Patent ID: 8192556

Claim:
A process for pickling steel, comprising: chemically pickling steel by contacting said steel with a process solution for a time sufficient to obtain a completely de-scaled surface; and managing redox potential of the process solution such that the redox potential, measured at process solution working temperature with a Pt/Ag/AgCl electrode, is at least 280 mV and up to 800 mV, such that said steel is chemically pickled; wherein the process solution comprises: a) one or more strong acids other than the complex fluoro acids of group b), and different from nitric acid and hydrochloric acid, in a total concentration of at least 10 g/l and at most 200 g/l, b) one or more complex fluoro acids of Si and/or anions thereof in concentrations from 50 to 500 mmoles per liter, c) optionally, a hydrogen peroxide stabilizer, d) iron(III) cations in concentrations from at least 3 g/l to at most 100 g/l, and e) a total of from 0.1 to 10 g/l of chloride ions and/or hydrochloric acid, the process solution containing in addition an amount of fluoride ions and/or hydrofluoric acid such that at least 1% and up to 100% of the iron(III) ions are present in the form of fluoride complexes, and such that the process solution contains less than 1 g/l of free fluoride ions and less than 1 g/l of free hydrofluoric acid.