February 2008
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February 2008
Effect of Gas selection on arc stability, chemistry, mechanical properties and diff. H2 contents of FCAW, MCAW, GMAW weldmetals
Effect of Gas selection on arc stability, chemistry, mechanical properties and diff. H2 contents of FCAW, MCAW, GMAW weldmetals
Viwek Vaidya
February 12th 2008
CWA Toronto Chapter conference
February 2008
The GMAW Set-up
Wire Feeder
Power Source
Water Cooler (optional)
Regulator / Flow meter
Shielding Gas
Welding Gun
Work Ground Clamp
Work piece (Base Material)
Wire
February 2008
FCAW, MCAW, GMAW FCAW, MCAW, GMAW
Contact tubeContact tube
Base metal
Electrode stick outElectrode stick outElectrode stick outElectrode stick out
Arc lengthArc lengthArc lengthArc length
Shielding gas
Gun Nozzle
Electrode wireElectrode wire
Welding ArcWelding Arc
February 2008
Observation of the welding arc 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!
February 2008
The functions of shielding gases areThe functions of shielding gases are
Protect the weld pool from atmosphere Provide a gas plasma - ionized gas Support metal transfer and bead wetting
February 2008
Thermal conductivity and plasma shapeThermal 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
February 2008
Thermal conductivity and plasma shape : Globular transferThermal 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!
February 2008
Penetration profilesPenetration profiles
Argon has a finger nail penetration profile consistent with spray transfer
CO2 and He have elliptical penetration consistent with the globular transfer
February 2008
Thermal conductivity and plasma shape : Spray TransferThermal conductivity and plasma shape : Spray Transfer
Low thermal conductivity Expanded plasma column Electron condensation
heating
February 2008
Thermal conductivity and plasma shape : Spray TransferThermal 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!
February 2008
Penetration profilesPenetration profiles
Argon has a finger nail penetration profile consistent with spray transfer
CO2 and He have elliptical penetration consistent with the globular transfer
February 2008
Introduction of oxygen through the contact tip in GMAW Aluminium
+ 20 %Annular gas: Argon + 1,5%O2
Annular gas: Argon + contact tip: +0,3 l/min O2
Dark deposited removed with rag or by brushing or final degreasing
Addition of Oxygen to argon increases arc speed by 20%Addition of Oxygen to argon increases arc speed by 20%
February 2008
Ar
Ar+% CO2 Ar+He+ % CO2 Ar+H2+ % CO2
Ar+ He+ CO2
NICKEL BASE ALLOYS GMAWNICKEL BASE ALLOYS GMAW
Appearance of the weld and stability of the pulsed transfer greatly improved with CO2 additions
February 2008
NICKEL BASE ALLOYS GMAWNICKEL BASE ALLOYS GMAW
Influence of CO2 addition on the pulse transfer stability
U peak
U droplet
detachment
Argon Argon+ CO2
Ar+ H2 + CO2
February 2008
0
5
10
15
20
25
30
35
40
45
NICKEL BASE ALLOYS GMAWNICKEL BASE ALLOYS GMAW
welding speed
Ar + CO2
+He+ CO2
+H2+ %CO2
Wel
din
g s
pee
d (
cm/m
n)
+26%
+17%+12%
stability of the pulse transfer
tran
sfer
sta
bilit
y
ene
rgy
dist
ribut
ion
&tr
ansf
er s
tabi
lity
Influence of CO2 addition on Welding speed
February 2008
INCONEL 625 INCONEL 600
Ar+ H2 + CO2
improvement in bead appearance
NICKEL BASE ALLOYS GMAWNICKEL BASE ALLOYS GMAW
February 2008
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
February 2008
Metal sheath - outer Metal sheath - outer envelopeenvelope
Metallic and nonMetallic and nonMetallic Fluxes &Metallic Fluxes &
powderspowders
JointJoint
FCAW & MCAW wire cross sectionFCAW & MCAW wire cross section
February 2008
FCAW weld with slag formationFCAW weld with slag formation
February 2008
Observation of the welding arc Observation of the welding arc
Video of Ar-CO2 systems - FCAW
To see above video, click here
February 2008
•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.
February 2008
GMAW chemistry variation with Ar-O2 mixes. GMAW chemistry variation with Ar-O2 mixes.
GMAW weldmetal chemistry
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0% 2% 4% 6% 8% 10% 12% 14% 16% 18% 20%
Ar-O2 ( O2 in %)
Ch
emst
ry v
aria
tions
% % Carbon
% Silicon
% Manganese
Wire Chemistry : C=0.1%, Si=0.9%, Mn=1.48%
Wire Chemistry : C=0.1%, Si=0.9%,
Wire Chemistry : C=0.1%, Si=0.9%,
Wire Chemistry : C=0.1%, Si=0.9%,
Wire Chemistry : C=0.1%, Si=0.9%,
Wire Chemistry : C=0.1%, Si=0.9%,
Wire Chemistry : C=0.1%, Si=0.9%,
Wire Chemistry : C=0.1%, Si=0.9%,
Wire Chemistry : C=0.1%, Si=0.9%, Mn=1.48%
February 2008
GMAW chemistry variations : Ar-CO2 systemGMAW chemistry variations : Ar-CO2 system
GMAW chemistry variation Ar-CO2
0
0.2
0.4
0.6
0.8
1
1.2
0 5 10 15 20 25 30 35 40
% CO2
% M
n, S
i and
C
%Carbon %Manganese %Silicon
Wire: Mn=1.25%, Si=0.73% C =0.08%,
February 2008
Mechanical properties : 1% Ni MCAW all tests with same lotMechanical properties : 1% Ni MCAW all tests with same lot
Shielding gas UTS MPa
YS MPa
% E Impacts Cv
J @ -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 30 61,72,95,92,79
February 2008
Classification of metal cored and FCAW wires in Canada and USClassification 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
February 2008
Weldmetal chemistries – E491 C6-H4Weldmetal 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 5% 0.05 1.37 0.77
Ar+25%CO2 12.5% 0.05 1.3 0.66
Ar+4%O2+
5%CO26.5% 0.04 1.25 0.67
CSA
W48
= %O2 + ½ % CO2
N/R 1.75 max 0.90 max
February 2008
Weldmetal mechanical property variation – E491 C6-H4Weldmetal mechanical property variation – E491 C6-H4
Shielding gas UTS MPa YS Mpa %E Impacts Cv
J @ -30ºC
Ar+2%O2 514 450 27.5 78
Ar+5%O2 499 430 29 77
Ar+10%CO2 542 467 29 92
Ar+25%CO2 514 435 25.5 112
Ar+4%O2+
5%CO2533 456 30 58
CSA
W48
500 min 410 min 22 min 27
February 2008
Carbon pick up in stainless steel weld deposits Ar-CO2Carbon pick up in stainless steel weld deposits Ar-CO2
Carbon pick up - GMAW : Ar-CO2
0%
5%
10%
15%
20%
25%
30%
0 0.01 0.02 0.03 0.04 0.05 0.06
% Carbon in deposit
%C
O2
in A
r
Series1
Wire Carbon = 0.012%
February 2008
FCAW wire storage conditions and worm trackingFCAW wire storage conditions and worm tracking
February 2008
FCAW wire storage conditions and worm trackingFCAW wire storage conditions and worm tracking
February 2008
Wire closing seam configurationWire closing seam configuration
Typical FCAW/MCAW wire cross sectionsTypical FCAW/MCAW wire cross sections
February 2008
FCAW wires – Hydrogen pick up susceptibilityFCAW wires – Hydrogen pick up susceptibility
FCAW wires - Hydrogen pick up
0
5
10
15
20
25
30
As received Exposed to 80'F/80%RH for 1 week
Exposure condition
Dif
fus
ible
H2
: m
l/10
0g
wire A wire B
February 2008
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
February 2008
Diffusible hydrogen content variation with Oxidiation potential
0
2
4
6
8
10
12
0 10 20 30 40 50 60
Oxidation potential O2% + 0.5*CO2%
Diff
usib
le h
ydro
gen:
ml/1
00g
dep
osite
d w
eldm
etal
GMAW MCAW FCAW
Gas Oxidation Potential
100% Argon 0%Ar-2% O2 2%Ar-5% CO2 2.5%Ar-15% CO2 7.5%Ar-20% CO2 10 %100% CO2 50%
Diffusible Hydrogen variation with oxidation potentialDiffusible Hydrogen variation with oxidation potential
February 2008
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
February 2008
FCAW wire storage conditions and worm trackingFCAW 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
February 2008
Deleterious effect of Nitrogen on impact energy: carbon steelsDeleterious effect of Nitrogen on impact energy: carbon steels
0
20
40
60
80
100
120
0 50 100 150 200 250 300
Weldmetal N2 content, ppm
Ener
gy: C
v Jo
ules
at -
40'C
Impact: Joules at -40'C
February 2008
Nitrogen additions to shielding gas for Duplex stainlessNitrogen 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..
February 2008
Choice of Shielding gasesChoice of Shielding gases
Too many to choose from Too complex for users Too complex for producers ALMIG ALTIG ALFLUX
February 2008
ConclusionsConclusions
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.
February 2008
Conclusions - continuedConclusions - 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.
February 2008
AcknowledgementsAcknowledgements
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.
February 2008
Thank you!