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2 Viwek Vaidya February 12th 2008
CWA Toronto Chapter conference Effect of Gas selection on arc stability, chemistry, mechanical properties and diff. H2 contents of FCAW, MCAW, GMAW weldmetals Viwek Vaidya February 12th 2008

3 The GMAW Set-up Wire Wire Feeder Power Source Water Cooler (optional)
Regulator / Flow meter Shielding Gas Welding Gun Work Ground Clamp Work piece (Base Material)

4 FCAW, MCAW, GMAW Electrode wire Gun Nozzle Shielding gas
Contact tube Gun Nozzle Shielding gas Electrode stick out Arc length Welding Arc Base metal 31

5 Observation of the welding arc
Video of metal transfers in – GMAW steel Please 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!

6 The functions of shielding gases are
Protect the weld pool from atmosphere Provide a gas plasma - ionized gas Support metal transfer and bead wetting

7 Thermal conductivity and plasma shape
Thermal Conductivity is the ease with which the gas will dissipate heat Argon has low thermal conductivity It is used for superior R-Value windows Helium has high thermal conductivity, CO2 also has high thermal conductivity than Argon Argon

8 Thermal conductivity and plasma shape : Globular transfer
Consider energy flow through He and CO2, both characterised with Higher thermal conductivity than Argon Narrow plasma column CO2 and Helium produce globular transfer cannot produce spray transfer!

9 Penetration profiles Argon has a finger nail penetration profile consistent with spray transfer CO2 and He have elliptical penetration consistent with the globular transfer

10 Thermal conductivity and plasma shape : Spray Transfer
Low thermal conductivity Expanded plasma column Electron condensation heating

11 Thermal conductivity and plasma shape : Spray Transfer
Wire melts in a fast fine droplet stream Wire end becomes pointed Spray transfer results in high deposition and good penetration Argon gives spray transfer!

12 Penetration profiles Argon has a finger nail penetration profile consistent with spray transfer CO2 and He have elliptical penetration consistent with the globular transfer

13 GMAW single wire deposition rates ( 0.045”& 0.035” )

14 GMAW – Aluminum welding – modulated pulse
10 drops /pulse 1 drop /pulse Pollution of gas Porosity level spray pulse Modulated Pulsed arc Spray modulated (interrupted spray)

15 Addition of Oxygen to argon increases arc speed by 20%
Introduction of oxygen through the contact tip in GMAW Aluminium or by brushing or final degreasing Dark deposited removed with rag + 20 % Annular gas: Argon + contact tip: +0,3 l/min O2 Annular gas: Argon + 1,5%O2

16 NICKEL BASE ALLOYS GMAW
Ar Ar+ He+ CO2 Ar+% CO2 Ar+H2+  % CO2 Ar+He+  % CO2 Appearance of the weld and stability of the pulsed transfer greatly improved with CO2 additions

17 NICKEL BASE ALLOYS GMAW
Ar+ H2 +  CO2 Influence of  CO2 addition on the pulse transfer stability D U peak D U droplet detachment Argon Argon+  CO2

18 NICKEL BASE ALLOYS GMAW
Influence of  CO2 addition on Welding speed +26% +17% +12% stability of the pulse transfer Welding speed (cm/mn) energy distribution & transfer stability welding speed transfer stability +  CO2 +H2+  %CO2 Ar +He+  CO2

19 NICKEL BASE ALLOYS GMAW
Ar+ H2 +  CO2 improvement in bead appearance INCONEL 625 INCONEL 600

20 Two-wire GMAW welding process can double productivity!
Extremely fast response power sources needed Two wires fed simultaneously into the same weld pool Wires powered to operate with peak pulses: Perfectly in phase = twin wire technique Perfectly out of phase = tandem wire technique

21 GMAW Dual wire process Automatic GMAW with dual wires: thickness: mm Carbon steel, stainless steels and aluminium alloys 2 wires connected at the same electrical potential Each wire connected at the different electrical potential Twin wire Tandem Technique

22 FCAW & MCAW wire cross section
Metal sheath - outer envelope Joint Metallic and non Metallic Fluxes & powders

23 FCAW weld with slag formation

24 Observation of the welding arc
Video of Ar-CO2 systems - FCAW To see above video, click here

25 Improved weld profile with FCAW+GMAW combination, due to better wetting.
Presence of oxidizing species through the FCAW wire 5/16 inch single pass fillet weld : 35 ipm dual wire as opposed to 16 ipm with single wire systems.

26 GMAW chemistry variation with Ar-O2 mixes.
Wire Chemistry : C=0.1%, Si=0.9%, Mn=1.48%

27 GMAW chemistry variations : Ar-CO2 system
Wire: Mn=1.25%, Si=0.73% C =0.08%,

28 Mechanical properties : 1% Ni MCAW all tests with same lot
Shielding gas UTS MPa YS MPa % E Impacts Cv -51ºC 100% CO2 554 497 30 71,62,64,49,69 Argon +15% CO2 613 577 32.5 75,62,68,82,45 Argon+10% He + 15% CO2 616 557 61,72,95,92,79

29 Classification of metal cored and FCAW wires in Canada and US
CSA W48-01/W48-06, CLASS E491C-6-H4/E491C-6M-H4 AWS A /ASME SFA 5.18, Class E70C-6-H4/E70C-6M-H4 FLUX CORED CSA W48-01/W48-06, Class E491T-1-H8/T-1M-H8, E491T-9-H8/T-9M-H8 AWS A /ASME SFA 5.20, Class E71T-1-H8/T-1M-H8, E71T-9-H8/T-9M-H8 CSA W48-01/W48-06, Class E492T-9-H8/T-9M-H8 AWS A /ASME SFA 5.20, Class E70T-1-H8/T-1M-H8, E70T-9-H8/T-9M-H8

30 Weldmetal chemistries – E491 C6-H4
Shielding gas Oxidation potential % Carbon % Manganese % Silicon Ar+2%O2 2% 0.06 1.13 0.56 Ar+5%O2 5% 0.05 1 0.47 Ar+10%CO2 1.37 0.77 Ar+25%CO2 12.5% 1.3 0.66 Ar+4%O2+ 5%CO2 6.5% 0.04 1.25 0.67 CSA W48 = %O2 + ½ % CO2 N/R 1.75 max 0.90 max

31 Weldmetal mechanical property variation – E491 C6-H4
Shielding gas UTS MPa YS Mpa %E Impacts Cv -30ºC Ar+2%O2 514 450 27.5 78 Ar+5%O2 499 430 29 77 Ar+10%CO2 542 467 92 Ar+25%CO2 435 25.5 112 Ar+4%O2+ 5%CO2 533 456 30 58 CSA W48 500 min 410 min 22 min 27

32 Carbon pick up in stainless steel weld deposits Ar-CO2
Wire Carbon = 0.012%

33 Effect of ambient humidity on diffusible H2 contents-SMAW
Same electrode lot, sealed in vacuum packed condition was shipped to various locations below and tested at different times of the year! Location + (Diff H2 ml/100g) Scotland Zurich Tokyo Rio New Orleans Cape Town January 2 1.7 4.4 2.8 3.4 August 3.6 3.1 4.5 3.7 4.6 2.9

34 FCAW wire storage conditions and worm tracking

35 FCAW wire storage conditions and worm tracking

36 Typical FCAW/MCAW wire cross sections
Wire closing seam configuration 15

37 FCAW wires – Hydrogen pick up susceptibility

38 Variation of diffusible hydrogen content and shielding gases
Parameters 100% CO2 Argon+15%CO2 Argon + 5% CO2 Wire dia. 1/16" 1/16" 1/16" Amps 299 312 323 Volts 28.5 28.5 27.5 E.S.O 3/4" 3/4" 3/4" Diffusible Hydrogen 7.5ml/100g 9.5ml/100g 10.4ml/100g R.H/Temp 45%/22.6'C 45%/22.6'C 45%/22.6'C

39 Diffusible Hydrogen variation with oxidation potential

40 FCAW/diffusible hydrogen and electrical stick out
Wire A Wire A Wire B Wire B 1.2mm dia. 1.2mm dia. 1.6mm dia. 1.6mm dia. 230 amps 230 amps 285 amps 285 amps 26 volts 26 volts 28 volts 28 volts 14 ipm 14 ipm 14 ipm 14 ipm ESO 10mm ESO 20mm ESO 10 mm ESO 20 mm 8.1ml/100g 5.5ml/100g 10.0ml/100g 9.0ml/100g

41 FCAW wire storage conditions and worm tracking
To avoid worm tracking and porosity store the wire properly Use shielding gas with higher oxidation potential Reduce welding amperage Weld with a longer stick out to preheat the wire Discard two layers of the spool and retry If possible recondition the wire – not generally recommended

42 Deleterious effect of Nitrogen on impact energy: carbon steels
250 ppm +

43 Nitrogen 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 balance 10% improvement in strength Better performance against pitting corrosion Beyond 6% Nitrogen in the gas will produces weld porosity.. Arcal 129 Ar+5 He+2%CO2+ 2% N2 for Duplex stainless steels

44 Choice of Shielding gases
Too many to choose from Too complex for users Too complex for producers ALMIG ALTIG ALFLUX

45 Conclusions Video 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 welds Fumes also increase with increasing CO2 content of the shielding gases Addition of 1-2% Oxygen to Argon seems to improve arc stability and arc speeds for Aluminum GMAW process Micro additions of CO2 to Argon + H2 or Argon+He mixtures improves stability of the GMAW welding of Inconel 625 alloys GMAW, FCAW, MCAW deposits in mild steel loose strength and alloying elements with increasing oxidation potential of the shielding gases Increasing CO2 content of the shielding gas may contribute to increased pick up of carbon in extra low carbon stainless steels GMAW deposits.

46 Conclusions - continued
Diffusible hydrogen of a FCAW weld deposit increases with higher levels of Argon contents in the shielding gas Improper storage of FCAW consumable can result in substantial increase in diffusible hydrogen content, causing worm tracking porosity. Some remedies have been suggested An 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.

47 Acknowledgements The 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.

48 Thank you!


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