Grade 2205 Duplex Stainless Steel

Corrosion resistance of 2205 grade
2205 grade stainless steel has excellent corrosion resistance, much higher than 316 grade. It resists localized corrosion types such as intergranular corrosion, crevice corrosion and pitting. The CPT of this type of stainless steel is about 35°C. This grade can resist chloride stress corrosion cracking (SCC) at 150°C. 2205 grade stainless steel is a suitable alternative to austenitic stainless steel, especially in premature failure environments and marine environments.

Compared with austenitic stainless steel, duplex stainless steel is less sensitive to intergranular corrosion. When duplex stainless steel is sensitized, carbides precipitate preferentially at the δ/γ phase boundary, δ precipitates on one side of the phase, and the phase boundary carbides δ/γ precipitate with difficulty and in small quantities. Since austenite grains and ferrite grains surround each other, the carbides on one side of the phase can be quickly supplemented by diffusion from the high-chromium ferrite interior, even if the precipitation of δ/γ phase boundary carbides creates a chromium-poor area, a continuous network cannot be formed, thereby avoiding the deepening of intergranular corrosion.

Duplex stainless steel has high stress corrosion resistance, which increases with the increase of ferrite content. The stress rupture sensitivity is minimum when the ferrite content is about 50%, because the crack originates from the austenite matrix and once it extends to the ferrite phase:

(1) Under low stress, it is difficult for slip to occur inside the ferrite phase and cause cracks;

(2) The dispersed ferrite has a negative potential relative to the austenite phase, which plays a cathodic protection role for the austenite phase;

(3) The austenite phase is dispersed in the ferrite matrix and mechanically prevents crack propagation due to the locking effect.

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