Duplex 2205 (UNS S31803)

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.

Duplex 2205 stainless steel, also known as UNS S32205 (formerly UNS S31803), is a type of stainless steel that is characterized by a mixed microstructure of austenite and ferrite, offering a combination of high strength and excellent corrosion resistance.

Specifications - Duplex 2205

• ASTM: A790, A815, A182
• ASME: SA790, SA815, SA182

Avesta Sheffield 2205 is a ferritic-austenitic stainless steel which combines many of the beneficial properties of both ferritic and austenitic steels. As a result of high chromium and molybdenum contents, the steel has very good pitting and uniform corrosion resistance, as well as high mechanical strength. 2205 has good weldability and can be welded using most of the techniques for stainless steels. Due to the balanced composition, when welded correctly, the heat-affected zone contains sufficient austenite to avoid risk of localized corrosion.

Key Properties

• Corrosion Resistance: Superior resistance to pitting and stress corrosion cracking, particularly in chloride-rich environments.
• Mechanical Strength: Offers high tensile strength and yield strength, suitable for applications requiring high mechanical performance.
• Weldability: Good weldability and can be welded using most techniques suitable for stainless steels, ensuring the maintenance of corrosion resistance in the welded joints.

What is Duplex 2205?

Duplex 2205 is a two-phase, ferritic, austenitic 22% chromium, 3% molybdenum, 5 to 6% nickel alloyed stainless steel. It is the most widely used duplex stainless steel grade and is characterized by high yield strength, double that of the standard austenitic stainless steel grades.

Duplex 2205 is a type of stainless steel that belongs to the family of duplex stainless steels, which are designed to have a combination of high strength and excellent corrosion resistance. Duplex 2205 is composed of a mixture of austenitic and ferritic phases, providing superior mechanical and corrosion resistance properties compared to traditional austenitic stainless steels.

Duplex 2205 has several advantages over other types of stainless steel, including:

Excellent corrosion resistance: Duplex 2205 offers superior resistance to pitting, crevice corrosion and stress-corrosion cracking compared to traditional austenitic stainless steels.

High strength: Duplex 2205 has higher strength than most other types of stainless steel, particularly in terms of its yield and tensile strength.

Good weldability: Duplex 2205 can be easily welded using conventional welding techniques, without affecting the properties of the material.

Good machinability: Duplex 2205 is relatively easy to machine, despite being a duplex stainless steel.

Duplex 2205 is commonly used in various industries such as chemical processing, oil and gas, pulp and paper, and marine applications. It is particularly suitable for use in corrosive environments where high strength and good corrosion resistance are required.

Overall, Duplex 2205 is an important material that offers a combination of strength, corrosion resistance, and ease of fabrication, making it a popular choice for various industrial applications.

What is the difference between duplex 2205 and 316 SS?

Generally, 2205 duplex stainless steel tends to be more expensive than 316 due to its unique composition and superior properties. The higher chromium, molybdenum, and nitrogen content, as well as the dual-phase microstructure, contribute to its higher cost.

Applications

• Heat Exchangers: Utilized in heat exchangers for gas and oil industries.
• Desalination Plants: The material of choice for heat exchangers and pipes in desalination plants due to its resistance to the corrosive nature of seawater.
• Chemical Processing: Used in pressure vessels, pipes, and tanks for handling various chemicals and chlorides.
• Industrial Machinery: Components such as rotors, fans, shafts, and press rolls that require high corrosion fatigue strength.

Chemical Composition - Duplex 2205

Design Features - Duplex 2205

• High Strength
• Exceptional uniform corrosion resistance
• Better heat conductivity and lower thermal expansion than austenitic steels
• Resistance to stress corrosion cracking
• Resistance to erosion
• Resistance to corrosion fatigue
• Resistance to pitting
• Resistance to crevace corrosion
• Resistance to sulfide stress corrosion cracking

Typical Applications - Duplex 2205

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

• Heat exchangers, tubes and pipe for production and handling of gas and oil
• Heat exchangers and pipes in desalination plants
• Pressure vessels, pipes, tanks and heat exchangers for processing and transport of various chemicals
• Pressure vessels, tanks and pipes in process industries handling chlorides
• Rotors, fans, shafts and press rolls where the high corrosion fatigue strength can be utilized
• Cargo tanks, piping and welding consumables for chemical tankers

Physical Properties

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

• Grade S31803 has similar physical properties to that of S32205.

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

• The high chromium content of duplex stainless steels that protects against corrosion, causes embrittlement at temperatures over about 300°C.
• At low temperatures duplex stainless steels have better ductility than the ferritic and martensitic grades. Duplex grades can readily be used down to at least -50°C.

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:

• Cutting edges must be kept sharp. Dull edges cause excess work hardening.
• Cuts should be light but deep enough to prevent work hardening by riding on the surface of the material.
• Chip breakers should be employed to assist in ensuring swarf remains clear of the work
• Low thermal conductivity of austenitic alloys results in heat concentrating at the cutting edges. This means coolants and lubricants are necessary and must be used in large quantities.

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

• 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.

Forms