**5. Conclusions**

The differences in the precipitate-induced selective corrosion in the hot-rolled and the cold-rolled 2205 duplex stainless steel were evaluated through microstructural analyses of the samples aged at 850 ◦C for different times, when combined with electrochemical methods. The Chi and Sigma phases precipitated in turn following aging treatment for the hot-rolled and cold-rolled materials, but the precipitation rate in the cold rolled sample was faster, as a result of the stored internal energy and increased defect density. The precipitation amount of sigma phase in the cold-rolled samples was higher as compared to the hot-rolled samples under the same aging conditions. Also, strain-induced martensite structure was also produced by the transformation of austenite under cold deformation.

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 samples was weaker when compared to the hot-rolled material after aging treatment. The pitting preferentially nucleated in the Cr-depleted region around the σ phase for the hot-rolled 2205 aged samples, while the corrosion resistance of the hot-rolled 2205 without σ phase increased closely to the level of the solution-annealed 2205. By contrast, not only the σ phase, but also the strain-induced martensite, as well as the defects, which were induced by cold deformation, had an important effect on the corrosion resistance of the cold-rolled 2205 DSS. Correspondingly, the initiation of pitting corrosion occurred at the phase boundary, defects, and martensite for the cold-rolled 2205 aged sample, leading to a lower corrosion resistance, when compared to the hot-rolled 2205.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2075-4701/8/6/407/s1, Figure S1: Comparison of electrochemical impedance spectroscopy between cold-rolled and hot-rolled 2205 duplex stainless steel in 3.5% NaCl, Figure S2: Equivalent circuit of electrochemical impedance spectroscopy for

2205 duplex stainless steel aging in 3.5% NaCl solution, Table S1: Fitting results of equivalent circuit of cold-rolled 2205 duplex stainless steel after long-term aging in 3.5% NaCl solution, Table S2: Fitting results of equivalent circuit of hot-rolled 2205 duplex stainless steel after long-term aging in 3.5% NaCl solution.

**Author Contributions:** T.G. performed research, analyzed the data and wrote the paper; Q.S. helped in the experimental part; J.W. and P.H. assisted in the data analysis and revised manuscript.

**Acknowledgments:** This research was supported by the National Natural Science Foundation of China (Grant No. 51371123) and Shanxi Province Science Foundation for Youths (201601D202033).

**Conflicts of Interest:** The authors declare no conflict of interest.
