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1This Presentation is provided to you by: WPSAmerica.comIndustry Standard Welding Procedures Software for AWS and ASME Codes
2Viwek Vaidya February 12th 2008 CWA Toronto Chapter conferenceEffect of Gas selection on arc stability, chemistry, mechanical properties and diff. H2 contents of FCAW, MCAW, GMAW weldmetalsViwek VaidyaFebruary 12th 2008
5Observation of the welding arc Video of metal transfers in – GMAW steelPlease note:Members will receive above video by request.It include other processes as well.(SAW, SMAW, FCAW, GMAW, PULSE MIG)Thank You for Your Support!
6The functions of shielding gases are Protect the weld pool from atmosphereProvide a gas plasma - ionized gasSupport metal transfer and bead wetting
7Thermal conductivity and plasma shape Thermal Conductivity is the ease with which the gas will dissipate heatArgon has low thermal conductivityIt is used for superior R-Value windowsHelium has high thermal conductivity, CO2 also has high thermal conductivity than ArgonArgon
8Thermal conductivity and plasma shape : Globular transfer Consider energy flow through He and CO2, both characterised with Higher thermal conductivity than ArgonNarrow plasma columnCO2 and Helium produce globular transfercannot produce spray transfer!
9Penetration profilesArgon has a finger nail penetration profile consistent with spray transferCO2 and He have elliptical penetration consistent with the globular transfer
10Thermal conductivity and plasma shape : Spray Transfer Low thermal conductivityExpanded plasma columnElectron condensation heating
11Thermal conductivity and plasma shape : Spray Transfer Wire melts in a fast fine droplet streamWire end becomes pointedSpray transfer results in high deposition and good penetrationArgon gives spray transfer!
12Penetration profilesArgon has a finger nail penetration profile consistent with spray transferCO2 and He have elliptical penetration consistent with the globular transfer
13GMAW single wire deposition rates ( 0.045”& 0.035” )
14GMAW – Aluminum welding – modulated pulse 10 drops /pulse1 drop /pulsePollution of gasPorosity levelspraypulseModulatedPulsed arcSpray modulated(interrupted spray)
15Addition of Oxygen to argon increases arc speed by 20% Introduction of oxygen through the contact tip in GMAW Aluminiumor by brushing or final degreasingDark deposited removed with rag+ 20 %Annular gas: Argon +contact tip: +0,3 l/min O2Annular gas:Argon + 1,5%O2
16NICKEL BASE ALLOYS GMAW ArAr+ He+ CO2Ar+% CO2Ar+H2+ % CO2Ar+He+ % CO2Appearance of the weld and stability of the pulsed transfer greatly improved with CO2 additions
17NICKEL BASE ALLOYS GMAW Ar+ H2 + CO2Influence of CO2 addition on the pulse transfer stabilityD U peakD UdropletdetachmentArgonArgon+ CO2
18NICKEL BASE ALLOYS GMAW Influence of CO2 addition on Welding speed+26%+17%+12%stabilityof the pulse transferWelding speed (cm/mn)energy distribution &transfer stabilitywelding speedtransfer stability+ CO2+H2+ %CO2Ar+He+ CO2
19NICKEL BASE ALLOYS GMAW Ar+ H2 + CO2improvement in bead appearanceINCONEL 625INCONEL 600
20Two-wire GMAW welding process can double productivity! Extremely fast response power sources neededTwo wires fed simultaneously into the same weld poolWires powered to operate with peak pulses:Perfectly in phase = twin wire techniquePerfectly out of phase = tandem wire technique
21GMAW Dual wire processAutomatic GMAW with dual wires: thickness: mmCarbon steel, stainless steels and aluminium alloys2 wires connectedat the same electrical potentialEach wire connectedat the differentelectrical potentialTwin wireTandem Technique
22FCAW & MCAW wire cross section Metal sheath - outerenvelopeJointMetallic and nonMetallic Fluxes &powders
24Observation of the welding arc Video of Ar-CO2 systems - FCAWTo see above video, click here
25Improved weld profile with FCAW+GMAW combination, due to better wetting. Presence of oxidizing species through the FCAW wire5/16 inch single pass fillet weld : 35 ipm dual wire as opposed to 16 ipm with single wire systems.
27GMAW chemistry variations : Ar-CO2 system Wire: Mn=1.25%, Si=0.73% C =0.08%,
28Mechanical properties : 1% Ni MCAW all tests with same lot Shielding gasUTS MPaYS MPa% EImpacts Cv-51ºC100% CO25544973071,62,64,49,69Argon +15% CO261357732.575,62,68,82,45Argon+10% He +15% CO261655761,72,95,92,79
29Classification of metal cored and FCAW wires in Canada and US CSA W48-01/W48-06, CLASS E491C-6-H4/E491C-6M-H4AWS A /ASME SFA 5.18, Class E70C-6-H4/E70C-6M-H4FLUX COREDCSA W48-01/W48-06, Class E491T-1-H8/T-1M-H8, E491T-9-H8/T-9M-H8AWS A /ASME SFA 5.20, Class E71T-1-H8/T-1M-H8, E71T-9-H8/T-9M-H8CSA W48-01/W48-06, Class E492T-9-H8/T-9M-H8AWS A /ASME SFA 5.20, Class E70T-1-H8/T-1M-H8, E70T-9-H8/T-9M-H8
30Weldmetal chemistries – E491 C6-H4 Shielding gasOxidation potential% Carbon% Manganese% SiliconAr+2%O22%0.061.130.56Ar+5%O25%0.0510.47Ar+10%CO21.370.77Ar+25%CO212.5%1.30.66Ar+4%O2+5%CO26.5%0.041.250.67CSAW48= %O2 + ½ % CO2N/R1.75 max0.90 max
32Carbon pick up in stainless steel weld deposits Ar-CO2 Wire Carbon = 0.012%
33Effect of ambient humidity on diffusible H2 contents-SMAW Same electrode lot, sealed in vacuum packed condition was shippedto various locations below and tested at different times of the year!Location+(Diff H2 ml/100g)ScotlandZurichTokyoRioNew OrleansCape TownJanuary22.214.171.124.4August126.96.36.199.74.62.9
41FCAW wire storage conditions and worm tracking To avoid worm tracking and porosity store the wire properlyUse shielding gas with higher oxidation potentialReduce welding amperageWeld with a longer stick out to preheat the wireDiscard two layers of the spool and retryIf possible recondition the wire – not generally recommended
42Deleterious effect of Nitrogen on impact energy: carbon steels 250 ppm +
43Nitrogen additions to shielding gas for Duplex stainless Up to 2 % additions of N2 advantageous for duplex stainless steel GMAW welding:Reduction of 10-15% ferrite improving ferrite/austenite balance10% improvement in strengthBetter performance against pitting corrosionBeyond 6% Nitrogen in the gas will produces weld porosity..Arcal 129Ar+5 He+2%CO2+2% N2 for Duplexstainless steels
44Choice of Shielding gases Too many to choose fromToo complex for usersToo complex for producersALMIGALTIGALFLUX
45ConclusionsVideo imaging of the welding arc shows that progressive increase in oxidation potential of the shielding gas, stabilizes the arc for GMAW welds in stainless and mild steel weldsFumes also increase with increasing CO2 content of the shielding gasesAddition of 1-2% Oxygen to Argon seems to improve arc stability and arc speeds for Aluminum GMAW processMicro additions of CO2 to Argon + H2 or Argon+He mixtures improves stability of the GMAW welding of Inconel 625 alloysGMAW, FCAW, MCAW deposits in mild steel loose strength and alloying elements with increasing oxidation potential of the shielding gasesIncreasing CO2 content of the shielding gas may contribute to increased pick up of carbon in extra low carbon stainless steels GMAW deposits.
46Conclusions - continued Diffusible hydrogen of a FCAW weld deposit increases with higher levels of Argon contents in the shielding gasImproper storage of FCAW consumable can result in substantial increase in diffusible hydrogen content, causing worm tracking porosity. Some remedies have been suggestedAn addition of up to 2% Nitrogen to an Argon+Helium+CO2 mixture shows improved control on ferrite content of the weldmetal, about 10% increase in strength and improved pitting corrosion resistance in case of duplex stainless steel GMAW welds.
47AcknowledgementsThe author would like to thank the research staff at the Air Liquide World Headquarters in Paris for providing guidance and stimulating discussions while the manuscripts were being drawn up. Thanks are also due to technical experts at Air Liquide Canada and data obtained from the certification center in Boucherville. Photographic support came from several CAP Audit reports, performed at various customer locations in Canada.Dr. Christian Bonnet, Dr. P. Rouault, Mr. J. M. Fortain, Mr. Pierre Geoffroy, Mr. Joe Smith and Mr. Jean Venne provided valuable technical support for this paper and are being recognized for their contribution.