WO2009155655A1

WO2009155655A1 - Manufacture of wear resistant composite components

Info

Publication number: WO2009155655A1
Application number: PCT/AU2009/000816
Authority: WO
Inventors: Jonathan Clowes Pemberton; Patrick Gerard Maher; Tymen Jacob Dinn Brom
Original assignee: Excalibur Steel Company Pty Ltd
Priority date: 2008-06-27
Filing date: 2009-06-26
Publication date: 2009-12-30
Also published as: ZA201100443B; AU2009262357A1; AU2009262357B2; CA2729051A1

Abstract

A method of manufacturing a wear resistant metal component having an outer shell and an inner body has a number of steps. Constituents of a wear-resistant metal alloy are placed within a steel outer shell. The shell is then heated to a point above the melting point of the alloy, and maintained at an elevated temperature for a sufficiently long time period to allow for diffusion of the alloy constituents. The component is then cooled, allowing for bonding of the alloy to the shell. In an alternative embodiment, the relative positions of the steel and the alloy are reversed.

Description

MANUFACTURE OF WEAR RESISTANT COMPOSITE COMPONENTS FIELD OF THE INVENTION

The present invention relates to the manufacture of wear resistant components including metal composites. The invention has been developed in relation to components for ground engaging tools. BACKGROUND TO THE INVENTION

Parts of earth moving machinery and related equipment are subject to significant wear during use, principally due to abrasion. In an attempt to reduce the effects of this abrasion, wear components are often mounted to earth moving buckets and similar machinery. Typical wear components include wear bars, bucket heel shrouds and ground engaging tools. The wear components are arranged to protect the parts of the machinery which would otherwise wear most rapidly. The wear components are designed to be relatively easy to replace, when worn. It is desirable to make these wear components from abrasive resistant materials, in order to extend their working life and provide an enhanced benefit. It is also necessary to use materials which can withstand substantial impact forces, and the resulting stresses within the material. In general, it has been found that materials of high resistance to abrasive wear, such as chromium white irons and tungsten carbide composites, are generally too brittle to withstand the impact forces to which the wear components are frequently subjected.

Additional difficulties have been experienced in successfully attaching components made of these materials to earth moving equipment. The materials are generally incapable of being welded, and the provision of holes and the like in the component for mechanical attachment can lead to unacceptable stress concentrations and resultant failure when in use.

As a result, most wear members are made from quenched and tempered steel, as this provides excellent strength properties along with a degree of resistance to abrasion. Attempts have been made to overcome the limitations of more highly abrasion resistant materials by bonding these materials to base metals such as steel. In one such process, white iron is cast to a block, which is then machined to a highly smooth finish. A steel substrate is similarly machined to a highly smooth finish. The steel substrate can then be vacuum brazed to the white iron block using a copper filler. This method requires very high machining tolerances, equating to a fraction of a millimetre. Additionally, the copper braze can provide a structural weak point in the wear member. In another process, white iron has been cast directly onto a steel plate in a foundry mould.

These processes both result in a white iron block having a steel plate bonded on one side. It is then possible to attach the white iron to a wearing structure by welding of the steel block to the structure. Such an operation can be problematic, as care must be taken not to 'pick up' and of the white iron in the weld, as this will compromise weld integrity.

The present invention seeks to provide a method of manufacturing a wear resistant component from a wear resistant alloy and a weldable metal which provides a bond across more than a single surface. The invention further seeks to provide a method of manufacturing such components which does not require an initial step of creating a wear resistant alloy before the component can be formed. SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a method of manufacturing a wear resistant metal component, the method having the steps of: providing a metal shell formed from a first metal, the metal shell defining an open receptacle; placing constituents of a metal alloy within the shell, one of the constituents being a primary binding constituent which has a lower melting point than that of the first metal; heating the shell and the constituents to an elevated temperature at which second metal melts; maintaining the shell at the elevated temperature for a time period sufficient for the alloy constituents to melt and diffuse within the primary binding constituent, and to bond to the shell; and cooling the shell to form a wear resistant metal component having an outer shell of the first metal and an inner body of the metal alloy, wherein the metal alloy has a greater resistance to abrasive wear than the first metal. According to a second aspect of the present invention there is provided a method of manufacturing a wear resistant metal component, the method having the steps of: providing an outer shell, the outer shell defining an open receptacle; locating a body portion within the outer shell, the body portion being spaced from internal walls of the shell and protruding from an opening or the receptacle, the body portion being formed from a first metal; placing constituents of a metal alloy within the shell, one of the constituents being a primary binding constituent which has a lower melting point than that of the first metal; heating the shell and the constituents to an elevated temperature at which second metal melts; maintaining the shell at the elevated temperature for a time period sufficient for the alloy constituents to melt and diffuse within the primary binding constituent, and to bond to the first metal; cooling the shell; and removing the shell to leave a wear resistant metal component having an outer casing of the metal alloy and an inner body of the first metal, wherein the metal alloy has a greater resistance to abrasive wear than the first metal. Advantageously, these methods allow for the direct formation of an alloy bonded the first metal, without requiring the use of a pre-cast alloy.

The step of heating the shell and constituents may be conducted at around atmospheric pressure. It is preferred that this is done in a furnace arranged to have a relatively low oxygen concentration. This may be a gas fired furnace. The presence of a low oxygen concentration, preferably below 2% by volume, reduces the propensity for oxidation of the first metal.

The first metal may be steel. It will be understood that this term includes a range of ferrous based alloys of various grades including but not limited to carbon steel, stainless steel, manganese steels, CrMo steels etc. The primary binding constituent may be iron, such as pig iron having a carbon content of about 4% by weight. The primary binding constituent may comprise at least 40% by weight of the metal alloy. Preferably, the primary binding constituent comprises 55-70% by weight of the metal alloy.

The elevated temperature must be higher than the melting temperature of the metal alloy. Nonetheless, it will be appreciated that the alloy may include relatively high melting point constituents, with these constituents having melting points higher than the elevated temperature.

Preferably, the high melting point constituents are provided in particles having a diameter less than 15mm. For some particularly high melting point constituents it is preferred for them to be provided in particles having a diameter less than 5mm.

One of the high melting point constituents may be ferrochrome.

The elevated temperature may be in the range 1200°C to 1400°C, and in a preferred embodiment of the invention is in the range 1250°C to 1300°C. The time period at which this temperature is maintained may be between 15 minutes and 120 minutes, and in the preferred embodiment of the invention is greater than 30 minutes. DESCRIPTION OF PREFERRED EMBODIMENT

It will be convenient to further describe the invention with reference to preferred embodiments of the method of the present invention. Other embodiments are possible, and consequently, the particularity of the following discussion is not to be understood as superseding the generality of the preceding description of the invention.

In a first embodiment of the invention, a wear resistant component is formed having an outer steel shell and an inner body of a wear resistant alloy such as white iron. The white iron has a single exposed face, which will be the wearing face in use. The remainder of the component has steel on the outside, and can thus be readily welded to machinery. Furthermore, the steel shell provides impact resistance to the component. Firstly, the steel shell is cast, fabricated and/or machined so as to form a receptacle into which the alloy will be formed.

Alloy constituents are placed within the receptacle. In this embodiment, the alloy includes a primary binding constituent, being pig iron (having about 4% carbon plus tramp material). It is anticipated that the primary binding constituent should constitute at least 40% by weight of the alloy. In the instant embodiment, the quantity of pig iron provided is in the range 55% to 70% by weight of the alloy. Other alloy constituents are provided in the quantities required to produce the desired composition in the final alloy.

A typical desired composition could be:

The maximum particle size of the constituents provided is dependent upon the melting temperature of each constituent. Where the melting temperature of a constituent is higher than the final alloy melting temperature, the particle size must be relatively small to allow for melting, mixing and diffusion of the constituent within the primary binding constituent. In the present embodiment, the maximum particle size of high melting point constituents is 25mm, although particle size less than 15mm is preferred as it allows for shorter hold times.

Where the melting point of a constituent is particularly high, for instance more than 100⁰C above the final alloy melting temperature, the maximum particle size of the constituents may be set at 5mm. In this embodiment ferroalloys such as ferrochrome, ferromanganese and ferromolybdenum, represent such particularly high melting point constituents.

The steel shell and alloy constituents are then placed within a furnace, and heated to an elevated temperature greater than the primary binding constituent and final alloy melting points (liquidus). In this embodiment, where the primary binding constituent's melting point is approximately 118O⁰C and final alloy melting point is about 121O⁰C, the elevated temperature is between 125O⁰C and 1300⁰C. In an alternative embodiment the desired composition could be:

In this embodiment, where the primary binding constituent's melting point is approximately 118O⁰C and final alloy melting point is about 128O⁰C, the elevated temperature is between 1300⁰C and 138O⁰C. In the range of examples where the final alloy compositions is broadly described as white iron the melting point of the final alloy composition may range typically from 1200⁰C and 1350⁰C, the elevated temperature will be between 25⁰C and 100°C above the melting point of the final alloy.

The furnace may be operated substantially at atmospheric pressure. Nonetheless, it is important for a low oxygen atmosphere (for instance, oxygen to be less than 2% by volume) to be maintained within the furnace, in order to reduce the propensity for the steel shell or the alloy constituents to oxidize. In the present embodiment, the furnace is gas-fired, with appropriate gas flow management to cause most of the available oxygen to be consumed in the combustion process. It may be advantageous to provide physical barriers of suitable configuration within the furnace to restrict the flow of gasses about the shell and to the alloy material within the shell.

The shell is maintained at the elevated temperature for a time period sufficient to permit melting and mixing of the alloy constituents. In the present embodiment this time period is between 30 minutes and 120 minutes, although it is anticipated that the use of a different alloy may reduce the time period to as little as 15 minutes.

It has been discovered that the maintenance of the shell at this temperature for this time period is sufficient for substantial homogenizing of the alloy constituents. When cooled and solidified, therefore, variations within the alloy are acceptably small. This discovery has allowed the removal of a preliminary step of alloy creation.

In addition, the maintenance of the shell at this temperature for this time period promotes the creation of a metallurgical bond between the steel and the alloy, thus increasing the strength of the wear resistant composite component.

Once the required time period has been reached, the component is cooled to allow the alloy to solidify. Further machining can then be performed on the component if required.

While the embodiment described uses a steel shell, it will be appreciated that the method may be used in conjunction with shells formed of different materials. Superalloys, titanium bases alloys, manganese steel and stainless steel are all materials to which a wear resistant alloy will bond, and thus may be suitable materials for the shell. Selection of an appropriate shell material will, of course, depend on the required properties of the component being formed. In a second embodiment of the invention, a wear resistant component is formed having an outer shell of a wear resistant alloy such as white iron, and an inner body of a steel substrate (or other suitable metal, such as a nickel or titanium based alloy). The substrate protrudes from a single face to provide a mounting portion of the component, for welding or other connection to machinery. The remainder of the component has the wear resistant alloy on the outside, and is thus resistant to wear.

The method of forming such a component is largely similar to the first embodiment. The primary difference is that the shell is formed from a sacrificial material, such as a ceramic material. The substrate is located within the shell, extending outwardly from the receptacle opening. Alloy components are then provided around the substrate, within the receptacle, and the process continues as outlined in relation to the first embodiment.

Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Claims

CLAIMS:

1. A method of manufacturing a wear resistant metal component, the method having the steps of: providing a metal shell formed from a first metal, the metal shell defining an open receptacle; placing constituents of a metal alloy within the shell, one of the constituents being a primary binding constituent which has a lower melting point than that of the first metal; heating the shell and the constituents to an elevated temperature above that at which primary binding constituent melts; maintaining the shell at the elevated temperature for a time period sufficient for the alloy constituents to diffuse within the primary binding constituent, and to bond to the shell; and cooling the shell to form a wear resistant metal component having an outer shell of the first metal and an inner body of the metal alloy, wherein the metal alloy has a greater resistance to abrasive wear than the first metal.

2. A method of manufacturing a wear resistant metal component, the method having the steps of: providing an outer shell, the outer shell defining an open receptacle; locating a body portion within the outer shell, the body portion being spaced from internal walls of the shell and protruding from an opening of the receptacle, the body portion being formed from a first metal; placing constituents of a metal alloy within the shell, one of the constituents being a primary binding constituent which has a lower melting point than that of the first metal; heating the shell and the constituents to an elevated temperature above that at which the primary binding constituent melts; maintaining the shell at the elevated temperature for a time period sufficient for the alloy constituents to diffuse within the primary binding constituent, and to bond to the first metal; cooling the shell; and removing the shell to leave a wear resistant metal component having an outer casing of the metal alloy and an inner body of the first metal, wherein the metal alloy has a greater resistance to abrasive wear than the first metal.

3. A method of manufacturing a wear resistant metal component as claimed in Claim 1 or Claim 2, wherein the step of heating the shell and constituents is conducted at about atmospheric pressure.

4. A method of manufacturing a wear resistant metal component as claimed in Claim 3, wherein the step of heating the shell and constituent is done in a furnace arranged to have a relatively low oxygen concentration.

5. A method of manufacturing a wear resistant metal component as claimed in Claim 4, wherein the oxygen concentration is below 2% by volume.

6. A method of manufacturing a wear resistant metal component as claimed in any one of Claims 3 to 5, wherein the furnace is a gas fired furnace.

7. A method of manufacturing a wear resistant metal component as claimed in any preceding claim, wherein the first metal is a ferrous based material.

8. A method of manufacturing a wear resistant metal component as claimed in any one of Claims 1 to 6, wherein the first metal is a nickel or titanium based alloy.

9. A method of manufacturing a wear resistant metal component as claimed in any preceding claim, wherein the primary binding constituent is iron.

10. A method of manufacturing a wear resistant metal component as claimed in any preceding claim, wherein the primary binding constituent comprises at least 40% by weight of the metal alloy.

11. A method of manufacturing a wear resistant metal component as claimed in Claim 10, wherein the primary binding constituent comprises 55-70% by weight of the metal alloy.

12. A method of manufacturing a wear resistant metal component as claimed in any preceding claim, wherein the alloy constituents include relatively high melting point constituents having melting points higher than the elevated temperature.

13. A method of manufacturing a wear resistant metal component as claimed in Claim 12, wherein the relatively high melting point constituents are provided in particles having a diameter less than 15mm.

14. A method of manufacturing a wear resistant metal component as claimed in Claim 13, where at least some relatively high melting point constituents are provided in particles having a diameter less than 5mm.

15. A method of manufacturing a wear resistant metal component as claimed in any preceding claim, wherein the elevated temperature is in the range 1200⁰C to 1400°C.

16. A method of manufacturing a wear resistant metal component as claimed in Claim 15, wherein the elevated temperature is in the range 125O⁰C to 1300⁰C.

17. A method of manufacturing a wear resistant metal component as claimed in any preceding claim, wherein the time period for which this temperature is maintained is greater than 15 minutes.

18. A method of manufacturing a wear resistant metal component as claimed in Claim 17, wherein the time period for which this temperature is maintained is greater than 30 minutes.

19. A method of manufacturing a wear resistant metal component as claimed in any preceding claim, wherein the time period for which this temperature is maintained is less than 120 minutes.