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Welding Practicefor the Sandvik Duplex Stainless SteelsSAF 2304, SAF 2205 and SAF 2507

Presented by

Frank Babish

Key PointsMetallurgical ConsiderationsWelding ProcessesComposition differences Base Metal and Filler MetalGood Mechanical and Corrosion Properties of WeldsImportance of Heat Input and Interpass TemperatureRole of NitrogenPost Weld CleaningDissimiliar JoiningJoint Design

Characteristics of Duplex stainless steelsExcellent resistance to stress corrosion cracking Very high mechanical strength Excellent resistance to pitting and crevice corrosion High resistance to general corrosion in a variety of environmentsLow thermal expansion High resistance to erosion corrosion and corrosion fatigue Good weldabilityLower life cycle cost

Duplex microstructureThe austenite islands (light) are embedded in a continuous ferrite (dark) matrix.The duplex microstructure typically contains 45-65% austenite and 35-55% ferrite.AusteniteFerrite

Yield Strength 0,2%Austenitic vs Duplex Stainless Steel

Coefficient of expansion(x10-6)C-1Austenitic stainless steelsapprox. 17Duplex stainless steelsapprox. 13Carbon steelapprox. 11,5

Thermal expansion, per C (20-100C)

Solidification mechanism of Duplex stainless steelAs duplex stainless steels solidify the grain structure transform from a fully ferritic material to a balanced austenite and ferrite microstructure

Solidification mechanism of a Duplex Stainless Steel

HAZ of weld in SAF 2507

Stress strain curvesAustenite, ferrite and duplex0,00,20,40,60,802004006008001000 austenite duplex (2205) ferriteStress [MPa]Strain

Reasons for the high strength of duplex stainless steelsl Content of ferrite

l Fine grained structure

l Nitrogen

Embrittling of Duplex Stainless Steels

Welding Processes

Conventional Processes

GTAWGMAWSAWSMAWFCAW

Avoid

AutogenousLow Energy ProcessesOr Perform PWHT

Filler Metals for the Welding of Duplex Stainless Steels

Mechanical properties of the Duplex Stainless SteelsSandvikUNSYield strengthTensile strengthElong.Hardness0,2% offset1,0% offsetA5VickersMPaksi.MPaksi.MPaksi.%min.min.min.min.min.min.min.approx.

SAF 2304S323044005845065600-82087-11925230SAF 2205S318034506550073680-88099-12825260SAF 2507S327505508064093800-1000116-14525290

Mechanical Properties of All Weld MetalFiller metalWeldingRpo,2Rp1,0RmA5ZImpact strength, JSandvikprocessMPaMPaMPa%%RT-40C

23.7.LTIG525595708345817115623.7.LSAW1)503671341017223.8.LRMMA62768177326466246

22.8.3.LTIG6107602820716022.8.3.LSAW1)57866477533531398422.9.3.LRMMA51273433524422.9.3.LTFCAW620-81630445643

25.10.4.LTIG672851286415011625.10.4.LSAW1)6877578782747916425.10.4.LRMMA6458502846331)Using Sandvik 15W flux

Mechanical properties of welded joints.Cross-weld tensile testParent metalFiller metalWeldingRp0.2MPaRmMPaA5, %SandvikSandvikprocessmin.typicalmin.typicaltypical

SAF 230423.7.LTIG4004466006503023.7.LSAW1)4004526006893023.8.LRMMA40046260064730

SAF 220522.8.3.LTIG4505536807842922.8.3.LSAW1)4505886807572622.9.3.LRMMA4505886807572822.9.3.LTFCAW45058568076028

SAF 250725.10.4.LTIG5506458008483225.10.4.LSAW1)5506288008423425.10.4.LRMMA550628800846331)Using Sandvik 15W flux

Charpy-V impact strength of welded jointsParent metalFiller metalWeldingImpact energy, JSandvikSandvikprocessRT-40C

SAF 230423.7.LTIG2137423.7.LSAW1)1051723.8.LRMMA4638

SAF 220522.8.3.LTIG28213322.8.3.LSAW1)544222.9.3.LRMMA524322.9.3.LTFCAW5544

SAF 250725.10.4.LTIG1107825.10.4.LSAW1)1005825.10.4.LRMMA58391)Using Sandvik 15W flux

Typical CPT Values from G-48A Tests for Parent Metals and Welded JointsSandvikFillerWeldingShieldingRootCPT CmetalprocessgasgasSAF 2304~15All weld metal23.7.LTIGAr-

Quench annealing of Duplex Steel weldsSandvikHolding temperatureQuenching C mediaSAF 2304930 - 1050WaterSAF 22051020 - 1100WaterSAF 25071080 - 1120Water

Intermetallic phase

Recommended heat inputSteelHeat inputInterpass temperature

SAF 23040,5 - 2,5 kJ/mm

Welding recommendationsSandvikHeat inputInterpass temperaturekJ/mmCSAF 23040,5 - 2,5

The roll of NitrogenNitrogen is a very important alloying element in DSSImproves corrosion resistance Improves austenite reformation

At TIG welding, the loss of nitrogen is compensated for by using Ar + 1 - 2%N2 as a shielding gas

Ferritic area in SAF 2507 weld owing to the loss of nitrogen in fusion lineShielding gas Ar 99,99%

Nitrogen addition to the shielding gasAr 99,99%Ar + 5% N2

Ferrite content in TIG-welds, SAF 2507Filler Shielding Root Ferrite content, vol-%metal gas gas + error with 95%Sandvik confidence interval25.10.4.L Ar Ar 55 + 4,525.10.4.L Ar 90% N2 + 10% H2 59 + 4,025.10.4.L Ar + 5% N2 90% N2 + 10% H2 33 + 4,0

Nitrogen Content in TIG welds of SAF 2507.N=0,25% in the filler metalFiller metal ShieldingRootWeight-% NSandvik gasgasin deposit

25.10.4.L Ar90% N2 + 10% H2 0,23

25.10.4.L Ar + 3% N290% N2 + 10% H2 0,27

25.10.4.L Ar + 6% N290% N2 + 10% H2 0,33

GMAW SHIELDING GASES

General recommendations:Short arc welding gives very convex beads.Ar+30 He+1 O2

Spray arc weldingAr+30 He+1 O2 (22Cr duplex)Ar+2 CO2(Super duplex)

Pulsed arc weldingAr+30 He+1 O2 (22Cr duplex)Ar(99,996%) for super duplex

Nitrogen Analysis from the Top of a TIG weld% Nitrogen in position (oclock)Analysis at35671112

Welder No. 10,170,180,150,160,190,19Top side

Welder No. 20,18-0,190,19-Top side0,20-0,210,20-Root side

Welder No. 30,22-0,210,20-Top side0,21-0,210,20-Root side

In all cases the filler metal had a nitrogen content of 0,25%

Stress relieving temperatures325 + 25C for 10 hours

Post Weld Cleaning

Dissimilar JointsSAF Carbon steelAISI 200AISI 904L,and 300-Sanicro 28,series254 SMO, etc.

2304 22.8.3.L22.8.3.L22.8.3.L 22.9.3.LR22.9.3.LR22.9.3.LR 22.9.3.LT22.9.3.LT22.9.3.LT

2205 22.8.3.L22.8.3.L22.8.3.L 22.9.3.LR22.9.3.LR22.9.3.LR 22.9.3.LT22.9.3.LT22.9.3.LT

2507 25.10.4.L25.10.4.LSanicro 60 25.10.4.LR25.10.4.LRSanicro 60

Joint preparationOne sided butt welding

Joint preparationButt welding from both sides

Tube to tube sheet welding.Joint preparation>WT>1.5 x WT45>3 mm (0.12) or >1.5 x WTr >1.5 x WTabcd

Hydrogen pick-up from covered electrodes Sandvik 25.10.4.LRMMAH2, ml/100 g

Hydrogen pick-up from SAW fluxH2, ml/100 gSAW

Hydrogen pick up from shielding gas at TIG weldingShielding gasAr + 5% H2Shielding gasAr + 10% H2TIG - no root gasH2, ml/100 g

Hydrogen pick up from shielding gasand root gas at TIG weldingTIG - with root gasH2, ml/100 gShielding gas ArRoot gas ArShielding gas ArRoot gas 90% N2 + 10% H2

ConclusionsKey Areas

Good WeldabilityUses Conventional Welding ProcessesJoint DesignRole of NitrogenHeat Input ImportantInterpass Temperature

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