EP2329052B1 - Composite tooth for working the ground or rock - Google Patents

Abstract

The present invention discloses a composite tooth for working the ground or rocks, said tooth comprising a ferrous alloy at least partially reinforced with titanium carbide according to a defined geometry, in which said reinforced portion comprises an alternating macro-microstructure of millimetric areas concentrated with micrometric globular particles of titanium carbide separated by millimetric areas essentially free of micrometric globular particles of titanium carbide, said areas concentrated with micrometric globular particles of titanium carbide forming a microstructure in which the micrometric interstices between said globular particles are also filled by said ferrous alloy.

Description

Object of the invention

The present invention relates to a composite tooth intended to equip a machine for working the soil or rocks. It relates in particular to a tooth comprising a metal matrix reinforced by particles of titanium carbide.

Definition

The term "tooth" is to be interpreted broadly and includes any element of any size, having a pointed or flattened shape, intended in particular for working the soil, the bottom of rivers or seas, rocks, on the surface or in the mines.

State of the art

Few means are known for modifying the hardness and impact resistance of a deep casting alloy "in the mass". The known means generally concern surface modifications of shallow depth (a few mm). For foundry teeth, the reinforcing elements must be present in depth in order to withstand significant and simultaneous localized stress in terms of mechanical stress, wear and impact, and also because a tooth is used on much of its length.

It is known to refill teeth with metal carbides (Technosphère® - Technogenia) by oxyacetylene welding. Such reloading makes it possible to deposit a carbide layer a few millimeters thick on the surface of a tooth. Such a reinforcement is however not integrated with the metal matrix of the tooth and does not guarantee the same performance as a tooth where a carbide reinforcement is entirely incorporated into the mass of the metal matrix.

The document EP 1 450 973 B1 describes a reinforcement of wearing parts made by placing in the mold intended to receive the casting metal, an insert consisting of reactive powders which react with each other thanks to the heat provided by the metal during the casting at very high temperature (> 1400 ° C). After reaction of SHS type, the powders of the reactive insert will create a relatively uniform porous cluster (conglomerate) of hard particles; once formed, this porous mass will be immediately infiltrated by the casting metal at high temperature. The reaction of the powders is exothermic and self-propagating, which allows a synthesis of the carbides at high temperature and considerably increases the wettability of the porous mass by the infiltration metal.

The document US 5,081,774 discloses different ways of disposing chromed cast iron inserts in a flat-shaped tooth to increase its performance. But we know that the limits of such a technique are on the one hand the massiveness of the reinforcement which tends to weaken the part and on the other hand, the insufficient connection (welding) between the inserts and the base metal of the part .

The document US5,337,801 (Materkowski ) discloses another method for depositing hard particles of tungsten carbide on the working surface of the teeth. It is in this case to prepare first steel inserts containing hard particles; these Inserts are then placed in the mold and then embedded in the cast base metal to make the workpiece. This procedure is long and expensive, does not exclude a possible reaction between the tungsten carbide and the metal inserts and does not always guarantee perfect welding of the hard particles to the base metal.

Goals of the invention

The present invention discloses a composite tooth for a tillage or rock tillage tool, particularly for excavating or dredging tools, with improved wear resistance while maintaining good impact resistance. This property is obtained by a composite reinforcement structure specifically designed for this application, a material that alternates on a millimeter scale dense zones in fine micrometric globular particles of metal carbides with zones that are practically free of them within the metallic matrix. of the tooth.

The present invention also provides a method for obtaining said reinforcing structure.

Summary of the invention

The present invention discloses a composite tooth for tillage or rock, said tooth comprising a ferrous alloy reinforced at least in part with titanium carbide in a defined geometry, wherein said reinforced portion comprises an alternating macro-microstructure of zones millimeters millimeter areas concentrated in micrometric globular particles of titanium carbide separated by millimetric areas substantially free of micrometric globular particles of titanium carbide, said micrometrically concentrated micrometric micrometric particles of micrometric titanium carbide particles in which the micrometric interstices between said globular particles are also occupied by said ferrous alloy.

• lesdites zones millimétriques concentrées ont une concentration en carbures de titane supérieure à 36.9 % en volume ;
• ladite partie renforcée a une teneur globale de carbure de titane entre 16.6 et 50.5 % en volume ;
• les particules micrométriques globulaires de carbure de titane ont une taille inférieure à 50µm ;
• la majeure partie des particules micrométriques globulaires de carbure de titane a une taille inférieure à 20 µm ;
• lesdites zones concentrées en particules globulaires de carbure de titane comportent 36.9 à 72.2 % en volume de carbure de titane ;
• lesdites zones millimétriques concentrées en carbure de titane ont une dimension variant de 1 à 12 mm ;
• lesdites zones millimétriques concentrées en carbure de titane ont une dimension variant de 1 à 6 mm ;
• lesdites zones concentrées en carbure de titane ont une dimension variant de 1.4 à 4 mm ;

According to particular embodiments of the invention, the composite tooth comprises at least one or an appropriate combination of the following characteristics:

• said concentrated millimeter areas have a concentration of titanium carbides greater than 36.9% by volume;
• said reinforced portion has an overall titanium carbide content between 16.6 and 50.5% by volume;
• the micrometric globular particles of titanium carbide have a size of less than 50 μm;
• most of the micrometric globular particles of titanium carbide has a size less than 20 microns;
• said zones concentrated in globular particles of titanium carbide comprise 36.9 to 72.2% by volume of titanium carbide;
• said millimetric areas of concentrated titanium carbide have a size ranging from 1 to 12 mm;
• said millimetric zones concentrated in titanium carbide have a dimension ranging from 1 to 6 mm;
• said concentrated areas of titanium carbide have a size ranging from 1.4 to 4 mm;

• mise à disposition d'un moule comportant l'empreinte de la dent avec une géométrie de renforcement prédéfinie ;
• introduction, dans la partie de l'empreinte de la dent destinée à former la partie renforcée (5), d'un mélange de poudres compactées comportant du carbone et du titane sous forme de granulés millimétriques précurseurs de carbure de titane ;
• coulée d'un alliage ferreux dans le moule, la chaleur de ladite coulée déclenchant une réaction exothermique de synthèse auto-propagée de carbure de titane à haute température (SHS) au sein desdits granulés précurseurs ;
• formation, au sein de la partie renforcée de la dent composite d'une macro-microstructure alternée de zones millimétriques concentrées en particules globulaires micrométriques de carbure de titane à l'emplacement desdits granulés précurseurs, lesdites zones étant séparées entre elles par des zones millimétriques essentiellement exemptes de particules globulaires micrométriques de carbure de titane, lesdites particules globulaires étant également séparées au sein desdites zones millimétriques concentrées de carbure de titane par des interstices micrométriques ;
• infiltration des interstices millimétriques et micrométriques par ledit alliage ferreux de coulée à haute température, consécutive à la formation de particules microscopiques globulaires de carbure de titane.

The present invention also discloses a method of manufacturing the composite tooth according to any one of claims 1 to 9 comprising the following steps:

• provision of a mold having the tooth impression with a predefined reinforcement geometry;
• introducing, into the part of the impression of the tooth intended to form the reinforced part (5), a mixture of compacted powders comprising carbon and titanium in the form of millimetric granules precursors of titanium carbide;
• casting a ferrous alloy into the mold, the heat of said casting triggering an exothermic reaction of self-propagating synthesis of high temperature titanium carbide (SHS) within said precursor granules;
• forming, within the reinforced portion of the composite tooth, an alternating macro-microstructure of millimetric zones concentrated in micrometric globular particles of titanium carbide at the location of said precursor granules, said zones being separated from each other by millimetric zones essentially free of micrometric globular particles of titanium carbide, said globular particles being also separated within said millimetric areas of concentrated titanium carbide by micrometric interstices;
• infiltration of the millimetric and micrometric interstices by said high-temperature ferrous casting alloy, subsequent to the formation of microscopic globular particles of titanium carbide.

• les poudres compactées de titane et de carbone comportent une poudre d'un alliage ferreux ;
• ledit carbone est du graphite.

According to particular embodiments of the invention, the method comprises at least one or a suitable combination of the following characteristics:

• the compacted powders of titanium and carbon comprise a powder of a ferrous alloy;
• said carbon is graphite.

The present invention also discloses a composite tooth obtained according to the method of any one of claims 11 to 13.

Brief description of the figures

The Figures 1a and 1b show a three-dimensional view of teeth without reinforcement according to the state of the art.

The Figures 1c to 1h show a three-dimensional view of teeth with reinforcement according to the invention.

The figure 2 shows illustrative examples of tools on which the teeth according to the invention are mounted. Excavation and drilling tools.

• l'étape 3a montre le dispositif de mélange des poudres de titane et de carbone ;
• l'étape 3b montre la compaction des poudres entre deux rouleaux suivie d'un concassage et d'un tamisage avec recyclage des particules trop fines ;
• la figure 3c montre un moule de sable dans lequel on a placé un barrage pour contenir les granulés de poudre compactée à l'endroit du renforcement de la dent de type 1d ;
• la figure 3d montre un agrandissement de la zone de renforcement dans laquelle se trouvent les granulés compactés comportant les réactifs précurseurs du TiC ;
• l'étape 3e montre la coulée de l'alliage ferreux dans le moule ;
• la figure 3f montre la dent de type 1b résultant de la coulée ;
• la figure 3g montre un agrandissement des zones à forte concentration en nodules de TiC - ce schéma représente les mêmes zones que dans la figure 4 ;
• la figure 3h montre un agrandissement au sein d'une même zone à forte concentration en globules de TiC - les globules micrométriques sont individuellement entourés par le métal de coulée.

FIG. 3a-3h shows the method of manufacturing the tooth represented in FIG. figure 1b according to the invention.

• step 3a shows the device for mixing titanium and carbon powders;
• step 3b shows the compaction of the powders between two rollers followed by crushing and sieving with recycling of the fine particles;
• the figure 3c shows a sand mold in which a dam has been placed to contain the compacted powder granules at the location of the reinforcement of the type 1d tooth;
• the figure 3d shows an enlargement of the reinforcement zone in which the compacted granules comprising TiC precursor reactants are located;
• step 3e shows the casting of the ferrous alloy in the mold;
• the figure 3f shows the type 1b tooth resulting from casting;
• the figure 3g shows an enlargement of areas with high concentrations of TiC nodules - this diagram represents the same areas as in the figure 4 ;
• the figure 3h shows an enlargement within the same zone with a high concentration of TiC globules - the Micrometric globules are individually surrounded by the casting metal.

The figure 4 represents a binocular view of a polished, unengaged surface of a section of the reinforced portion of the tooth according to the invention with millimetric areas (in light gray) concentrated micrometric globular titanium carbide (TiC globules). The dark part represents the metal matrix (steel or cast iron) filling at the same time the space between these concentrated zones in micrometric globular titanium carbide but also the spaces between the globules themselves. (See figures 5 and 6 ).

The figures 5 and 6 represent SEM electron microscopic views of micrometric globular titanium carbide on polished and untouched surfaces at different magnifications. We see that in this particular case most of the globules of titanium carbide have a size less than 10 microns.

The figure 7 represents a view of micrometric globular titanium carbide on a fracture surface taken by SEM electron microscope. It can be seen that the globules of titanium carbide are perfectly incorporated in the metal matrix. This proves that the casting metal completely infiltrates (impregnates) the pores during casting once the chemical reaction between titanium and carbon is initiated.

Legend

1. 1. Millimeter zones concentrated in micrometric globular particles (nodules) micrometric titanium carbide (bright areas)
2. 2. millimetric interstices filled with ferrous casting alloy generally free of particles micrometric globular titanium carbide (dark areas)
3. 3. micrometric interstices between TiC nodules also infiltrated by casting alloy
4. 4. micrometric globular titanium carbide, in the concentrated areas of titanium carbide
5. 5. titanium carbide reinforcement
6. 6. gas defects
7. 7. (free)
8. 8. mixer of Ti and C powders
9. 9. hopper
10. 10. roll
11. 11. crusher
12. 12. exit grid
13. 13. sieve
14. 14. recycling of fine particles to the hopper
15. 15. sand mold
16. 16. dam containing the compacted granules of Ti / C mixture
17. 17. ladle
18. 18. tooth type 1d

Detailed description of the invention

In materials science, the SHS or " s elf-propagating h igh temperature s ynthesis" reaction is a self-propagating, high-temperature synthesis reaction in which reaction temperatures are generally greater than 1500 ° C or even 2000. ° C. For example, the reaction between titanium powder and carbon powder to obtain titanium carbide TiC is highly exothermic. Only a little energy is needed to initiate the reaction locally. Then, the reaction will spontaneously propagate to the entire mixture of reagents thanks to the high temperatures reached. After initiation of the reaction, one has a reaction front which is propagated spontaneously (self-propagated) and which makes it possible to obtain titanium carbide from titanium and carbon. The titanium carbide thus obtained is said to be "obtained in situ" because it does not come from the cast ferrous alloy.

The reactant powder mixtures comprise carbon powder and titanium powder and are compressed into plates and then crushed to obtain granules ranging in size from 1 to 12 mm, preferably from 1 to 6 mm, and particularly preferably from 1.4 to 4 mm. These granules are not 100% compacted. They are generally compressed between 55 and 95% of the theoretical density. These granules allow easy use / handling (see Fig. 3a-3h).

These millimetric granules of mixed carbon and titanium powders obtained according to the diagrams of FIG. 3a-3h constitute the precursors of the titanium carbide to be created and make it possible to easily fill mold parts of various or irregular shapes. These granules can be held in place in the mold 15 by means of a dam 16, for example. The shaping or assembly of these granules can also be done using an adhesive.

The composite tooth for tillage or rocks according to the present invention has a reinforcing macro-microstructure which can also be called an alternating structure of zones concentrated in micrometric globular particles of titanium carbide separated by zones which are practically free. Such a structure is obtained by the reaction in the mold of the granules comprising a mixture of powders of carbon and titanium. This reaction is initiated by the heat of casting of the cast iron or steel used to sink any the piece and therefore both the unreinforced and the reinforced part (see Fig. 3rd ). The casting therefore triggers an exothermic reaction of self-propagating synthesis at high temperature of the mixture of powders of carbon and titanium compacted in the form of granules (self-propagating high-temperature synthesis - SHS) and previously placed in the mold 15. The reaction then has the distinction of continuing to spread as soon as it is initiated.

This high temperature synthesis (SHS) allows easy infiltration of all millimetric and micrometric interstices by cast iron or casting steel ( Fig. 3g & 3h ). By increasing the wettability, the infiltration can be done on any thickness or depth of reinforcement of the tooth. It advantageously makes it possible, after SHS reaction and infiltration by an external casting metal, to create one or more reinforcement zones on the tooth comprising a high concentration of micrometric globular particles of titanium carbide (which could also be called clusters of nodules), which areas have a size of the order of a millimeter or a few millimeters, and which alternate with areas substantially free of globular titanium carbide.

Once these granules have reacted according to an SHS reaction, the zones of reinforcement where these granules were found show a concentrated dispersion of micrometric globular particles 4 of TiC carbide (globules) whose micrometric interstices 3 have also been infiltrated by the casting metal. which is here cast iron or steel. It is important to note that the millimetric and micrometric interstices are infiltrated by the same metallic matrix as that which constitutes the unreinforced part of the tooth; this allows a total freedom of choice of the casting metal. In the Finally, in the tooth obtained, the reinforcement zones with a high concentration of titanium carbide are composed of globular micrometer particles of TiC in a large percentage (between approximately 35 and approximately 70% by volume) and of the ferrous infiltration alloy.

Micrometric globular particles are understood to mean globally spheroidal particles having a size ranging from a few μm to a few tens of μm at the most, the vast majority of these particles having a size of less than 50 μm, and even 20 μm, or even less than 10 μm. We also call them TiC globules. This globular form is characteristic of a method for obtaining titanium carbide by self-propagating synthesis SHS (see Fig. 6 ).

Obtaining pellets (Ti + C version) for strengthening the tooth

The process for obtaining the granules is illustrated in FIG. 3a-3h. The granules of carbon / titanium reagents are obtained by compaction between rollers 10 in order to obtain strips that are then crushed in a crusher 11. The mixture of the powders is made in a mixer 8 consisting of a tank equipped with blades , to promote homogeneity. The mixture then passes into a granulation apparatus through a hopper 9. This machine comprises two rollers 10, through which the material is passed. Pressure is applied to these rollers 10, which compresses the material. A strip of compressed material is obtained at the outlet, which is then crushed in order to obtain the granules. These granules are then sieved to the desired particle size in a sieve 13. An important parameter is the pressure applied to the rollers. At most this pressure is high, at most the band, and therefore the granules will be compressed. It is thus possible to vary the density of the strips, and consequently of the granules, between 55 and 95% of the theoretical density which is 3.75 g / cm ³ for the stoichiometric mixture of titanium and carbon. The apparent density (taking into account the porosity) is then between 2.06 and 3.56 g / cm ³ .

The degree of compaction of the bands depends on the applied pressure (in Pa) on the rollers (diameter 200 mm, width 30 mm). For a low level of compaction, of the order of 10 ⁶ Pa, we obtain a density on the bands of the order of 55% of the theoretical density. After passing through the rollers 10 to compress this material, the apparent density of the granules is 3.75 x 0.55, ie 2.06 g / cm ³ .

For a high level of compaction, of the order of 25 × 10 ⁶ Pa, a density on the strips of 90% of the theoretical density is obtained, ie a bulk density of 3.38 g / cm ³ . In practice one can go up to 95% of the theoretical density.

Therefore, the granules obtained from the raw material Ti + C are porous. This porosity varies from 5% for highly compressed granules, to 45% for slightly compressed granules.

In addition to the level of compaction, it is also possible to adjust the granulometric distribution of the granules and their shape during the operation of crushing strips and sieving Ti + C granules. Unwanted particle size fractions are recycled at will (see Fig. 3b ). The granules obtained generally have a size between 1 and 12 mm, preferably between 1 and 6 mm, and particularly preferably between 1.4 and 4 mm.

Realization of the reinforcement zone in the composite tooth according to the invention

The granules are made as described above. To obtain a three-dimensional structure or superstructure / macro-microstructure with these granules, they are placed in the areas of the mold where it is desired to reinforce the workpiece. This is achieved by agglomerating the granules either by means of an adhesive, or by confining them in a container, or by any other means (dam 16). The bulk density of the stack of Ti + C granules is measured according to ISO 697 and depends on the level of compaction of the bands, the granulometric distribution of the granules and the crushing mode of the bands, which influences the shape of the granules .
The bulk density of these Ti + C granules is generally of the order of 0.9 g / cm ³ to 2.5 g / cm ³ depending on the level of compaction of these granules and the density of the stack.

Before reaction, there is therefore a stack of porous granules composed of a mixture of titanium powder and carbon powder.

• la porosité microscopique présente dans les espaces à forte concentration en carbure de titane, dépendant du niveau de compaction initial de ces granulés ;
• les espaces millimétriques entre les zones à forte concentration en carbure de titane, dépendant de l'empilement initial des granulés (densité en vrac) ;
• la porosité venant de la contraction volumétrique lors de la réaction entre Ti + C pour obtenir le TiC.

During the Ti + C → TiC reaction, there is a volumetric contraction of about 24% when passing reagents to the product (contraction coming from the density difference between the reagents and the products). Thus, the theoretical density of the Ti + C mixture is 3.75 g / cm ³ and the theoretical density of the TiC is 4.93 g / cm ³ . In the final product, after the reaction to obtain TiC, the casting metal will infiltrate:

• the microscopic porosity present in spaces with a high concentration of titanium carbide, depending on the initial level of compaction of these granules;
• the millimeter spaces between the zones with a high concentration of titanium carbide, depending on the initial stacking of the granules (bulk density);
• the porosity coming from the volumetric contraction during the reaction between Ti + C to obtain the TiC.

Examples

• titane, H.C. STARCK, Amperit 155.066, moins de 200 mesh,
• carbone graphite GK Kropfmuhl, UF4, > 99.5 %, moins de 15 µm,
• Fe, sous la forme Acier HSS M2, moins de 25 µm,
• proportions :
  • Ti + C 100 g Ti - 24.5 g C
  • Ti + C + Fe 100 g Ti - 24.5 g C - 35.2 g Fe Mélange 15 min dans mélangeur Lindor, sous argon.

La granulation a été effectuée avec un granulateur Sahut-Conreur.
Pour les mélanges Ti+C+Fe et Ti+C, la compacité des granulés a été obtenue en faisant varier la pression entre les rouleaux de 10 à 250.10⁵ Pa.
Le renforcement a été effectué en plaçant des granulés dans un container métallique, qui est ensuite judicieusement placé dans le moule à l'endroit où la dent est susceptible d'être renforcée. Ensuite on coule l'acier ou la fonte dans ce moule.In the examples that follow, the following raw materials were used:

• titanium, HC STARCK, Amperit 155.066, less than 200 mesh,
• graphite carbon GK Kropfmuhl, UF4,> 99.5%, less than 15 μm,
• Fe, in the form of HSS M2 steel, less than 25 μm,
• proportions:
  • Ti + C 100 g Ti - 24.5 g C
  • Ti + C + Fe 100 g Ti - 24.5 g C - 35.2 g Fe Mix 15 min in Lindor mixer, under argon.

Granulation was carried out with a Sahut-Conreur granulator.
For the Ti + C + Fe and Ti + C mixtures, the compactness of the granules was obtained by varying the pressure between the rolls by 10 to 250 × 10 ⁵ Pa.
Reinforcement has been done by placing granules in a metal container, which is then conveniently placed in the mold where the tooth is likely to be reinforced. Then we cast the steel or cast in this mold.

Example 1

In this example, it is intended to make a tooth whose reinforced zones comprise an overall volume percentage of TiC of about 42%. For this purpose, a band is produced by compaction at 85% of the density theoretical of a mixture of C and Ti. After crushing, the granules are sieved to obtain a pellet size of between 1.4 and 4 mm. A bulk density of the order of 2.1 g / cm ³ (35% of space between the granules + 15% of porosity in the granules) is obtained.

The granules are placed in the mold at the location of the part to be reinforced, which thus comprises 65% by volume of porous granules. A chromium cast iron (3% C, 25% Cr) was then cast at about 1500 ° C in a non-preheated sand mold. The reaction between Ti and C is initiated by the heat of melting. This casting is done without a protective atmosphere. After reaction, 65% by volume of zones with a high concentration of approximately 65% of globular titanium carbide, ie 42% by global volume of TiC in the reinforced part of the tooth, are obtained in the reinforced part.

Example 2

In this example, it is intended to produce a tooth whose reinforced zones comprise an overall Tic volume percentage of approximately 30%. For this purpose, a 70% compaction band of the theoretical density of a mixture of C and Ti. After crushing, the granules are sieved to obtain a pellet size of between 1.4 and 4 mm. A bulk density of the order of 1.4 g / cm ³ (45% of space between the granules + 30% of porosity in the granules) is obtained. The granules are placed in the part to be reinforced, which thus comprises 55% by volume of porous granules. After reaction, in the reinforced part, 55% by volume of zones with a high concentration of approximately 53% of globular titanium carbide are obtained, ie approximately 30% by total volume of TiC in the reinforced part of the tooth.

Example 3

In this example, it is intended to make a tooth whose reinforced areas comprise an overall volume percentage of TiC of about 20%. For this purpose, a band is made by compaction at 60% of the theoretical density of a mixture of C and Ti. After crushing, the granules are sieved so as to obtain a granule size of 1 and 6 mm. A bulk density of the order of 1.0 g / cm ³ (55% of space between the granules + 40% of porosity in the granules) is obtained. The granules are placed in the part to be reinforced, which thus comprises 45% by volume of porous granules. After reaction, 45% by volume of zones concentrated to about 45% of globular titanium carbide, or 20% by volume of TiC in the reinforced portion of the tooth, are obtained in the reinforced portion.

Example 4

In this example, it was sought to attenuate the intensity of the reaction between carbon and titanium by adding a ferrous alloy powder. As in Example 2, it is intended to make a tooth whose reinforced areas comprise an overall volume percentage of TiC of about 30%. For this purpose, a compaction band is produced at 85% of the theoretical density of a mixture by weight of 15% of C, 63% of Ti and 22% of Fe. After crushing, the granules are sieved to obtain a granule size between 1.4 and 4 mm. A bulk density of the order of 2 g / cm ³ (45% of space between the granules + 15% of porosity in the granules) is obtained. The granules are placed in the reinforced part, which thus comprises 55% by volume of porous granules. After reaction, in the reinforced part, 55% by volume of zones with a high concentration are obtained. approximately 55% of globular titanium carbide, ie 30% by volume of global titanium carbide in the reinforced macro-microstructure of the tooth.

The following tables show the many possible combinations. <b><u> Table 1 </ u> (Ti + 0.98 C) </ b> Overall percentage of TiC obtained in the reinforced microstructure after reaction Ti + 0.98 C in the reinforced part of the tooth. Compaction of the granules (% of the theoretical density which is 3.75 g / cm ³ ) 55 60 65 70 75 80 85 90 95 Filling the reinforced part of the part (% vol.) 70 29.3 31.9 34.6 37.2 39.9 42.6 45.2 47.9 50.5 65 27.2 29.6 32.1 34.6 37.1 39.5 42.0 44.5 46.9 55 23.0 25.1 27.2 29.3 31.4 33.4 35.5 37.6 39.7 45 18.8 20.6 22.2 23.9 25.7 27.4 29.1 30.8 32.5 this table shows that with a level of compaction ranging from 55 to 95% for the bands and therefore the granules, it is possible to practice filling levels in granules in the reinforced part ranging from 45 to 70% by volume (ratio between the volume total pellets and the volume of their confinement). Thus, to obtain an overall concentration of TiC in the reinforced portion of about 29% vol. (in bold letters in the table), we can proceed to different combinations such as for example 60% of compaction and 65% of filling, or 70% of compaction and 55% of filling, or else 85% of compaction and 45% of filling . To obtain granular filling levels in the reinforced portion up to 70% by volume, it is necessary to apply a vibration to compact the granules. In this case, the ISO 697 standard for measuring the degree of filling is no longer applicable and the quantity of material in a given volume is measured. Relationship between the compaction level, the theoretical density and the percentage of TiC obtained after reaction in the granule Compaction of granules 55 60 65 70 75 80 85 90 95 Density in g / cm ³ 2.06 2.25 2.44 2.63 2.81 3.00 3.19 3.38 3.56 TiC obtained after reaction (and contraction) in% vol. in the granules 41.8 45.6 49.4 53.2 57.0 60.8 64.6 68.4 72.2 Here, we have represented the density of the granules as a function of their level of compaction and deduced the volume percentage of TiC obtained after reaction and thus contraction of about 24% vol. Granules compacted to 95% of their theoretical density thus make it possible to obtain after reaction a concentration of 72.2% vol. in TiC. Bulk density of the stack of pellets compaction 55 60 65 70 75 80 85 90 95 Filling the reinforced part of the part in% vol 70 1.4 1.6 1.7 1.8 2 2.1 2.2 2.4 2.5 65 1.3 * 1.5 1.6 1.7 1.8 2.0 2.1 2.2 2.3 55 1.1 1.2 1.3 1.4 1.5 1.7 1.8 1.9 2.0 45 0.9 1.0 1.1 1.2 1.3 1.4 1.4 1.5 1.6 (*) Bulk density (1.3) = theoretical density (3.75 g / cm ³ )) x 0.65 (filling) x 0.55 (compaction) In practice, these tables are used by the user of this technology, which sets an overall percentage of TiC to be made in the reinforced portion of the tooth and which, as a result, determines the filling level and the compaction of the granules. that he will use. The same tables were made for a mixture of Ti + C + Fe powders.

Ti + 0.98 C + Fe

Nous entendons par poudre de fer : fer pur ou alliage de fer.

• Densité théorique du mélange : 4.25 g/cm³
• Retrait volumétrique lors de la réaction : 21 %

Tableau 4 Pourcentage global de TiC obtenu dans la macro-microstructure renforcée après réaction Ti + 0.98 C + Fe dans la partie renforcée de la dent Compaction des granulés (% de la densité théorique qui est de 4.25 g/cm³) 55 60 65 70 75 80 85 90 95 Remplissage de la partie renforcée de la pièce (% vol) 70 25.9 28.2 30.6 32.9 35.5 37.6 40.0 42.3 44.7 65 24.0 26.2 28.4 30.6 32.7 34.9 37.1 39.3 41.5 55 20.3 22.2 24.0 25.9 27.7 29.5 31.4 33.2 35.1 45 16.6 18.1 19.6 21.2 22.7 24.2 25.7 27.2 28.7 A nouveau, pour obtenir une concentration globale en TiC dans la partie renforcée d'environ 26 % vol (en lettres grasses dans le tableau), on peut procéder à différentes combinaisons comme par exemple 55 % de compaction et 70 % de remplissage, ou 60 % de compaction et 65 % de remplissage, ou 70 % de compaction et 55 % de remplissage, ou encore 85 % de compaction et 45 % de remplissage. Tableau 5 Relation entre le niveau de compaction, la densité théorique et le pourcentage de TiC, obtenue après réaction dans le granulé en tenant compte de la présence de fer Compaction des granulés 55 60 65 70 75 80 85 90 95 Densité en g/cm³ 2.34 2.55 2.76 2.98 3.19 3.40 3.61 3.83 4.04 TiC obtenu après réaction (et contraction) en %vol. dans les granulés 36.9 40.3 43.6 47.0 50.4 53.7 57.1 60.4 63.8 Tableau 6 Densité en vrac de l'empilement des granulés (Ti + C + Fe) Compaction 55 60 65 70 75 80 85 90 95 Remplissage de la partie renforcée de la pièce en % vol. 70 1.6 1.8 1.9 2.1 2.2 2.4 2.5 2.7 2.8 65 1.5* 1.7 1.8 1.9 2.1 2.2 2.3 2.5 2.6 55 1.3 1.4 1.5 1.6 1.8 1.9 2.0 2.1 2.2 45 1.1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 (*) Densité en vrac (1.5) = densité théorique (4.25) x 0.65 (remplissage) x 0.55 (compaction) Here, the inventor has targeted a mixture to obtain 15% by volume of iron after reaction. The proportion of mixture that has been used is: $$\mathrm{100}\mathrm{g\; Ti}\mathrm{+}\mathrm{25.5}\mathrm{g\; C}\mathrm{+}\mathrm{35.2}\mathrm{g\; Fe}$$

We mean by iron powder: pure iron or iron alloy.

• Theoretical density of the mixture: 4.25 g / cm ³
• Volumetric shrinkage during the reaction: 21%

<b><u> Table 4 </ u></b> Overall percentage of TiC obtained in the reinforced microstructure after reaction Ti + 0.98 C + Fe in the reinforced part of the tooth Compaction of the granules (% of theoretical density which is 4.25 g / cm ³ ) 55 60 65 70 75 80 85 90 95 Filling the reinforced part of the part (% vol) 70 25.9 28.2 30.6 32.9 35.5 37.6 40.0 42.3 44.7 65 24.0 26.2 28.4 30.6 32.7 34.9 37.1 39.3 41.5 55 20.3 22.2 24.0 25.9 27.7 29.5 31.4 33.2 35.1 45 16.6 18.1 19.6 21.2 22.7 24.2 25.7 27.2 28.7 Again, to obtain an overall concentration of TiC in the reinforced part of about 26% vol (in bold letters in the table), one can proceed to different combinations such as for example 55% compaction and 70% filling, or 60%. % compaction and 65% filling, or 70% compaction and 55% filling, or 85% compaction and 45% filling. Relationship between the compaction level, the theoretical density and the percentage of TiC, obtained after reaction in the granule taking into account the presence of iron Compaction of granules 55 60 65 70 75 80 85 90 95 Density in g / cm ³ 2.34 2.55 2.76 2.98 3.19 3.40 3.61 3.83 4.04 TiC obtained after reaction (and contraction) in% vol. in the granules 36.9 40.3 43.6 47.0 50.4 53.7 57.1 60.4 63.8 Bulk density of the stack of pellets (Ti + C + Fe) compaction 55 60 65 70 75 80 85 90 95 Filling the reinforced part of the piece in% vol. 70 1.6 1.8 1.9 2.1 2.2 2.4 2.5 2.7 2.8 65 1.5 * 1.7 1.8 1.9 2.1 2.2 2.3 2.5 2.6 55 1.3 1.4 1.5 1.6 1.8 1.9 2.0 2.1 2.2 45 1.1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 (*) Bulk density (1.5) = theoretical density (4.25) x 0.65 (filling) x 0.55 (compaction)

Advantages

The present invention has the following advantages over the state of the art in general:

Better shock resistance

With the present process, there are porous millimetric granules which are crimped into the metal infiltration alloy. These millimetric granules are themselves composed of microscopic particles of globular TiC also crimped in the metal alloy infiltration. This system makes it possible to obtain a tooth with a reinforcement zone comprising a macrostructure within which there is an identical microstructure on a scale approximately a thousand times smaller.

The fact that the reinforcement zone of the tooth comprises small globular particles of titanium carbide, hard and finely dispersed in a metal matrix which surrounds them, makes it possible to avoid the formation and crack propagation (see Fig. 4 & 6 ). There is thus a double dissipative system of cracks.

Cracks generally originate at the most fragile places, which in this case are the TiC particle or the interface between this particle and the infiltration metal alloy. If a crack originates at the interface or in the micrometric particle of TiC, the propagation of this crack is then impeded by the infiltration alloy which surrounds this particle. The toughness of the infiltration alloy is greater than that of the TiC ceramic particle. The crack needs more energy to pass from one particle to another, to cross the micrometric spaces that exist between the particles.

Maximum flexibility for implementation parameters

In addition to the level of compaction of the granules, it is possible to vary two parameters which are the granulometric fraction and the shape of the granules, and therefore their bulk density. On the other hand, in an insert reinforcement technique, it is only possible to vary the level of compaction thereof in a limited range. In terms of the shape that we want to give the reinforcement, given the design of the tooth and the place that we want to strengthen, the use of granules allows more opportunities and adaptation.

Advantages in manufacturing

• moins de dégagement gazeux,
• moindre susceptibilité à la crique,
• meilleure localisation du renforcement dans la dent.

La réaction entre le Ti et le C est fortement exothermique. L'élévation de température provoque un dégazage des réactifs, c'est-à-dire des matières volatiles comprises dans les réactifs (H₂O dans le carbone, H₂, N₂ dans le titane). Au plus la température de réaction est élevée, au plus ce dégagement est important. La technique par granulés permet de limiter la température, de limiter le volume gazeux et permet une évacuation plus facile des gaz et ainsi de limiter les défauts de gaz. (voir Fig. 7 avec bulle de gaz indésirable).The use as reinforcement of a stack of porous granules, has certain advantages at the level of manufacture:

• less gassing,
• less susceptibility to the crack,
• better localization of reinforcement in the tooth.

The reaction between Ti and C is strongly exothermic. The rise in temperature causes degassing of the reagents, that is to say volatile materials included in the reagents (H ₂ O in carbon, H ₂ , N ₂ in titanium). The higher the reaction temperature, the greater this clearance is important. The granular technique makes it possible to limit the temperature, to limit the gaseous volume and allows an easier evacuation of the gases and thus to limit the gas defects. (see Fig. 7 with unwanted gas bubble).

Low susceptibility to crack during the manufacture of the tooth according to the invention

The coefficient of expansion of the TiC reinforcement is lower than that of the ferrous alloy matrix (TiC expansion coefficient: 7.5 × 10 ^-6 / K and the ferrous alloy: about 12.0 × 10 ^-5 / K). This difference in the expansion coefficients has the consequence of generating tensions in the material during the solidification phase and also during the heat treatment. If these voltages are too great, cracks may appear in the room and lead to scrapping it. In the present invention, a small proportion of TiC reinforcement (less than 50% by volume) is used, resulting in less stress in the part. In addition, the presence of a more ductile matrix between the micrometric globular particles of TiC in alternating zones of low and high concentration makes it possible to better manage any local voltages.

Excellent maintenance of reinforcement in the tooth

In the present invention, the boundary between the reinforced portion and the unreinforced portion of the tooth is not abrupt because there is a continuity of the metal matrix between the reinforced portion and the unreinforced portion, which allows the protect against a complete tearing of the reinforcement.

Test results

• calcaire dur : 2.5 fois ;
• mélange d'argile dure, de sable et de gravier compactés : 2.9 fois ;
• mélange de sable et d'argile dure : 3.2 fois ;
• mélange de schiste et de sable : 3.4 fois.

Globalement la durée de vie de la dent type 1f (voir Fig. 1f) avec 30 % vol de TiC dans la partie renforcée est 2.5 à 3.4 fois plus longue par rapport à une dent identique en acier trempé.The advantages of the tooth according to the present invention over non-composite teeth are an improvement in wear resistance of the order of 300%. In more detail, and depending on the test circumstances (dredging), the following performances (expressed in tooth life for a given working volume) have been observed for the products produced according to the invention (reinforcement type Fig. 1f generally comprising a volume percentage of TiC of 30 vol% - Example 2), compared to identical hardened steel teeth.

• hard limestone: 2.5 times;
• mixture of hard clay, compacted sand and gravel: 2.9 times;
• mixture of sand and hard clay: 3.2 times;
• mixture of shale and sand: 3.4 times.

Overall the life of the tooth type 1f (see Fig. 1f ) with 30% vol TiC in the reinforced part is 2.5 to 3.4 times longer compared to an identical hardened steel tooth.

Claims (13)

1. A composite tooth for working the ground or rocks, said tooth comprising a ferrous alloy at least partially reinforced (5) with titanium carbide according to a defined geometry, wherein said reinforced portion (5) comprises an alternating macro-microstructure of millimetric areas (1) concentrated with micrometric globular particles of titanium carbide (4) separated by millimetric areas (2) essentially free of micrometric globular particles of titanium carbide (4), said areas concentrated with micrometric globular particles of titanium carbide (4) forming a microstructure in which the micrometric interstices (3) between said globular particles (4) are also filled by said ferrous alloy.
2. The tooth according to claim 1, wherein said millimetric concentrated areas have a concentration of micrometric globular particles of titanium carbide (4) greater than 36.9% by volume.
3. The tooth according to any of claims 1 or 2, wherein said reinforced portion has a global titanium carbide content between 16.6 and 50.5% by volume.
4. The tooth according to any of the preceding claims, wherein the micrometric globular particles of titanium carbide (4) have a size of less than 50µm.
5. The tooth according to any of the preceding claims, wherein the major portion of the micrometric globular particles of titanium carbide (4) has a size of less than 20 µm.
6. The tooth according to any of the preceding claims, wherein said areas concentrated with globular particles of titanium carbide (1) comprise 36.9 to 72.2% by volume of titanium carbide.
7. The tooth according to any of the preceding claims, wherein said areas concentrated with titanium carbide (1) have a dimension varying from 1 to 12 mm.
8. The tooth according to any of the preceding claims, wherein said areas concentrated in titanium carbide (1) have a dimension varying from 1 to 6 mm.
9. The tooth according to any of the preceding claims, wherein said areas concentrated in titanium carbide (1) have a dimension varying from 1.4 to 4 mm.
10. A method for manufacturing by casting a composite tooth according to any of claims 1 to 9, comprising the following steps:

    - providing a mold comprising the imprint of the tooth with a predefined reinforcement geometry;

    - introducing, into the portion, of the imprint of the tooth intended to form the reinforced portion (5), a mixture of compacted powders comprising carbon and titanium in the form of millimetric granules precursor of titanium carbide;

    - casting a ferrous alloy into the mold, the heat of said casting triggering an exothermic self-propagating high temperature synthesis (SHS) of titanium carbide within said precursor granules;

    - forming, within the reinforced portion (5) of the tooth, an alternating macro-microstructure of millimetric areas concentrated (1) with micrometric globular particles of titanium carbide (4) at the location of said precursor granules, said areas being separated from each other by millimetric areas (2) essentially free of micrometric globular particles of titanium carbide (4), said globular particles (4) being also separated within said millimetric areas concentrated (1) with titanium carbide by micrometric interstices (3);

    - infiltration of the millimetric (2) and micrometric (3) interstices by said high temperature cast ferrous alloy, following the formation of microscopic globular particles of titanium carbide (4).
11. The manufacturing method according to claim 10, wherein the mixture of compacted powders of titanium and carbon comprises a powder of a ferrous alloy.
12. The manufacturing method according to any of claims 10 or 11, wherein said carbon is graphite.
13. The tooth obtained according to any of claims 10 to 12.

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