The electrochemical polishing behavior of duplex stainless steel(SAF 2205) in phosphoric-sulfuric mixed acids

In this paper the electrochemical polishing behavior of duplex stainless steel (DSS) in phosphoric-sulfuric mixed acids with volume ratios of 1:1, 2:1, and 3:1 was studied. The electrochemical polishing was conducted at 70 degrees C by using arotating disc electrode. Before the polishing, the steel specimens were heated at 1080 degrees C for 10 min and cooled with different rates to obtain dissimilar microstructures. Experimental results show that a brightening surface of each DSS specimen can be obtained by polishing in the mixed acids at 70 degrees C. However, the dissolution rate between alpha and gamma phases in a DSS specimen is different during potentiostatic polishing in the mixed acids and the rate of alpha phase is obviously higher than that of gamma phase. However, the difference in the dissolution rate can be reduced as the DSS specimen was polished in a highH(3)PO(4)-content mixed acid. Some small round sigma-phases were found to precipitate along the alpha/gamma interface in a DSS specimen, which can be obtained by heating at 1080 degrees C and then cooling in the furnace. The presentation of sigma phase increased the hardness and microstructure fraction of the gamma phase in the DSS specimen. Moreover, the sigma phase can be leveled together with alpha and gamma phases as polishing in the 3:1 v/v mixed acid.