EP3563951A1 - Composite tooth with tapered insert - Google Patents

Abstract

The present invention discloses a composite tooth for working the soil or rocks, said tooth comprising a ferrous alloy reinforced at least in part by an insert, said part reinforced by the insert making it possible, after reaction in situ, to obtain an alternating macro-microstructure of millimeter zones concentrated in micrometric globular particles of titanium carbides separated by millimeter zones substantially free of micrometric globular particles of titanium carbides, said zones concentrated in micrometric globular particles of titanium carbides forming a microstructure in which the micrometric interstices between said globular particles are also occupied by said ferrous alloy characterized in that said macro-microstructure generated by the insert is at least 2 mm apart, preferably at least 3 mm from the distal surface of said tooth.

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 made in a foundry comprising a metal matrix reinforced by a substantially frustoconical or pyramidal insert comprising particles of titanium carbides formed during an in situ reaction at the time of casting of the cast iron.

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". Known means generally relate to shallow surface modifications (a few millimeters). 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 layer of carbides a few millimeters thick on the surface of a tooth. Such a reinforcement is however not integrated in the metal matrix of the tooth and does not guarantee the same performance that a tooth where a carbide reinforcement is fully incorporated into the mass of the metal matrix.

The document WO2010031660 discloses a composite tooth for tillage or rock, made in the foundry and comprising a ferrous alloy reinforced at least in part with titanium carbide formed in situ according to a defined geometry. The reinforced part of the tooth comprises an alternating macro-microstructure of millimetric zones concentrated in micrometric globular particles of titanium carbides separated by millimetric zones globally free of micrometric globular particles of titanium carbides. Concentrated areas of micrometric globular particles of titanium carbides form a microstructure in which the micrometric interstices between the globular particles are also occupied by said ferrous alloy.

Goals of the invention

The present invention aims to improve the performance of composite teeth of the prior art, it aims to provide improved resistance against wear while maintaining good impact resistance. This property is obtained by a reinforcing insert specifically designed for this application, insert comprising a structure alternating on a millimetric scale dense areas micrometric globular fine particles of metal carbides formed in situ with areas that are practically free within of the metal matrix of the tooth, the macro-microstructure of the insert having a substantially frustoconical flattened shape or a pyramid shape, preferably truncated with a rectangular or square base, said shape being hollow. The recess of the insert allows a faster "filling" of the titanium carbide insert in situ formation during casting.

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

Summary of the invention

The present invention discloses a composite tooth for working the soil or rocks, said tooth comprising a ferrous alloy reinforced at least in part by an insert in which said reinforced part by the insert allows, after in situ reaction, to obtain an alternating macro-microstructure of millimetric zones concentrated in micrometric globular particles of titanium carbides separated by millimetric zones substantially free of micrometric globular particles of titanium carbides, said zones concentrated in micrometric globular particles of titanium carbides forming a microstructure in which the micrometric interstices between said globular particles are also occupied by said ferrous alloy and wherein said macro-microstructure generated by the insert is spaced a few millimeters from the distal surface of the tooth, preferably at least 2 to 3 mm, and especially pr 4, 5 or even 6 mm from the distal surface of the tooth. It is essential that the reinforced portion does not scratch the surface of said tooth.

• L'insert a une forme tronconique aplatie ou une forme pyramidale tronquée à base rectangulaire ou carrée, pleine ou au moins partiellement creuse ;
• lesdites zones millimétriques concentrées ont une concentration en particules globulaires micrométriques de carbures de titane supérieure à 35% en volume ;
• ladite partie renforcée par l'insert a une teneur globale de carbures de titane entre 25 et 45 % en volume;
• les particules micrométriques globulaires de carbures de titane ont une taille inférieure à 50µm, préférablement inférieure à 20 µm;
• lesdites zones concentrées en particules globulaires de carbures de titane comportent 36.9 à 72.2 % en volume de carbures de titane ;
• lesdites zones concentrées en carbures de titane ont une dimension variant de 0.5 à 12 mm, de préférence variant de 0.5 à 6 mm, de manière particulièrement préférée variant entre 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:

• The insert has a flattened frustoconical shape or a truncated pyramidal shape with a rectangular or square base, solid or at least partially hollow;
• said concentrated millimeter areas have a concentration of micrometric globular particles of titanium carbides greater than 35% by volume;
• said insert-reinforced portion has an overall titanium carbide content between 25 and 45% by volume;
• the micrometric globular particles of titanium carbides have a size of less than 50 μm, preferably less than 20 μm;
• said zones concentrated in globular particles of titanium carbides comprise 36.9 to 72.2% by volume of titanium carbides;
• said concentrated zones of titanium carbides have a dimension ranging from 0.5 to 12 mm, preferably ranging from 0.5 to 6 mm, particularly preferably ranging from 1.4 to 4 mm.

The present invention also discloses a method of manufacturing the composite tooth according to any one of claims 1 to 7.

• mise à disposition d'un insert sous forme de granulés millimétriques d'un mélange de poudres compactées comportant du carbone et du titane précurseurs de carbures de titane ; celui-ci peut être obtenu par moulage avec de la colle ou par confinement dans une enveloppe métallique qui fondra lors de la coulée.
• introduction de l'insert dans le moule de la dent de sorte que ledit insert est maintenu à quelques millimètres de la surface distale de la dent ;
• coulée d'un alliage ferreux dans le moule, la chaleur de ladite coulée déclenchant une réaction exothermique de synthèse auto-propagée de carbures de titane à haute température (SHS) au sein desdits granulés précurseurs;
• formation, au sein de l'insert de la dent, d'une macro-microstructure alternée de zones millimétriques concentrées en particules globulaires micrométriques de carbures de titane à l'emplacement desdits granulés précurseurs, lesdites zones étant séparées entre elles par des zones millimétriques substantiellement exemptes de particules globulaires micrométriques de carbures de titane, lesdites particules globulaires étant également séparées au sein desdites zones millimétriques concentrées de carbures de titane par des interstices micrométriques, dans ladite macro-microstructure ;
• infiltration des interstices millimétriques, des interstices micrométriques par ledit alliage ferreux de coulée à haute température, consécutive à la formation de particules microscopiques globulaires de carbures de titane.
• l'insert est réalisé par moulage ou confinement.

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

• provision of an insert in the form of millimetric granules of a mixture of compacted powders comprising carbon and titanium precursors of titanium carbides; this can be obtained by molding with glue or by confinement in a metal casing which will melt during casting.
• inserting the insert into the tooth mold so that said insert is held a few millimeters away from the distal surface of the tooth;
• casting a ferrous alloy into the mold, the heat of said casting triggering an exothermic reaction of self-propagating synthesis of high temperature titanium carbides (SHS) within said precursor granules;
• forming, within the tooth insert, an alternating macro-microstructure of millimetric zones concentrated in micrometric globular particles of titanium carbides at the location of said precursor granules, said zones being separated from each other by millimetric zones substantially free from micrometric globular particles of titanium carbides, said globular particles being also separated within said millimetric concentrated zones of titanium carbides by micrometric interstices, in said macro-microstructure;
• infiltration of the millimetric interstices, micrometric interstices by said ferrous casting alloy at high temperature, subsequent to the formation of microscopic globular particles of titanium carbides.
• the insert is made by molding or confinement.

The present invention also discloses a composite tooth obtained according to the method of the invention.

Brief description of the figures

• The figure 1a shows a three-dimensional view of a commercial tooth to be reinforced according to the invention. This type of tooth can have very variable dimensions ranging from an average of a few tens of centimeters to more than one meter
• The figure 1b shows a schematic three-dimensional view of a tooth with frustoconical reinforcement flush with the surface of the distal end of the tooth according to the state of the art.
• The Figures 1c and 1d show reinforced teeth according to the invention with an insert of substantially frustoconical shape full or at least partially hollow. The insert is here at a distance of a few millimeters from the surface at the distal end of the reinforced tooth. It does not therefore touch the surface of the tooth.
• The Figures 2a-2h represent the method of manufacturing the tooth according to the invention.
  • step 2a shows the device for mixing titanium and carbon powders;
  • step 2b shows the compaction of the powders between two rollers followed by crushing and sieving with recycling of the fine particles;
  • the Figure 2c shows a sand mold in which a dam has been placed to contain the compacted powder granules at the location of the tooth reinforcement;
  • the figure 2d shows an enlargement of the reinforcement zone in which the compacted granules comprising TiC precursor reactants are located;
  • step 2e shows the casting of the ferrous alloy in the mold;
  • the figure 2f schematically shows the tooth resulting from casting;
  • the figure 2g shows an enlargement of the zones with a high concentration of TiC globules - this diagram represents the same zones as in the figure 3 ;
  • the figure 2h 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 3 represents a binocular view of a non-etched polished surface of a section of the reinforced portion of the tooth according to the invention with millimetric zones (in light gray) concentrated micrometric globular titanium carbides (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 carbides but also the spaces between the globules themselves. (See figures 4 and 5 ).
• The figures 4 and 5 represent electron SEM microscopic views of micrometric globular titanium carbides on polished and unattacked surfaces at different magnifications. We see that in this particular case most of the globules of titanium carbides have a size less than 10 microns.
• The figure 6 represents a view of micrometric globular titanium carbides on a fracture surface taken by SEM electron microscope. It is seen that the corpuscles of titanium carbides 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 during the SHS reaction.
• The figure 7 represents two longitudinal sections of an example tooth according to the invention, the two sections being perpendicular to each other. In this figure, the insert is hollow frustoconical.
• The figure 8 represents two longitudinal sections of another example of tooth according to the invention, the two sections being perpendicular to each other. The insert of the figure 8 comprises several tunnels traversing longitudinally the truncated cone.
• The figure 9 represents two three-dimensional views of a tooth according to the invention, the two views being perpendicular to one another.
• The figure 10 represents a three-dimensional view of a tooth according to the invention comprising an insert in the form of a truncated pyramid with a rectangular or square base. In this example, the insert is full.
• The figure 11 represents a metal containment for the compacted granules of Ti / C mixture. This confinement makes it possible to put the mixture of granules in a frustoconical flattened form, at least partially hollow.

Legend

1. 1. Millimeter areas concentrated in micrometric globular particles (nodules) micrometric titanium carbides (bright areas)
2. 2. millimetric interstices filled with the ferrous casting alloy globally free of micrometric globular particles of titanium carbides (dark areas)
3. 3. micrometric interstices between TiC nodules also infiltrated by casting alloy
4. 4. micrometric globular titanium carbides, in the zones concentrated in titanium carbides
5. 5. A frustoconical or pyramidal shaped insert, full or partially or completely hollow, fully integrated into the cast iron matrix and a few millimeters away from the distal end of the tooth.
6. 6. gas defects
7. 7. metal containment for compacted granules of Ti / C mixture
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

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, there is a reaction front which propagates 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 and has not been added in the form of milled ICT in the mold.

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. These granules are not 100% compacted. They are generally compressed between 55 and 95% of the theoretical density. These granules allow easy use / manipulation (see Fig. 2a-2h ).

These millimetric granules of mixed carbon and titanium powders obtained according to the diagrams of figure 2a-2h are the precursors of the titanium carbide to be created.

The composite tooth for working the soil or rocks according to the present invention comprises a frustoconical or pyramidal type insert preferably truncated rectangular or square base, preferably of the hollow type, made in grains by a mixture of carbon powders and titanium and allowing, after SHS reaction, obtaining a macro-microstructure, that is to say a reinforcement network that can also be called a three-dimensional alternating structure of zones concentrated in micrometric globular particles of titanium carbides separated by areas that are practically free. Such a structure is obtained by the reaction in the mold of the granules comprising a mixture of carbon powders and titanium and having been previously shaped either by clogging grains with glue in a mold or simply in a perforated metal enclosure which will at least partially melt during casting. The SHS reaction is initiated by the heat of casting of the cast iron or steel used to pour the whole piece of the tooth and thus both the unreinforced and the reinforced part (see Fig. 2nd ). The casting thus 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), previously agglomerated as a frustoconical insert, preferably at least partially hollow and 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 casting or casting steel ( Fig. 2g & 2h ). By increasing the wettability, the infiltration can be done on any thickness or depth of reinforcement of the tooth. It advantageously makes it possible to create, after SHS reaction and infiltration by an external casting metal, an insert not flush with the distal end of the tooth and comprising a high concentration of micrometric globular particles of titanium carbides (which could be also called clusters of nodules), which areas having a size of the order of a millimeter or a few millimeters, and which alternate with areas substantially free of globular titanium carbides.

Once these granules have reacted according to an SHS reaction, the reinforcement zones where these granules were found show a concentrated dispersion of micrometric globular particles 4 of TiC carbides (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 tooth finally obtained, the reinforcement zones with a high concentration of titanium carbides are composed of globular micrometric particles of TiC in significant percentage (between about 35 and about 70% by volume) and ferrous alloy infiltration.

Micrometric globular particles are understood to mean globally spheroidal particles having a size ranging from a micrometer to a few tens of micrometers at 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. 5 ).

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

The process for obtaining the granules is illustrated in figure 2a-2h . 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, the more 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 for compressing this material, the apparent density of the granules is 3.75 x 0.55, or 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 of frustoconical type flattened or pyramidal type preferentially truncated rectangular or square base, or a superstructure / macro-microstructure with these granules, they are placed in a mold 7 insert and granules are agglomerated either by means glue, or by any other means such as a perforated metal containment which will melt at least partially during casting. The insert mold is for example an elastomer mold making it possible to give the desired final shape to the insert 5. The insert, of frustoconical shape hollow or not, will be arranged in such a manner in the casting mold not to be flush with the distal surface of the tooth. Care must be taken to maintain a space of a few millimeters between the end of the insert and the outer surface obtained after casting of the tooth at the point where this distance is the smallest, namely the distal end of the tooth which is the most subject to wear. The distance will vary depending on the size of the tooth. It should be at least 1mm, preferably at least 2 or 3 mm and particularly preferably at least 4 or 5 mm.

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 an agglomerate of porous granules composed of a mixture of titanium powder and carbon powder, forming a flattened frustoconical insert or a truncated pyramidal insert with a rectangular or square base, the insert being able to be solid or less partially hollow.

The insert is then placed in the mold 15 of the tooth, in the area of the mold where it is desired to reinforce the part. The insert is placed as illustrated by the Figures 7 to 10 so that it does not scratch the surface of the tooth once it is formed. Then, the metal to form the tooth is poured into the mold 15.

• la porosité microscopique présente dans les espaces à forte concentration en carbures de titane, dépendant du niveau de compaction initial de ces granulés ;
• les espaces millimétriques entre les zones à forte concentration en carbures 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.
• éventuellement l'espace central creux de l'insert si celui-ci est creux au départ.

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 carbides, depending on the initial compaction level of these granules;
• the millimeter spaces between the zones with a high concentration of titanium carbides, 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.
• possibly the hollow central space of the insert if it is hollow at the beginning.

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.
L'insert a été réalisé en confinant des granulés Ti+C dans un contenant métallique perforé (tôle mince perforée) qui a été ensuite placé judicieusement dans le moule de coulée de la dent à quelques millimètres de la surface du moule, à l'endroit où la dent est susceptible d'être renforcée. Ensuite, on coule l'acier ou la fonte dans ce moule et le contenant perforé fond en libérant l'espace pour l'infiltration par le métal de coulée.In the following example, 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.
The insert was made by confining Ti + C granules in a perforated metal container (perforated thin sheet) which was then judiciously placed in the casting mold of the tooth a few millimeters from the surface of the mold, at the location where the tooth is likely to be strengthened. Then, the steel or cast iron is poured into this mold and the perforated container melts freeing the space for infiltration by the casting metal.

Example 1

In this example, a powdered ferrous alloy is added to the carbon-titanium mixture to reduce the intensity of the reaction between carbon and titanium. It is intended to produce a tooth whose reinforced zones comprise an overall volume percentage of TiC of approximately 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. We have the granules in a confinement which thus comprises after tamping and / or vibration 60% by volume of porous granules taking into account the perforations made. After reaction, 60% by volume of zones with a high concentration of approximately 55% of globular titanium carbides, ie 33% by volume of total titanium carbides in the reinforced macro-microstructure of the tooth, are obtained in the reinforced part.

The following tables show the many possible combinations. <b><u> Table 1 </ 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 with 23% perforation (% vol) 80 22.9 25.0 27.1 29.2 31.2 33.3 35.4 37.5 39.6 75 21.5 23.4 25.4 27.3 29.3 31.2 33.2 35.1 37.1 70 20.0 21.9 23.7 25.5 27.3 29.2 31.0 32.8 34.6 65 18.6 20.3 22.0 23.7 25.4 27.1 28.8 30.5 32.2 55 15.8 17.2 18.6 20.0 21.5 22.9 24.3 25.8 27.2 45 12.9 14.1 15.2 16.4 17.6 18.7 19.9 21.1 22.3

To obtain an overall concentration of TiC in the reinforced part of about 25% vol (in bold letters in the table), one can proceed to different combinations such as for example 60% compaction and 80% filling, or 65% compaction and 75% filling, or 70% compaction and 70% filling, or 85% compaction and 55% filling. <b><u> Table 2 </ u></b> 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. 80 1.9 2.0 2.2 2.4 2.6 2.7 2.9 3.1 3.2 75 1.8 1.9 2.1 2.2 2.4 2.6 2.7 2.9 3.0 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 $$\left(*\right)\mathrm{Bulk\; density}\left(\mathrm{1.5}\right)=\mathrm{theoretical\; density}\left(\mathrm{4.25}\right)\times \mathrm{0.65}\left(\mathrm{filling}\right)\times \mathrm{0.55}\left(\mathrm{compaction}\right)$$

Advantages of the tooth according to the invention Better resistance of the insert to cracking and breaking

The present invention makes it possible to reduce the phenomenon of cracking of the tooth, during its manufacture but also in use.

During the manufacture of the teeth, the rejection rate is reduced, in particular thanks to hollow frustoconical cones or truncated pyramids. hollow which reduce overall the concentration of ceramics in the room. Too much ceramic presence potentially causes cracking and / or infiltration defects.

On the other hand, the wear of the teeth in use is reduced by the inserts of the present invention. Indeed, the cracking of the ceramic is decreased when the insert is not immediately exposed on the surface. The rupture primers that could weaken the tooth in service are thus limited.

Moreover, the cracks generally originate in the most fragile places, which are in this case 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, the shape and the wall thickness of the frustoconical or pyramidal insert can be varied when the latter is hollow.

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

The expansion coefficient 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 ^-6 / 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, the recesses in the insert make it possible to reduce the proportion of TiC reinforcement (less than 45% by volume in the macro-microstructure reinforced), resulting in less tension in the room. 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 insert and the unreinforced portion of the tooth is not abrupt because there is a continuity of the metal matrix between the insert and the unreinforced portion, thanks to the frustoconical inserts and pyramidaux hollow, which allows to protect it against a complete tearing of the insert.

Reduced costs and increased speed of tooth formation

The small volume of a frustoconical or hollow pyramidal insert also reduces the overall amount of TiC, decreasing the cost of the workpiece in the same way.

The hollows also allow a faster "filling" of the insert during casting.

Test results

The advantages of the tooth according to the present invention with respect to a composite tooth of the invention described above as shown in FIG. figure 1b are an improvement of the resistance to breakage during test bench bending tests of the order of 300%. In more detail, and according to the test circumstances, it was possible to observe the following performances (expressed in kN, which represents the maximum load before breaking) for the products made according to the invention (reinforcement of type Fig. 8 generally having a volume percentage of TiC of 33% - Example 1) compared to identical teeth with type reinforcement Fig. 1a : 2.8 times.

Claims (13)

Composite tooth for working the soil or rocks, said tooth comprising a ferrous alloy reinforced at least in part by an insert (5), said reinforced part by the insert (5) allowing, after in situ reaction, to obtain an alternating macro-microstructure of millimetric zones (1) concentrated in micrometric globular particles of titanium carbides (4) separated by millimetric zones (2) substantially free of micrometric globular particles of titanium carbides (4), said zones concentrated in micrometrically-sized micrometric particles of titanium carbides (4) in which the micrometric interstices (3) between said globular particles (4) are also occupied by said ferrous alloy and characterized in that said macro-microstructure generated by the insert ( 5) is at least 2 mm apart, preferably at least 3 mm away from the distal surface of said tooth. Tooth according to claim 1, characterized in that the insert (5) has a flattened frustoconical shape or a truncated pyramidal shape with a rectangular or square base, solid or at least partially hollow. Tooth according to any one of the preceding claims, wherein said concentrated millimeter areas have a concentration of micrometric globular particles of titanium carbides (4) greater than 35% by volume. Tooth according to any one of the preceding claims, wherein said portion reinforced by the insert (5) has an overall content of titanium carbides between 25 and 45% by volume. Tooth according to any one of the preceding claims, wherein the micrometric globular particles of titanium carbides (4) have a size of less than 50 .mu.m, preferably less than 20 .mu.m. Tooth according to any one of the preceding claims, wherein said zones concentrated in globular particles of titanium carbides (1) comprise 36.9 to 72.2% by volume of titanium carbides. Tooth according to any one of the preceding claims, wherein said concentrated areas of titanium carbides (1) have a dimension ranging from 0.5 to 12 mm, preferably ranging from 0.5 to 6 mm, particularly preferably ranging from 1.4 to 4. mm. A method of manufacturing by casting a composite tooth according to any one of claims 1 to 7, comprising the following steps: - providing an insert in the form of millimetric granules of a mixture of compacted powders comprising carbon and titanium precursors of titanium carbides, - Introducing the insert (5) into the mold (15) of the tooth so that said insert (5) is held a few millimeters from the distal surface of the tooth; casting a ferrous alloy in the mold (15), the heat of said casting triggering an exothermic reaction of self-propagating synthesis of high temperature titanium carbides (SHS) within said precursor granules; forming, within the insert (5) of the tooth, an alternating macro-microstructure of concentrated millimetric zones (1) in micrometric globular particles of titanium carbides (4) at the location of said precursor granules, said zones being separated from each other by millimetric zones (2) substantially free of micrometric globular particles of titanium carbides (4), said globular particles (4) being also separated within said concentrated millimetric zones (1) of titanium carbides by interstices micrometric (3) in said macro-microstructure; - infiltration millimetric interstices (2), micrometric interstices (3) by said ferrous alloy casting at high temperature, following the formation of microscopic globular particles of titanium carbides (4). Manufacturing method according to claim 8, wherein the insert (5) has a flattened frustoconical shape or a truncated pyramidal shape with rectangular base, solid or at least partially hollow The manufacturing method according to any one of claims 8 or 9, wherein the mixture of compacted powders of titanium and carbon comprises a powder of a ferrous alloy. The manufacturing method according to any one of claims 8 or 10, wherein said carbon is graphite. Manufacturing method according to any one of claims 8 to 11, wherein the insert is made by molding or by confinement. Tooth obtained according to the method of any one of claims 8 to 12.

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