Selective Dissolution Characteristics of 26Cr-7Ni-2.5Mo-3W Duplex Stainless Steel in H_2SO_4/HCl Mixed Solution

摘要

Selective dissolution of hyper duplex stainless steel was studied by potentiodynamic and potentiostatic test in various concentrations of H2SO_4/HCI solutions at various temperatures. There were two peaks in the active-to-passive transition region in potentiodynamic test in 2M H2SO_4 + 0.5 M HC1 solution at 60 deg C. In potentiostatic tests, the curve at -340mV showed stable current density. As the potential increased, the current density increased and at above -310 mV potential, there was a much longer initial period of nonsteady current value. As the potential reached at -280 mV, the current density started to be stabilized and the current density was completely stabilized at -250 mV. It was found that a preferential dissolution of ferrite phase occurred at -330 mV and with the increase of potential, austenite phase was corroded at a high rate. On the other hand, both two phases were passivated at the potential above - 270 mV, so that selective dissolution was absent.