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Welding Practice for the Sandvik Duplex Stainless Steels SAF 2304, SAF 2205 and SAF 2507 Presented by Frank Babish

Key Points l Metallurgical Considerations l Welding Processes l Composition differences Base Metal and Filler Metal l Good Mechanical and Corrosion Properties of Welds l Importance of Heat Input and Interpass Temperature l Role of Nitrogen l Post Weld Cleaning l Dissimiliar Joining l Joint Design

Characteristics of Duplex stainless steels l Excellent resistance to stress corrosion cracking l Very high mechanical strength l Excellent resistance to pitting and crevice corrosion l High resistance to general corrosion in a variety of environments l Low thermal expansion l High resistance to erosion corrosion and corrosion fatigue l Good weldability l Lower life cycle cost

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

Yield Strength 0, 2% Austenitic vs Duplex Stainless Steel SAF 2507 600 500 SAF 2205 SAF 2304 400 6 Mo+N 300 316 L 200 100 0 904 L

Coefficient of expansion (x 10 -6)°C-1 Austenitic stainless steels Duplex stainless steels Carbon steel approx. 17 approx. 13 approx. 11, 5

Thermal expansion, per °C (20 -100°C) Duplex Carbon steel AISI 316 L 0 5 10 15 -6 20 (x 10 )

Solidification mechanism of Duplex stainless steel l As 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 curves Austenite, ferrite and duplex 1000 austenite duplex (2205) ferrite Stress [MPa] 800 austenite 600 duplex ferrite 400 200 0 0, 2 0, 4 Strain 0, 6 0, 8

Reasons for the high strength of duplex stainless steels l Content of ferrite l Fine grained structure l Nitrogen

Embrittling of Duplex Stainless Steels

Welding Processes Conventional Processes Avoid l GTAW l Autogenous l GMAW l Low Energy Processes l SAW l Or Perform PWHT l SMAW l FCAW

Filler Metals for the Welding of Duplex Stainless Steels Parent Welding metal process Sandvik Filler metal. Chemical composition, wt-% Sandvik C Si Mn P S Cr max. Ni Mo N Ferrite All weld metal, % SAF 2304 TIG, MIG, SAW MMA 23. 7. L 23. 8. LR 7 9 - 0, 14 0, 12 30 -40 SAF 2304 TIG, MIG, SAW and MMA SAF 2205 FCAW 2209 0. 020 2209 -16, 17 0, 030 2209 -15 0, 04 2209 LT 0. 030 8 9 9 9 3 3 0, 14 0, 12 0, 15 0. 15 30 -40 0, 4 0, 020 25 10 4 0, 7 0, 030 0, 025 25 10 4 0, 9 0, 030 0, 025 25, 5 9, 5 4 0, 25 30 -40 0, 020 0, 4 1, 5 0, 020 0, 015 23 0, 030 <0, 9 0, 5 0, 030 0, 025 25 0, 5 <1, 0 <0, 5 <1. 0 SAF 2507 TIG, (MIG), SAW 25. 10. 4. L 0, 020 0, 3 MMA 25. 10. 4. LR 0, 030 0, 5 25. 10. 4. LB 0, 040 0, 4 1, 6 0, 8 1. 5 0, 020 0, 030 0. 015 0, 025 0. 025 22, 5 22 22. 5

Mechanical properties of the Duplex Stainless Steels Sandvik UNS Yield strength 0, 2% offset 1, 0% offset MPa ksi. min. Tensile strength Hardness Vickers ksi. min. Elong. A 5 % min. MPa min. SAF 2304 S 32304 400 58 450 65 600 -820 87 -119 25 230 SAF 2205 S 31803 450 65 500 73 680 -880 99 -128 25 260 SAF 2507 S 32750 550 80 640 93 800 -1000 116 -145 25 290 approx.

Mechanical Properties of All Weld Metal Filler metal Welding Sandvik process Rpo, 2 Rp 1, 0 MPa Rm MPa A 5 % Z % Impact strength, J RT -40°C 23. 7. L 23. 8. LR TIG SAW 1) MMA 525 503 627 708 671 773 34 34 26 58 171 101 62 156 72 46 22. 8. 3. L 22. 9. 3. LR 22. 9. 3. LT TIG SAW 1) MMA FCAW 610 578 512 620 760 775 734 816 28 33 33 30 207 139 52 56 160 84 44 43 25. 10. 4. L TIG 25. 10. 4. L SAW 1) 25. 10. 4. LR MMA 672 687 645 851 878 850 28 27 28 150 91 46 116 64 33 1)Using Sandvik 15 W flux 595 681 664 757 46 53 44 64 47

Mechanical properties of welded joints. Cross-weld tensile test Parent metal Sandvik Filler metal Sandvik Welding Rp 0. 2 process min. MPa typical SAF 2304 23. 7. L 23. 8. LR TIG SAW 1) MMA 400 400 446 452 462 SAF 2205 22. 8. 3. L 22. 9. 3. LR 22. 9. 3. LT TIG SAW 1) MMA FCAW 450 450 553 588 585 SAF 2507 25. 10. 4. LR TIG SAW 1) MMA 550 550 645 628 1)Using Sandvik 15 W flux

Charpy-V impact strength of welded joints Parent metal Sandvik Filler metal Sandvik Welding process Impact energy, J RT -40°C SAF 2304 23. 7. L 23. 8. LR TIG SAW 1) MMA 213 105 46 74 17 38 SAF 2205 22. 8. 3. L 22. 9. 3. LR 22. 9. 3. LT TIG SAW 1) MMA FCAW 282 54 52 55 133 42 43 44 SAF 2507 25. 10. 4. LR TIG SAW 1) MMA 110 100 58 78 58 39 1)Using Sandvik 15 W flux

Typical CPT Values from G-48 A Tests for Parent Metals and Welded Joints Sandvik Filler metal Welding process Shielding gas Root gas 23. 7. L 23. 8. LR TIG SAW 1) MMA Ar Ar - All weld metal Joint 22. 8. 3. L TIG TIG Ar Ar Ar - 2% N 2 Ar 90 N 2 + 10 H 2 (or pure N 2) 20 -23 23 -25 All weld metal Joint 22. 8. 3. L 22. 9. 3. LR SAW 1) MMA - - 20 -25 SAF 2304 All weld metal Joint ~15 SAF 2205 <15 <15 30 SAF 2507 80 All weld metal Joint Autogenous TIG welding 25. 10. 4. L TIG Ar Ar Ar Joint 25. 10. 4. L TIG Ar + 2% N 2 All weld metal Joint 25. 10. 4. LR SAW 1) MMA - 1)Using CPT °C Sandvik 15 W flux Ar 90 N 2 + 10 H 2 (or pure N 2) - 40 40 -45 40 -50 45 -55 40 -50

Quench annealing of Duplex Steel welds Sandvik Holding temperature °C Quenching media SAF 2304 930 - 1050 Water SAF 2205 1020 - 1100 Water SAF 2507 1080 - 1120 Water

High quenching temp Rapid cooling s e id m ium C o hr r t i n Low quenching temp. Slow cooling In te rm et al li cs

Intermetallic phase

Recommended heat input Steel Heat input Interpass temperature SAF 2304 0, 5 - 2, 5 k. J/mm <250°C SAF 2205 0, 5 - 2, 5 k. J/mm <250°C SAF 2507 0, 2 - 1, 5 k. J/mm <150°C m ium C o hr n itr s e id In te rm et al li cs

Welding recommendations Sandvik Heat input k. J/mm Interpass temperature °C SAF 2304 0, 5 - 2, 5 <250 SAF 2205 0, 5 - 2, 5 <250 SFA 2507 0, 2 - 1, 5 <150

The roll of Nitrogen l Nitrogen is a very important alloying element in DSS ü Improves corrosion resistance ü Improves austenite reformation l At TIG welding, the loss of nitrogen is compensated for by using Ar + 1 - 2%N 2 as a shielding gas

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

Nitrogen addition to the shielding gas Ar 99, 99% Ar + 5% N 2

Ferrite content in TIG-welds, SAF 2507 Filler metal Sandvik Shielding gas Root Ferrite c + error with 95% confidence interval 25. 10. 4. L Ar Ar 55 + 4, 5 25. 10. 4. L Ar 90% N 2 + 10% H 2 59 + 4, 0 25. 10. 4. L Ar + 5% N 2 90% N 2 + 10% H 2 33 + 4, 0

Nitrogen Content in TIG welds of SAF 2507. N=0, 25% in the filler metal Filler metal Sandvik Shielding gas Root gas Weight-% N in deposit 25. 10. 4. L Ar 90% N 2 + 10% H 2 0, 23 25. 10. 4. L Ar + 3% N 2 90% N 2 + 10% H 2 0, 27 25. 10. 4. L Ar + 6% N 2 90% N 2 + 10% H 2 0, 33

GMAW SHIELDING GASES l General recommendations: ü Short arc welding gives very convex beads. Ar+30 He+1 O 2 ü Spray arc welding Ar+30 He+1 O 2 (22 Cr duplex) Ar+2 CO 2(Super duplex) ü Pulsed arc welding Ar+30 He+1 O 2 (22 Cr duplex) Ar(99, 996%) for super duplex

Nitrogen Analysis from the Top of a TIG weld % Nitrogen in position (o’clock) 3 5 6 7 11 12 Welder No. 1 0, 17 0, 18 0, 15 0, 19 Top side Welder No. 2 0, 18 0, 20 - 0, 19 0, 21 0, 19 0, 20 - Top side Root side Welder No. 3 0, 22 0, 21 - 0, 21 0, 20 - Top side Root side 0, 16 In all cases the filler metal had a nitrogen content of 0, 25% Analysis at

Stress relieving temperatures 325 + 25°C for 10 hours

Post Weld Cleaning Pitting potential Pickling bath or pickling paste HNO 3 -HF 360 220 120 80 Wire brush Blasting

Dissimilar Joints SAF Carbon steel AISI 200 and 300 series AISI 904 L, Sanicro 28, 254 SMO, etc. 2304 22. 8. 3. L 22. 9. 3. LR 22. 9. 3. LT 2205 22. 8. 3. L 22. 9. 3. LR 22. 9. 3. LT 2507 25. 10. 4. LR Sanicro 60

Joint preparation One sided butt welding

Joint preparation Butt welding from both sides

Tube to tube sheet welding. Joint preparation 45° >3 mm (0. 12”) or >1. 5 x WT b a >WT c d r >1. 5 x WT

Hydrogen pick-up from covered electrodes Sandvik 25. 10. 4. LR MMA H 2, ml/100 g

Hydrogen pick-up from SAW flux SAW H 2, ml/100 g

Hydrogen pick up from shielding gas at TIG welding H 2, ml/100 g TIG - no root gas Shielding gas Ar + 5% H 2 Shielding gas Ar + 10% H 2

Hydrogen pick up from shielding gas and root gas at TIG welding H 2, ml/100 g TIG - with root gas Shielding gas Ar Root gas Ar Shielding gas Ar Root gas 90% N 2 + 10% H 2

Conclusions Key Areas l Good Weldability l Uses Conventional Welding Processes l Joint Design l Role of Nitrogen l Heat Input Important l Interpass Temperature