WO2015033359A1

WO2015033359A1 - Chemical carriers and processes for producing locally alloyed cast items

Info

Publication number: WO2015033359A1
Application number: PCT/IS2014/050008
Authority: WO
Inventors: Ingolfur Thorbjornsson; Jon Thor Thorgrimsson
Original assignee: Malmsteypa Thorgrims Jonssonar; Nyskopunarmidstod Islands
Priority date: 2013-09-03
Filing date: 2014-09-03
Publication date: 2015-03-12

Abstract

The invention provides chemical carriers and processes to enhance cast iron items locally, by introducing such chemical carriers that enhance local properties through a local alloy where desired. The carriers can have different composition and generally comprise a carrier base structure of a suitable base composition, and the carrier can further comprise one or more external surface layers deposited on or into the original surface of the base and of a different composition than the base, to deliver desired chemicals and provide desired properties locally. By the introduction of carriers, gradient zones are obtained surrounding the carriers that show superior strength and increased strength as compared to both the bulk cast iron material and the material of the carrier base.

Description

Chemical carriers and processes for producing locally alloyed cast items

FIELD OF INVENTION

The present invention relates to cast metal objects and in particular from from cast iron such as ductile cast iron, and objects that require local properties such as high wear resistance. The invention provides chemical carriers that are used to introduce desired local properties in such objects.

TECHNICAL BACKGROUND AND PRIOR ART Objects made from high alloyed or heat treated wear resistant materials are used in many fields in various heavy duty equipment, such as in manufacturing equipment, heavy industry machinery, vehicles, vessels, etc. It may be desired to have certain high strength properties only locally, to maintain ductility, machinability and fracture toughness and/or to reduce overall cost by reducing amount of costly alloy additives as well as lowering the environmental impact of heavy metals and maintaining ease of recyclability. The art discloses processes for making objects with local strengthening and examples of such objects.

DE 102004047850 discloses a method for producing a cast iron object, the method comprising placing one or more thin-walled metal inserts near the surface of a mold and casting from molten metal an object, wherein the insert has dissolved to enhance the strength of surface regions of the object.

US 5,052,464 discloses methods for casting objects with an improved surface layer by a process involving mixing ceramic particles with a metal powder and molding the mixture with a binder, and placing the molded mixture on the internal wall of a mold into which molten metal is poured, forming an object with a surface layer.

US 6,443,211 discloses a method for forming light-weight composite metal castings incorporating metalurgically bonded inserts, the method comprising coating an insert with a first layer and a second layer and casting, such that the second layer melts while leaving at least a portion of the first layer as diffusion barrier. WO 2009081420 discloses processes for producing cast iron objects comprising placing metal alloy inserts into a mold which is filled with iron melt, after the object solidifies it is subjected to an austenization process. Further methods and means to introduce and control local properties in cast items would be appreciated in the art.

SUMMARY OF INVENTION The present invention provides chemical carriers, processes to enhance cast metal items locally and cast items made by such processes, by introducing in cast items chemical carriers that enhance local properties through local alloying where desired. The carriers can have variable chemical composition and generally comprise a carrier base structure of a suitable base composition and one or more surface layers deposited on or into the original surface(s) (primary surface) of the carrier base and have a different composition than the carrier base, to deliver desired chemicals and provide desired properties locally in the cast item.

It is appreciated that by the introduction of chemical carriers according to the invention, gradient zones are obtained radially surrounding the carriers, that show superior wear resistance and increased strength as compared to both the bulk cast or ductile iron material and the material of the carrier base. This is the result of material dispersing from the carrier into the melt, and chemical components from the melt entering the surface and interior of the carrier, and material from the surface layers dispersed within the gradient region, to create a continuous gradient boundary with beneficial properties. It is feature of the present invention that the surface layers are arranged and adhered on the chemical carrier such that substance from the liquid cast melt will reach the primary surface of the carrier base, to ensure efficient wetting of the carrier base with the melt. In other words, the surface layer(s) are suitably porous, microscopically, to allow the melt to penetrate through the layer and come in contact both with the particles of the adhered surface layer(s) and the primary surface of the carrier. Thus, the surface layer(s) must not be so dense and thick as to prevent efficient wetting of the carrier.

In a first aspect, the invention provides a process for introducing local properties in a cast item comprising : providing a chemical carrier comprising a carrier base structure, wherein the carrier comprises one or more surface layers on the carrier base, placing said chemical carrier in a desired position within in a mold for casting said locally alloyed item, wherein the carrier is placed inside the cavity of the mold to be filled with the cast melt, such the carrier will become fully emerged and embedded. Cast metal melt is poured in the mold to fill the cavity in order to cast the item, the melt having a desired suitable temperature to partially melt said carrier. Then the cast metal melt is allowed to cool, to solidify the partially melted chemical carrier and the cast item with the chemical carrier embedded in a desired location under the surface of the cast item (sub-surface location). Another aspect sets forth a cast item with desired local properties, the item comprising an embedded chemical carrier as described herein comprising a carrier base and one or more surface layer on said carrier base. The term surface layer in this context also encompasses layers added by diffusion process into and/or under the surface of the base. The chemical carriers are placed within the mold for casting the item prior to the casting such that chemicals from the carrier and surface layers are distributed in the casting process radially along a gradient extending from said carrier and/or such that chemicals extend along a gradient into the carrier, providing a functional gradient zone surrounding and enclosing the chemical carrier inside the cast item.

Yet a further aspect provides a chemical carrier for introducing local properties in a cast item, comprising a carrier base structure, configured to be placed in a mold for casting said cast item such that the carrier will be fully enclosed within the cast item (in a subsurface location). The carrier has one or more surfaces with a surface layer arranged thereon with a chemical composition which is different than the composition of the carrier base structure, and from which layer(s) material disperses during casting of said cast item within the cast melt, to create a gradient distribution of said material extending from the surface of the carrier into said alloy item.

By the processes and chemical carriers provided herein it is possible to create objects with greatly enhanced local properties where functional gradient zones created by the chemical carriers enhance strength while substantially maintaining ductility of the bulk material of the items, thus making items with local properties that are different from the properties of the bulk material or the materials of the carrier, such as items with lower wear rate, than for either material itself.

BRIEF DESCRIPTION OF FIGURES Figure 1 : Cross-section view of a cast item of the invention (2C-5 specimen).

Figure 2 : A three-micrograph composite that shows a cross-section of the 2C-5 specimen. Figure 3 : The figure combines results from XEDS, hardness testing and a

micrograph for a cast item (2B-2 specimen). The graph shows the distribution of Cr and Ni following a cross-section through the insert, FGZ and the ductile iron bulk material and the corresponding hardness measurements (the diamond marks show the location of the hardness measurements).

Figure 4: SEM in-lens picture showing the carbide distribution in the FGZ-i

interface.

Figure 5 : (a) SEM in-lens image of the FGZ of the 2B-2 specimen; (b) SEM image of the same and the distribution of Fe, Cr, and Ni along the right-most (vertical) line in (b) and vertical line in (a); (c) the XEDS maps of Cr, Ni, and Fe along the rightmost line in (b).

Figure 6: Combined results from XEDS, hardness testing and a micrograph for the 2C-5 specimen. The graph shows the distribution of Cr and Ni following cross- section through the insert, FGZ and the ductile iron bulk material and the

corresponding hardness measurements. (The diamond marks are the hardness measurements).

Figure 7: (a) SEM in-lens image of the FGZ of the 2C-5 specimen and the

distribution of Fe, Cr, and Ni along the right-most (vertical) line; (b) the XEDS

maps of Cr, Ni, and Fe along the vertical line in (a). Figure 8 : A secondary electron image (SE) taken with the SEM of the FGZ-i

interface, the FGZ and the insert material of the 2C-1 specimen.

Figure 9 : Secondary electron images of the FGZ-i interfaces for (a) 2C-1 specimen and (b) 2C-3 specimen.

Figure 10: Secondary electron images of the FGZ-i interfaces at higher magnifications for (a) 2C-1 and (b) 2C-3 specimens.

Figure 11 : SEM images of the dense and more refined carbide structure in the FGZ (next to the FGZ-i interfaces) compared to the outer part of the FGZ, the smaller carbides are pointed out with arrows, the larger are indicate with the two top-most arrows in (a). Figure 12: SEM pictures of the cross-section of the 2C-5 specimen showing the insert at the bottom of the pictures, to the right is shown the chemical composition of the area marked with red boxes no. 1 and 2 in (a), (b) is at higher magnification, showing WC particles integrated into the chromium carbide structure.

Figure 13 : Pictures from optical microscope of the cross-section view of the FGZ and the insert bulk material in (a) specimen 2C-1 showing the chromium carbides bridging between the insert bulk material and (b) of the chromium carbides

bridging in the 2C-2 specimen.

Figure 14: Hardness measurements of the cross-section of 2C-5 through insert vs.

perforated hole.

Figure 15 : A schematic of how the wear rate was measured with a cylinder-on-disc line contact configuration.

Figure 16: Picture of 2B-1 and 2C-3 after wear rate tests, showing the squares formed after the wear rate testing from the hardened steel cylinder rolling on the surfaces, (b) higher magnification of the wear surface of 2B-1 after wear rate

testing. Figure 17 : Measured wear rate and coefficient of friction of the specimens tested.

Figure 18: Measured wear rate and coefficient of friction of the specimens of the invention as well as in previous study on earlier samples and on known wear

resistant materials such as Hadfield (HF) steel and Hardox 500 (HD).

DETAILED DESCRIPTION

The inventors have developed special chemical carriers and processes to introduce, distribute and react chemical substances locally in cast metal items, in order to provide customised local properties in the items. The carriers and processes by which the carriers are introduced provide functional gradient zones (FGZ) surrounding the embedded chemical carriers within the cast items, providing added strength and in many

embodiments substantially enhanced wear resistance.

Illustrative tests of metallic brake pads made with the present invention demonstrated superior wear rate of the locally strengthened pads as compared to the bulk cast metal. It is contemplated herein that intense braking action with heat creation and dissipation of the heat may in fact enhance further the desired local properties of the strengthened cast items, in that further substance from the carrier disperses as a result of heat, in the FGZ in the wear region which is just adjacent to the distal surface of the carrier. Thus accordingly, items with carriers such as described herein have in preferred embodiments replenishing carriers, where the chemical carriers act as source of desired substance, released into the FGZ during use. This is further supported by experiments where cast specimen are treated with austempering, which not only increases strength of the bulk alloy, as expected, but also increases strength of the FGZ, by increased formation of carbides such as chromium carbides (see Figures 9 and 10 and discussion below in Example 4.)

The term metallic melt, metal melt or 'melt' includes any conventional metals and metal alloys that are used to cast items from metal, e.g. iron or iron alloys. The terms alloy and cast alloy refer to in the context herein in general both to traditional cast iron and iron alloys, including ductile cast iron, nodular cast iron, malleable iron and various iron alloys. In typical but non-limiting embodiments the bulk material is regular ductile iron with about 3.5% C (carbon) and about 2.5% Si (silicon). The term cast item, cast iron item, alloy item or cast alloy item refer generally to items cast or processed from melted metal, such as melted iron or alloy thereof as defined herein above.

The term chemical carrier refers to a solid structure from a suitable material such as is further exemplified herein. The chemical carrier of the invention can be of a wide variety of shape, composition and configuration such as further illustrated and exemplified herein, according to the particular cast item to be made, the desired local properties and the desired spatial distribution of the properties which is desired. Thus, the carrier can be but is not limited to general shapes such as plate, cylinder, roll, rod, bar, cube, straight, bent or curved, knee shaped bar or rod, solid or hollow, flakes, wire, wire mesh or any combination thereof. It follows that in some embodiments the shape of the carrier is determined by the surface shape of the item to be cast, and in particular of the surface shape of the part of the item where it is intended to strengthen the material by use of a chemical carrier according to the present invention. Accordingly, in certain embodiments, the carrier has a shape substantially similar to the shape of a portion of the item to be cast, with same general curvature etc. as the respective portion of the item.

The chemical carrier comprises a base, which base has adhered to it layers, coatings or other type of arranged surface layers, of other chemical composition than that of the base. The surfaces of the carrier base itself, prior to adding of the surface layers, are referred to as primary surfaces. The term surface layer herein also encompasses a layer of substance added by melting or diffusion process into and/or under the surface of the base creating penetrating layers of other composition than that of the base. Such penetrating layers can thus in some embodiments have material both on the primary surface, and immediately underneath the primary surface, intermixed with substance from the carrier base.

In some embodiments the carrier comprises both a penetrating layer and a deposited layer.

The composition of the base is such that it will partially melt when the cast melt at suitable temperature is poured over the chemical carrier to fully immerse the carrier. The carrier must not completely melt so as not to disperse homogeneously within the melt but substance from the carrier remain at substantially high concentration at the site of the original placement of the carrier within the casting mold into which the melt is poured. This is in order to distribute the substances and the derived desired properties as desired locally in a region of the item, forming a gradient extending from (and to) the surface of carrier, and/or below the carrier. Substance will dissolve/ disperse from the carrier and disperse into the surrounding melt, and preferably substances from the melt will diffuse into the partially molten carrier, to form a gradient zone in the boundary region between the carrier (and/or from within the carrier) and the enclosing melt. As further discussed herein, heat and stress exerted on the item after its formation may release further substance from the carrier and/or enhance the properties of the FGZ, such as through further formation of strengthening carbides.

It follows that the carrier is preferably of a material with a higher melting point than that of the melted cast metal. In preferred embodiments various types of steel are used, including but not limited to steel types such as stainless steel grades: AISI 304, AISI 316, UNS S30400; AMS 5501, 5513, 5560, 5565; ASME SA182, SA194 (8), SA213,

SA240; ASTM A167, A182, A193, A194, and duplex stainless steel such as SAF 2304, and the like. It is found that materials with no or only little content of nitrogen are preferred, such as preferably less than 0.1% nitrogen.

As mentioned above, the chemical carriers are provided with one or more surface layers with one or more substances. Thus, the carrier acts as a chemical carrier for the surface layer substances that get distributed selectively and locally, depending on the location of the carrier within the cast item, and the surface(s) on which are arranged surface layers.

As the carrier comes in contact with the molten cast metal the heat will affect the carrier and partially melt the carrier (its surfaces) ensuring a continuous interface between base and carrier, wetting the surfaces of the carrier. The relative melting of the carrier depends on the composition of the carrier, the thickness and shape of the carrier and temperature and cooling rate of the cast items.

Surface layers on the carrier are selected and arranged so as to disperse substance from the surface layer in the casting process, affecting the cast adjacent and in vicinity of the carrier, in particular in vicinity to the portion(s) of the carrier having thereon deposited surface layers. Thus, the dispersed substance will generally form a concentration gradient, with highest concentration by or inside the partially melted carrier and diminishing in the general direction away from the carrier. As the adhered surface layer or at least part thereof is melted and dispersed and as mentioned above also a part of the carrier base structure is partially melted, not only will substances disperse away from the carrier, but material from the melt can disperse into the carrier, such as in particular carbon and/ boron substance from the cast melt or surface layer, forming a general gradient of such substance(s) extending into the carrier base, creating a boundary region of mixed material extending from below the original surface of the carrier base and some distance away from the surface, into the cast melt.

The boundary region is herein generally referred to as a functional gradient zone (FGZ). It is a very advantageous feature of the invention that the functional gradient zone creates continuous boundary region as illustrated in the accompanying Examples and Figures. We refer herein to the original surfaces of the carrier prior to arranging thereon surface layers, as primary surface layers. When the carrier is located in the ready-made cast item and the FGZ has been created, the FGZ generally refers to the interface region of the carrier and surrounding bulk material where changes to the composition of both the surrounding bulk and carrier are observed. In some embodiments of the invention, chrome, wolfram and/or nickel have dispersed from the carrier into the surrounding melt, and these elements may form strengthening carbides in the FGZ area. Such metal carbide(s) is/are in some embodiments used as substance in the surface layers.

Also, in some embodiments, carbon diffuses in the process from the cast melt into the carrier surface, resulting in carbide formations (e.g. chromium carbide) which increase the hardness as compared to non-melted more central part of the carrier. Thus the FGZ in some embodiments extends to within the chemical carrier.

The surface layer(s) can be applied on the carrier with various methods, where those preferred include deposition methods such as but not limited to flame spraying, plasma spraying, physical or chemical vapour technologies. It follows that it is preferred to deposit the layers so as to create generally porous layers, to enhance distribution of the layer substance(s) in the boundary region and mixing boundary substances. As mentioned above, this further enhances wetting of the carrier primary surface by the cast melt. Thus the actual thickness may vary and the amount of layer is generally more suitably referred to by weight per area. In general the surface layers can be in the range 0 - 2000 g/m², wherein the minimum limit refers to embodiments with no deposited surface layer but where an FGZ is created around the carrier with the materials from the cast melt and carrier base. In some embodiments, surface layers can thus be in the range from about 50 to about 2000 g/m², such as from about 50 to about 1500 g/m², such as in the range from 50-1000 g/m² or in the range 100-1000 g/m², such as in the range 100-850 g/m², such as but not limited to in the range 100-250 g/m², 250-500 g/m², or 500-850 g/m². Accordingly, it follows that the surface layer can have varying thickness within the general range from about 0 to about 250 pm, such as but not limited to 10 m to about 250 pm, such as in the range 10 to 100 pm, such as in the range 20- 100 pm, such as about 10 pm, about 15 pm, about 25 pm, about 50 pm, about 75 pm or about 100 pm.

In order to get surface layers with preferred porosity, it is an advantage of the invention that the surface substance(s) is suitably deposited such that the substance does not fully melt in the deposition process, to prevent forming a film type layer, but the deposition technique used is configured so as to deposit the material in a more grainy/powdery type layer, allowing the deposited substance to readily disperse and melt/mix into the cast melt, and allowing substance from the cast melt to penetrate the surface layer and into the surface of the carrier base. It is also within the scope of the invention to provide a layer with diffusion of

substance(s) into and under the surface of the base. Diffusion control processes are well known to the skilled person such as carburizing, boronizing, and optionally followed by quenching process. The thickness of enriched layer of substance(s) depends on diffusion process and are well known to the skilled person. General range of thickness, but not limited such as for carburizing is up to 1.5 mm and such as for boronizing is up to 0.2 mm.

Such layer can also in some embodiments be a surface layer which is both on the surface and with substance diffusing into and under the surface. As mentioned, the carrier can have in principle any desired shape, in some embodiments the carrier has a substantially two-dimensional shape, such as in the shape of a plate, a grid, a mesh or the like. Such plate, grid or mesh may however also be bent, curved, cylindrical, or other suitable shape based on the shape of the item to be cast and the desired location within the item of properties provided for by the chemical carrier.

When the carrier base is a plate or the like structure, it is suitably perforated or otherwise configured with holes or channels, to allow flow of melt from one side to the other and to fully surround and encapsulate the carrier.

The carrier can in some embodiments be generally defined as having one or more distal surface and one or more proximal surfaces, where a distal surface generally faces the surface of the cast item, whereas a proximal surface generally faces the center of the item, or faces a direction other than towards the nearest surface of the item. This is applicable in particular for a carrier being placed generally in the vicinity of a surface of the cast item. Thus, the distal surface of the carrier is a surface generally facing a surface of the cast item, but still being located underneath the surface fully enclosed by the cast melt in the production process (in a sub-surface location). In these

embodiments, the distal surface may have deposited on it a first type of surface layer (a first surface layer with a first composition) or more than one surface layer, whereas the proximal surface may have no surface layer or a different surface layer or layers (i.e. a second surface layer with a second composition). This is useful in embodiments wherein the carrier is designed to bring certain feature to the surface portion of the cast item, where this can be obtained by a suitable carrier having a desired surface layer on its distal surface, providing a FGZ generally towards the surface of the item. In other embodiments however, the main surfaces of the carrier base can be arranged in the cast item at some other angle than substantially parallel to a surface of the cast item, such as at a 90° angle, or any other angle of choice, depending on the item in question and desired properties.

In certain embodiments the carrier is placed in the cast mold so that at least a portion of the distal surface of the carrier is at a distance from the surface of the cast item such as but not limited to within a range from about 0.5 mm to about 25 mm, such as in a range from 0.5 mm to about 15 mm, such as within a range of about 2 mm to about 12 mm or the range from about 1 mm to about 10 mm, such as about 0.5 mm, about 0.8 mm, about 1 mm, about 2 mm, about 4 mm, about 5 mm, about 6 mm, about 8 mm about 10 mm or about 12 mm. One exemplary embodiment is illustrated in Figure 14, where a thin perforated plate shaped carrier is placed about 9-10 mm from the outer surface of the cast item. As can be observed in this example, the FGZ is distributed from about 6 mm depth from the surface to about 13 mm depth.

It follows that when using surface layers on the carrier, a broader range of substances can be distributed locally with the use of the carrier, and as demonstrated herein, desired substances can be formed in the formation of the FGZ by reaction in the processes described herein.

The carrier base is typically comprised of but not limited to a material such as the above mentioned stainless steel materials. An adhered surface layer may in some embodiments comprise substances including tungsten carbide, chromium carbide, wolfram carbides, and other carbides, carbon, boron, and metals such as but not limited to molybdenum, nickel, and any mixtures thereof, including a mixture of metals and/or mixtures of carbides and metals, with our without further compounds. Carbides may also be formed by layers of the respective metal(s) such as any of the above mentioned, e.g. tungsten, chromium, nickel, which react with carbon from the cast metal in the casting process, reacting to form carbides of the metal(s).

It is an advantage of the invention that metals and/or metal carbides are dispersed from the carrier surface layers into the FGZ, strengthening the bulk material surrounding the carrier, while substantially maintaining the ductility of the bulk material. Thus can be provided items with certain desired characteristics derived from the bulk material but certain characteristics obtained through the mix of substance into the bulk in the FGZ.

In certain embodiments, more than one surface layer is deposited on to a surface of the carrier base, wherein the first layer may have a different composition and/or thickness or density than the second layer.

It is as well an advantage of the invention that material from the cast itself can at least in certain embodiments diffuse into the carrier, and thus a gradient of substance from the cast extending towards and into the carrier can be formed, to further obtain desired properties in the area of the carrier and desired properties of the local alloy in the area of the carrier.

According to the process of the invention, the iron/metal melt when poured into a mold will typically be at a temperature in the range from about 1200 to about 1500°C when poured into said mould, such as in the range 1200-1450°C, and preferably in the range 1250-1450°C, such as in the range 1350-1450°C. In some embodiments, the cast item is austenized, involving a step of austenisation. The austenisation process as such can be conducted according to conventional procedures, that generally involve re-heating the solidified and cooled item and keeping at a high temperature (such as about 900°C) for a certain period, after which the item is cooled by immersing in a brine solution which typically is at a temperature in the range of 250- 400°C, such as in the range 250-350°C and preferably in the range 350-370°C. By applying the austenisation process diffusion in and around the FGZ is enhanced, carbide formation is enhanced and this results in increased strength of the FGZ and thus increased strength and wearability of the locally strengthened part of the produced item. Such increased carbide formation and enhanced distribution from substance from the carrier (e.g. from surface layers) can also be affected when use of the cast items involve much heat impact, e.g. in brake pads that absorb heat during intense braking action.

EXAMPLES Example 1 : Fabrication of carrier

Chemical carriers were made from steel where different types steel types have been tested. Carrier types CI, C2 and C3 were made from grade AISI 304 type steel (18-20% Cr, also Ni), C4 and C5 from grade AISI 316 type steel (16-20% Cr, with Ni, Mo), and C6 and C7 were from grade SAF 2304 type steel (23-25% Cr) Carriers C4 and C5 were deposited with surface layers of wolfram carbide and minor amount of boron, whereas C3 was deposited with twice the amount as C4 and C5.

The carriers were made from perforated material, either so-called 3@5 or 4@6 perforation (referred to below as (S) (small), and (L) (large), where 3@5 indicates round holes with a 3 mm diameter with 5 mm spacing between holes and 4@6 indicates round holes with 4 mm diameter and 6 mm spacing.

Example 2 : Casting of items

Table 1

Item no. Carrier type Austempering Carrier layers

2C-1 CI (S) - 2C-2 CI (L) -

2C-3 C2 (S) X -

2C-5 C3 (S) WC, B (2x amount in 2B-1 and 2B-2)

2B-1 C4 (S) WC, B

2B-2 C5 (S) X WC, B

Surface layers on carriers C3, C4, C5 in specimens 2C-5, 2B-1, and 2B-2 were deposited on one side with thermal spraying, on the distal side, facing the wear surface of the specimens. The terms (S) and (L) are as explained in Example 1. WC refers to wolfram carbide, and B refers to boron.

Example 3 : Properties of the functional gradient zone (FGZ) in specimens

The functional gradient properties of the specimens of the invention are due to the gradient microstructure that forms in the casted part during solidification and cooling of the melt when chemical components diffuse from the chemical carrier into the ductile iron and vice versa.

Pictures from cross-sections of Specimen 2C-5 are shown in FIG. 1 and FIG. 2. In FIG. 1. The carrier is labelled as 1, surrounding ductile iron 2, and the approximate boundaries of the FGZ 3 are marked with the vertical lines. FIG. 2 shows an optical micrograph (a three-micrograph composite) where the FGZ gradient microstructure can clearly be seen. The microstructure and chemical

composition analysis indicates that chromium carbide particles 5 are forming in a dense layer close to the carrier 1 but then gradually decreasing and mixing with a typical ductile iron microstructure, nodular graphite 6 surrounded by ferrite and pearlite. These phases are labelled in the figure.

As can be seen in the figure, the carrier material 1 has a thin layer 4 (<200 μιτι) next to the carrier bulk material that has a different microstructure than the carrier bulk material, indicating that part of the carrier material has been modified by diffusion of chemical species to and from the carrier during solidification. FIG. 3 shows the distribution of Cr and Ni through a cross-section of the 2B-2 specimen and the results of corresponding hardness measurements (the diamond marks in the lower right panel show the location of the hardness measurements). The distribution is shown through the carrier, FGZ and the ductile iron bulk material (upper panel). The specimen has been heat treated with austempering (ADI treated) and a surface layer with WC and B was deposited on one side of the carrier. The carrier is on the far left in the picture in the bottom-right panel, with the deposited surface layer on the right side of the carrier, in contact with the FGZ region.

The highest hardness value of 800 HV, was measured in the boundary layer of the FGZ, bordering the carrier. The composition and the microstructure indicate that this layer is more dense, as can be seen from FIG. 4.

Carbon diffusion from the ductile iron into the carrier results in chromium carbide formation where there originally was carrier material, as can be seen from the hardness values, where the gradient points at the interfaces of the carrier and ductile iron have higher values than inside the carrier.

Chemical composition analysis was also done by using a line scan feature in the SEM with XEDS equipment. This feature allows the chemical composition to be measured along a line as can be seen in Figure 5 along with a so called in-lens image from the SEM. The in- lens image is also shown in Figure 4 where a more detailed structure of the boundary layer of the FGZ is visible. The figure shows clearly the interface between the FGZ and the remains of the insert, herein referred to as FGZ-i interface, can be seen at higher magnification than in Figure 4. As can be seen from Figure 5(a)-(c) the Cr content is varying over the FGZ-i interface which seems to have a two-layer structure.

FIG. 6 shows a corresponding micrograph as in FIG. 3 but of specimen 2C-5, with corresponding hardness measurement values. It shows the distribution of chromium and nickel through a cross-section of the specimen. This specimen has not been heat treated for austempering, but the insert was configured with a layer on one side, with WC and B (twice as much as in specimen 2C-5). The composition and microstructure also here indicate the material close to the carrier as being dense with refined chromium carbide structure. There also appears to be some formation of chromium carbides inside the carrier, as witnessed by the hardness value of the first points at the boundaries. (The highest hardness value, 516 HV, was measured in the FGZ-i interface.) Chemical composition line scan analysis was also done for the cross-section of the 2C-5 specimen shown in Figure 6 by using SEM with XEDS equipment. The results are shown in Figure 7 along with in lens image from the SEM. The Cr content varies over the FGZ-i interface, from the insert to the FGZ. The dents in Figure 7a are the marks after the diamond used in the hardness testing. The in-lens image of the FGZ-i interface in 2C-5 (Figure 7) does not show as well the structure as in Figure 5 for 2B-2. The fine carbide structure is not as visible most likely due to shorter etching time of the 2C-5 specimen. The thickness of the FGZ-i interface in the 2B-2 (with austempering) were the hardness is the highest seems to be thicker than for the 2C-5 specimen that did not go through austempering heat treatment, as can be seen when comparing Figure 3 (2B-2) vs. Figure 6 (2C-5) and Figure 5 vs. Figure 7. This and the results of the hardness testing indicates, that during the heat treatment, chemical species such as carbon and chromium diffuse and form more carbides, that increases the hardness of this layer. This suggests that the austempering is not only beneficial for the ductile iron bulk material strength but also allows more formation of carbides and/or higher order carbides that render higher hardness.

Example 4: Electron micrograph of the FGZ - further composition analysis:

To explore the effect of austempering on the FGZ, Scanning electron microscopy (SEM) was used to compare specimen 2C-1 and 2C-3, with microstructural and spatial elemental composition analysis with XEDS (X-ray Energy Dispersive Spectroscopy).

FIG. 8 shows a secondary electron image taken with the SEM of the FGZ -carrier interface (FGZ-i) of the 2C-1 specimen. The chemical composition in the labelled areas 1, 2, 3, 4 is shown in Table 1 below. It is evident from the SEM picture in FIG. 8 that the FGZ-i sector has a different structure than the outer FGZ and the elemental content varies.

Table 2

FIG. 9 shows secondary electron images taken with SEM of the innermost layer of the FGZ of the 2C-1 and 2C-3 specimens. Both types have long thin chromium-rich grains in the FGZ-i area but there is a difference in the microstructure; the 2C-3 sample shows very small pieces distributed all over the FGZ-i area, while there is little of this in the 2C- 1 sample. This can be seen more clearly in FIG. 10 which shows the areas of the respective samples at higher magnification.

This indicates that during heat treatment, small nuclei of chromium carbides can grow, which results in increased hardness of the inner most layer of the FGZ as the hardness measurements show.

The microstructural analysis further shows that the FGZ close to the carrier (next to the FGZ-i (interface)) area has a more dense and refined carbide structure than the FGZ material further away from the insert, see Figure 11.

The thickness of the FGZ interface in the 2B-2 specimen (with austempering) where the hardness is highest appears to be thicker than in the 2C-5 specimen that was not treated with austempering, this is seen when comparing FIG. 3 and FIG. 5. This and the results of the hardness testing indicates that during the heat treatment chemical species such as carbon and chromium can diffuse and form more carbides during the austempering treatment, that increases the hardness of this segment of the FGZ. Thus the

austempering is not only beneficial for the ductile iron bulk material to increase the strength but also leads to more formation of carbides and/or higher order carbides that render high hardness. The adding of tungsten carbide (WC) to the insert in an attempt to incorporate WC into the FGZ was successful as can be seen in Figure 12(a). The WC is integrated into the chromium carbide structure as can be seen in Figure 12(b). The amount of WC is higher close to the FGZ-i interface as expected.

An important factor regarding the FGZ formation and its structure is the distribution of the gradient zone. Ideally the FGZ is continuous and bridges the gap, perforated holes (holes) in the insert material. This was observed in the specimens examined (Table 2) and is indicated with drawn lines in Figure 1 of the 2C-5 specimen and is also clearly seen from the microstructure shown in Figure 13(a) of 2C-1 (3 mm holes) and Figure 13(b) of 2C-2 (4mm holes), where chromium carbide bridging can be seen between the insert bulk material (in the original insert holes). The 2C-2 specimen in Figure 13(b) was etched for a shorter time than 2C-1 (in Figure 13(a)) but polished with finer grid; thus there is some difference in the appearance of the pictures in (a) and (b). The hardness was measured in the area which was the perforated hole of the insert before casting and the results were compared to the hardness through the insert and the FGZ formed. An example of this is shown in Figure 14; the hardness is high in the former perforated hole because of the chromium bridging, i.e. the continuity of the FGZs. The continuous structure of the FGZ in and around the insert and the original insert holes will give better wear resistance in high wear and abrasive environment than if it was non- continuous phase.

Example 5: Wear Rate testing

The standard wear rate testing was done on 2B-1, 2C-1, 2C-2, 2C-3 and 2C-5 specimens listed in Table 1. The wear rate test equipment is described in detail in B. Podgornik et a I., Improvement of ductile iron wear resistance through local surface reinforcement. Wear, 274-275, pp. 267-273, (2012). The main setup can be seen in Figure 15. Four measurements were taken on each specimen; Figure 16 shows a picture of one of the specimens showing areas that were worn with a sliding cylinder made out of hardened steel. The results from the testing are shown in Figure 17.

Three out of five specimens, specimen 2B-1, 2C-2 and 2C-3, measured with zero wear rates at least for one area out of four as can be seen from standard deviation bars in Figure 17. The 2C-3 specimen (with 18-20Cr% and austempering, small holes) had the lowest wear rate, 0.6- 10^"5mm³/l\lm, which is very low and barely detectable with this test method. The 2C-1 has a CI type carrier; i.e. with 18-20Cr%, small holes and no austemperating heat treatment. Thus this agrees well with the hardness measurements of the specimens and shows the austempering heat treatment increases the wear resistance of locally alloyed specimens. The wear rates of the specimen products in these tests are compared to the performance to known wear resistant materials such as fully hardened Hadfield Mn steel, Austempered Ductile Iron (ADI), Hardox^® 500 and earlier samples previously tested, these results are shown in Figure 18. All the specimens of the invention shown in Figure 17 measured with very low wear rates compared to regular ductile iron and even regular austempered ductile iron see Figure 18. They also all had lower wear rates than was measured for Hardox 500 (marked as HD in Figure 18) with the same test method and equipment. The 2B-1, 2C-2 and 2C-3 specimens had lower wear rates than measured for Hadfield steel (HF). As shown in Figure 16, tested surface of the samples were done in different distance from the insert surface. Figures 3 and 6 show how the hardness vary with the distance from the insert surface and due to this the results from 2C1 and 2C5 can be seen as tested with more distance from the insert surface than 2B1, 2C2 and 2C3, resulting in higher wear rate.

Claims

A process for introducing local properties in a cast metal item, comprising providing a chemical carrier comprising a carrier base, the carrier having one or more surface layers adhered on one or more surface on the carrier base, said one or more surface layers having different composition than the composition of said carrier base,

placing said chemical carrier in a desired position within a mold for casting said alloy item such that iron melt poured into said mold to cast said item fully surrounds and encapsulates said chemical carrier,

pouring a metallic melt having a desired suitable temperature in said mold to cast said item, such that the melt fully surrounds and encapsulates said chemical carrier and partially melts said chemical carrier, and

- allowing said cast metallic melt to cool, to solidify said partially melted

chemical carrier and to solidify the cast item with said chemical carrier embedded in a desired location in said cast item.

The process of claim 1, wherein said one or more surface layer is porous, such that said metallic melt wets said one or more surface of the carrier base.

The process of claim 1 or 2, wherein said metallic melt is cast iron or ductile iron.

The process of any of claims 1 to 3, wherein said chemical carrier is placed in proximity to a surface of said mold to be located in proximity to a surface of the cast item.

The process of any of claims 1 to 4, wherein substance from said one or more surface layer(s) is dispersed during the process, to form a concentration gradient extending in the item radially from said surface layer of the carrier.

The process of any of claims 1 to 5, wherein said surface layer is deposited on said one or more surface of said carrier base.

7. The process of any of claims 1 to 5, wherein at least one of said one or more surface layer(s) is a surface layer within the surface of the base, added by a diffusion process.

8. The process of any of the preceding claims, wherein at least one of said one or more surface layer is a distal surface layer adhered on a distal surface of the carrier base. 9. The process of claim 8, wherein said chemical carrier comprises at least one distal surface on the carrier base onto which is adhered a first surface layer having a first composition, and at least one proximal surface onto which is adhered a second surface layer having a second composition. 10. The process of any of the preceding claims, wherein said one or more surface layer comprises a substance selected from carbon, chromium, tungsten, boron, molybdenum, nickel, chromium carbide , tungsten carbide, molybdenum carbide, nickel carbide and any mixture thereof. 11. The process of any of the preceding claims, wherein said one or more surface layer has a density in the range from about 50 to about 1000 g/m², and preferably in the range from about 100 to about 850 g/m².

12. The process of any of the preceding claims, wherein said one or more surface layer has a thickness in the range from about 0 μιη to about 500 μιη.

13. The process of any of the aforementioned claims, wherein said iron melt is at a temperature in the range from 1200 to 1500°C when poured into said mold. 14. The process of any of claims 1 to 6 and 8 to 13, wherein said surface layer is

deposited on said item by a method selected from the group consisting of flame spray, thermal spray, chemical, and physical vapour technologies.

15. The process of any of the aforementioned claims, further comprising an

austenisation step.

16. The process of any of the aforementioned claims, forming within the solidified cast item a functional gradient zone surrounding the embedded carrier, with a concentration gradient of one or more substances radially from at least one surface of said carrier.

17. A locally alloyed cast item with desired local properties, comprising a fully

embedded chemical carrier within a cast metal item, the carrier comprising a carrier base and one or more surface layer on said base having a different composition than said carrier base, wherein substance from said one or more surface layer is dispersed in the item in the vicinity of the carrier, said carrier base being partially melted in the making of said item, such that chemicals from said carrier are distributed radially along a gradient extending from said carrier and substance from the cast iron melt is introduced in the surface of the carrier, creating a functional gradient zone in the boundary region between the embedded chemical carrier and enclosing cast metal material.

18. The cast item of claim 17 wherein at least one of said one or more surface layer comprises a surface layer within the surface of the carrier base, which layer is added by diffusion process.

19. The cast item of any of claims 17 and 18, wherein said one or more surface layer comprises a substance selected from carbon, chromium, tungsten, boron, molybdenum, nickel, chromium carbide, tungsten carbide, molybdenum carbide, nickel carbide and any mixture thereof.

20. The cast item of claim 19, wherein said one or more surface layer comprises a substance selected from carbon, boron, and any mixture thereof.

21. The cast item of any of claims 17 to 20, wherein said chemical carrier has distal surface with one or more surface layer, which distal surface is in proximity and in parallel with at least a portion of a surface of the cast item.

22. A chemical carrier for introducing local properties in a cast locally alloyed item, configured to be placed in a mold for casting said alloy item, the carrier comprising a carrier base, and one or more surface layer adhered on one or more surface of said carrier base, wherein said surface layer has a different composition than the composition of said carrier base.

23. The chemical carrier of claim 22, wherein said surface layer is porous so as to allow wetting of said one or more surface of said carrier base by a cast melt poured into said mold.

24. The chemical carrier of claim 22, wherein said one or more surface layer is

selected from the group consisting of a deposited surface layer and diffused surface layer.

25. The chemical carrier of any of claims 22 to 24, comprising a distal surface and a proximal surface, configured to be placed in a mold for casting said alloy item in proximity to a wall of said mold, such that said distal surface is more distal within said item than said proximal surface, wherein a distal surface layer is deposited on said distal surface, with a chemical composition which is different than the composition of the carrier base structure, from which distal surface layer material disperses during casting of said alloy item with the alloy melt, to create a gradient distribution of said material extending from said distal surface into said alloy item.

26. The chemical carrier of any of claims 22 to 25, wherein said layer has an areal density in the range of about 0 - 2000 g/m², and preferably in the range 50 to about 1500 g/m².

27. The chemical carrier of any of claims 22 to 26, wherein said layer comprises a substance selected from carbon, chromium, chromium carbide, tungsten, tungsten carbide, boron, molybdenum, molybdenum carbide, nickel, nickel carbide, and any mixture thereof.

28. The chemical carrier of any of claims 22 to 27, wherein said surface layer is

deposited on the carrier with a method selected from flame spray, plasma spray and physical and chemical vapour deposition technologies.