CENTRIFUGAL CAST COMPOSITE METAL PRODUCT

Description

[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.

Claims

1. A centrifugally cast composite metal product having an axis of rotational symmetry and an axially extending exterior surface and a mass of at least 5kg and comprising a ferrous metal matrix and 5-50 vol% solid particles of a refractory material 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, the refractory particles having a density that is within 20% of the density of the ferrous metal 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.

2. The composite metal product defined in claim 1, wherein the first concentration of refractory particles is 50-120 vol% higher than the nominal volume percentage of the refractory material in the product.

3. The composite metal product defined in claim 1 or claim 2, wherein the product includes an exterior surface layer that extends less than 50% of the radial thickness of the product from the exterior surface.

4. The composite metal product defined in any one of the preceding claims, wherein the exterior surface layer of the product extends 1-50 mm from the exterior surface of the product.

5. The composite metal product defined in any one of the preceding claims, wherein the ferrous metal is an alloy comprising any one of the following alloys:

(a) Hadfield steel, for use for example in gyratory crusher mantles, comprising:

1.0 - 1.4 wt% C

0.0 - 1.0 wt% Si,

10 - 15 wt% Mn,

0.0 - 3.0 wt% Mo,

0.0 - 5.0 wt% Cr,

0.0 - 2.0 wt% Ni,

with the remainder being Fe and incidental impurities;

(b) 420C stainless steel, for use for example in shaft sleeves in slurry pumps, comprising:

0.3 - 0.5 wt% C,

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; and

(c) high chromium white cast iron, comprising:

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.

6. The composite metal product defined in any one of the preceding claims wherein the mass is at least 20kg.

7. A method of centrifugally casting a composite metal product as defined in any one of claims 1 to 6, the method comprising:

(a) forming a slurry comprising solid refractory particles dispersed in a liquid ferrous metal, the refractory particles comprising 5-50 vol% 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 20% of the density of the metal host at the casting temperature; and

(b) pouring the slurry into a mould for the product and centrifugally casting the product in the mould by rotating the mould about the axis subsequent to and/or during pouring the slurry into the mould to obtain the product,

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.

8. The method of centrifugally casting a composite metal product as defined in claim 7, wherein steps (a) and (b) are carried out under an inert environment.

9. The method of centrifugally casting a composite metal product as defined in claim 7 or claim 8, wherein step (b) comprises rotating the mould at a 10-120 G-Factor.

10. The method of centrifugally casting a composite metal product as defined in any one of claims 7 to 9 comprising adding (a) niobium or (b) two or more than two of niobium and titanium and tungsten to a melt containing the ferrous 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 a casting temperature.

11. The method of centrifugally casting a composite metal product as defined in any one of claims 7 to 10 wherein the mass of the product is at least 20kg.

Ansprüche

1. Zentrifugal gegossenes Verbundmetallprodukt mit einer Rotationssymmetrieachse und einer sich axial erstreckenden Außenfläche und einer Masse von mindestens 5 kg, das eine Eisenmetallmatrix und 5-50 Vol.-% feste Teilchen eines feuerfesten Materials in der gesamten Eisenmetallmatrix umfasst, wobei die feuerfesten Teilchen bei einer Gießtemperatur unlöslich sind, wobei die feuerfesten Teilchen Karbide und/oder Boride und/oder Nitride von einem oder mehr als einem der neun Übergangsmetalle Titan, Zirkonium, Hafnium, Vanadium, Niob, Tantal, Chrom, Molybdän und Wolfram sind, wobei die Teilchen eine chemische Mischung, im Gegensatz zu einer physikalischen Mischung, der Carbide und/oder Boride und/oder Nitride der Übergangsmetalle sind, wobei die feuerfesten Teilchen eine Dichte aufweisen, die innerhalb von 20 % der Dichte des Eisenmetalls bei seiner Gießtemperatur liegt, wobei eine erste Konzentration von feuerfesten Teilchen in einer äußeren Oberflächenschicht des Produkts in einem Bereich von 10-40 Vol.-% des Gesamtvolumens der äußeren Oberflächenschicht liegt, und wobei eine zweite Konzentration von feuerfesten Teilchen in einer inneren Schicht des Produkts in einem Bereich von 2-4,5 Vol.-% des Gesamtvolumens der Innenschicht liegt.

2. Verbundmetallprodukt nach Anspruch 1, wobei die erste Konzentration von feuerfesten Teilchen 50-120 Vol.-% höher ist als der nominale Volumenprozentsatz des feuerfesten Materials im Produkt.

3. Verbundmetallprodukt nach Anspruch 1 oder Anspruch 2, wobei das Produkt eine äußere Oberflächenschicht beinhaltet, die sich weniger als 50 % der radialen Dicke des Produkts von der äußeren Oberfläche erstreckt.

4. Verbundmetallprodukt nach einem der vorhergehenden Ansprüche, wobei sich die äußere Oberflächenschicht des Produkts 1-50 mm von der Außenfläche des Produkts erstreckt.

5. Verbundmetallprodukt nach einem der vorhergehenden Ansprüche, wobei das Eisenmetall eine Legierung ist, die eine der folgenden Legierungen umfasst:

(a) Hadfield-Stahl, zur Verwendung z. B. in Mänteln für Kreiselbrecher, umfassend:

1,0 - 1,4 Gew.-% C

0,0 - 1,0 Gew.-% Si,

10 - 15 Gew.-% Mn,

0,0 - 3,0 Gew.-% Mo,

0,0 - 5,0 Gew.-% Cr,

0,0 - 2,0 Gew.-% Ni,

wobei der Rest Fe und beiläufige Verunreinigungen sind;

(b) Edelstahl 420C, zur Verwendung z. B. in Wellenschutzhülsen in Schlammpumpen, umfassend:

0,3 - 0,5 Gew.-% C,

0,5 - 1,5 Gew.-% Si,

0,5 - 3,0 Gew.-% Mn,

0,0 - 0,5 Gew.-% Mo,

10 - 14 Gew.-% Cr,

0,0 - 1,0 Gew.-% Ni,

wobei der Rest Fe und beiläufige Verunreinigungen sind; und

(c) hochchromhaltiges weißes Gusseisen, umfassend:

1,5 - 4,0 Gew.-% C,

0,0 - 1,5 Gew.-% Si,

0,5 - 7,0 Gew.-% Mn,

0,0 - 1,0 Gew.-% Mo,

15 - 35 Gew.-% Cr,

0,0 - 1,0 Gew.-% Ni,

wobei der Rest Fe und beiläufige Verunreinigungen sind.

6. Metallverbundprodukt nach einem der vorhergehenden Ansprüche, wobei die Masse mindestens 20 kg beträgt.

7. Verfahren zum Schleudergießen eines Verbundmetallprodukts nach einem der Ansprüche 1 bis 6, das Verfahren umfassend:

(a) Bilden einer Aufschlämmung, die in einem flüssigen Eisenmetall dispergierte feste feuerfeste Teilchen umfasst, wobei die feuerfesten Teilchen 5-50 Vol.-% des Gesamtvolumens der Aufschlämmung umfassen, wobei die feuerfesten Teilchen bei einer Gießtemperatur unlöslich sind und wobei die feuerfesten Teilchen eine Dichte aufweisen, die innerhalb von 20 % der Dichte des Metallwirts bei der Gießtemperatur liegt; und

(b) Gießen der Aufschlämmung in eine Form für das Produkt und Schleudergießen des Produkts in die Form durch Drehen der Form um die Achse nach und/oder während des Gießens der Aufschlämmung in die Form, um das Produkt zu erhalten,

wobei die feuerfesten Teilchen Karbide und/oder Boride und/oder Nitride von einem oder mehr als einem der neun Übergangsmetalle Titan, Zirkonium, Hafnium, Vanadium, Niob, Tantal, Chrom, Molybdän und Wolfram sind, wobei die Teilchen ein chemisches Gemisch, im Gegensatz zu einem physikalischen Gemisch, der Karbide und/oder Boride und/oder Nitride der Übergangsmetalle sind.

8. Verfahren zum Schleudergießen eines Verbundmetallproduktes nach Anspruch 7, wobei die Schritte (a) und (b) unter einer inerten Umgebung durchgeführt werden.

9. Verfahren zum Schleudergießen eines Verbundmetallproduktes nach Anspruch 7 oder Anspruch 8, wobei Schritt (b) das Drehen der Form bei einem 10-120 G-Faktor umfasst.

10. Verfahren zum Schleudergießen eines Verbundmetallprodukts nach einem der Ansprüche 7 bis 9, umfassend die Zugabe von (a) Niob oder (b) zwei oder mehr als zwei von Niob und Titan und Wolfram zu einer Schmelze, die das Eisenmetall in einer Form enthält, die feste feuerfeste Teilchen aus Niobcarbid, die bei einer Gießtemperatur unlöslich sind, und/oder feste feuerfeste Teilchen einer chemischen Mischung von zwei oder mehr als zwei von Niobcarbid und Titancarbid und Wolframcarbid, die bei einer Gießtemperatur unlöslich sind, erzeugt.

11. Verfahren zum Schleudergießen eines Verbundmetallproduktes nach einem der Ansprüche 7 bis 10, wobei die Masse des Produktes mindestens 20 kg beträgt.

Revendications

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.

Drawing