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  1. This Presentation is provided to you by: WeldCanada.comIndustry Standard Welding Procedures Software CSA, AWS, ASME and API Welding Codes

  2. 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 Contact tube Gun Nozzle Shielding gas Electrode stick out Arc length Welding Arc Base metal

  5. Observation of the welding arc • Video of metal transfers in – GMAW steel Please note: Members will receive above video by e-mail 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. 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

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

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

  16. 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 +H2+  %CO2 +  CO2 Ar +He+  CO2

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

  18. GMAW Dual wire process Automatic GMAW with dual wires: thickness: 1.5 - 6mm 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

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

  20. FCAW weld with slag formation

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

  22. 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.

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

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

  25. Mechanical properties : 1% Ni MCAW all tests with same lot

  26. Classification of metal cored and FCAW wires in Canada and US METAL CORED; • CSA W48-01/W48-06, CLASS E491C-6-H4/E491C-6M-H4 • AWS A5.18-95/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 A5.20-95/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 A5.20-95/ASME SFA 5.20, Class E70T-1-H8/T-1M-H8, E70T-9-H8/T-9M-H8

  27. Weldmetal chemistries – E491 C6-H4

  28. Weldmetal mechanical property variation – E491 C6-H4

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

  30. FCAW wire storage conditions and worm tracking

  31. FCAW wire storage conditions and worm tracking

  32. Typical FCAW/MCAW wire cross sections Wire closing seam configuration

  33. FCAW wires – Hydrogen pick up susceptibility

  34. 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" 299 312 323 Amps Volts 28.5 28.5 27.5 3/4" E.S.O 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

  35. Diffusible Hydrogen variation with oxidation potential

  36. 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 10 mm ESO 10mm ESO 20mm ESO 20 mm 8.1ml/100g 5.5ml/100g 10.0ml/100g 9.0ml/100g

  37. 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

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

  39. 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

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

  41. 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.

  42. 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.

  43. 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.

  44. Thank you!