FR2504426A1 - CAST PIECE COMPRISING COMPACT, WEAR-RESISTANT PARTS AND METHOD FOR MANUFACTURING SUCH A PIECE - Google Patents

Abstract

WEAR RESISTANT TO WEAR, CHARACTERIZED IN THAT IT INCLUDES A PENETRATION RESISTANT COMPONENT CONTAINING CARBIDE PARTICLES OF A SIZE OVER 38 MICRONS, A FIRST METAL MATRIX, THE PARTICLES BEING BOUND TO THE FIRST MATRIX AND BEING PROVIDED PRACTICALLY INSIDE THE SAME, AND A SECOND METAL MATRIX, THIS SECOND MATRIX IS LINKED TO THE PENETRATION RESISTANT COMPONENT.

Description

The present invention relates to the field of castings resistant to

wear and their manufacture

  Specifically, the present invention relates to the field of

  do castings for earthworks, repair

  resistant to wear and resistant safety devices

so much for penetration.

  In the field of earthmoving equipment, the useful life of the teeth in contact with the ground

  worked is an important factor in the labor economy

vail performed.

  The lifespan of these teeth is affected by the envi-

  reason in which they operate, this environment

  can create conditions of wear by abrasion, eff-

  strong at impacts, temperature variations, vibrations

  corrosion and corrosion on the surface of the teeth, all these factors tending to reduce the useful life of the tooth or tool The downtime to replace worn or broken tools and the cost of these tools have led to a broad development of a variety of tools

  designed to have longer lifespans.

  In some cases, these improved tools include carbides embedded in the working surface of the tool by casting processes (see for example the patents

US 4,040,902 and 4 14 or 170).

  These casting techniques raise problems when

  we want to obtain castings with sections

  relatively thin or when you want to

  cer carbide particles on the surface of an accessory

  re vertical, as well as on a horizontal portion,

of a casting.

  In order to reduce the dissolution of particles of car-

  bure during casting, and the resulting eta fragile phase (M 6 C or M 12 C carbides containing tungsten and iron) produced at the carbide-steel interfaces, the cemented carbide particles used must have a dimension

  greater than 3 mm The increase in the size of the

  ticules reduces the surface of the carbide-steel interface.

  However, in the thin sections of a casting having a thickness only slightly greater than the size of the carbide particles, the carbides can act in connection with the mold to rapidly and excessively cool the liquid metal circulating between the carbides and cause thus an incomplete filling

in these thin sections.

  It is also difficult to maintain large areas.

  case-hardened tiles uniformly distributed in a vertical section of a casting without filling this section with carbide from the bottom to the top so as to maintain

  carbides in position during casting This can

  draw the aforementioned voids and / or an incomplete filling

  due to excessive cooling of the liquid metal.

  In Australian patent no AU-BI-31 362/77, we

  seeks to avoid the aforementioned casting problems in bro-

  there is a powder of a low alloy steel and heat treatable with a powder of tungsten carbide or a powder of carbide of a solid solution of tungsten and molybdenum, and then compressing the mixture and by sintering it practically to the maximum theoretical density

  to obtain a compact part (hereinafter called simple-

  "compact") of the resulting mixture We then pour low alloy steel around this sintered compact

  of steel and carbide to obtain a Tou-

  However, in this Australian patent, the steel powders used are limited to steels with low chromium content.

  The present invention provides a tough tenacious body

  both to wear in which carbide particles having

  a dimension larger than 38 microns are drowned practically

  only in a first metallic matrix The composite

  above carbide particles and the first ma-

  metallic trice is linked to a second metallic matrix.

  Preferably, the carbide particles are particles

  cemented carbide, preferably containing carbon

  tungsten bure Preferably also, the carbide particles constitute 30 to 80% by weight of the composite and

  have a dimension greater than 425 microns.

  Also preferably, the second metal matrix

  lique practically surrounds the composite with carbide particles and the first metallic matrix. The first metallic matrix is preferably made of steel, preferably made of stainless steel, and in particular made of

an austenitic stainless steel.

  The second metal matrix is steel, pre-

  reference in low alloy steel or austenitic steel

  tick, and in particular an austenitic stainless steel.

  It is also preferred that the cemented carbide particles used mainly contain tungsten carbide and a binder chosen from cobalt, nickel, their alloys with one another or their alloys with other metals.

  It was also found that when the first ma-

  metal trice was austenitic stainless steel, the density of the first matrix had to be lower than 90%, and even go down to 75 to 85% of the density

theoretical maximum.

  The present invention also provides a process in which the carbide particles are mixed with the powder constituting the first metal matrix, and in which the mixture is then compacted isostatically and sintered. A second metal matrix or liquid metal is then bonded to this "compact "The liquid metal can be poured practically around the compact or, depending on the application, for example to provide a surface

  wear, liquid metal may not surround completely

the composite body.

  It is therefore an object of the present invention to reduce the fragile phases produced when sinking

  liquid metal around carbides.

  It is also an object of the present invention to provide a product having excellent characteristics of resistance to wear, to corrosion and to drilling,

as well as good tenacity.

  Another object of the invention is to provide a pro-

  assigned to manufacture an earthmoving tool or a

  security device resistant to penetration.

  The invention will be better understood on reading the

  detailed description given below as an example

  only, in conjunction with the appended drawing in which FIG. 1 is an isometric view of a shoemaker of

  cast lock according to the present invention.

  Fig 2 is a cross section of the realization

  tion of fig 1, according to arrows II-II.

  Fig 3 is a cross-sectional view of a mold cavity used to produce the embodiment of Fig 1 of the present invention; and Fig 4 is a cross-sectional view of a

  production of an excavator tooth according to the present

the 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

  carbide and steel particles The carbide particles used

  are preferably particles of tungs carbide-

  cemented tene having a dimension of 38 microns or preferably greater than 425 microns In particular, these cemented carbide particles must have a dimension

between 3.35 and 1.70 mm.

  It has been found that sintered composite materials containing cemented carbide particles whose dimensions are included in the range cited last

  resist penetration by drilling very well.

  Other improvements in resistance can be obtained.

  wear resistance and penetration resistance to drilling using carbide particles having a

  bimodal particle size In this embodiment, the dimension

  size of the smallest carbide particles is chosen

  to allow them to find accommodation in the interstices

  between the larger carbide particles, increasing 2 el) 4 4? 6

thus resistance to wear.

  Cemented carbides may have a binder

  metallic chosen from cobalt, nickel or al-

  cobalt-nickel bondings In addition to tungsten carbide, cemented carbide may contain smaller amounts of other carbides, such as tantalum carbide, niobium carbide, hafnium carbide, carbide of

  zirconium and vanadium carbide.

  We found that we could use in this process

  cemented carbide waste, ground and sieved.

  Although you can replace all or a

  part of the cemented carbide particles in the material

  composite ria by tungsten carbide particles larger than 38 microns, this is undesirable since tungsten carbide powder binds less readily to steel, tends to fracture easily and resistance to wear and shock obtained is generally less than in the case of cemented tungsten carbides

  of the same particle size.

  The steel powder used in this invention may be an alloy steel, but it is preferably a steel

  stainless due to its greater resistance to corrosion

  However, the preferred stainless steels in this invention are austenitic stainless steels because of their high resistance to wear and impact from ambient temperature to cryogenic temperatures. Among these austenitic stainless steels, the AISI type 301 qualities are preferred. , 302, 3 o 4 and 304 L,

  due to their high curing speed.

  In addition to the carbide and steel powders in the feed, organic binders are also added to prevent any segregation and obtain a uniform distribution of the

  carbides during mixing and to maintain this uni-

formity after this one.

  Then, the powder mixture is compacted by compress-

  uniaxial sion in a mold or by hydrostatic pressure in a preform mold, preferably about

  2.5 10 pascals, the prebsion should not be inferior

less than 0.7 10 2 pascals.

  After compaction, the body obtained is sintered at a temperature preferably below the melting point of the steel and in particular in the range from 1 o 4 o to 12300 C for 20 to 90 minutes, thus avoiding the formation of the eta phases at l cemented carbide-steel interface, while

  providing a solid metallurgical bond between the car-

cemented bure and steel.

  In most cases, the bond between steel and cemented carbide takes the form of a layer alloyed with

  the cemented carbide-steel interface This layer is composed

  mainly of cobalt and iron and its thickness

  is typically less than 40 microns.

  This bond is important for retaining

  keeps coarse cemented carbide particles at

inside the steel matrix.

  It has been found that the sintered compacts using austenitic stainless steel powder have a microporosity with communicating pores and have a density of steel binder less than 90% of the theoretical value and more typically between 75 and% of theoretical value To increase the density of

  compact bodies, isosta- compression can be used

  hot tick, infiltration or increase the packing pressures These processes also improve the retention

  carbides in the composite body

  tration used can be chosen from any one

  than copper-based or silver-based brazing materials that wet both stainless steel and carbides. The compact sintered body is then placed inside a mold and molten metal is poured around it to obtain a casting. The casting process used can be any of those well known in the art. prefer the casting process described in US Pat. No. 4,024,902 The compact material can be preheated 29 c O 4426 before pouring the molten metal into

the mold.

  This molten metal can be a ferrous or non-ferrous alloy, and is preferably steel The type of steel used is not necessarily identical to that contained in the compact material When the characteristics of mechanical strength and impact resistance and corrosion are important, the cast steel is preferably

  an austenitic stainless steel.

  be low alloyed and austenitic manganese steels

  ticks. The cast steel forms a metallurgical bond with the steel binder in the compact with minimal reaction with the cemented carbides. The formation of the eta phase is thus reduced because the specific surface of the carbides coming into contact with the liquid steel. has been reduced. The use of compacts in cemented carbides and in steel also makes it possible to bind carbides in a variety of concentrations, positions and orientations, both on the surface and below the surface of the cast bodies.

  The process and the products according to the present invention

  tion will appear better in the detailed examples below.

before:

Example 1

  A number of teeth 1 of the wear-resistant and impact-resistant excavation machine are produced (see FIG. 4) comprising compact parts 3 A mixture is prepared

  uniform consisting of 60% by weight of granules of

  cemented tungsten bure, with cobalt, of grain size

  between 3.18 and 4.76 mm and 40% by weight of

  dre of austenitic stainless steel 304 L atomized to less than 150 microns (manufactured by Hoeganaes Corporation of New Jersey), by dry mixing with 1.25% by weight of paraffin and 0.75% by weight of ethylcellulose The mixture

  is manually packed in a poly mold cavity

  elastomeric urethane in the form of the desired compact

  (50.8 mm long, 19.1 mm wide, 6.35 mm thick-

  sized) to allow cold isostatic packing of the powder, taking into account a sintering shrinkage of 1% After the cold isostatic packing at 2.5 10 2 pascals, the packed preform is removed from the mold and sintered under vacuum at 11500 C for 60 minutes The sintered bodies are then placed in a sand mold which has 8 cavities formed in the shape of the teeth of the desired excavation machine The components necessary for the preparation of a low alloy steel AISI 4340 are melted in an induction furnace, the compact parts are preheated and the steel cast in the mold at a temperature between 1680 and 17300 C, to form the excavator tooth shown in fig 4, in which the steel 4340 (item 5) is linked to two connecting faces

  at an angle of the compact part 3.

  Metallographic examination shows that the stainless steel matrix has an austenitic structure

  with some intergranular chromium carbides, desi-

  Known as sensitization, which is typical of austenitic stainless steels cooled slowly after sintering. Sensitization can be eliminated by

  subsequent heat treatment in solution Inter-

  sides of the stainless steel matrix and cemented carbides have a continuous bonding area of approximately

  microns thick of a main alloy

  iron and cobalt particles carbide particles

  scattered tee appear devoid of thermal cracks

  with a minimum amount of dissolution, fusion or degradation of the dispersed carbide phase at the interface limits or in their vicinity There is a certain degree of fusion or mixing of the stainless steel and a certain degradation of the carbides when the liquid metal comes into contact with the carbides on the surface of the compact part However, below this surface, the interfacial limits of the carbides are generally

04426

  well-defined except for the area of diff

  Above-mentioned melting of the iron-cobalt alloy No potentially harmful concentration of the eta phases is observed. Test pieces were struck several times (5 and 6 times) with a spherical hammer at room temperature and at the temperature of liquid nitrogen (-1950 c) and we find that these test pieces have good resistance

  impact and are not subject to fragile fractures

  However, it should be noted that when the percentage by weight of cemented carbides in the composite material

  increases, impact resistance may be slightly reduced

  pick, but resistance to wear and penetration by

piercing increases in this case.

  Microhardness measurements of a section of the casting tooth show average hardnesses (indentations) of approximately 75 R "C", 29 R "C" and 38 R "C" inside a section through cemented carbide, stainless steel

  304 L and 4340 steel respectively (-3.18 mm from the inter-

stainless steel faces).

Example 2

  Fig 1 shows a resilient locking box

  both in drilling 10 produced by casting a low alloy steel of type 4340 around plates of carbide and sintered 304 L stainless steel (101.6 mm in length, 63.5 mm in width, 3.18 to 4.76 mm thick) and plates (82.6 mm

  long, 63.5 mm wide, 3.18 to 4.76 mm thick

  The position of one of the sintered plates 12 is shown

  felt in dashes in the figure The plates are prepared by uniformly mixing a mixture of 50 O by weight of shavings of cemented tungsten carbide, with cobalt, of a particle size comprised between 2.30 and 1.70 mm, 50% by weight an AISI 304 L stainless steel powder less than 150 microns and 10 by weight of binders (chlorothene Nu and

  0.75 ethylcellulose) Stainless steel powder forms

  mant the matrix containing the dispersed cemented carbide phase is packed in a polyurethane mold formed at

04426

  dimensions of the plates The mold is then closed, placed in a rubber bag in which a vacuum is created and

  which is closed hermetically and then compressed isostati-

  only at 2.5 10 pascals After removing the compact plate from the rubber bag and the mold, it is

  sintered in a vacuum oven at 11500 C for 60 minutes.

  These drilling resistant plates are then placed

  on the front, back and sides of a bot cavity

  locking tier in a mold FIG. 3 is a section view of a sand mold 30 having a cavity formed between a cap 32 and a lower section 34 The sintered plates 12 are seen held in position in the cavities of the side walls by nails 36 and 40 which

  are incorporated in the lower section 34 of the mold 30.

  Particles of cemented carbide 42 were deposited on the bottom of the cavity Before placing the cap 32 on

  the lower section 34, the carbide particles

  tees 42 and the plates 12 are preheated The cap 32 is then placed on the lower section 34 and low-alloy molten steel 4340 is seen in the mold cavity.

  The objective of the present invention in this application

  safety cation is to provide a lock boot

  3.2 mm thick sintered carbide and stainless steel plates coated with steel for

  provide protection against penetration by drilling.

  It is another object of this invention that when

  manufacture of this locking boot, the or the plates

  maintain their shape and the carbide particles remain uniformly dispersed in the plates when

  molten steel flows around them to fill the cavity

  remaining tee of the walls of the shoemaker After destruction of two 3.2 mm diameter masonry drills, the front section 14 of the shoemaker 10 shown in fig 1 was not

not attacked.

  A sectional view of the shoemaker containing the plate

  carbide and stainless steel is shown in fig 2.

  There is slight melting of the stainless steel when the molten alloy steel is poured around the sintered plate of carbide and stainless steel and the carbides remain uniformly distributed in the plate 12 The degradation of the carbides is very weak and does not observe any fragile phase at the carbide-steel interfaces 4340 Une

  metallurgical bond occurs between the structure also

  tenitic of stainless steel and the structure of cast steel 4340 The carbide particles 42 in the bottom wall 20 of the case can be replaced by plates identical or similar to those shown

in the side walls 22.

Example 3

  We make 4 mm thick plates

  both for drilling and impacting 15 plates are thus prepared consisting of a uniform mixture of 60% by weight of shavings of cemented tungsten carbide, with cobalt, of a particle size between 2.30 and 3.2 mm, 40% in weight of 304 L stainless steel powder less than 150 microns, 2% by weight of chlorothene Nu, 1% by weight of ethylcellulose and 1/4% by weight of armide wax ("Armido") A second group of 15 plates with 70 56 by weight of cemented carbide chips from 2.4 to 1.7 mm, and 30% by weight of stainless steel powder

  304 L less than 150 microns, mixed in the same way.

  Wax "Armido" and ethylcellulose are added to the powder mixture, during mixing, to serve as a compression lubricant and prevent the segregation of particles.

  carbide when mixing and filling the mold.

  Then, the matrix powder containing the cemented carbide phase dispersed in a preform mold is packed

  made of polyurethane The mold is then closed with a cover

  suitable ring and placed in a rubber bag or a rubber balloon in which a vacuum is made which is hermetically closed and which is then compressed isostatically to approximately 2.5 10 2 pascals The plates are then sintered in a vacuum oven 11500 C

for 60 minutes.

  We can then incorporate these plates in a room

  molded using previous casting techniques

  described or any of the casting methods

known in the art.

Claims (19)

  1 Durable wear-resistant body, characterized by   the fact that it has a penetration resistant component   tration containing carbide particles of a size   sion greater than 38 microns, a first metallic matrix, the particles being bonded to the first matrix and being arranged practically inside thereof, and a second metallic matrix, this second matrix   being linked to the penetration resistant component.   2 body according to claim 1, wherein the   particles are particles of cemented carbides.   3 Durable wear-resistant body, characterized by   the fact that it has a penetration-resistant component   tion containing particles of cemented carbides a first metallic matrix, the particles of cemented carbides being linked to this first matrix and being   arranged practically inside, and a second ma-   metal trice linked to the penetration resistant component   tration. 4 Body according to claim 3, wherein the   second metal matrix practically surrounds the compound   resistant to penetration.   Body according to one of claims 1, 2 or 3,   in which the first metallic matrix is a steel austenitic stainless.   6 Body according to claim 5, wherein the   second metal matrix is steel.   7 body according to claim 3, wherein the   particles of cemented carbides have a larger dimension smaller than 425 microns.   8 Body according to claims 2 or 3, wherein   particles of cemented carbides are particles tungsten carbide.   9 Body according to claim 7, wherein the particles of cemented carbides further comprise a binder selected from the group consisting of cobalt, nickel, their alloys with each other and their alloys with other metals.   The body of claim 5, wherein the density of the austenitic stainless steel matrix is   less than 90% of the theoretical density.   11 Body according to claim 10, wherein the   density of the matrix is 75 to 85% of the theoretical density.   12 Body according to claim 3, wherein the   particles of cemented carbides have an irregular shape.   13 Process for preparing a tough tenacious product   both in wear, characterized by the fact that a mixture of cemented carbide particles is packed with a first steel powder, and this compact material is bonded to a molten metal. 14 The method of claim 13, wherein the particles of cemented carbides constitute 30 to 80% by weight of the compact.   The method of claim 13, wherein   the compact material is sintered before casting.   16 The method of claim 13, wherein the   tamping stage includes isostatic tamping.   17 The method of claim 13, wherein particles of cemented carbides are selected.   having a dimension greater than 425 microns for the uti- read into the mixture.   18 Process for the preparation of a tough, resistant product   both in wear and tear, characterized by the fact that a   mixture of particles of cemented carbides and a   metallic to form a compact material and a molten metal is poured in the vicinity of the compact material for bond to this molten metal.   19 The method of claim 18, wherein   the molten metal practically surrounds the compact material.   Method according to one of claims 18 or 19,   in which particles of cemented carbides having a size greater than 425 microns are selected to use them in the mixture.   21 The method of claim 18, wherein   the compact material is sintered below the temperature   metal powder melting before casting.   22 Metal casting, characterized in that it comprises a base, a wall extending out of the plane of the base, a compact material of particles   pulverulent, particles of cemented carbides   held inside the compact material, the latter being linked to the wall and being practically contained inside of it.   23 Metal casting according to claim 22, in which the wall has a predetermined thickness, the compact material has another predetermined thickness,   and the first is greater than the second.   24 A metal casting according to claim 22, in which the particles of cemented carbides are practically uniformly distributed throughout the compact material.   A metal casting according to claim 22, wherein the particles of cemented carbides   have a size greater than 38 microns.   26 Tough wear-resistant body according to one of the   Claims 1, 2 or 3, wherein the particles of   carbides have a bimodal particle size.