CN105899311B

CN105899311B - Composite metal product

Info

Publication number: CN105899311B
Application number: CN201480071708.4A
Authority: CN
Inventors: 汤心虎; K.F.多尔曼
Original assignee: Weir Minerals Australia Ltd
Current assignee: Weir Minerals Australia Ltd
Priority date: 2013-12-30
Filing date: 2014-12-30
Publication date: 2020-07-14
Anticipated expiration: 2034-12-30
Also published as: WO2015100472A1; BR112016015487B1; AU2014374832A1; PL3089839T3; EP3089839A1; CA2934084C; EP3089839B1; AU2014374832B2; EA033878B1; BR112016015487A2; EA201691326A1; CL2016001685A1; EP3089839A4; CA2934084A1; PE20160906A1; ZA201603623B; CN105899311A; US20170022588A1

Abstract

A centrifugally cast composite metal product having an axis of rotational symmetry and a mass of at least 5kg, the centrifugally cast composite metal product comprising a matrix metal and insoluble solid refractory particles of refractory material in a non-uniform distribution throughout the metal matrix. The density of the particles is within 30% of the density of the matrix metal at its casting temperature.

Description

Composite metal product

Technical Field

The present disclosure relates to a method of centrifugal casting of a composite metal product, typically of a mass in the range 20 to 5000kg, which contains a main metal matrix, typically an iron-based metal matrix, and includes an outer surface layer of hard insoluble refractory particles, nominally 1 to 20mm thick, for increased wear resistance.

The disclosure also relates to centrifugally cast composite metal products.

Background

In the context of the present disclosure, the term "refractory particles" is understood to include particles of one or more than one of the following nine transition metals, high melting point carbides and/or nitrides and/or borides, dispersed in a hard matrix metal: titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten, the matrix metal acting as the binding phase. Each of these refractory particles is a particle of refractory material and is referred to herein as "refractory material". Typically, the matrix metal is an iron-based metal alloy. The matrix metal may also be a nickel-based and cobalt-based superalloy.

In the context of the present disclosure, the term "insoluble" is understood to mean, in the sense of each layer, that the refractory material is insoluble in the matrix metal at the casting temperature (typically in the range of 1200 to 1600 ℃ for iron-based matrix metals). May have limited solubility. However, the refractory particles are substantially different from the matrix metal in terms of the casting process stages and negligible elemental separation in the refractory particles present in the solidified product.

Disclosure of Invention

In a first aspect, embodiments of a centrifugally cast composite metal product having an axis of rotational symmetry and a mass of at least 5kg, typically at least 10kg, and more typically at least 20kg, and comprising a metal matrix and insoluble solid particles of refractory material in a non-uniform distribution throughout the matrix metal, wherein the density of the particles is within 30%, typically within 20%, of the density of the metal matrix at its casting temperature, are disclosed.

The composite metal product comprises two distinct regions throughout the solidified material, namely a region of insoluble solid particles of refractory material and a region of matrix metal at least substantially free of refractory particles, wherein the refractory particles are substantially different from the matrix metal with respect to negligible elemental separation in the refractory particles present at the casting temperature and in the solidified product.

The inventive feature that the solid particles of refractory material are insoluble in the metal matrix at the casting temperature and after solidification distinguishes the present invention from prior art solutions, such as JPS632864, which adds iron alloys (a) Fe-W, (b) Fe-Mo and (c) Fe-Cr to a matrix iron-based alloy, forming (a) tungsten carbide, (b) molybdenum carbide and (c) chromium carbide, respectively, which are soluble to different degrees in the matrix metal at conventional casting temperatures. Thus, in these systems, the volume percentage of hard insoluble refractory carbides in the microstructure is significantly reduced, and the dissolved tungsten and/or molybdenum and/or chromium may adversely and variably affect the physicochemical properties of the matrix metal at room temperature (e.g., reducing toughness and differential reaction to heat treatment).

In some embodiments, the refractory particles can have a higher density than the matrix metal, in which case there will be a higher concentration of refractory particles near the outer surface of the composite centrifugally cast metal product.

In some embodiments, the refractory particles can have a lower density than the matrix metal, in which case there will be a higher concentration of refractory particles near the inner surface of the composite centrifugally cast metal product.

In some embodiments, the non-uniform distribution of refractory particles can include a first concentration of refractory particles in an outer or inner surface layer of the product that is higher than a second concentration of refractory particles in another layer of the product.

In some embodiments, the first concentration of refractory particles in the outer surface layer of the product may be at least 50 vol%, typically at least 60 vol%, typically at least 70 vol%, and more typically from 50 vol% to 120 vol% higher than the nominal refractory volume percentage in the product.

In some embodiments, the first concentration of refractory particles in the product outer surface layer may be at least 10%, typically at least 20%, typically less than 40%, and more typically in the range of 10% to 40% of the total volume of the outer surface layer.

In some embodiments, the second concentration of refractory particles in the further layer of product may be in the range of from 2 vol% to 4.5 vol%, typically in the range of from 2 vol% to 3.5 vol% of the total volume of the further layer.

In some embodiments, a product outer or inner surface layer may extend from the outer or inner surface by at least 5%, typically at least 20%, more typically at least 25% of the radial thickness of the product.

In some embodiments, a product outer or inner surface layer may extend from the outer or inner surface by less than 50%, typically at least 40%, more typically less than 30%, and more typically less than 20% of the radial thickness of the product.

In some embodiments, the outer or inner surface layer of the product may extend at least 10mm, typically at least 20mm, typically less than 50mm, typically from 1mm to 50mm, and more typically from 5mm to 20mm from the outer or inner surface.

In some embodiments, the first concentration of refractory particles in the outer surface layer of the product may range from at least 5 vol%, typically at least 10 vol%, typically from 5 vol% to 90 vol%, and more typically from 10 vol% to 40 vol% of the total volume of the particles.

In some embodiments, the total concentration of refractory particles in the product may be at least 5 vol%, typically at least 10 vol%, and more typically in the range of 5 vol% to 50 vol% of the total volume of the product.

In some embodiments, the total concentration of refractory particles in the product can range from 5 vol% to 40 vol% of the total volume of the product.

In some embodiments, the total concentration of refractory particles in the product can be in the range of 5 vol% to 20 vol% of the total volume of the product.

In some embodiments, the refractory particles may be carbides and/or borides and/or nitrides of one or more than one transition metal, where the particles are chemical mixtures of transition metal carbides and/or borides and/or nitrides as opposed to physical mixtures. In other words, with respect to carbides, the refractory particles may be of the type described as: (M)₁,M₂) C or (M)₁,M₂,M₃) Type C, wherein "M" is a transition metal. One example discussed further below is (Nb, Ti, W) C.

The base metal can be any suitable base metal. The matrix metal may be an iron-based alloy, such as stainless steel or austenitic manganese steel, or cast iron. The matrix metal may be a non-ferrous based matrix metal such as titanium or a titanium alloy.

In some embodiments, the matrix metal may be an alloy comprising any one of the following alloys:

(a) hadfield high manganese steel for use in gyratory crusher caps, for example;

(b) such as 420C stainless steel for mud pump shaft casings;

(c) high chromium white cast iron.

As used in some embodiments, hadfield high manganese steels may include:

1.0-1.4wt％C，

0.0-1.0wt％Si，

10-15wt％Mn，

0.0-3.0wt％Mo，

0.0-5.0wt％Cr，

0.0-2.0wt％Ni，

the remainder being iron and incidental impurities.

As used in some embodiments, the 420C stainless steel may include:

0.3-0.5wt％C，

0.5-1.5wt％Si，

0.5-3.0wt％Mn，

0.0-0.5wt％Mo，

10-14wt％Cr，

0.0-1.0wt％Ni，

the remainder being iron and incidental impurities.

As used in some embodiments, the high chromium white cast iron may include:

1.5-4.0wt％C，

0.0-1.5wt％Si，

0.5-7.0wt％Mn，

0.0-1.0wt％Mo，

15-35wt％Cr，

0.0-1.0wt％Ni，

the remainder being iron and incidental impurities.

The composite metal product may be any product suitable for centrifugal casting and requiring high wear resistance and high toughness properties. Examples of such products include gyratory crusher casings for primary, secondary or tertiary crushers, slurry pump shaft sleeves, rollers used in crushers (including large diameter rollers on the order of 1m in diameter and with radial wall thicknesses in the range of 300 to 400 mm), and other components of crushers and pumps.

In a second aspect, embodiments are disclosed wherein the composite metal product of the first aspect may be a gyratory crusher shell of a primary, secondary or tertiary crusher.

In a third aspect, embodiments are disclosed wherein the composite metal product of the first aspect may be a mud pump shaft casing.

In a fourth aspect, embodiments are disclosed of a method of centrifugally casting a composite metal product having an axis of rotational symmetry and a mass of at least 5kg, typically at least 10kg, and more typically at least 20kg, and comprising a heterogeneous dispersion of insoluble solid refractory particles of a matrix metal and a refractory material, the method comprising:

(a) forming a slurry comprising solid refractory particles dispersed in a liquid matrix metal, wherein the refractory particles comprise from 5 to 50 vol%, typically from 5 vol% to 40 vol%, of the total volume of the slurry, wherein the refractory particles are insoluble at the casting temperature, and wherein the refractory particles have a density within 30%, typically within 20%, of the density of the metal matrix at its casting temperature; and

(b) pouring the slurry into a mold for the metal product and centrifugally casting the product in the mold to provide a non-uniform distribution of insoluble solid particles throughout the matrix metal.

In some embodiments, step (a) may include forming refractory particles in situ in the molten matrix metal and dispersing the particles in the molten form of the matrix metal.

In some embodiments, step (a) may include adding refractory particles to the molten form of the metal matrix.

In some embodiments, steps (a) and (b) may be performed in an inert environment, such as in an inert atmosphere.

In some embodiments, step (b) may comprise preparing the mold by forming an inert environment within the mold.

In some embodiments, step (b) may include rotating the mold about an axis after or during pouring of the slurry into the mold so that the concentration of refractory particles at or near the outer surface of the product or at or near the inner surface of the product is higher than the concentration of particles elsewhere in the product.

In some embodiments, step (b) may comprise rotating the mold by a factor of 10-120G, wherein the G-factor (G-factor) is the centrifugal force exerted on the rotating body divided by gravity.

In some embodiments, step (b) may comprise rotating the mold at a peripheral speed of 2.5 to 25 m/s.

In some embodiments, step (b) may comprise rotating the die for a sufficient time to achieve a non-uniform distribution of the solid particles throughout the matrix metal.

In some embodiments, step (b) may comprise rotating the mold until the metal matrix solidifies.

In some embodiments, step (b) may comprise pouring the slurry into a mold at a casting temperature in the range of 1200 ℃ -.

In some embodiments, the method may include selecting production parameters to form the slurry of step (a) having a desired flowability for processing in step (b).

The production parameters may include any one or more of particle size, reactivity, density and solubility of the refractory material, as described in international patent application PCT/AU2011/000092(WO2011/094800) filed in the name of the present applicant. The disclosure in this international application is incorporated herein by cross-reference. The density and solubility of the refractory material are discussed below.

The density of the particulate refractory material, as compared to the density of the liquid matrix metal, is one of the parameters of consideration in the process of the present disclosure for controlling the dispersion of the refractory particles in the hot matrix metal.

The matrix iron-based liquid metal matrix had a nominal density of 6.9g/cc at 1400 ℃. When refractory particles in the form of tungsten carbide (WC) particles having a density of 15.7g/cc at 25 ℃ are added to a matrix iron-based metal to form a slurry, the WC particles will sink to the bottom of the slurry. When refractory particles in the form of titanium carbide (TiC) particles having a density of 4.8g/cc at 1400 ℃ are added to the same matrix iron-based metal to form a slurry, the TiC particles will be suspended on top of the slurry. The refractory particles in the form of niobium carbide have a density of 7.7g/cc at 1400 c, which is quite close to the density of 6.9g/cc of the matrix iron-based liquid metal, and are less prone to the aforementioned segregation in the liquid matrix iron-based metal than TiC or WC.

TiC has a density of 4.9g/cc at 25 ℃ and dissolves completely in NbC having a density of 7.8g/cc at 25 ℃. Thus, refractory particles having a density in the range of 4.9-7.8g/cc at 25 ℃ can be obtained by selecting (Nb, Ti) C particles having the desired niobium and titanium contents.

Tungsten carbide (WC) has a density of 15.7g/cc at 25 ℃ and is mostly soluble in NbC, TiC and (Nb, Ti) C. Thus, refractory particles having a density in the range of 4.8-15.7g/cc at 25 ℃ can be obtained by selecting (Nb, Ti, W) C particles having the desired contents of niobium, titanium and tungsten.

All refractory particles described by the formula (Nb, Ti, W) C are insoluble in the liquid iron-based matrix metal at casting temperatures in the range of 1200-1600 ℃.

Niobium carbide and titanium carbide have similar crystal structures and are isomorphous.

From the above it is evident that selecting the desired ratio of Nb to Ti in the (Nb, Ti) C compound or the desired ratio of Nb to Ti to W in the (Nb, Ti, W) C compound results in a refractory material having a desired density within 20% of the density of the iron-based matrix metal.

For all intents and purposes, the addition of insoluble (i.e., having minimal solid dissolution in the matrix liquid metal) refractory particles to produce centrifugally cast castings of composite metal products in accordance with the methods of the present disclosure produces products exhibiting very similar physicochemical properties as the matrix metal and having significantly improved wear resistance due to the presence of a high volume percentage of hard refractory particles in the microstructure of the matrix metal in a controlled dispersion.

For example, at elevated temperatures, the solubility of refractory materials in the (Nb, Ti, W) C form in liquid matrix metals of the following form is negligible (<0.3 wt%): (a) liquid hadfield high manganese steel, (b) liquid 420C stainless steel, and (C) liquid high chromium white cast iron. (Nb, Ti, W) C of the desired density is added to the three matrix metal alloys followed by centrifugal casting of the composite metal product and standard heat treatment processes for each metal matrix to produce a microstructure in the product comprising a dispersion of predominantly niobium-titanium-tungsten carbides in the matrix metal that is substantially free of niobium, titanium and tungsten, i.e. negligible transition metal segregation into the refractory slurry particles of liquid matrix metal.

Thus, the effect of the particulate refractory material on the physical (e.g., melting point) and chemical (e.g., reaction to thermal treatment) properties of the matrix metal is negligible.

In addition, applicants have discovered, among other things, that providing a composite metal product having a microstructure comprising niobium carbide particles and/or a chemical (as opposed to physical) mixture of two or more of niobium carbide, titanium carbide, and tungsten carbide dispersed in a matrix metal matrix greatly improves the wear resistance of the hard metal material without adversely affecting the contribution that other alloying elements have on other properties of the composite metal product.

In addition and as noted above, applicants have found, inter alia, that the density of the chemical mixture particles of two or more of niobium carbide, titanium carbide and tungsten carbide can be adjusted to a sufficient degree relative to the density of the matrix metal forming the composite metal product matrix. This opportunity for density control is an important finding with respect to centrifugally cast castings of hard metal materials.

In particular, by virtue of this finding, it is possible to produce centrifugally cast castings having a controlled uneven distribution of the composite metal product, i.e. particles segregated in various parts of the casting. This is important for the end use of the casting where a high concentration of wear resistant particles is desired near the surface of the hard metal casting.

Furthermore, the applicant has found that castings forming composite metal products such as the following do not have a significant adverse effect on the corrosion resistance and toughness of the ferrous material in the base metal: the casting of the composite metal product comprises niobium carbide particles and/or particles of a chemical mixture of two or more of niobium carbide, titanium carbide and tungsten carbide dispersed in a matrix metal forming the matrix of the composite metal product in a range of from 5 to 50 vol%, typically from 5 to 40 vol%, more typically from 5 to 20 vol%, based on the total volume of the composite metal product. Thus, the present disclosure makes it possible to achieve the wear resistance of the composite metal product without losing other desirable material properties.

Accordingly, in a fifth aspect, there is provided a method of centrifugally casting a composite metal product having an axis of rotational symmetry and a mass of at least 5kg and comprising insoluble solid refractory particles of a matrix metal and a non-uniformly distributed refractory material, the method comprising: adding (a) niobium or (b) two or more of niobium, titanium and tungsten to a melt comprising a matrix metal in the form of: producing solid refractory particles of niobium carbide that are insoluble at the casting temperature, and/or a chemical mixture of two or more of niobium carbide, titanium carbide and tungsten carbide that are insoluble at the casting temperature, wherein the solid refractory particles are in the range of 5 to 50 vol%, typically 5 to 40%, more typically 5 to 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 matrix metal.

The terms "chemical mixture of niobium carbide and titanium carbide" and "niobium/titanium carbide" are understood hereinafter to be similar. Furthermore, the term "chemical mixture" is understood in the present context to mean that niobium carbide and titanium carbide are not present in the mixture as single metal carbide particles, but as particles of niobium/titanium carbide, (Nb, Ti) C.

The terms "niobium carbide and chemical mixture of titanium carbide and tungsten carbide" and "niobium carbide/titanium/tungsten carbide" are understood hereinafter to be similar. Furthermore, the term "chemical mixture" is understood in the present context to mean that niobium carbide and titanium carbide and tungsten carbide are not present in the mixture as single metal carbide particles, but as particles of niobium carbide/titanium/tungsten, (Nb, Ti, W) C.

Niobium carbide, titanium carbide and tungsten carbide each have a Vickers hardness of about 25Gpa, which is about 10Gpa greater than the hardness of chromium carbide (nominally 15 Gpa). Thus, composite metal products having a microstructure comprising 5 to 50 vol%, typically 5 to 40 vol%, more typically 5 to 20 vol% niobium carbide and/or niobium/titanium/tungsten carbide have excellent wear resistance properties. Applicants have recognized that niobium carbide, titanium carbide and tungsten carbide, and niobium/titanium carbide and niobium/titanium/tungsten carbide are substantially chemically inert to the other components in the composite metal product, such that these components will provide the product with the properties selected for it. For example, the addition of chromium to cast iron alloys still produces chromium carbide and provides corrosion resistance.

Niobium, titanium and tungsten may be added to the melt of the matrix metal to form a slurry in any suitable form, bearing in mind the need to form insoluble solid particles of niobium carbide and/or niobium/titanium/tungsten carbide in the composite metal product.

For example, the method may include adding niobium in the form of iron-niobium to the melt, such as iron-niobium particles. In this case, the iron-niobium dissolves in the melt and the free niobium and carbon produced chemically combine to form an insoluble solid niobium carbide in the melt.

The method may further include adding niobium to the melt as elemental niobium.

The method may further include adding niobium and titanium as iron-niobium-titanium to the melt.

The method may further include adding niobium, titanium, and titanium as iron-niobium-titanium to the melt.

The method may further include adding niobium in the form of niobium carbide particles to the melt.

The method may further include adding niobium and titanium in the form of insoluble solid niobium/titanium carbide particles to the melt.

The method may further comprise adding niobium and titanium and tungsten in the form of insoluble solid niobium carbide/titanium/tungsten particles to the melt.

In each of these cases, the solidified metal alloy may be formed from a slurry of niobium carbide and/or niobium carbide/titanium/tungsten particles suspended in the melt. If the weight fraction of these carbides in the melt slurry is too high, the fluid properties of the slurry may be adversely affected such that a poor casting of the melt may result.

The insoluble niobium/titanium carbide solid particles may be of the formula (Nb)_x,Ti_y) Any suitable chemical mixture of C.

The insoluble niobium carbide/titanium/tungsten solid particles may be of the general formula (Nb)_x,Ti_y,W_z) Any suitable chemical mixture of C. For example, niobium carbide/titanium/tungsten may be (Nb)_0.25,Ti_0.50,W_0.25)C。

Niobium and/or titanium and/or tungsten may be added to the melt to produce insoluble niobium carbide and/or niobium/titanium carbide/tungsten solid particles in the range of 12-33 wt% of the total weight of the cast product.

Niobium and/or titanium and/or tungsten may be added to the melt to produce insoluble niobium carbide and/or niobium/titanium/tungsten carbide solid particles in the range of 12-25 wt% of the total weight of the cast product.

The amount of niobium carbide and/or niobium carbide/titanium/tungsten particles in the microstructure of the solidified hard metal material may depend on the system.

The applicant is particularly concerned with solid hard composite metal products comprising a matrix metal in the form of an iron-based alloy, such as iron-based alloys described as high chromium white cast iron, stainless steel and austenitic high manganese steel (such as hadfield steel). For iron-based alloys, the amount of insoluble solid particles of refractory material in the form of niobium carbide and/or niobium/titanium/tungsten carbide may be in the range of 5 to 50 vol%, typically 5 to 40 vol%, more typically 5 to 20 vol% of the total volume of the cast composite metal product in the final composite metal product.

The particle size of the niobium carbide and/or niobium/titanium/tungsten carbide may be in the range of 1-150 μm in diameter.

The method may comprise agitating the slurry with an inert gas or magnetic induction or any other suitable means to disperse the dispersed particles of niobium carbide and/or niobium/titanium/tungsten carbide in the slurry.

The method may include adding niobium carbide particles and/or niobium carbide/titanium/tungsten particles to a melt of a matrix iron-based metal under inert conditions (such as argon blanketing) to reduce the degree of oxidation of the niobium carbide and/or niobium carbide/titanium/tungsten when added to the melt.

The method may further comprise adding iron-niobium and/or iron-titanium and/or iron-tungsten and/or iron-niobium-titanium-tungsten to the melt under inert conditions (such as argon blanketing) to reduce the degree of oxidation of niobium and/or titanium and/or tungsten when added to the melt.

In the case where the cast composite metal product requires niobium/titanium/tungsten carbide particles, the method further comprises pre-melting the iron-niobium and iron-titanium and iron-tungsten and/or iron-niobium-titanium-tungsten under inert conditions, forming a liquid phase that is a homogeneous chemical mixture of iron, niobium, titanium and tungsten, and allowing the chemical mixture to solidify. The chemical mixture may then be processed as desired, for example by crushing to the desired particle size, and then added to the melt (comprising carbon) under inert conditions. Iron, niobium, titanium, and tungsten dissolve in the melt and chemically combine with carbon to form niobium/titanium/tungsten carbide in the melt.

Other aspects, features and advantages will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, the principles of the invention disclosed.

Drawings

Although any other form may fall within the scope of the method and resulting composite metal product as described in the summary, specific embodiments of the method and resulting composite metal product will now be described by way of example and with reference to the accompanying drawings, in which:

fig. 1 is a view illustrating a general centrifugal casting method;

FIG. 2 is a partial SEM image of one of the samples from a centrifugally cast test cylinder "37863" (A05 matrix metal +5 vol% NbC particles) produced in experimental work associated with the invention;

FIG. 3 includes cross-sectional views of optical images of samples from centrifugally cast test cylinders "37628", "37629" and "37630" (A05 matrix metal +5 vol% NbC particles) produced in experimental procedures associated with the invention;

FIG. 4 is a graphical representation of hardness versus distance from the outer surface to the inner surface of the sample described with respect to FIG. 3;

FIG. 5 includes optical images of sample sections from centrifugally cast test cylinders "37631", "37632" and "37636" (A05 matrix metal +12 vol% NbC particles) produced in experimental procedures associated with the invention;

FIG. 6 is a graphical representation of hardness versus distance from the outer surface to the inner surface of the sample described with respect to FIG. 5;

FIG. 7 includes optical images of cross-sections of samples from centrifugally cast test cylinders "37634" and "37635" (A05 matrix metal +17 vol% NbC particles) produced in experimental procedures associated with the invention;

FIG. 8 is a graphical representation of hardness versus distance from the outer surface to the inner surface of the sample described with respect to FIG. 7;

FIG. 9 includes optical images of cross-sections from samples of centrifugally cast test cylinder A352(C21 matrix metal +10 vol% NbC particles) produced in experimental procedures associated with the invention;

FIG. 10 is an optical image of an outer layer cross-section of the sample shown in FIG. 9 after etching of the sample;

FIG. 11 is an optical image of a cross-section of a sample of centrifugally cast test cylinder A323 cylinder (A49 matrix metal +15 vol% NbC particles); and

FIG. 12 is a graphical representation of hardness versus distance from the outer surface to the inner surface of the sample profile described with respect to FIG. 11;

FIG. 13 is a schematic representation of NbC particle enriched outer layer thickness versus the nominal vol% NbC in the total composition of a centrifugally cast cylinder of A05 matrix metal + NbC particles; and

figure 14 is a schematic of the vol% of NbC in the NbC particle-enriched outer layer relative to the nominal vol% of NbC in the total composition of a centrifugally cast cylinder of a05 matrix metal + NbC particles.

Detailed description of the embodiments

Fig. 1 is derived from the internet and illustrates in diagrammatic form the basic steps in a centrifugal casting method.

These centrifugal casting steps include forming a molten melt and pouring the melt into a suitable mold and rotating the mold (in the case of the arrangement shown in this figure) about a vertical axis at a desired rotational rate to form a cast product.

Under another arrangement, such as the one used to carry out the experimental operations described below, the casting mold is placed horizontally and the mold is rotated about a horizontal axis.

In the context of the present disclosure, typically the molten melt comprises hard insoluble solid refractory particles in a matrix metal and the cast product is a composite metal product, typically having a mass in the range of 5kg to 5000kg, having an iron-based metal matrix (matrix metal) and comprising an outer surface layer of hard insoluble solid refractory particles unevenly distributed in the iron-based metal matrix, in particular having a nominal thickness of 1-20mm, which refractory particles provide wear resistance at the surface layer.

The actual centrifugal casting conditions may be selected in any given case based on the desired characteristics of the actual product to be cast. Casting conditions include, for example, the rate and time of rotation of the mold, cooling conditions, and conditions under which the casting is conducted, for example, in an inert atmosphere.

The refractory particle performance requirements may include:

density greater or less than the matrix iron-based metal.

Hardness exceeding 15 GPa.

A diameter of less than 500 microns, preferably less than 50 microns.

10-80 vol% refractory particles are present in the hard surface layer.

Refractory particles in the composite metal product are from 5 to 50 vol%, typically from 5 to 40 vol%, more typically from 5 to 40 vol%.

The composite metal product produced by the centrifugal casting method of the present invention includes only the following products (illustrative):

1. slurry pump shaft sleeve

● stainless steel cylinder

● size: a diameter in the range of 25-400mm, a wall thickness in the range of 10-50mm and a length of 2000 mm.

● outer surface layer, 1-10mm thick, comprising a high concentration of insoluble hard insoluble refractory particles.

The prior art includes hard-face welding of stainless steel cylinders to obtain a tungsten carbide surface layer of approximately 1mm thickness. The hard facing layer then requires grinding/machining to achieve a smooth finish.

Centrifugally casting a slurry pump shaft sleeve according to the present invention allows the manufacture of a cylinder of approximately 2000mm in length and with a desired smooth hard surface layer in one casting operation. In addition, the long cylinder may be cut to produce a large number of shaft sleeves in the 60 to 300mm range in length.

2. Outer surface of gyratory crusher mantle

The standard composition of a gyratory crusher mantle is austenitic high manganese steel (hadfield steel). The initial hardness of hadfield steel is approximately 200 brinell Hardness (HB), the surface layer of the steel product hardens to approximately 550HB in use, while the inside remains lower hardness and extremely high toughness. The yield strength of the hadfield steel with a hardness of 200HB is about 1/3 for the tensile strength. Severe plastic deformation may occur in use before article hardening to 550HB occurs. As a result, the crusher mantle wears out rapidly and undergoes excessive plastic deformation in the early stages of operation. All previous attempts to improve the initial hardness and yield strength of hadfield steels have always resulted in unacceptable loss of toughness and a high risk of catastrophic splitting in service.

Centrifugally casting a hadfield steel crusher shell according to 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 casting blank provides a more wear resistant material with minimal loss of toughness.

3. White cast iron

Centrifugal casting of high chromium white cast iron containing refractory particles produces a composite metal product having a surface layer containing a high concentration of refractory particles for improved wear resistance.

4. Grinding rod, hammer head, ground engaging tools (ground engaging tools)

Centrifugal casting of grinding rods, hammer head tips, ground working tools from high chromium white cast iron containing refractory particles produces a surface layer containing a high concentration of refractory particles for improved wear resistance.

Experimental work

In order to study the invention, the applicant carried out a lot of experimental work on specific refractory particles, i.e. NbC particles, in different iron-based matrix metals.

In particular, experimental work investigated the effect of NbC particle vol%, wall thickness and centrifugal force on NbC-rich zones in centrifugally cast products.

In experimental work, fourteen cylinders were centrifugally cast in a horizontally placed centrifugal casting apparatus.

Fourteen cylindrical shaft sleeves with different concentrations of NbC particles and iron-based matrix metal were centrifugally cast, machined, and then tested as described briefly below.

Four a301 cylinders (a05 matrix metal +5 vol% NbC particles based on total volume).

Four a303 cylinders (a05 matrix metal +12 vol% NbC particles based on total volume).

Four a304 cylinders (a05 matrix metal +17 vol% NbC particles based on total volume).

One a352 cylinder (C21 matrix metal +10 vol% NbC particles based on total volume).

An a323 cylinder (a49 matrix metal +15 vol% NbC particles based on total volume).

A05 is a eutectic high Cr cast iron, C21 is 420C stainless steel, and A49 is a hypoeutectic high Cr cast iron. The nominal composition of the iron-based alloys a05, C21 and a49 is as follows, the amounts of the elements being given in wt%:

alloy (I)	Cr	Mn	C	Ni	Si	Fe
							A05	27	2.0	3.0		0.5	Balance weight
C21
		14	2.0	0.5	1.0	1.0	Balance weight
A49								28	1.5	1.5	2.0	1.5	Balance weight

1. Results and discussion

Twelve cylinders based on a05 steel with different nominal compositions were centrifugally cast at different rotational speeds (RPM).

1.1. Centrifugal casting of four A301 cylinders (A05 matrix metal +5 vol% NbC particles based on total volume)

Four cylinders containing 5 vol% NbC particles in a eutectic high Cr cast iron matrix metal were centrifugally cast at different rotational speeds or centrifugal forces. The casting temperature is in the range of 1400 ℃ to 1500 ℃. The density difference between the NbC particles and the matrix metal at the casting temperature is approximately 12%. The cylinder dimensions and casting conditions are listed in table 1.

TABLE 1 Cylinder size and casting conditions comprising 5 vol% NbC particles

Task number	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

Each 400mm cylinder is divided into three rings of approximately 280mm, 20mm and 100mm in length. A 20mm thick ring was used for inspection and metallurgical analysis.

1.1.1. Examination of metallurgy

The samples were prepared from 20mm thick rings each, by cutting a section through the thickness and forming a ring at two locations approximately 15mm apart. Each cut is made perpendicular to the outer and inner circumference of the ring. The width of the sample decreases from the outer surface to the inner surface. The samples were mounted, lapped and polished according to standard metallurgical procedures, and then etched with Acidified Ferric Chloride (AFC) for metallurgical inspection. The microstructure of the sample was examined by scanning electron microscopy. Also, optical stereo microscopy is used for macroscopic inspection of samples.

Analysis of the samples from the cylinders confirmed that the cast microstructure in each case comprised the a05 eutectic high Cr cast iron matrix metal and solid NbC particles that were not uniformly distributed throughout the matrix metal. Fig. 2 is an SEM image of a cross section of one of the samples. Figure 2 shows the non-uniform distribution of NbC particles in the matrix metal. The figure shows that NbC is undetectable in the matrix metal. More specifically, it was found that NbC particles were insoluble in the matrix metal at the casting temperature and in the cast cylinder.

Fig. 3 is an optical image of a sample cross-section from cylinders "37628", "37629", "37630", and "37655".

Figure 3a shows that the sample from cylinder "37628" has an NbC particle-enriched outer layer with a thickness of about 2 mm. Inside the outer layer, there are three layers numbered 2-4 in the figure. There is a boundary between the layers. Each layer is about 3-5mm thick. Layers 2-4 form an inner region having a lower concentration of NbC particles than the outer layer.

Fig. 3b shows that the sample from cylinder "37629" has a similar layered (e.g., ribbon-like) structure, but with more layers than in fig. 3 a. The outer layer (indicated by the number 1 in the figure) with a high concentration of NbC particles was about 2mm thick and NbC particles were evenly distributed throughout the sample. The outer layer 1 and the innermost layer (indicated by the numeral 6 in the figure) are the most distinct, while the layers between them (i.e. the layers 2-5 in the figure) are very similar to each other in appearance, but still are different layers separated by a border. The microstructures of

layers

1 and 6 were found to be very different from each other and from the microstructures of layers 2-5. The microstructures of layers 2-5 were found to be very similar to each other. Each layer 1-6 has a thickness of about 3-4 mm.

The cylinder "37630" was cast at the highest rotational speed. Figure 3c shows the sample having three layers. The casting had the lowest concentration of NbC particles in the inner layer compared to the other three cylinder samples. The high rotational speed allowed more NbC particles to reach the outer layer, resulting in the thickest layer of NbC particles for all castings.

The casting "37655" was cast at the same rotational speed as the cylinder "37628", but with a wall thickness of 5mm greater. Figure 3d shows that the NbC particle-enriched layer thickness in the sample from cylinder "37655" was about 3.5mm, which is greater than the thickness in the sample from cylinder "37628". This indicates that the thicker wall results in a thicker zone of enriched NbC particles even with the same rotational speed.

(a) The volume fraction of NbC particles in the NbC particle-enriched outer layer and (b) the low NbC particle concentration inner layer was calculated from SEM images of different regions in the layer at 100 magnifications. The values shown in table 2 are the average of a number of measurements.

TABLE 2 NbC particles at the outer and inner layers

From table 2, it is apparent that the rotation speed during casting has an effect on the NbC particle enriched outer layer of the casting cylinder. Samples from drum "37630", cast at the highest speed, had the highest layer thickness and the highest volume fraction of NbC particles. The sample from cylinder "37629", cast at the second highest speed, had a near volume fraction of NbC, but a thickness of almost half the thickness of the sample "37630" layer. Comparing the samples from cylinders "37628" and "37655" shows that despite the same rotational speed, if the casting wall thickness is greater (i.e., more material), the NbC particle-rich outer layer and its volume fraction are also greater.

Furthermore, the presence of NbC particles in the inner layer of non-enriched NbC particles for all four castings was of similar level, collectively described as the internal region of each sample. Most NbC particles observed in this internal region are of a typical "chinese script" morphology. A small number of spherical and dendritic NbC particles were also observed.

1.1.2. Hardness and ferrite measurements

A Vickers hardness transverse test (hardnessreverse test) loaded with 10kg was performed on the polished surface of each sample. The measurements started at the Outer Diameter (OD) of each sample, then passed through the thickness of the sample at 1mm intervals, and ended at the Inner Diameter (ID) of the sample.

Table 3 shows the average hardness and ferrite readings for each of the two zones. The transverse stiffness profile is shown in fig. 4.

TABLE 3 hardness and ferrite measurements

As is apparent from table 3 and fig. 4, the NbC particle-enriched outer layer of each sample is significantly harder than the inner layer region of the sample, with the highest hardness value typically at the outer layer surface of each sample, and the hardness decreases uniformly from the outer surface to about 8mm, and then remains substantially constant throughout the remainder of the sample. In addition, ferrite measurements of the four castings showed a general tendency for the NbC particles to enrich the outer layer, i.e., have higher ferrite measurements than the layer forming the inner region. The difference in ferrite content is small with the NbC particle enriched outer layer in the range from 13 to 16% and the inner region in the range from 9 to 10%.

1.1.3. Summary of the invention

All four a301 centrifugal castings (a05 matrix metal +5 vol% NbC particles) exhibited NbC segregation, resulting in a high NbC particle concentration in the outer layer of each sample.

All four castings exhibited layers below the NbC particle-rich outer layer that differed from each other at the boundary. Each casting having a different number of layers.

The thickness and hardness of the enriched layer of NbC particles and the volume fraction of NbC particles in the centrifugally cast cylindrical outer layer depend on different casting parameters, including the casting rotation rate and wall thickness.

Samples from cylinders "37628" and "37655" were cast at the same rotational speed but with different material qualities, resulting in different sizes. Sample "37655" had a slightly thicker NbC particle-enriched outer layer and it contained a greater number of different band-shaped layers through the thickness of the sample.

The sample of cylinder "37629" is similar to the sample of cylinder "37628", although it was cast at a higher rotation rate. The faster rotation rate did not affect the thickness of the enriched outer layer of NbC particles, but it did slightly affect the volume fraction of NbC particles in the outer layer.

The sample of cylinder "37630" was cast at the fastest rotational speed, and this is directly reflected in several features. The sample had the thickest enriched layer of NbC particles and the highest volume fraction of NbC particles in the outer layer. Therefore, the hardness of the outer layer is the highest record in this set of cylinders.

Ferrite measurements of the four castings showed a general tendency for NbC particles to enrich the outer layer, i.e. have higher ferrite measurements than the layer forming the inner zone. The difference in ferrite content is small, with the NbC particle enriched outer layer having ferrite in the range of 13 to 16% and the inner region in the range of 9 to 10%.

1.2. Centrifugal casting of four A303 cylinders (A05 matrix Metal +12 vol% NbC particles)

The four cylinders were cast under the same conditions as the four cylinders described in section 1.1 above, with the same matrix metal (a05), but a 12% higher total NbC volume fraction. The cylinder dimensions and rotational speeds are listed in table 4.

TABLE 4 mission number and size of cylinders containing 12 vol% NbC

Task numbering	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

Each 400mm cylinder is divided into three rings of approximately 280mm, 20mm and 100mm in length. A 20mm thick ring was used for inspection and metallurgical analysis. Samples were prepared and tested using the same methods described in section 1.1 above.

Fig. 5 is an optical image of the sample from cylinders "37631", "37632", "37633" and "37636".

As is evident from fig. 5, as in the case of the cylinder containing a low volume fraction of NbC particles described in section 1.1 above, the NbC particles form a non-uniform distribution in the matrix metal across the casting thickness, and the outer layer of the sample has a higher concentration of NbC particles.

Similarly, SEM analysis confirmed that NbC was undetectable in the matrix metal as in the case of the cylinders containing low volume fractions of NbC particles described in section 1.1 above. More specifically, it was found that NbC particles were insoluble in the matrix metal at the casting temperature and in the casting cylinder.

The volume fraction of NbC particles in the NbC particle-enriched outer layer and the thickness of the outer layer were calculated from SEM images of different regions in the layer at 100 magnifications. The values shown in table 5 are the average of a number of measurements.

TABLE 5 average% by vol of skin thickness and NbC particles

Vickers hardness traverse tests were carried out on the polished surface of each sample under a load of 10 kg. The measurements started at the Outer Diameter (OD) of each sample, then passed through the thickness of the sample at 1mm intervals, and ended at the Inner Diameter (ID) of the sample.

Table 6 shows the average hardness and ferrite readings for each of the two zones. The transverse stiffness profile is shown in fig. 6.

TABLE 6 hardness and ferrite measurements

As is evident from tables 5 and 6 and fig. 5 and 6, the same basic results were obtained for the higher volume percentage of cylinder a303 as cylinder a301 described in section 1.1 above.

1.3. Centrifugal casting of four A304 cylinders (A05 matrix Metal +17 vol% NbC particles)

Four a304 cylinders were centrifugally cast using the same conditions as cylinders a301 and a303 described in sections 1.1 and 1.2 above, respectively, with the same matrix metal a05, 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 (cylinder "37634", cast at 920rpm, cylinder "37635", cast at 1100rpm, cylinder "37636", cast at 1280 rpm) were tested.

Fig. 7 includes optical images of cross sections of the sample from cylinders "37634" and "37635".

As is evident from fig. 7, as in the case of the low volume fraction cylinders of NbC particles described in sections 1.1 and 1.2 above, the NbC particles formed a non-uniform distribution in the matrix metal across the casting thickness, and the outer layer of the sample had a higher concentration of NbC particles. The cross-section shows an outer layer (or region) enriched in NbC particles and an inner region (which may include multiple layers separated by boundaries) of low NbC particle content.

In addition, SEM analysis confirmed that NbC was undetectable in the matrix metal as in the case of the low volume fraction cylinders of NbC particles described in sections 1.1 and 1.2 above. More specifically, it was found that NbC particles were insoluble in the matrix metal at the casting temperature and in the casting cylinder.

The test work showed that the NbC particle enriched outer layer thicknesses of the samples of cylinders "37634", "37635" and "37636" were 12mm, 13mm and 15mm, respectively.

The volume concentration of NbC particles in the outer layer of these samples was 28% cylinder "37634", 25% cylinder "37635", and 29% cylinder "37636".

Table 7 shows the average hardness and ferrite readings for each of the inner and outer regions of the samples from cylinders "37634" and "37635". The transverse stiffness profile is shown in fig. 8.

TABLE 7 hardness and ferrite readings

As is evident from table 7 and fig. 7-8, the high volume percentage of cylinder a304, as described for cylinders a301 and a303 in sections 1.1 and 1.2 above, gave the same basic results.

Centrifugal casting of A352 cylinders (C21 matrix Metal +10 vol% NbC particles)

An A352 cylinder was centrifugally cast from matrix metal C21 and 10 vol% NbC pellets.

Samples were prepared and tested as described above.

Fig. 9 includes an optical image of a cross-section of a cylinder a352 sample.

As is evident from fig. 9, as in the case of the other test cylinders described above, the NbC particles formed a non-uniform distribution in the matrix metal through the casting thickness, and the outer layer of the sample had a higher concentration of NbC particles.

In addition, SEM analysis confirmed that NbC was undetectable in the matrix metal as in the case of the other test cylinders described above. More specifically, it was found that NbC particles were insoluble in the matrix metal at the casting temperature and in the casting cylinder.

As shown in fig. 9, the high bC enrichment layer was 20mm thick, which was 50% of the total radial thickness of the sample. It was found that the sample contained about 25 vol% NbC particles.

After etching, three 20mm thick sublayers of an enriched outer layer of NbC particles were marked and are shown in fig. 10. Figure 10 shows that directional solidification occurs across the sublayer during centrifugal casting. It was found that the cylindrical structure contributes significantly to the wear resistance of the casting.

Centrifugal casting of A323 cylinders (A49 matrix metal +15 vol% NbC particles).

An A323 cylinder was centrifugally cast from matrix metal A49 and 15 vol% NbC pellets. Samples were prepared and tested as described above.

1.5.1. Examination of metallurgy

Fig. 11 includes an optical image of a section of an a323 cylindrical sample. As is evident from fig. 11, as in the case of the other test cylinders described above, the NbC particles formed a non-uniform distribution in the matrix metal throughout the thickness of the casting, and the outer layer of the sample had a higher concentration of NbC particles.

Furthermore, SEM analysis confirmed that NbC was undetectable in the matrix metal as in the case of the other test cylinders described above. More specifically, it was found that NbC particles were insoluble in the matrix metal at the casting temperature and in the casting cylinder.

As is evident from fig. 11, the NbC particle-enriched outer layer is a very different band along the entire outer edge of the circle. This is visible on both the macroscopic and microscopic level.

The depth of the enriched outer layer of NbC particles was found to be uniform along the circumference, at about 7-8mm, i.e., about 25-30% of the radial thickness of the sample. The volume fraction of NbC of the outer layer was also found to be consistent in the examination region, about 28-31% of the total volume of the outer layer.

In addition to the NbC concentration, the microstructures of the outer and inner layers were found to have other significant differences. The NbC particles in the NbC particle-enriched outer layer are mostly round without any sharp edges, whereas those of the inner layer have a variety of shapes, including from round to very pointed dendritic shapes. The matrix structure of the enriched outer layer of NbC particles and other layers can be distinguished primarily by the presence/absence of a "chinese script" type of NbC particle structure in the austenite dendrites of the matrix. This NbC structural type was found to be widely present in the inner layer, but it was hardly present in the NbC particle-enriched outer layer. This results in different thermal properties of the NbC particle-enriched outer layer and the inner layer.

A very unique microstructure was found at the boundary of the NbC particle-rich outer and inner layers. The microstructure is characterized by NbC particles that are predominantly cross-shaped (dendritic). Some of the particles of this region resemble a mixture of rounded and dendritic shapes.

1.5.2. Hardness & ferrite

Vickers hardness traverse tests were carried out on the polished surfaces of both samples under a load of 10 kg. The measurements started at the outermost edge of the sample, then passed through the thickness of the casting at 1mm intervals, and ended at the innermost edge of the sample. Table 8 shows the average hardness and ferrite readings for the NbC particle enriched outer and inner layers of each sample. The NbC particle-enriched outer layer of each sample is described in the table as the "outer zone" and the inner layer of each sample is described in the table as the "inner zone". The transverse stiffness profile is shown in fig. 12.

TABLE 8 hardness and ferrite measurements

For each sample, a higher concentration of NbC particles in the enriched outer layer (outer zone) of NbC particles naturally results in a higher hardness than the inner zone. The hardness results correlate with volume fraction results, with the higher volume fraction of NbC in sample 4719CC-B giving a higher hardness result than sample 4719 CC-A. There was no significant difference in ferrite content between the two regions of each sample.

Referring to fig. 12, the hardness traversal test shows that for both samples, the hardness is highest at the outermost edge of the sample (e.g., the first test point in both tests), and the hardness is about 425Vickers at the boundary of the two zones. The inner (bulk) region maintains a consistent hardness throughout most of its thickness.

2. Summary of the invention

2.4. Functional graded material

In the test work outlined above, a series of NbC particles containing a volume percent of matrix metal (a05, a49, and C21) were centrifugally cast and examined. The results are summarized and shown in table 9.

TABLE 9 summary of centrifugally cast group A300 alloys

The volume fraction of refractory particles in the NbC particle-rich outer layer of the casting is up to 31% of the volume of the outer layer. Furthermore, high rotation speeds increase the vol% of NbC, but the effect is usually very small. The volume percent of NbC particles varied from 2-6% in the interior region of each casting.

The relationship between the thickness of the NbC particle-enriched outer layer and the total vol% of NbC in the product composition, and the relationship between the vol% of NbC in the NbC particle-enriched outer layer and the total vol% of NbC in the product composition were analyzed, and the results are presented in fig. 13 and 14, respectively.

As can be seen from the figure:

(a) it has been found that the thickness of the NbC-rich outer layer of each centrifugally cast cylinder is directly dependent on the nominal bulk NbC content in the product composition (see fig. 13); and

(b) it has been found that the final NbC content in the NbC particle-enriched outer layer of each centrifugally cast cylinder depends on the nominal bulk NbC content in the product composition, which for a particular a05 matrix metal tends to stabilize at a maximum content of about 28-30% and 50-120 vol% higher than the nominal volume percentage of refractory material in the entire product spanning the range of nominal NbC vol% covered in fig. 14.

It was also found that the thickness of the enriched outer layer of NbC particles and the concentration of NbC particles in each centrifugally cast cylinder was independent of the cast G-factor in the range of 50-102.

In the foregoing description of the preferred embodiments, specific terminology is 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 "back", "inner" and "outer", "upper", "lower", "upper" and "lower", and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

In this specification, the word "comprising" is to be understood as meaning "open", i.e. "including", and is therefore not limited to the meaning "closed", i.e. "consisting of … … only". The corresponding meaning applies to the words "comprising" and "including" s, when the corresponding words are present.

Furthermore, the foregoing describes only some embodiments of the invention and modifications, improvements, additions and/or alterations may be made thereto without departing from the scope and spirit of the disclosed embodiments, which are to be interpreted as illustrative and not in a limiting sense.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. Likewise, various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Moreover, each individual feature or component of any given collection can constitute additional embodiments.

By way of example, although the embodiments of the invention described above include different types of steel as the matrix metal (such as stainless steel or austenitic manganese steel), the invention is not limited to this type of matrix metal and extends to any suitable matrix metal. For example, the matrix metal may comprise any one or more of the transition metal elements Ti, Cr, Zr, Hf, V, Nb and Ta.

By way of further example, while the embodiments of the invention described above have focused on NbC as the insoluble solid particulate material of the refractory material, the invention extends to other refractory materials.

By way of further example, while the embodiments of the invention described above have focused on NbC particles having a density higher than that of the matrix metal, and thus having a higher concentration of refractory particles toward the outer surface of the composite metal product, the invention also extends to embodiments having refractory particles having a density lower than that of the matrix metal, and thus having a higher concentration of refractory particles toward the inner surface of the composite metal product.

By way of further example, although the above experimental operations were performed on a centrifugally cast cylinder, it will be readily appreciated that the present invention is not limited to this particular shape casting and extends to any shape product that can be centrifugally cast.

Claims

1. A centrifugally cast composite metal product having a rotational axis and an axially extending outer surface and a mass of at least 5kg and comprising an iron metal matrix and 5-50 vol% insoluble solid particles of refractory material throughout the iron metal, wherein:

(i) the refractory particles are carbides and/or borides and/or nitrides of a transition metal; or

(ii) The refractory particles are carbides and/or borides and/or nitrides of more than one transition metal, wherein the particles are chemical mixtures of carbides and/or borides and/or nitrides of the more than one transition metal, the chemical mixtures being different from the physical mixtures,

the refractory particles have a density that is within 20% of the density of the ferrous metal at its casting temperature, wherein the refractory particles are formed in radial layers of the product and comprise an outer surface layer, and wherein there is a non-uniform distribution of refractory particles, the non-uniform distribution comprising a first concentration of particles in one layer of the product being higher than a second concentration of particles in another layer of the product.

2. The composite metal product of claim 1, wherein the first concentration of refractory particles is in the outer surface layer of the product and is in the range of 10-40 vol% of the total volume of the outer surface layer.

3. A composite metal product according to claim 1 or 2, wherein the second concentration of refractory particles in the further layer of the product is in the range of 2 to 4.5 vol% of the total volume of the further layer.

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

5. The composite metal product of claim 1, wherein the outer surface layer of the product extends less than 50% of the radial thickness of the product from the outer surface of the product.

6. The composite metal product according to claim 1, wherein the outer surface layer of the product extends 1-50mm from the outer inner surface of the product.

7. The composite metal product of claim 1, wherein the first concentration of refractory particles is in the product outer surface layer and is in the range of 5-90% of the total volume of the particles.

8. A composite metal product according to claim 1, wherein the total concentration of refractory particles in the product is in the range of from 5 to 50 vol% of the total volume of the product.

9. A composite metal product according to claim 1, wherein the total concentration of refractory particles in the product is in the range of from 5 to 40 vol% of the total volume of the product.

10. The composite metal product of claim 1 having a mass of at least 20 kg.

11. The composite metal product of claim 1 having a mass of at least 50 kg.

12. The composite metal product of claim 1 having a mass of at least 75 kg.

13. The composite metal product of claim 1, wherein the refractory particles have a density that is within 15% of the density of the iron metal at its casting temperature.

14. The composite metal product of claim 1 wherein the iron metal is an iron-based alloy.

15. The composite metal product of claim 1 wherein the iron metal is stainless steel or austenitic manganese steel or cast iron.

16. The composite metal product of claim 14, wherein the iron-based alloy comprises any one of the following alloys:

(a) hadfield high manganese steel for gyratory crusher mantles;

(b) 420C stainless steel for a mud pump shaft sleeve;

(c) high chromium white cast iron.

17. The composite metal product of claim 14, wherein the iron-based alloy is a hadfield manganese steel comprising:

1.0-1.4wt％C，

0.0-1.0wt％Si，

10-15wt％Mn，

0.0-3.0wt％Mo，

0.0-5.0wt％Cr，

0.0-2.0wt％Ni，

the remainder being iron and incidental impurities.

18. The composite metal product of claim 14, wherein the iron-based alloy is a 420C stainless steel comprising:

0.3-0.5wt％C，

0.5-1.5wt％Si，

0.5-3.0wt％Mn，

0.0-0.5wt％Mo，

10-14wt％Cr，

0.0-1.0wt％Ni，

the remainder being iron and incidental impurities.

19. The composite metal product of claim 14, wherein the iron-based alloy is a high chromium white cast iron comprising:

1.5-4.0wt％C，

0.0-1.5wt％Si，

0.5-7.0wt％Mn，

0.0-1.0wt％Mo，

15-35wt％Cr，

0.0-1.0wt％Ni，

the remainder being iron and incidental impurities.

20. The composite metal product of claim 1 comprising a gyratory mill shell of a primary, secondary or tertiary crusher.

21. The composite metal product of claim 1 comprising a mud pump shaft sleeve.

22. The composite metal product of claim 1, wherein the density of the particles is within 30% of the density of iron metal at its casting temperature.

23. A method of centrifugally casting a composite metal product having a rotational axis and an axially extending outer surface and a mass of at least 5kg and comprising a heterogeneous dispersion of insoluble solid refractory particles of a ferrous metal matrix and a refractory material, the method comprising:

(a) forming a slurry comprising solid refractory particles dispersed in a liquid iron metal, wherein:

(i) the refractory particles are carbides and/or borides and/or nitrides of transition metals; or

wherein the refractory particles comprise 5 to 50 vol% of the total volume of the slurry, the refractory particles are insoluble at the casting temperature, and the refractory particles have a density within 20% of the density of the metal matrix at its casting temperature; and

(b) pouring the slurry into a mold for the product and centrifugally casting a mass of at least 5kg of product in the mold by: rotating the mold about an axis after and/or during pouring of the slurry into the mold to cause refractory particles to form in radial layers of the product and to obtain a non-uniform distribution of insoluble solid particles throughout the matrix metal, wherein the concentration of insoluble refractory particles in one layer of the product is higher than the concentration of particles elsewhere in the product.

24. The method of centrifugally casting a composite metal product as recited in claim 23 wherein steps (a) and (b) are conducted in an inert environment.

25. A method of centrifugally casting a composite metal product as claimed in claim 23 or claim 24 comprising preparing the mold by creating an inert environment in the mold.

26. A method of centrifugally casting a composite metal product as recited in claim 23 wherein step (b) comprises rotating the mold by a factor of 10-120G.

27. The method of centrifugally casting a composite metal product as recited in claim 23 wherein step (b) includes rotating the mold at a peripheral speed of 2.5-25 meters per second.

28. The method of centrifugally casting a composite metal product as recited in claim 23 wherein step (b) comprises rotating the mold until the matrix metal solidifies.

29. The method of centrifugally casting a composite metal product as recited in claim 23 wherein step (b) comprises rotating the mold for a time sufficient to achieve a non-uniform distribution of solid particles throughout the matrix metal.

30. The method of centrifugally casting a composite metal product as recited in claim 23 wherein step (b) comprises pouring the slurry into a mold at a casting temperature in the range of 1200-1650 ℃.

31. The method of centrifugally casting a composite metal product as recited in claim 23 wherein step (b) comprises pouring the slurry into a mold at a casting temperature in the range of 1350 ° and 1550 ℃.

32. The method of centrifugally casting a composite metal product as recited in claim 23 wherein the mass of the composite metal product is at least 20 kg.

33. The method of centrifugally casting a composite metal product as recited in claim 23 wherein the mass of the composite metal product is at least 50 kg.

34. A method of centrifugally casting a composite metal product as recited in claim 23 wherein the mass of the composite metal product is at least 75 kg.

35. The method of centrifugally casting a composite metal product of claim 23, comprising: adding (a) niobium or (b) two or more of niobium, titanium and tungsten to a melt comprising an iron metal in the form of: resulting in solid refractory particles of niobium carbide that are insoluble at casting temperatures and/or solid refractory particles of a chemical mixture of two or more of niobium carbide, titanium carbide and tungsten carbide that are insoluble at casting temperatures.