
1 Alloy Cr Mn IC Ni 'Si Fe
A05 27 2.0 13.0 0.5 balance
C21 14 .. t2.O __ 0.5 1.0 1.0 Balance
A49 28 1.5 1.5 2.0 1.5 Balance
1, RESULTS AND DISCUSSION
Twelve A05 steel-based cylinders with different
nominal chemical compositions were centrifugally cast at
various rotational speeds (RPM).
1.1. Centrifugal casting of four A301 cylinders (h05
host metal + 5 vol% NbC particles)
Four cylinders containing 5 vol% NbC particles in AOS
eutectic high Cr cast iron host metal were centrifugally
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cast at various rotational speeds or centrifugal forces.
The casting temperature was in a range of 1400-1500 C.
The density difference between the NbC particles and the
host metal at the casting temperature was approximately
12%. The cylinder dimensions and casting conditions are
in Table 1.
Table 1. Dimensions and casting conditions of cylinders
containing 5 vol% NbC particles
Jobtlo. ID(mm) OD(mm) Length (mm) RPM
37628 91 1.20 400 924
37629 905 1.30 400 1100
37630 91 130 400 1285
37655 82.3 120 400 924
Each 400mm cylinder was sectioned into three rings of
roughly 280mm, 20mm and 100mm in length. The 20mm-thick
rings were used for inspection and metallurgical analysis.
1.1.1. Metallurgical Examination
Samples were prepared from each 20mm-thick ring by
cutting through the thickness at two locations roughly
15mm apart and forming cross-sections of the rings. Each
cut was made perpendicular to the outer and inner
circumference of the ring. Hence the width of the sample
decreased from outer surface to the inner surface. The
samples were mounted, ground and polished following
standard metallographic procedures, and were then etched
with Acidified Ferric Chloride (AFC) for metallographic
examination. The microstructures of the samples were
examined with a scanning electron microscope. Also, an
optical stereomicroscope was used for macroscopic
examination of the samples.
Analysis of the samples from the cylinders
established that the casting microstructure in each
instance comprised the A05 eutectic high Cr cast iron host
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metal and a non-uniform distribution of solid NbC
particles throughout the host metal. Figure 2 is a SEM
image of a section of one of the samples. Figure 2 shows
the non-uniform distribution of NbC particles in the host
metal. The Figure indicates that NbC was undetectable in
the host metal. More particularly, the NbC particles
were found to be insoluble in the host metal at the
casting temperature and in the cast cylinders.
Figure 3 comprises optical images of cross-sections
of samples from cylinders "37628", "37629", "37630", and
"37655".
Figure 3a shows that the sample from cylinder "37628"
had a NbC particle-rich outer layer of about 2mm
thickness. Internally of the outer layer there are three
layers numbered 2-4 in the Figure. There are boundaries
between the layers. Each layer is about 3-5mm thick. The
layers 2-4 form an inner region having a lower
concentration of NbC particles than the outer layer.
Figure 3b shows that the sample from cylinder "37629"
had a similar layered (i.e. banded) structure, but with
more layers than shown in Figure 3a. The high
concentration NbC particle outer layer (identified by the
numeral 1 in the Figure) is about 2mm thick with NbC
particles spread uniformly throughout the sample. The
outer layer 1 and the innermost layer (identified by the
numeral 6 in the Figure) are the most distinct, and the
layers in between (i.e. layers 2-5 in the Figure) are very
similar to one another in terms of appearance but are
nevertheless distinct layers separated by boundaries. The
microstructures of layers 1 and 6 were found to be very
different from each other as well as from the
microstructures of layers 2-5. The microstructures of
layers 2-5 were found to be quite similar to each other.
Each layer 1-6 is about 3-4mm thick.
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Cylinder "37630" was cast at the highest rotation
speed. Figure 3c shows that the sample had three layers.
Compared to the samples of the other three cylinders, this
casting had the lowest NbC particle concentration in the
inner layers. The high rotation speed forced more NbC
particles to the outer layer, resulting in the thickest
high concentration NbC particle layer of all the castings.
Cylinder "37655" was cast at the same rotation speed
as cylinder "37628", but was cast with a 5mm thicker wall
thickness. Figure 3d shows that the NbC particle-rich
layer in the sample from cylinder '37655" was about 3.5mm
thick, greater than that in the sample from cylinder
"37628". This shows that even if rotation speeds are the
same, a thicker wall results in a thicker NbC particle-
rich zone.
The NbC particle volume fractions of (a) the NbC
particle-rich outer layer and (b) the low concentration
NbC particle inner layer were calculated from SEM images
of various areas of the layers at 100x magnification. The
values shown in Table 2 are the averages of multiple
measurements.
Table 2. NbC particles in outer and inner layers
NbC-rich layer Inner
layer volliNbC
ID
thickness mm .vol%NbC
37628 2 12.9 2.0
37629 2 13.6 2.6
37630 3-5 14.2 2.4
37655 3.5 13.5 3.4
From Table 2, it is evident that the rotation speed
during the casting had an effect on the NbC particle-rich
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outer layer of the cast cylinders. The sample for cylinder
"37630", which was cast at the highest speed, had the
highest layer thickness and the highest volume fraction of
the NbC particles. The sample for cylinder "37629", which
was cast with the second highest speed, came close in
terms of NbC volume faction, but the thickness of the
layer was almost half that of the layer in sample "37630".
Comparing the samples for cylinders "37628" and "37655"
shows that even with the same rotation speed, if the
casting wall thickness is greater (i.e. more material),
then the NbC particle-rich outer layer and its volume
fraction of NbC particles are greater as well.
In addition, all four castings had stellar levels of
NbC particles present in the non-concentrated NbC particle
inner layers, collectively described as an inner region
for each sample. Most of the NbC particles observed in the
inner regions were typical "Chinese script" morphology. lk
small amount of spherical and dendritic NbC particles were
also Observed.
1.1.2.liardness and ferrite measurements
Vickers hardness traverse tests with a load of 10kg
were carried out on the polished surfaces of each sample.
The measurements started at the outside diameter (OD) of
each sample and then traversed through the thickness of
the sample at lmm intervals to finish at the inside
diameter (ID) of the sample.
Table 3 shows the average hardness and ferrite
readings for each of the two regions. Traverse hardness
profiles are shown in Figure 4.
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Table 3. Hardness and ferrite measurements
mmunnmu]unnn.nii777,7777.7757.777.7777777,777771
gam$000:Aumm4444$AasffignomugmomemmummmA
Outer 640 13.4
37628
Inner 536 9.4
Outer 676 16.2 ..
37629
Inner 557 10.4
Outer 660 12.6
37630
Inner 551 8.9
Outer 608 14.2
37655
Inner 531 9.7
It is evident from Table 3 and Figure 4 that the NbC
particle-rich outer layer of each of the samples was
considerably harder than the inner region of the sample
and that the highest hardness values were typically at the
outer surface of each sample and decreased uniformly to
around 8 mm from the outer surface and remained generally
constant through the remainder of the sample. In
addition, the ferrite measurement results for the four
castings showed a general trend of the NbC particle-rich
outer layer having higher ferrite measurements than the
layers forming the inner regions. The differences in
ferrite content were minor, with the NbC particle-rich
outer layers ranging from 13 to 16% while the inner
regions ranged between 9 and 10%.
1.1.3.Summary
= All four of A301 centrifugal castings (A05 host
metal + 5 vol% NbC particles) exhibited NbC segregation,
resulting in outer layers of each sample having high
concentrations of NbC particles.
= All four castings exhibited layers below the NbC
particle-rich outer layer which were marginally different
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from each other. Each casting had a different number of
layers.
= The thickness and hardness of the NbC particle-
rich layers and the volume fractions of NbC particles in
the outer layers of the centrifugally cast cylinders
depended on the different casting parameters, including
casting rotation rate and wall thickness.
= Samples for cylinders "37628" and "37655" were
cast at the same rotation speeds but with different
material mass, resulting in different dimensions. The
"37655" sample had a slightly thicker NbC particle-rich
outer layer and it also contained a larger number of
different banded layers through the thickness of the
samples.
The sample for cylinder "37629" was similar to
the sample for cylinder "37628", despite being cast at a
higher rotation speed. The faster rotation speed did not
affect the thickness of the NbC particle-rich outer layer,
but it did affect the volume fraction of NbC particles in
the outer layer slightly.
= The sample for cylinder "37630" sample was cast
at the fastest rotation speed, and this was reflected
directly on several features. The sample had the thickest
NbC particle-rich outer layer and the highest volume
fraction of NbC particles in the outer layer.
Consequently, the hardness of the outer layer was the
highest recorded for this group of cylinders.
= The ferrite measurement results for the four
castings showed a general trend of the NbC particle-rich
outer layer having higher ferrite measurements than the
layers forming the inner regions. The differences in
ferrite content were minor, with the NbC particle-rich
outer layers ranging from 13 to 16% while the inner
regions ranged between 9 and 10%.
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1.2. Centrifugal casting of four A303 cylinders (A05
host metal + 12 vol% NbC particles)
Four cylinders were cast under the same conditions as
the four cylinders described in section 1.1 above, with
the same host metal (A05), but with a higher overall NbC
volume fraction of 12%. The cylinder dimensions and
rotational speeds are in Table 4.
Table 4. Job codes and dimension of cylinders containing
12vol% of NbC
JobNo. ID(mm) OD(mm) Length(mm) RPM
TRW 89 VO 400 922
37632 95 VW 400 1104
Min 90 VW 400 1280
37863 81 EM 400 925
Each 400mm cylinder was sectioned into three rings of
roughly 280mm, 20mm and 100mm in length. The 20mm-thick
rings were used for inspection and metallurgical analysis.
Samples were prepared and tested using the same
methodology described in section 1.1 above.
Figure 5 comprises optical images of samples from
cylinders "37631", "37632", "37633", and "37636".
It is evident from Figure 5 that, as was the case
with the lower NbC particle volume fraction cylinders
described in section 1.1 above, the NbC particles formed a
non-uniform distribution in the host metal through the
thickness of the castings, with the outer layers of the
samples having higher concentrations of NbC particles.
Similarly, as was the case with the lower NbC
particle volume fraction cylinders described in section
1.1 above, SEM analysis established that NbC was
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undetectable in the host metal. More
particularly, the
NbC particles were found to be insoluble in the host metal
at the casting temperature and in the cast cylinders.
The NbC particle volume fractions of the NbC
particle-rich outer layers and the thicknesses of the
outer layers were calculated from SEM images of various
areas of the layers at 100x magnification. The values
shown in Table 5 are the averages of multiple
measurements.
Table 5 Thickness of outer layer and average vol%NbC
particles
7
NbC tam NbC layer
Sample OD (mm) D(mm) RPM
thitkoess (tom) volume fraction (%)
37631 130 89 6 25.0$8 922
37632 130 95 7 26.027 1104
37633 130 so Mn, 5. Mat? 28.989 1280
37863 130 81 5 28.45 925
Vickers hardness traverse tests with a load of 10kg
were carried out on the polished surfaces of each sample.
The measurements started at the outside diameter (OD) of
each sample and then traversed through the thickness of
the sample at lmm intervals to finish at the inside
diameter (ID) of the sample.
Table 6 shows the average hardness and ferrite
readings for each of the two regions. Traverse hardness
profiles are shown in figure 6.
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Table 6. Hardness and Ferrite measurements
Ferrite Reading
SarmAe Region HV10
(94 magnetic)
37631 Outer 671 12.8
inner 515 10.4
37632 Outer 772 115
inner 584 9.8
37633 Outer 821 14.6
inner 587 10.4
37863 Outer 771 15.2
inner 593 11.5
It is evident from Tables 5 and 6 and Figures 5 and 6
that the same basic results were obtained with the higher
volume percentage of the A303 cylinders as with the A301
cylinders described in section 1.1 above.
1.3. Centrifugal casting of four A304 cylinders (A05
host metal + 17 vol% NbC particles)
Four A304 cylinders were centrifugally cast using the
same conditions as the A301 and A303 cylinders described
in sections 1.1 and 1.2, respectively, above, with the
same A05 host metal, but with a higher volume fraction of
NbC particles. Samples were prepared and tested as
described in sections 1,1 and 1.2 above. Only three
cylinders were examined (cylinder "s37634" cast at 920rpm,
cylinder "37635" cast at 1100rpm and cylinder "37636" cast
at 1280 rpm).
Figure 7 comprises optical images of cross-sections
of samples from cylinders "37634" ancr37635".
It is evident from Figure 7 that, as was the case
with the lower NbC particle volume fraction cylinders
described in sections 1.1 and 1.2 above, the NbC particles
formed a non-uniform distribution in the host metal
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through the thickness of the castings, with the outer
layers of the samples having higher concentrations of NbC
particles. The cross-sections show a NbC particle-rich
outer layer (or region) and a lower NbC particle
concentration inner region (which may include multiple
layers separated by boundaries).
In addition, as was the case with the lower NbC
particle volume fraction cylinders described in sections
1.1 and 1.2 above, SEM analysis established that NbC was
undetectable in the host metal. More particularly, the
NbC particles were found to be insoluble in the host metal
at the casting temperature and in the cast cylinders.
The test work indicated that the thicknesses of the
NbC particle-rich outer layers in the samples for
cylinders "37634", "37635" and "37636" were 12mm, 13mm and
15mm, respectively.
The volume concentrations of the NbC particles in the
outer layers of these samples were 28% for cylinder
"37634", 25% for cylinder "31635" and 29% for cylinder
"37636".
Table 7 shows the average hardness and ferrite
readings for each of the inner and outer regions of the
samples from cylinders "37634" and"37635". Traverse
hardness profiles are shown in Figure 8.
Table 7. Hardness and Ferrite readings
Ferrite Reading
Sample Region HVI.0
(% magnetic)
37634 Outer 664 1/7
inner 546 1119
37635 Outer 661 11.7
inner 513 10.1
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It is evident from Table 7 and Figures 7 and 8 that
the same basic results were obtained with the higher
volume percentage of the A304 cylinders as with the A301
and A303 cylinders described in sections 1.1 and 1.2
above.
1.4. Centrifugal casting of an A352 cylinder (C21
host metal .4- 10 vol% NbC particles)
One A352 cylinder was centrifugally cast from a C21
host metal with 10 vol% NbC particles. Samples were
prepared and tested as described above. .
Figure 9 comprises an optical image of a cross-
section of a sample of the A352 cylinder.
It is evident from Figure 9 that, as was the case
with the other test cylinders described above, the NbC
particles formed a non-uniform distribution through the
thickness of the casting, with the outer layer of the
sample having a higher concentration of NbC particles.
In addition, as was the case with the other test
cylinders described above, SEM analysis established that
NbC was undetectable in the host metal. More
particularly, the NbC particles were found to be insoluble
in the host metal at the casting temperature and in the
cast cylinders.
As shown in Figure 9, the NbC-rich layer is a 20mm
thick layer, 50% of the total radial thickness of the
sample. It was found that the sample contained about
25vo1% of NbC particles.
After etching, three sub-layers of the 20 mm thick
NbC particle-rich outer layer were identified, and are
shown in Figure 10. Figure 10 shows that there was
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directional solidification across the sub-layers during
centrifugal casting. It has been found that the columnar
structure made a significant contribution to the wear
resistance of the casting.
1.5. Centrifugal casting of an A323 cylinder (A49
host metal 15 vol% NbC particles)
One A323 cylinder was centrifugally cast from a A49
host metal and 15 vol% NbC particles. Samples were
prepared and tested as described above. .
1.5.1. Metallurgical Examination
Figure 11 comprises an optical image of a cross-
section of a sample of the A323 cylinder. It is evident
from Figure 11 that, as was the case with the other test
cylinders described above, the NbC particles formed a non-
uniform distribution through the thickness of the casting,
with the outer layer of the sample having a higher
concentration of NbC particles.
In addition, as was the case with the other test
cylinders described above, SEM analysis established that
NbC was undetectable in the host metal. More
particularly, the NbC particles were found to be insoluble
in the host metal at the casting temperature and in the
cast cylinders.
As is evident from Figure 11, the NbC particle-rich
outer layer is a very distinct band along the entire outer
edge of the circle. This was visible at both macroscopic
and microscopic levels.
The depth of the NbC particle-rich outer layer was
found to be consistent along the circumference at about 7-
8m, i.e. approximately 25-30% of the radial thickness of
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the sample. The NbC volume fraction of this outer layer
was also found to be consistent in the examined areas at
about 28-31 vol% of the total volume of the outer layer.
Apart from the NbC concentrations, the
microstructures of the outer and the inner layers were
found to have other significant differences. The NbC
particles in the NbC particle-rich outer layer were mostly
round without any sharp edges, while those in the inner
layers had a variety of shapes, ranging from round to
pointy dendritic shapes. The matrix structure of the NbC
particle-rich outer layer and the other layers could be
distinguished primarily by the presence/absence of
"Chinese script" type NbC particles structure in the
austenite dendrites of the matrix. This type of NbC
structure was found extensively in the inner layers, but
it was almost non-existent in the NbC particle-rich outer
layer. This resulted in a difference in thermal
characteristics of the NbC particle-rich outer layer and
the inner layers.
A very unique microstructure was found at the
boundary of the NbC particle-rich outer layer and the
inner layers. The microstructure was characterised by the
NbC particles being predominantly cross-shaped
(dendritic). Some particles in this region resembled a
shape that was a mixture of round and dendritic.
1.5.2 Hardness & Ferrite
Vickers hardness traverse tests with a load of 10kg
were carried out on polished surfaces of two samples. The
measurements started at the outermost edges of the samples
and then traversed through the thickness of the castings
at lmm intervals to finish at the innermost edges. Table 8
shows the average hardness and ferrite reading for the NbC
particle-rich outer layer and the inner layers of each
sample. The NbC particle-rich outer layer of each sample
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is described as the "outer region" in the Table and the
inner layers of each sample are described as the "inner
region" in the Table. Traverse hardness profiles are
shown in Figure 12.
Table 8. Hardness and Ferrite measurements
minammmmommmammmwmmimmmmimirwmammgmomviminmm
M
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Outer 455 22.9
4719CC-A
Inner 357 21.2
Outer 526 19.1
4719CC-B
Inner 355 17.6
The higher NbC particle concentration of the NbC
particle-rich outer layer (the outer region) naturally
resulted in a higher hardness than the inner region for
each sample. The hardness results correlated with the
volume fraction results, where a higher NbC volume
fraction of the 4719CC-B sample gave a higher hardness
result than the 419CC-A sample. There was no significant
difference in ferrite content between the two regions of
each sample.
With reference to Figure 12, the hardness traverse
tests showed that for both samples, the hardness was the
highest at the very outer edge of the samples (i.e. the
first test points for both tests) and the hardness at the
boundary of the two regions was around 425 Vickers. The
inner (bulk) region maintained consistent hardness
throughout most of its thickness.
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2. CONCLUSIONS
2.4. Functionally Graded Materials
In the test work summarised above, host metals (A05,
A49 and C21) with a range of volume percentages of NbC
particles were centrifugally cast and examined. The
results are summarized and presented in Table 9.
Table 9. Summary of centrifugally cast A300-family
1 0 alloys
FM MCC NbC-rich Layer
G-force
ft Code Host Metal Bulk NbC RPM
(G) Thickness NbC
Den. (vol%) (mm) (vol%)
1 A323 A49 15 920 50 7-8 28-33
924 52 2 13 .
1100 74 2 14
2 A301 A05 5
1285 102 3-5 14
924 52 3.5 13.5
922 52 6 , 25
3 A303 A05 12 1104 75 7 26
1280 101 5.7 29
925 53 5 28
920 52 12 28
1100 . 74 13 25
4 A304 ADS 17
1280 101 15 29
5 A352 021 10 925 67 15-17 24
_
The volume fraction of refractory particles in the
NbC particle-rich outer layers of the castings were up to
31% in volume of the outer layer. In addition, high
rotation speeds increased the NbC vol%, but the effects
were typically very small. In the inner region of each
casting, the volume percentage of NbC particles varied in
the range from 2-6%.
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The relationship between thickness of the NBC
particle-rich outer layer and the overall vol% of NBC in
the product compositions and the relationship between the
vol% of NBC in the NbC particle-rich outer layer and the
overall vol% NbC in the product compositions were analysed
and the results are presented in Figures 13 and 14,
respectively.
As can be seen from the Figures:
(a) the thickness of the NBC-rich outer layer of each
centrifugally cast cylinder was found to be directly
dependent on the nominal bulk NbC content in the product
composition (see Figure 13); and
(b) the final NbC content in the NbC particle-rich
outer layer of each centrifugally cast cylinder was found
be dependent on the nominal bulk NbC content in the
product composition, with the NbC content tending to level
off at a maximum content of around 28-30% in the outer
layer for the particular A05 host metal and being 50-120
vol% higher than the nominal volume percentage of the
refractory material in the whole product across the
nominal NbC vol% range covered by Figure 14.
It was also found that the thickness of and the NbC
particle concentration in the NbC particle-rich outer
layer in each of the centrifugally cast cylinders WAS
independent of the casting G-Factor in a range of 50-102.
In the foregoing description of preferred
embodiments, specific terminology has been resorted to for
the sake of clarity. However, the invention is not
intended to be limited to the specific terms so selected,
and it is to be understood that each specific term
includes all technical equivalents which operate in a
similar manner to accomplish a similar technical purpose.
Terms such as "front" and "rear", "inner" and "outer",
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"above", "below", "upper" and "lower" and the like are
used as words of convenience to provide reference points
and are not to be construed as limiting terms.
The reference in this specification to any prior
publication (or information derived from it), or to any
matter which is known, is not, and should not be taken as,
an acknowledgement or admission or any form of suggestion
that prior publication (or information derived from it) or
known matter forms part of the common general knowledge in
the field of endeavour to which this specification
relates.
In this specification, the word "comprising" is to be
understood in its "open" sense, that is, in the sense of
"including", and thus not limited to its "closed" sense,
that is the sense of "consisting only of". A
corresponding meaning is to be attributed to the
corresponding words "comprise", "comprised" and
"comprises" where they appear.
In addition, the foregoing describes only some
embodiments of the invention(s), and alterations,
modifications, additions and/or changes can be made
thereto without departing from the scope and spirit of the
disclosed embodiments, the embodiments being illustrative
and not restrictive.
Furthermore, invention(s) have been described in
connection with what are presently considered to be the
most practical and preferred embodiments, it is to be
understood that the invention is not to be limited to the
disclosed embodiments, but on the contrary, is intended to
cover various modifications and equivalent arrangements
included within the spirit and scope of the invention(s).
Also, the various embodiments described above may be
implemented in conjunction with other embodiments, e.g.,
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aspects of one embodiment may be combined with aspects of
another embodiment to realize yet other embodiments.
Further, each independent feature or component of any
given assembly may constitute an additional embodiment.
By way of example, whilst the embodiments of the
invention described above comprise different types of
steel (such as a stainless steel or an austenitic
manganese steel) as the host metal, the invention is not
limited to this type of host metal and extends to any
suitable host metal. By way of example, the host metal
may contain wherein the host metal contain any one or more
of the transition metal elements Ti, Cr, Zr, Hf, V, Nb,
and Ta.
By way of further example, whilst the embodiments of
the invention described above focus on NbC as the material
of the insoluble solid particles of refractory material,
the invention also extends to other refractory materials.
By way of further example, whilst the embodiments of
the invention described above focus on NbC particles which
have a density that is higher than that of the host metal,
whereby there are higher concentrations of the refractory
particles towards exterior surfaces of the composite metal
products, the invention also extends to embodiments in
which the refractory particles have a density that is
lower than that of the host metal, whereby there are
higher concentrations of the refractory particles towards
an interior surface of the composite metal product.
By way of further example, whilst the experimental
work described above was carried out on centrifugally cast
cylinders, it can readily be appreciated that the
invention is not limited to this particular shape casting
and extends to any shape product that can be centrifugally
cast.
