Pitting corrosion of thermally aged cast duplex stainless steel for primary coolant pipes of nuclear power plants

ABSTRACT

The pitting corrosion of thermally aged Z3CN20.09M cast duplex stainless steel (CDSS) was investigated using potentiodynamic polarisation and electrochemical impedance spectroscopy. Both pitting potential and charge transfer resistance values of thermally aged specimens became less positive with aging time, while passive current density increased, indicating that thermal aging causes degradation in pitting corrosion resistance. The pitting potential of thermally aged specimens after annealed is higher than that of thermally aged specimens revealing that the pitting corrosion resistance of annealed specimens has been improved. The α’ phase precipitation during thermal aging in ferrite brings the Cr-enriched and Cr-depleted zone microstructures which mainly induced the degradation of pitting corrosion resistance. The microsegregation of Cr element or Cr enriched and Cr-depleted zones will be alleviated or even removed due to the Cr-rich α’ phases dissolution during the process of annealing. So, the pitting corrosion resistance of annealed specimens is improved.

KEYWORDS:

• Cast duplex stainless steel
• thermal aging
• α′ phase
• pitting corrosion
• pitting potential

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Mingkai Liu http://orcid.org/0000-0003-3867-5700

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [grant number 51501001 ] and Anhui Provincial Natural Science Foundation [grant number 1508085QE102].