Process for pickling stainless steel in the absence of nitric acid and in the presence of chloride ions

Process for pickling stainless steels selected from the group consisting of the austenitic, ferritic and martensitic series, duplex steels, superaustenitic and superferritic steels, and Ni or Ni/Cr based superalloys, carried out at a temperature of between 20° and 70° C., with the use of a pickling solution containing the following basic ingredients:

• H2SO4 (free acid):
• 50 to 200 g/l
• HF (free acid):
• 0 to 60 g/l
• F− anion (total):
• 5 to 150 g/l
• SO42− anion (total):
• 50 to 350 g/l
• Fe3+ in a quantity of at least 15 g/l,
• Cl-anion in a quantity of between 0.1 and 10 g/l
• in said solution the total free acid (H2SO4+HF) is between 1 and 7 g equivalent/l where by “free acid” is meant the acid that does not constitute the anion bound in the form of salts or complexes with the metal cations present in the solution:
• and feeding a sufficient amount of oxidant into said pickling solution during the pickling process in order to oxidize at least part of the Fe2+ ions, formed in the pickling process, to Fe3+ ions in order to maintain the Fe3+/Fe2+ ratio at a value of at least 0.2 and the redox potential of the solution at a value of between +230 and +800 mV.