WO2010136055A1

WO2010136055A1 - Wear element for earth working machine with enhanced wear resistance

Info

Publication number: WO2010136055A1
Application number: PCT/EP2009/005802
Authority: WO
Inventors: Jorge Triginer; Jose Sanchez; Jose Lopez; Jorge Alcala; Jordi Brufau Guinovart
Original assignee: Metalogenia S.A.
Priority date: 2009-05-29
Filing date: 2009-08-10
Publication date: 2010-12-02

Abstract

Wearing element with enhanced wear resistance related to wearing elements, such as cast steel teeth to be specially used in machinery for earth-moving, ground- engaging and/or rock-cutting applications, as well as to inserts to be included within the wearing elements, to enhance their wear resistance thus prolonging their service life.

Description

WEAR ELEMENT FOR EARTH WORKING MACHINE WITH ENHANCED WEAR RESISTANCE

Field of the invention

The present invention relates to wearing elements, such as cast steel teeth to be specially used in machinery for earth-moving, ground-engaging and/or rock- cutting applications, as well as to inserts to be included within the wearing elements, to enhance their wear resistance thus prolonging their service life.

Background of the Invention (Prior Art)

The insertion-casting of hard bodies into cast steel parts to enhance their wear resistance has been previously described in the state-of-the-art, as per example in US-5,081 ,774 (Kuwano). This document describes a replaceable composite excavating tooth that comprises wear-resistant Cr-cast iron inserts having a higher hardness than a tooth body and being insert-cast into the tooth body. The performance of the excavating tooth is improved by locating the wear-resistant material as an integral insert at a central part between the top and bottom surfaces and determining the width of the insert substantially the same as the width between both side surfaces of the tooth body. The insert extends from the tip end towards an attachment part of the tooth and terminates at a limiting position for the potential use of the teeth. Tooth replacement is then needed once the limiting position is reached.

From the different materials used in the state-of-the-art to constitute the hard bodies, or inserts, special attention has been given to the family of cermet materials

(hard cemented ceramic-metal composites) due to their outstanding combination of hardness and toughness. Such properties have led to their common use in wear applications where abrasion and impact resistance are required. Insertion of cermet bodies into iron-based wearing elements by means of casting processes, where a metal is poured into a mold cavity containing the cermet, has been reported to be problematic. Specifically, the prior art concerning insert-casting of a WC-based cermet (cemented tungsten carbide) has been recognized to lead to the dissolution of the constituting WC particles. This problem has been avoided by the introduction of protective inter-layers between poured molten iron-based alloy and the WC particles; for cast iron and steel (US-4,764,255, Fischer); for cast iron (US- 4,584,020, Waldenstrom); and for cast steel ("Reinforcing Steel Castings With Wear-Resisting Cast Iron" Liteinoe Proizvodstvo, No. 7, p. 27 (1986), Furman et al.). These inter-layers are constituted by metallic alloys that are intended to remain, at least, partially intact in the finished product. In addition to selecting suitable high temperature alloys, the art teaches the use of sufficiently thick inter-layers (sheets), preferably in-between 1 and 8 mm thickness, whose melting temperatures are >50 ⁰C above that of the poured metal and more preferably 200 ⁰C above of that of the poured metal in the art taught in US-4,764,255 and US-4,584,020. On the other hand, the inter-layers comprise a low-melting temperature alloy, such as copper, in the art taught by Furman. Moreover, Waldenstrom and Fischer disclose that the inter-layers shall be sufficiently thick as not to dissolve during the pouring of the steel. In Waldestrom, the structure produced thereby is thus regarded to have improved resistance against crack propagation because of the crack-arresting properties of the inter-layers. In the provided example, the cross-sectional microstructure of the inserted WC part is constituted by less than five cemented carbide particles across two outer regions where penetration of the cast iron occurs. Within such particles, formation of inter-diffusion and pure cast-alloy zones is taught by US-4,584,020.

International application number WO-90/11383-A1 (Materkowski) discloses a procedure by which the cemented carbide particles are placed inside a mold and cast iron is poured to produce inserts. In this application, the pouring temperature of the iron-based alloy becomes significantly lower than that of the steel, which prevents dissolution of the particles from occurring. Excepting Fischer, all of the above disclosures involve the infiltration of crushed cemented carbide particles by liquid metal, where the resulting inserts are then introduced into larger castings thus producing the final part. In the case of Fisher, the cermet is placed inside a protective container and the cast metal is poured around. Since the penetration of the molten metal is prevented by the container, the resulting bonding between cermet and container occurs by shrink-fit.

Attention has also been given in the state-of-the-art to the use of other high hardness materials, such as ceramic oxides and monolithic ceramics in general, as reinforcing agents. Probably because of their inherent low toughness, monolithic ceramics have not yet found application as bulk inserts for wear enhancement. Such ceramics have however been used extensively as reinforcing constituents in metal matrix composites for light-weight structures. For instance, continuous (reticulated) ceramic/metal matrix composites have been manufactured by infiltrating a highly porous ceramic or three-dimensional cellular ceramic structure with a liquid metal or alloy. In this context, prior art is taught by WO-2008/051591-A1 (Gonzalez-Rocha); US-7,290,586-B2 (Sambrook); "Processing of Ceramic-metal Interpenetrating composites, Journal of the European Ceramic Society 29 (2009) 837-842 [10]" (Binner et al.); and "Bi-continuous metal matrix composites, Materials Science and Engineering A303 (2001) 37-45" (Peng et al.). The above art discloses fabrication of infiltrated bulk reticulated cellular ceramic foams, where the following strategies are applied to favor metal infiltration: (i) selection of a low-melting temperature alloy, (ii) use of external pressure; (iii) heating of the mould prior to infiltration.

None of the previous prior art documents describe nor mention a wear- resistant component such as a cast steel tooth, having a low-porosity secure bond between a reticulated cellular-ceramic-based insert and cast steel which infiltrates the ceramic by gravity pouring.

Prior art concerning ceramic materials infiltrated by molten steel for reinforcing purposes is disclosed in "Processing and microstructure of metal matrix composites prepared by pressureless Ti-activated infiltration using Fe-base and Ni- base alloys, Materials Science and Engineering A 393 (2005) 229-238", (Lemster et al). Although this disclosure concerns processing of steel matrix composites with embedded ceramic particles, it is noted that (i) it does not constitute the ceramic phase from ceramic foams, and (ii) attention is not given to the use of the so- processed composites as inserts in a wear component for earth-moving applications, such as the ones under consideration in the present invention.

Summary of the invention

The present invention relates to the processing of enhanced wear resistant components such as teeth for earth-moving, ground-engaging and/or rock-cutting machinery, having engineered high-performance bonds between inserts harder than steel and the cast steel element where the insert is placed. An important object of the invention is thus to improve the wear life of the component by introducing inserts with outstanding hardness within a tougher impact-resistant cast steel. It has been discovered that the quality of the bonding that is developed between the cermet/ceramic inserts and the cast steel is critical to the performance of the component and to the avoidance of sudden failures. This quality is directly related to the avoidance of macro-porosity as described in the first embodiment, and to the large surface area provided in the second embodiment so that mechanical interlocking occurs between the molten metal and the ceramic insert. The reinforced wearing elements that are an object of the present invention have particular use in ground-engaging works in which the downtime cost is significantly high. The reinforced wearing elements of this invention thus allow the extension of effective working time within consecutive replacements. The reinforced wearing elements of this invention may substitute conventional ground-engaging tools (or elements), which are generally manufactured exclusively from low alloy steels.

Therefore, the invention refers to different embodiments for reinforcing cast steel wearing elements whose use is intended in a wide spectrum of applications. The applications range from those mainly subjected to wear solicitations, to others where penetration against the ground plays a critical role in successful operation. A first object of the invention refers to a wearing element with a cermet insert as defined in claims 1 to 20; a second object of the invention refers to a wearing element with a ceramic foam insert as defined in claims 21 to 30; and a third object of the invention refers to a self supporting insert with a hard reinforcement body as defined in claims 31 to 43. Description of the drawings The present disclosure includes the following figures to illustrate the invention:

Figure 1 shows a scheme of the existing bonding zones between the insert and the cast metal.

Figure 2 shows a magnification of the two bonding zones.

Detailed Description of the Preferred Embodiments The object of the present invention is the enhancement of the wear resistance of a wearing element, constituted by a gravity-cast steel containing at least one hard bulk insert, i.e. cemented carbide, or ceramic foam, or both, characterized in that the bonding between the material of said insert and the cast steel guarantees the safe-operation of the wearing elements or reinforced components in service, preventing therefore, breakage of the elements related with defects in said bonding.

As stated before, the first object of the invention describes a first embodiment that refers to wearing elements or components, that at least comprise an insert made up of a cemented carbide or cermet body, whose hardness is substantially higher than the hardness of the cast steel that constitutes the unreinforced parts of the wearing element. Hence, the wearing element for earth/rock engaging/moving machines is constituted by a gravity-cast steel containing at least one bulk insert of cemented carbide. At least two bonding zones (2, 3) between insert and steel are defined. These comprise: a first bonding zone (2) where the cementing matrix of the cemented carbide is substituted by cast steel; a second bonding zone (3) where the carbide of the cemented carbide insert reacts with the cast steel, enriching the carbon content of the steel and lowering its melting temperature. The wearing element is characterized in that the second bonding zone (3) has a controlled thickness, so as to restrict or prevent formation of macro- porosity in the bonding zone between insert and steel, thus avoiding premature failure of said element under service.

According to this first embodiment, the bonding is enhanced through the control of the properties of the steel during the insert-casting process and/or through the specific design of a protective coating layer. Compositional and geometrical design/placing of said insert in conjunction with the casting processes are optimized so as to prevent the problems stated in the prior-art.

The preferred cermet used for the inserts of this first embodiment comprises tungsten carbide particles preferably cemented by a cobalt matrix. In this case, the aforementioned optimization of the bonding is performed through one or a combination of the following strategies. First, the temperature of the molten steel reaching the insert's surface is controlled, so that it does not exceed 50°C above its melting temperature. Second, usage of an improved WC/metallic binder ratio provides control over the penetration of the steel into the cermet insert. Third, usage of a specific outer layer that provides protection against the dissolving action of the steel.

According to the first strategy mentioned above, the use of protective inter- layers as the ones taught in the prior-art is removed by controlling the temperature of the poured steel to ensure that it comes into contact with the cermet in less than 100⁰C above, and more preferably less than 50⁰C above, of its own melting temperature. In doing so, it is recognized that the dissolution of the cermet can be prevented by the freezing of the molten steel in the vicinity of the insert. In components whose reinforced regions exhibit large variations in cross-sectional areas, the temperature of the steel contacting the insert becomes more uniform by using risers or cores to prevent shrink-hole formation. Optimization of the microstructural bond involving removal of macro-porosity is thus carried-out by enforcing the above temperature range in the molten steel. In this context, it is recognized that the following processes are involved in the formation of the microstructural/metallurgical bond: (i) Partial dissolution of the WC particles in the cermet by the steel.

(ii) Infiltration of the steel in the bulk of the inserts by the substitution of the metallic binder, leading to the presently referred first bonding zone (2). During this infiltration process, the metallic binder of the cermet is confined at the inner core zone (1) of the insert. This alters the constitution of the insert so that its inner core (1) contains a greater fraction of binder as compared to in the original insert prior to insertion.

(iii) Formation of two tungsten-rich regions around the insert, herein referred to as second bonding zone (3). The first region (3. a), adjacent to the original surface of the insert and to the first bonding zone (2), is constituted by a solid solution whose tungsten content may exceed 60 wt%. WC particles are likely to re-precipitate in such solid solution. The microstructural morphology of the first tungsten-rich region (3. a) is that of clusters embedded within the second region (3.b). The second region (3.b) involves formation of a second solid solution whose overall tungsten content is within 12% and 60 wt%. This second region (3.b) of said second bonding zone (3) extends up to a zone (4), which is constituted by steel that is not enriched by the reaction with the cermet and thus maintains its original composition. An invariant reaction within the Fe and W phase diagram is promoted in this second region (3.b) of said second bonding zone (3), leading to the formation of a Fe-W stochiometric compound. Depending on the agitation of the steel and aggressiveness of the infiltration process, the abovementioned clusters may become scattered within the second region (3.b) of said second bonding zone (3).

A fundamental aspect in the above processes concerns this second region (3.b) within said second bonding zone (3), where the high carbon content of the iron- based matrix resulting from the dissolution of WC particles significantly reduces the melting temperature to a temperature that may approximate to 1130⁰C, similar to that associated with the eutectic point in the Fe-C phase diagram. Shrinkage during solidification leads to the formation of significant pores in this second region (3.b) of the second bonding zone (3), limiting the load resisting capacity of the inserted part. The above-mentioned steel pouring temperature condition where the molten steel contacts the insert, being less than 50 to 100⁰C above the steel's melting temperature, significantly reduces the dissolution of the WC particles of the cermet, thereby decreasing the thickness of said second bonding zone (3) to less than 3 mm, and more preferably less than 1 mm. Under these temperature conditions, the shrinkage of the second bonding zone (3) is minimized to a point where porosity is controlled to a maximum pore size of 3 mm, and preferably porosity is completely removed.

Substitution of the metallic binder of the cermet, more preferably (but not limited to) cobalt, by the molten steel, leads to the in situ production of WC-steel inter-penetrated inserts. This modification occurs on a micro-structural scale for the first bonding zone (2).

Application of the presently disclosed art allows incorporation of bulk WC- based inserts whose equivalent thickness or diameter preferably exceeds 6 mm into large steel castings, without any of the manufacturing defects mentioned in the prior art. It is recognized that complete infiltration occurs in the limit of the above dimensions by substitution of the metallic binder by the molten steel. By increasing the cross-sectional area of the insert, an inner core remains where steel infiltration is restricted, while smaller cross-sectional dimensions than the limit result in complete insert burnout, where the totality of the binder phase becomes liquid causing permanent deformation or even total dissolution of the insert. As previously disclosed, the preferred cermet (bulk) is constituted by hard ceramic tungsten carbide particles in a metallic cobalt or cobalt-based matrix. The preferable fraction of the cobalt or cobalt based matrix lies between 7 and 20 wt%. An increase of the binder content within these limits enhances the toughness of the insert's core (1) after insertion strongly reducing its hardness and is therefore undesirable to the present application. For cobalt contents below 7 wt%, infiltration becomes increasingly difficult. Moreover, since the enrichment in cobalt gained in the insert's core (1) after insertion is relatively small for such low binder content, the toughness enhancement in this region becomes negligible. By using the above- mentioned cermets in steel components that have been conventionally heat treated, it is recognized that although the Vickers hardness after insertion in the insert's core (1) and in the first bonding zone (2) is decreased to the range of 7-10 GPa for a WC- Co cermet whose original hardness was of 12.5 GPa prior to infiltration, this feature is counteracted by the associated increase in toughness. The used insert preferably contains more than 40% of its cross-sectional area comprised from WC particles whose equivalent diameter is in excess of 4 microns. Although some dissolution in the surface of such particles occurs by the action of the steel in the first bonding zone (2), the induced microstructural changes still allow achievement of the aforementioned Vickers hardness.

Alternatively, it has been recognized that the protection of the insert's surface by a clad coating diminishes the amount of penetration of the steel into the insert as well as the dissolution of the WC particles. The protective layer thus reduces carbon enrichment of the steel surrounding the insert, so that the spatial variation in melting temperature of said steel is insufficient as to induce pore formation. In contrast to the prior art, the present protective layers are tailored so that they fully melt in contact with the steel. Different protective layers have been herein tested whose thickness vary between 0.05 to 1 mm. Good results are obtained with a metallic tungsten layer or tungsten-containing layer so that the composition of the surrounding/penetrating steel is enriched in tungsten. Another protective layer taught herein is a NiCr or NiCrAIY coating that is preferably plasma sprayed on top of a bond coating to favor its adhesion to the insert's surface. In the latter case, the resulting molten steel is thus enriched in Ni and Cr, which is a beneficial feature during the final hardening of the product through conventional heat treatments. Note that in none of the presently used layers, the surrounding steel is enriched by elements such as carbon that would reduce its melting temperature. Although the layers thus reduce the temperature of the penetrating steel, such penetration is still allowed to occur, effectively favoring development of the previously disclosed bonding between insert and steel.

The second object of the invention is a reinforced wearing element for earth/rock engaging/moving machines constituted by a gravity-cast steel that contains at least one insert comprising a cellular tridimensional ceramic foam having an open-celled porous structure that is substantially or entirely penetrated by the cast steel. During the manufacturing of said wearing element, infiltration of the ceramic foam occurs without using any external means to increase infiltration pressure. Such pressureless infiltration is possible because the combination of the fluidic properties of the liquid steel at casting temperature is sufficient as to wet and penetrate the cells of the foam.

The use of ceramic foams of different nature as reinforcing elements in aluminum, copper or cast iron castings is known in the state-of-the-art. In these cases, the infiltration of the ceramic foam is generally favored by the application of external pressure (increasing the infiltration pressure). However, prior to this document, a gravity-cast steel wearing element being reinforced by infiltrating a ceramic foam has not been previously disclosed. Since steel has much higher melting temperatures than the casting materials referred above, means for the infiltration of ceramic foams by steel and thus for the successful reinforcement of steel castings are taught herein.

In particular, the insert included in the wearing element as an object of this second embodiment of the invention is a three-dimensional cellular ceramic foam with an open-cell porous structure that is substantially or completely penetrated by gravity pouring of the molten steel. The material of said insert is preferably a zirconia-based ceramic, such as, for example, zirconia-calcia (ZrO₂-CaO), zirconia- magnesia (ZrO₂-MgO), zirconia-yttria, (ZrO₂-Y₂O₃), or also a zirconia-alumina (ZrO₂- AI₂O₃) composite. The ceramic insert can likewise be formed by alumina-silicates (AI₂O₃-SiO₂) such as mullite, or high alumina (AI₂O₃) materials such as, for example, white or tabular alumina, or aluminate materials such as, for example, aluminate spinels.

Although from the abovementioned materials, high alumina or aluminate ceramics can be the ones with the highest hardness and may be expected to provide the highest wear resistance, it is well known that wettability of such ceramics by steel is comparatively poorer than that of other ceramics. In this context, it has been recognized that coating of any of the above-mentioned ceramic foams with an alumina-silicate material such as mullite facilitates infiltration by virtue of the greater wettability of mullite by the molten steel. The ceramic foam of this teaching can be constituted by the immersion of said ceramic foams into a slurry of the coating material followed by its firing.

Infiltration tests performed using the aforementioned ceramic foams have proven that it is possible to inter-penetrate foams of average porosity between 10 and 60 pores per inch (10 to 60 ppi), and preferably 30 ppi. In doing so, the enhanced properties of the resulting interpenetrated composite are assured by its fine microstructure. To further enhance the wear-impact properties of the resulting infiltrated foam, it is also convenient that the fraction of the ceramic phase does not exceed 35% volume in the interpenetrated (reinforced) region.

Another feature of the ceramic foam inserts considered is that they may have a functionally graded porosity, i.e. a tailored variation of the size and volume fraction of the pores along a thickness of the foam, enhancing penetration of the steel. A further embodiment of the invention consists of a hybrid insert, i.e. a first ceramic foam insert as described before with a second insert that is introduced in said first insert so that said first insert is at least partially surrounding said second insert. Said second insert is preferably comprised by a cermet core, most preferably made of cemented tungsten carbide, that is therefore introduced inside a ceramic foam of the types described previously. Said second insert can be partially clad by a protective coating layer that can be made from tungsten, ferro-tungsten, or a tungsten containing alloy, as well as from NiCr and NiCrAIY. The ceramic foam insert may be partially clad by a mullite layer to enhance the wettability of said ceramic foam insert by steel.

Due to the different wearing responses of the infiltrated ceramic foam and the cermet, the resulting hybrid inserts exhibit a higher wearing rate at the outer ceramic foam. During service, the inserts thus become gradually pointed, favoring penetration of the reinforced wearing elements, i.e. teeth, into the ground. It has been found that during manufacturing, the ceramic foam acts as an insulator thus increasing the thickness of the second bonding zone (3). The hybrid inserts thus exhibit a stronger tendency to the development of porosity within the surrounding foam as compared to bulk tungsten carbide inserts. The aforementioned protective inter-layers are then preferably applied to the tungsten carbide core prior to its insertion within the foam.

Although the presently disclosed processing strategies improve adhesion between all of the above described inserts and steel, it is important to note that the mechanical strength of the inserts is lower than that of the heat treated steel. Hence, insertion fundamentally reduces the load bearing capacity of the reinforced element even though the wear resistance is increased. To minimize such problem, different criteria have been developed to position the insert within the wear element. Likewise, a secure fixation system based on low-carbon wires protruding from the insert and connecting it with the mold has also been developed. Such fixation system guarantees that the insert is placed near the neutral axis of the wearing element. In doing so, it is ensured that when the applied load leads to failure at the outer surface of the wearing element, i.e. tooth, the surface of the inserted element is still subjected to a bending stress lying below its mechanical strength. This therefore results in a component whose mechanical strength is the same as that of the unreinforced (conventional) product, even though it exhibits an outstanding wear resistance. In order to assure a perfect fixation of the insert within the mold of the wearing element, another object of the invention refers to a self-supporting insert with a hard reinforcement body. Said self-supporting insert for wearing elements, comprises a reinforcement body harder than 500 HV with at least two holes, said holes house at least two fixation rods, made from a low carbon steel or similar material, that extend outward from the holes so as to protrude beyond the surface of the body for supporting and positioning said insert within the mold cavity of the wearing element.

The reinforcement body of the self-supporting insert can be any of the options already described in the previous objects of invention, i.e. a cermet, a ceramic foam, or a combination of both. All these options for the insert's body can also be protected/clad/enhanced in the ways already described.

When the body of said self-supporting insert is a cermet, said insert can be at least partially clad by a protective coating layer that is preferably made from tungsten, ferro-tungsten or other tungsten-containing alloy, as well as from NiCr and NiCrAIY.

Claims

1. Wearing element for earth/rock engaging/moving machines constituted by a 5 gravity-cast steel containing at least one bulk insert of cemented carbide, in which at least two bonding zones within a bonding region between insert and steel are defined:

- A first bonding zone where the cementing matrix of the cemented carbide is substituted by cast steel,

10 - A second bonding zone where the carbide of the cemented carbide insert is reacted with the cast steel, enriching the carbon content of the steel and lowering its melting temperature, characterized in that said second zone of the bonding region has a controlled thickness so as to restrict or prevent formation of macro-porosity in the 15 bonding region between insert and steel, thus precluding premature failure of said element under service.

2. Wearing element according to claim 1 , where said second zone has a thickness less than 3 mm.

3. Wearing element according to claim 1 , wherein said second zone contains pores 20 no larger than 3 mm.

4. Wearing element according to claim 1 , where said insert is a tungsten carbide based cermet.

5. Wearing element, according to claim 4, wherein said cementing matrix is a cobalt or cobalt alloy whose weight fraction is less that 20% of the insert prior to

25 insertion.

6. Wearing element according to claim 1 , wherein said insert is at least partially clad by a protective coating layer.

7. Wearing element according to claim 6, wherein said layer is made from tungsten, ferro-tungsten, a tungsten-containing alloy, or NiCr / NiCrAIY plasma sprayed

30 coatings.

8. Wearing element according to claim 4, where the tungsten content in said second bonding zone is above 12%.

9. Wearing element according to claim 1 , where the steel is cast at a pouring temperature less than 100⁰C above its melting temperature.

35 10. Wearing element according to claim 5, where the insert's core has increased cobalt content after casting of said element, thus improving its toughness.

11. Wearing element according to claim 1 , characterized in that risers are used to homogenize the temperature of the steel contacting said insert.

12. Wearing element according to claim 1 , where the steel is cast at a pouring 5 temperature more than 5O⁰C above its melting temperature.

13. Wearing element according to claim 12, characterized in that cores are used to homogenize the temperature of the steel contacting said insert.

14. Wearing element according to claim 1 , wherein said insert is completely surrounded by the cast steel.

10 15. Wearing element according to claim 1 , wherein said insert is at least partially surrounded by a ceramic foam.

16. Wearing element, according to claim 15, wherein said ceramic foam is a cellular tridimensional ceramic foam having an open-celled porous structure that is substantially or entirely penetrated by the cast steel. 15

17. Wearing element according to claim 16, characterized in that the tridimensional cellular ceramic foam is made from zirconia (ZrO₂) or a zirconia-containing material such as ZrO₂-CaO, ZrO₂-MgO, ZrO₂-Y₂O₃ or a composite such as AI₂O₃-

ZrO₂.

18. Wearing element according to claim 16, characterized in that the tridimensional 20 cellular ceramic insert is made from alumina-silicates (AI₂O₃-SiO₂) such as mullite, or high alumina (AI₂O₃) materials, or zirconia toughened alumina materials, or aluminate materials such as alumina spinels.

19. Wearing element according to claim 15, characterized in that the average porosity of the foam is between 10 and 60 pores per inch (ppi) and it is preferably 30 ppi.

25 20. Wearing element according to claim 15, characterized in that the volume percentage of the ceramic phase of the cellular foam is less than 35%, with the majority of the remaining volume of the insert being open pores penetrated by the cast steel.

21. Wearing element for earth/rock engaging/moving machines constituted by a 30 gravity-cast steel containing at least one insert comprising a cellular tridimensional ceramic foam having an open-celled porous structure that is substantially or entirely penetrated by the cast steel.

22. Wearing element according to claim 21 , characterized in that the tridimensional cellular ceramic foam insert is made from zirconia (ZrO₂) or a zirconia-containing

35 material such as ZrO₂-CaO, ZrO₂-MgO, ZrO₂-Y₂O₃ or a composite such as AI₂O₃- ZrO₂.

23. Wearing element according to claim 21, characterized in that the tridimensional cellular ceramic foam insert is made from alumina-silicates (AI₂O₃-SiO₂) such as mullite, or high alumina (AI₂O₃) materials, or zirconia toughened alumina

5 materials, or aluminate materials such as alumina spinels.

24. Wearing element according to claim 21 , characterized in that the average porosity of the insert is between 10 and 60 pores per inch (ppi) and it is preferably 30 ppi.

25. Wearing element according to claim 21 , characterized in that the volume percentage of the ceramic phase of the cellular foam insert is less than 35%, with

10 the majority of the remaining volume of the insert being open pores penetrated by the cast steel.

26. Wearing element according to claims 21 to 25 characterized in that the foam insert is at least partially clad by an alumina-silicate layer such as mullite.

27. Wearing element according to claim 21 , characterized by the incorporation of a 15 least one second insert within or at least partially surrounded by said first insert.

28. Wearing element according to claim 27, wherein said second insert is a tungsten carbide cermet with cobalt matrix.

29. Wearing element according to claim 27, wherein said second insert is at least partially clad by a protective coating layer.

20 30. Wearing element according to claim 29, wherein said layer is made from tungsten, ferro-tungsten, or a tungsten-containing alloy, or NiCr / NiCrAIY plasma sprayed coatings.

31. Self-supporting insert for wearing elements, characterized in that it comprises a reinforcement body harder than 500 HV with at least two holes, said holes

25 housing at least two fixation rods extending outward from the holes so as to protrude beyond the surface of the body for supporting and positioning said insert within a mold cavity.

32. Self-supporting insert according to claim 31 , wherein said fixation rods are made from a low carbon steel or similar material.

30 33. Self-supporting insert according to claim 31 , wherein said insert is at least partially clad by a protective coating layer.

34. Self-supporting insert according to claim 33, wherein said layer is made from tungsten, ferro-tungsten or other tungsten-containing alloy, or NiCr / NiCrAIY plasma sprayed coatings.

35 35. Self-supporting insert according to claim 31 , wherein said body is a tungsten carbide based cermet.

36. Self-supporting insert, according to claim 35, wherein said cemented matrix of said body contains less that 13wt% cobalt.

37. Self-supporting insert, according to claim 31 , wherein said reinforcement body is at least partially surrounded by a ceramic foam.

38. Self-supporting insert, according to claim 31 , wherein said reinforcement body is a ceramic foam.

39. Self-supporting insert, according to claim 37 and 38, wherein said ceramic foam is a cellular tridimensional ceramic foam having an open-celled porous structure that is substantially or entirely penetrated by the cast steel.

40. Self-supporting insert, according to claim 39, characterized in that the average porosity of the ceramic foam is between 10 and 60 pores per inch (ppi) and it is preferably 30 ppi.

41. Self-supporting insert, according to claim 39, characterized in that the volume percentage of the ceramic phase of the cellular foam is less than 35%, with the majority of the remaining volume of the insert being open pores penetrated by the cast steel.

42. Self-supporting insert, according to claim 39, characterized in that the tridimensional cellular ceramic foam is made from zirconia (ZrO₂) or a zirconia- containing material such as ZrO₂-CaO, ZrO₂-MgO, ZrO₂-Y₂O₃ or a composite such as AI₂O₃- ZrO₂.

43. Self-supporting insert, according to claim 39, characterized in that the tridimensional cellular ceramic foam is made from alumina-silicates (AI₂O₃-SiO₂) such as mullite, or high alumina (AI₂O₃) materials, or zirconia toughened alumina materials, or aluminate materials such as alumina spinels.