[0001] The present disclosure relates to a centrifugally cast composite metal product with
improved wear resistance and having an axis of rotational symmetry, and a method of
centrifugally casting said product.
[0002] 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".
The host metal or metal matrix of the invention is is a ferrous metal. The host metal
may also be nickel-based and cobalt-based superalloys, however, this does not form
part of the present invention.
[0003] 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
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 the refractory material particles to the host metal during the casting
method and in the solidified product.
[0004] WO 2011/094800 A1 discloses a hard metal material comprising 5-50 volume % particles of a refractory
material dispersed in a host metal. The method for forming the hard metal material
comprises forming a slurry of 5-50 volume % particles of the refractory material dispersed
in a liquid host metal in an inert atmosphere and pouring the slurry into a mould
and forming a casting of the component.
[0005] WO 95/24513 A1 discloses a cast ferrous alloy which contains in addition to iron and inevitable
impurities the following components wherein all percentages relate to the percentage
content by weight: carbon 1.05 to 3.8 %, chromium 2.0 to less than 8.0 %, molybdenum
1.0 to 8.0 %, tungsten 1.05 to 8.0 %, niobium 1.0 to 10.0 %, and vanadium 1.0 to 10.0
% and which may further contain one or more of the following optional elements in
the following percentage amounts by weight: manganese up to 1.5 %, silicon up to 1.5
%, cobalt up to 5.0 %, nickel up to 5.0 %, titanium up to 3.0 %, nitrogen up to 3.0
%, and cerium and/or other rare earth element(s) up to 0.2 % in total. Such alloys
can be cast into rolling mill rolls with attractive mechanical properties and wherein
unwanted carbide precipitation can be avoided.
[0006] US 8141615 B1 discloses a method for centrifugally casting engine cylinders. A mold is charged
with molten aluminum alloy and particulate silicon monoxide having an average size
of 0.01 mm to 0.04 mm. The mold is rotated at a velocity and period of time to distribute
the particulate silicon monoxide on an inner cylinder surface. The mold is allowed
to cool until the aluminum alloy solidifies. A casting is demolded characterized in
a uniform inner cylinder surface of the particulate silicon monoxide in an amount
of 25 volume % and thickness 1 to 5 millimeters.
[0007] CN 103418768 A discloses a method for centrifugally casting a particle-reinforced brake disc comprising
the steps of molten syrup preparation, casting mold preheating, pouring for mold filling,
centrifugal forming, deceleration for halt and cooling after demolding, wherein a
casting mold is made of non-magnetic materials, the centrifugal forming is carried
out in a magnetic field, the highest centrifugal rotating speed is 800-3000 r/min,
the magnetic field direction is vertical to or parallel to the axis direction of the
centrifugal casting mold, and the stability intensity of the constant stable magnetic
field is 0.01-0.8T.
[0008] JP S58 116970 A discloses a casting which has a highly abrasion resistant layer and a highly tough
layer, formed by charging molten metal and powder of a hard metallic compound differing
in specific gravity in a casting mold and forming a mixed layer and a metallic layer
by the centrifugal forces developed by the rotation of the casting mold.
[0009] JP S58 6769 A discloses a method for producing castings wherein the outside surface is resistant
to abrasion and the core part is strong and tough easily and inexpensively in the
composite castings of cylindrical or columnar shapes, by forming a high hardness layer
containing tungsten carbide particles on the outside surface of the outer layer to
one body.
SUMMARY OF THE DISCLOSURE
[0010] 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
solid particles of a refractory material in a non-uniform distribution throughout
the ferrous metal matrix, the refractory particles being insoluble at a casting temperature,
the refractory particles being carbides and/or borides and/or nitrides of one or more
than one of the nine transition metals titanium, zirconium, hafnium, vanadium, niobium,
tantalum, chromium, molybdenum and tungsten, 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, wherein the particles have a density that is within 20%, of
the density of the metal host at its casting temperature wherein a first concentration
of refractory particles in an exterior surface layer of the product is in a range
of 10-40 vol% of the total volume of the exterior surface layer, and wherein a second
concentration of refractory particles in an interior layer of the product is in a
range of 2-4.5 vol% of the total volume of the interior layer.
[0011] 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.
[0012] 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
metal 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 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).
[0013] The embodiments of the invention are defined in the appended claims.
[0014] 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 (
WO2011/094800) in the name of the present applicant. Density and solubility of the refractory materials
are discussed below.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] All refractory particles, described by the formula (Nb,Ti,W)C, are insoluble in liquid
ferrous metals at casting temperatures in the range 1200-1600°C.
[0020] Niobium carbide and titanium carbide have similar crystal structures and are isomorphous.
[0021] 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 metal.
[0022] 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 % of hard refractory material
particles in the microstructure of the host metal.
[0023] For example, the solubility of a refractory material in the form of (Nb,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 (Nb,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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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 metal 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.
[0029] Accordingly, also disclosed is a method of centrifugally casting a composite metal
product having an axis of rotational symmetry and a mass of at 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 vol%, typically 5-40 vol%, more typically 5-20 vol%, 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.
[0030] 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, (Nb,Ti)C.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] The method may also comprise adding the niobium to the melt as elemental niobium.
[0036] The method may also comprise adding the niobium and the titanium to the melt as ferro-niobium-titanium.
[0037] The method may also comprise adding the niobium and the titanium and tungsten to
the melt as ferro-niobium-titanium-tungsten.
[0038] The method may also comprise adding the niobium to the melt in the form of particles
of niobium carbide.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] The insoluble solid particles of niobium/titanium carbides may be any suitable chemical
mixture of a general formula (Nb
x,Ti
y)C.
[0043] The insoluble solid particles of niobium/titanium/tungsten carbides may be any suitable
chemical mixture of a general formula (Nb
x,Ti
y,Wz)C. By way of example, the niobium/titanium /tungsten carbides may be (Nb
0.25,Ti
0.50,W
0.25) C.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] The applicant is concerned particularly with solid hard composite metal products
that include host metals in the form of ferrous metals, such as ferrous metals described
as high chromium white cast irons, stainless steels, and austenitic manganese steels
(such as Hadfield steels). For ferrous metals 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 is
in a range of 5-50 vol%, typically 5-40 vol%, more typically 5-20 vol%, of the total
volume of the cast composite metal product.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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-tungsten 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 chemically
combine with carbon to form niobium/titanium /tungsten carbides in the melt.
[0053] 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
[0054] 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" (A05 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" (A05 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;
Figure 5 comprises optical images of cross-sections of samples from centrifugally
cast test cylinders "37631", "37632", "37633", and "37636" (A05 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" (A05 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 + 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.
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
[0055] Figure 1 was sourced from the internet and illustrates in diagrammatic form the basic
steps in a centrifugal casting method.
[0056] 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.
[0057] 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.
[0058] 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 particles
that provide enhanced wear resistance in the surface layer.
[0059] 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.
[0060] 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 vol%, typically 5-40 vol%, more typically 5-40 vol%, refractory particles in
the composite metal product.
[0061] 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.
[0062] 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.
[0063] 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
[0064] The standard composition of gyratory crusher mantles is austenitic manganese steel
(Hadfield steel). The initial hardness of Hadfield steel is approximately 200 Brinell
(HB) and the surface layer of the steel work hardens to approximately 550 HB 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 HB 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.
[0065] 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 steel composition in the body
of the casting, provides a more wear-resistant material with minimal loss of toughness.
3. White cast irons
[0066] 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
[0067] 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.
EXPERIMENTAL WORK
[0068] 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.
[0069] 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.
[0070] In the experimental work fourteen cylinders were centrifugally cast in a horizontally
arranged centrifugal casting arrangement.
[0071] 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 (A05 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).
[0072] 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 A05, C21, and A49
ferrous metals are as follows, with the amounts of each element in wt%:
Alloy |
Cr |
Mn |
C |
Ni |
Si |
Fe |
A05 |
27 |
2.0 |
3.0 |
|
0.5 |
balance |
C21 |
14 |
2.0 |
0.5 |
1.0 |
1.0 |
Balance |
A49 |
28 |
1.5 |
1.5 |
2.0 |
1.5 |
Balance |
1. RESULTS AND DISCUSSION
[0073] 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 (A05 host metal + 5 vol% NbC particles)
[0074] Four cylinders containing 5 vol% NbC particles in A05 eutectic high Cr cast iron
host metal were centrifugally 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
Job No. |
ID (mm) |
OD (mm) |
Length (mm) |
RPM |
37628 |
91 |
130 |
400 |
924 |
37629 |
90.5 |
130 |
400 |
1100 |
37630 |
91 |
130 |
400 |
1285 |
37655 |
82.3 |
130 |
400 |
924 |
[0075] 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
[0076] 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.
[0077] Analysis of the samples from the cylinders established that the casting microstructure
in each instance comprised the A05 eutectic high Cr cast iron host 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.
[0078] Figure 3 comprises optical images of cross-sections of samples from cylinders "37628",
"37629", "37630", and "37655".
[0079] 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.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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
ID |
NbC-rich layer |
Inner layer vol%NbC |
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 |
[0084] From Table 2, it is evident that the rotation speed during the casting had an effect
on the NbC particle-rich 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.
[0085] In addition, all four castings had similar 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. A small amount of spherical and dendritic NbC particles
were also observed.
1.1.2.Hardness and ferrite measurements
[0086] 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 1mm intervals
to finish at the inside diameter (ID) of the sample.
[0087] Table 3 shows the average hardness and ferrite readings for each of the two regions.
Traverse hardness profiles are shown in Figure 4.
Table 3. Hardness and ferrite measurements
Sample |
Region |
HV10 |
Ferrite Reading (% magnetic) |
37628 |
Outer |
640 |
13.4 |
Inner |
536 |
9.4 |
37629 |
Outer |
676 |
16.2 |
Inner |
557 |
10.4 |
37630 |
Outer |
660 |
12.6 |
Inner |
551 |
8.9 |
37655 |
Outer |
608 |
14.2 |
Inner |
531 |
9.7 |
[0088] 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
[0089]
- 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 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%.
1.2. Centrifugal casting of four A303 cylinders (A05 host metal + 12 vol% NbC particles)
[0090] 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
Job No. |
ID (mm) |
OD (mm) |
Length (mm) |
RPM |
37631 |
89 |
130 |
400 |
922 |
37632 |
95 |
130 |
400 |
1104 |
37633 |
90 |
130 |
400 |
1280 |
37863 |
81 |
130 |
400 |
925 |
[0091] 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.
[0092] Figure 5 comprises optical images of samples from cylinders "37631", "37632", "37633",
and "37636".
[0093] 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.
[0094] 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 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.
[0095] 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
Sample |
OD (mm) |
ID (mm) |
NbC layer thickness (mm) |
NbC layer volume fraction (%) |
RPM |
37631 |
130 |
89 |
6 |
25.098 |
922 |
37632 |
130 |
95 |
7 |
26.027 |
1104 |
37633 |
130 |
90 |
Min. 5, Max. 7 |
28.989 |
1280 |
37863 |
130 |
81 |
5 |
28.45 |
925 |
[0096] 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 1mm intervals
to finish at the inside diameter (ID) of the sample.
[0097] Table 6 shows the average hardness and ferrite readings for each of the two regions.
Traverse hardness profiles are shown in Figure 6.
Table 6. Hardness and Ferrite measurements
Sample |
Region |
HV10 |
Ferrite Reading (% magnetic) |
37631 |
Outer |
671 |
12.8 |
Inner |
515 |
10.4 |
37632 |
Outer |
772 |
11.5 |
Inner |
584 |
9.8 |
37633 |
Outer |
821 |
14.6 |
Inner |
587 |
10.4 |
37863 |
Outer |
771 |
15.2 |
Inner |
593 |
11.5 |
[0098] 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)
[0099] 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 "37634" cast at 920rpm, cylinder "37635" cast at 1100rpm and
cylinder "37636" cast at 1280 rpm).
[0100] Figure 7 comprises optical images of cross-sections of samples from cylinders "37634"
and"37635".
[0101] 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 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).
[0102] 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.
[0103] 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.
[0104] The volume concentrations of the NbC particles in the outer layers of these samples
were 28% for cylinder "37634", 25% for cylinder "37635" and 29% for cylinder "37636".
[0105] 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
Sample |
Region |
HV10 |
Ferrite Reading (% magnetic) |
37634 |
Outer |
664 |
12.7 |
Inner |
546 |
10.9 |
37635 |
Outer |
661 |
11.7 |
Inner |
513 |
10.1 |
[0106] 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 + 10 vol% NbC particles)
[0107] One A352 cylinder was centrifugally cast from a C21 host metal with 10 vol% NbC particles.
Samples were prepared and tested as described above.
[0108] Figure 9 comprises an optical image of a cross-section of a sample of the A352 cylinder.
[0109] 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.
[0110] 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.
[0111] 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 25vol%
of NbC particles.
[0112] 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 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)
[0113] 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
[0114] 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.
[0115] 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.
[0116] 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.
[0117] The depth of the NbC particle-rich outer layer was found to be consistent along the
circumference at about 7-8mm, i.e. approximately 25-30% of the radial thickness of
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.
[0118] 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.
[0119] 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
[0120] 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 1mm 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 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
Sample |
Region |
HV10 |
Ferrite Reading (% magnetic) |
4719CC-A |
Outer |
455 |
22.9 |
Inner |
357 |
21.2 |
4719CC-B |
Outer |
526 |
19.1 |
Inner |
355 |
17.6 |
[0121] 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.
[0122] 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.
2. CONCLUSIONS
2.4. Functionally Graded Materials
[0123] 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 alloys
# |
Code |
FMMCC |
RPM |
G-force (G) |
NbC-rich Layer |
Host Metal Desc. |
Bulk NbC (vol%) |
Thickness (mm) |
NbC (vol%) |
1 |
A323 |
A49 |
15 |
920 |
50 |
7-8 |
28-33 |
2 |
A301 |
A05 |
5 |
924 |
52 |
2 |
13 |
1100 |
74 |
2 |
14 |
1285 |
102 |
3-5 |
14 |
924 |
52 |
3.5 |
13.5 |
3 |
A303 |
A05 |
12 |
922 |
52 |
6 |
25 |
1104 |
75 |
7 |
26 |
1280 |
101 |
5-7 |
29 |
925 |
53 |
5 |
28 |
4 |
A304 |
A05 |
17 |
920 |
52 |
12 |
28 |
1100 |
74 |
13 |
25 |
1280 |
101 |
15 |
29 |
|
|
|
|
5 |
A352 |
C21 |
10 |
925 |
67 |
15-17 |
24 |
[0124] 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%.
[0125] 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.
[0126] 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.
[0127] 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.
[0128] 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",
"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.
[0129] 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.
[0130] 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.
[0131] In addition, the foregoing describes only some embodiments of the invention (s),
and the present invention is only limited by the scope of the appended claims.
[0132] 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 ferrous host metal. By way of example, the ferrous host metal may
contain any one or more of the transition metal elements Ti, Cr, Zr, Hf, V, Nb, and
Ta.
[0133] 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, as defined in claim 1.
[0134] 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.
[0135] 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 and has an axis of rotational symmetry.
1. Produit métallique composite coulé par centrifugation ayant un axe de symétrie de
rotation et une surface extérieure s'étendant axialement et une masse d'au moins 5kg
et comprenant une matrice de métal ferreux et 5-50% en volume de particules solides
d'un matériau réfractaire à travers la matrice de métal ferreux, les particules réfractaires
étant insolubles à une température de coulée, les particules réfractaires étant des
carbures et/ ou des borures et/ ou des nitrures d'un ou plusieurs des neuf métaux
de transition titane, zirconium, hafnium, vanadium, niobium, tantale, chrome, molybdène
et tungstène. où les particules sont un mélange chimique, par opposition à un mélange
physique, des carbures et/ ou des borures et/ ou des nitrures des métaux de transition,
les particules réfractaires ayant une densité qui est à moins de 20% de la densité
du métal ferreux à sa température de coulée, dans lequel une première concentration
de particules réfractaires dans une couche de surface extérieure du produit est dans
une plage de 10-40% en volume du volume total de la couche de surface extérieure,
et dans laquelle une deuxième concentration de particules réfractaires dans une couche
intérieure du produit est dans une plage de 2-4,5% en volume du volume total de la
couche intérieure.
2. Produit métallique composite défini selon la revendication 1, dans lequel la première
concentration de particules réfractaires est de 50-120% en volume supérieure au pourcentage
de volume nominal du matériau réfractaire dans le produit.
3. Produit métallique composite défini selon la revendication 1 ou la revendication 2,
dans lequel le produit comprend une couche de surface extérieure qui s'étend sur moins
de 50% de l'épaisseur radiale du produit à partir de la surface extérieure.
4. Produit métallique composite défini selon l'une quelconque des revendications précédentes,
dans lequel la couche de surface extérieure du produit s'étend sur 1-50 mm à partir
de la surface extérieure du produit.
5. Produit métallique composite défini selon l'une quelconque des revendications précédentes,
dans lequel le métal ferreux est un alliage comprenant l'un quelconque des alliages
suivants :
(a) Acier Hadfield, pour utilisation par exemple dans les manchons de concasseur giratoire,
comprenant :
1,0 - 1,4% poids de C
0,0 - 1,0% en poids de Si,
10 - 15% en poids de Mn,
0,0 - 3,0% en poids de Mo,
0,0 - 5,0% en poids de Cr,
0,0 - 2,0% en poids de Ni,
avec le reste étant du Fe et des impuretés accessoires ;
(b) Acier inoxydable 420C, pour utilisation par exemple dans des manchons d'arbres
dans des pompes à boue, comprenant :
0,3 - 0,5% en poids de C,
0,5 - 1,5% en poids de Si,
0,5 - 3,0% en poids de Mn,
0,0 - 0,5% en poids de Mo,
10 - 14% en poids de Cr,
0,0 - 1,0% en poids de Ni,
avec le reste étant du Fe et des impuretés accessoires ; et
(c) fonte blanche à haute teneur en chrome, comprenant :
1,5 - 4,0% en poids de C,
0,0 - 1,5% en poids de Si,
0,5 - 7,0% en poids de Mn,
0,0 - 1,0% en poids de Mo,
15 - 35% en poids de Cr,
0,0 - 1,0% en poids de Ni,
avec le reste étant du Fe et des impuretés accessoires.
6. Produit métallique composite défini selon l'une quelconque des revendications précédentes,
dans lequel la masse est d'au moins 20 kg.
7. Procédé de coulée par centrifugation d'un produit métallique composite tel que défini
selon l'une quelconque des revendications 1 à 6, le procédé comprenant :
(a) la formation d'une suspension comprenant des particules réfractaires solides dispersées
dans un métal ferreux liquide, les particules réfractaires comprenant 5-50% en volume
du volume total de la suspension, avec les particules réfractaires étant insolubles
à une température de coulée, et avec les particules réfractaires ayant une densité
qui est à moins de 20% de la densité de l'hôte métallique à la température de coulée
; et
(b) verser la suspension dans un moule pour le produit et la coulée par centrifugation
du produit dans le moule par la rotation du moule autour de l'axe après et/ ou durant
le versement de la suspension dans le moule pour obtenir le produit,
les particules réfractaires étant des carbures et/ ou des borures et/ ou des nitrures
d'un ou plusieurs des neuf métaux de transition titane, zirconium, hafnium, vanadium,
niobium, tantale, chrome, molybdène et tungstène, où les particules sont un mélange
chimique, par opposition à un mélange physique, des carbures et/ ou des borures et/
ou des nitrures des métaux de transition.
8. Procédé de coulée par centrifugation d'un produit métallique composite selon la revendication
7, dans lequel les étapes (a) et (b) sont réalisées dans un environnement inerte.
9. Procédé de coulée par centrifugation d'un produit métallique composite tel que défini
selon la revendication 7 ou la revendication 8, dans lequel l'étape (b) comprend la
rotation du moule à un facteur G de 10-120.
10. Procédé de coulée par centrifugation d'un produit métallique composite tel que défini
selon l'une quelconque des revendications 7 à 9 comprenant l'ajout (a) de niobium
ou (b) de deux ou plus parmi le niobium et le titane et le tungstène à une masse fondue
contenant le métal ferreux sous une forme qui produit des particules réfractaires
solides de carbure de niobium qui sont insolubles à une température de coulée et/
ou des particules réfractaires solides d'un mélange chimique de deux ou plus de carbure
de niobium et de carbure de titane et de carbure de tungstène qui sont insolubles
à une température de coulée.
11. Procédé de coulée par centrifugation d'un produit métallique composite tel que défini
selon l'une quelconque des revendications 7 à 10, dans lequel la masse du produit
est d'au moins 20 kg.