3. • Fully austenitic steels was first produced in 1950’s.
• One example was Avesta H030 (6Mo steel).
• These types of steels was very sensitive for intermetallic
precipitations.
• In 1970’s a new type of N-alloyed fully austenitic steel was
introduced:
• Avesta 254 SMO (20Cr, 18Ni, 6,1Mo, 0,20N)
And then...
• Avesta 654 SMO (24Cr, 22Ni, 7,3Mo, 0,50N)
FULLY AUSTENITICS – History
4. 6Mo-steels found its first applications in the
offshore industry
FULLY AUSTENITICS – History
5. Parent material EN ASTM/AWS C N Cr Ni Mo Other
Grade 904L
4529
254 SMO
4565
1.4539
1.4529
1.4547
1.4565
N08904
N08926
S31254
S34565
0,01
0,01
0,01
0,02
-
0,20
0,20
0,45
20
20
20
24
25
25
18
18
4,3
6,4
6,1
4,5
Cu 1,5
Cu
Cu
Mn 6
Welding
consumable
EN AWS4)
MMA 904L
P12 R Bas
P625
P54
P16
20 25 5 Cu L
Ni Cr 21 Mo Fe Nb
Ni Cr 22 Mo 9
-
Ni Cr 25 Mo 16
E385
ENiCrMo-12
ENiCrMo-3
-
ENiCrMo-13
0,02
0,02
0,02
0,02
0,02
-
-
-
0,35
-
20,5
21,5
21,5
25,5
25,0
25,0
Rest
Rest
25,5
Bal,
4,5
9,5
9,5
5,0
15,5
Cu 1,5
Nb 2,2 Fe<2
Nb 3,5 Fe<1,5
Cu 0,8
Nb<0,1
Wire 904L
P12
P12-0Nb
P54
P16
20 25 5 Cu L
Ni Cr 22 Mo 9 Nb
Ni Cr 22 Mo 9
-
Ni Cr 25 Mo 16
ER385
ERNiCrMo-3
ERNiCrMo-20
-
ERNiCrMo-13
0,01
0,01
0,01
0,02
0,01
-
-
-
0,35
-
20,0
22,0
22,0
26,0
25,0
25,5
Rest
Rest
22,0
Rest
4,5
9,0
9,0
5,5
16,0
Cu 1,5
Nb 3,6 Fe<1
Nb<0,1 Fe<1
N0,35
Nb<0,1 Fe<1
FCW FCW-3D
P12
- ENiCrMo3T1 0,02 – 21,5 Rest 9,0 Nb 3,3 Fe<1
FULLY AUSTENITICS – Chemical Composition
7. Development of welding consumables:
1. “SMO composition” will cause Mo-segregation (4-11%Mo)
giving reduced corrosion resistance
2. High Mo-content will increase the risk getting hot cracking.
3. High content of Ni (i.e. Nickel base) will depress the
tendency of segregation
Nickel based filler with high Mo (9/15 Mo)
FULLY AUSTENITICS – Chemical Composition
8. P12/P12-0Nb/P16
• P12 is the standard filler for welding 6-Mo steels however
some alternative exists:
• P12-0Nb gives extra low content of secondary phases which
favours high ductility (KV~200J). Positive when welding
SAW.
• P16 can be used if requires extra safety against pitting
corrosion in root runs etc.
FULLY AUSTENITICS – Chemical Composition
9. 254 SMO welded using
AVESTA P12
254 SMO welded using
AVESTA P12-0Nb
Root, x600 Root, x600
FULLY AUSTENITICS – Microstructure
10. 6-Mo steels solidify with a fully austenitic structure
without any presence of ferrite.
Ferrite has positive influence dissolving impurities such as
sulphur, phosphorus etc that easily forms low solidifying
phases that segregate to the grain boundaries
and causes films of segregation.
6-Mo steels are therefore produced
with lowest possible amounts of
impurities.
FULLY AUSTENITICS – Microstructure
11. The segregation makes 6-Mo reduces the
properties:
• Decreased corrosion resistance
• Decreased impact strength - ductility
• Risk of getting hot cracking
FULLY AUSTENITICS – Microstructure
15. 254 SMO
• Extremely good resistance against pitting and crevice
corrosion
• Cu additions gives improves the resistance in sulphur
containing acids
• Good resistance against stress corrosion cracking
654 SMO
• Superior resistance against pitting and crevice corrosion
• Cu additions gives improved resistance in sulphur containing
acids
• Very good resistance against stress corrosion cracking
FULLY AUSTENITICS – Corrosion properties
16. • Fully austenitic stainless steels possess extremely good
corrosion resistance.
• Very good resistance against stress corrosion cracking.
• Very good impact strength even at low temperatures.
• Somewhat more sensitive for hot cracking than 304/316
type steels.
FULLY AUSTENITICS – Conclusion properties
18. Heat input= Current x Voltage
Travel speed
A x V
1000 x mm/s
=kJ/mm
254/654 SMO should be welded
with a heat input not exceeding
1,2 kJ/mm
FULLY AUSTENITICS – Heat input
19. • Avoid small joint angels
• Full penetration is necessary (root gap)
• Machining of edges or plasma cutting followed by smooth
grinding
• Cleaning after preparation
Never weld 254 SMO without filler metal
unless the complete construction can be
quench annealed after welding
FULLY AUSTENITICS – Joint preparation
20. GMAW, SMAW, GTAW
I-joint, t=1,5-3 mm
A=2-2,5 mm
V-joint, t=4-16 mm
A=70°
B=1,5-2 mm (ss 0,5-1,5 mm)
C=2-2,5 mm
A
B
C
A
FULLY AUSTENITICS – Joint preparation
21. 3-4 mm
90°
90°
Welding 254 SMO using SAW
requires big care about joint
preparation.
Welding is best performed using X-
joint or double U-joint.
Dilution and heat input must be
minimised thus the risk of getting hot
cracking is rather big.
Root land: 3-4 mm
Joint angel: 80-90°
FULLY AUSTENITICS – Joint preparation
22. • Closer between tack welds compared to mild steel and
austenitic standard steels
• Tack welds should be removed before welding
FULLY AUSTENITICS – Joint preparation
23. AVESTA P12-R Basic ENiCrMo-12 / NiCr21MoFeNb
- For welding 6-Mo steels.
- Medium Niobium content highest safety against
cracking.
AVESTA P16 Basic ENiCrMo-13 / ENiCr25Mo16
- For welding 7-Mo & 4565 steels
- Composition similar to alloy 59
AVESTA P625 Basic ENiCrMo-3 / NiCr22Mo9Nb
-High Niobium content for high temperature
applications.
- For welding P625 nickel base material.
FULLY AUSTENITICS - Welding methods MMA
AVESTA P54 Basic
- Iron based filler for oxidising environment
- For welding 254 SMO, 7-Mo & 4565 steels
24. FULLY AUSTENITICS - Welding methods MIG
AVESTA P54
AVESTA P12 ENiCrMo-3 / NiCr22Mo9Nb
AVESTA P16 ENiCrMo-13 / NiCr25Mo16
AVESTA P12-0Nb ENiCrMo-20 / NiCr22Mo9
MIG/MAG welding is best performed using a pulsed arc. Spray arc gives
somewhat lower arc stability with enhanced spatter.
25. MIG/MAG welding
Shielding gases:
1. Ar+30%He +0,03%NO
3. Ar or Ar+0,03%NO (MISON Ar/AGA)
Gas flow: 14-16 l/min
Ar + He-addition Pure Ar
FULLY AUSTENITICS - Welding methods
26. Always use rot gap: 2-2,5 mm
Shielding gas: Ar or Ar + 2%N2
Purging gas: Ar or Ar + 2%N2 or 90%N2 + 10%H2
Welding should not be performed without the addition of filler metal
AVESTA P54
AVESTA P12 ENiCrMo-3 / NiCr22Mo9Nb
AVESTA P16 ENiCrMo-13 / NiCr25Mo16
AVESTA P12-0Nb ENiCrMo-20 / NiCr22Mo9
FULLY AUSTENITICS - Welding methods TIG
28. GTAW (TIG)
• Increased nitrogen content (up to 3%) give increased corrosion resistance.
• Welding without filler metal give low result
• P16 can be used for root runs to increase the safety against pitting corrosion
FULLY AUSTENITICS - Welding methods TIG
30. Submerged arc welding (SAW)
• SAW welding of 254 and 654 SMO should be performed using a basic
flux type AVESTA 805.
• Flux 805 is an agglomerated slightly Cr-compensated flux with
basicity 1,7 (Bonizewski)
• Welding should take place considering the risk of getting hot cracking.
• By using Avesta P12-0Nb or P16 the safety is somewhat higher due to
a “sigma phase free” weldment
FULLY AUSTENITICS - Welding methods SAW
32. Bildplacering
• High energy and focused arc
• High welding speed
• High quality weld metals with low deformation
• Good weld metal properties i.e.
impact toughness
• Good penetration using keyhole
• Plate thickness up to 8 mm
• Suitable for:
• Automatic and mechanised welding
• Longitudinal pipe welding
• Root PAW followed by TIG or SAW
• Filler wire unless PWHT can be performed
Characteristics
FULLY AUSTENITICS - Welding methods PAW
33. Plasma (PAW)
Plasma welding should be performed with the addition of filler
P12/P12-0Nb/P16.
Welding without filler should be avoided thus this will cause high
segregation of Mo resulting in a lower corrosion resistance
unless quench annealing can be performed.
Shielding gas
Ar (10-15 l/min)
Plasma gas
Ar or Ar+20%He+2%N2 (5-7 l/min)
Purging gas
Ar or 90N2+10H2 (30-40 l/min)
FULLY AUSTENITICS - Welding methods PAW
34. • All welding methods suitable (FCW low availability)
• Sufficient root gap to ensure full penetration
• Max heat input 1,2 kJ/mm
• Always weld with addition of filler metal (Ni-bas)
Be careful with:
• striking scars
• crevice
• oxides
• grinding
FULLY AUSTENITICS – Conclusions Welding
methods
37. Hot cracking can be caused by:
• High degree of restrain
• High heat input
• Wrong joint angel
FULLY AUSTENITICS – Be aware of…
38. Welding should always be performed using sufficient rot gap
for good penetration.
2-2,5 mm root gap
FULLY AUSTENITICS – Be aware of…
39. Stainless steels are relatively sensitive for porosity caused
by moist electrodes, moist in weld joint, colour (primer) or
lack of shielding gas.
FULLY AUSTENITICS – Be aware of…
40. Striking scars, grinding scars, surface oxides, crevice all
decreases the corrosion resistance
repair welding must be performed using filler
FULLY AUSTENITICS – Be aware of…
41. The fluidity and arc stability when MIG/MAG welding is somewhat
lower than for type 316L-Si. Welding should be performed using a
pulsed arc and preferable with a 30% He addition.
FULLY AUSTENITICS – Be aware of…
42. • 6Mo-steels should be welded using nickel based fillers
• Welding without filler give Mo-segregation low
corrosion resistance/cracking
• Too a high heat input and improper joint figuration can
cause hot cracking
• Small root gap increases the risk for incomplete
penetration and porosity
Use right filler, follow specifications and weld with
recommended heat input max 1,2 kJ/mm
FULLY AUSTENITICS – Conclusions
47. FULLY AUSTENITICS – Information material
• Guidelines - How to weld …
• Under development
• Welding procedures
• Fact sheets
• Brochures
• Data sheets
• The Avesta Welding Manual (Ed. 3.)
• Web site
www.avestawelding.com
