Duplex 2205 (UNS S31803)

Duplex 2205 (UNS S31803), or Avesta Sheffield 2205 is a ferritic-austenitic stainless steel.

The high amounts of molybdenum and chromium content in 2205 offer strength, improved pitting and consistent stress corrosion cracking resistance. 2205 integrates the best features of austenitic and ferritic steels (as well as nearly equal amounts of austenite and ferrite) and can be welded with common stainless steel welding techniques – its uniform composition minimizes localized corrosion.

Specifications - Duplex 2205

Chemical Composition - Duplex 2205 

C Cr Fe Mn Mo N Ni P S Si
Max        Max          Max Max Max
.03% 22%-23% BAL 2.0% 3.0% -3.5% .14% - .2% 4.5%-6.5% .03% .02% 1%

Design Features - Duplex 2205

Typical Applications - Duplex 2205

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

Physical Properties

The physical properties of grade 2205 stainless steels are tabulated below.

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 782 190 13.7 14.2 - 19 - 418 850

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.

The super duplex gradesare even more resistant to corrosion.

Heat Resistance

Fabrication

Fabrication of all stainless steelsshould be done only with tools dedicated to stainless steel materials. Tooling and work surfaces must be thoroughly cleaned before use. These precautions are necessary to avoid cross contamination of stainless steel by easily corroded metals that may discolour the surface of the fabricated product.

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.

Machinability

Although machinable, the high strengths of duplex stainless steels makes machining difficult. As an example, machining of 2205 is around 20% slower than for 304.

Machining can be enhanced by using the following rules:

Heat Treatment

Duplex stainless steelscannot be hardened by heat treatment. They can however be work hardened.

Solution treatment or annealing can be done by rapid cooling after heating to around 1100°C.

Weldability

Duplex stainless steelshave good weldability. All standard welding processes can be used. They 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 steelis 2209.


Grade Reasons for choosing the grade



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