SE454058B - SEE, NUTS-RESISTANT FORM BODY AND WAY TO MAKE IT - Google Patents

Description

The brittle n-phase (M6C or M12C carbides containing tungsten and iron), the carbide particles used should typically have a size of at least 3.2 mm. An increase in particle size reduces the area of the carbide-steel interface. In the thin sections of a casting, which have a thickness of only slightly more than the carbide grain size, the carbides together with the mold can cause a rapid and extensive cooling of the molten metal flowing between the carbide particles, which can consequently cause an incomplete filling in these thin sections.

It is also impractical to keep large carbide particles uniformly distributed along a vertical section of a casting without filling this section with carbide from the bottom up, so that the carbide is held in position during casting. This can lead to the above-mentioned mists and / or an incomplete filling due to excessive cooling of the melt.

Australian Patent Specification AU-Bl-31362/77 seeks to avoid the above-mentioned casting problems by grinding or mixing a heat-treatable, low-alloy steel powder and a powder consisting of tungsten carbide or a solid solution of tungsten carbide and molybdenum. carbide, whereupon the resulting mixture is pressed and sintered to substantially full compact density. Low alloy steel is then cast around the sintered cemented carbide body to form a finished component. However, this Australian patent limits the steel powder used to a low chromium steel powder.

The present invention provides a tough, abrasion resistant body in which carbide particles having a grain size greater than 400 mesh are embedded substantially in a first metallic matrix. The above-mentioned composite of carbide particles and a first metal matrix are then bonded by means of a second metal matrix. Preferably, the carbide particles utilized are cemented carbide particles, preferably cemented carbide particles, which contain tungsten carbide. The carbide particles preferably constitute 30-80% by weight of the composite and have a grain size above 40 mesh.

The composite of carbide particles and the first metallic matrix are preferably substantially surrounded by the second metallic matrix.

The first metallic matrix preferably consists of steel, preferably stainless steel, and even more preferably an austenitic stainless steel.

The second metallic matrix preferably consists of steel, preferably a low-alloy steel or austenitic steel and most preferably an austenitic stainless steel.

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

It has also been found that when the first metallic matrix is an austenitic stainless steel, the first matrix may have a density of less than 90% or as low as 75-85%, calculated on the compact density.

According to the present invention there is also provided a process in which the carbide particles are mixed with a powder of the first metallic matrix, whereupon this mixture is isostatically pressed and sintered.

A second metallic matrix or molten metal is then bonded to said compact. The molten metal can be cast substantially around the compact, or depending on the purpose of use, in such a way as to obtain an abrasion resistant surface, the molten metal not having to fully incorporate the composite.

An object of the present invention is therefore to reduce the amount of brittle phases which are generated by casting molten metal around carbides.

Another object of the invention is therefore to provide a product which has excellent abrasion, corrosion and drilling resistance and also has good toughness. Yet another object of the invention is to provide a method by which a soil or rock tillage tool or a penetration-resistant safety device can be manufactured.

The invention will be described in more detail below with reference to the accompanying drawings. Fig. 1 shows an isometric view of a cast coffin according to the present invention. Fig. 2 shows a cross section along the line II-II in Fig. 2. Fig. 3 shows a cross section through a mold cavity, which is used in the production of the embodiment of the invention shown in Fig. 1.

Fig. 4 shows a cross section through an embodiment of an excavating tool stand according to the present invention.

According to the present invention, 30-80% by weight of carbide particles are mixed with 70-20% by weight of steel powder to form a substantially uniform mixture of carbide and steel.

The carbide particles used are preferably tungsten carbide based cemented carbide particles having a size of 400 mesh or preferably over 40 mesh. Preferably, these cemented carbide particles should have a size of -6 + 12 mesh (US standard sieve series) or between 0.13 and 0.066 inches (1.7-3.3 mm).

It has been found that sintered composites, which contain cemented carbide particles within this most preferred size range, are resistant to penetration of drills.

Further improvements in abrasion resistance and drilling penetration resistance can be achieved by using carbide particles with a bimodal grain size distribution. In this embodiment of the invention, the size of the smaller carbide particles is selected in such a way that they fit in the spaces between the larger carbide particles, whereby a further increase of the abrasion resistance is achieved.

The bonded carbide or cemented carbide may have a metallic binder selected from cobalt, nickel or Co-Ni alloys. In addition to tungsten carbide, the core metal may contain minor amounts of other carbides, such as tantalum carbide, niobium carbide, hafnium carbide, zirconium carbide and vanadium carbide. Crushed and screened cemented carbide waste has been found to be suitable for use in the present invention. Although tungsten carbide particles with a size of over -400 mesh can be used instead of all or part of the cemented carbide particles in the composite, tungsten carbide powder is not preferred because it does not bind to the steel as easily, has a greater tendency to break and generally gives lower abrasion resistance. and impact resistance than bonded tungsten carbides of the same particle size.

The steel powder used in the present invention may be an alloy steel but is preferably a stainless steel due to the greater resistance of these steels to corrosion. However, the most preferred stainless steels are austenitic stainless steels, as they have high abrasion resistance and impact at temperatures from room temperatures down to cryogenic temperatures. Of the austenitic stainless steels, the AISI steels 301, 302, 304 and 304L are preferred due to their high machining hardness.

In addition to the carbide and steel powder, the batch may contain organic binders to prevent segregation and provide a uniform distribution of the carbides during mixing and retention of the uniform mixture after mixing the components.

After mixing, the powder mixture is uniaxially pressed into a mold or isostatically into a preform, preferably at about 25 kp / mm 2 but not below 7 kp / mm 2.

After pressing, the compact is sintered at a temperature which is preferably below the melting point of the steel, preferably in the range 100 DEG-123 DEG C., for 10 to 90 minutes, thereby avoiding the generation of n-phases at the cemented carbide and steel interface. and wherein a strong metallurgical bond is still obtained between the cemented carbide and the steel. .

In most cases, the bond between the steel and the cemented carbide has the shape of an alloy layer at the interface between cemented carbide and steel. This layer consists mainly of cobalt and iron and typically has a thickness below 40 μm. This joint is important to ensure the retention or retention of coarse cemented carbide particles in the steel matrix.

It has been found that the thus sintered press bodies, which use austenitic stainless steel powder, generally exhibit an interconnected or open microprosity and have a steel binder density of less than 90% of the theoretical maximum density and in typical cases 75-85% of the theoretical maximum density. To increase the density of the compacts, one can use isostatic hot pressing, infiltration or increased compression pressures. These processes will also result in improved carbide retention in the composite. The infiltrant used can be selected from any copper-based or silver-based solder, which is capable of wetting both stainless steel and carbide. The sintered compact is then placed in a mold, and molten metal is cast around the compact to form a casting. The casting method used can be any casting method well known to those skilled in the art. Preferably, however, the casting method described in U.S. Patent 4,024,902 is utilized. Preheating of the compact may be utilized prior to the casting of the molten metal in the mold.

The molten metal may be an iron-based or non-ferrous alloy and is preferably steel.

The type of steel used does not have to be identical to the type of steel used in the compact. When impact resistance, strength and corrosion resistance are important, the cast steel is preferably an austenitic stainless steel. Low alloy steels and austenitic manganese steels can also be used.

The cast steel forms a metallurgical bond with the steel binder in the compact, whereby a minimal degree of reaction occurs with the cemented carbide. The generation of n-phase is thereby minimal, since the surface area of the carbides which come into contact with the molten steel has been made as small as possible.

The utilization of the compacts formed of cemented carbide and steel also enables the carbide to be bonded in varying concentrations and orientation positions relative to the surface and below the surface of the castings.

The method and products of the present invention will be exemplified in the following with some embodiments.

EXAMPLE 1 A number of abrasion- and impact-resistant excavator stands 1 (see Fig. 4) with compacts 3 were prepared. A uniform mixed mixture consisting of 60% by weight of cemented carbide grains formed from cobalt-bonded tungsten carbide having a grain size of 3.2-4.75 mm and 40% by weight of spray-sprayed austenitic stainless steel powder having a grain size under 100 mesh (149 μm) and consisted of stainless steel type AISI 304L and manufactured by Hoeganaes Corporation of New Jersey) was prepared by dry blending together with 1.25% by weight paraffin and 0.75% by weight ethylcellulose. The mixture was manually pressed into a molding cavity formed of polyurethane elastomer with the desired compact body shape (50.8 x 19.1 x 6.4 mm), the mold cavity being dimensioned to allow for shrinkage by isostatic powder cold pressing plus 1% sintering shrinkage. . After the isostatic cold pressing at 24.6 kp / mm 2, the pressed preform body was removed from the mold and then subjected to vacuum sintering at 110 ° C for eo min. The sintered bodies were then placed in a sand mold having eight recesses formed into the desired shape of the excavator stand. The constituents to form a low alloy steel of type AISI 4340 were melted in an induction furnace, the compacts were preheated and the steel was made in the mold via 177 DEG-113 DEG C. to form the excavator stand in Fig. 4, in which the steel material 5 of type AISI 4340 was bonded. two angled surfaces of the compact 3.

A metallographic examination showed that the stainless steel matrix contained an austenitic structure with a certain amount of intergranular chromium carbides, which can be called sensitization, which is typical of slowly cooled austenitic stainless steels after sintering. Sensitization can be eliminated through a subsequent dissolution treatment. The interfaces between the cemented carbide and the stainless steel matrix contained a continuous bond zone, which was about 15 microns thick and consisted of an alloy consisting mainly of iron and cobalt. The cemented carbide particles distributed in the matrix appear to be free from thermal cracking with a minimal amount of dissolution, melting or decomposition of the dispersed carbide phase at or near the boundary layer. There was some melting or mixing of stainless steel and some degradation of the carbides, where the molten metal came into contact with the carbides at the surface of the compact. Below the surface of the compact, the interfaces of the carbide particles were substantially sharp with the exception of the above-mentioned diffusion zone of iron cobalt alloy. No potentially harmful concentrations of n-phases were observed.

The specimens were repeatedly (five and six times) subjected to blows with a ball hammer at room temperature and also at the temperature of liquid nitrogen (-196 ° C) and were found to have good impact resistance with little sign of brittle type fracture. It should be noted, however, that the impact resistance at a higher percentage of cemented carbide in the composite may be slightly reduced but that the resistance of the composite to wear and drilling penetration would increase in such a case.

Microhardness measurements on a section of the excavator stand present in the cast condition showed an average hardness of about 75 HRC, 29 HRC and 38 HRC respectively within a cut through the cemented carbide, the stainless steel type 304L and the steel type 4340 (3.2 mm from the interfaces for stainless steel).

EXAMPLE 2 A drilling-resistant locking box 10, shown in Fig. 1, was made by casting a molten alloy steel alloy of type AISI 4340 around a hard metal plate, which consisted of a sintered mixture of carbide particles and stainless steel of type 304L. and which had a length of 102 mm, a width of 63.5 mm and a thickness of 3.2-4.7 mm, and similarly constructed boards with a length of 82.5 mm, a width of 63.5 mm and a thickness of 3.2. -4.75 mm. The position of one of the sintered discs 12 is shown in broken lines.

The boards had been made by uniformly mixing a mixture of 50% by weight of tungsten carbide pan, which had a size of -8 + 12 mesh and consisted of cobalt-bonded tungsten carbide, 50% by weight of stainless steel powder, which had a size of -100 mesh and consisted of stainless steel. of type AISI 304L, and 10% by weight of binder (CHLORUTHENE Nu and 0.75 ethylcellulose).

The mixture of stainless steel powder and the dispersed cemented carbide phase was packed in a polyurethane mold, which was formed to the dimensions of the boards. The mold was sealed, placed in a rubber bag, which was evacuated and sealed and then isostatically pressed at 24.6 kp / mm 2. After the pressed disk was removed from the rubber bag and the mold, the disk was sintered in a vacuum oven at 115 ° C for 60 minutes.

The drilling-resistant discs were then placed in the front, rear and side surfaces of the casing cavity in a mold. Fig. 3 shows a section through a sand mold 30, which has a mold cavity formed between a piston part 32 and a die part 34. The sintered discs 12 are shown held in position relative to the side walls of the mold cavity 454 058 by means of pins 36 and 40, which are embedded. in the mold part 34 of the mold 30. Carbide particles 42 have been placed on the bottom surface of the mold. Prior to the insertion of the piston portion 32 into the die portion 34, the cemented carbide particles 42 and discs 12 had been preheated. The piston part 34 was then placed in the die part 34, and molten alloy steel of type AISI 4340 was cast in the mold cavity. The object of the present invention in connection with this safety use is to provide a locking box which is protected against penetration of drills due to the presence of the 3.2 mm thick discs of a sintered mixture of stainless steel and cemented carbide particles, these discs being enclosed in a steel material.

A further object and new feature of the present invention is that the disc or discs in the manufacture of a casket will retain their shape and that the carbide particles remain uniformly distributed in the discs as the molten steel is cast around them to fill the remaining the part of the dimensionality of the walls of the locking box. After destruction of two cemented carbide drills with a diameter of 3.2 mm, the front section 14 of the reading box in Fig. 1 could not have been pierced or penetrated.

A section cut through the lock case with the hard metal and stainless steel plate is shown in Fig. 2. Slight melting occurred in the stainless steel when the molten steel alloy was cast around the cemented carbide plates, and the carbine grains remained uniformly distributed in the plates 12. Very little degradation of the carbide and a minimum of brittle phases at the interfaces between the carbide and the steel of type 4340 arose. A metallurgical joint was formed between the austenitic structure of the stainless steel and the structure of the cast steel of type 4340.

The carbide particles 42 at the bottom wall 20 of the locking box can be replaced with disks which are similar to or similar to the disks used in the side walls 22.

EXAMPLE 3 Drill-resistant and shock-resistant discs with a thickness of 4 mm were prepared. Fifteen discs consisted of a uniform mixture of 60% by weight, having a grain size of 2.38-3.2 mm (-8 + 12 mesh) and consisting of tungsten-bonded tungsten carbide grains, 40% by weight of stainless steel powder, consisting of steel type AISI 304L and had a grain size of -100 mesh (below 149 μm), 2 wt. CHLOROTHENE Now, 1 wt% ethylcellulose and 0.25 wt% ARMIDO wax. A second group of fifteen sheets was made of 70% by weight of cemented carbide chips (-8 + 12 mesh) and 30% by weight of stainless steel type AISI 304L (-100 mesh), mixed in a similar manner. The ARMIDO wax and ethylcellulose were added to the powder mixture during the mixing process and served as a press lubricant to prevent the carbide particles from seeping in during the mixing and filling of the mold. The matrix powder, which contained the hard dispersed carbide phase, was then packed in a preform consisting of polyurethane. The packed preform was fitted with a suitable lid and sealed and placed in a rubber sack or balloon, which was evacuated, sealed and pressed isostatically at about 24.5 kp / mm 2. The slices were then sintered in a vacuum oven at 115 ° C for 60 minutes.

These sheets can now be inserted into a casting piece using the casting technique described above or any other known casting technique. D.

Modifications are possible within the scope of the appended claims.

Claims (10)

454 us 10 15 20 25 30 12 PATENT CLAIMS 1. l. Tough, abrasion resistant body, characterized in that it comprises at least one penetration-resistant component, which has been formed by powder metallurgical methods during pressing and diffusion bonding in the solid state via about 1o4o-123o ° c and which a first stainless steel matrix and tungsten carbide hard metal particles bonded and substantially enclosed therefrom having a particle size of at least 400 mesh (37 μm), preferably at least 40 mesh (420 μm) and preferably having an irregular particle shape, and a second metallic matrix , which is bound to the penetration-resistant component and in which this component is embedded. Body according to claim 1, characterized in that the tungsten carbide cemented carbide particles contain a binder metal from the group of cobalt and nickel and their alloys with each other and / or with other metals. Body according to Claim 1 or 2, characterized in that the second metallic matrix substantially surrounds the penetration-resistant component. Body according to claim 1, 2 or 3, characterized in that the first stainless steel matrix consists of an austenitic stainless steel, which preferably has a density of less than 90%, more preferably 75-85%, of the theoretical compact density. Body according to one of Claims 1 to 4, characterized in that the second metallic matrix consists of steel. Body according to one of Claims 1 to 5, characterized in that the tungsten carbide hard metal particles have a submodule particle size distribution. Body according to one of Claims 1 to 6, characterized in that the second metallic matrix is a cast metal material. 8. A process for producing a tough, abrasion resistant product, characterized in that a mixture of tungsten carbide cemented carbide particles having a particle size of at least 400 mesh (37 μm), preferably at least 40 mesh (420 μm), and a first stainless steel steel powder is pressed into at least one compact, of which the tungsten carbide cemented carbide particles preferably constitute 30-80% by weight and in which the tungsten carbide cemented carbide particles are preferably distributed substantially uniformly and preferably have a bimodal particle size distribution, that the compact in - 230 ° C and that a molten metal is cast against or around this or these compacts to be bonded to the same or the same. - 9. A method according to claim 8, characterized in that the molten metal is brought substantially around the compression body or bodies. 10. A method according to claim 8 or 9, characterized in that the compaction body or bodies are sintered isostatically.