**Tao Gao, Jian Wang \*, Qi Sun and Peide Han \***

College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China; u.best.ok@163.com (T.G.); imsunqi@163.com (Q.S.)

**\*** Correspondence: wangjian@tyut.edu.cn (J.W.); hanpeide@126.com (P.H.); Tel.: +86-351-601-8843 (J.W. & P.H.)

Received: 14 April 2018; Accepted: 25 May 2018; Published: 01 June 2018

**Abstract:** Precipitate phases often play an important role on the corrosion resistance of 2205 Duplex stainless steels (DSS). In the present paper, the microstructure and the corrosion resistance of the hot-rolled and cold-rolled 2205 steels aged for different times at 850 ◦C was investigated through XRD, SEM, and potentiodynamic polarization. It was discovered that the Chi(χ) phase and Sigm(σ) phase were precipitated in turn following the aging treatment of the hot-rolled and cold-rolled steels, but the precipitate amount in the cold-rolled samples was significantly higher when compared to the hot-rolled samples. The corrosion resistance of the solution-annealed cold-rolled samples was similar to the hot-rolled samples, but the corrosion resistance of the cold-rolled sample with precipitate was weaker when compared to the hot-rolled sample following aging treatment. Pitting preferentially initiates in the Cr-depleted region from the σ phase in the aged hot-rolled 2205, becoming increasingly severe during aging for a long lime. Adversely, the initiation of pitting corrosion might occur at the phase boundary, defects, and martensite in the aged cold-rolled 2205. The σ phase was further selectively dissolved through the electrochemical method to investigate the difference in microstructure and corrosion behavior of the hot-rolled and cold-rolled 2205 duplex stainless steels.

**Keywords:** pitting; sigma phase; 2205; duplex stainless steel
