Composite Metal Product

Abstract

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

Claims

1. A centrifugally cast composite metal product having an axis of rotational symmetry and a mass of at least 20 kg and comprising a metal host and insoluble solid particles of a refractory material in a non-uniform distribution throughout the host metal, wherein the particles have a density that is within 20% of the density of the metal host at its casting temperature, and wherein the non-uniform distribution of refractory particles comprises a first concentration of particles in an exterior or interior surface layer of the product that is higher than a second concentration of particles in another layer in the product.

2. (canceled)

3. The composite metal product defined in claim 1, wherein the first concentration of refractory particles in the exterior surface layer of the product is in a range of 10-40 vol % of the total volume of the exterior surface layer.

4. The composite metal product defined in claim 1, wherein the second concentration of refractory particles in the other layer of the product is in a range of 2-4.5 vol % of the total volume of the other layer.

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

6. The composite metal product defined in claim 1, wherein the exterior or interior surface layer of the product extends less than 50% of the radial thickness of the product from the exterior or interior surface of the product.

7. The composite metal product defined in claim 1, wherein the exterior or interior surface layer of the product extends 1-50 mm from the exterior or interior surface of the product.

8-9. (canceled)

10. The composite metal product defined in claim 1 having a mass of at least 50 kg.

11. The composite metal product defined in claim 1 having a mass of at least 75 kg.

12. (canceled)

13. The composite metal product defined in claim 1, wherein the refractory particles are carbides and/or borides and/or nitrides of one or more than one transition metal where the particles are a chemical mixture (as opposed to a physical mixture) of the carbides and/or borides and/or nitrides of the transition metals.

14. (canceled)

15. The composite metal product defined in claim 1, wherein the host metal is an alloy comprising any one of the following alloys: (a) Hadfield steel, for use for example in gyratory crusher mantles; (b) 420C stainless steel, for use for example in shaft sleeves in slurry pumps; and (c) high chromium white cast iron.

16. The composite metal product defined in claim 15, wherein the host metal is Hadfield steel 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.

17. The composite metal product defined in claim 15, wherein the host metal is a 420C stainless steel 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.

18. The composite metal product defined in claim 15, wherein the host metal is a 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.

19. The composite metal product defined in claim 1, wherein the host metal a non-ferrous metal.

20. The composite metal product defined in claim 1 comprising a gyratory crusher mantle for a primary, secondary or tertiary crusher.

21. The composite metal product defined in claim 1 comprising a slurry pump shaft sleeve.

22-24. (canceled)

25. The method of centrifugally casting a composite metal product as defined in claim 37, wherein steps (a) and (b) are carried out under an inert environment.

26-27. (canceled)

28. The method of centrifugally casting a composite metal product as defined in claim 37, wherein step (b) comprises rotating the mould at a 10-120 G-Factor.

29-36. (canceled)

37. A method of centrifugally casting a composite metal product having an axis of rotational symmetry and a mass of at least 5 kg and comprising a host metal and a non-uniform dispersion of insoluble solid refractory particles of a refractory material, the method comprising: (a) forming a slurry comprising solid refractory particles dispersed in a liquid host metal, with 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 cause a concentration of insoluble refractory particles at or near an exterior surface or at or near an interior surface of the product that is higher than the concentration of particles elsewhere in the product and obtaining a non-uniform distribution of insoluble solid particles throughout the host metal.

38. A method of centrifugally casting a composite metal product having an axis of rotational symmetry and a mass of at least 5 kg and comprising a host metal and a non-uniform distribution of insoluble solid 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 a casting temperature, with the solid refractory particles being in a range of 5-50 vol % of the total volume of the product, and centrifugally casting the product in a mould by rotating the mould about the axis subsequent to and/or during pouring the slurry into the mould to cause a concentration of insoluble refractory particles at or near an exterior surface or at or near an interior surface of the product that is higher than the concentration of particles elsewhere in the product and obtaining a non-uniform distribution of insoluble solid refractory particles throughout the host metal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0105] 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:

[0106] FIG. 1 is a diagram that illustrates a typical centrifugal casting method;

[0107] FIG. 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;

[0108] FIG. 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;

[0109] FIG. 4 is a graph of hardness versus distance from outer surfaces to inner surfaces of the samples described in relation to FIG. 3;

[0110] FIG. 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;

[0111] FIG. 6 is a graph of hardness versus distance from outer surfaces to inner surfaces of the samples described in relation to FIG. 5;

[0112] FIG. 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;

[0113] FIG. 8 is a graph of hardness versus distance from outer surfaces to inner surfaces of the samples described in relation to FIG. 7;

[0114] FIG. 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;

[0115] FIG. 10 is an optical image of a cross-section of the outer layer of the cross-section of the sample shown in FIG. 9 after etching the sample;

[0116] FIG. 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

[0117] FIG. 12 is a graph of hardness versus distance from outer surfaces to inner surfaces of sections of the sample described in relation to FIG. 11.

[0118] FIG. 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

[0119] FIG. 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

[0120] FIG. 1 was sourced from the internet and illustrates in diagrammatic form the basic steps in a centrifugal casting method.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] Refractory particle property requirements may include: [0126] Density greater than or less than the host ferrous metal. [0127] Hardness in excess of 15 GPa. [0128] Diameter less than 500 microns, preferably less than 50 microns. [0129] 10-80 vol % refractory particles present in the hard surface layer. [0130] 5-50 vol %, typically 5-40 vol %, more typically 5-40 vol %, refractory particles in the composite metal product.

[0131] The composite metal products produced by the centrifugal casting process of the invention include by way of example only the following products:

[0132] 1. Slurry pump shaft sleeves [0133] Stainless steel cylinders [0134] Size: ranging from 25-400 mm diameter, 10-50 mm wall thickness and 2000 mm long. [0135] Outer surface layer, 1-10 mm thick, containing a high concentration of hard, insoluble refractory particles.

[0136] 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.

[0137] Centrifugally casting a slurry pump shaft sleeve in accordance with the invention permits the manufacture of a cylinder approximately 2000 am 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.

[0138] 2. Outer Surface of Gyratory Crusher Mantles

[0139] 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 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.

[0140] 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.

[0141] 3. White Cast Irons

[0142] 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.

[0143] 4. Breaker Bars, Hammer Tips, Ground Engaging Tools

[0144] 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.

[0145] Experimental Work

[0146] 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.

[0147] 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.

[0148] In the experimental work fourteen cylinders were centrifugally cast in a horizontally arranged centrifugal casting arrangement.

[0149] 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. [0150] Four A301 cylinders (A05 host metal+5 vol % NbC particles of the total volume). [0151] Four A303 cylinders (A05 host metal+12 vol % NbC particles of the total volume). [0152] Four A304 cylinders (A05 host metal+17 vol % NbC particles of the total volume). [0153] One A352 cylinder (C21 host metal+10 vol % NbC particles of the total volume). [0154] One A323 cylinder (A49 host metal+15 vol % NbC particles of the total volume).

[0155] 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 alloys are as follows, with the amounts of each element in wt %:

TABLE-US-00001 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

[0156] Twelve A05 steel-based cylinders with different nominal chemical compositions were centrifugally cast at various rotational speeds (RPM).

[0157] 1.1. Centrifugal casting of four A301 cylinders (A05 host metal+5 vol % NbC particles)

[0158] 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-US-00002 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

[0159] Each 400 mm cylinder was sectioned into three rings of roughly 280 mm, 20 mm and 100 mm in length. The 20 mm-thick rings were used for inspection and metallurgical analysis.

[0160] 1.1.1. Metallurgical Examination

[0161] Samples were prepared from each 20 mm-thick ring by cutting through the thickness at two locations roughly 15 mm 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.

[0162] 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. FIG. 2 is a SEM image of a section of one of the samples. FIG. 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.

[0163] FIG. 3 comprises optical images of cross-sections of samples from cylinders 37628, 37629, 37630, and 37655.

[0164] FIG. 3a shows that the sample from cylinder 37628 had a NbC particle-rich outer layer of about 2 mm 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 3-5 mm thick. The layers 2-4 form an inner region having a lower concentration of NbC particles than the outer layer.

[0165] FIG. 3b shows that the sample from cylinder 37629 had a similar layered (i.e. banded) structure, but with more layers than shown in FIG. 3a. The high concentration NbC particle outer layer (identified by the numeral 1 in the Figure) is about 2 mm 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 3-4 mm thick.

[0166] Cylinder 37630 was cast at the highest rotation speed. FIG. 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.

[0167] Cylinder 37655 was cast at the same rotation speed as cylinder 37628, but was cast with a 5 mm thicker wall thickness. FIG. 3d shows that the NbC particle-rich layer in the sample from cylinder 37655 was about 3.5 mm 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.

[0168] 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 100 magnification. The values shown in Table 2 are the averages of multiple measurements.

TABLE-US-00003 TABLE 2 NbC particles in outer and inner layers NbC-rich layer ID thickness mm vol % NbC Inner layer 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

[0169] 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.

[0170] 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.

[0171] 1.1.2. Hardness and Ferrite Measurements

[0172] Vickers hardness traverse tests with a load of 10 kg 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 1 mm intervals to finish at the inside diameter (ID) of the sample.

[0173] Table 3 shows the average hardness and ferrite readings for each of the two regions. Traverse hardness profiles are shown in FIG. 4.

TABLE-US-00004 TABLE 3 Hardness and ferrite measurements Ferrite Reading Sample Region HV10 (% 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

[0174] It is evident from Table 3 and FIG. 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%.

[0175] 1.1.3. Summary [0176] 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. [0177] 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. [0178] 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. [0179] 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. [0180] 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. [0181] 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. [0182] 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%.

[0183] 1.2. Centrifugal Casting of Four A303 Cylinders (A05 Host Metal+12 Vol % NbC Particles)

[0184] 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-US-00005 TABLE 4 Job codes and dimension of cylinders containing 12 vol % 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

[0185] Each 400 mm cylinder was sectioned into three rings of roughly 280 mm, 20 nm and 100 mm in length. The 20 mm-thick rings were used for inspection and metallurgical analysis. Samples were prepared and tested using the same methodology described in section 1.1 above.

[0186] FIG. 5 comprises optical images of samples from cylinders 37631, 37632, 37633, and 37636.

[0187] It is evident from FIG. 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.

[0188] 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.

[0189] 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 100 magnification. The values shown in Table 5 are the averages of multiple measurements.

TABLE-US-00006 TABLE 5 Thickness of outer layer and average vol % NbC particles NbC layer NbC layer thickness volume fraction Sample OD (mm) ID (mm) (mm) (%) RPM 37631 130 89 6 25.098 922 37632 130 95 7 26.027 1104 37633 130 90 Min. 5, 28.989 1280 Max. 7 37863 130 81 5 28.45 925

[0190] Vickers hardness traverse tests with a load of 10 kg 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 1 mm intervals to finish at the inside diameter (ID) of the sample.

[0191] Table 6 shows the average hardness and ferrite readings for each of the two regions. Traverse hardness profiles are shown in FIG. 6.

TABLE-US-00007 TABLE 6 Hardness and Ferrite measurements Ferrite Reading Sample Region HV10 (% 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

[0192] It is evident from Tables 5 and 6 and FIGS. 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.

[0193] 1.3. Centrifugal Casting of Four A304 Cylinders (A05 Host Metal+17 Vol % NbC Particles)

[0194] 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 920 rpm, cylinder 37635 cast at 1100 rpm and cylinder 37636 cast at 1280 rpm).

[0195] FIG. 7 comprises optical images of cross-sections of samples from cylinders 37634 and 37635.

[0196] It is evident from FIG. 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).

[0197] 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.

[0198] The test work indicated that the thicknesses of the NbC particle-rich outer layers in the samples for cylinders 37634, 37635 and 37636 were 12 mm, 13 mm and 15 mm, respectively.

[0199] 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.

[0200] 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 FIG. 8.

TABLE-US-00008 TABLE 7 Hardness and Ferrite readings Ferrite Reading Sample Region HV10 (% magnetic) 37634 Outer 664 12.7 Inner 546 10.9 37635 Outer 661 11.7 Inner 513 10.1

[0201] It is evident from Table 7 and FIGS. 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.

[0202] 1.4. Centrifugal Casting of an A352 Cylinder (C21 Host Metal+10 Vol % NbC Particles)

[0203] One A352 cylinder was centrifugally cast from a C21 host metal with 10 vol % NbC particles. Samples were prepared and tested as described above.

[0204] FIG. 9 comprises an optical image of a cross-section of a sample of the A352 cylinder.

[0205] It is evident from FIG. 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.

[0206] 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.

[0207] As shown in FIG. 9, the NbC-rich layer is a 20 mm thick layer, 50% of the total radial thickness of the sample. It was found that the sample contained about 25 vol % of NbC particles.

[0208] After etching, three sub-layers of the 20 mm thick NbC particle-rich outer layer were identified, and are shown in FIG. 10. FIG. 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.

[0209] 1.5. Centrifugal Casting of an A323 Cylinder (A49 Host Metal+15 Vol % NbC Particles)

[0210] One A323 cylinder was centrifugally cast from a A49 host metal and 15 vol % NbC particles. Samples were prepared and tested as described above.

[0211] 1.5.1. Metallurgical Examination

[0212] FIG. 11 comprises an optical image of a cross-section of a sample of the A323 cylinder. It is evident from FIG. 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.

[0213] 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.

[0214] As is evident from FIG. 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.

[0215] The depth of the NbC particle-rich outer layer was found to be consistent along the circumference at about 7-8 mm, 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.

[0216] 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.

[0217] 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.

[0218] 1.5.2. Hardness & Ferrite

[0219] Vickers hardness traverse tests with a load of 10 kg 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 1 mm 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 FIG. 12.

TABLE-US-00009 TABLE 8 Hardness and Ferrite measurements Ferrite Reading Sample Region HV10 (% magnetic) 4719CC-A Outer 455 22.9 Inner 357 21.2 4719CC-B Outer 526 19.1 Inner 355 17.6

[0220] 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.

[0221] With reference to FIG. 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

[0222] 2.4. Functionally Graded Materials

[0223] 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-US-00010 TABLE 9 Summary of centrifugally cast A300-family alloys FMMCC Bulk NbC-rich Layer Host Metal NbC G-force Thickness NbC # Code Desc. (vol %) RPM (G) (mm) (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 15-12 24

[0224] 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%.

[0225] 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 FIGS. 13 and 14, respectively.

[0226] As can be seen from the Figures:

[0227] (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 FIG. 13); and

[0228] (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 FIG. 14.

[0229] 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.

[0230] 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.

[0231] 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.

[0232] 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.

[0233] In addition, the foregoing describes only some embodiments of the invention(s), and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.

[0234] Furthermore, invention(s) have been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention(s). Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment.

[0235] By way of example, whilst the embodiments of the invention described above comprise different types of steel (such as a stainless steel or an austenitic manganese steel) as the host metal, the invention is not limited to this type of host metal and extends to any suitable host metal. By way of example, the host metal may contain wherein the host metal contain any one or more of the transition metal elements Ti, Cr, Zr, Hf, V, Nb, and Ta.

[0236] 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.

[0237] By way of further example, whilst the embodiments of the invention described above focus on NbC particles which have a density that is higher than that of the host metal, whereby there are higher concentrations of the refractory particles towards exterior surfaces of the composite metal products, the invention also extends to embodiments in which the refractory particles have a density that is lower than that of the host metal, whereby there are higher concentrations of the refractory particles towards an interior surface of the composite metal product.

[0238] 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.