Stainless Steel-2205

2205 is a ferritic-austenitic (duplex) stainless steel. It combines many of the most beneficial properties of ferritic and austenitic steels. Due to its high content of chromium and molybdenum, it exhibits excellent resistance to pitting and uniform corrosion. The duplex microstructure ensures high resistance to stress corrosion cracking and provides high mechanical strength. The weldability of 2205 is very good.

Microstructure

2205 has a balanced chemical composition, resulting in a microstructure containing approximately equal amounts of ferrite and austenite.
When 2205 is subjected to quench annealing at around 1050°C, its microstructure generally consists of 30–50% ferrite. The grain size, measured by interlayer spacing, is very fine and varies depending on the product form, but is typically in the range of 5–10 micrometers (μm).
Higher annealing temperatures increase the ferrite content. However, a fully ferritic structure is only obtained when the steel is heated to very high temperatures.
Like all duplex steels, 2205 is more prone to the precipitation of intermetallic phases than austenitic stainless steels. The sigma phase (σ-phase) can form in the temperature range of 700–975°C, and 475°C embrittlement can occur in the range of 350–525°C.
Nevertheless, under normal welding and heating processes, there is no risk of embrittlement for this steel.

Design Features

• High strength
• High resistance to pitting corrosion and crevice corrosion
• High resistance to stress corrosion cracking, corrosion fatigue, and erosion corrosion
• Good resistance to sulfide stress corrosion cracking
• High resistance to uniform corrosion
• Low thermal expansion and higher thermal conductivity than austenitic stainless steels
• Good weldability
• High energy absorption

Hot Working / Forming

Hot working is performed within the temperature range of 1150–950°C. It should be noted that the mechanical strength of this material is low at high temperatures. Brittleness may occur below 950°C due to strain and simultaneous exposure within the σ-phase precipitation range. Quench annealing is generally required after hot working.

Cold Working / Forming

Due to its high yield strength, greater force is required for the cold working of 2205 compared to austenitic stainless steels. The work hardening rate is shown in Figure 7.
Most manufacturing processes suitable for stainless steels can be applied to 2205. However, due to its high mechanical strength and lower ductility, operations such as deep drawing, stretch forming, and spinning are more challenging than with austenitic stainless steels.
It is generally recommended to perform quench annealing after cold deformation exceeding 10%.