Stainless Steel – Grade 2205 Duplex (UNS S32205)

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

Stainless Steel – Grade 2205 Duplex (UNS S32205)

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

Stainless Steel – Grade 2205 Duplex (UNS S32205)

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

Table 1 - Composition ranges for 2205 grade stainless steels

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

Physical Properties

Stainless Steel – Grade 2205 Duplex (UNS S32205)

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 Specification Comparison

Stainless Steel – Grade 2205 Duplex (UNS S32205)

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

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

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