DK162881B - PROCEDURE FOR MANUFACTURING A TIGHT, Wear-Resistant Formula - Google Patents

Description

DK 162881 B

BACKGROUND OF THE INVENTION The present invention relates to a process for producing a tough, wear-resistant mold body with a sintered, pierced-proof member containing cemented carbide particles bonded to a stainless steel matrix and substantially disposed within said matrix. the pierced secured portion is at least partially embedded in an additional matrix of cast steel and bonded thereto, by compressing a mixture of the cemented carbide particles and a stainless steel sinter steel powder into a press blank, sintering 10 of the press blank and casting a steel melt around the press blank.

In particular, these moldings can be used as abrasion-resistant castings for excavators and for piercing-proof safety devices such as safes.

To extend the life of e.g. teeth for engraving-15 machines and similar moldings, which are subject to severe abrasion, abrasion, temperature variations, vibrations and corrosion, it has already been proposed to embed sintered cemented carbide-tungsten carbide particles into a cast steel matrix and thereby cast suitable 20 molds (U.S. Patents Nos. 4,024,902 and 4,140,170).

However, these known casting methods present problems when designing relatively thin cross-section moldings or when applying 25 carbide particles to the surface of a vertically extending abutment on as well as a horizontal region of a molding, as the direct contact between the cast steel melt and the cemented carbide particles lead to a surface solution of the cemented carbide particles and thus also to a reduction in their particle size.

In order to reduce the dissolution of the carbide particles during casting and the resulting brittle eta phase (M6C or M3C carbide containing tungsten and iron) produced at the carbide-steel interface, the 35 carbide particles used must typically have a size of at least 3 mm. An increase in the size of the carbide particles decreases

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the interface between carbide and steel occurs. However, the carbides in thin cross-sections of a molding having a thickness only slightly larger than the carbide size may cooperate with the mold to rapidly and vigorously cool the liquid metal flowing between the carbides, thereby effecting an incomplete filling. these thin sections.

It is also impossible to hold large cemented carbide particles evenly distributed along a vertical section of a casting without filling this section with carbide from the bottom to hold the carbides in place during casting.

This can lead to the aforementioned voids and / or incomplete filling due to excessive cooling of the melt.

U.S. Patent No. 4,101,318 seeks to avoid the aforementioned casting problems by grinding a heat treatable, low alloy steel powder with a tungsten carbide powder or a carbide powder with a solid solution of tungsten molybdenum and then pressing and sintering a blank to substantially full density. resulting mixture. Low alloy steel is then molded around the sintered steel carbide material to form a finished component. However, this patent limits the steel powders used to low chromium content steels.

DE Publication No. 2,630,932 discloses abrasion-resistant composite materials and 25 moldings thereof, as well as a process for their preparation, in which a mixture of cemented carbide particles and a stainless steel sintering powder is compressed and the pressing material is sintered. The weight ratio of cemented carbide to sintered steel matrix is hereby 1: 1 to 1: 0.1. The cemented carbide is used according to Example 1 of this printing in the form of balls with a diameter of 10 mm. The cemented carbide and sinter steel mixture is compressed by this known method isostatically at a pressure of from 80 x 106 to 400 x 106 Pa at room temperature and sintered at a temperature of 1000 to 1400 ° C in an inert atmosphere. Thereby, no casting casting of it according to this embodiment is anticipated for the 3

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known method produced sinter body.

In a further embodiment of the method known from DE Publication No. 2,630,932, the cemented carbide particles are not mixed with sintered steel powder and compressed but directly embedded in cast steel, which is associated with the above described disadvantage of dissolving the cemented carbide particles into the cast steel melt and formation of brittle eta phase.

DE Publication No. 2,754,999, Example 10 4, also discloses a process for producing tough, wear-resistant moldings in which sintered hard-metal particles are molded with a stainless steel melt. The sintered cemented carbide particles used herein are, according to Example 1 of this publication, made by powder metallurgy. In addition to tungsten carbide, chromium carbide and molybdenum carbide, the powder mixture for the preparation of the hard-metal particles contains 0.621 wt.% Nickel and 4.354 wt.% Iron as a binder. The powder mixture is pre-compressed agglomerated into grains ranging in size from 250 to 1000 μιη, compressed under a pressure of 146.7 x 106 Pa, sintered at 1050 to 1150 ° C and finally sintered for 1.5 hours at 1258 ° C. The sinter cemented metal thus prepared consists of tungsten monocarbide grains which are uniformly dispersed in a bead-like matrix (cf. pages 27, 25 lines 11-13).

Although, in DE Publication No. 2,754,999 (page 12, lines 1-5), reference is made to the avoidance of the formation of undesirable η carbides, according to Example 4, the cemented carbide made according to Example 1 is directly cast over with a cast steel melt. . However, as mentioned, the direct contact between the cast steel melt and the cemented carbide leads to superficial dissolution of the latter and thus to the formation of brittle eta phase at the interface between cemented carbide and cast steel.

The invention has for its object to provide a method for producing tough, abrasion-resistant moldings of the kind mentioned at the outset, wherein the risk 4

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for the formation of brittle eta phases is minimized and with which it manages to produce particularly abrasion-resistant, corrosion-resistant and pierced-proof moldings with good toughness.

This object is achieved according to the invention by mixing 30 to 80% by weight tungsten carbide and cobalt and / or nickel tungsten carbide particles with a particle size between 1.68 and 3.3 mm with 20 to 70% by weight powdered stainless steel and mixing the powder mixture -10 is compressed at a pressure greater than 68.9 x 10 6 Pa and sintered at a temperature between 1038 and 1232 ° C for 20 to 90 minutes.

By embedding the cemented carbide particles into the sinter steel matrix, it is achieved that the cast steel melt comes into direct contact with the sinter steel surface only, but not with the surface of the cemented carbide particles, so that the risk of brittle eta phase formation is minimized that can hardly be avoided. In addition, according to the invention, the original grain size of the cemented carbide particles is also maintained in the cast-molded finished product so that it is not necessary, as is the case in the prior art, to reduce the specific surface of the cemented carbide phase by using as large balls as possible. . Instead, according to the invention, small particle sizes can be used, which in turn allows cheap carbide waste to be added for meaningful and particularly advantageous recycling.

In the process of the invention, preferably, austenitic stainless steel sinter steel matrix is used and preferably a low alloy or austenitic stainless steel cast steel matrix, the cast steel matrix preferably completely enclosing the composite of cemented carbide particles and sinter steel matrix.

The cemented carbide particles used consist of tungsten carbide and a binder selected from the group 35 of cobalt, nickel, their alloys with each other and their alloys with other metals.

In addition, it has been found that the sinter steel matrix, for 5

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insofar as it consists of austenitic stainless steel, it may be less than 90% dense; can have a density of 75 to 85%.

The invention will now be described in more detail with reference to the drawing, in which: FIG. 1 is an isometric view of a molded security or money box according to the present invention; FIG. 2 is a cross-section through the embodiment of FIG. 1 on the line II-II of FIG. 1, 10 FIG. 3 is a cross-section through a mold cavity used to make the embodiment of FIG. 1 of the present invention, and FIG. 4 is a cross-section through an embodiment of an excavator tooth according to the present invention.

According to the present invention, 30 to 80 weight percent carbide particles are mixed with 70 to 20 weight percent steel powder to produce a substantially uniform mixture of carbide and steel. The carbide particles used are preferably cemented tungsten carbides having a particle size 20 between 1.68 and 3.3 mm.

It has been found that sintered composite bodies containing carbide particles within this size range are resistant to penetration by drilling.

Further improvements in abrasion resistance and piercing security can be achieved using carbide particles with a bimodal size distribution. In this embodiment of the invention, the size of the smaller carbide particles is selected to allow them to fit into the gaps formed between the larger carbide particles, thereby further increasing the wear resistance.

The cemented carbide may have a metallic binder selected from cobalt, nickel or cobalt-nickel alloys. In addition to tungsten carbide, the cemented carbide may contain minor amounts of other carbides such as tantalum carbide, niobium carbide, hafnium carbide, zirconium carbide, and vanilla.

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6 dium carbide.

Crushed and sieved wastes of cemented carbide have been found to be suitable for use in this process.

The preferred stainless steels according to the invention are the 5 austenitic stainless steels because of their resistance to abrasion and impact from room temperature down to cryogenic temperatures. Of the austenitic stainless steels, AISI types 301, 302, 304 and 304L are preferred because of their high deformation hardening rates. In addition to the carbide and steel powders in the mixture, organic binders are also added to prevent segregation and produce uniform distribution of the carbides and maintain a uniform mixture after mixing.

After mixing, the mixture of powders 15 is compressed by a one-axis pressing in a die or isostatic pressing in a preform, preferably at approximately 241.3 x 10 6 Pa but not less than 68.9 x 106 Pa.

After compression, the compressed blank is sintered at a temperature preferably below the melting point of steel 20, and most preferably in the range of 1040 ° C to 1230 ° C for 20 to 90 minutes, thereby avoiding the formation of eta phases in the interface between cemented carbide and steel and yet providing a strong metallurgical bond between the cemented carbide and the steel.

In most cases, the bond between the steel and the cemented carbide takes the form of an alloy layer at the interface between cemented carbide and steel. This layer consists mainly of cobalt and iron and is typically less than 50 μπι thick. This bonding is important to ensure the retention of the coarse cemented carbide particles within the steel matrix.

It has been found that the sintered blanks using austenitic stainless steel powder generally exhibit interconnected microporosity and have a steel binder density of less than 90 percent of the theoretical and more typically of 75 to 85 percent of the theory. For 7

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To increase the density of the blanks, hot, iso-static pressing, permeation or increased compression pressure can be used. These processes will also result in improved carbide retention in the subject. The permeation agent 5 used can be selected from copper-based or silver-based brazing materials which moisten both stainless steel and carbide.

The sintered blank is then placed within a mold and liquid metal is molded around it to produce a molding blank. The molding method used may be any of those known to those skilled in the art. However, it is preferred to use the casting method disclosed in US Patent No. 4,024,902. Preheating the workpiece can be used prior to casting the liquid metal into the mold.

The liquid metal may be an iron alloy or a non-iron alloy and is preferably steel. The type of steel used does not have to be identical to the one used in the workpiece.

When impact, strength and corrosion properties are important, the cast steel is preferably an austenitic stainless steel. Low alloy steels and manganese steels can also be used.

The cast steel forms a metallurgical bond with the steel binder in the compressed blank with a minimal amount of reaction with the cemented carbides. The formation of eta phase is thereby reduced as the surface areas of the carbides which come into contact with the liquid steel have been reduced.

The use of compressed carbide and steel blanks also allows the carbides to be bonded in various concentrations, positions and orientations both on the surface and below the surface of moldings.

The process and products of the present invention will become more apparent upon review of the following detailed examples.

Example # 1.

35 A number of excavator teeth 1 (see Fig. 4) were prepared with compressed blanks 3. A uniformly mixed 8

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Mixture composed of 60 parts by weight 3 to 4.5 mm cobalt cemented tungsten carbide granulate and 40 parts by weight minus 100 mesh atomized, austenitic stainless steel powder (manufactured by Hoganås Corporation of New Jersey) was prepared by dry mix with 1.25 parts by weight paraffin and 0.75 parts by weight of ethyl cellulose. The mixture was manually compressed into an elastomeric polyurethane mold cavity of the desired shape for the workpiece (50 mm long, 19 mm wide and 6 mm thick), dimensioned to allow cold, isostatic compression plus one 10 percent sintering shrinkage. After cold isostatic pressing at 241 x 10 6 Pa, the compressed blank was removed from the mold and vacuum sintered at 1150 ° C for 60 minutes. The sintered items were then placed in an eight recess sand mold designed to the required shape of the excavator tooth. The ingredients for preparing an AISI 4340 low alloy steel were melted in an induction furnace, the blanks preheated and the steel cast into the mold at 1680 to 1720 ° C to form the one shown in FIG. 4, in which the 4340 steel is bonded to two angularly connected faces of the workpiece 3.

A metallographic study showed that the stainless steel matrix contained an austenitic structure with some intergranular chromium carbides referred to as "sensitization" which is typical of slow-cooled austenitic stainless steels after sintering. Sensitization can be eliminated by subsequent solution heat treatment. The interface between the cemented carbide and the steel matrix contained a continuous bonding zone approximately 15 μια thick of an alloy composed mainly of iron and cobalt. The distributed cemented carbide particles appeared free of heat cracking with a minimal extent of dissolution, melting or degradation of the distributed carbide phase at or near the interface boundaries.

There was some melting or mixing of the stainless steel and some decomposition of carbides where the liquid metal touched the carbides at the surface of the compressed workpiece. However, beneath the surface of the blank, the carbide interfaces were generally sharp except for the aforementioned diffraction.

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iron cobalt alloy fusion zone. No potentially harmful concentrations of eta phases were observed.

Samples were repeatedly (five and six times) estimated with a ball pen hammer at room temperature and at the liquid nitrogen temperature (-196 ° C) and were found to have good impact resistance with little signs of brittle fracture. However, it should be noted that with a larger weight percent of cemented carbides in the composition, the impact resistance could be slightly reduced, but the resistance to abrasion and drill penetration would be increased.

Microhardness measurements of a cut of the cast excavator tooth showed average hardness (impression) of approx.

75 Rockwell C, 29 Rockwell C and 38 Rockwell C within a cross-line in the cemented carbide, the stainless steel 304L steel and the 4340 steel (3.1 mm from the stainless steel interface surfaces).

Example # 2.

An embodiment of FIG. 1, drill resistance 20 skilled safety or money box by casting low-alloy 4340 steel around sintered stainless 304L steel carbide plates (100 mm long x 63 mm wide x 3 to 4.5 mm thick) and plates (81 mm long x 63 mm wide x 3 to 4.5 mm thick). The location of one of the sintered plates 12 is shown in dotted line. The plates were made by uniform mixing of a mixture of 50.0 parts by weight -8 + 12 meshes of cobalt cemented tungsten carbide, 50.0 parts by weight 100 meshes of AISI 304L stainless steel powder and 10 parts by weight binders (Chloruthen Nu and 0.75 ethyl cellulose).

The stainless steel matrix powder containing that of shared hard carbide phase was packed in a polyurethane mold shaped to the plate dimensions. The mold was then sealed, placed in a rubber bag, which was evacuated and sealed and then isostatically pressed at 241 x 106 Pa. The 35 compressed plate, after being removed from the rubber mummy bag and mold, sintered in a vacuum oven at 1150 ° C for 60 minutes.

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minutes.

The drill-resistant plates were then placed in the front, back and sides of the box hole in a mold.

FIG. 3 shows a section through a sand mold 30 with a cavity 5 formed between an upper part 32 and a lower part 34. Sintered plates 12 are shown held in place in the sidewall cavities of nails 36 and 40 inserted into the lower part 34 of the mold 30 Cemented carbide particles 42 have been deposited on the bottom surface of the cavity. Prior to placing the upper part 32 on the lower part 34, the cemented particles 42 and the plates 12 were preheated. The upper part 32 was then placed in the lower part 34 and liquid low alloy 4240 steel was cast into the mold cavity.

The purpose of the invention in this security application is to provide the cash box with 3 mm thick sintered stainless steel and cemented carbide sheets encased in steel for protection against boron penetration.

It is a further object and novel feature of this invention that in the manufacture of the money box, the plate (s) will retain their shape and the carbide particles will remain uniformly distributed within the plates when casting liquid steel around them which fills the remaining box. -væghulrum. After the destruction of two 3 mm masonry drills, the front section 14 of the 1 does not penetrate the safety box.

FIG. 2 shows a section through the money box containing plates of carbide and stainless steel. A slight melting of the stainless steel occurred when the liquid steel alloy was cast around the sintered stainless steel plate and 30 carbide and the carbides remained uniformly distributed in the plate 12.

There was very little carbide decomposition and a minimum of brittle phases at the interface between carbide and 4340 steels.

A metallurgical bond was formed between the austenitic structure of the stainless steel and the molded 4340 steel structure. The carbide particles 42 in the bottom wall 20 of the box can be replaced by plates which are identical or similar to 11

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those shown in the side walls 22.

Example # 3.

4 mm thick, drill and impact resistant sheets were made. Fifteen plates consisted of a uniformly blended mixture of 60 parts by weight 2.4 to 3 mm cobalt cemented tungsten carbide particles, 40 parts by weight minus 100 meshes of stainless 304L steel powder, 2 parts by weight of chloroethene Nu, 1 part by weight of ethyl cellulose and 1/4 part by weight of armidox wax. Another group 10 of 15 sheets was made with 70 parts by weight of 2.4 to 3 mm cemented carbide particles and 30 parts by weight (-100 mesh) of stainless 304L steel powder mixed in a similar manner. The armido wax and ethyl cellulose were added to the powder mixture during mixing as a pressing lubricant to prevent segregation of the carbide particles during mixing of the mold filling. Next, the matrix powder containing the distributed hard carbide phase was packaged in a preform made of polyurethane. The packaged mold with a suitably fitted lid was then sealed and placed in a rubber bag or balloon which was evacuated, sealed and isostatically pressed at approx.

241 x 10® Pa. The plates were then sintered in a vacuum oven at 1150 ° C for 60 minutes.

These plates can now be incorporated into a molding using the previously described molding method or any known molding method.

Claims (1)

DK 162881 B PATENT REQUIREMENT. A method of producing a tough, abrasion-resistant mold body with a sintered, pierced-proof portion containing cemented carbide particles bonded to a stainless steel matrix 5 and substantially disposed within this matrix, the pierced-proof portion being at least partially embedded in a further matrix of cast steel and bonded thereto, by compressing a mixture of the hard metal particles and a stainless steel sintering steel powder 10 into a press blank, sintering the press blank and casting a steel melt about the blank, characterized in that 30 to 80 tungsten carbide and cobalt and / or nickel tungsten carbide particles as a binder having a particle size between 1.68 and 3.3 mm are mixed with 20 to 70% by weight of powdered stainless steel and the powder mixture is compressed at a pressure of more than 68.9 x 106 Pa and sintered at a temperature between 1038 and 1232 ° C for 20 to 90 minutes.