AU655212B2 - Metal cored electrode - Google Patents

Description

t I.

655212

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S): Alloy Rods Global, Inc.

ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

INVENTION TITLE: Metal cored electrode *I The following statement is a full description of this invention, including the best method of performing it known to me/us:- *hi la BACKGROUND OF THE INVENTION Statement of Related Application This invention is a modification of the invention described and claimed in AU-B-62425/90.

Field of the Invention This invention relates to a metal cored electrode for CO 2 gas shielded metal arc welding, and more particularly to a cesium-containing seamed metal cored electrode for reverse polarity welding.

Description of the Prior Art Relatively expensive inert gases such as argon and helium have long been employed to shield welding arcs from the *o atmosphere for obtaining high quality welds in reverse polarity as well as straight polarity welding and in A.C. welding processes. The art much prefers reverse polarity welding (where the workpiece is negative) because a negative workpiece is hotter than a positive workpiece which permits better penetration. See, U.S. Patent Nos. 2,806,128, 2,932,722 and 3,147,362 and the patents cited therein; and also Cushman, "Electrode for Spatter-Free Welding of Steel in Carbon Dioxide," Welding Research Supplement, January 1961 at pages 14-s to 21-s. As this art discloses in some detail, CO 2 containing gases are employed as shielding gases in place of inert gases to reduce the cost of gas shielded welding. Such gases generally include 25% or more CO 2 and 75% or less inert gases. However, metal transfer through CO 2 shielded arcs tends to be globular in form and to be particularly hard to control 940930,p:\oper\phh,88955-91.273,1 in reverse welding processes. This results in unstable arcs and excessive spatter levels which leads to low quality welds, reduced weld efficiency and high clean-up costs.

U.S. Patent No. 2,932,722 discloses an improved electrode which provides a coating containing so-called emissive agents including cesium (carbonate or hydroxide) in combination with other alkali metals to develop a spray form of metal transfer and thereby to reduce the spatter emissions.

However, as disclosed in U.S. Patent No. 2,932,722, welding with cesium-coated electrodes can only be controlled when operating with straight polarity (where the electrode is negative and the work piece is positive).

U.S. Patent Nc. 3,147,362 discloses that the cesium-containing coating of the electrode of U.S. Patent No.

2,932,722 is so hygroscopic that the cesium compounds tend to break down and that surface films tend to create electrical contact problems. Thus, this patent proposes to provide emissive materials in a fill. The core materials, including metal scraps coated with alkali metal carbonates (comprising oo 20 less than 1% cesium carbonate and more than 99% rubidium, potassium, sodium and lithium carbonate), are compacted in a metal tube and the filled tube is then extruded and drawn.

According to this improvement, the cesium and other highly i hygroscopic ingredients in the core are sealed against atmospheric moisture and there are no electrical contact problems experienced of cesium-containing coatings.

The metal cored electrode disclosed by U.S. Patent No. 3,147,362 has not received commercial acceptance because commercial composite electrodes are preferably not made by filling tubes. Rather, flat metal strips are continuously formed into U-shaped configurations, filled with core ingredients, and then bent into tubes having seams defined by adjacent edges of the strips and finally drawn to size.' It is 2.

very difficult to continuously and accurately feed cesium containing compounds into such strips because cesium readily absorbs moisture from the atmosphere and then forms clumps which begin to plug the equipment. In addition, moisture from the atmosphere is unavoidably drawn through the seams of composite electrodes into the core, which may then result in high levels of diffusible hydrogen in weld deposits.

Desirably, electrodes deposit high quality welds with less than hydrogen per gram of deposited weld metal (preferably by reverse polarity CO 2 gas shielded welding processes) even after having been exposed to moisture for several days while, e.g., laying on a shelf.

SUMMARY OF THE INVENTION The invention described and claimed in AU-B-62425/90 provides a seamed metal cored electrode containing small amounts of cesium and other alkali metals for CO2 gas shielded welding. Spray type metal transfer, stable arcs and reduced spattering are obtained during reversed polarity as well as straight polarity D.C. and A.C. welding not withstanding moisture pickup which inevitably occurs during the fabrication process and later through the seam of the electrode. The ingredients in the core of the metal tube of the electrode comprise, by weight percent of the metal cored electrode, from 0.01% to 0.5% cesium and at least one other alkali metal selected from the group consisting of lithium, sodium, potassium, and rubidium in a weight ratio of from about 0.1 to about 3.0 cesium/other alkali metal, from about 0.3% to about 10% of at least one metallic alloying element, up to 0.01% of boron and the balance being iron and incidental impurities.

At least about 0.01% cesium is needed to effectively stabilize the welding arc and more than about cesium tends to make the welding arc sluggish. Preferably, the 4 electrode contains from .07% to cesium for obtaining very low spatter levels. The other alkali metal ingredient is preferably comprised mainly of sodium because electrodes embodying the present invention comprising cesium and sodium emissive compounds have significantly improved arc stability and reduced spatter levels in reverse polarity welding processes compared with electrodes embodying the present invention containing potassium or lithium compounds in place of sodium compounds. Mcat preferably, electrodes of the present invention contain about 0.04% to about 0.17% sodium in addition to the cesium for developing spray metal transfer.

Common metallic alloying elements including 0.2% to 2% silicon, 0.1% to 3% manganese, and u.tionally up to titanium, up to 0.5% columbium, up to 0.5% aluminum, up to 3% nickel, up to 3% chromium and up to 3% cobalt may be present in o "total amounts of from about 0.3% to about 10% for obtaining the desired properties in the weld deposit. They may be provided as an alloying ingredient or in the cesium source as a inclusion.

We have now found in accordance with the present invention that the level of boron present in the electrode core may be increased up to about 0.08% by weight of the electrode without detrimentally affecting the electrode performance.

The boron may be added as a nicroalloying ingredient in accordance with the disclosure of U.S. Patent No.

4,282,420, which is hereby incorporated by reference.

The balance of the core ingredients comprises iron together with incidental impurities, including the type of impurities routinely contained in metals such as carbon, 5a DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Exemplary electrodes for CO, gas shielded welding embodying the invention of AU-B-62425/90 generally have seamed ferrous metal tubes with core ingredients (based on their weight alone) which include: 0.5% to 1% cesium chromate; 0.5% to 1.5% sodium carbonate; 18% to 26% ferroalloys of silicon, manganese and titanium, in order to provide 0.2% to 2% silicon, 0.1% to 3% manganese and up to 0.5% titanium (based on the electrode weight); and the balance comprising iron powder together with

*C

5 oxygen, nitrogen, sulfur, phosphorous and the like and inclusions normally contained in metal cored electrodes such as the anions and cations with the alkali metals (which are provided in the form of salts).

In a preferred embodiment of the invention, the electrode contains less than about 1% moisture in its core, based upon the weight of the tube and the core materials after exposure to 80% relative humidity at 37'C (80'F) for nine days.

Electrodes, embodying the present invention, having less than about 1% moisture in their core with the core ingredients, effectively promote stable welding arcs and reduce spatter.

Preferably the electrode contains less than about moisture, and most preferably, less than 0.3% moisture for S.. depositing quality welds having less than 5ml hydrogen/gram weld metal deposit, no porosity or other unacceptable defects.

Other details, objects and advantages of the invention including methods of practicing it will become apparent as the following description of presently preferred embodiments thereof proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanyizlg drawings present results comparative tests conducted on electrodes, given by way of example only, embodying the invention of AU-B-62425/90 wherein: Figure 1 generally shows the effect of the cesium/alkali metal ratio on spatter levels of welds deposited by a presently preferred electrode; Figure 2 generally shows the effect of the cesium/alkali metal ratio on amp variations; and Figure 3 generally shows the effect of the cesium/alkali metal ratio on voltage variations.

incidental impurities, mainly carbon. The core ingredients normally comprise from about 5% to about 30% of the total electrode weight. The tube which may be from about Imm or less up to about 3mm or more in diameter, may be comprised of carbon, stainless or alloy steel.

Electrodes having seamed 1.2mm (0.045 inch) diameter mild steel tubes and about 17% of core ingredients present within the above limits were tested against a comparative electrode without cesium-containing salts in a gas shielded reverse polarity welding process using a DC power source at about 260 amps, 29 volt. The shielding gas was nominally 100% CO 2 Six inch long welds were deposited in a flat position and the spatter emissions were collected and weighed. The spatter level was then determined per kilogram of weld metal deposited.

Figures I to 3 generally present the results of the comparative tests. The encircled data point indicates the results of the tests conducted with an electrode which did not o. (contain cesium. Figure 1 shows that the spatter level was 20 significantly reduced with the addition of 0.4 to 2.6 cesium/sodium. Similarly, Figures 2 and 3 show that the amp and voltage variations were also significantly reduced with the addition of small amounts of cesium. These figures also show :..that there was a dramatic improvement in properties over the e" 25 comparative electrode by electrodes containing about 0.8 cesium/sodium with perhaps some increase in voltage and amp variation beginning at about 2 weight percent cesium/sodium.

Optimum spatter levels were obtained with electrodes comprising 1.2 to 1.8 weight percent cesium/sodium, which electrodes contained 0.20% cessium/0.17% of sodium and 0.07% cesium/0.04% sodium respectively.

Similar'comparative tests conducted on electrodes of this embodiment of the p.ae ent. invention and commercially available electrodes (which do not contain cesium) adapted for

CO

2 gas shielded welding demonstrated that the electrodes embodying the -proent- invention deposited a flat bead profile in horizontal fillet welds at higher wire speeds and travel speeds than did the comparative commercial electrodes. The commercial electrodes produced arcs that were buried by molten puddle when welding at high wire speeds, which subjects the deposited weld metal to the danger of lack of fusion or slag entrapment.

Cesium and the other alkali metals may be provided in any suitable form in addition to chromate salts. Thus they may be provided as tartrates, permanganates, titanates, aluminates, stearates, carbonates, columbiates, tantalates, zirconates and like compounds, which may also include iron, nickel, chromium, calcium and the like. Cesium chromate is a preferred cesium source. Electrodes containing cesium chromate I as a cesium source were exposed to 80% relative ;20 (130°F) for 120 hours. Those electrodes deposited high quality welds having no porosity or other detectable defect in a CO 2 *2 gas shielded welding test.

Cesium titanate is another preferred cesium source.

Leucoxene and other natural titanate sources may advantageously 25 include such metallic alloying elements as chromium and columbium, but also impurities such as calcium and fluorine.

Whatever the source of cesium and the other ingredients, ;electrodes embodying the present invention contain up to 3% chromium, up to 0.5% titanium and up to 0.5% columbium.

Preferably, the electrode contains no more than 0.06% titanium and more preferably no more than 0.02% titanium for good spray transfer. Also the electrode preferably contains no more than 0.1% columbium and more preferably no more than 0.05% columbium for good spray transfer. The alkali metals may also be provided as halogen salts, but these salts are not preferred because they are extremely hygroscopic. Thus, they are particularly difficult to transport and feed through weighing equipment while manufacturing electrodes. Such hygroscopic salts may be agglomerated by baking a water glass film on the particles to facilitate their use as alkali metal sources.

Preferably, the other alkali metals in addition to cesium includes no more than trace amounts of rubidium which is highly ;ygroscopic.

In addition to single salts, cesium may be provided as a double salt from natural sources or synthetically. Thus, cesium aluminum silicate may be provided from pollucite.

Alternatively, and more costly, double salts such as cesium aluminum colubiate may be synthesized by sol-gel or other processes. Whatever may be the source of cesium and other ingredients, electrodes embodying the present invention contain no more than 0- 5% aluminum, which tends to form refractory aluminum oxides on the metal being transferred. Preferably, the electrodes contain less than 0.1% aluminum for minimizing gobular metal transfer across the welding arc and more S..preferably less than 0.01% aluminum for obtaining spray transfer across the arc. Figure 1 includes two data points identified by carets which summarize the results of spatter tests on metal cored electrodes generally similar to the above identified electrodes of the test, but containing cesium in the form of a cesium aluminum columbiate double salt. Thus, Figure S: 1 indicates that double salts containing aluminum and other refractory elements such as columbium or tantalum may also be useful sources of cesium in the present invention. However, double salts including halogen salts such as cesium fluorotitanate or the like are not preferred because halogen salts are generally hygroscopic.

-9- The alloying ingredients are preferably provided with the alkali metal-containing compounds and/or as alloys including ferroalloys, but the impurities associated with them should not substantially adversely affect the welding process or the deposited weld metal. The iron is normally in powder form.

Preferably the electrode contains less than.about 1% by total electrode weight moisture after exposure to 800 relative humidity at 35°C (80 0 F) for nine days for reducing the effect of moisture upon the cesium during the welding process and the deposited weld metal. More preferably, the electrode contains less than 0.5% moisture for providing an extended shelf life.

Electrodes containing less than 0.3% moisture exposed to highly humid atmospheres have produced high quality welds.

15 EXAMPLES Example 1: C Additional CO 2 gas shielded welding tests were performed with other electrodes having a 17% fill which had in their 20 cores alloying ingredients including up to 6% silicon, up to 12% manganese and up to 1% titanium, at least about 70% iron and emissive agents in the following amounts (based the weight of the core ingredients alone): 25 TABLE 1 Electrode Ingredient A B C D Cs 2 TiO 1.40 Cs 2

CO

3 0.5-1.0 0.5-1 Na 2 CO 1.25 1.25

K

2

CO

3 0.4-0.7 .3 Li 2

CO

3 0.5 These electrodes had improved arc stability, and reduced spatter levels as well as flatter bead shapes and less rollover compared with commercially available electrodes not 940808,p:\oper\pbb88955-91.217,9 -9a containing cesium.

EXAMPLE 2 This example is of electrodes falling within the claims and including boron in the recited 0.01-0.08 weight percent range. Table 2 provides the composition of electrode samples E through K. As indicated in Table 2, the percentages shown for the electrode components are weight percentages of the electrode fill material. The percentage of the total electrode weight for each component can be calculated by accounting for the fill percentage provided in the first row of Table 2, the percentage of the electrode which is the fill material. It may be seen from Table 2 that electrode sample "E did not include boron, while electrode examples F through K included boron in the range of 0.0106 to 0.075 weight s 6: percent of the electrode weight. Also, each electrode had a 1.014 ratio of cesium to other alkali metal (here sodium).

ee Table 3 provides the weld deposit chemistry for weld deposits produced using electrode samples E through K and the 20 claimed process. The values were obtained by running a deposit chemistry pad at standard welding parameters and testing on an optical emission spectrometer.

m0 0 Table 4 provides tested mechanical properties for the *weld deposits. It may be seen that the addition of titanium 25 to electrode examples J and K significantly improved the impact properties of the weld deposits. It is believed that the addition of titanium acts to increase the recovery of boron in the weld deposit.

It was found that the addition of boron to electrode examples F through K resulted in no significant negutive effects on the general welding performance of those electrodes. Also, with respect to the spatter levels, amperage variation and voltage variation, each of the experimental electrodes E through K exhibited levels of those properties which correlate to the levels provided in the present application's specifications and figures for a ratio of cesium to other alkali metals.

940808,p:\oper\phb,8895591.217,9 C Ot C a *e S* a. a. a. a S. C. S 9 b- TABLE 2: Electrode Compositions Having Greater Than 0.01 to 0.08 Weight Percent Boron Example E F G H I J K Fill -W 16.5 16.5 16.9 17.2 16.9 17.0 17.0 electrode Sodium* 1.0 1.0 1.0 1.0 1.0 1.0 (43.4% Na) Silico 6.7 6.7 6.7 6.7 6.7 6.7 6.7 (67% Mn, 17% Si, 1.7% Cesium 1.0 1.0 1.0 1.0 1.0 1.0 nluiobat (43% Cs, Al, Manganese 6.7 6.7 6.7 6.7 6.7 6.7 6.7 (100% M n) Table 2 cont...

940808, p: Xoperlphh, 88955-91. .217,9 90 SO S 9. C. 04 9 0. 5* 9 0 0 99 S~ 9. 09 9* C. 9 **9C 9 9 99 09 9c Table 2 cont,...

Iron j 72.8 72.45 72.05 71.55 70.3 71.05 71.05 Powder 100% Fe) Ferro- I 10.5 10.5 10.5 10.5 10.5 10.0 silicon (48% Si) Ferro- 0 0.35 0.75 1.25 2.5 0.75 0.75 boron powder (18% B) Ferro- 0 0 0 0 0 1.5 titanium powder (29% Ti, 22% -W B 0 0.0106 0.0226 0.0377 0.075 0.0226 0.0226 of total electrode wt.) %1 Ti of 0 0 0 0 0 0,074 0,099 total electrode Table 2 cont...

940808, p: Xoperiphh, 88955-91. 217,9 a. a a. a a. a a. a. a 9d- Table 2 cont...

All percentages of components for the fill material are by weight of the fill material unless otherwise indicated.

940808, p: loperlphh, 88955-91. 217,9 V VS V. S. *V *V es V. V V V. V~ VV *V~V V.

9 e- TABLE Weld Deposit Comoositionb Usingi Examples E-K Example E F G H I J K C 0.028 0.026 0.027 0.027 0. 14a 0.030 0.029 Mn 1.49 1.60 1.71 1.68 1.64 1.66 1.72 Si 0.40 0.47 0.56 0.56 0.59 0.57 0.57 p 0.007 0.007 0.007 0.007 0.006 0.007 0.007 S 0.012 0.012 0.013 0.013 0.016 0.013 0.013 Ti 0 0 0 0 0 0.011 0.015 B 0.0006 0.0039 0.0091 0.0223 0.0875 0.0109 001 a This appears to be an anomalous reading for C.

b All percentages are weight percentages of total deposit weight.

9408 08, p: Jperlphh, 88955-91. 217,9 CC *C Ca C CC C C Ce C.

CO CC CC C COCOCCA 0* CS C S C SC 55 CC Ce *S C* CC CS S be..

CC C .5CC CC C S *C C C. *e C. 00.0- CC 9f- TABLE 4: Mechanical Properties of Weld Deposits Electrode E F G H IJK Example______ Ultimate 86.5 88.8 89.2 93.5 No 93.5 96.0 Tensile tensile Strength results (ksi) available Yield 80.5 81.3 81.4 85.5 No 86.0 90.0 Strength tensile (ksi) results __________available Elong. 25 25 24 1 No 24 23 tensile results available CVN 22 25 12 6 2 26 39 Impacts 0 0 (ft. 19 19 10 6 2 28 37 lbs.) 940808, p: oper~phh, 88955-91. .217,9 While certain presently preferred embodiments.the PrC-qcnt i numntinh been described, it is to be distinctly understood that the invention is not limited thereto, but may be variously embodied within the scope of the following claims.

Claims (15)

1. A metal cored electrode for CO 2 gas shielded welding having core ingredients in a ferrous metal tube, the metal tube having a seam; and the core ingredients including (by weight of the electrode): from 0.01% to 0.5% cesium; at least one other alkali metal selected from the group consisting of lithium, sodium, potassium and rubidium in a weight ratio of from about 0.1 to about 3.0 cesium/other alkali metal(s); from 0.3% to 10% of at least one metallic alloying element selected from the group consisting of 15 from 0.2% to 2% silicon, 1 from 0.1% to 3% manganese, up to 0.5% titanium, up to 0.5% columbium, up to 0.5% aluminum, up to 3% chromium, up to 3% nickel, and up to 3% cobalt; from above 0.01% up to 0.08% boron; and the balance iron and incidental impurities.

2. The electrode of claim 1, comprising from 0.07% to 0.2% cesium.

3. The electrode of claim 1, wherein the other at least one alkali metal is selected from the group consisting of sodium, potassium and lithium. 940930,p:\oper\plh88955-91.273,11 1 I

4. The electrode of claim 1, wherein the other alkali metal comprise sodium. The electrode of claim 4, wherein sodium comprises from 0.04% to 0.17%.

6. The electrode of claim 4, comprising a weight ratio of from 0.8 to 2 cesium/sodium.

7. The electrode of claim 4, comprising a weight ratio of from 1.2 to 1.8 cesium/sodium.

8. The electrode of claim 1, wherein the core ingredients comprise less than 1% moisture based upon the weight of the metal cored electrode after exposure to relative humidity at 35'C for nine days.

9. The electrode of claim 1, wherein the core "ingredients comprise less than 0.5% moisture based on the weight of the metal cored electrode after exposure to relative humidity at 35'F (80'F) for nine days. The electrode of claim i, wherein the core ingredients comprise less than 0.3% moisture based on the o weight of the metal cored electrode after exposure to relative humidity at 35'C (80'F) for nine days. 11I. The electrode of claim 1, wherein the cesium is provided as cesium chromate.

12. The electrode of claim 1, wherein the cesium is provided as cesium titanate. provided as cesium titanate.

13. The electrode of claim 1, wherein the cesium is provided as cesium carbonate.

14. A CO 2 gas shielded welding process comprising the steps of: arc welding a workpiece with a metal cored electrode of claim 1; providing a gas shield about the arc comprising at least about 25% CO 2 and applying reverse polarity from a power source whereby the workpiece is negative and the electrode is positive. The process of claim 14, wherein the power is supplied by an AC source.

16. The process of claim 14, wherein the power is applied by a DC source.

17. A CO 2 gas shielded welding process comprising the 2 steps of: arc welding a workpiece with a metal cored Selectrode of claim 1; providing a gas shield about the arc comprising at "least about 25% CO 2 and 2 applying straight polarity from a power source whereby the workpiece is positive and the electrode is negative. 14.

18. An elestrc~ee--& r gswldn r-e substantially as hereinbefore described with refe cet the drawings and/or Examples.

19. The steps, featur compositions and compounds disclosed herei referred to or indicated in the specifica In and/or claims of this application, in 'idually or collectively, and any and all combinations ef ny wo eE morc ef said steps or; foatarcc. DATED this 2nd day of January 1992. Alloy Rods Global, Inc. by DAv)ES COLLISON CAVE Patent Attorneys for the applicant(s) 550 I ABSTRACT OF THE DISCLOSURE A metal cored electrode for CO 2 gas shielded welding has 5% to 30% core ingredients in a ferrous metal tube with a seam. The core includes, based upon the weight of the electrode: from about 0.01% to about 0.5% cesium, from about 0.1 to about 3.0 cesium/other alkali metal(s) on a weight basis, the other alkali metals selected from the group consisting of lithium, sodium, potassium and rubidium; and from about 0.3% to about 10% of alloying elements selected from silicon, manganese, and optionally titanium, columbium, aluminum, nickel, chromium and cobalt; up to 0.08% boron; and balance iron together with incidental impurities. The electrodes are used in reverse and straight polarity DC and AC CO 2 gas shielded welding processes for providing stable arcs and reduced spatter levels as well as high quality weld deposits. to: so *e 4: so* I g *5