Views:6 Author:Ronsco Publish Time: 2020-06-05 Origin:Stainless Steel Knowledge
Duplex 2205 is a nitrogen-reinforced duplex stainless steel whose development objective is to solve common corrosion problems encountered with 300 series stainless steel. "Duplex" describes a stainless steel series that is neither completely austenitic like 304 stainless steel nor pure ferrite like 430 stainless steel. The structure of 2205 duplex stainless steel consists of an austenite molten pool surrounded by a continuous ferrite phase. In the annealed state, 2205 contains about 40-50% ferrite. 2205 is usually called the workhorse grade and is the most widely used grade in the duplex stainless steel series. Duplex 2205 stainless steel (ferrite and austenite) is widely used in applications requiring good corrosion resistance and strength. S31803 grade stainless steel has been modified many times to form UNS S32205, which was approved in 1996. This grade of stainless steel has higher corrosion resistance.
At temperatures above 300°C, brittle micro-components of this grade will precipitate, while at temperatures below -50°C, these micro-components will undergo a transition from toughness to brittleness. Therefore, this grade of stainless steel is not suitable for use at these temperatures.
What are the characteristics of Duplex 2205?
High resistance to chloride stress corrosion cracking
Resistant to chloride pitting and crevice corrosion
Good general corrosion resistance
Good resistance to sulfide stress corrosion resistance
Good weldability and workability
Grade 2205 stainless steel has excellent corrosion resistance, much higher than Grade 316. It can resist local corrosion types, such as intergranular, crevice and pitting corrosion. The CPT of this stainless steel is about 35°C. This grade is resistant to chloride stress corrosion cracking (SCC) at a temperature of 150°C. Grade 2205 stainless steel is a suitable substitute for austenitic stainless steel, especially in premature failure environments and marine environments.
The most suitable heat treatment for this grade is solution treatment (annealing), with a temperature between 1020-1100°C, followed by rapid cooling. Level 2205 can be hardened by work, but not by thermal methods.
Except for welding without filler metal, which leads to excessive ferrite, most standard welding methods are suitable for this grade. AS 1554.6 pre-qualified 2205 with 2209 welding rods or welding rods, so that the deposited metal has the correct balanced two-phase structure.
Adding nitrogen to the shielding gas ensures that enough austenite is added to the structure. The heat input must be kept at a low level, and heat before and after use must be avoided. The coefficient of thermal expansion at this level is very low. Therefore, the deformation and stress are less than the austenitic grade.
The machinability at this level is low due to high strength. The cutting speed is reduced by nearly 20% compared with 304.
Materials of this grade are also affected by their strength. This level of bending and forming requires equipment with greater capacity. The ductility of grade 2205 is lower than that of austenitic grades; therefore, cold heading is not possible for this grade. In order to perform cold operations at this level, intermediate annealing should be performed.
In what applications is Duplex 2205 used?
Chemical treatment vessels, pipes and heat exchangers
Pulp mill digester, bleach scrubber, chip pre-steamer
Food processing equipment
Oil field pipelines and heat exchangers
Flue gas desulfurization equipment