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2. for the Sandvik Duplex Stainless Steels
Welding Practice
for the Sandvik Duplex Stainless Steels
SAF 2304, SAF 2205 and SAF 2507
Presented by
Frank Babish 1

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

4. Characteristics of Duplex stainless steels
Excellent 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 environments
Low thermal expansion
High resistance to erosion corrosion and corrosion fatigue
Good weldability
Lower life cycle cost

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

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

7. Coefficient of expansion (x10-6)°C-1
Austenitic stainless steels approx. 17
Duplex stainless steels approx. 13
Carbon steel approx. 11,5 3

8. Thermal expansion, per °C (20-100°C)5 10 15 20
Duplex
Carbon steel
AISI 316L
(x10 -6 ) 4

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

10. Solidification mechanism of a Duplex Stainless Steel12

11. HAZ of weld in SAF 2507 13

12. Stress strain curves Austenite, ferrite and duplex
1000
austenite
duplex (2205)
ferrite
800
austenite
duplex
600
Stress [MPa]
ferrite
400
200
0,0
0,2
0,4
0,6
0,8
Strain

13. Reasons for the high strength of duplex stainless steels
l Content of ferrite
l Fine grained structure
l Nitrogen 7

14. Embrittling of Duplex Stainless Steels15

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

16. Filler Metals for the Welding of Duplex Stainless Steels
Parent Welding Filler metal Chemical composition, wt-%
metal process Sandvik C Si Mn P S Cr Ni Mo N Ferrite
Sandvik max. max. max. All weld
metal, %
SAF 2304 TIG, MIG, SAW 23.7.L 0,020 0,4 1,5 0,020 0, ,
MMA 23.8.LR 0,030 <0,9 0,5 0,030 0, ,
SAF 2304 TIG, MIG, SAW ,5 1,6 0, , ,
and MMA ,17 0,030 <1,0 0,8 0,030 0,025 22, ,
SAF ,04 <0,5 0,8 0,030 0, ,
FCAW 2209LT <
SAF 2507 TIG, (MIG), SAW L 0,020 0,3 0,4 0,020 0, ,
MMA LR 0,030 0,5 0,7 0,030 0, ,
LB 0,040 0,4 0,9 0,030 0,025 25,5 9,5 4 0, 5

17. Mechanical properties of the Duplex Stainless Steels
Sandvik UNS Yield strength Tensile strength Elong. Hardness
0,2% offset 1,0% offset A5 Vickers
MPa ksi. MPa ksi. MPa ksi. %
min. min. min. min. min. min. min. approx.
SAF 2304 S
SAF 2205 S
SAF 2507 S 6

18. Mechanical Properties of All Weld Metal
Filler metal Welding Rpo,2 Rp1,0 Rm A5 Z Impact strength, J
Sandvik process MPa MPa MPa % % RT -40°C
23.7.L TIG
23.7.L SAW1)
23.8.LR MMA
L TIG
L SAW1)
LR MMA
LT FCAW
L TIG
L SAW1)
LR MMA
1)Using Sandvik 15W flux 8

19. Mechanical properties of welded joints. Cross-weld tensile test
Parent metal Filler metal Welding Rp0.2 MPa Rm MPa A5, %
Sandvik Sandvik process min. typical min. typical typical
SAF L TIG
23.7.L SAW1)
23.8.LR MMA
SAF L TIG
L SAW1)
LR MMA
LT FCAW
SAF L TIG
L SAW1)
LR MMA
1)Using Sandvik 15W flux 9

20. Charpy-V impact strength of welded joints
Parent metal Filler metal Welding Impact energy, J
Sandvik Sandvik process RT -40°C
SAF L TIG
23.7.L SAW1)
23.8.LR MMA
SAF L TIG
L SAW1)
LR MMA
LT FCAW 55 44
SAF L TIG
L SAW1)
LR MMA
1)Using Sandvik 15W flux 10

21. Typical CPT Values from G-48A Tests for Parent Metals and Welded Joints
Sandvik Filler Welding Shielding Root CPT °C
metal process gas gas
SAF ~15
All weld metal 23.7.L TIG Ar - <15
Joint 23.7.L TIG Ar Ar <15
Joint 23.7.L SAW1) - - <15
Joint 23.8.LR MMA - - <15
SAF
All weld metal L TIG Ar
Joint L TIG Ar Ar 20-23
Joint L TIG Ar - 2% N2 90 N H
(or pure N2)
All weld metal L SAW1)
Joint L SAW1)
All weld metal LR MMA
Joint LR MMA
SAF
Autogenous TIG welding 40
All weld metal L TIG Ar
Joint L TIG Ar Ar 40-45
Joint L TIG Ar 90 N H
Joint L TIG Ar + 2% N2 90 N H
All weld metal L SAW 1)
Joint L SAW 1)
All weld metal LR MMA
Joint LR MMA
1)Using Sandvik 15W flux 11

22. Quench annealing of Duplex Steel welds
Sandvik Holding temperature Quenching
°C media
SAF Water
SAF Water
SAF Water 14

23. Chromium nitrides Intermetallics High quenching temp Rapid cooling
Low quenching temp.
Slow cooling 16

24. Intermetallic phase 17

25. Recommended heat input
Steel Heat input Interpass temperature
SAF ,5 - 2,5 kJ/mm <250°C
SAF ,5 - 2,5 kJ/mm <250°C
SAF ,2 - 1,5 kJ/mm <150°C
Chromium nitrides
Intermetallics 18

26. Welding recommendations
Sandvik Heat input Interpass temperature
kJ/mm °C
SAF ,5 - 2,5 <250
SAF ,5 - 2,5 <250
SFA ,2 - 1,5 <150 19

27. The roll of Nitrogen
Nitrogen is a very important alloying element in DSS
ü Improves corrosion resistance
ü Improves austenite reformation
At TIG welding, the loss of nitrogen is compensated for by using Ar %N2 as a shielding gas 20

28. Ferritic area in SAF 2507 weld owing to the loss of nitrogen in fusion line
Shielding gas Ar 99,99% 21

29. Nitrogen addition to the shielding gas
Ar 99,99%
Ar + 5% N2 22

30. Ferrite content in TIG-welds, SAF 2507
Filler Shielding Root Ferrite content, vol-%
metal gas gas error with 95%
Sandvik confidence interval
L Ar Ar ,5
L Ar % N2 + 10% H ,0
L Ar + 5% N % N2 + 10% H ,0 23

31. Nitrogen Content in TIG welds of SAF 2507. N=0,25% in the filler metal
Filler metal Shielding Root Weight-% N
Sandvik gas gas in deposit
L Ar 90% N2 + 10% H ,23
L Ar + 3% N2 90% N2 + 10% H ,27
L Ar + 6% N2 90% N2 + 10% H ,33 24

32. GMAW SHIELDING GASES General recommendations:
Short arc welding gives very convex beads.
Ar+30 He+1 O2
Spray arc welding
Ar+30 He+1 O2 (22Cr duplex)
Ar+2 CO2(Super duplex)
Pulsed arc welding
Ar(99,996%) for super duplex

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

34. Stress relieving temperatures
°C for 10 hours 26

35. Post Weld Cleaning Pitting potential Pickling bath or pickling paste
HNO3-HF
360
220
120 80
Wire
brush
Blasting 27

36. Dissimilar Joints SAF Carbon steel AISI 200 AISI 904L,
and 300- Sanicro 28,
series 254 SMO, etc.
L L L
LR LR LR
LT LT LT
L L L
L L Sanicro 60
LR LR Sanicro 60 28

37. Joint preparation One sided butt welding29

38. Joint preparation Butt welding from both sides30

39. Tube to tube sheet welding. Joint preparation
45°
>1.5 x WT
>3 mm (0.12”) or >1.5 x WT b a
>WT c d
r >1.5 x WT 31

40. Hydrogen pick-up from covered electrodes Sandvik 25.10.4.LR
MMA
H2, ml/100 g 32

41. Hydrogen pick-up from SAW flux
H2, ml/100 g 33

42. Hydrogen pick up from shielding gas at TIG welding
H2, ml/100 g
TIG - no root gas
Shielding gas
Ar + 10% H2
Shielding gas
Ar + 5% H2 34

43. Hydrogen pick up from shielding gas and root gas at TIG welding
H2, ml/100 g
TIG - with root gas
Shielding gas Ar
Root gas Ar
Shielding gas Ar
Root gas 90% N2 + 10% H2 35

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