JPH0237261B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to the field of wear-resistant castings and their production. More particularly, the present invention relates to the field of abrasion resistant civil engineering castings and drill bit penetration resistant safety devices.

BACKGROUND OF THE INVENTION In the field of civil engineering equipment, the service life of the teeth in contact with the formation being worked is important for the economic success of the civil engineering work being carried out.

The lifespan of these teeth is affected by the environment in which they are operated. Typically, the environments encountered create conditions such as wear, shock loads, temperature changes, vibration and corrosion on the tooth surfaces, all of which contribute to reducing tooth or tool life. A wide variety of tools have been developed that are designed to improve the service life of tools in terms of downtime for things like changing cutters and the high cost of tooling for replacing worn and damaged tools. It's here.

In some cases, these improved tool designs involved embedding carbide into the machined surface of the tool via a casting process (see, eg, US Pat. Nos. 4,024,902 and 4,140,170).

These casting techniques are used when it is required to produce castings with relatively thin cross-sections or when it is necessary to distribute carbide particles on the surfaces of structures that are vertical as well as horizontal parts of the casting. Problems arise.

Dissolution of carbide particles during casting and the resulting formation of brittle carbide-steel interfaces (eta)
phase (M ₆ C containing tungsten and iron or
The _sintered carbide particles utilized are typically at least 3.2 mm in order to minimize the
(1/8 inch) grain size. Increasing the particle size reduces the area of the carbide-steel interface.
However, in thin cross-sections of castings with thicknesses only slightly greater than the grain size of the carbides, the carbides act with the mold to rapidly and excessively cool the molten metal flowing between them. As a result, these thin portions are incompletely filled with molten metal, causing defects such as cavities and voids. Filling the vertical section of the casting with carbide from the bottom upwards will keep the large sintered carbide particles evenly distributed along the vertical section of the casting, keeping the carbide in place during casting. It is not possible to do so. This leads to the aforementioned voids and/or incomplete filling due to excessive cooling of the molten metal.

Australian Patent No. AU-BI-31362/77
No. 2, the above-mentioned process was carried out by milling heat treatable low alloy steel powder with tungsten carbide powder or tungsten molybdenum solid solution carbide powder and then compressing and sintering the resulting mixture into a compact of substantially full density. We are trying to avoid the casting problems of . Low alloy steel is then cast around the sintered steel-carbide compact to form the finished part. However, this Australian patent limits the steel powder used to low chromium steel.

(Problems to be Solved by the Invention) Therefore, the problem to be solved by the present invention is to eliminate the drawbacks in the prior art described above.

Accordingly, one object of the present invention is to minimize the brittle phase produced when pouring molten metal around carbides.

It is therefore another object of the present invention to provide a product which has excellent toughness as well as resistance to wear, corrosion and penetration by drill bits.

Another object of the invention is to provide such a method by which a safety device can be provided which has resistance to penetration by earthmoving tools or drill bits.

SUMMARY OF THE INVENTION According to the present invention, a tough wear-resistant member is described having carbide particles having a particle size greater than 400 mesh substantially embedded in a first metal matrix. There is. The composite of carbide particles and a first metal matrix is bonded to a second metal matrix. Preferably, the carbide particles are sintered carbide particles, most preferably containing tungsten carbide. Preferably, the carbide particles constitute 30-80% by weight of the composite and have a particle size greater than 40 mesh.

Preferably, the second metal matrix substantially surrounds the carbide particle and first metal matrix composite.

The first metal matrix is preferably composed of steel, preferably stainless steel, most preferably austenitic stainless steel.

Preferably, the second metal matrix is comprised of steel, preferably low alloy steel or austenitic steel, most preferably austenitic stainless steel.

It is also preferred that the sintered carbide particles utilized contain primarily tungsten carbide and a binder selected from cobalt, nickel, their alloys with each other or with other metals. be.

It has also been found that when the first metal matrix is an austenitic stainless steel, the density of the first matrix is less than 90% or 75-85% of the theoretical density.

According to the invention, there is also provided a method in which carbide particles are mixed with a homogeneous metal matrix powder and the mixture is then isostatically compacted and sintered. A second metal matrix or molten metal is then bonded to the compact. The molten metal is cast substantially around the compact, or in applications where it provides a wear surface, the molten metal is not cast completely around the composite.

EXAMPLES The nature of the invention will become more apparent by reference to the following detailed description in conjunction with the accompanying drawings.

According to the invention, 30-80% by weight of carbide particles and
70-20% by weight of steel powder is mixed to produce a substantially homogeneous mixture of carbide and steel. The carbide particles used are preferably sintered tungsten carbide having a particle size of 400 mesh, preferably greater than 40 mesh. Most preferably, these sintered carbide particles have a particle size of -6+12 mesh (US sieve series) or 3.3 to 1.7 mm (0.13 to
should have a grain size of 0.066 inch).

Sintered composites containing cemented carbide particles within this most preferred size range have been found to be resistant to penetration by a drill bit. Further improvements in abrasion resistance and resistance to penetration by drill bits are obtained by utilizing carbide particles having two sets of size distributions. In this embodiment of the invention, the particle size of the smaller carbide particles is selected to fit into the gaps formed between the larger carbide particles, thereby further increasing wear resistance.

The cemented carbide may have a metal binder selected from cobalt, nickel or cobalt-nickel alloys. In addition to tungsten carbide, the sintered carbide may contain smaller amounts of other carbides, such as tantalum carbide, niobium carbide, hafnium carbide, zirconium carbide, bamdium carbide. It has been found that crushed and screened regenerated return sintered carbide is suitable for use in this process.

Tungsten carbide particles larger than -400 mesh may be substituted for all or part of the sintered carbide particles in the composite, but tungsten carbide powder is not preferred. That is, tungsten carbide powder has poorer bonding to steel, is more susceptible to fracture, and generally has lower wear and impact resistance than sintered tungsten carbide of the same particle size.

The steel powder used in this invention may be alloy steel, but stainless steel is more suitable because of its high corrosion resistance. However, the most preferred stainless steel is an austenitic stainless steel. That is,
Austenitic stainless steels have high wear and impact resistance from room temperature to cryogenic temperatures.
AISI type among austenitic stainless steel
Classes 301, 302, 304 and 304L are suitable because of their high work hardening rates.

In addition to the carbides and steel powder in the sintering furnace charge, organic binders are also added to prevent segregation and to evenly distribute the carbides during mixing and to maintain a homogeneous mixture after mixing. be done.

After mixing, the powder mixture weighs 700Kg/cm ²
(10.000Psi), preferably around 2.450
It is compacted by uniaxial compression in a die or by isostatic compression in a mold of a partially sintered powder before sintering, at a pressure of Kg/cm ² (35.000 Psi).

After crimping, the compact is preferably heated to a temperature below the melting point of the steel, most preferably 1038-1232°C (1900-1900°C).
2250〓) for 20 to 90 minutes,
This avoids the formation of an eta phase at the sintered carbide-steel interface, yet provides a strong metallic bond between the sintered carbide and the steel.

In many cases, the bond between the steel and the cemented carbide takes the form of an alloy layer present at the cemented carbide-steel interface.
This layer is primarily composed of cobalt and iron and typically has a thickness of less than 40 microns. This bonding is important to ensure the retention of coarse cemented carbide particles in the steel matrix.

As-sintered compacts utilizing austenitic stainless steel powders generally exhibit an interconnected microporous structure and are less than 90% of the theoretical density, and more typically 75-85% of the theoretical density. It was found that the steel has a binder density. Methods such as hot isostatic pressing, molten metal percolation (infiltration), and increasing compaction pressure may be used to increase the density of the compact. These methods also improve carbide retention in the composite. The infiltrant used may be selected from steel-based or silver-based brazing materials that wet both stainless steel and carbides.

The sintered compact is then placed in a mold and molten metal is poured around it to form a casting. The casting procedure used can be any of those well known to those skilled in the art. However, it is preferred to use the casting procedure described in US Pat. No. 4,024,902. Preheating of the compact may be used prior to casting the molten metal into the mold.

The molten metal is a ferrous or non-ferrous alloy, preferably steel. The type of steel utilized does not have to be the same as that contained in the compact. Where impact, strength and corrosion properties are important, the steel being cast is preferably an austenitic stainless steel. Low alloy steels and austenitic manganese steels may also be utilized.

The cast steel forms a metallic bond with the steel binder in the compact, and the amount of reaction with the cemented carbide is minimal.
This minimizes motor phase formation. The reason is that the surface area of the carbide in contact with the molten steel is minimized.

The use of sintered carbide-steel compacts also allows carbides to be bonded onto and subsurface of the casting in various concentrations, locations, and orientations.

The methods and products of the invention will be further elucidated by consideration of the detailed examples below.

Example 1 A number of wear and impact resistant excavator teeth 1 (see FIG. 4) with compacts 3 were made. 60% by weight of 3.2 to 4.8 mm (1/8 to 3/16 inch) powdered sintered tungsten carbide particles and 40% by weight of -100 mesh type 304L austenitic stainless steel spray powder (Hoeganaes Corporation of New Jersey)
A homogeneous mixture consisting of (product) was prepared by dry mixing with 1.25% by weight paraffin and 0.75% by weight ethyl cellulose. This mixture is molded into the desired molded shape *Length 50.8 mm (2 inches),
Width 19.1mm (3/4 inch) Thickness 6.4mm (1/4 inch)
The compact was manually packed into the cavity of an elastomeric polyurethane mold, the dimensions of which were determined taking into account cold isostatic powder compaction and 1% sintering shrinkage. 2450Kg/ ^cm2 (35.000psi)
After cold isostatic pressing at , the green compact was removed from the mold and then heated to 1149°C (2100〓).
vacuum sintered for 60 minutes. The sintered body was then placed in a sand mold with eight recesses shaped into the required excavator tooth shape. The ingredients to produce AISI4340 low alloy steel were melted in an induction furnace, the compact had been preheated, and then the steel
Cast at 1677~1732℃ (3050~3150〓)
Forming the excavator tooth shown in the figure, 4350 steel 5 is bonded to two angular faces of the compact 3.

Metallographic examination has shown that the stainless steel matrix contains an austenitic structure with some grain boundary chromium carbides called sensitization. This sensitization is a characteristic of austenitic stainless steel that is slowly cooled after sintering, and can be eliminated by subsequent solution heat treatment. The cemented carbide-stainless steel matrix interface was primarily an alloy of iron and cobalt and contained a continuous bonding zone approximately 15 microns thick. No thermal decomposition was observed in the dispersed particles of cemented carbide, and there was minimal dissolution, melting, or degradation of the dispersed carbide phase at or near the interface. Some melting or mixing of the stainless steel and some deterioration of the carbide were observed where the molten metal came into contact with the carbide on the surface of the compact. However, below the surface of the compact, the carbide interfaces were generally sharp, except for the diffusion zone of the iron-cobalt alloy. No potentially harmful eta phase concentration was observed.

The test sample was heated to room temperature and liquid nitrogen temperature -196℃.
When repeatedly struck (5-6 times) with a ball peen hammer at (-320〓), it was found to have good impact resistance, with almost no brittle fractures observed. It should be noted, however, that as the weight percentage of sintered carbide in the composite increases, resistance to wear and penetration by drill bits increases, although impact resistance may decrease somewhat.

Microhardness measurements of cross-sections of as-cast excavator teeth were performed using sintered carbide, 304L stainless steel and
4340 steel (stainless steel interface) exhibited average hardness (indentation) of approximately 75, 29, and 38 on the Rockwell C scale in the lateral plane at each section of 3.2 mm (0.125 inch), respectively.

EXAMPLE 2 A lockbox 10 resistant to penetration by a drill bit as shown in FIG.
304L Stainless Steel - Carbide Plate (Length
101.6mm (4 inches), width 63.5mm (2 1/2 inches),
Thickness: 3.2-4.8 mm (1/8-3/16 inch) and plate [length: 82.6 mm (1/4 inch), width: 63.5 mm (2
1/2 inch), thickness 3.2~4.8mm (1/8~3/16 inch)
Produced by casting molten metal of 4340 low alloy steel around. The position occupied by one of the sintered plates 12 is indicated by a dashed line. This plate is
50.0 wt% -8+12 mesh cobalt sintered tungsten carbide chips and 50.0 wt% -8+12 mesh cobalt sintered tungsten carbide chips;
100 mesh AISI304L stainless steel powder,
It was made by homogeneously mixing a mixture with 10.0% by weight of a binder (chlorinated solvent, trade name Chlorotene Nu and Ethyl Cellulose).

A matrix stainless steel powder containing a dispersed hard carbide phase was packed into a polyurethane mold shaped to the dimensions of the plate. The mold was then sealed, evacuated and placed in a sealed rubber bag, then weighed at 2450Kg/cm ²
(35,000psi) isostatic compression molding. After the molded plates were removed from the rubber bag and mold, they were sintered in a vacuum oven at 1149°C (2100°C) for 60 minutes.

Drill bit penetration resistant plates were then placed in the mold on the front, back and sides of the lockbox cavity. FIG. 3 shows a cross-section of a sand mold 30 having a cavity formed between an upper mold portion 32 and a lower mold portion 34. FIG. The sintered plate 12 is held in place within the side wall cavity by nails 36, 40 embedded in the lower mold portion 34 of the sand mold 30. Sintered carbide particles 42 were placed on the bottom of the cavity.
Prior to placing upper mold 32 on lower mold 34, sintered carbide particles 42 and plate 12 were preheated. Upper mold 32 was then placed over lower mold 34 and molten type 4340 low alloy steel was cast into the mold cavity.

The purpose of the invention for use in this safety equipment is to provide a 3.2
The object of the present invention is to provide a lock box with a mm (1/8 inch) thick sintered stainless steel-sintered carbide plate.

Another object and novel feature of this invention is that, in manufacturing the lockbox, the plate retains its shape as molten steel is cast around the plate to fill the wall cavity of the lockbox, and that the carbide particles remain in the plate. The goal is to maintain a uniformly dispersed state. Even though two 1/8 inch drill bits for masonry materials such as concrete and mortar were damaged, the front portion 14 of the lock box 10 shown in FIG. 1 was not penetrated by the drill bits.

A cross section of a lockbox containing a carbide-stainless steel plate is shown in FIG. When the molten alloy steel is cast around the sintered stainless steel-carbide plate, the stainless steel will melt slightly;
The carbide remained uniformly dispersed throughout the plate 12. The carbides were only slightly degraded and the brittle phase at the carbide-4340 steel interface was minimal. Stainless steel austenitic structure and
A metallic bond was created between the 4340 cast steel structures. The carbide particles in the bottom wall 20 of the box may be replaced with plates identical or similar to those shown in the side walls 22.

Example 3 A 4.0 mm (5/32 inch) thick plate was made that was resistant to penetration and impact by a drill bit. 60% by weight 2.4~3.2mm (3/32~
1/8 inch), (-8+12 mesh) cobalt sintered tungsten carbide chips and 40% by weight -
15 pieces consisting of a homogeneous blend of 100 mesh of 304L stainless steel powder, 2% by weight of the aforementioned chlorothene Nu, 1% by weight of ethyl cellulose and 1/4% by weight of a wax with the trade name Amidowax. 70 plates were made
A second groove of 15 plates was made with a similar mixture of weight percent (-8+12 meshes) of sintered carbide chips and 30 weight percent (-100 meshes) of stainless steel powder. The aforementioned Armid wax and ethyl cellulose were added to the powder mixture during mixing as compression lubricants to prevent segregation of carbide particles during mixing and mold filling. The matrix powder containing the dispersed hard carbide phase was then packed into a green powder mold made from polyurethane. The packed mold was then sealed with a suitable cover and placed in a rubber bag or balloon, which was evacuated, sealed and isostatically compressed to approximately 2450 Kg/cm ² (35,000 psi). The plate is then heated to 1149°C (2100°C) in a vacuum furnace.
〓) for 60 minutes.

These plates can then be assembled into a casting using any of the casting techniques described above or other casting techniques known in the art.

Many modifications are possible within the scope of the claims.

(Effects of the Invention) As described above, according to the present invention, it is possible to minimize the brittle phase generated when molten metal is cast around carbide, and improve wear resistance, corrosion resistance, and toughness. It is possible to provide a product that has excellent resistance to penetration by a drill bit, and it also makes it possible to manufacture a civil engineering tool or a safety device that has resistance to penetration by a drill bit.

[Brief explanation of drawings]

FIG. 1 is an isometric view of a cast lockbox according to the present invention. FIG. 2 is a sectional view taken along the line -- of the embodiment shown in FIG. FIG. 3 is a cross-sectional view of the mold cavity used to produce the FIG. 1 embodiment of the invention. FIG. 4 is a sectional view of one embodiment of an excavator tooth according to the present invention. 1... Teeth for excavator, 3... Molded body, 5... Steel,
10... Lock box, 12... Sintered plate, 14... Front part, 20... Bottom wall, 22... Side wall, 30... Sand mold, 32... Upper mold, 34... Lower mold, 36, 40... ... Nail, 42 ... Sintered carbide particles.

Claims (1)

[Claims] 1. About 1038℃ to about 1232℃ (about 1900〓 to about 2250℃)
A penetration resistant component formed by powder metallurgy with compaction and solid state diffusion bonding at temperatures within the range of 〓), with a particle size greater than 400 mesh, and containing cobalt, nickel, cobalt. a first metal matrix of stainless steel and sintered tungsten carbide particles comprising a binder selected from the group consisting of alloys of nickel and nickel, and cobalt and alloys of nickel and other metals; a second metal matrix; and a second metal matrix; A tough wear resistant element, wherein the penetration resistant component is bonded to and embedded within the second metal matrix. 2. A tough wear-resistant element as claimed in claim 1, wherein the second metal matrix substantially surrounds the penetration-resistant component. 3. A strong wear-resistant body according to claim 1, wherein the first metal matrix is made of austenitic stainless steel. 4. A strong wear-resistant body according to claim 3, wherein the second metal matrix is made of steel. 5. A tough wear-resistant body according to claim 1, wherein the sintered tungsten carbide particles have a particle size larger than 40 mesh. 6. Claim 3 provides that the first metal matrix, that is, the austenitic stainless steel matrix has a theoretical density of
A tough wear-resistant material characterized by having a density of 90% or less. 7. Claim 6 provides that the austenitic stainless steel matrix comprises:
A tough wear-resistant body characterized by having a density of 75 to 85% of the theoretical density. 8. A tough wear-resistant body according to claim 1, wherein the sintered tungsten carbide particles have an irregular shape. 9. A tough wear-resistant body according to claim 1, wherein the sintered tungsten carbide particles have a bimodal particle size distribution. 10 A compact formed by molding a mixture of sintered tungsten carbide particles and metal powder containing a binder selected from the group consisting of cobalt, nickel, alloys of cobalt and nickel, and alloys of cobalt and nickel with other metals. and sintering the compact by sintering the compact at a temperature below the melting point of the steel, most preferably within the range of 1038-1232°C (1900-2250〓) for 20-90 minutes. from about 1038°C to about 1232°C, comprising the steps of: bonding tungsten carbide particles with a first metal matrix; and casting a metallic liquid adjacent to the compact and bonding the compact with a second metal matrix. ℃ (approx. 1900〓
a penetration resistant component formed by powder metallurgy with forming and solid-state diffusion bonding at temperatures in the range from about a first metal matrix of stainless steel and sintered tungsten carbide particles comprising a binder selected from the group consisting of nickel, alloys of cobalt and nickel with each other, and alloys of cobalt and nickel with other metals; the penetration resistant component such that the tungsten carbide particles are bound to and substantially disposed within the first metal matrix; and a second metal matrix. . A method of manufacturing a tough abrasion resistant element, wherein the penetration resistant component is bonded to and embedded within the second metal matrix. 11 In the statement of claim 10,
Said method, characterized in that said metallic liquid substantially surrounds said molded body. 12 In the statement of claim 10,
The method comprises the step of selecting sintered tungsten carbide particles having a particle size greater than 40 mesh for use in the mixture.