AU707637B2 - Improved flux-cored welding wire - Google Patents

Description

2 TITLE: IMPROVED FLUX-CORED WELDING WIRE The present invention relates to a welding wire and in particular to a cored welding wire. The present invention also relates to a welding method.

Flux-cored welding wires comprise a core of flux enclosed within a metal sheath. Flux-cored welding wires are generally produced by taking a strip of metal and rolling it into a shape, such as a shape, that permits a dosage of welding flux to be added. Further rolling of the strip closes the io strip into a cylindrical shape that acts to contain the flux and to form the welding wire. Flux-cored welding wires are generally produced in a continuous manner by passing a strip of metal from a coil through a series of rollers.

The core of the flux-cored welding wires, as the name suggests, contains flux material for the weld. Alloying elements and arc stabilisers can also be added to the core and this allows great flexibility in the composition of wire and the weld metal produced therefrom. The fluxing and alloying ingredients usually only form a portion of the core material, 20 with the balance being iron powder.

fee One of the major classes of flux-cored welding wires is the so-called rutile wires. This term, which is widely used in the industry, relates to flux cored welding wires that include the mineral rutile as a major component in the core. In general, the rutile constitutes between 40% to 60%, by weight, o ~of the core material, although it is possible that the rutile coo• content may vary outside this range. The rutile acts as a slag forming agent and also assists in providing a smoother running arc.

Commercially available rutile wires can also include microalloying amounts of Ti and B to improve weld mechanical properties, particularly low temperature impact. The amount of B added to the wire, generally by adding B or a B-containing component to the core, is usually controlled to produce a level of B of up to 0.01% in the weld metal. The amount of Ti in the core is usually controlled to produce Ti levels of up to 0.10% in the weld metal.

GN:AM:07:16539.C 19 April 1996 Typical rutile wires contain the following ingredients in the core: a a a The present invention provides an improved flux cored welding wire.

In a first aspect, the present invention provides a flux cored welding wire having a metal sheath and a core, characterised in that the core includes particles of an alumina-containing material said particles being predominantly sized below 1 micron.

The particles of alumina containing material preferably comprise particles of substantially pure alumina. For convenience, the invention will hereinafter be described with GWN:HHF:#16539.RS1 23 December 1998 4reference to particles of alumina. However, unless the context indicates otherwise, this term should be taken to include both particles of substantially pure alumina and particles of alumina-containing material.

The particles of alumina preferably have a small particle size. The particles of alumina are preferably predominantly sized below 1 micron, more preferably sized within the range of 0.2 to 0.4 microns.

Alternatively, larger sized particles of alumina that comprise an aggregate of smaller alumina particulates may be used. The alumina particulates that are found in the aggregated particles are preferably predominantly sized below 1 micron, more preferably sized within the range of 0.2 to 0.4 microns.

is The particles of alumina are preferably added to the core in an amount that comprises 0.5 to 3.0 wt% of the core material, with an amount of about 1% by weight being especially suitable.

For example, the inventors have found that fine grained 20 particles of alumina supplied by Norton Company and produced by sol-gel technology are particularly suitable for use in the present invention. These particles are described in Australian Patent Application No. 37680/85, filed in the name of Norton Company on i5 January 1985. The entire contents of this patent application are incorporated herein by cross-reference. The alumina particles supplied by Norton Company are sintered particles of substantially pure alpha-alumina and have a grain oo size of less than 1 micrometre. The particles are produced by I. seeding an alumina gel, drying and sintering.

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30 The flux cored welding wire of the present invention is preferably a rutile wire. The rutile wire may be microalloyed with other components such as Ti and B. Manganese (Mn) is another alloying element that is known to have a considerable effect on the weld mechanical properties of rutile welding wires and this element may also be present in the flux-cored welding wires of the present invention. The amount of Mn in the wire may be such that weld metal from the wire has an Mn content of 1.0 to 2.0 wt%.

GN:AM:07:16539.C 19 April 1996 I

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Flux cored welding wires in accordance with the present invention may be used in all known flux-cored arc welding techniques known to be suitable for welding with cored wires.

They can be used with Ar-CO 2 shielding and also CO 2 shielding.

It has been found that flux cored welding wires of the present invention produce welds having improved mechanical properties, especially low temperature impact, when compared with welds made from wires that do not incorporate particles of small particle size alumina. Although the applicants do not wish to be bound by theory, it is postulated that improvements in the mechanical properties of the weld metal arise from the increased formation of fine acicular ferrite in the as-welded microstructure. It is further postulated that the presence of the particles of alumina in the core of the wire assists in nucleating inclusions that are made up of titanium oxides or crystalline compounds containing titanium oxides. These Ti-containing inclusions then promote formation of the acicular ferrite microstructure.

According to another aspect, the present invention 20 provides a flux cored welding wire that includes one or more components that promote formation of Ti-containing inclusions in weld metal formed from welding with the wire, a flux cored welding wire that includes one or more components that promote formation of Ti-containing inclusions in weld metal formed from welding with the wire, said one or more components having a similar crystal structure to MnO.TiO 2 inclusions.

In this aspect, the welding wire is preferably a rutile wire that contains Mn and is microalloyed with at least Ti and B. The one or more components that promote formation of Ticontaining inclusions in the weld metal may be fine grained particles of alumina, as discussed with reference to the first aspect of the present invention. Alternatively, other fine grained particulate material that has a similar crystal structure to MnO.TiO 2 inclusions, may be used as the one or more components that promote the formation of Ti-containing inclusions in the weld metal. Using fine grained particulate material having a similar crystal structure to the crystal TNB:JL:#16539.rs2 7 May 1999 structure of the Ti-containing inclusions should provide nuclation sites for the formation of the Ti-containing inclusions during the welding process. The Ti-containing inclusions subsequently promote the formation of acicular ferrite in the microstructure of the weld metal, which provides a weld metal having good mechanical properties.

In a further aspect, the present invention provides a method for welding including feeding a welding wire to a hot zone to form weld metal, characterised in that the weld metal contains Ti-containing inclusions having a method for welding including feeding a welding wire to a hot zone to form weld metal, characterised in that the weld metal contains Ticontaining inclusions having a crystal structure similar to MnO.TiO 2 inclusions therein.

The method of the invention may use a flux cored welding wire as described herein.

Any known welding technique may be used in the method of the present invention. Flux cored arc welding is especially suitable. Shielding is preferably used, with Ar-CO 2 shielding 20 and CO 2 shielding being but two examples thereof.

9 e The invention will now be further described with go reference to the following Example.

EXAMPLE

S: A series of microalloyed rutile wires were fabricated, with the flux composition based upon all-positional microalloyed rutile wires manufactured by the applicant.

These wires include Mn, Ti and B in the core. The core components were modified in accordance with the description :given in Table i. The wires were then tested by arc welding with either an argon-carbon dioxide shield or a carbon dioxide shield. The weld metal was tested for tensile strength, elongation and Charpy Vee-notch impact strength at low temperature. The weld metal was also analysed for composition. The results are shown in Table 1.

The welding wires designated by formulation numbers 785, 786 and 787 and 7115, 7117 and 7118 are in accordance with the most preferred form of the invention ("sol gel alumina" TNB:JL:#16539.rs2 7 May 1999 I ay1 6A being used to designate the alumina sourced from Norton Company). These wires all provided suitable welding operation and tensile properties. Significant increases in Charpy veenotch impact strength were also recorded for wire formulation Nos. 785, 7115, 7117, and 7118.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically disclosed. It is to be understood that the invention is considered to encompass all such variations and modifications that are all within its spirit and scope.

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o o .e TNB:JL:#16539.rs2 7 May 1999 lv TABLE 1 MICROALLOYED RUTILE-FLUX WIRES (RP3 TYPE) Formula Comments on Formulation Weld Metal Properties Weld Composition Number T.S.(MPa) CVN at C Mn Ti Al B

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Argon Carbon Dioxide Shielded 767 Satisfactory operation 624 22 40 0.04 1.38 0.04 .012 0.007 778 767 1.5% bauxite added 641 26 54 0.04 1.40 0.05 .012 0.006 785 778 1.5% sol gel alumina 586 31 97 0.03 1.45 0.03 .009 0.004 786 785 1% sol gel alumina 613 27 34 0.05 1.41 0.03 .009 0.008 787 785 2% sol gel alumina 585 29 40 0.05 1.39 0.04 .008 0.009 788 785 1% Al/Mg added 675 19 76 0.05 1.60 0.06 .022 0.009 789 785 but reduced Mn 616 28 98 0.05 1.31 0.04 .007 0.007 790 789 but fill reduced to 14.5% (same 606 28 114 0.04 1.48 0.03 .004 0.008 alloying Carbon Dioxide Shielded 7110 Satisfactory operation 615 26 33 0.04 1.25 0.05 .012 0.006 7115 7110 1.5% sol gel alumina 612 24 62 0.04 1.26 0.04 .011 0.009 7117 7110 1% sol gel alumina 622 25 82 0.04 1.19 0.04 .013 0.007 7118 7 110 0.5% sol gel alumina 619 26 62 0.04 1.27 0.05 .013 0.008 8 THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A flux cored welding wire having a metal sheath and a core, characterised in that the core includes particles of an alumina-containing material, said particles being predominantly sized below 1 micron.

2. A welding wire as claimed in claim 1 wherein the particles of alumina containing material comprise particles of alumina.

3. A welding wire as claimed in claim 1 or claim 2 wherein the particles are sized predominantly within the range of 0.2 to 0.4 rim.

4. A welding wire as claimed in claim 2 wherein the 'o 1 particles of alumina comprise aggregates of smaller alumina 15 particulates 5. A welding wire as claimed in claim 4 wherein the o alumina particulates are sized predominantly less than 1 rim.

6. A welding wire as claimed in any one of the preceding claims wherein the particles are present in an 20 amount of 0.5 to 3.0 wt% of the core material.

7. A welding wire as claimed in claim 6 wherein the particles are present in an amount of about 1% of the core material.

8. A welding wire as claimed in any one of the 25 preceding claims wherein the core material further includes the following components: Rutile 40 to 60 wt% Fused mixed oxide (containing boron) 5 to 25 wt% Potassium titanate 0 to 10 wt% Sodium aluminium floride 0 to 4 wt% Feldspar 0 to 5 wt% Manganese metal 10 to 20 wt% Ferrosilicon 5 to 15 wt% Aluminium Magnesium 0 to 5 wt% Aluminium Metal 0 to 3 wt% GWN:HHF:#16539.RS1 23 December 1998

Claims (5)

1. 9. A welding wire as claimed in claim 8 wherein manganese is present in an amount such that weld metal from the wire has a manganese content of 1.0 to 2.0 wt%. A flux cored welding wire that includes one or more components that promote formation of Ti-containing inclusions in weld metal formed from welding with the wire, said one or more components having a similar crystal structure to MnO.TiO 2 inclusions.
2. 11. A welding wire as claimed in claim 10 wherein the welding wire comprises a rutile wire that contains Mn and is microalloyed with Ti and B.
3. 12. A welding wire as claimed in claim 10 or 11 wherein said one or more components that promote formation of Ti- containing inclusions include fine grained particulate material having a similar crystal structure to said Ti- containing inclusions. 20 13. A method for welding including feeding a welding wire to a hot zone to form weld metal, characterised in that the weld metal contains Ti-containing inclusions having a crystal structure similar to MnO.TiO 2 inclusions therein.
4. 14. A welding wire substantially as hereinbefore described with reference to the example. a. DATED: 7 May 1999 CARTER SMITH BEADLE Patent Attorneys for the Applicants: ~WELDING INDUSTRIES LIMITED and COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANISATION
5. 16539.rs2 7 May 1999 ABSTRACT A flux-cored welding wire includes fine particles of alumina in the core. The alumina is preferably sized less than 1 Aum and may be present in an amount of 0. 5 to 3 wt- of the core material. The welding wire is preferably a rutile wire. .0 64 S. 5* 5* S GN:AM:07: 16539.C 19 April 1996