DuplexSS-5

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Metallurgy and Materials Engineering DepartmentUniversity of Indonesia2007

Karakteristik Dan Pemilihan Material

Duplex Stainless Steel

Dr.-Ing. Bambang SuharnoDr. Ir. Sri Harjanto

University of Indonesia

Department of Metallurgy and Materials Engineering UI

History of Duplex Stainless Steel

1929 : Avesta Jernverke (25% Cr, 5% Ni)1933 : J-Holtzer Company, France,

salah komposisi dari 18%Cr-9%Ni-2.5%Mo (AustenitikSS) menjadi 20%Cr-8%ni-2.5%Mo (Duplex SS)dimana terdapat fasa ferrite dalam matriks austenite, ketika di heat treatment ternyata tidak sensitif terhadapintergranular corrosion

1970 : Duplex di kembangkan di Germany danSwedia (sejalan dengan ditemukannya AOD process)1980 : Dikembangkan Super Duplex SS, ditandaidengan nilai PREN > 40 (= %Cr + 3.3% Mo + 16% N)



Phase Diagram of Duplex SSUniversity of

Indonesia


Metallurgy of Duplex SS

Selama solidification, duplex pertama kali membentuk ferrite Pada penurununan temperatur austenite terbentukPada cast duplex

a structure of austenite islands in a ferrite matrix (dark)Pada wrought alloys

the microstructure has a morphology of laths of austenite in ferrite matrix (dark)

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Typical Microstructure of Duplex SS (wrought and cast)

wrought

cast



Microstructure of Duplex SS

Duplex stainless steels have microstructures a mixture of austenite and ferrite

The microstructure shows an image of a duplex 3RE60 grade

ferrite



Ferrite Phase

Keberadaan ferrite dalam austenite menyebabkan: better intergranular corrosion resistance and stress corrosion cracking resistance

Dibandingkan dengan “austenitic stainless steel”Tetapi keberadaan ferrite dalam austenite juga:

Menyebabkan terjadinya reaksi pembentukan berbagaivariety of secondary phases,

Berakibat terhadap corrosion resistance mechanical properties (khususnya impact toughness)



Karakteristik Duplex Stainless Steels

Austenitic stainless steel: good weldability and low-temperature toughness,their chloride SCC resistance and strength are comparatively poor.

Ferritic stainless steel:good resistance to chloride SCC but have poor toughness, especially in the welded condition.

A duplex microstructure with high ferrite content can therefore have poor low-temperature notch toughness, whereas a structure with high austenite content can possess low strength and reduced resistance to chloride SCC.

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Karakteristik Duplex Stainless SteelMemiliki mikrostruktur a mixture of austenite and ferrite. resistant to stress corrosion cracking, meski tidak sebaikferritic stainless steelKetangguhannya (toughness)

Lebih tinggi dibanding ferritic stainless steel Tetapi lebih rendah dibanding austenitic stainless steel

Their strength is 2 X greater than austenitic SS (annealed) Have general corrosion resistances = or >> than 304 and 316in general their pitting corrosion resistances are >> than 316. They suffer reduced toughness below –50°C and after exposure above 300°C

so are only used between these temperaturesare also magnetic easily differentiate them from common austenitic SS (non magnetic)



Stess-Strain Curves for Duplex SS



Sifat Mekanik Duplex SSUniversity of

Indonesia


Application of Duplex SS

Chemical processing, transport and storage Oil and gas exploration, offshore rigs and refiningMarine environments Pollution control equipment Pulp & paper industryDesalination plants and seawater systems

Pressure vessels, reactor tanks and heat exchangersRotors, impellers and shafts in industrial equipmentDigesters, storage and clarifier tanks, stock washers for the pulp and paper industryAbsorber towers, FGD systems in pollution control

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Duplex Stainless Steels

Duplex stainless steel: usually have a low carbon additions of molybdenum, nitrogen, tungsten, and copper.

Typical Cr contents are 20 to 30% and Ni contents are 5 to 10 %.The specific advantages offered by duplex stainless steels over conventional austenitic stainless steels are

strength, chloride stress-corrosion cracking resistance, and pitting corrosion resistance.



Heat treatmentUR 35N (2304) = 980°CUR 45N (2205) = 1050°CUR 47/52N+ (2507) = 1120°C

Temperature and cooling rate (water cooling) essential to produce a sound structure.

Fixes the phase balance and the partition of elements between phases.Dissolves intermetallic phases.

Heat treatment temperature

PREN valuesUR 35N (2304) = 26%UR 45N (2205) = 33/36%UR 47/52N+ (2507) = 42%

High Cr+Mo+WIncrease drastically the risk of brittle intermetallicphases precipitations.

Strong alpha forming effect.Improve general and localized corrosion resistance.‘’PREN=Cr+3,3(Mo+0,5W)+16N’’

ChromiumMolybdenum(Tungsten)

UR 35N (2304) = 4%UR 45N (2205) = 5,5%UR 47/52N+ (2507) = 7%

Cost is high !Strong gamma forming effect .Improves low temperature impact strength.

Nickel

UR 35N (2304) = 0,12%UR 45N (2205) = 0,17%UR 47/52N+ (2507) = 0,25%(Be careful with low N2 contents !)

Risk of porosities (welding) .Chromium nitrides precipitates.

Strong gamma forming effect. Efficient even for rapid thermal cycles (HAZ).Positive effect on localized corrosion at ambient improves mechanical properties

Nitrogen

COMMENTSCOMMENTSOTHER EFFECTS OTHER EFFECTS

TO CONSIDERTO CONSIDERAIMAIMELEMENTS AND ELEMENTS AND

PROCESS PROCESS VARIABLESVARIABLES

METALLURGY OF DUPLEX STAINLESS STEELSMETALLURGY OF DUPLEX STAINLESS STEELS



Group of Duplex Stainless Steel

1. Lean duplex, 2304 (S32304), which contain little or free of MoFe-23Cr-4Ni-0.1N

2. Standard 2205 (S32205)for more than 80% of duplex useFe-23Cr-5.5Ni-3Mo-0.15NPREN = 30 -36 (Pitting Resistant Index)

3. High alloy 25 %Cr duplexsuch as 255 (S32550) and S31260Fe-25Cr-5Ni-2.5Mo-0.17N-CuPREN = 32 - 40

4. Superduplex, with 25-26 %Cr and increased Mo and Nsuch as 2507 (S32750)Fe-25Cr-7Ni-3.5Mo-0.25N-W-CuPREN > 40



Pitting Resistance Index

Composition also plays a major role in the corrosion resistance of duplex stainless steels.

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Pitting Resistance Index

Seri 2507 PREN = [Cr%] + 3.3 [Mo%] + 16 [N%] ≥ 40

S=0.001.274.07250.020

OthersNMoNiCrC

Seri 2304 PREN (Cr%) + 3.3 (Mo%) = 16 (N%) ≥ 24

S = 0.0010.10.24230.020

OthersNMoNiCrC

Seri 2205 PREN = [Cr%] = 3.3 [Mo%] = 16 [N%] ≥ 34

S=0.0010.183.15.622.10.020

OthersNMoNiCrC



Komposisi Duplex SS

UNS Number

Type C Mn P S Si Cr Ni Mo N Cu Other

S31200 ... 0.03 2.00 0.045

0.030

1.00

24.0-26.0

5.5-6.5 1.20-2.00

0.14-0.20

... ...

S31260 ... 0.03 1.00 0.030

0.030

0.75

24.0-26.0

5.5-7.5 2.5-3.5 0.10-0.20

0.20-0.80

W0.10-0.20

S31803 ... 0.03 2.00 0.030

0.020

1.00

21.0-23.0

4.5-6.5 2.5-3.5 0.08-0.20

...

S32001 ... 0.03 4.0-6.0

0.040

0.030

1.00

22.0-23.0

1.00-3.00

0.60 0.05-0.17

1.00

S32205 2205 0.03 2.00 0.030

0.020

1.00

19.5-21.5

4.5-6.5 3.0-3.5 0.14-0.20

...

S32304 2304 0.03 2.50 0.040

0.030

1.00

21.5-24.5

3.0-5.5 0.05-0.60

0.05-0.20

0.05-0.60

S32520 ... 0.03 1.50 0.035

0.020

0.80

24.0-26.0

5.5-8.0 3.0-4.0 0.20-0.35

0.50-2.00

S32550 255 0.04 1.50 0.040

0.030

1.00

24.0-27.0

4.5-6.5 2.9-3.9 0.10-0.25

1.5-2.5

S32750 2507 0.03 1.20 0.035

0.020

0.80

24.0-26.0

6.0-8.0 3.0-5.0 0.24-0.32

0.50

S32760 ... 0.03 1.00 0.030

0.010

1.00

24.0-26.0

6.0-8.0 3.0-4.0 0.20-0.30

0.50-1.00

c

S32900 329 d 0.06 1.00 0.040

0.030

0.75

23.0-28.0

2.5-5.0 1.0-2.0 ... ...

S32950 ... 0.03 2.00 0.035



THE DUPLEX STAINLESS STEELS FAMILYTHE DUPLEX STAINLESS STEELS FAMILY

Composition Grade (%)

YS Rp 0,2 (Mpa)

UTS/Rm (Mpa) A% USA EU

UR 35N (2304) > 400 > 600 > 25 32304 4362

UR 45N (2205) > 480 > 680 > 25 31803, 32205 (+A923) 4462

UR 47N+/52N+ (2507) > 560 > 760 > 25 32750

32550/325204410 4507

Composition Grade (%) C Cr Ni Mo Cu N PREN

Corrosion resistance similar

to

UR 35N (2304) 0,02 23 4 > 0,1 0,2 0,12 > 24 316L

UR 45N (2205) 0,02 22 5,7 3,1 - 0,18 33/36 317L, 317LMN, 904…

UR 47N+/52N+ (2507) 0,02 25,5 7 3,7 -/1,5 0,25 >40 904L, 6MO



HIGH STRENGTHHIGH STRENGTH

Duplex stainless steels yield strength range Duplex stainless steels yield strength range from 400Mpa (UR 35N) to 560Mpa (UR 52N+)from 400Mpa (UR 35N) to 560Mpa (UR 52N+)

ASTMASTM

(47N+) 32550(47N+) 32550(52N+) 32750(52N+) 32750

(B25) 31254

317LMN904L

304L

317L316L

40

50

60

70

80

Yield strengthYield strength((KsiKsi))

30

20

(35N) 32304(35N) 32304

(45N) 31803(45N) 318033220532205

DUPLEXDUPLEX

Austenitic

EU StandardEU Standard

DUPLEXDUPLEX

(47 N+) 4410(47 N+) 4410(52 N+) 4507(52 N+) 4507

(45 N) 4462(45 N) 4462

(35 N) 4362(35 N) 4362

(B26) 4529

(B25) 45474439

(B6) 453944044307

200

300

400

500

600

RpRp 0.2%0.2%(MPA)(MPA)

Austenitic

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4

8

12

16

20

24

28

0 4 8 12 16 20 24 28 32 4036

32

AUSTENITE

A+M

MARTENSITE

A+M+F

FERRITE

Cr equivalent

317 LN316L

304L UR 52N+/S32205UR45N/S31803

UR 35N/S32304

F+M

50α / 50γ

100%

UR B26 / 6 Mo N08926

UR B66 /S31266

5%

20%

S32520/550/750/760

DUPLEX

Cr% + Mo% + 1,5 Si% + 0,5 Nb% + 5 V% + 3 Al%

UR B25S31254

SR50A32050

Ni equivalent0%

11-2.5

12-4.5.1.512-6.5.2.5

SCHAEFFLERSCHAEFFLER--DELONG DELONG DiagramDiagram



STRESS CORROSION CRACKINGSTRESS CORROSION CRACKING

Constant-strain tests in autoclaveAbove the curve, SCC occurs.Open circles mean no SCC for UNS 32520/UR 52N+

Duplex stainless steels behave much better than austenitic stainless steels

0 32

100 210

200 390

300°C

0.001 0.1 10 Cl- (%)

AISI 304

UR 35N

UR 45N

UR 52N+

No cracking570

AISI 316



Duplex vs Austenitic SSUniversity of

Indonesia


Sifat korosi Duplex SS

Sifat ketahanan korosiMemiliki ketahanan SCC lebih baik dari Austenitic SSMemiliki ketahanan korosi pitting dan korosi batas butir

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Pembentukan Fasa Kedua(Intermetallic phase)

The high alloy content of duplex stainless steels also makes them susceptible to the formation of intermetallic phases from extended exposure to high temperatures.Significant intermetallic precipitation may lead to

a loss of corrosion resistance and sometimes to a loss of toughness.



PRECIPITATIONS OBSERVED IN FUNCTION OF TIME AND PRECIPITATIONS OBSERVED IN FUNCTION OF TIME AND TEMPERATURETEMPERATURE

(UR 45 N - 4462)

1 10 100 1000 104s1 10 100 1000 104h 105hHours

0

300

500

800

1000

1200

1400

SAFE SERVICE RANGE (- 50, 300°C)

LONG TERM SERVICE ⇒ EMBRITTLEMENTα −−> α ' Cu --> ε EMBRITTLEMENTMaximum service limit

α −−−> σα −−−> χ

Heat treatment (α= γ = 50 %)Increase of ferrite content

FERRITE 100 %

(Seconds)

Temperature (°C)

Time

LOW TEMPERATURE BRITTLENESS (θ <- 50°C)

Heat treatmentrange

DO NOTUSE



Possible Precipitates in Duplex SSUniversity of

Indonesia


10 100 1000 10000

1890

1470

1110

750

390

1000

800

600

200

400

Seconds10 hours

S32304 S31803 S32520°C °F

TTT TTT diagramsdiagrams

SIGMA

Alpha’

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Sigma Phase

Sigma (σ) = Fe-30Cr-4Ni and 4-7% MoHas harmful effects

on the mechanical properties, ductility and toughnessit is detrimental to corrosion resistance

Sigma phase precipitates in Duplex SS over a wider temp range and in a shorter time

The presence of ferriteenhances the precipitation of sigma phase

The diffusion rate of sigma phase forming elements (Cr, Mo, W) in ferrite is 100 times faster than in austeniteSigma phase can form from 600 – 1000OC



Morphology of Sigma Phase



Chi Phase

Chi (λ) phaseis commonly found in duplex SS but it is usually in much smaller quantities than sigma phase

It is also as harmful as sigma phase to the propertiesIt is more detrimental to pitting resistance than sigma phaseChi and Sigma phase are not distinguishable using optical microscope (can be distinguished by TEM)Chi phase precipitates in the range 700 – 900OCUpon long term aging, chi phase will convert to sigma phase



Chi Phase

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Welding

Duplex stainless steels have good weldabilityThey are not quite as easily welded as the austenitic grades

but low thermal expansion in duplex grades reduces distortion and residual stresses after welding.

The recommended filler material for 2205 stainless steel is 2209



Welding Duplex Stainless Steels

Weldability of duplex stainless steels are better than ferritic stainless steels, but generally not as good as austenitic materials.Control of heat input is important. Solidification cracking and hydrogen cracking are concerns when welding duplex stainless steelsModifications to the alloy compositions have been made to improve corrosion resistance, workability, and weldability. In particular, nitrogen additions have been effective in improving pitting corrosion resistance and weldability

DuplexSS-5

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