Duplex 2205 Stainless Steel

Welding Characteristics:

• Possesses good weldability
• Should not generally be welded without filler metal as this may result in excessive ferrite

Heat Treatment:

• Annealing temperature range is 1868 to 2012°F (1020 to 1100°C)
• Cannot be hardened by heat treatment – but Duplex 2205 does work-harden
• Special consideration is needed to compensate for a higher coefficient of thermal expansion to avoid warping and distortion

Processing – Hot Forming:

Most Duplex 2205 producers recommend a maximum hot forming temperature between 2010 and 2100°F (1100 to 1150°C). If the shape of the work piece is not compact, the edges may be significantly cooler than the bulk, and there is risk of cracking in the cooler regions.

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Processing – Cold Forming:

Duplex 2205 has shown good formability in a variety of fabrications. The high strength of Duplex 2205 can pose problems. Even when the equipment has sufficient power, allowance must be made for higher spring-back caused by the grade’s high strength.

Machinability:

Duplex 2205 is somewhat more difficult to machine than the 300 series austenitic stainless steels. Higher cutting forces are required and more rapid tool wear is typical. Some guidelines for machining are: A) Use powerful, rigid machines with extremely strong rigid mounting of tools and work piece, B) Minimize vibration by keeping the tool extension as short as possible, C) Use a nose radius on the tool, no longer than necessary, for carbides that have a sharp edge while still providing adequate strength, D) Design machining sequences to always provide for a depth of cut below the work hardened layer resulting from the previous passes.

Topics Covered

Introduction
Key Properties
    Composition
    Mechanical Properties
    Physical Properties
Grade Specification Comparison
Possible Alternative Grades
Corrosion Resistance
Heat Resistance
Heat Treatment
Welding
Machining
Fabrication
Applications

Chemical Composition 

Fe, <0.03% C, 21-23% Cr, 4.5-6.5% Ni, 2.5-3.5% Mo, 0.8-2.0% N, <2% Mn, <1% Si, <0.03% P, <0.02% S 

Introduction

Duplex 2205 stainless steel (both ferritic and austenitic) is used extensively in applications that require good corrosion resistance and strength. The S31803 grade stainless steel has undergone a number of modifications resulting in UNS S32205, and was endorsed in the year 1996. This grade offers higher resistance to corrosion.

At temperatures above 300°C, the brittle micro-constituents of this grade undergo precipitation, and at temperatures below -50°C the micro-constituents undergo ductile-to-brittle transition; hence this grade of stainless steel is not suitable for use at these temperatures.

Key Properties

The properties that are mentioned in the below tables pertain to flat rolled products such as plates, sheets and coils of the ASTM A240 or A240M. These may not be uniform across other products such as bars and pipes.

Composition

Table 1 provides the compositional ranges for grade 2205 duplex stainless steel.

Table 1 - Composition ranges for 2205 grade stainless steels

Grade

 

C

Mn

Si

P

S

Cr

Mo

Ni

N

2205 (S31803)

Min

Max

-

0.030

-

2.00

-

1.00

-

0.030

-

0.020

21.0

23.0

2.5

3.5

4.5

6.5

0.08

0.20

2205 (S32205)

Min

Max

-

0.030

-

2.00

-

1.00

-

0.030

-

0.020

22.0

23.0

3.0

3.5

4.5

6.5

0.14

0.20

Mechanical Properties

The typical mechanical properties of grade 2205 stainless steels are listed in the table below. Grade S31803 has similar mechanical properties to that of S32205. 

Table 2 - Mechanical properties of 2205 grade stainless steels

Grade

Tensile Str
(MPa) min

Yield Strength
0.2% Proof
(MPa) min

Elongation
(% in 50mm) min

Hardness

Rockwell C (HR C)

Brinell (HB)

2205

621

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448

25

31 max

293 max

Physical Properties

The physical properties of grade 2205 stainless steels are tabulated below. Grade S31803 has similar physical properties to that of S32205.

Table 3 – Physical properties of 2205 grade stainless steels

Grade

Density
(kg/m3)

Elastic
Modulus

(GPa)

Mean Co-eff of Thermal
Expansion (μm/m/°C)

Thermal
Conductivity (W/m.K)

Specific
Heat
0-100°C

( J/kg.K)

Electrical
Resistivity
(nΩ.m)

0-100°C

0-315°C

0-538°C

at 100°C

at 500°C

2205

7800

190

13.7

14.2

-

19

-

418

850

Grade Specification Comparison

Table 4 provides the grade comparison for 2205 stainless steels. The values are a comparison of functionally similar materials. Exact equivalents may be obtained from the original specifications.

Table 4 - Grade specification comparisons for 2205 grade stainless steels

Grade

UNS
No

Old British

Euronorm

Swedish

SS

Japanese

JIS

BS

En

No

Name

2205

S31803 / S32205

318S13

-

1.4462

X2CrNiMoN22-5-3

2377

SUS 329J3L

Possible Alternative Grades

Given below is a list of possible alternative grades, which may be chosen in place of 2205.

Table 5 - Grade specification comparisons for 2205 grade stainless steels

Grade

Reasons for choosing the grade

904L

Better formability is needed, with similar corrosion resistance and lower strength.

UR52N+

High resistance to corrosion is required, e.g. resistance to higher temperature seawater.

6%Mo

Higher corrosion resistance is required, but with lower strength and better formability.

316L

The high corrosion resistance and strength of 2205 are not needed. 316L is lower cost.

Corrosion Resistance

Grade 2205 stainless steel exhibits excellent corrosion resistance, much higher than that of grade 316. It resists localized corrosion types like intergranular, crevice and pitting. The CPT of this type of stainless steel is around 35°C. This grade is resistant to chloride stress corrosion cracking (SCC) at temperatures of 150°C. Grade 2205 stainless steels are apt replacements to austenitic grades, especially in premature failure environments and marine environments.  

Heat Resistance

The high oxidation resistance property of Grade 2205 is marred by its embrittlement above 300°C. This embrittlement can be modified by a full solution annealing treatment. This grade performs well at temperatures below 300°C.

Heat Treatment

The best suited heat treatment for this grade is solution treatment (annealing), between 1020 - 1100°C, followed by rapid cooling. Grade 2205 can be work hardened but cannot be hardened by thermal methods.

Welding

Most standard welding methods suit this grade, except welding without filler metals, which results in excess ferrite. AS 1554.6 pre-qualifies welding for 2205 with 2209 rods or electrodes so that the deposited metal has the right balanced duplex structure.

Adding nitrogen to the shielding gas ensures that adequate austenite is added to the structure. The heat input must be maintained at a low level, and the use of pre or post heat must be avoided. The co-efficient of thermal expansion for this grade is low; hence the distortion and stresses are lesser than that in austenite grades.

Machining

The machinability of this grade is low due to its high strength. The cutting speeds are almost 20% lower than that of grade 304.

Fabrication

The fabrication of this grade is also affected by its strength. Bending and forming of this grade requires equipment with larger capacity. Ductility of grade 2205 is lesser than austenitic grades; therefore, cold heading is not possible on this grade. In order to carry out cold heading operations on this grade, intermediate annealing should be carried out.

Applications

Some of the typical applications of duplex steel grade 2205 are listed below:

• Oil and gas exploration
• Processing equipment
• Transport, storage and chemical processing
• High chloride and marine environments
• Paper machines, liquor tanks, pulp and paper digesters

 

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