Duplex Stainless
Steels
Contents
Answers for today’s challenges........................................................................4
The expert’s voice................................................................................................5
Product positioning..............................................................................................6
Product suitability..................................................................................................8
Chemical composition.........................................................................................9
Mechanical properties.....................................................................................10
Physical properties............................................................................................13
Corrosion resistance.........................................................................................14
Product assortment..........................................................................................16
Fabrication...........................................................................................................17
2
We believe in a world
that lasts forever
The world needs and deserves innovations that pass the test of time and are able to be recycled
and used again at the end of their lifecycle.
Outokumpu stainless steel is durable in the most challenging of conditions delivering ever longer
project lifecycles. The recycled content of Outokumpu advanced materials varies between 70% and
90% depending on the grade and Outokumpu stainless steel is also fully recyclable. The properties
of Outokumpu advanced materials, also make them an economically sustainable solution.
Our vision of a world that lasts forever not only reflects these properties but also our ongoing
commitment to innovation and the development of lasting customer relationships.
Outokumpu Duplex 2205 in Marina Bay bridge, Singapore3
Winning the future –
useful answers for
today’s challenges
The use of stainless steel is increasing fast due to the material's durability, corrosion
resistance and aesthetics. If the right grades are selected, stainless steel lasts hundreds
of years. In the long run, stainless steel is also often the least expensive material, thanks
to low maintenance costs.
Trend 1:
Global economics and striving for stability
When it comes to costs, all parties seek stability. In large-scale
construction projects, the right material choices can multiply savings.
Outokumpu Duplex stainless steel has excellent strength, which often
means the same structure can be built with less material: for example,
tank walls can be considerably thinner. Compared to other grades with
comparable corrosion resistance, the nickel content of Outokumpu Duplex is very low. This means greater price stability and
easier budgeting.
Trend 2:
Rising environmental awareness
In previous years, temporary structures built for world fairs and events
for example, could be demolished after the event. Such a waste
of labour and disregard for the environment is simply not acceptable anymore. Environmental responsibility and legislation have an
increasing impact on operations in every industry. Proof of responsibility
is demanded for the whole life cycle of the product. Those who can offer
action instead of words in social and environmental responsibility will be
the winners of tomorrow.
4
Outokumpu Duplex is an environmentally sound choice from
many different viewpoints:
• It uses recycled steel as its main raw material and it is 100%
recyclable
• Very low level of metal ion is released into the environment.
• Less need of hazardous coatings
• Thanks to high strength, it is possible to reduce the weight of the structures and therefore lower energy consumption in transport, construction and usage
Trend 3:
Ensuring safety, pleasing the eye
In addition to corrosion resistance and durability, constructors face
increasing demands for a human approach: it is no longer enough that
the tanks, vessels and buildings “do their job”. They need to be safe for
both the builders and the employees and be aesthetically pleasing. In
short, Outokumpu Duplex makes it possible to fabricate strong, fascinating structures while reducing the total weight.
The expert's voice
“
Duplex stainless steel was developed by Outokumpu more
than 80 years ago and since that time we have produced more than
half the world’s volume of duplex. Our long history with duplex gives us
a unique insight into the challenges faced by our customers and the
experience and solutions to help them meet these challenges.
Today we offer a complete family of duplex grades and we work with
our customers to select the grade which provides the most suitable
corrosion resistance for its intended use. Duplex grades utilize a more
cost-effective alloy composition – lower nickel and higher nitrogen
content – which provides better price stability than austenitic grades.
Moreover in addition to great corrosion resistance, duplex grades also
offer higher mechanical strength, more than twice as high as standard
austenitic stainless steels or carbon steels. The main advantage of this
is to save weight in the steel structure by reducing the thickness of the
material. This is successfully utilized in applications such as pressure
piping in the oil & gas and offshore industries as well as in large pressure vessels and in large stationary storage tanks in the pulp and paper
industry. The potential weight saving together with high corrosion resistance, less maintenance and no requirement for protective coatings
provides a foundation for more cost effective solutions compared to
carbon steel, particularly when the total life cycle cost is considered.
Outstanding life cycle performance is a strong factor in the choice
of duplex within the building and construction sector where its use
is growing due to a combination of advantageous properties: high
strength, high durability (i.e high corrosion resistance, high wear and
fatigue resistance) and aesthetic surface finishes. The high strength
and toughness of duplex delivers high energy absorption capacity
which combined with reasonable high temperature properties delivers
enhanced fire resistance. This is utilized in blast and fire walls on
offshore platforms to provide safety for the platform personnel.
These beneficial aspects of duplex are also of great interest for other
areas such as evaporator shells in desalination plants, cargo tanks in
chemical tankers, in the severe environments of mining and minerals
processing and in vehicles and chassis components for rail
cars, road tankers and automotive applications.
Claes Tigerstrand,
Outokumpu Research & Development
Duplex applications:
•Pressure piping systems for seawater, chemicals, oil and gas handling etc.
•Pressure vessels like digesters, evaporators, fermenters, autoclaves, water heaters, road tankers etc.
•Storage tanks for pulp, chemicals, biofuels, beverages, grains, ore slurry etc.
•Structural components for bridges, sluice/flood gates, steel frameworks, rebars for concrete structures etc.
•Blast and fire walls on off shore platforms
•Cargo tanks in chemical tankers
•Evaporators in desalination plants
•Heat exchangers in petrochemical plants
•Suction roll shells in paper machines
•Flue-gas cleaning equipment
•Rotors, impellers and shafts
•Vehicle and chassis components
5
More strength – less material
Put simply, the benefit of Outokumpu Duplex lies in weight reduction. You gain more
strength with less material. Below, you can see an example of what happens when
standard austenitic steel is substituted with Outokumpu Duplex.
Calculate your weight savings on the Internet
General benefits provided by Outokumpu Duplex grades:
•Thinner gauges due to higher strength – weight savings and lower cost
•Higher durability and reduced maintenance – longer service life
•Cost efficient alloying by lower nickel content – lower price volatility
Additional benefits - LDX™ concept:
•Leaner alloying compared the regular duplex grades
(i.e. less nickel and higher nitrogen content) – added strength and performance ensuring highest value for money
•LDX 2101® and LDX 2404® can potentially provide more cost efficient solutions for storage tanks and other
structural components
Additional benefits - newly launched EDX™ concept:
•Enhanced properties of already established grades
•EDX 2304™ is primarily developed for offshore topside applications to provide better corrosion performance than standard 2304 or 316L
Additional benefits - newly launched FDX™ concept:
•The new FDXTM product family exhibits a unique combination of high strength and substantially improved formability
utilizing Transformation Induced Plasticity (TRIP)
•The increased formability of FDX 25™ and FDX 27™ allows for utilization of duplex in more complex components such as forming intensive heat exchanger plates
6
E-tools at outokumpu.com offers interactive tools for materials
selection, rough estimation on wall thickness calculations etc.
Less material means benefits in every step of the
project
With Outokumpu Duplex, you can purchase, transport, weld and
assemble less material. When thinking of the cost of labour, savings
can be significant.
Pipes: reduction in wall thickness and weight
between grades 304L and LDX 2101®
Design data
Pressure = 16 bar
Temperature = 50˚C
OD = 610 mm
Grade 304L
Grade LDX 2101®
WT = 6.0 mm
WT = 3.0 mm
Weight = 90 metric Weight = 45 metric tons
tons
Required
Pipe length = 1000 m
Min WT acc to EN 13480-3
Weld factor z = 0.7
304L = 5.8 mm
LDX 2101® = 2.9 mm
WT = wall thickness
OD = outer diameter
Strength, Rp0.2,[MPa], hot rolled coil
Duplex as a substitute for
austenitic in storage tanks
304L
85 metric tons
LDX 2101®
61 metric tons
[m]
600
20
550
18
500
16
Required thickness duplex
Required thickness austenitic
350
300
10
250
2205
4565
254 SMO®
4439
4307
4404
200
4438
904L
4432
150
0
10
20
30
40
50
60
70
80
90
Corrosion resistance, CPT typical
2
14 13 12 11 10 9 8 7 6 5 4 3 2 1
EDX 2304
2304
4
[mm]
2207
®
400
12
6
LDX 2101®
450
14
8
LDX 2404®
Duplex
Austenitic
Figure 1. Great combination of high strength and adequate corrosion
resistance.
Tank cost example 1:
Austenitic steel versus Outokumpu Duplex
Tank cost example 2:
Carbon steel versus Outokumpu Duplex
When the same tank is manufactured from Outokumpu Duplex instead
of conventional austenitic steel, the biggest savings are made in manufacturing phase, thanks to less amount of material needed. The tank
walls can be significantly thinner, yet safe in use.
When the same tank is manufactured from Outokumpu Duplex instead
of carbon steel, the biggest savings come in the maintenance phase:
carbon steel needs to be properly protected in the manufacturing
phase and again after certain periods of usage. All this means extra
labour, which can be avoided using Outokumpu Duplex.
Table 1
Table 2
304L
LDX 2101®
Plate thickness (API 650)
6-14 mm
6-8 mm
Material cost*
240 kEUR
197 kEUR
Welding and assembly cost
81 kEUR
55 kEUR
Surface treatment cost
55 kEUR
55 kEUR
Total manufacturing cost
136 kEUR
110 kEUR
Total initial cost
376 kEUR
Potential cost saving ~18%
Tank size: diameter 20 m, height 20 m.
*Based on typical costs provided by tank manufacturers
and sub-suppliers.
307 kEUR
Carbon steel
A516-60/S235
LDX 2101®
Total initial cost*
366 kEUR
307 kEUR
Recoating cost
75 Euro/m
x 2500 m2
2
No surface
protection required!
Elapsed time between
maintenance events
15 years
Life cycle duration
30 years
30 years
Operating cost
125 kEUR
0 kEUR
Total life cycle cost
491 kEUR
307 kEUR
Potential cost saving ~37%
Tank size: diameter 20 m, height 20 m.
*Based on material, welding, assembly, surface treatment and coating costs.
7
Project checklist
– when to go with Duplex?
Are some of the characteristics listed below relevant for your application?
Then Outokumpu Duplex might be your material of choice.
Demands for material
• resistance to uniform corrosion
• resistance to pitting and crevice corrosion
• resistance to stress corrosion cracking and
corrosion fatigue
• high mechanical strength
• good abrasion and erosion resistance
• good fatigue resistance
• high energy absorption
• low thermal expansion
8
• good weldability
• good formability
• service temperature range within -40°C to 250°C*
*maximum allowable design temperature = 325°C in ASME II-D 2013.
The recipe for success:
ingredients according
to your needs
What makes Outokumpu Duplex such a strong material? The secret lies in connecting
the best of both microstructures: Combining austenite and ferrite. The result is two
crystallographic phases, each with a composition sufficient to make it corrosion resistant.
Favorable properties of both phases can be utilised in one alloy.
The chemical composition of duplex grades gives good corrosion resistance and desired mechanical and physical properties. Outokumpu
can supply you with stainless grades especially designed to meet your
needs.
Molybdenum improves corrosion resistance
Molybdenum improves corrosion resistance in most environments,
particularly in acids and chloride containing environments.
Alloying elements and their purpose
Chromium makes it stainless
A minimum of about 11% chromium has to be added to steel to form
the passive layer that makes it stainless. Outokumpu Duplex steels
have a high chromium level, between 21 and 25%. These contents
improve the corrosion resistance.
Nickel adds toughness
Nickel helps to obtain the desired phase balance and provides toughness. Duplex steels contain a relatively small amount of nickel, between
1.5 and 7%.
Nitrogen adds strength and corrosion resistance
Nitrogen is a very important addition as it gives a substantial increase
in strength and pitting and crevice corrosion resistance. At the same
time it strongly stabilises the austenite phase. Furthermore, nitrogen
improves welding properties.
Outokumpu LDX 2101® in footbridge, Sölvesborg Sweeden
9
Table 3. Chemical composition.
Austenitic
Duplex
Outokumpu
steel name
International steel No
EN
ASTM
UNS
ISO
FDX 25TM
1.4635
-
S82012
-
LDX 2101®
1.4162
-
S32101
2304
1.4362
-
FDX 27TM
1.4637
EDX 2304TM
Chemical composition, % by weight Typical values
C
N
Cr
Ni
Mo
Others
0.022
0.23
20.2
1.4
0.4
Mn Cu
4162-321-01-E
0.03
0.22
21.5
1.5
0.3
5Mn Cu
S32304
4362-323-04-I---
0.02
0.10
23.0
4.8
0.3
Cu
-
S82031
-
0.023
0.18
20.1
3.0
1.25
Mn Cu
1.4362
-
S32304
4362-323-04-I
0.02
0.18
23.8
4.3
0.5
Cu
LDX 2404®
1.4662
-
S82441
4662-824-41-X
0.02
0.27
24.0
3.6
1.6
3Mn Cu
2205
1.4462
-
S322051
4462-318-03-I
0.02
0.17
22.0
5.7
3.1
4501
1.4501
-
S32760
4501-327-60-I
0.02
0.27
25.4
6.9
3.8
2507
1.4410
-
S32750
4410-327-50-E
0.02
0.27
25.0
7.0
4.0
4307
1.4307
304L
S30403
4307-304-03-I
0.02
18.1
8.1
4404
1.4404
316L
S31603
4404-316-03-I
0.02
17.2
10.1
2.1
–
904L
1.4539
904L
N08904
4539-089-04-I
0.01
20.0
25.0
4.3
1.5Cu
254 SMO®
1.4547
-
S31254
4547-312-54-I
0.01
20.0
18.0
6.1
Cu
0.20
1
Mechanical properties
The mechanical and physical properties are beneficial characteristics of
Outokumpu Duplex. The mechanical strength is superior compared to
austenitic or ferritic stainless steels, and the physical properties offer
new possibilities. This is a clear advantage for structural applications,
such as pressure vessels and beam constructions.
Pressure vessel approvals
Outokumpu duplex grades 1.4362 (2304), 1.4462 (2205), 1.4501
(4501) and 1.4410 (2507) are listed in EN 10028-7.
10
W Cu
Also available as S31803
European material approval EAM 0045-01:2012/01 for LDX 2101®
(1.4162) is available for cold rolled 0.5-6.4 mm and hot rolled
3.0-10.0 mm. (LDX 2101® is partly listed in EN 10088).
Work are in progress for European and ASME approvals of LDX 2404®.
In ASME II-D 2007 (Metric) edition grades S31803 (2205), S32304
(2304) and S32750 (2507) are listed for general use between -30°C to
+325°C. Data for LDX 2101® can be found in ASME code case 2418-1.
Table 4. Mechanical properties for flat products at room temperature.
Minimum values,
according to EN 10088
LDX
Outokumpu
typical values
P
H
C
P (15 mm)
H (4 mm)
C (1 mm)
530
500
560
610
2101®
Proof strength
Rp0.2
MPa
450
480
Tensile strength
Rm
MPa
650
680
700
700
755
810
Elongation
A5
%
30
30
30/201
38
35
293
Hardness
HB
225
235
992
450
450
600
620
2304
Proof strength
R p0.2
MPa
400
400
Tensile strength
Rm
MPa
630
650
650
670
765
790
Elongation
A5
%
25
20
20/201
40
30
263
210
235
992
Hardness
HB
TM*
EDX 2304
Proof strength
R p0.2
MPa
420*
500*
500*
600
600
Tensile strength
Rm
MPa
630*
690*
690*
750
770
Elongation
A5
%
25*
25*
25*
30
30
Hardness
HB
290*
290*
290*
550
520
645
640
LDX 2404®**
Proof strength
Rp0.2
MPa
480
550
Tensile strength
Rm
MPa
680
750
750
750
825
850
Elongation
A5
%
25
25
25/20 1)
33
30
243
Hardness
HB max
290
290
290
230
250
500
510
630
690
2205
Proof strength
R p0.2
MPa
460
460
Tensile strength
Rm
MPa
640
700
700
750
840
880
Elongation
A5
%
25
25
20/201
35
30
263
Hardness
HB
230
250
1012
550
580
700
730
2507
Proof strength
R p0.2
MPa
530
530
Tensile strength
Rm
MPa
730
750
750
830
905
940
Elongation
A5
%
20
20
20/201
35
30
243
Hardness
HB
250
270
1032
P = hot rolled plate
H = hot rolled coil and sheet
C = cold rolled coil and sheet
*Mechanical properties according to NORSOK Material Data Specification MDS-D35.
**Mechanical properties according to next revision of EN 10088-2 (to be published end of 2013).
1 Refers to A80 for gauges less than 3 mm. 2 HRB (Rockwell B-scale). 3 A .
80
11
Temperature and embrittlement
High energy absorption
Duplex steels are more prone to precipitation of intermetallic phases,
nitrides and carbides than corresponding austenitic steels, causing
embrittlement and reduced corrosion resistance. The formation of
intermetallic phases such as sigma phase occurs in the temperature
range 600-950°C and decomposition of ferrite occurs in the range
350-525°C (475°C embrittlement). Exposures at these temperatures
should therefore be avoided. In proper welding and heat treatment the
risk of embrittlement is low. However, certain risks exist, for example at
heat treatment of thick sections, especially if the cooling rate is low.
The combination of high strength and ductility gives Outokumpu Duplex
a very good ability to absorb energy. This makes it a perfect material
for applications like blast walls on offshore platforms and car body
components.
Due to the risk of embrittlement, duplex steels should not be used at
temperatures above 250-325°C (See Figure 2). The maximum temperature depends on grade and the design rules being used.
Figure 2. Curves for 50% reduction of impact toughness compared to
solution annealed condition.
Good fatigue strength of base material
The high tensile strength of Outokumpu Duplex also implies high fatigue
strength in the base material. The fatigue strength of the duplex steels
follows the proof strength of the material. Our technical experts can
provide you with more detailed information, if needed.
For welds, the benefit of the high fatigue strength of the parent or base
material is limited. The fatigue strength is, like other materials, reduced
by unfavorable weld geometry, residual stresses, distortions and weld
defects.
Table 5. Impact toughness. Minimum values according to
EN 10028-7 transverse direction for hot rolled plate.
LDX 2101®*
2304
LDX 2404®**
2205
2507
20°C
60 (801)
90
60
100
90
-40°C
27 (501)
40
40
40
40
Temperature (˚C)
1100
1000
2507
2205
900
*Values from internal standard, AM 611.
**Values from internal standard, AM 641. according to
internal specification.
1
Value according to EAM-0045-01:2012/01 for thicknessess up to and including 10mm.
LDX-2101®
800
2304
700
600
500
400
300
0.01
(36 s)
12
0.02
(6 min)
1,0
10
100
1000
Time (h)
Physical properties:
new opportunities
Compatible with carbon steel
Outokumpu Duplex grades have a lower thermal expansion ratio
(approximately 13 × 10 -6/°C) and higher thermal conductivity than
austenitic steels. This means that there are fewer problems with
temperature expansions caused by connecting Outokumpu Duplex
with carbon steels. Duplex is a good alternative for lining carbon steel
vessels operated with large cyclic temperature variations.
Magnetic properties
Duplex stainless steels are more magnetic than austenitic grades due
to higher ferrite content. But for safety reasons magnets shall not be
used to lift duplex sheets.
Table 6. Physical properties of duplex
stainless steels, according to EN 10088.
Physical property
20°C
200°C
Density [g/cm3]
7.8
-
Modulus of elasticity [GPa]
200
186
Poisson ratio [Dimensionless]
0.3
-
-
13.5
Thermal conductivity [W/m°C]
15
17
Thermal capacity [J/kg°C]
500
560
Electric resistivity [μΩ/m]
0.8
0.9
Linear expansion from
20°C to 200°C (x10-6/°C)
Palm oil tank farm in LDX 2101®. Photo courtesy of Loders Croklaan.
13
Corrosion resistance in a
wide range of environments
The corrosion resistance of Outokumpu Duplex is generally very good. The resistance is
especially good in environments such as halide containing media, oxidising acids, and hot
alkaline solutions. This means that, for example, heat exchangers, water heaters, offshore
equipment, storage tanks, sulphate pulp digesters, black liquor evaporators and flue gas
cleaning equipment greatly benefit from the material properties of duplex steels.
Uniform corrosion
The uniform corrosion resistance is generally considered good if the
corrosion rate is less than 0.1 mm/year. Thanks to their high chromium
content, duplexes offer excellent corrosion resistance in many media,
especially in alkaline solutions.
Pitting and crevice corrosion: heat exchangers, water
heaters, offshore equipment, storage tanks etc.
In chloride solutions LDX 2101® has better resistance than 4307 and
in some cases as good as 4404. Grade 2304 is in most cases equivalent to 4404, while the other more highly alloyed duplex steels show
even better resistance. The resistance to pitting and crevice corrosion
is often illustrated by the pitting resistance equivalent (PRE) for the
material. The most commonly used formula for PRE is:
PRE = %Cr + 3.3 x %Mo + 16 x %N
The PRE value can be used for the ranking of different stainless steels,
see Table 7. A more in depth way to rank steels is measuring the Critical Pitting corrosion Temperature (CPT). Outokumpu uses an electrochemical method, ASTM G150, based on the in-house developed
Avesta Cell, see Figure 3.
Chloride and sulphide induced stress corrosion
cracking: boreholes and gas wells etc.
All duplex grades are much more resistant than the standard austenitic
grades to chloride induced stress corrosion cracking (SCC). Thus, the
14
duplex grades can tolerate higher chloride contents at elevated
temperatures. In the presence of hydrogen sulphide and chlorides (e.g.
sour conditions in bore holes and gas wells) the risk of stress cracking,
at low temperatures, increases. In these environments Outokumpu
Duplex grades, especially 2205 and 2507, have demonstrated good
resistance.
Corrosion fatigue and intergranular corrosion
The combination of high mechanical strength and very good resistance
to corrosion gives duplex steels superior corrosion fatigue strength. Due
to the duplex microstructure and low carbon content, the duplex grades
have a good resistance to intergranular (intercrystalline) corrosion.
Erosion corrosion
In general, stainless steel offers good resistance to erosion corrosion.
Duplex grades are especially good due to their combination of high
surface hardness and good corrosion resistance.
Galvanic corrosion
Galvanic corrosion may occur when two dissimilar metals are electrically connected (as by welding) in an electrolyte. Stainless steel is in
most cases more nobler than other metallic materials. The more noble
metal is protected while the less noble metal is more severely attacked
by corrosion. The electrolyte, area ratio, and the less noble metal determines the corrosion rate. Stainless steel in contact with carbon
steel rebars fully cast in concrete does not cause galvanic corrosion of
the carbon steel reinforcement due to the high pH in concrete. Galvanic
corrosion does not occur between different grades of stainless steels
as long as both grades are in passive state.
The Outokumpu Corrosion Handbook
Atmospheric corrosion
Atmospheric corrosion is not a unique form of corrosion, but a
collective term to denote the corrosion of surfaces in the atmosphere.
When stainless steel is exposed to an aggressive atmosphere it is
primarily stained. This is sometimes referred to as tea staining, but it
Table 7. PRE values for different
grades.
Outokumpu
steel name
PRE
CPT, (˚C)
18
100
LDX 2101®
26
90
4404
24
80
FDX 25TM
25
70
2304
26
60
27
50
EDX 2304
28
40
LDX 2404®
33
30
904L
34
2205
35
254 SMO®
43
2507
43
FDX 27
TM
For more information on corrosion and corrosion resistance in different
media, see further the Outokumpu Corrosion Handbook. You can obtain
your own copy from your local sales office.
Figure 3. Typical critical pitting corrosion temperatures (CPT) in 1M NaCl measured according to ASTM
G150 using the Avesta Cell. Test surfaces wet ground to 320 mesh. CPT varies with product form and
surface finish.
4307
TM
can also be attacked by localised corrosion with time, particularly at
high chloride levels as in marine atmospheres. Today there are duplex
grades available for any type of atmosphere.
20
*
10
0
4307 LDX 2101®
4404
2304
4432 EDX 2304TM LDX 2404® 2205
904L
2507
254 SMO®
span CPT min. -CPT max.
*
= Less than 10° C
15
Product assortment
and services
Outokumpu Duplex is available in various shapes and sizes to
suit your needs.
• Hot rolled quarto plate
• Hot rolled coil and plate
• Cold rolled coil and sheet
• Precision strip
• Semifinished (bloom, billet, ingot and slab)
• Bar, wire rod and rebar
• Welded tube, pipe, fittings and threaded fittings
• Structural sections, DUPROF TM
• Fasteners
Our added value services ease your project and offer ways
to save expenses at critical points
• Edge preparation
• Cut to shape
• Bending
• Surface finishing: 1D, 2E, 2B, 2R
• Polishing
• Construction kits
• Prefabrication
• Modified chemical analysis
• Slit coils
• Package solutions
• Welding advice
• Technical support/Project administration
‘2B’ surface finish – perfect for food & health sectors
Surface finish characteristics are not merely a question of appearance.
The quality affects the corrosion resistance as well as the cleansability
of dirt and bacteria, which is paramount in the food industry and health
sector. Outokumpu can additionally offer a ‘2B’ surface finish in duplex
stainless steels, which most often fulfills the industry surface requirements without any further surface treatment – saving both time and
money.
See our product programme in the online tool Stainless Steel
Finder at outokumpu.com
16
Table 8. Surface finishes.
Finish
Type of process route
Surface appearance
1D
Hot rolled, heat treated,
pickled.
Standard for most steel
types to ensure good
corrosion resistance;
also common finish for
further processing. Rough
and dull.
2E
Cold rolled, heat treated,
mechanically descaled
followed by pickling.
Rough and dull.
2B
Cold rolled, heat treated,
pickled, skin passed. Skin
passing can be done by
tension levelling.
Smooth surface with low
lustre.
2R
Cold rolled, bright annealed.
Smoother and brighter
than 2B.
Fabrication
Outokumpu Duplex offers excellent opportunities when constructing challenging and durable
structures. However, due to the high strength of the material, the working process is
somewhat different than with austenitic or ferritic steels. Outokumpu is prepared to assist
you with every technical aspect of fabrication. We can provide you with the necessary
training, computer simulations and detailed instructions.
Welding
Outokumpu Duplex can be welded with most of the methods used for
austenitic stainless steel:
• Shielded metal arc welding (SMAW)
• Gas tungsten arc welding TIG (GTAW)
• Gas metal arc welding MIG (GMAW)
• Flux-cored arc welding (FCAW)
• Plasma arc welding (PAW)
• Submerged arc welding (SAW)
• Others: Laser, resistance and high frequency (HF) welding
In general, the main issue with welding Outokumpu Duplex is to maintain the phase balance in the heat affected zone without precipitations. The chemical composition balances the microstructure. Therefore, it is important to have the right welding consumable and the right
procedure.
The following general instructions should be considered:
1. Weld without preheating
2. Allow the material to cool between passes, preferably to below 150°C. For 2507 ≤ 100°C
3. Duplex filler material is required and recommended with the
exception for LDX 2101® which may be welded without filler material in some cases
4. The recommended arc energy should be kept within specified limits
5. The heat input should be adapted to the steel grade and adjusted to the thickness of the welded material
6. Edge preparation angle should be about 10° greater and the land should be somewhat smaller compared to welding standard
austenitics
7. If welded with filler, post-weld annealing is not necessary. In cases where heat treatment is considered, e.g. for stress relieving, it should
be carried out in accordance with the temperatures stated in Table 9, but with the minimum temperature increased by 30-50°C, to secure full dissolution of intermetallic phase in the weld metal
8. GTAW and PAW methods: addition of nitrogen (1-2%) in the shielding/
purging gas is recommended
Table 9. Characteristic heat treatment temperatures, °C.
LDX 2101®
2304
LDX 2404®
2205
2507
Hot forming
1100 - 900
1100 - 900
1120 - 900
1150 - 950
1200 - 1025
Quench annealing
1020 - 1080
950 - 1050
1000 - 1120
1020 - 1100
1040 - 1120
Stress relief annealing
1020 - 1080
950 - 1050
1000 - 1120
1020 - 1100
1040 - 1120
17
Table 10. Welding consumables.
Steel grade
Consumable ISO designation
Typical chemical composition, % by wt.
C
Cr
Ni
Mo
N
23 7 NL
0.02
23.5
8.0
0.3
0.14
22 9 3 NL
0.02
22.5
8.5
3.0
0.15
23 7 NL
0.02
23.5
8.0
0.3
0.14
22 9 3 NL
0.02
22.5
8.5
3.0
0.15
23 7 NL
0.02
23.5
8.0
0.3
0.14
22 9 3 NL
0.02
22.5
8.5
3.0
0.15
22 9 3 NL
0.02
22.5
8.5
3.0
0.15
23 7 NL1
0.02
23.5
8.0
0.3
0.14
22 9 3 NL1
0.02
22.5
8.5
3.0
0.15
22 9 3 NL
0.02
22.5
8.5
3.0
0.15
22 9 3 NL
0.02
22.5
8.5
3.0
0.15
25 9 4 NL
0.02
25
9.5
3.5
0.25
FDX 25TM
LDX 2101®
2304
FDX 27
TM
EDX 2304TM
LDX 2404®
2205
2507
1 Although both 23 7 NL and 22 9 3 NL welding consumables can be used, it is recommended to use the higher alloyed 22 9 3 NL filler in order to match the
higher tensile strength and improved corrosion resistance of the EDX 2304™ grade.
Welding to other steels including carbon steels
Outokumpu Duplex can be easily welded to other steels including
carbon steels. The filler type can be duplex. When duplex steels are
welded to carbon steels an alternative is to use a filler of 23Cr13Ni2Mo
type. In most cases duplex filler offers more strength and better corrosion resistance. When joining duplex to super austenitic steels, please
contact Outokumpu for assistance. Filler metals for joining similar
duplex steels, see table 10.
18
Post weld treatment
In order to restore the stainless steel surface and achieve good corrosion resistance, it is necessary to perform a post weld treatment.
There are both mechanical methods (e.g. brushing, blasing, grinding)
and chemical methods (e.g. pickling) available. The applicable method
depends on the type of imperfections to be removed, as well as corrosion resistance, hygiene and aesthestic requirements.
The Outokumpu Welding Handbook
For more information on welding and post weld treatment, please see
the Outokumpu Welding Handbook.
Table 11. Things to consider
Forming
Cutting, shearing
Outokumpu Duplex is suitable for all forming techniques. The higher
strength and the lower elongation compared to austenitic stainless steel
will however impose some differences in forming behaviour: Generally
a higher force is needed. On the other hand, since duplex design often
implies downgauging, the force level can be similar to
austenitics. If the forming technique is not already decided, we recommend choosing the most appropriate one for duplex stainless steels.
Maximum thickness for shearing and
punching is 80-85% of that of austenitic
steel.
Roll bending
More bending force will be needed
compared to other stainless steels.
Through the downgauging, this effect
will however be smaller than anticipated.
The springback due to the higher strength
is large when roll bending.
Break bending
Avoid sharp bending radius. Minimum ratio
between inner radius to sheet thickness
should not be less than 2.
Deep drawing
If drawing is dominant, formability is
comparable to austenitic stainless steel.
If stretching is dominant, formability is
closer to ferritic steels.
Stable setup
Due to the higher strength the cutting forces will be higher, which
increases the risk of vibrations. The trick is to have a stable setup. Use
the shortest possible tool extension, good and rigid clamping.
Roll forming
The high strength of the sheet has to be
considered in the design of the rolls.
If properly designed there are no problems
in roll forming Duplex.
Sharp tools
Use cutting tools with a positive geometry. Duplex grades are prone
to work hardening, a dull geometry will generate a hard surface and
decrease the tool life.
Tooling use
Strong, durable tools (hardness, HRC larger
than 500, Ra-value preferably lower than
0.2 micrometers).
Lubrication
Because of the high strength of
Outokumpu Duplex and extreme pressure
additives are useful in complex forming
operations.
FDX 25™ and FDX 27™
The new FDX product family exhibits substantially improved formaility. The elongation after fracture is typically about 40% compared to
about 30% for other duplex grades, which make them more suitable for
advanced forming.
Machining
The high strength will of course effect the machinability, but not as much
as expected. Some technical guidance when machining duplex, is given
below. See also the duplex machining guidelines for further details.
Avoid “build up edge”
Stainless steels have a tendency to stick to the tool. Problems occur
when the cutting speed is too low. The main difference between carbon
steel and stainless steels when machining is that you face problems if
you run too slowly. The result will be poor surface finish and short tool
life. The problem is solved by increasing the cutting speed.
LDX 2101®
The lean duplex grade LDX 2101® has superior machinability compared
to other duplex grades. Even if you compare with the low alloyed
standard austenitic grades LDX 2101® is easier to machine.
19
1528EN-GB:1. December, 2013.
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forever.
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long lasting solutions for the tools of modern life
and the world’s most critical problems: clean energy,
clean water and efficient infrastructure. Because we
believe in a world that lasts forever.
Information given in this brochure may be subject to alterations without notice. Care has been taken to ensure that the contents of this publication are accurate but
Outokumpu and its affiliated companies do not accept responsibility for errors or for information which is found to be misleading. Suggestions for or descriptions of the
end use or application of products or methods of working are for information only and Outokumpu and its affiliated companies accept no liability in respect thereof. Before
using products supplied or manufactured by the company the customer should satisfy himself of their suitability.
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