Patent ID: 7229506

Claim:
A process for pickling martensitic or ferritic stainless steel, said process comprising contacting the martensitic or ferritic stainless steel with a pickling solution comprising: 5 to 13.5 g/l of Fe(III) ions, an amount of Fe(II) such that the total amount of Fe(III)+Fe(II) is not above a limiting value of 110 g/l, 50 to 120 g/l of free sulfuric acid and 5 to 40 g/l of free HF at a temperature in the range 15 to 29° C., for a time of 5 to 25 minutes, said pickling solution having a redox potential, measured at 25° C. with a platinum electrode and relative to an Ag/AgCl reference electrode, of 100 to 240 mV.