February 2008 This Presentation is provided to you by: WPSAmerica.com Industry Standard Welding Procedures Software for AWS and ASME Codes.

February 2008

This Presentation is provided to you by:

WPSAmerica.comIndustry Standard Welding Procedures Software for AWS and ASME Codes

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!