NOVEMBER 200746

The submerged arc welding processhas been used for many years bymanufacturers seeking to improvequality, increase productivity, reducecosts, and enhance welder comfort. Thisautomated arc welding process utilizescontinuous solid or cored (composite)electrodes with a granular welding flux.The fluxs main function is to shield themolten weld pool from the atmosphere.The flux is deposited along the weld jointahead of the welding arc(s). The high current-carrying capacity of the electrodesand the ability to utilize welding proce-dures employing multiple electrodesmake the submerged arc process a goodchoice for downhill welding applicationsrequiring deep penetration, high deposi-tion rates, fast travel speed, or some com-bination thereof.

The A5.17 and A5.23 Specifications

The American Welding Society classi-fies carbon and low-alloy submerged arcelectrodes and fluxes with two specifica-tions. These are AWS A5.17/A5.17M,Specification for Carbon Steel Electrodesand Fluxes for Submerged Arc Welding, andAWS A5.23/A5.23M, Specification forLow-Alloy Steel Electrodes and Fluxes forSubmerged Arc Welding. These specifica-tions make use of both U.S. CustomaryUnits and the International System ofUnits [SI]. Solid electrodes under bothspecifications are classified based upontheir chemical compositions. Tubular(composite) electrodes are classifiedbased upon the weld deposit compositiondeveloped with the electrode and a partic-ular flux. Fluxes are not classified inde-pendently but are classified with an elec-trode of a specific classification basedupon the mechanical properties of the

weld metal deposited in a 1 in [25 mm]thick groove joint with the flux-electrodecombination. The test groove joint typi-cally requires 12 to 15 weld passes to com-plete. The A5.23/A5.23M low-alloy speci-fication also has specific requirements forweld deposit composition. TheA5.17/A5.17M carbon steel specificationdoes not.

Revisions to A5.23/A5.23M Specification

The 2007 editions of both the AWSA5.17/A5.17M carbon steel and AWSA5.23/A5.23M low-alloy steel submergedarc specifications have been published thisyear. The A5.17/A5.17M-97 (R2007) edi-tion is simply a reaffirmation of the

AWS Adds Two-Run Optionfor Flux-Electrode

Classification

AWS Adds Two-Run Optionfor Flux-Electrode

Classification

DENNIS D. CROCKETT is a consultant, The Lincoln Electric Co., Cleveland, Ohio; chairman, A5M Subcommittee on Carbon andLow-Alloy Steel Electrodes for Flux Cored Arc Welding; past chair, A5B Subcommittee on Carbon and Low-Alloy Steel Electrodes andFluxes for Submerged Arc Welding; and a member of the A5 Committee on Filler Metals and Allied Materials.

Fig. 1 Cross section of multiple pass flux-electrode classification weld.

Fig. 2 Charpy and tensile specimen locations for multiple pass classification test.

Important revisions to AWS filler metal specification A5.23 are explained in detail

BY DENNIS D. CROCKETT

Crocket Layout:Layout 1 10/5/07 5:46 PM Page 46

ANSI/AWS A5.17/A5.17M-97 specificationissued in 1997. No technical changes weremade to that specification. However, majorchanges have been incorporated into theA5.23/A5.23M:2007 low-alloy specifica-tion. The most noteworthy of these changesis the addition of a two-run classificationsystem. The AWS A5B Subcommittee onCarbon and Low-Alloy Steel Electrodesand Fluxes for Submerged Arc Welding hasadded a two-run classification option inrecognition of the fact that mechanicalproperties obtained on a two-run and otherlimited-pass welds with a given flux-electrode combination can be significantlydifferent than the mechanical propertiesobtained on multiple pass welds using thesame flux-electrode combination.

Two-Run and Multiple Pass Welds

The differences in the mechanical prop-erties obtained on multiple pass welds fromthose developed on two-run and other lim-ited pass welds can be attributed in greatpart to their respective microstructures. Inmultiple pass welding, the reheating of eachweld pass by the subsequent weld pass hasthe effect of refining the grain structure ofthat pass. As a result, the completed multi-ple pass weld consists of a network of finegrain regions that serve to enhance theCharpy V-notch properties of the weld Figs. 1, 2. The use of higher-basicity fluxescan further improve the V-notch propertiesof multiple pass welds by reducing the grainboundary oxygen (oxide) inclusion levels.Also, any adverse effect from admixturewith the base plate is minimized due to thelow dilution factor.

On two-run (limited-pass) welds, thegrain refinement mechanism describedabove for multiple pass welds is minimal.The second pass of a two-run weld consistsentirely of as-deposited microstructurethat is not conducive typically to develop-ing good weld metal V-notch properties Fig. 3. In addition, the base plate dilutionfactor of limited pass welds can exceed50%. As a result, the mechanical proper-ties obtained with any flux-electrode com-bination on a limited pass weld can be ex-pected to vary with the base platecomposition. The approaches taken to de-velop good Charpy V-notch properties onlimited-pass welds are of necessity differ-ent than those used for multiple passwelds. These include, for example, the de-sign of special fluxes that promote finergrain weld structures and the use of elec-trodes alloyed with molybdenum, tita-nium, and/or boron to promote a fine aci-cular ferrite structure and to retard thegrowth of grain boundary ferrite.

Limitation of Existing ClassificationThe existing multiple pass flux-elec-

trode classification provides users a rea-

sonable basis for identifying candidateflux-electrode combinations to meet theirmultiple pass application requirements.However, for limited pass applicationssuch as the fabrication of structural steelshapes, pipe for oil and gas transmission,and wind towers the usefulness of multiplepass flux-electrode classifications for iden-tifying candidate flux-electrode combina-tions that meet their application require-ments is questionable. It is for this reasonthat a two-run flux-electrode classificationoption has been added to the AWSA5.23/A5.23M specification. The low-alloy A5.23/A5.23M specification was se-lected as the residence document for thetwo-run classification because (1) low-alloy electrodes classified under this spec-ification are commonly used to developgood mechanical properties on limitedpass welds, and (2) the strength level re-quirements in this document are higherthan those found in the A5.17/A5.17Mcarbon steel specification and better meetthe requirements of commercial practice.

The two-run weld test assembly is anominal 1/2 in [12 mm] thick butt jointweld which is welded with one pass on eachside. The base plate material and weldingconditions are defined in the specification.Full-size Charpy V-notch impact speci-mens and a 0.250 in diameter longitudinaltensile test specimen are machined from

the completed weldment and tested to de-termine conformance to mechanical prop-erty requirements Fig. 4. The two-runflux-electrode classification has no weldmetal composition requirement.

The Classification System Outlined

The classification system is outlined asfollows.

FXTXXG EXX HX, where,

The letter F indicates a submerged arcwelding flux. The letters XT indicate the minimumtensile strength on a two-run classifica-tion. The X in the fourth position indicatesthe condition of heat treatment, if any. The X in the fifth position indicatesCharpy V-notch properties. The G, when present, indicates that thetest joint was not constructed from one ofthe steels prescribed in the specificationbut from another steel as agreed to be-tween purchaser and supplier. The EXX indicates the classification ofelectrode used in producing the weld. The HX is an optional, supplementalhydrogen designator. This designator isoptional and does not constitute part ofthe flux-electrode classification.

47WELDING JOURNAL

Fig. 3 Cross section of two-run flux-electrode classification weld.

Fig. 4 Charpy and tensile specimen location for two-run classification test.

Crocket Layout:Layout 1 10/5/07 5:46 PM Page 47

Two examples of flux-electrode two-run classifications are given below. The ex-amples shown are in U.S. CustomaryUnits.

Example 1. F7TA4-EM12K is a com-plete designation for a flux-electrode two-run classification. It refers to a flux that,when used with an EM12K electrode toweld the base plate prescribed in accor-dance with the two-run welding conditions

called for in the AWS A5.23/A5.23M:2007specification, will produce weld metal inthe as-welded condition having a mini-mum tensile strength of 70,000 psi andCharpy V-notch impact strength of at least20 ftlbf at 40F.

Example 2. F8TA2G-EA1 is a completedesignation for a flux-electrode two-runclassification. It refers to a flux that, whenused with an EA1 electrode to weld the

test plate in accordance with the two-runwelding conditions called for in the AWSA5.23/A5.23M:2007 specification, willproduce weld metal in the as-welded con-dition having a minimum tensile strengthof 80,000 psi and Charpy V-notch impactstrength of at least 20 ftlbf at 20F. TheG in the classification indicates that thebase steel used is not one of the test steelsprescribed in the specification but is someother steel (such as an API 5LX70 pipesteel) as agreed between purchaser andsupplier.

Additional Changes to A5.23

In addition to the two-run classifica-tion, higher classification strength levelshave been added to the AWSA5.23/A5.23M:2007 revision to reflect theuse of higher-strength steels in practicetoday. Changes were also made to compo-sition requirements for EB9 electrodesand B9 weld deposits, as well as changes tothe diameter tolerance for composite elec-trodes. This revision includes new classifi-cations EA1TiB and EA2TiB, that aretitanium-boron-containing electrodesuseful in developing improved CharpyV-notch impact properties on single-passwelds.

NOVEMBER 200748

For info go to www.aws.org/ad-index

For info go to www.aws.org/ad-index SEE US AT THE FABTECH/AWS SHOW BOOTH #7046

Crocket Layout:Layout 1 10/5/07 5:49 PM Page 48