WO2014043746A1

WO2014043746A1 - Reducing grain size

Info

Publication number: WO2014043746A1
Application number: PCT/AU2013/001053
Authority: WO
Inventors: Rimma LAPOVOK; Juri Estrin; John Donaldson; Graham MCINTOSH; Malgorzata LEWANDOWSKA
Original assignee: Monash University
Current assignee: Monash University
Priority date: 2012-09-21
Filing date: 2013-09-16
Publication date: 2014-03-27
Anticipated expiration: 2015-03-21

Description

REDUCING GRAIN SIZE

FIELD OF THE INVENTION

The invention relates to the reduction of grain size of a body of material such as steel and other metals. BACKGROUND

Various materials such as steel and other metals are made up of microscopically-sized "grains". The atoms within each grain are arranged in an ordered crystalline structure whereas the grains meet at highly irregular boundaries.

Grain size can be influenced (e.g. by working and/or thermally treating the material) and influences the material properties. Ultra-fine grained materials (i.e. materials in substance having a maximum grain size in the range of 100 to 200nm) exhibit unique properties that are not observed in the same materials with larger grain sizes.

Accordingly it is desirable for some applications to reduce the grain size of material.

To the inventors' knowledge, ultra-fine grained materials have not yet been produced in large volume quantities for a number of various applications.

It is an object of at least a preferred form of the invention to provide for the production of ultra-fine grained materials in industrial quantities, or at least to provide alternatives for those concerned with grain size reduction.

It is not admitted that any of the information in this patent specification is common general knowledge, or that the person skilled in the art could be reasonably expected to ascertain or understand it, regard it as relevant or combine it in any way at the priority date. SUMMARY OF THE INVENTION

The inventors have recognised that grain size can be reduced in the laboratory by subjecting material to various extrusion-like processes, and that existing extrusion-like processes are not suited to production on industrial scales due to a drastic rise in frictional forces associated with scaling-up material processing equipment to suit industrial production.

Accordingly, one aspect of the invention provides a device, for reducing a grain size of a body of material, including a chamber for receiving the body and fluid such that the fluid spaces the body from side wall(s) of the chamber; a die and seal arrangement opening from the chamber and dimensioned to sealingly engage the body; a mechanism for pressurizing the fluid to drive the body through the die and seal arrangement; wherein the die and seal arrangement is configured to turn the body, preferably by about 90°, to produce a turned body of material.

The turned body of material is preferably of substantially equal cross-sectional area to the body of material, and most preferably of substantially identical cross-sectional shape to the body of material. The die and seal arrangement may open into a further pressurizable chamber.

The mechanism for pressurizing the fluid may include a piston movable with the side wall(s) of the chamber. The fluid may be any of the types known in the art. Preferably the fluid is at least predominantly hydrocarbon.

Another aspect of the invention provides a method, of reducing a grain size of a body of material, such as steel and other materials, including supplying the body to a chamber; pressurizing fluid spacing the body from side wall(s) of the chamber to drive the body through a die and seal arrangement opening from the chamber; wherein the die and seal arrangement is configured to turn the body to produce a turned body of material. The method may include pressurizing a chamber into which the die and seal arrangement opens.

Preferably the pressurizing the fluid includes moving a piston within the side wall(s) of the chamber.

The turned body of material may be supplied to the chamber as the body of material. Preferably the method includes 8 to 16 passes of the body through the die and seal arrangement.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a schematic cross-section view of an exemplary device for reducing grain size. DETAILED DESCRIPTION OF THE EMBODIMENTS

Figure 1 illustrates a device 1 for reducing the grain size of a billet of material A. The device 1 includes structure in the form of an upright cylindrical wall 2. A pressurizable chamber 3 is formed within the cylindrical wall 2. The chamber 3 opens at its lower end through a die and seal arrangement 4 into a further pressurizable chamber 5. The upper periphery of the chamber 3 is closed by a downwardly extending cylindrical ram closely fitting within the interior of the wall 2 and sealing against the wall with the aid of a seal 7 at its free end which is downwardly directed towards the chamber 3.

The device 1 is configured to process billets of material having a constant horizontal cross-section along their vertical length such as simple upright cylinders. The die and seal arrangement 4 is dimensioned relative to the internal diameter of the wall 2 so that the die and seal arrangement sealingly receives the billet A whilst the billet A is spaced from the walls 2.

The die and seal arrangement 4 sealingly engages about the periphery of the billet A. The die and seal arrangement could be a simple integral component, or a more complex arrangement. By way of example separate die elements (i.e. elements for working the billet A) and separate sealing elements may be provided.

In operation, the chamber 3 is filled with an incompressible fluid which is most preferably a hydrocarbon based lubricant. The ram 6 constitutes a piston within the wall 2. The ram 6 includes a drive arrangement of any suitable type known in the art, such as a hydraulic system independent of the chamber 3, for downwardly driving the ram 6 (and seal 7 carried thereby). The ram 6, seal 7 and ram driving mechanism (not shown) thus together constitute a mechanism for pressurizing the fluid within the chamber 3.

When the fluid in the chamber 3 is adequately pressurized it serves to drive the billet A in a first direction (downwardly in the illustrated example) and through the die and seal arrangement 4. The annular space separating the billet A from the wall 2 carries a hydro-dynamic layer of lubricant and prevents the billet A frictionally engaging the interior of the wall 2.

The die and seal arrangement 4 serves to turn the material to move in a second direction (horizontally in the illustrated example) non-parallel to the first direction. As the material is forced to turn through the die it undergoes substantial shearing

corresponding to about 115% plastic strain. This working of the material leads to a reduction in the grain size.

In preferred forms of the invention, the die and seal arrangement 4 is configured to produce a turned body of material B having a substantially identical cross-sectional shape and area to the input body of material A. The material is subjected to shear deformation by extrusion through two intersecting "channels" of equal cross-section, and the same dimensions are maintained after extrusion. Following this approach, deformation is localised in the small area around the plane at which the vertical path of the billet A meets the horizontal path of the billet B. As a result, a large uniform plastic strain is imposed on the material without reduction of the initial cross-section. The material is subjected to a simple shear under relatively low pressure compared with existing extrusion processes.

Since the cross-section of the billet is unchanged, the turned body of material B can be returned to the chamber 3 for multiple passes through the device 1. This repeated pressing leads to significant grain refinement and enhanced mechanical properties. Typically 8 to 16 passes through the device 1 (corresponding to a strain of about 900% to 2000%) will produce a stable, ultra-fine grained structure.

This example of the invention 1 includes the chamber 5 on the downstream side of the die and seal arrangement 4 to receive the turned body of material B. The device 1 further includes another mechanism for pressurizing to pressurize the downstream chamber 5 to a pressure below that of the pressure in the chamber 3. The differential pressure between the chambers 3, 5 pushes the billet A through the die and seal arrangement 4. This dual chamber approach is beneficial for the extrusion of low ductility materials as their possible fracture is suppressed by the pressure in the downstream hydrostatic chamber 5.

According to at least preferred forms of the invention, the micro-structure of the produced material has been found to be more homogenous than material produced by other methods.

Various preferred variants of the invention can be applied to produce ultra-fine grain structures, such as large diameter billet greater than about 2 inches in diameter, in a broad range of metals and alloys, such as steel, titanium and titanium alloys, nickel- based alloys, tungsten, aluminium and aluminium alloys, magnesium and magnesium alloys, and copper and copper alloys.

Claims

1. A device, for reducing a grain size of a body of material, including a chamber for receiving the body and fluid such that the fluid spaces the body from side wall(s) of the chamber; a die and seal arrangement opening from the chamber and dimensioned to sealingly engage the body; a mechanism for pressurizing the fluid to drive the body through the die and seal arrangement; wherein the die and seal arrangement is configured to turn the body to produce a turned body of material.

2. The device of claim 1 wherein the die and seal arrangement is configured to turn the body about 90°.

3. The device of claim 1 or 2 wherein the turned body of material is of substantially equal cross-sectional area to the body of material.

4. The device of claim 1 , 2 or 3 wherein the turned body is of material of substantially identical cross-sectional shape to the body of material.

5. The device of any one of claims 1 to 4 wherein the die and seal arrangement opens into a further pressurizable chamber.

6. The device of any one of claims 1 to 5 wherein the mechanism for pressurizing the fluid includes a piston movable with the side wall(s) of the chamber.

7. The device of any one claims 1 to 6 wherein the fluid is at least predominantly hydrocarbon.

8. A method, of reducing a grain size of a body of material, including supplying the body to a chamber; pressurizing fluid spacing the body from side wall(s) of the chamber to drive the body through a die and seal arrangement opening from the chamber; wherein the die and seal arrangement is configured to turn the body to produce a turned body of material.

9. The method of claim 1 wherein the die and seal arrangement is configured to turn the body about 90°.

10. The method of claim 8 or 9 wherein the turned body of material is of substantially equal cross-sectional area to the body of material.

1 1. The method of claim 8, 9 or 10 wherein the turned body is of material of substantially identical cross-sectional shape to the body of material.

12. The method of any one of claims 8 to 11 further including pressurizing a chamber into which the die and seal arrangement opens.

13. The method of any one of claims 8 to 12 wherein the pressurizing the fluid includes moving a piston within the side wall(s) of the chamber.

14. The method of any one claims 8 to 13 wherein the fluid is at least predominantly hydrocarbon.

15. The method of any one of claims 8 to 14 further including supplying the turned body of material to the chamber as the body of material.

16. The method of claim 15 including 8 to 16 passes of the body through the die and seal arrangement.