EP1450973B1 - Cast part with enhanced wear resistance - Google Patents

Abstract

The invention concerns a cast wear part with its structure reinforced by at least a type metal carbide, and/or metal nitride, and/or boride, and/or metal oxides, and/or intermetallic compounds, referred to below as constituents. The invention is characterized in that the raw materials used as reagents for said constituents have been introduced in a mould (1) before casting in the form of compacted powder inserts or preforms (3) or the form of slurries (4), and the reaction of said powders has been activated in situ by casting a metal, forming a porous conglomerate in situ, and said metal has infiltrated the porous conglomerate, thus forming a reinforced structure leading to inclusion of said constituents in the structure of the metal used for casting, thereby creating a reinforcing structure on the wear part (2).

Description

Object of the invention

The present invention relates to the realization of a casting having increased wear resistance by improving the abrasion resistance while maintaining an acceptable impact resistance on the reinforced parts.

Technological background on which the invention is based

Mineral extraction and fragmentation facilities, particularly milling and crushing equipment, are subject to numerous performance and cost constraints.

Examples of these include, in the field of aggregate processing, cement and ores, wear parts such as ejectors and anvils of vertical axis crushers, hammers and beaters of horizontal axis crushers, cones for crushers, vertical shredder tables and rollers, armor plates and ball or bar mills. Mining facilities include oil sands pumps, drilling pumps, mine pumps and dredging teeth.

Suppliers of wear parts of these machines are faced with increased demands for wear elements meeting both impact resistance and abrasion resistance requirements.

Traditional materials generally respond to one or the other type of these stresses but are very rarely resistant to both impact and abrasion. Indeed, ductile materials have a high impact resistance, but very poorly support abrasion. On the other hand, hard and abrasion-resistant materials are very resistant to violent shocks.

Historically, the first reflections on this problem have led to an exclusively metallurgical approach that consisted in offering manganese steels that are highly resistant to shocks and nevertheless achieving intermediate hardness levels of the order of 650 to 700 Hv (Vickers hardness).

Other alternatives such as chrome cast iron have also been proposed. These make it possible to reach hardness levels of the order of 700 to 850 Hv after an adequate heat treatment. These values are reached for alloys containing a percentage of carbides up to 35%.

At that time, bimetallic castings have also emerged, they nevertheless have the disadvantage of being limited to simple shaped parts which greatly reduces their potential for industrial application.

Wear parts are generally considered consumables, which means that apart from purely technical constraints, there is also an economic constraint that limits the possibilities to solutions with an average cost of about US $ 4 / Kg. . It is generally estimated that this price level, which is twice as high as that of coins wear, represents the threshold of economic acceptability for customers.

Description of the solutions according to the state of the art

Obtaining a wear part, resistant to abrasion and shock has already been the subject of various studies.

In this context, we have naturally turned to composite parts based on ceramics and in this context, the applicant already discloses in WO 99/47264 an alloy based on iron and ceramic very resistant to wear and shocks.

In WO 98/15373 the applicant proposes to introduce into a mold, before casting, a porous ceramic slab which is infiltrated by the metal during casting. The possibilities of application of this invention are nevertheless limited to parts of high section and alloys with a high flowability. Furthermore, the positioning of these ceramic slabs is rather conditioned by imperfections of infiltration by the cast metal than by the need for the use of the part.

Without aiming for the same objectives, Merzhanov, in the document WO / 9007013, discloses a porous refractory material obtained by cold pressing the raw material of an exothermic mixture of powders under vacuum followed by the initiation of the combustion of the mixture. This is a self-propelled reaction. By this process, it obtains extremely hard materials but without any impact resistance. This is mainly due to the high porosity of the products.

Moreover, in the document WO / 9011154, the same inventor proposes a similar method, where this time the powder mixture, after having reacted, is subjected to at pressures up to 1000 bar. This invention results in the production of layers highly resistant to abrasion but with insufficient resistance to shocks. The aim here is above all to provide surfaces for abrasive tools that are highly stressed in this direction.

In general, the use of very pure powders such as powders of titanium, boron, tungsten, aluminum, nickel, molybdenum, silicon, carbon, .. results in extremely porous bodies after reaction with porosity levels close to 50% . These then require compression subsequent to the reaction resulting in compaction and therefore an increase in density, essential for industrial use.

The complexity of implementing such a process, the control of the reactions and the cost of the raw materials still considerably hinder the industrialization of these technologies.

German Patent Application 1949777 - Lehmann discloses a method of manufacturing cast iron parts highly resistant to wear. In this process, carbide powders are combined with combustible binders and / or metal powders having a low melting temperature. During casting, the binder gives way to the casting metal which then coats the carbide particles. In this process, there is no self-propagating chemical reaction and all the highly wear-resistant particles are present from the start in the mold.

Numerous documents disclose such a coating of hard particles including US-P-5,052,464 and US-P-6,033,791-Smith which are based on the presence of hard particles before casting which is intended to infiltrate the pores between ceramic particles.

The invention avoids the pitfalls of the state of the art by producing wear parts of an original constitution and manufactured by an original and simple process, so inexpensive.

Goals of the invention

The present invention aims to provide wear parts resistant to both abrasion and shock at an economically justifiable price and a method for their production. It aims in particular to solve the problems related to the solutions proposed according to the state of the art.

Summary of the invention

The present invention relates to a wear part, made in the foundry, with structure reinforced by at least one type of metal carbide, and / or metal nitrides, and / or metal oxides, and / or metal borides, as well as intermetallic compounds, hereinafter referred to as the components, characterized in that the raw materials serving as reagents for said components were introduced into a mold, before casting, in the form of inserts or preforms of compacted powders or under form of slips, in that the reaction of said powders is initiated in situ by the casting of a metal, forming a porous conglomerate in situ, and in that said metal infiltrates the porous conglomerate, thus constituting a reinforced structure, to result in an addition of said conglomerate in the structure of the metal used for casting the part, and thus create a reinforcing structure on the wear part.

One of the key aspects of the present invention shows that the porous conglomerate, created in situ, infiltrated later by the casting has a Vickers hardness. greater than 1000 Hv ₂₀ , the wear part thus obtained offering toughness greater than the toughness of the pure ceramics envisaged and at least equal to 10 MPa m .

According to one of the features of the invention, the reaction in situ between the raw materials, ie the reactants for said components, is self-propagating and is initiated by the heat of the casting forming a very porous conglomerate capable of being infiltrated simultaneously by the cast metal without particular modification of the reinforcing structure.

According to a particularly advantageous embodiment of the invention, the reaction between the raw materials is carried out at atmospheric pressure and without any particular gaseous protective atmosphere, and without requiring compression after reaction.

The raw materials, intended to produce the component, belong to the group of ferroalloys, preferably FerroTi, FerroCr, FerroNb, FerroW, FerroMo, FerroB, FerroSi, FerroZr or FerroV, or belong to the group of oxides, preferably TiO ₂ , FeO, Fe ₂ O ₃ , SiO ₂ , ZrO ₂ , CrO ₃ , Cr ₂ O ₃ , B ₂ O ₃ , MoO ₃ , V ₂ O ₅ , CuO, MgO and NiO or in the group of metals or their alloys, preferably, iron, nickel, titanium or aluminum and also carbon, boron or nitride compounds.

Brief description of the figures

FIG. 1 shows a slurry 1 spread at the places where it is desired to strengthen the casting 2 in the mold 1.

FIG. 2 shows the invention in the form of reinforcing inserts 3 in the casting 2 in the mold 1.

Figures 3, 4, and 5 show hardness imprints for a chrome cast iron (Fig.3), a pure ceramic (Fig.4) and a reinforced alloy (Fig.5) to the ceramic according to the present invention.

Figure 6 shows TiC particles in an iron alloy, resulting from an in situ reaction of FerroTi with carbon to give TiC in an iron-based matrix. The particle size of TiC is of the order of a few microns.

Detailed description of the invention

The present invention provides casting parts whose wear surfaces are reinforced by placing in the mold, before casting, elements consisting of powders, capable of reacting in situ and under the sole action of the heat of the casting.

For this purpose, reactive elements, in compacted powders, are used which are fixed in the mold in the form of slabs or inserts 3 of desired shapes, or in the form of a coating 4 covering the mold 1 to 1. where room 2 is likely to be reinforced.

The elements that can react in situ give rise to hard compounds such as carbides, borides, oxides, nitrides or intermetallic compounds. These, once formed, will be added to the carbides possibly already present in the casting alloy so as to further increase the proportion of hard particles with a hardness Hv> 1300 and which contribute to the increase of the resistance. to wear. These are "infiltrated" at about 1500 ° C by the cast metal, and form an addition of abrasion resistant particles incorporated in the structure of the metal used for casting (Fig.6).

Moreover, unlike the processes of the state of the art, it is not necessary to use pure metal powders to obtain this reaction in situ. The proposed method advantageously allows the use of ferroalloys or inexpensive oxides to obtain extremely hard particles embedded in the matrix formed by the metal of the casting at the place where a reinforcement of the resistance to wear is necessary.

Not only, the invention does not require any densification, thus compression, a posteriori, reinforced structural parts, but takes advantage of the porosity thus created in said parts to allow a high temperature infiltration of the cast metal in the interstices (Fig. 6).

This does not require any particular protective atmosphere and is at atmospheric pressure with the heat provided by the casting, which obviously has a particularly positive impact on the cost of the process. This gives a structure with very advantageous characteristics in terms of simultaneous resistance to impact and abrasion.

The hardness values achieved by the particles thus introduced into the reinforced surfaces are in a range from 1300 to 3000 Hv. Following infiltration by the cast metal, the resulting compound has a hardness higher than 1000 Hv ₂₀ while maintaining a tenacity of greater than 10 MPa √ m. The tenacity is measured by indentation which means that an impression is made using a pyramidal diamond indenter subjected to a calibrated load.
Under the effect of the load, the material deforms and can develop cracks at the vertices of the impression. The measuring the length of the cracks allows an evaluation of the toughness (Figures 3, 4 and 5).

The raw materials, intended to produce the component, belong to the group of ferroalloys, preferably FerroTi, FerroCr, FerroNb, FerroW, FerroMo, FerroB, FerroSi, FerroZr or FerroV, they can also belong to the group of oxides, preferably the TiO ₂ , FeO, Fe ₂ O ₃ , SiO ₂ , ZrO ₂ , CrO ₃ , Cr ₂ O ₃ , H ₂ O ₃ , MoO ₃ , V ₂ O ₅ , CuO, MgO and NiO, or the group of metals or their alloys, preferably iron, nickel, titanium or aluminum and also carbon, boron or nitride compounds.

By way of example, the reactions used in the present invention are generally of the type:

FeTi + C -> TiC + Fe

TiO ₂ + Al + C -> TiC + Al ₂ O ₃

Fe ₂ O ₃ + Al -> Al ₂ O ₃ + Fe

Ti + C -> TiC

Al + C + B ₂ O ₃ -> B ₄ C + Al ₂ O ₃

MoO ₃ + Al + Si -> MoSi ₂ + Al ₂ O ₃

These reactions can also be combined with each other.

The reaction rate can be controlled by different additions of metals, alloys or particles not participating in the reaction. These additions can also be used advantageously to modify, as needed, the toughness or other properties of the composite created in situ. This is represented by the following illustrative reactions:

Fe ₂ O ₃ + 2Al + x Al ₂ O ₃ -> (1 + x) Al ₂ O ₃ + 2Fe

Ti + C + Ni -> TiC + Ni

Description of a preferred embodiment of the invention

The first preferred embodiment of the invention consists of compacting by simple pressing to cold the selected reactive powders. This is done in a compression mold taking up the desired shape of the insert or preform 3, possibly in the presence of a binder, for reinforcing the casting 2. This insert or preform will then be fixed in the mold of casting 1 at the desired place.

In powders, a particle size distribution is chosen with a D50 is between 1 and 1000 microns, and preferably less than 100 μ. Practical experience has shown that this particle size achieves an ideal compromise between the handling of the raw material, the infiltrability of the porous product and the control of the reaction.

During casting, the hot metal initiates the reaction of the preform or the insert which is transformed into a conglomerate with a porous structure of hard particles. This conglomerate, still at high temperature, is itself infiltrated and drowned by the casting metal constituting the part. This step is done between 1400 and 1700 ° C depending on the casting temperature of the alloy chosen to make the part.

A second preferred embodiment is the use of a slip (paste) 4 containing the various reactive elements to coat parts of the mold 1 or cores. The application of one or more layers is possible depending on the desired thickness. These different layers are then allowed to dry before pouring the metal into the mold 1. This molten metal will also initiate the reaction to create a porous layer which is infiltrated immediately after its reaction to form a structure that is particularly resistant to both impact and to wear.

Claims (11)

1. Wear part produced in a foundry, comprising a reinforced structure, said reinforced structure comprising at least one component selected from the group consisting of metallic carbides, metallic nitrides, borides, metallic oxides and intermetallic compounds, characterised in that :

   - said components are formed by a reaction in situ from raw materials acting as reagents for said components, said reagents being beforehand introduced into a mould (1) before the casting in the form of inserts or preformed shapes of compacted powders (3) or in the form of barbitones (4);

   - the reaction in situ of said powders is triggered by the casting of a metal;

   - said reaction in situ forms a porous conglomerate;

   - said casting metal infiltrates said porous conglomerate so as to result in the inclusion of said conglomerate in the structure of the metal used for the casting, thus creating a reinforced structure on the wear part (2).
2. Wear parts according to Claim 1, characterised in that said porous conglomerate is created in situ and is infiltrated by the cast metal, in that said conglomerate has a Vickers hardness between 1300 and 3000 Hv and in that said reinforced structure on the wear part has an impact resistance of over 10MPa√m.
3. Method for the production of wear parts with a structure reinforced by at least one component selected from the group consisting of metallic carbides, metallic nitrides, borides, metallic oxides and intermetallic compounds, characterised in that :

   - said components are formed by a reaction in situ from raw materials acting as reagents for said components, said reagents being beforehand introduced into a mould (1) before the casting in the form of inserts or preformed shapes of compacted powders (3) or in the form of barbitones (4);

   - the reaction in situ of said powders is triggered by the casting of a metal;

   - said reaction in situ forms a porous conglomerate;

   - said casting metal infiltrates said porous conglomerate so as to result in the inclusion of said conglomerate in the structure of the meal used for the casting, thus creating a reinforced structure on the wear part (2);

   - said reaction in situ between the raw materials for forming said components after said reaction is triggered and sustained by the heat of the casting.
4. Method for the production of the wear parts according to Claim 3, characterised in that the reaction between the raw materials forms a very porous conglomerate capable of being simultaneously infiltrated by the cast metal without any particular alteration of the reinforced structure.
5. Method for the production of wear parts according to Claim 3 or 4, characterised in that the reaction between the raw materials takes place at atmospheric pressure without requiring any compression after the reaction of the powders.
6. Method for the production of wear parts according to any one of Claims 3 to 5, characterised in that the reaction between the raw materials does not require any specific gaseous protective atmosphere.
7. Method for the production of wear parts according to any one of Claims 3 to 6, characterised in that said raw materials belong to the group consisting of ferrous alloys, preferably FerroTi, FerroCr, FerroNb, FerroW, FerroMo, FerroB, FerroSi, FerroZr and FerroV.
8. Method for the production of wear parts according to any one of Claims 3 to 6, characterised in that said raw materials belong to the group of oxides, preferably TiO₂, FeO, Fe₂O₃, SiO₂, ZrO₂, CrO₃, Cr₂O₃, B₂O₃, MoO₃, V₂O₅, CuO, MgO and NiO.
9. Method for the production of wear parts according to any one of Claims 3 to 6, characterised in that said raw materials belong to the group of metals or their alloys, preferably iron, titanium, nickel or aluminium.
10. Method for the production of wear parts according to any one of Claims 3 to 6, characterised in that said raw materials comprise carbon, boron, or nitride compounds.
11. Use of the wear parts produced according to any one of the preceding claims for applications requiring simultaneous resistance to both wear and impact.

Images