**4. Conclusions**

The corrosion behaviors of copper bearing steels were studied, and the accumulation of copper on the surface of corroded steels after the removal of rust was observed and analyzed. The following conclusions can be made:

(1) Steel with a high copper content (>3%) had a high initial corrosion rate due to its obvious two-phase microstructure. The corrosion rates of all copper bearing steels tended to be smooth after a certain period of corrosion.

(2) A complete copper coating was obtained on the surfaces of the steels after a periodic immersion wet/dry cyclic corrosion test. The oxidation of the matrix and the diffusion of copper atoms at the interface formed a quasi-layered structure consisting of the matrix, copper coating, and upper rust layer.

(3) The copper coating was generated from the matrix itself during the corrosion process at 25 ◦C. A lower corrosion rate, longer corrosion time, and higher copper content were favorable for the formation of a copper enriched layer.

(4) Copper-bearing steel with copper coating shows better corrosion resistance property.

**Author Contributions:** Conceptualization, N.L.; methodology, N.L.; validation, L.Y., S.W. and H.Z.; formal analysis, N.L., Z.J.; investigation, H.Z.; resources, L.Y., C.W., H.Z. and F.A.; data curation, L.Y. and C.W.; writing—original draft preparation, N.L.; writing—review and editing, N.L. and Z.J.; supervision, H.Z. and Z.J.; project administration, H.Z.; funding acquisition, N.L., L.Y., C.W. and H.Z. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the State Key Laboratory of Metal Material for Marine Equipment and Application-School of Material and Metallurgy, University of Science and Technology Liaoning co-project, gran<sup>t</sup> number No. SKLMEA-USTL 2017010 and HGSKL-USTLN 201905.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data is contained within the article.

**Acknowledgments:** The authors thank Wei Sha from Queen's University Belfast, UK, for some helpful discussions.

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