Immersion pickling of oxide layer on hot-rolled 2205 duplex stainless steel in sulfuric acid with different additives

Abstract

The oxide layer formed after hot-rolling of duplex stainless steel (DSS) alloy 2205 was studied by electron probe microanalysis (EPMA) with wavelength dispersive spectrometry (WDS). Immersion pickling of the oxide layer on hot-rolled 2205 DSS in sulfuric acid at 80 °C with different additives was investigated via open-circuit potential and SEM imaging. The effects of different pickling solutions on descaling capacity were discussed. Results showed that the outer layer of the oxide layer was mainly iron oxide, whereas the maximum concentration of oxidized Cr occurred inside the layer; oxidized Cr extended far beyond the oxide/metal interface. The removal capacity of the oxide layer was weak with a sulfuric acid solution of 300 g/L. Many surface oxides appeared after the 20 min immersion test. After adding 1 mol/L NaCl, the pickling effect was significantly improved, and the open-circuit potential reduced from 0.3V to –0.32V. However, after a 20-min substrate immersion test, the surface was rough. Continuous addition of 50 g/L hexamethylenetetramine could remove the oxide in 20 min, resulting in a surface with a metallic luster. The initial potential of the reaction was –0.325 V. The potential then rose rapidly to –0.312 V within 280 s. The rapid increase in potential could be attributed to the inhibitory effect of hexamethylenetetramine. The optimum pickling process was as follows: 300 g/L H2SO4 + 1 mol/L NaCl+ 50 g/L hexamethylenetetramine solution at 80 °C in 20 min.