LU84105A1 - CAST PIECE COMPRISING WEAR RESISTANT TABLETS AND MANUFACTURING METHOD THEREOF - Google Patents

Description

2

The present invention relates to the field of wear-resistant castings and their manufacture. More specifically, the present invention relates to the field of wear-resistant castings intended for earthworks, as well as penetration-resistant security devices.

In the field of decking equipment, the useful life of the teeth coming into contact with the ground to be treated is important for the economic success of the work to be performed,

The lifespan of these teeth is influenced by the ambient environment in which they are used. Specifically, the ambient media encountered can create conditions of abrasion wear, impact stress, temperature variation, vibration and corrosion on the surface of the teeth, all of these factors tending to shorten the life of the teeth. teeth or tools. The high costs of downtime, as well as the costs of replacing worn and broken tools, have resulted in the development of a wide variety of tools designed to improve their service life during their commissioning.

In some cases, to obtain these improved tools, carbide has been incorporated into their working surface by casting methods (see, for example, U.S. Patents 4,024,902 and 4,I40 .I70).

These casting techniques pose problems when it is desired to produce castings having relatively thin cross sections or when it is desired to deposit particles of a carbide on the surface of a vertical extension, as well as on a horizontal part of 'a casting.

35 In order to minimize the dissolution of the carbide particles during the casting, as well as the / // ~ ......

3 fragile eta phase (carbide M ^ C or containing 'tungsten and iron) forming at the carbide / steel interfaces, the cemented carbide particles used • must specifically have a granularity of at least 5 * 175 mm. If we increase the granularity of the particles, we reduce the carbide / steel interface area. However, in the thin sections of a casting having a thickness which is only slightly greater than the granularity of the carbide particles, the carbides can act in conjunction with the mold to rapidly and excessively cool the molten metal. * flowing between the carbide particles, thus giving rise to an incomplete filling in these thin sections * 15 It is also impossible to maintain large particles of cemented carbide dispersed uniformly along a vertical section of a cast part s.ans fill this section with carbide particles from bottom to top to keep these particles in place during casting. This may result in the formation of empty spaces and / or incomplete filling which has been mentioned. above, further to excessive cooling of the • molten mass.

, 25 According to Australian patent n ° AU-B1-31362 / 77 * an attempt is made to avoid the abovementioned problems during the * casting by kneading a low alloy steel powder which can be subjected to a heat treatment, with a powder of tungsten carbide or a carbide powder in solid solution of tungsten-molybdenum, the mixture thus formed is then pressed and sintered at practically its maximum density to form a tablet. The low alloy steel is then poured around the sintered steel / carbide tablet to form a final component. However, this Australian patent limits the steel powders used to a low chromium 4 steel.

According to the present invention, a tenacious and wear-resistant body is described in which carbide particles with a granularity greater than 5,400 meshes are coated practically in a first metallic matrix * The above composite product consisting of particles carbide and a first metal matrix is linked to a second metal matrix. Preferably, the carbide particles are particles of a cemented carbide, preferably containing tungsten carbide. Preferably, the carbide particles represent 30 to 80 $ by weight of the composite product and they have a granularity greater than 40 stitches.

Preferably, the second metal matrix substantially surrounds the composite product consisting of carbide particles and the first metal matrix *

Preferably, the first metal matrix 20 is made of steel, preferably of stainless steel and, more preferably, of an austenitic stainless steel.

Preferably, the second metallic matrix consists of steel, preferably of a low-alloy T 25 steel or an austenitic steel and, better still, an austenitic stainless steel * * It is also preferable that the particles of the cemented carbide used mainly contain tungsten carbide, as well as a binding agent chosen from cobalt, nickel, their mutual alloys or their alloys with other metals *

It has also been found that, if the first metal matrix was made of austenitic stainless steel, it could have a density of less than $ 90, or even a density as low as $ 75 to $ 85.

/ - i.

s

Also, according to the present invention, there is provided a method in which the carbide particles are mixed with the powders. of the first metallic matrix, the mixture thus obtained then being subjected to isostatic compression and to sintering · A second metallic matrix or a molten metal is then bonded to the compressed product thus' formed. The molten metal may be poured practically around the compressed product or according to the intended application, for example, when forming a wear surface, the molten metal may not be completely incorporated into the composite product.

It is therefore an object of the present invention to minimize the brittle phases formed during the casting of molten metal around carbide particles.

Accordingly, an object of the present invention is also to provide a product having excellent properties of resistance to wear, corrosion and puncture, as well as good toughness.

Another object of the present invention is to provide a method for manufacturing an earthmoving tool or a security device resistant to penetration.

The exact nature of the present invention will appear more clearly on reading the detailed specification given below with reference to the accompanying drawings in which: Figure 1 is an isometric view of a blocking box next the present invention; Figure 2 is a cross section of the embodiment illustrated in Figure 1, this section being taken along arrows II-II thereof; h '6 Figure 3 is a cross section of a mold cavity used to obtain the embodiment of the present invention which is illustrated in Figure 1 $ 5 Figure 4 is a cross section of an embodiment of an excavator tooth according to the present invention.

According to the present invention, 30 to 80% by weight of carbide particles are mixed with 70 to 20% by weight of steel powder to obtain a practically uniform mixture of carbide and steel. Preferably, the carbide particles used are particles of carbide and cemented tungsten with a granularity of 400 meshes or, better still, of more than 40 meshes. According to a much preferred characteristic, these particles of cemented carbide must have a granularity of —6 + 12 meshes (series of American sieves) or a granularity being between 3 * 302 and 1.676 mm respectively.

It has been found that sintered composite products containing cemented carbide particles within this much preferred range of granularities resist penetration by drilling.

The wear resistance and resistance to penetration by drilling can be further improved by using carbide particles having a bimodal particle size. According to this embodiment of the invention, the granularity of the smallest carbide particles is chosen so that they can fit into the interstices formed between the largest carbide particles, thus further increasing the resistance to wear.

The cemented carbide can comprise a metallic binder chosen from cobalt, nickel or cobalt-nickel alloys. In addition to tungsten carbide, cemented carbide may contain weaker /. '/ x ~ \ 7 \ \ quantities of other carbides such as tantalum carbide, niobium carbide, hafnium carbide, zirconium carbide and vanadium carbide. It has been found that crushed and sieved fragments of cemented carbide can be used in this process.

Although particles of tungsten carbide with a granularity greater than -400 mesh may be substituted in whole or in part for the particles of cemented carbide in the composite product, tungsten carbide powder is not preferred , since it binds less easily to steel, tends to fracture easily and generally gives poorer resistance to wear and impact than carbide particles. . cemented tungsten having the same granularity.

The steel powder used according to the present invention may consist of alloy steel but preferably of stainless steel due to the better corrosion resistance offered by the latter. However, the most preferred stainless steels are aust.enitic stainless steels because of their high resistance to wear and impact from room temperature to temperatures; 25 cryogenic. Among the austenitic stainless steels, the AISI types 301, 302, 304 and 304L are preferred because of their high work hardening speed.

In addition to the carbide and steel powders involved in the feed, organic binding agents are also added in order to prevent segregation and obtain a uniform distribution of the carbide particles during mixing, as well as the maintenance of a mixture. uniform after the mixing operation.

After the latter, the powder mixture is compressed by uniaxial pressing in a die or 8 by isostatic pressing in a blank mold, preferably under a pressure of about 2,450 kg / cm2, but not less than 700 kg / cm2 .

After compression, the product obtained is sintered at a temperature, preferably below the melting point of the steel and, better still, at a temperature in the range from 1.038 to 1.232 ° C for 20 to 90 minutes, thus avoiding the formation of eta phases at the cemented carbide / steel interface, while nevertheless obtaining a strong metallurgical bond between the cemented carbide and the steel.

In most cases, the bond between steel and cemented carbide is in the form of an alloy layer at the cemented carbide / steel interface. This layer consists mainly of cobalt and iron and is specifically less than 40 microns thick. This bond is important to ensure the retention of large particles · of cemented carbide 11 inside the steel matrix.

It has been found that after sintering, the compressed products obtained using an austenitic stainless steel powder generally had micropores bonded together and that the density of the steel binder was less than $ 90 and was , 25 more specifically, from $ 75 to $ 85 of theory. In order to increase the density of the compressed products, it is possible to adopt isostatic pressing, infiltration or higher compression pressures. These methods also provide better retention of the carbide particles in the composite product. The infiltration product used can be chosen from one of the copper or silver-based brazing materials which permeate both stainless steel and carbide particles.

35 After sintering, the compressed product is then deposited in a mold, then a molten metal is poured around this product to obtain a cast part. The casting method adopted can be any of the methods well known to those skilled in the art. However, it is preferable to adopt the casting method described in United States Patent No. 4,024,902. A preheating of the compressed product can be used before pouring the molten metal into the mold.

The molten metal can be a ferrous or non-ferrous alloy, but preferably this metal is steel. The type of steel used does not necessarily have to be the same as that contained in the compressed product. When the properties of impact resistance, solidity and corrosion are important, the cast steel is preferably an austenitic stainless steel. Manganese austenitic steels and low-alloy steels can also be used. · The cast steel forms a metallurgical bond with the steel binder in the compressed product, reacting at least with the particles of cemented carbide. The formation of the eta phase is thus minimized since both the specific surface of the carbide particles coming into contact with the molten metal is reduced to a minimum.

The use of compressed products consisting of cemented carbide and steel also makes it possible to bind the carbide particles in various concentrations, positions and orientations, both on and below the surface of the castings.

The process and the products according to the present invention will appear more clearly on reading the examples detailed below.

EXAMPLE 1 A number of teeth 1 of ex-wear and impact resistance are produced (see fig.

/ Λ

Igure 4) comprising compressed products 3 * A uniform mixture consisting of 60% by weight of cobalt / cemented tungsten carbide granules of 3 * 175 to 4 * 762 mm is prepared, as well as $ 40 by weight of a pou * »5 dre atomized of austenitic stainless steel 304L at least 100 mesh (manufactured by" Hoeganaes Corporation ”, New Jersey) by dry mixing with $ 1.25 by weight of paraffin and 0.75% by weight of ethyl- The mixture is manually compressed in a mold cavity of polyurethane elastomer having the desired shape of the compressed product (length: 50.8 mm; width: 19.05 mm; thickness i 6.35 mm), the dimensions being calculated. to allow compression, isostatic to cold of the powder plus 1% shrinkage shrinkage, After cold isostatic compression to 2,450 kg / cm2, the compressed blank is removed from the mold and subjected to vacuum sintering at 1,149 ° C for 60 minutes, 0h then deposits the sintered bodies in a sand mold with eight cavities having the shape required for the 20 excavator teeth. The ingredients intended to form a low-alloy steel AISX 4340 are melted in an induction furnace, the compressed products are subjected to preheating, then the steel is poured into the mold at a temperature between 1.676 and '25 1.732 ° C to form the excavator tooth illustrated in FIG. 4 in which the steel 4340 designated by the reference numeral 5 is linked to two angularly associated faces of the compressed product 3 ·

Metallographic examination reveals that the stainless steel matrix has an austenitic structure with certain intergranular chromium carbide particles, this characteristic being referred to as "sensitization" 1, which is specific to slowly cooled austenitic stainless steels after sintering. This sensitization can be eliminated by a heat treatment.

U

later in solution. The cemented carbide / stainless steel matrix interfaces have a continuous bonding area with a thickness of about 15 microns. and consisting of an alloy comprising mainly iron and cobalt · The dispersed particles of cemented carbide seem to be free from thermal crackers with a minimum degree of dissolution, fusion or degradation of the phase of carbide dispersed in or near the interfacial boundaries. Some melting or mixing of the stainless steel occurs, as well as some degradation of the carbide particles when the molten metal comes into contact with the carbide particles on the surface of the compressed product. However, below this surface, the interfacial limits of the carbide particles are generally accentuated except in the aforementioned zone of diffusion of the iron / cobalt alloy. No virtually harmful concentration of eta phases is observed.

20 Test pieces are struck several times (five and six times) with a spherical hammer at room temperature and at the temperature of liquid nitrogen (-195 ° C.) and it is found that they have a good impact resistance and that they have few traces of fractures of the type due to brittleness. ... However, it should be noted that with a higher weight percent of cemented carbide particles in the composite product, the impact resistance could be reduced slightly, while the resistance to wear and penetration by £> rage increases.

Measurements of micro-hardness of a section of the excavator tooth after casting reveal average hardnesses (indentations) of approximately 75 -R ”Ç", 2.9 R "CM 35 and 38 RnCn in a cross section of the cemented carbide , 304L stainless steel and steel /: · 12 4340 (3.175 mm of the interfaces of stainless steel) respectively ·. · · /

Example 2

A drilling resistant blocking box 10 of the type shown in FIG. 1 is formed by pouring low-alloy steel in fusion quality 4340 around sintered plates of 3Ö4L stainless steel / carbide (length: 101.6 mm 5 width: 63.5 mm 3 thickness: 3.175 to 4.762 mm), as well as around plates having the following dimensions: length: 82.55 mm; width ï 63.5 mm; thickness: 3.175 to 4.762 mm, The position of one of the sintered plates 12 is illustrated by the lines in broken lines. These plates are formed using a uniform mixture of 50% by weight of cobalt / tungsten carbide shavings cemented at -8 + 12 meshes, 50 # by weight -AISI 304L stainless steel powder at -100 mesh and · 10% by weight of binders ("Nu chlorothene" and 0.75 # ethyl cellulose), 20 The stainless steel powder of the matrix containing the hard and dispersed carbide phase is compressed in a polyurethane mold shaped to the dimensions of the plates. Then seal the mold, place it in a rubber bag in which to vacuum and seal, after which an isostatic pressure of 2,450 kg / cm2 is applied After having removed it from the rubber bag and from the mold, the compressed plate is subjected to sintering in a vacuum oven at 1.149 ° C. for 60 minutes, then the drilling resistant plates are placed in the front face, the rear face and the sides of the cavity of the blocking box of a mold,

FIG. 3 illustrates a section of a sand mold 30 in which a cavity is formed between a top section 32 and a bottom section 34. The sintered plates 12 illustrated in this figure are now 13 bare in place in the cavities of the side walls by nails 36 and 40 which are embedded in the bottom part 34 of the mold 30. Particles of cemented carbide 42 have been deposited on the base surface of the cavity. Before placing the top section 32 on the bottom section 34 * the cemented carbide particles 42 and the plates 12 are subjected to preheating · The top section 32 is then placed in the bottom section 34 and poured 5 10 1 * low-alloy molten steel. 434-0 in the mold cavity.

From the safety point of view, the object of the present invention is to equip the blocking box with wrought stainless steel / carbide carbide plates of 3 * 175 rom thickness wrapped in steel for provide protection. against penetration by drilling.

According to another object and a new characteristic of the present invention, during the realization of the blocking box, the plate or plates retain their shape, while the particles of carbide I remain uniformly dispersed in these plates, during— that is poured from molten steel around the latter, filling the remaining quality of the wall.

25 of the blocking box. After the destruction of two masonry drills with a diameter of 3 * 175 rom, the "front section 14 of the box 10. Illustrated in FIG. 1 has not yet been perforated.

Figure 2 shows a cross section of the blocking box containing the carbide / stainless steel plate. The stainless steel undergoes little fusion when the molten alloy steel is poured around the sintered stainless steel / carbide plate and the carbide particles remain uniformly dispersed in the plate 12. The carbide particles undergo very little degradation and there is a minimum of 14 fragile phases at the carbide / steel interfaces 4340 · A metallurgical connection is obtained between the austenitic structure of stainless steel • and the structure of cast steel 4340 · The particles of 5 carbide 42 contained in the base wall 20 of the box can be replaced by identical or similar plates to those illustrated in the side walls 22.

Example 3 - 10 Drill and impact resistant plates are made to a thickness of 3.969 mm · Fifteen plates are made of a uniform mixture of $ 60. by weight of cobalt / cemented tungsten carbide shavings from 2,381 to 3 * 175 mm (-8 + 12 mesh), from $ 40 to 15 weight of 304L stainless steel powder to -100 mesh, from 2% by weight of "Nu11 chlorothene, 1% by weight of ethyl cellulose and $ 1/4 by weight of wax ·" armido "· A second group of 15 plates is formed with $ 70 by weight of cemented carbide shavings (-8 +12 meshes) and $ 20 30 by weight of 304L stainless steel powder (-100 meshes) which are mixed in the same way · During the mixing operation, add armido wax and ethyl cellulose in the powder mixture as a pressing lubricant in order to prevent the segregation of the carbide particles during the mixing operation and during the filling of the mold. Next, the powder constituting the matrix and containing is compressed. the carbide phase hard and dispersed in a blank mold made of polyurethane. After compression, the mold with a suitable cover is sealed and placed in a bag or a rubber balloon in which a vacuum is made, which is sealed and which is subjected to an isostatic pressure at approximately 2,450 kg / cm 2 * Then the plates are sintered in a vacuum oven. 1 * 149 ° C for 60 minutes,

AT

15

These plates can then be incorporated into a casting by adopting casting techniques described previously or one or the other casting method known in the art.

5 Amendments can be envisaged within the scope of the claims below.

l ·

Claims (26)

1. Stubborn body and resistant to wear *, characterized in that it comprises: an element * resistant to penetration and having carbide particles 5 with a granularity greater than 400 meshes; a first metallic matrix, these particles being linked to and located practically inside this first matrix; as well as a second metal matrix which is linked to this penetration resistant element. 2. Stubborn and wear-resistant body according to claim 1, characterized in that the particles are particles of cemented carbide. 3 · Stubborn and wear-resistant body, characterized in that it comprises an element resistant to penetration and having particles of cemented carbide; a first metallic matrix, these cemented carbide particles being bonded to and located practically inside this matrix; as well as a second metallic matrix linked to this penetration resistant element. 4 · Stubborn and wear-resistant body according to claim 3> characterized in that the second metal matrix surrounds practically '25 the penetration-resistant element. 5. Tenacious and wear-resistant body according to any one of claims 1 to 3; characterized in that the first metallic matrix consists of an austenitic stainless steel, 6. Stubborn and wear-resistant body according to claim 5, characterized in that the second metallic matrix is made of steel, ! 7 · Stubborn and wear-resistant body sui- | vant claim 3j characterized in that the particles of cemented carbide have a granularity greater than 40 meshes. AT . 8. Stubborn body and resistant to 1 * wear according to any one of claims 2 and 3 "ca ~ acted in that the carbide particles. case-hardened. consist of tungsten carbide * 5 9 * Stubborn and wear-resistant body according to claim J9 characterized in that the cemented carbide particles also comprise a binder chosen from the group comprising cobalt, nickel, their mutual alloys and their alloys 10 with others metals, 10. Stubborn and wear-resistant body according to claim 5, characterized in that the austenitic stainless steel matrix has a density of less than 90 # · 15 11 · Stubborn and wear-resistant body according to claim 10, characterized in that this matrix has a density of 75 to 85 # · 12. Stubborn and wear-resistant body according to claim 3? characterized in that the particles of cemented carbide have an irregular shape. 13 · Stubborn and wear-resistant product prepared by a process comprising the steps of compressing a mixture of cemented carbide particles and a first steel powder, then bonding - ··, a metal in fusion with the compressed product thus obtained. '14. Product prepared by the process according to claim 13? characterized in that the particles of cemented carbide represent 30 to 80 # by weight of the compressed product. 15 · Product prepared by the process according to claim 13? characterized in that it comprises the additional step of sintering the compressed product before casting. 16. Product prepared by the process according to claim 13, characterized in that the step of A - A v: ':: .-' A! 18 compression involves performing iso-static compression, ’ 17, product prepared by the following process • claim 13, characterized in that it comprises the additional step of choosing cule carbide carbide particles with a granularity greater than 40 meshes in order to use them in this mixture , 18, A method comprising the steps of compressing a mixture of particles of cemented carbide 10 and a metal powder to form a compressed product, then pouring a metallic liquid near this compressed product and then bonding the latter to the metallic liquid, 19 · A method according to claim 18, 15 characterized in that the metallic liquid practically surrounds the compressed product, 20, Method according to any one of. Claims 18 and 19, characterized in that it comprises the additional step of choosing 20 particles of cemented carbide with a granularity greater than 40 meshes in order to use them in this mixture, 21, Method according to claim 18, characterized in that it comprises the additional step. 25 consisting in sintering the compressed product at a temperature below the melting temperature of the metal powder before casting, 22, Cast metal part comprising a base part; a wall part extending 30 outside the plane of this base part; a compressed product consisting of powder particles; particles of cemented carbide contained in this compressed product, the latter being bonded to and practically contained in this wall-forming part, 35 23, Metallic part cast according to re vendication 22, characterized in that the wall has a: -. first predetermined thickness; the compressed product has a second predetermined thickness and the first predetermined thickness is greater than the second * 24. Metal part cast according to re-vendication 22, characterized in that the particles of cemented carbide are distributed almost uniformly in the compressed product. »25 · Metallic part cast according to re vendication 22, characterized in that the particles 10 of cemented carbide have a granularity, greater than 400 meshes, 26. Stubborn and wear-resistant body according to any one of Claims 1 to 35, characterized in that the carbide particles have a bimodal particle size, v ;. :