Martensitic Transformation Induced by Electro-Chemical Polishing in Metastable Austenitic Stainless Steel

We determined that a severe martensitic transformation during electrochemical polishing (EP) in 16Cr-5Ni metastable austenitic stainless steel was caused solely by EP. The specimen was treated by EP, then sealed in a quartz tube to protect the surface, then annealed at 1150 °C to form a single austenite phase, and again subjected to EP. As the duration of the second EP increased, the fraction of martensite increased to 72.2% when the duration is 160s at 20V of voltage. However, Ferritescope measurements showed that the martensite fraction of the whole specimen was < 1%; comparison of these results suggests that the martensite transformation by EP was limited to the surface. Calculation of the temperature-dependent difference in Gibbs free energy between α’ martensite and austenite confirmed that the energy applied to the specimen during EP is sufficient to cause martensitic transformation at room temperature.