Welding Duplex Stainless Steel

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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  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

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

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

Yield Strength 0,2% Austenitic vs Duplex Stainless Steel SAF 2507

600 500

SAF 2205

SAF 2304

400

6Mo+N

300

316L 200 100 0

904L

Coefficient of expansion (x10-6)°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 316L 0

5

10

15

-6 20 (x10 )

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

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

0,0

0,2

0,4

Strain

0,6

0,8

Reasons for the high strength of duplex stainless steels



Content of ferrite



Fine grained structure



Nitrogen

Embrittling of Duplex Stainless Steels

Welding Processes Conventional Processes

Avoid

 GTAW

 Autogenous

 GMAW

 Low Energy Processes

 SAW

 Or Perform PWHT

 SMAW  FCAW

Filler Metals for the Welding of Duplex Stainless Steels Parent Welding metal process Sandvik

Filler metalChemical composition, wt-% Sandvik C Si Mn P S Cr max. max. 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 30-40

SAF 2304 TIG, MIG, SAW and MMA SAF 2205 FCAW

2209 0.020 2209-16,17 0,030 2209-15 0,04 2209LT 0.030

8 9 9 9

3 3 3 3

0,14 0,12 0,15 0.15

30-40 30-40 30-40 30-40

0,4 0,020 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 0,25 0,25

30-40 30-40 30-40

0,020 0,4 1,5 0,020 0,015 23 0,030