DX2205Austeno-ferritic Stainless steel offergrade DX2205

Chemical composition

This grade complies with:

> Stainless Europe Material Safety Data Sheet n°1 (European Directive 2001/58/EC).

> European directive 2000/53/EC on end-of-life vehicles and later modifications.

> NFA 36 711 standard “Stainless Steel intended for use in contact with foodstuffs, products and beverages for human and animal consumption (non packaging steel).”

General characteristics

The principal features of DX2205 are:

> An excellent corrosion resistance, with a minimum PREN value of 35

> Twice as high yield strength as our grade 18-9E (1.4301, Type 304)

> Service temperature range: -40 °C to 300 °C

Applications

> Equipment and piping for the chemical industry, oil and gas industries and desalination plants

> Heat exchangers

Product range

Forms: sheet, blank, coil, strip, tubeThicknesses: 0.6 - 9 mm (>9 mm on demand)Width: up to 2000 mm (depends on thickness)Finishes: hot rolled, cold rolled

Metallurgical properties

The grade DX2205 is a stainless steel of the austeniticferritic group, whose structure is composed of a mix of ferritic (α) and austenitic (γ) phases. The dual phase structure of the alloy makes it possible to obtain elevated yield strength values whilst still maintaining sufficientductility. The hardening is indeed provided by the ferritic phase, whereas the austenitic lattice enables to preserve both ductility and toughness.

The mixed structure confers a good resistance to stress corrosion cracking to grade DX2205 and also makes it insensitive to tergranular corrosion. Its high chromium and molybdenum content makes it resistant against both pitting and uniform corrosion.

Continuous use of DX2205 at temperatures above 300 °C is not recommended for the following reasons:

> between 350 and 550 °C: loss of ductility by embrittlement of the ferritic phase due to the formation of a so-called α’ phase, possibly accompanied by other embrittling phases; this is a classical phenomenon encountered with ferritic stainless steels, more commonly referred to as “475 °C embrittlement”.

> between 600 and 950 °C: embrittling sigma phase precipitation, related to the high chromium and molybdenum content.

European designation (1)

X2CrNiMoN22-5-3/1.4462

Grades C Si Mn Cr Ni Mo N

% 0.020 0.30 1.80 22.80 5.50 3.10 0.17

(1) According to NF EN 10088

Typical values - PREN = 35

American designation (2)

UNS S32205

Microstructure of DX2205 (dark areas represent the ferritic phase)

700

300

400

500

600

Sigma800

900

1000

Time (hours)Time (minutes)1 2 4 6 8 10 20 40 60 2 4 10 20

Temperature °C

α’475 °C

(2) According to ASTM A240

T° C

Concentration % H2 SO

4

10 20 30 40 50 60 70 80 90 98

20

30

40

50

Physical Properties

Cold rolled and annealed sheet.

Density d kg/dm3 20 °C 7.8

Melting temperature - °C - 1460

Specific heat c J/kg.K 20 °C 460

Thermal conductivity k W/m.K 20 °C 16

Mean coefficient ofThermal expansion* α 10-6/K 20-100 °C

20-200 °C13.013.5

Electric resistivity ρ Ω mm2/m 20 °C 0.8

Magnetic - - - yes

Young’s Modulus E 103.MPa 20 °C 200

*Thermal expansion 25% lower than that of 316, comparable with carbon steel

(E 103 MPa)ρ (Ω mm2/m) x 10-2 k (W/m.k)

20 200 400 600

10

15

20200

100

k

E

ρ

0 200 400 600

21

17

20

16

19

15

18

W/m.k

304 (18-9E)

DX2205

Mechanical properties

In annealed conditionAccording ISO 6892-1, part 1,test piece perpendicular to rolling direction.

Test piece:Length= 80 mm ( thickness < 3 mm).Length= 5,65 √ So (thickness ≥ 3 mm).

1 MPa= 1 N/mm2. Typical values.(1) Ultimate Tensile Strength (UTS). (2) Yield Strength (YS). (3) Elongation (A).

At high temperatures

Temperature 50°C 100°C 150°C 200°C 250°C

Rp0,2(MPa) ≥ 420 ≥ 360 ≥ 335 ≥ 315 ≥ 300

Rm(MPa) ≥ 640 ≥ 590 ≥ 570 ≥ 550 ≥ 540

Corrosion resistance

This grade is particularly recommended under severe corrosion conditions, where it can replace highly alloyed austenitic stainless steels.conditions, where it can replace highly alloyed austenitic stainless steels.

Uniform corrosion

Chlorideconcentration (g/l)

1 5

Fluorideconcentration (ppm)

0 400 1000 0 400 1000

pH

6 316L DX2205

4

2UNS

S32550

1 Ti/Ni

Resistance of DX2205 according to chloride and fluoride content and pH Limiting service conditions of DX2205in sulphuric acid (maximum corrosion rate= 0,2 mm/year)

316L (18-11ML)

DX2205

317L

Temperature (°C)

Temperature (°C)

ConditionRm (1)

(MPa)Rp

0,2 (2)

(MPa)A(3)

%HRB

Cold rolled* 840 620 29 98

Forming

This grade can generally be used for forming applications. Since its yield strength is about double that of 1.4301, Type 304, the use of presses or section rolling equipment with suitable power is required.

The aptitude for stretch forming is determined by the dome height of the Erichsen test, whereas the deep drawing ability is defined by the limiting drawing ration (LDR).

BendingFor thicknesses below 0.8 mm, a minimum bending radius of 0.5 x thickness is recommended. For heavier gauges, the bending radius must be at least 1.5 x thickness.

Corrosion rate (mm/year)

10 50 100

0.36

316L (18-11ML)

DX2205

0.27

0.18

0.09

Cl-(g/l) Res

ista

nce

of D

X22

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ft c

ellu

lose

pr

oduc

tion

pro

cess

)

Corrosion rate (mm/year)3.5

3

2.5

2

1.5

1

0.5

Res

ista

nce

of D

X22

05 in

aci

d or

gani

c en

viro

nmen

ts

316L (18-11ML) DX2205304L (18-9L)

Formic acid

Oxalic acid

Acetic acid

Corrosion rate (mm/year)0.7

0.6

0.5

0.4

0.3

0.2

1

Res

ista

nce

of D

X22

05 in

the

NA

CE T

M 0

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. N

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H 0

,5%

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ent

H2S

pres

sure

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osph

ere

at 2

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, pH

3

316L (18-11ML) DX2205

60 °C

24 °C Maximum chloride content (ppm Cl-)

Res

ista

nce

of D

X22

05 in

P20 5

(t

rans

port

atio

n of

pho

spho

ric a

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.M

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um c

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ide

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re (f

or in

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54

%P

20

5-H

2SO

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-F <

1%

-HF<

0,2

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1200

800

400 316L (18-11ML)

DX2205

30 50 70 °CStress corrosion crackingDue to its dual phase structure, DX2205 is hardly sensitive to stress corrosion cracking. It shows adequate resistance in acid gas environments (C02 + H2S).

Intergranular corrosionDue to both its low carbon content and its dual phase structure, DX2205 resists well to intergranular corrosion.

Pitting corrosionGiven its higher chromium, molybdenum and nitrogen content, our DX2205 exhibits very good resistance against pitting corrosion.Its performance is in fact superior to that of both 304L and 316L. The pitting corrosion resistance ranking of stainless steels is generally established by means of the PREN (Pitting Resistance Equivalent Number= %Cr+3.3*%Mo+16*%N) formula. DX2205’s value typically lies around 35.7 compared to 24.1 for the 1.4401, Type 316 grade or 18 for the 1.4301, Type 304 grade.

Crevice corrosionDX2205 resists well to this type of corrosion characterized by the depassivation pH, which is measured by electrochemical methods. The lower the pH (acid), the higher the performance of the alloy. At 30 °C, the pH of DX2205 is about 1, whereas it lies around 1.8 for a molybdenum alloyed austenitic grade (316) or 3 for a ferritic grade (430).

Limiting yield strength (% Rp0,2)

Infl

uenc

e of

tem

pera

ture

on

non-

crac

king

lim

itin

g yi

eld

stre

ngth

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t TM

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pH2S:

1 b

ar.

100

80

60

20 °C 60 °C

40

20

316L (18-11ML)

DX2205

GradeEuropean

designationASTMA240

Erichsen cup test* (mm)

Limiting Drawing Ratio* (LDR)

DX2205 1.4462 UNS S32205 9.5 1.9-1.95

*Valid for 0.8 mm sheet

Pitting potential in aerated NaCI 30 g/I at 70°C

400

200

316L (18-11ML)

DX2205

304L (18-9L)

Pitting potential (mV/SCE)

500

1000

316L (18-11ML)

DX2205

Pitting potential (mV/SCE)

20 40 60 °CPitting potential in aerated NaCI 30g/I according to temperature

pH

+

-

1

1.5

2

2.5

Crev

ice co

rrosio

n re

sista

nce

: dep

assiv

atio

n pH

316L (18-11ML)

201D (17-4Mn)

301 (17-7A)

K30 (430)

DX2205

304L (18-9L)

20

316L (18-11ML)

DX2205

Pitting potential (mV/SCE)

Critical crevice temperature of INCO type specimens in a 10% FeCl3, 6 H2O environment

10

0

Welding

Welding process

No filler material With filler metal

Shielding gas*Typical thicknesses Thicknesses

Filler material

Rod Wire

Resistance:spot, seam

≤ 2 mm

TIG < 1.5 mm > 0.5 mmModified “4462”

ER 22.09Modified “4462”

ER 22.09Argon (1)

Argon + Helium (1)

PLASMA < 1.5 mm > 0.5 mmModified “4462”

ER 22.09Argon

Argon + Helium

MIG > 0.8 mmModified “4462”

ER 22.09

Argon + 2 % CO2Argon + 2 % CO2

Argon + 2% C02 + He

S.A.W. > 2 mmModified “4462”

ER 22.09

Electrode Repairs E 22.09

Laser < 5 mm Helium + Nitrogen (25%)

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Aperam Stainless Europe1-5 rue Luigi CherubiniFR-93212 La Plaine Saint Denis Cedex

InformationTel. : +33 1 71 92 06 52Fax : +33 1 71 92 07 97www.aperam.com/stainlesseuropestainless.europe@aperam.com

DX2205 is an austenitic-ferritic alloy of which the chemical analysis and heat treatment have been optimized in order to obtain a ferrite content in the base metal of between 38 et 55 %.In the case of welding without filler material, local fusion followed by rapid cooling takes place. Primary solidification starts with the ferritic phase, while the too rapid cooling prevents the regression of the ferrite into austenite, which leads to ferrite contents up to 90 % in the case of welding without particular care. The structure of the HAZ (Heat Affected Zone), having also undergone the welding thermal cycle, will be enriched in ferrite too, compared to the initial structure. An excess of ferrite (above 75 %) reduces both corrosion resistance and ductility.

Recommendations: in all cases, welding energy should be sufficiently high (> 2,5 kJ/cm) in order to avoid too rapid cooling.The energy must not be too high (< 20 kJ/cm) however, in order to ensure sufficient cooling to avoid the risk of precipitation of intermetallic phases in turn. The use of a top/bottom shielding gas is recommended. Nitrogen must be added in the case of welding without filler metal or adapted to the filler metal in the other case. Pre- and post heating must be avoided.

Weld properties: the austenitic-ferritic structure of DX2205 (primary solidification of the ferritic phase) eliminates the risk of hot cracking. If welded under the wrong conditions, this alloy can become sensible to cold cracking. To avoid all risks, no hydrogenated gas must be used for the purpose of welding and all filler materials must be correctly dried (temperature above 250 °C in most cases). Post weld heat treatment is not required in any form. The welds must be mechanically or chemically descaled and subsequently passivated (decontaminated).

Heat treatment and finishing

Heat treatmentAfter cold forming, an annealing treatment of a couple of minutes at 1050 +/- 25°C, followed by air cooling restores the structure andeliminates internal stresses. After heat treatment, pickling followed by passivation must be carried out.PicklingBy acid mix (20% HNO3 + 2% HF) at room temperature or at 60°C. By sulphuric-nitric bath (10% H2SO4 + 0.5% HNO3) at room temperature or at60 °C. Pickling pastes for welds.PassivationNitric acid bath (10 – 25 %) at 20 °C. Passivating pastes for welds.

Size range

Width (mm)

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.20 1.50 2.00 2.50 3.00 4.50

1 500

1 000

2.00 3.00 3.50 4.00 4.50 5.00 6.00 7.00 8.00 9.00 10 <120

Width (mm)

Quarto plates(ArcelorMittal Industeel)Hot rolled HRAP 1D

2 000

1 500

1 250

1 000

3 200

2 800

2 500

thickness (mm)

1 300

2 000

Cold rolled 2D, 2B Cold rolled 2E

thickness (mm)

* Hydrogen strictly forbidden, both top and bottom. (1) in the case of welding without filler material the gas of protection must be added by nitrogen: 5 in 20 %