Pickling behavior of 2205 duplex stainless steel hot-rolled strips in mixed solutions of HNO3-HF

Abstract

The pickling behaviour of 2205 DSS hot-rolled strips after annealing and sand blasting was studied in the mixed solutions of HNO3-HF using weight loss rate, surface analysis, corrosion potential, and electrochemical impedance spectroscopy measurements. The pickling rate decreased as the concentration of HNO3 increased in the mixed solutions of x HNO3 + 25 g l-1 HF (x = 40 ∼ 200 g l-1) at 50 C due to passivation. The passivating effect of HNO3 became weak as its concentration was less than 80 g l-1. The pickling rate increased noticeably when the concentration of HF in the mixed solutions of 120 g l-1 HNO3 + y HF (y = 5 ∼ 80 g l-1) at 50 C was increased. The dissolution of the metal under the oxide scale may have changed from the passive state to the active state as the HF concentration was higher than 25 g l-1. The pickling dissolution accelerated noticeably as the temperature rose from 40 to 60 C. With the optimised pickling process, 2205 DSS hot-rolled strips can be pickled industrially with good efficiency and surface topography.