19. sandvik matr. tech , clemente tallarico
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SandvikTRANSCRIPT
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High Alloyed Duplex and Austenitic Stainless Steels. Aspects on Welding
and Fabrication
Clemente Tallarico
Author:
Claes-Ove Pettersson
Peter Stenvall
Zhiliang Zhou
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Sandvik Materials Technology
Contents
Introduction
Materials High alloyed Austenitic Stainless Steels
High alloyed Duplex Stainless Steels
Physical and mechanical properties
Machinability and cold working
Welding Joint preparation
Heat input
Shielding and purging gases
Filler metals
Welding Processes
Welding defects
Discussion and conclusions
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Introduction
Harry Brearly 1913
Classification of Stainless Steels
Martensitic
Martensitic-Austenitic
Ferritic
Austenitic
Austenitic-Ferritic
Development of new steels is ongoing for, in principle, all five groups
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Materials
This presentation focus on Austenitic and Austenitic-Ferritic Stainless Steels
Following examples are chosen:
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Properties as a function of alloy content
In general, increasing alloy content => higher corrosion resistance
PRE as a function of alloy content
010
203040
5060
N08904 S31254 S32654
Alloy
PR
E=
Cr+
3.3
xM
o+
16
xN
PRE as a function of alloy content
0
10
20
30
40
50
60
S32205 S32750 S32707
Alloy
PR
E=C
r+3.3
xM
o+16xN
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Properties as a function of alloy content
Mechanical properties, Proof strength
Proof strength, 0,2% offset as function of alloy
content, MPa
0
200
400
600
800
S32205 S32750 S32707
N08904 S31254 S32654
Alloy
Pro
of
str
en
gth
,
0,2
%,M
Pa
Austenitic
Austenitic-Ferritic
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Properties as a function of alloy content
Elongation, A5
Elongation,A5, as function of alloy
content
0
10
20
30
40
S32205 S32750 S32707
N08904 S31254 S32654
Alloy
Elo
ngat
ion,
A5
%
Austenitic
Austenitic-ferritic
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Structure stability
Structure stability decreases with increasing alloy content (Cr, Mo)
Sensitive temperature range
Austenitic, 900 1050C
Austenitic-Ferritic, 800 950C
Austenitic-Ferritic steels are also prone to 475C embrittlement
Influences welding6 0 0
6 5 0
7 0 0
7 5 0
8 0 0
8 5 0
9 0 0
9 5 0
10 0 0
10 5 0
1 10 10 0 10 0 0 10 0 0 0
Time, minT
em
pe
ratu
re,
C
S 3 2 7 5 0
S 3 2 7 0 7
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Machinability and Cold working
The machinabilty decreases with increasing alloy content
Austenitic-Ferritic steels somewhat better compared to the
austenitic, eg. N08904 in the
same area and even lower than
S32750
Excessive wear on the rake face of the tungsten carbide bit
Machinability
Corrosion res.
AISI 304
AISI 316
SAF 2205
SAF 2507
Austenitic
Duplex
SAF2707HD
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Cold working
More force needed with increasing yield strength (increasing alloy content)
Austenitic-Ferritic steels give more spring back than Austenitic steels at cold forming
A cold work up to approximately 10% can be done without stress relieving (These steels have good resistance to stress corrosion
cracking)
Local heat treatment of the cold worked area is very difficult and not recommended
If heat treatment is necessary, a full quench annealing cycle has to be done (Often difficult in practice)
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Welding(Joint preparation)
Compared to 300-series stainless steels, high alloyed duplex and
austenitic steels need a wider
gap and a more open angle due
to the poorer fluidity of the weld
metal
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Heat input
Excess heat input shall always be avoided when welding
stainless steels
Austenitic steels more sensitive to excess heat input than
austenitic-ferritic steels
Very important that the interpass temperature is kept
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Shielding gas and Purging gas
Nitrogen is an important element
Austenite formation
Corrosion resistance
At TIG welding with pure argon as shielding and root gas,
nitrogen is lost and must be
compensated for in order to
maintain the corrosion resistance
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Ferritic area in UNS 32750 weld owing to the loss of nitrogen in fusion line
Shielding gas Ar 99,99%
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Filler metal
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Filler metal
Highly alloyed austenitic steels are with advantage welded with nickel-based filler metals
Austenitic-ferritic stainless steels are welded with austenitic-ferritic filler metal with the exception of dissimilar joints with
highly alloyed austenitic steels. Then nickel-based fillers have to
be used
Welding austenitic-ferritic steel with nickel-based filler metal gives phenomenons like
Un mixed zones (UMZ)
Nitrogen depleted fusion line
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Filler metal
UMZ in root area with sigma Ferritic area in fusion line UMZ in top of weld
Root with normal duplex
structure. Filler 27.9.5.L
Top of weld, normal duplex
structure
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Welding processes
The highly alloyed stainless steels are welded by the common arc welding processes
Welding processes giving high heat inputs, eg SAW shall be used with care for the highest alloyed steels
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Welding defects
Porosity can occur in nitrogen alloyed steels
At for instance SAW a dry flux is important.
Drying at 370-380C for 4 hours
Too high travel speeds at SAW also promote hot cracking. Aim for an oval shaped weld pool!
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Discussion and conclusion
In general, higher alloy content of a stainless steel => improved properties regarding corrosion resistance and mechanical
strength. Problem solvers in severe corrosive environments
Higher alloyed steels => more knowledge needed in fabrication regarding welding, cold working and heat treatment
Close contact with the material supplier recommended
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Firstname Surname
Title
Unit, Sandviken Sweden
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